Next Article in Journal
Diversity of Mycogenic Oxide and Chalcogenide Nanoparticles: A Review
Next Article in Special Issue
Functionalizing Diatomite-Based Micro-Arc Coatings for Orthopedic Implants: Influence of TiO2 Addition
Previous Article in Journal
A Bio-Inspired Decision-Making Method of UAV Swarm for Attack-Defense Confrontation via Multi-Agent Reinforcement Learning
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Electrospun Nanofiber-Based Bioinspired Artificial Skins for Healthcare Monitoring and Human-Machine Interaction

Key Laboratory of Materials Physics of Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450001, China
*
Authors to whom correspondence should be addressed.
Biomimetics 2023, 8(2), 223; https://doi.org/10.3390/biomimetics8020223
Submission received: 27 April 2023 / Revised: 22 May 2023 / Accepted: 23 May 2023 / Published: 26 May 2023
(This article belongs to the Special Issue Bioinspired Surfaces and Functions)

Abstract

:
Artificial skin, also known as bioinspired electronic skin (e-skin), refers to intelligent wearable electronics that imitate the tactile sensory function of human skin and identify the detected changes in external information through different electrical signals. Flexible e-skin can achieve a wide range of functions such as accurate detection and identification of pressure, strain, and temperature, which has greatly extended their application potential in the field of healthcare monitoring and human-machine interaction (HMI). During recent years, the exploration and development of the design, construction, and performance of artificial skin has received extensive attention from researchers. With the advantages of high permeability, great ratio surface of area, and easy functional modification, electrospun nanofibers are suitable for the construction of electronic skin and further demonstrate broad application prospects in the fields of medical monitoring and HMI. Therefore, the critical review is provided to comprehensively summarize the recent advances in substrate materials, optimized fabrication techniques, response mechanisms, and related applications of the flexible electrospun nanofiber-based bio-inspired artificial skin. Finally, some current challenges and future prospects are outlined and discussed, and we hope that this review will help researchers to better understand the whole field and take it to the next level.

Graphical Abstract

1. Introduction

The advancement of wearable electronics has been attracting more and more attention recently due to their ability to simulate the haptic perception of human skin to identify changes in detected external information through different electrical signals [1,2,3,4,5]. Unlike traditional rigid electronic devices that cannot maintain polymorphic contact with the human body, wearable electronic products can serve for health management or providing other smart functions, which greatly enrich people’s daily needs. Among them, bioinspired artificial skin is considered to be an important component of wearable electronic devices that can be affixed to the surface of human muscles or joints to collect physiological signals, with promising applications in the areas of real-time healthcare monitoring and human-machine interaction (HMI) [6,7,8,9,10,11,12,13]. Therefore, the design of artificial skin needs to be considered on skin-like flexible materials, mainly focusing on the stable monitoring of artificial skin in use, wearing comfort, and physical and chemical properties suitable for human skin. Electrospinning-based flexible devices provide a practical path for human skin construction based on such flexible material substrates [14,15,16,17,18].
Typically, electrospinning is a particular method of fiber manufacturing that uses a solution or melt of polymer for jet spinning under a high voltage electric field, which produces nanometer diameter polymer fibers with flexibility and continuity. The idea of electrospinning was conceived in 1600 by William Gilbert, who observed in his research that water droplets would form cones in an electric field [19]. In 1887, Charles V. Boys used a viscous liquid to pull out fibers while on the edge of an insulated dish connected to a power source, and the method of extracting fibers from a viscoelastic liquid under strong electric field conditions was first reported. In 1902, the electrospinning technology was patented by John Cooley and William Morton, respectively, and the prototype of the electrospinning device was determined [20]. From 1964–1969, a number of papers were published by Jeffrey Taylor, mathematically describing and simulating the process of changing a viscous polymer solution from a sphere to a cone at an electrospinning nozzle under the effects of a high-voltage electric field, achieving a breakthrough of electrospinning technology [21,22,23,24]. However, electrospinning technology development has stalled because of the absence of microscopic-scale characterization tools. It was not until the beginning of this century with the popularization of electron microscopy that the technology began to receive more and more attention from researchers, and the performance and applications were developed as never before. Through the process of developing new strategies to control structures and performances of electrospun nanofibers, electrospinning technology had already been used extensively in the area of bio-inspired artificial skin.
Artificial skin, as bionic human skin, needs to meet the characteristics of the high elasticity and breathability of human skin [25]. In the electrospinning process, polymer solution jets are stretched in a strong electric field to form nanofibers ranging from a few nanometers to 500 nanometers in diameter, which are then deposited on a collection plate to form a nanofiber film [26,27,28]. Compared with the thin film type flexible substrate material, the mesh structure of the nanofiber membrane makes it flexible and breathable, with a great ratio of surface area and thermal stability, which can better meet the material requirements of artificial skin [29,30,31,32,33]. The performance of electrospun nanofibers can be further enhanced by adding different nano-fillers to develop artificial skin with different structures and different functions [34,35,36,37,38,39].
In this review, we aim to present a complete overview of electrospun nanofiber-based bioinspired artificial skin for healthcare monitoring and HMI. We begin with an introduction to the apparatus and principles of electrospinning to give the reader a basic understanding of electrospinning technology. Then, as shown in Figure 1, we summarize the materials that can be used for electrospinning, reviewing pure organic polymer solutions and composites incorporated with nanofillers for electrospinning, respectively. Afterward, we discuss four common sensing mechanisms for artificial skin devices, including sensing principles, application areas, and advantages and disadvantages. Moreover, we also focus on reviewing and highlighting the recent research advances in human healthcare monitoring and HMI based on electrospun nanofibers for bionic artificial skin. Finally, after a simple summary, we discuss new directions for the development of bionic artificial skin and the challenges that need to be faced in the future. This review is expected to help researchers acquire more comprehensive understanding of the area to then advance it to the next level.

2. Electrospinning Method

There are many methods producing fibers from synthetic polymers such as dry spinning, gel spinning, melt spinning, wet spinning, etc. [40]. However, limited by equipment and technology, the diameter of the extracted fibers could not reach the submicron level, which seriously restricts their further application. It was not until Charles V. Boys proposed the method of extracting fibers from viscoelastic liquids under high voltage in 1887 that electrospinning technology received widespread attention from researchers and was further developed. So far, the current electrospinning technology can produce very fine diameter fibers, from a few nanometers to a few microns, and even less than 1 nanometer [41]. Fibers less than 500 nm in diameter prepared by electrospinning are often referred to as nanofibers, and this fabrication technology can be used from different scientific and engineering aspects. The lightweight and porous characteristics of flexible electrospinning materials make it very suitable for the research of multi-functional materials, such as flexible devices for bionic artificial skin, etc.
As illustrated in Figure 2, the major components of the electrospinning device include a conductive collector, a syringe pump, a syringe, a spinneret, a high voltage power source, etc. [23,42]. In the preparation process, a polymer precursor solution with the appropriate concentration, viscosity, and conductivity is transferred into the syringe, and the syringe tip is connected to the high voltage power supply, so that droplets flowing from the needle form a Taylor cone by electrostatic action. When the electric field strength is further enhanced by increasing the voltage, the Taylor cone will generate charged jets and be stretched to a certain extent due to bending instability. In this process, the jet will become longer and thinner with the specific surface area greatly increasing, which also accelerates the volatilization of the solvent [43]. Therefore, it will solidify rapidly and finally deposit nanofibers on the collecting plate. Following deposition, the bulk of the charge on the fibers is rapidly dissipated through a grounded conductive collector. However, owing to the low conductivity of the general polymer material, there will still be part of the charge remaining on the fiber surface, which will lead to mutual repulsion with other jets of the identical charge. Therefore, electrospinning nanofiber films can only reach a very thin thickness, typically less than 1 mm.
Electrospinning involves electrohydrodynamic processes in which droplets are charged to produce a jet [23]. When the electric field force on the solution reaches a critical value that overcomes the apparent tension, the Taylor cone ejects charged jets in the direction along the cone head, and then stretches under an electric field to form nanofibers. In this process, the critical voltage V is calculated according to the following formula:
V = 4 H 2 L 2 [ ln ( 2 L R ) 1.5 ] ( 1.3 π R γ ) ( 0.09 )
where L is the length of the jet, H is the distance among the electrodes, R is the radius of the syringe nozzle, and γ is the apparent tension of the polymer solution. The Taylor cone ejects a charged jet initially moving in a direct line, and the length of the direct line can be calculated by:
L = 4 k Q 2 π ρ 2 I 2 { [ ( 2 σ Q π k ρ E ) 1 3 ] 2 r 0 2 }
where k is the solution electrical conductivity, Q is the propulsion speed of the propulsion pump, I is the electric current flowing across the jet, ρ is the solution density, r0 is the original radius of the jet, σ is the surface charge of the jet, and E is the strength of the electric field. Different experimental parameters or spinning solutions require different critical voltages to generate the jet, and the linear motion length of the jet is an important guide to set the distance between the nozzle and the collector.
During the electrospinning process, the processing parameters directly impact the structure, shape, and properties of the fabricated nanofibers. Processing parameters mainly include factors such as the electrospinning solution, electrospinning process, temperature, and humidity during electrospinning. On one hand, the properties of the electrospinning solution are governed by the molecular weight and molecular weight density distribution of polymer. On the other hand, this is also closely related to the viscosity, conductivity, and surface tension of the polymer solution along with the volatility and conductivity of the solvent. In addition, the effect of adding surfactants and inorganic salts on the polymer blend solution should be considered. The key to the formation of a polymer solution suitable for electrospinning lies in the solubility parameters of a suitable solvent [44]. However, besides the high solubility parameter, the volatility of the solvent also affects the curing speed of the spray and has an impact on the formation of the fiber surface structure. When the solvent volatility is fast, the fibers form a smooth surface as the high volatility may lead to immediate solidification after the jet. On the contrary, when the volatility is low, it is hard to form micropores on the surface of the fibers, which leads to a rougher fiber surface. Too low of a volatility can lead to spinning failure because the fibers remain in a liquid state when deposited on the collection plate.
Additionally, if the discharge constant of the solvent is too large, it will lead to a greater electrostatic rejection between the charges on the surface of the jet, and larger voltage, will be required to stabilize the jet, which is also not conducive to electrospinning. Commonly used solvents for electrospinning include acetone, dimethylformamide, alcohol, methylene chloride, tetrahydrofuran, etc. Electrospinning process parameters mainly include electric field intensity, spinning fluid flow, etc. The electric field strength depends on the voltage, and only when the voltage reaches a threshold value, the Taylor cone can emit a jet which eventually forms a fiber. The magnitude of the imposed voltage can directly determine the magnitude of the charge that the jet carries and the electrostatic rejective force between surface charges. Usually, a higher voltage is more conducive to the formation of finer fibers. The velocity of the spinning solution flow has some subtle effects on the diameter of the fiber. Usually, increasing the speed causes the formation of larger diameter nanofibers, but in different solution systems, the pattern is not exactly the same. The environment during electrospinning, which includes the environmental temperature and relative humidity, is also significant to the formation of fibers. The increase in temperature reduces the adhesive force and apparent tension of the polymer solution, which facilitates finer fiber formation. However, too high of a temperature hastens the evaporation of the solvent, which limits the length of the spray extension. Therefore, the temperature should be controlled in an appropriate range during electrospinning. Similarly, when the relative humidity is low, it facilitates the formation of fine fibers with dry surfaces, but too low a relative humidity will result in excessive evaporation in the jet which affects the jet’s extension length [45]. Both the temperature and relative humidity have two-sided effects on electrospinning and need to be adjusted according to the situation.
Electrospun nanofibers are broadly used to construct flexible bioinspired artificial skin due to its high ratio surface area, unique porous network structure, and stability [46]. With the benefit of a high relative surface area, especially the insensitivity and excellent elasticity of nanofiber membranes to mechanical deformation, the resulting sensing device can have improved detection capabilities, making it a good e-skin candidate for the field of healthcare monitoring and HMI.

3. Materials

Electrospinning technology has now been utilized in various fields. Different kinds of materials can be used to prepare nanofibers, such as most natural or synthesized organic polymers, which could be used directly for electrospinning once they are soluble in a suitable solvent. Generally, it is usually necessary that the small molecules self-assemble and produce sufficient chain entanglement or chemical binding to the solution-gel. In addition, by doping polymer solutions with additives such as nanoparticles, nanotubes, nanosheets, and other nanofibers, the resulting hybrid solutions can also be electrospun [47,48,49,50,51,52,53,54].

3.1. Pure Polymer Nanofibers

In general, electrospun polymer solutions require dissolved polymers with a sufficiently high molecular weight and a suitable solvent, because if the molecular weight is not high enough, chain entanglement is limited and electrospinning would generate beads instead of fibers. Among the more than one hundred polymers that for solution electrospinning can be used directly, common polymers include polycaprolactone (PCL) [55], polylactic acid (PLA) [56,57,58,59], polyaniline (PANI) [60,61,62,63], polypyrrole (PPy) [64,65], DNA [66], poly (lactic-co-glycolic acid) (PLGA) [67], Polyvinyl alcohol (PVA) [68,69,70,71,72,73,74,75,76,77], and gelatin are widely used in the manufacturing of biomedical scaffolds [78]. What is more, synthetic polymers are also often used in electrospinning, such as polystyrene (PS), and polyvinyl chloride (PVC) are used in areas related to environmental protection and monitoring. Interestingly, polyvinylidene fluoride (PVDF) and its copolymers can be also used for electrospun nanofibers and have good performance in the field of artificial skin and flexible sensing [79,80,81,82,83,84,85]. For example, Huang et al. proposed a strategy of nanofiber mats with conductivity for wearable devices by first coating MWCNTs on electrospun polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) fibers and then embedding them on the PVDF-HFP nanofiber surface using a further thermal welding process to obtain both breathable and conductive MWCNTs/PVDF-HFP nanofiber mats [86], which have excellent application prospects in the area of wearable electronic devices. Figure 3a shows the SEM images of PVDF-HFP nanofibers after ten minutes of thermal annealing treatment with MWCNTs at 120, 130, and 140 °C environments, respectively. It can be clearly observed that PVDF-HFP fibers did not reach the melting point and no fusion with MWCNTs occurred at 120 °C. The nanofibers started to fuse at 130 °C, and the fusion effect between fibers was more obvious at 140 °C. However, excessive fusion also results in a significant decrease in the permeability of the fiber mat. In addition to using thermal treatment methods to improve the performance of electrospun nanofiber mats, undoped nanofiller hybrid types of polymeric electrospun composite nanofiber mats can be fabricated by arranging coaxial nozzles or using nozzles facing the collector. Cheol Sang Kim et al. made electrospun PVDF and filament protein (SF) nanofibers into composite fiber mats by placing two nozzles facing each other’s mats [87]. Figure 3b shows the SEM images of the composite fiber mats at 0%, 10%, and 20% SF nanofiber ratios. Through piezoelectric tests and tensile experiments, this electrospun nanofiber composite mat exhibits better mechanical properties and biocompatibility than a single material, showing a potential use of electrospinning technology in the area of flexible sensing relevant to human healthcare monitoring.

3.2. Polymer Composite Nanofibers Incorporated with Nanofillers

Usually, to enhance the properties of electrospun nanofibers, different kinds and concentrations of conductive and non-conductive fillers are doped into the organic polymer solution to be electrospun (Figure 4a) [88,89,90,91,92,93,94]. For example, Kuo et al. presented a flexible electrospun optoelectronic device by mixing the inorganic chalcogenide quantum dots and cellulose nanocrystal composites (IPQDs/CNC) into a PVDF solution for the next electrospinning process [95]. Figure 4b–e show FE-SEM images, TEM images, and the confocal fluorescent spectrum of these composite nanofibers made from a hybrid electrospinning solution with an IPQDs doping content of 1 v/v%. The addition of IPQDs leads to improved electrical conductivity and the adhesion of the mixed electrospinning solution, and the resulting nanofibers were slender and smoother. The improved piezoelectric properties of the composite nanofiber devices can be ascribed to the phase change of the crystal structure. Electrospun composite nanofibers are not only used to make piezoelectric sensors, but also triboelectric sensors. Park et al. firstly proposed to blend MXene (Ti3C2Tx) nanosheets into a PVDF matrix [96], and the resulting hybrid material (PVDF/MXene composite, PMC) was electrospun and used for the negative layer of triboelectric nanogenerators (TENG). Figure 4f shows FE-SEM images of PMC nanofibers; Figure 4g and h show TEM images of PMC nanofibers at different scales, indicating that MXene nanosheets have been successfully embedded into the PVDF matrix. Compared with the pure PVDF nanofiber and nylon nanofiber anodes, PMC nanofibers exhibited excellent performance in terms of permittivity and surface charge density, with an increase of 270% and 80%, respectively.
Among the reported hybrid solutions for electrospun nanofibers, graphene nanosheets are one of the most popular nanofiller choices for enhancing the conductivity of composite nanofibers. In 2020, Luo et al. proposed a new strategy of electrospinning composite nanofibers based on PVDF and graphene nanosheets (GNSs) for TENGs by adding GNSs to the electrospun precursor solution with pre-optimized PVDF for magnetic stirring [98]. Compared to pure PVDF nanofibers, the composite nanofibers made by electrospinning have a smoother fiber surface with denser pores, and the fiber morphology did not change significantly with the increase of GNSs concentration (Figure 5a). Interestingly, a hybrid PVDF-based electrospinning strategy developed by Jiang et al. has been previously reported to construct piezoelectric nanogenerators by doping with GNSs. [99]. However, the difference is that they also added barium titanate nanoparticles (BaTiO3). Figure 5b–d show the SEM images of PVDF fibers, 0.15 wt% Gr-BT/PVDF composite nanofibers, and TEM images, respectively. The pure PVDF fiber has a smooth surface, while the surface morphology of the composite nanofibers is rough, as graphene nanosheets and BaTiO3 nanoparticles are incorporated into the fibers. The piezoelectric performance of the composite nanofiber mat was significantly improved due to the synergistic effect of BaTiO3 and GNSs.

4. Working Mechanism

To date, the vast majority of reported artificial skin sensors work by a mechanism that transforms external mechanical stimuli into electrical signals, which can be understood as the ability to perceive external forces such as pressure, shear, strain, and distortion deformation, etc. The main operating principles are piezoresistive [100], capacitive [101], piezoelectric [102], and triboelectric effects [103]. Figure 6 shows four typical sensing mechanisms in the area of flexible electronics [104]. Depending on the mechanism of sensing, flexible sensors can be classified as piezoresistive, capacitive, piezoelectric, and triboelectric sensors [105,106,107]. Each of these four types has its own unique characteristics.

4.1. Piezoresistive Effect

The piezoresistive sensor is designed based on the piezoresistive effect and it was first used commercially. When pressure or strain is exerted externally, the resistance of the sensor changes. Traditional piezoresistive sensors have poor flexibility and ductility, and can only measure strain in a specific direction. In recent years, researchers have been devoted to developing innovative materials that are stretchable, highly sensitive, and flexible for making piezoresistive sensors for human motion detection, artificial skin, and other applications. For example, many piezoresistive composite sensors are formed by embedding conductive fillers such as carbon black, gold nanoparticles (AuNPs), silver nanoparticles (AgNPs), etc., into flexible electrospun nanofibers. What is more, conductive fillers with the same role include metal nanowires, carbon nanotubes (CNTs), graphene, and Ag nanosheets, which are also selected to be doped into the flexible substrates such as polydimethylsiloxane (PDMS), polyurethane (PU), hydrogels, etc. [108,109]. Therefore, conductive polymer composites are considered to be the most promising flexible piezoresistive sensors due to their wider choice of materials and structural design.

4.2. Capacitive Effect

Capacitive sensors are usually made of a flexible medium layer sandwiched between two electrodes. The change of capacitance is affected not only by the external pressure magnitude, but also by the parallel plate electrodes’ relative position to each other, which has the advantages of high sensitivity, lower energy consumption, as well as good static detection capability. The main disadvantage is that negative effects caused by parasitic capacitance accumulated during use [110]. The preparation method of flexible capacitive sensors mainly uses metal films as electrodes, and the elastomer was sandwiched between the electrode plates as dielectric layers. Generally, low-modulus elastic dielectrics include PDMS, Ecoflex, acrylic elastomers, etc., and are commonly employed. However, the sensitivity and reaction time of capacitive sensors are usually not particularly good due to the inherent viscoelasticity of elastic dielectrics. To improve the capacitive sensor sensitivity, elastomeric dielectrics can choose dielectric materials with micro/nanostructures, and the electrospun nanofibers are favorable candidates. Usually materials with micro/nanostructures can also produce a large deformation at low pressure, thus achieving the purpose of improving sensor sensitivity.

4.3. Piezoelectric Effect

Piezoelectric sensors are based on dipole-polarized piezoelectric materials that produce a voltage due to a change in potential under an applied strain, allowing a transformation of mechanical stimuli into electrical signals, which has the advantage of high sensitivity and stability. However, the disadvantage is that it is not suitable for measuring static pressure signals and there are some limitations in low frequency detection, so it is widely used for dynamic monitoring. An essential parameter to measure the properties of a piezoelectric sensor is the piezoelectric coefficient. Materials used for piezoelectric sensors are usually divided into inorganic and organic classes, and the inorganic class includes barium titanate, zinc oxide, lead zirconate titanate, etc. They all have the disadvantage of poor flexibility while organic materials such as PVDF and PP are usually highly flexible but not conductive enough [111]. Therefore, additives are often used to enhance their piezoelectric properties. Moreover, the high electric voltage field during the electrospinning preparation is very favorable for the polarization of the piezoelectric material.

4.4. Triboelectric Effect

Triboelectric sensors can transform external mechanical signals into triboelectric signals through electrostatic and triboelectric effects. The basic working principle is that as two different non-electric substances come into contact with each other, the charge transfer will occur, generating a positive and negative electrostatic charge [112]. When the contact surfaces are separated, a voltage difference is created between the surfaces of these two materials, and the circuit formed by the wires between the two materials generates an electric current. Triboelectric sensors have the advantages of being self-powered, high instantaneous power, etc. However, the output performance is always affected by the amplitude and frequency of the mechanical stimulation. In order to relatively improve the output performance, researchers have now developed flexible triboelectric sensors with special structures and functions. As triboelectric sensors only generate an electrical signal when subjected to mechanical stimulation, they are only suitable for dynamic sensing, the same as piezoelectric sensors [113,114]. Moreover, signal interference generated by external parameters such as humidity and temperature variations is also an obvious problem to be solved in its practical application.

5. Application of the Electrospinning Nanofibers Based Artificial Skins

In recent years, various artificial skins have been reported successively and have played an important role in healthcare [115,116,117,118,119,120,121,122,123,124,125], HMI, and other fields [126,127,128,129,130,131,132,133]. Compared with other traditional electronic sensors, artificial electronic skin can meet the demand of human health monitoring and HMI when it is used in seamless and stable contact with human skin and obtains low impedance physiological signals [134,135,136,137,138]. Therefore, it has higher requirements on material permeability, tensile resistance, and biocompatibility [139]. Due to its high porosity, high toughness, and small mass, electrospun nanofiber-based bioinspired artificial skins with high flexibility and a three-dimensional porous mesh structure are often considered as the first choice [140,141,142,143,144,145,146,147,148,149,150].

5.1. Healthcare Monitoring

With the advancement of flexible electronics, electrospun nanofiber-based artificial skin is increasingly being used for human health monitoring [151,152,153,154,155,156,157,158,159,160,161,162]. Comfortable, accurate, and real-time collection of physiological electrical signals is important for determining human health conditions. After prolonged conformal contact with human skin or joints, the ability to avoid elevated impedance caused by sweat and to withstand repeated mechanical deformation are crucial issues that need to be addressed [163,164,165,166,167,168,169,170]. Therefore, a flexible conductor with high permeability and stretchability (liquid-metal fiber mat, LMFM) was developed by Zheng et al. in 2021 [171]. The preparation is based on the coating of liquid metal (eutectic gallium-indium alloy, EGaln) on an electrospun fiber mat (styrene-butadiene-styrene, SBS). After the pre-stretching process, the liquid metal between the elastomeric SBS nanofibers formed a lattice-like structure and the LMFM maintained a high permeability to both gases and liquids (Figure 7a). In tensile tests, EGaIn-SBS can achieve over 1800% stretching while the conductor impedance remains at a low level without significant change during the process, showing ultra-high conductivity and electrical stability (Figure 7b). Therefore, an EGaIn-SBS containing three layers of printable gain electrodes was further developed that can be worn on the arm to acquire low-impedance ECG signals. As a result of its ultra-high elasticity, there is no significant change in signal waveform under stretch or compression compared to commercial ECG skin patches (Figure 7c). In addition, it can also realize the monitoring of sweat discharged from human skin, multimodal monitoring, and treatment of human skin by heating, and has a great application potential in medical monitoring.
In 2022, Pan et al. developed a self-assembly fabrication process for wearable devices based on wet heterostructure electrospinning technology [172]. Electrospinning micro-pyramidal arrays (EMPAs) with unique structures were constructed using a far-field electrospinning device with a charged grounded aluminum foil with bumps as the collector (Figure 7d). PVDF was used as the proof-of-concept material to fabricate the EMPAs-based films, and the SEM images showed a uniform planar distribution of the micro-pyramidal structure on the film, and typical features of the pyramidal structure were shown with the tilted three prongs intersecting at the apex (Figure 7e,f). Since the micro-pyramid structure microfibers constructed the permeable network, the film with EMPAs was ultra-thin, ultra-light, breathable, and suitable to be adopted as the artificial skin. Therefore, a piezoelectric capacitive sensor based on EMPAs was developed to collect pulse signals in real time for human health monitoring with high permeability and sensitivity. Figure 7g shows the clear obtained pulse peaks that reflect physiological indicators without any degradation of the signal waveform for four hours when a driver wore it for a long time without affecting normal work, which is of great importance for human health diagnosis. Similarly, inspired by human muscle fibers, Chen et al. proposed an electrospun fiber-based piezoelectric sensor which can capture human pulse signals for health monitoring (Figure 7h) [173]. Electrospun barium titanate/polyvinylidene fluoride (BTO/PVDF) nanofibers are modified mainly by using polydopamine (PDA). Groups of DA formed cross-links with the BTO nanoparticles due to van der Waals forces as well as attached to the PVDF polymer fibers, encasing the protruding BTO nanoparticles and making the fiber surface smooth. In addition, the piezoelectric performance had been greatly improved. Figure 7i shows the microscopic images of smooth nanofibers after 5 wt% PDA doping. After a simple encapsulation process, a piezoelectric fabric based on electrospun nanofibers was fabricated for monitoring pulse signals in real time. The ability of the device to monitor human health was verified by distinguishing weak changes in the pulse signals of the wearer in different states (Figure 7j).
In addition to myoelectric and pulse signals, electrospinning nanofiber-based artificial skin can also be used for several other health monitoring applications. For instance, Wang et al. developed a TENG-based nanofiber electronic skin (SANES) for respiratory monitoring and diagnosis during sleep (Figure 8a) [174], which was characterized by good permeability, high sensitivity, and was easy to wear. SANES is mainly assembled by the top encapsulation layer, middle functional layer, and bottom substrate layer, and all three nanofiber functional layers are prepared by electrospinning. The PA66 and PAN sandwiched in the middle were used as electrodes with a layer of Au of 100 nm thickness at the surface, respectively. The upper and lower parts are protected from electrode interference by PA66 and PAN as cover layers, respectively. The device is placed on the abdomen of the test subject, which monitors the occurrence of OSAHS during sleep based on the movement of the abdominal skin during breathing and records the number of apneas and hypoventilation states (Figure 8b). Classifying or alerting according to the severity has great application prospects in the area of personal sleep health monitoring. In addition to directly collecting physiological electrical signals for real-time monitoring of the human body, electrospun nanofiber-based devices can also monitor and provide early warnings of human health and safety by establishing medical monitoring systems. In 2022, Yu et al. prepared a triboelectric energy harvesting sensor (TEHS) using triboelectric fiber films made by electrospinning technology and built a medical monitoring system by multiple TEHS devices [175]. The system contains several sensors, a controller, a data processing unit, and a display unit (Figure 8c). Figure 8d shows the application of the system in a practical scenario, where the TEHS is mounted on a wheelchair, a nursing bed, and a human body to sense and monitor the human motion through the electrical response generated by the TEHS.

5.2. Intelligent HMI

As artificial intelligence emerges and develops, artificial skin plays a crucial role not only for medical monitoring, but also for intelligent HMI [176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191]. Besides the monitoring of physiological parameters and the movement status of the human body, multifunctional artificial skin based on electrospun nanofibers can be used for mechanical control [192,193], on-demand therapy [194,195], and gesture recognition and intelligent control [196,197,198,199,200,201,202,203,204,205,206,207]. In 2022, a wearable flexible electrode (nano-liquid metal (LM)-based highly robust stretchable electrode, NHSE) that can be used for game control and thermal therapy was proposed by Li et al. [208]. Figure 9a illustrates the simple fabrication process, which crucially involves the manufacturing of mechanically robust and highly elastic nanofiber scaffolds by electrospinning polyurethane nanofibers, followed by electrospraying liquid metal (LM) nanoparticles into the TPU nanofiber scaffold to form a composite structure that simulates the interaction of water and web. LM provides electrical conductivity and the nanofiber scaffold provides the mechanical properties, achieving 500% tensile capacity without any additive binder. After 33,000 times of a 100% tensile cycle test, the impedance change is only 5%, showing high stability. Based on this, two NHSEs were partially activated and laser cut, then assembled to obtain a multifunctional artificial skin with a bilayer structure containing a capacitive sensor array and a wireless control unit. Figure 9b shows that the device was able to accurately recognize external signals and thus control the activities of the characters in the game under different conditions in tests, and it also enabled the input and recognition of numbers. It proves excellent potential in the area of HMI. Previously, Wan et al. have reported the development of MXene/protein nanocomposite fiber-based artificial skin for highly sensitive pressure sensing [209]. It can be used not only for disease diagnosis and motion detection, but also for human–machine interactive pressure detection. The individual pressure sensors are assembled by MXene impregnated silk protein nanofiber membranes and silk protein fiber membranes with MXene ink printed electrodes. When the external pressure increases in the operating range, the intensity of the generated current increases. Figure 9c shows an optical image of a 5 × 5 sensor array consisting of multiple sensors. Once the finger touches the sensor array, the magnitude and position of the applied pressure is quickly detected and sent to the user terminal via a wireless transmission module (Figure 9d).
Different sensors have different working mechanisms; common flexible sensors used for HMI are not only pressure sensors, but also humidity sensors. During the COVID-19 epidemic, a flexible non-contact sensing array based on humidity sensing was reported by Yang et al. [210]. The single sensor (MG/PA66 humidity sensor, MPHS) is a composite material made of two-dimensional graphene flakes embedded in an electrospun PA66 nanofiber by ultrasonic treatment (Figure 10a). The characteristics of the electrospun nanofiber network give the composite a physical structure with a large ratio surface area, in addition to the PA66 chemical structure rich in water-absorbing functional groups, ensuring a high response to humidity. MPHS can be arranged to form a humidity sensing array for HMI in non-contact mode. As shown in Figure 10b, the sensing system for non-contact manipulation based on MPHS consisted of an MPHS, wireless transmission unit, analysis unit, and signal processing circuit. The motion control of the trolley can be achieved by non-contact sliding of the finger over the sensor array, indicating significant application prospects of this non-contact manipulation device in the public health field.
In addition to remote control, pressure detection, and game control, artificial skin made of electrospun nanofibers has extensive applications in areas such as healthcare and fire alarms. For example, Zhang et al. proposed a ventilatable artificial skin with real-time temperature monitoring and the ability to perform anti-infection heating therapy in 2019 [211]. The device consists of an electrospun moxifloxacin hydrochloride (MOX) nanofiber network with high toughness, gas permeability, and stability that can be used as a flexible heater when coated with a thermosensitive polymer film printed with a conductive pattern. Figure 10c shows real-time variations in resistance and temperature as the e-skin grasps and releases the beaker containing hot water, demonstrating the excellent thermal response of the e-skin. Figure 10d shows images of the temperature distribution of the e-skin when mounted on the human hand as a flexible heater, illustrating the ability of the electronic skin to be used as a flexible heater for human thermal therapy. Similar to this device, Ling et al. developed an electrospun flame retardant silk/graphene nanoionotronic e-skin (SGNI) with extremely high temperature sensitivity for integrating portable fire alarm systems [212]. When SGNI is exposed to a high temperature environment, the intelligent fire alarm system will sound an alarm and send an alarm message once the temperature reaches the alarm threshold. By using the ability of SGNI to respond to fire hazards, a concept was developed that could sense the position of the fire source and then control the robot to make evasive maneuvers in actual hazardous HMI situations (Figure 10e). Once the location of the robot installed on the SGNI skin is close to the fire source, the SGNI can sense the fire temperature and location within 6s and send signals back to the control unit to command the robot to actively avoid hazards and make a move away from the fire source, which provides highly promising applications in the area of secure and intelligent HMI.

6. Summary and Outlook

Due to the characteristics of high stretchability and superior porosity of electrospun nanofibers, they meet the demand of soft and air permeable artificial skin materials. As a result, electrospun nanofiber-based artificial skin has been rapidly developed and widely used. In this paper, we have reviewed the latest advances in electrospun nanofiber-based bioinspired artificial skin, mainly focusing on the electrospinning fabrication process and its influencing factors, materials selection and incorporation, sensing mechanisms of artificial skin, healthcare monitoring, and HMI application. A wide variety of abundant nanofibers have been designed and assembled by researchers through electrospinning by selecting suitable organic polymer solutions and process parameters. Therefore, flexible smart devices have made great progress in multifunctional sensing and bioapplicability, and many artificial skins with better performance have been developed based on them. In the future, with the enhancement of production technology, the application prospect of bioinspired artificial skin based on electrospun nanofibers will be more extensive. However, although significant advancements have been achieved in the preparation and design of various electrospun bionic skin devices, there are still many obvious issues remaining to be addressed and more work needs to be done in the following aspects.

6.1. Low Preparation Effectivity of Electrospun Artificial Skins

Bioinspired artificial skin based on electrospun nanofibers has low efficiency in the manufacturing process, including the fabrication of the spinning solution, electrospinning process, and nanofiber membrane for artificial skin assembly. For the current production technology, mass production on a large scale is difficult and costly to achieve. Such problems can only be solved with the development of production and manufacturing technologies.

6.2. Biosafety Issues of Bionic Artificial Skin

While the reported artificial skin tends to be fabricated by materials with good biocompatibility, there is still a long way to go before they can be truly used in the human body. As material science continues to advance, the issue of biosafety is a primary consideration for artificial skin.

6.3. Signal Interference Problem in Multi-Directional Detection

Although excellent progress has been obtained in unidirectional sensing of flexible bionic skin, the sensors produce similar signal changes when faced with external forces in different directions simultaneously. In practical applications, there are many situations where the force direction cannot be determined, so achieving effective identification and detection of multidirectional forces is still a challenge, and developing new materials or methods that can decouple multidirectional forces is a direction that future research needs to focus on.

6.4. The Processing of the Acquired Signals by Artificial Skin

In practical applications, the collected signals by the artificial skin on the human body will be interfered with by various factors, and the extraction of effective signals in a large number of signals is currently an important issue which should be tackled. The application of machine learning to assist in signal processing of artificial skin is an effective and promising solution for this field in the future.

6.5. System Integration of Artificial Skin Devices

As a crucial component in the field of flexible sensing for healthcare monitoring and HMI, how to integrate multiple modules (such as the data processing module, data transmission module, energy supply module, etc.) into the same platform is a big challenge for the current technology, which is a problem that must be solved for bioinspired artificial skin based intelligent systems to move toward more application scenarios.
Although there are still some urgent issues regarding the biosafety and application details of electrospun nanofiber-based bionic artificial skin, that does not take away from the fact that it is a promising manufacturing method for artificial skin. In the future, with the enhancement of production technology, the application prospect of bioinspired artificial skin based on electrospun nanofibers will be more extensive.

Author Contributions

Investigation, X.C. and L.L.; writing-original draft preparation, X.C. and L.L.; writing-review and editing, H.L., Z.X., L.L., Z.P. and Y.M.; supervision, L.L., Z.P. and Y.M.; project administration, L.L., Z.P. and Y.M.; funding acquisition, L.L., Z.P. and Y.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by China Postdoctoral Science Foundation (2022TQ0281) and the Foundation for Outstanding Young Teachers in Universities of Henan Province (2021GGJS014).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

  1. Cheng, T.; Zhang, Y.; Lai, W.-Y.; Huang, W. Stretchable Thin-Film Electrodes for Flexible Electronics with High Deformability and Stretchability. Adv. Mater. 2015, 27, 3349–3376. [Google Scholar] [CrossRef]
  2. Zhang, Y.; Zhang, T.; Huang, Z.; Yang, J. A New Class of Electronic Devices Based on Flexible Porous Substrates. Adv. Sci. 2022, 9, 2105084. [Google Scholar] [CrossRef]
  3. Kang, S.; Zhao, K.; Yu, D.-G.; Zheng, X.; Huang, C. Advances in Biosensing and Environmental Monitoring Based on Electrospun Nanofibers. Adv. Fiber Mater. 2022, 4, 404–435. [Google Scholar] [CrossRef]
  4. Ding, Y.; Hou, H.; Zhao, Y.; Zhu, Z.; Fong, H. Electrospun polyimide nanofibers and their applications. Prog. Polym. Sci. 2016, 61, 67–103. [Google Scholar] [CrossRef]
  5. Kimmel, D.W.; Leblanc, G.; Meschievitz, M.E.; Cliffel, D.E. Electrochemical Sensors and Biosensors. Anal. Chem. 2012, 84, 685–707. [Google Scholar] [CrossRef]
  6. Leng, Z.; Zhu, P.; Wang, X.; Wang, Y.; Li, P.; Huang, W.; Li, B.; Jin, R.; Han, N.; Wu, J.; et al. Sebum-MembraneInspired Protein-Based Bioprotonic Hydrogel for Artificial Skin and Human-Machine Merging Interface. Adv. Funct. Mater. 2023, 33, 2211056. [Google Scholar] [CrossRef]
  7. Yang, J.C.; Mun, J.; Kwon, S.Y.; Park, S.; Bao, Z.; Park, S. Electronic Skin: Recent Progress and Future Prospects for Skin-Attachable Devices for Health Monitoring, Robotics, and Prosthetics. Adv. Mater. 2019, 31, 1904765. [Google Scholar] [CrossRef]
  8. Chortos, A.; Bao, Z. Skin-inspired electronic devices. Mater. Today 2014, 17, 321–331. [Google Scholar] [CrossRef]
  9. Ahmed, F.E.; Lalia, B.S.; Hashaikeh, R. A review on electrospinning for membrane fabrication: Challenges and applications. Desalination 2015, 356, 15–30. [Google Scholar] [CrossRef]
  10. Liu, D.; Zhu, P.; Zhang, F.; Li, P.; Huang, W.; Li, C.; Han, N.; Mu, S.; Zhou, H.; Mao, Y. Intrinsically Stretchable Polymer Semiconductor Based Electronic Skin for Multiple Perceptions of Force, Temperature, and Visible Light. Nano Res. 2023, 16, 1196–1204. [Google Scholar] [CrossRef]
  11. Zhu, M.; Li, J.; Yu, J.; Li, Z.; Ding, B. Superstable and Intrinsically Self-Healing Fibrous Membrane with Bionic Confined Protective Structure for Breathable Electronic Skin. Angew. Chem. 2022, 134, e202200226. [Google Scholar]
  12. Persano, L.; Dagdeviren, C.; Su, Y.; Zhang, Y.; Girardo, S.; Pisignano, D.; Huang, Y.; Rogers, J.A. High performance piezoelectric devices based on aligned arrays of nanofibers of poly(vinylidenefluoride-co-trifluoroethylene). Nat. Commun. 2013, 4, 1633. [Google Scholar] [CrossRef] [PubMed]
  13. Chen, J.; Huang, X.; Sun, B.; Jiang, P. Highly Thermally Conductive Yet Electrically Insulating Polymer/Boron Nitride Nanosheets Nanocomposite Films for Improved Thermal Management Capability. ACS Nano 2019, 13, 337–345. [Google Scholar] [CrossRef] [PubMed]
  14. Liu, X.; Xu, H.; Zhang, M.; Yu, D.-G. Electrospun Medicated Nanofibers for Wound Healing: Review. Membranes 2021, 11, 770. [Google Scholar] [CrossRef]
  15. Yang, M.; Cheng, Y.F.; Yue, Y.; Chen, Y.; Gao, H.; Li, L.; Cai, B.; Liu, W.J.; Wang, Z.Y.; Guo, H.Z.; et al. High-performance flexible pressure sensor with a self-healing function for tactile feedback. Adv. Sci. 2022, 9, 2200507. [Google Scholar] [CrossRef] [PubMed]
  16. Inagaki, M.; Yang, Y.; Kang, F. Carbon Nanofibers Prepared via Electrospinning. Adv. Mater. 2012, 24, 2547–2566. [Google Scholar] [CrossRef]
  17. Si, Y.; Yu, J.; Tang, X.; Ge, J.; Ding, B. Ultralight nanofibre-assembled cellular aerogels with superelasticity and multifunctionality. Nat. Commun. 2014, 5, 5802. [Google Scholar] [CrossRef]
  18. Wang, L.; Chen, Y.; Lin, L.; Wang, H.; Huang, X.; Xue, H.; Gao, J. Highly Stretchable, Anti-Corrosive and Wearable Strain Sensors Based on the PDMS/CNTs Decorated Elastomer Nanofiber Composite. J. Chem. Eng. 2019, 362, 89–98. [Google Scholar] [CrossRef]
  19. Kenry; Lim, C.T. Nanofiber technology: Current status and emerging developments. Prog. Polym. Sci. 2017, 70, 1–17. [Google Scholar] [CrossRef]
  20. Thenmozhi, S.; Dharmaraj, N.; Kadirvelu, K.; Kim, H.Y. Electrospun nanofibers: New generation materials for advanced applications. Mater. Sci. Eng. B 2017, 217, 36–48. [Google Scholar] [CrossRef]
  21. Barhoum, A.; Pal, K.; Rahier, H.; Uludag, H.; Kim, I.S.; Bechelany, M. Nanofibers as new-generation materials: From spinning and nano-spinning fabrication techniques to emerging applications. Appl. Mater. Today 2019, 17, 1–35. [Google Scholar] [CrossRef]
  22. Sun, B.; Long, Y.Z.; Zhang, H.D.; Li, M.M.; Duvail, J.L.; Jiang, X.Y.; Yin, H.L. Advances in three-dimensional nanofibrous macrostructures via electrospinning. Prog. Polym. Sci. 2014, 39, 862–890. [Google Scholar] [CrossRef]
  23. Xue, J.; Xie, J.; Liu, W.; Xia, Y. Electrospun Nanofibers: New Concepts, Materials, and Applications. Acc. Chem. Res. 2017, 50, 1976–1987. [Google Scholar] [CrossRef] [PubMed]
  24. Holland, C.; Numata, K.; Rnjak-Kovacina, J.; Seib, F.P. The Biomedical Use of Silk: Past, Present, Future. Adv. Healthc. Mater. 2019, 8, 1800465. [Google Scholar] [CrossRef]
  25. Ziai, Y.; Petronella, F.; Rinoldi, C.; Nakielski, P.; Zakrzewska, A.; Kowalewski, T.A.; Augustyniak, W.; Li, X.; Calogero, A.; Sabała, I.; et al. Chameleon-inspired multifunctional plasmonic nanoplatforms for biosensing applications. NPG Asia Mater. 2022, 14, 18. [Google Scholar] [CrossRef]
  26. Luo, C.J.; Stoyanov, S.D.; Stride, E.; Pelan, E.; Edirisinghe, M. Electrospinning versus fibre production methods: From specifics to technological convergence. Chem. Soc. Rev. 2012, 41, 4708. [Google Scholar] [CrossRef]
  27. Wang, C.; Wang, J.; Zeng, L.; Qiao, Z.; Liu, X.; Liu, H.; Zhang, J.; Ding, J. Fabrication of Electrospun Polymer Nanofibers with Diverse Morphologies. Molecules 2019, 24, 834. [Google Scholar] [CrossRef]
  28. Li, Y.; Zhu, J.; Cheng, H.; Li, G.; Cho, H.; Jiang, M.; Gao, Q.; Zhang, X. Developments of Advanced Electrospinning Techniques: A Critical Review. Adv. Mater. Technol. 2021, 6, 2100410. [Google Scholar] [CrossRef]
  29. Keirouz, A.; Chung, M.; Kwon, J.; Fortunato, G.; Radacsi, N. 2D and 3D electrospinning technologies for the fabrication of nanofibrous scaffolds for skin tissue engineering: A review. WIREs Nanomed. Nanotechnol. 2020, 12, e1626. [Google Scholar] [CrossRef]
  30. Du, Y.; Zhang, X.; Liu, P.; Yu, D.G.; Ge, R. Electrospun nanofiber-based glucose sensors for glucose detection. Front. Chem. 2022, 10, 944428. [Google Scholar] [CrossRef]
  31. Cheng, S.; Lou, Z.; Zhang, L.; Guo, H.; Wang, Z.; Guo, C.; Fukuda, K.; Ma, S.; Wang, G.; Someya, T.; et al. Ultrathin Hydrogel Films toward Breathable Skin-Integrated Electronics. Adv. Mater. 2022, 35, 2206793. [Google Scholar] [CrossRef] [PubMed]
  32. Ding, J.; Zhang, J.; Li, J.; Li, D.; Xiao, C.; Xiao, H.; Yang, H.; Zhuang, X.; Chen, X. Electrospun polymer biomaterials. Prog. Polym. Sci. 2019, 90, 1–34. [Google Scholar] [CrossRef]
  33. Guan, X.; Xu, B.; Wu, M.; Jing, T.; Yang, Y.; Gao, Y. Breathable, washable and wearable woven-structured triboelectric nanogenerators utilizing electrospun nanofibers for biomechanical energy harvesting and self-powered sensing. Nano Energy 2021, 80, 105549. [Google Scholar] [CrossRef]
  34. Zhang, M.; Song, W.; Tang, Y.; Xu, X.; Huang, Y.; Yu, D. Polymer-Based Nanofiber–Nanoparticle Hybrids and Their Medical Applications. Polymers 2022, 14, 351. [Google Scholar] [CrossRef]
  35. Liu, H.; Jiang, W.; Yang, Z.; Chen, X.; Yu, D.; Shao, J. Hybrid films prepared from a combination of electrospinning and casting for offering a dual-phase drug release. Polymers 2022, 14, 2132. [Google Scholar] [CrossRef]
  36. Zhang, C.-L.; Yu, S.-H. Nanoparticles meet electrospinning: Recent advances and future prospects. Chem. Soc. Rev. 2014, 43, 4423. [Google Scholar] [CrossRef]
  37. Jiang, C.; Wu, C.; Li, X.; Yao, Y.; Lan, L.; Zhao, F.; Ye, Z.; Ying, Y.; Ping, J. All-electrospun flexible triboelectric nanogenerator based on metallic MXene nanosheets. Nano Energy 2019, 59, 268–276. [Google Scholar] [CrossRef]
  38. Li, Y.; Zhou, B.; Zheng, G.; Liu, X.; Li, T.; Yan, C.; Cheng, C.; Dai, K.; Liu, C.; Shen, C.; et al. Continuously prepared highly conductive and stretchable SWNT/MWNT synergistically composited electrospun thermoplastic polyurethane yarns for wearable sensing. J. Mater. Chem. C 2018, 6, 2258–2269. [Google Scholar] [CrossRef]
  39. Wu, D.; Xie, X.; Zhang, J.; Ma, Y.; Hou, C.; Sun, X.; Yang, X.; Zhang, Y.; Kimura, H.; Du, W. Embedding NiS Nanoflakes in Electrospun Carbon Fibers Containing NiS Nanoparticles for Hybrid Supercapacitors. Chem. Eng. J. 2022, 446, 137262. [Google Scholar] [CrossRef]
  40. Xue, J.; Wu, T.; Dai, Y.; Xia, Y. Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications. Chem. Rev. 2019, 119, 5298–5415. [Google Scholar] [CrossRef]
  41. Jiang, S.; Chen, Y.; Duan, G.; Mei, C.; Greiner, A.; Agarwal, S. Electrospun nanofiber reinforced composites: A review. Polym. Chem. 2018, 9, 2685–2720. [Google Scholar] [CrossRef]
  42. Leote, R.J.B.; Beregoi, M.; Enculescu, I.; Diculescu, V.C. Metallized electrospun polymeric fibers for electrochemical sensors and actuators. Curr. Opin. Elrctrochem. 2022, 34, 101024. [Google Scholar] [CrossRef]
  43. Liu, R.; Hou, L.; Yue, G.; Li, H.; Zhang, J.; Liu, J.; Miao, B.; Wang, N.; Bai, J.; Cui, Z.; et al. Progress of Fabrication and Applications of Electrospun Hierarchically Porous Nanofibers. Adv. Fiber Mater. 2022, 4, 604–630. [Google Scholar] [CrossRef]
  44. Peng, S.; Jin, G.; Li, L.; Li, K.; Srinivasan, M.; Ramakrishna, S.; Chen, J. Multi-functional electrospun nanofibres for advances in tissue regeneration, energy conversion & storage, and water treatment. Chem. Soc. Rev. 2016, 45, 1225–1241. [Google Scholar]
  45. Nauman, S.; Lubineau, G.; Alharbi, H.F. Post Processing Strategies for the Enhancement of Mechanical Properties of ENMs (Electrospun Nanofibrous Membranes): A Review. Membranes 2021, 11, 39. [Google Scholar] [CrossRef] [PubMed]
  46. Lu, T.; Cui, J.; Qu, Q.; Wang, Y.; Zhang, J.; Xiong, R.; Ma, W.; Huang, C. Multistructured Electrospun Nanofibers for Air Filtration: A Review. ACS Appl. Mater. Interfaces 2021, 13, 23293–23313. [Google Scholar] [CrossRef]
  47. Su, Y.; Li, W.; Cheng, X.; Zhou, Y.; Yang, S.; Zhang, X.; Chen, C.; Yang, T.; Pan, H.; Xie, G.; et al. High-performance piezoelectric composites via beta phase programming. Nat. Commun. 2022, 13, 4867. [Google Scholar] [CrossRef] [PubMed]
  48. Li, H.; Kang, Z.; He, E.; Wu, X.; Ma, X.; Yang, D.P.; Diao, Y.; Chen, X. A fish-scale derived multifunctional nanofiber membrane for infected wound healing. Biomater. Sci. 2022, 10, 5284–5300. [Google Scholar] [CrossRef]
  49. Basha, R.Y.; Sampath Kumar, T.S.; Doble, M. Electrospun Nanofibers of Curdlan (β-1,3 Glucan) Blend as a Potential Skin Scaffold Material. Macromol. Mater. Eng. 2017, 30, 1600417. [Google Scholar]
  50. Parangusan, H.; Ponnamma, D.; Al-Maadeed, M.A.A. Stretchable Electrospun PVDF-HFP/Co-ZnO Nanofibers as Piezoelectric Nanogenerators. Sci. Rep. 2018, 8, 754. [Google Scholar]
  51. Hosseini-Alvand, E.; Khorasani, M.T. Fabrication of electrospun nanofibrous thermoresponsive semi-interpenetrating poly(N-isopropylacrylamide)/polyvinyl alcohol networks containing ZnO nanoparticle mats: Characterization and antibacterial and cytocompatibility evaluation. J. Mater. Chem. B 2023, 11, 890–904. [Google Scholar] [CrossRef] [PubMed]
  52. Liang, J.; Zhao, H.; Yue, L.; Fan, G.; Li, T.; Lu, S.; Chen, G.; Gao, S.; Asiri, A.M.; Sun, X. Recent advances in electrospun nanofibers for supercapacitors. J. Mater. Chem. A 2020, 8, 16747–16789. [Google Scholar] [CrossRef]
  53. Zhang, L.; Yin, M.; Wei, X.; Sun, J.; Xu, D. Recent advances in morphology, aperture control, functional control and electrochemical sensors applications of carbon nanofibers. Anal. Biochem. 2022, 656, 114882. [Google Scholar] [CrossRef]
  54. Badoei-Dalfard, A.; Shahba, A.; Zaare, F.; Sargazi, G.; Seyedalipour, B.; Karami, Z. Lipase immobilization on a novel class of Zr-MOF/electrospun nanofibrous polymers: Biochemical characterization and efficient biodiesel production. Int. J. Biol. Macromol. 2021, 192, 1292–1303. [Google Scholar] [CrossRef] [PubMed]
  55. He, R.; Li, J.; Chen, M.; Zhang, S.; Cheng, Y.; Ning, X.; Wang, N. Tailoring moisture electroactive Ag/Zn@cotton coupled with electrospun PVDF/PS nanofibers for antimicrobial face masks. J. Hazard. Mater. 2022, 428, 128239. [Google Scholar] [CrossRef]
  56. Leonés, A.; Sonseca, A.; López, D.; Fiori, S.; Peponi, L. Shape memory effect on electrospun PLA-based fibers tailoring their thermal response. Eur. Polym. J. 2019, 117, 217–226. [Google Scholar] [CrossRef]
  57. Ranjbar-Mohammadi, M.; Shakoori, P.; Arab-Bafrani, Z. Design and characterization of keratin/PVA-PLA nanofibers containing hybrids of nanofibrillated chitosan/ZnO nanoparticles. Int. J. Biol. Macromol. 2021, 187, 554–565. [Google Scholar] [CrossRef]
  58. Hajikhani, M.; Emam-Djomeh, Z.; Askari, G. Fabrication and characterization of mucoadhesive bioplastic patch via coaxial polylactic acid (PLA) based electrospun nanofibers with antimicrobial and wound healing application. Int. J. Biol. Macromol. 2021, 172, 143–153. [Google Scholar] [CrossRef]
  59. Adomavičiūtė, E.; Pupkevičiūtė, S.; Juškaitė, V.; Žilius, M.; Stanys, S.; Pavilonis, A.; Briedis, V. Formation and Investigation of Electrospun PLA Materials with Propolis Extracts and Silver Nanoparticles for Biomedical Applications. J. Nanomater. 2017, 2017, 8612819. [Google Scholar]
  60. Munawar, M.A.; Schubert, D.W. Revealing Electrical and Mechanical Performances of Highly Oriented Electrospun Conductive Nanofibers of Biopolymers with Tunable Diameter. Int. J. Mol. Sci. 2021, 22, 10295. [Google Scholar] [CrossRef]
  61. Garrudo, F.F.F.; Mikael, P.E.; Rodrigues, C.A.V.; Udangawa, R.W.; Paradiso, P.; Chapman, C.A.; Hoffman, P.; Colaco, R.; Cabral, J.M.S.; Morgado, J.; et al. Polyaniline-polycaprolactone fibers for neural applications: Electroconductivity enhanced by pseudo-doping. Mater. Sci. Eng. C Mater. Biol. Appl. 2021, 120, 111680. [Google Scholar] [CrossRef]
  62. Wang, M.; Tremblay, P.L.; Zhang, T. Optimizing the electrical conductivity of polyacrylonitrile/polyaniline with nickel nanoparticles for the enhanced electrostimulation of Schwann cells proliferation. Bioelectrochemistry 2021, 140, 107750. [Google Scholar] [CrossRef] [PubMed]
  63. Munawar, M.A.; Schubert, D.W. Thermal-Induced Percolation Phenomena and Elasticity of Highly Oriented Electrospun Conductive Nanofibrous Biocomposites for Tissue Engineering. Int. J. Mol. Sci. 2022, 23, 8451. [Google Scholar] [CrossRef] [PubMed]
  64. Veeralingam, S.; Badhulika, S. Bi(2)S(3)/PVDF/Ppy-Based Freestanding, Wearable, Transient Nanomembrane for Ultrasensitive Pressure, Strain, and Temperature Sensing. ACS Appl. Bio Mater. 2021, 4, 14–23. [Google Scholar] [CrossRef] [PubMed]
  65. Zarei, M.; Samimi, A.; Khorram, M.; Abdi, M.M.; Golestaneh, S.I. Fabrication and characterization of conductive polypyrrole/chitosan/collagen electrospun nanofiber scaffold for tissue engineering application. Int. J. Biol. Macromol. 2021, 168, 175–186. [Google Scholar] [CrossRef] [PubMed]
  66. Wang, H.; Wang, D.; Peng, Z.; Tang, W.; Li, N.; Liu, F. Assembly of DNA-unctionalized gold nanoparticles on electrospun nanofibers as a fluorescent sensor for nucleic acids. Chem. Commun. 2013, 49, 5568–5570. [Google Scholar] [CrossRef]
  67. Wu, J.; Zhang, Z.; Gu, J.; Zhou, W.; Liang, X.; Zhou, G.; Han, C.C.; Xu, S.; Liu, Y. Mechanism of a long-term controlled drug release system based on simple blended electrospun fibers. J. Control. Release 2020, 320, 337–346. [Google Scholar] [CrossRef]
  68. Bandatang, N.; Pongsomboon, S.A.; Jumpapaeng, P.; Suwanakood, P.; Saengsuwan, S. Antimicrobial electrospun nanofiber mats of NaOH-hydrolyzed chitosan (HCS)/PVP/PVA incorporated with in-situ synthesized AgNPs: Fabrication, characterization, and antibacterial activity. Int. J. Biol. Macromol. 2021, 190, 585–600. [Google Scholar] [CrossRef]
  69. Senthil, R.; Sumathi, V.; Tamilselvi, A.; Kavukcu, S.B.; Aruni, A.W. Functionalized electrospun nanofibers for high efficiency removal of particulate matter. Sci. Rep. 2022, 12, 8411. [Google Scholar] [CrossRef]
  70. Coskuner Filiz, B.; Basaran Elalmis, Y.; Bektas, I.S.; Kanturk Figen, A. Fabrication of stable electrospun blended chitosan-poly(vinyl alcohol) nanofibers for designing naked-eye colorimetric glucose biosensor based on GOx/HRP. Int. J. Biol. Macromol. 2021, 192, 999–1012. [Google Scholar] [CrossRef]
  71. Hejabri Kandeh, S.; Amini, S.; Ebrahimzadeh, H. Simultaneous trace-level monitoring of seven opioid analgesic drugs in biological samples by pipette-tip micro solid phase extraction based on PVA-PAA/CNT-CNC composite nanofibers followed by HPLC-UV analysis. Mikrochim. Acta 2021, 188, 275. [Google Scholar] [CrossRef] [PubMed]
  72. Liang, Q.; Pan, W.; Gao, Q. Preparation of carboxymethyl starch/polyvinyl-alcohol electrospun composite nanofibers from a green approach. Int. J. Biol. Macromol. 2021, 190, 601–606. [Google Scholar] [CrossRef] [PubMed]
  73. Wu, S.; Li, K.; Shi, W.; Cai, J. Preparation and performance evaluation of chitosan/polyvinylpyrrolidone/polyvinyl alcohol electrospun nanofiber membrane for heavy metal ions and organic pollutants removal. Int. J. Biol. Macromol. 2022, 210, 76–84. [Google Scholar] [CrossRef]
  74. Mohamady Hussein, M.A.; Ulag, S.; Abo Dena, A.S.; Sahin, A.; Grinholc, M.; Gunduz, O.; El-Sherbiny, I.; Megahed, M. Chitosan/Gold Hybrid Nanoparticles Enriched Electrospun PVA Nanofibrous Mats for the Topical Delivery of Punica granatum L. Extract: Synthesis, Characterization, Biocompatibility and Antibacterial Properties. Int. J. Nanomed. 2021, 16, 5133–5151. [Google Scholar] [CrossRef] [PubMed]
  75. Li, B.; Xia, X.; Chen, J.; Xia, D.; Xu, R.; Zou, X.; Wang, H.; Liang, C. Paclitaxel-loaded lignin particle encapsulated into electrospun PVA/PVP composite nanofiber for effective cervical cancer cell inhibition. Nanotechnology 2021, 32, 015101. [Google Scholar] [CrossRef] [PubMed]
  76. Pathmanapan, S.; Sekar, M.; Pandurangan, A.K.; Anandasadagopan, S.K. Fabrication of Mesoporous Silica Nanoparticle–Incorporated Coaxial Nanofiber for Evaluating the In Vitro Osteogenic Potential. Appl. Biochem. Biotechnol. 2021, 194, 302–322. [Google Scholar] [CrossRef] [PubMed]
  77. Bazzi, M.; Shabani, I.; Mohandesi, J.A. Enhanced mechanical properties and electrical conductivity of Chitosan/Polyvinyl Alcohol electrospun nanofibers by incorporation of graphene nanoplatelets. J. Mech. Behav. Biomed. Mater. 2022, 125, 104975. [Google Scholar] [CrossRef]
  78. Ghosh, S.K.; Adhikary, P.; Jana, S.; Biswas, A.; Sencadas, V.; Gupta, S.D.; Tudu, B.; Mandal, D. Electrospun gelatin nanofiber based self-powered bio-e-skin for health care monitoring. Nano Energy 2017, 36, 166–175. [Google Scholar] [CrossRef]
  79. Liao, Y.; Wang, R.; Tian, M.; Qiu, C.; Fane, A.G. Fabrication of polyvinylidene fluoride (PVDF) nanofiber membranes by electro-spinning for direct contact membrane distillation. J. Membr. Sci. 2013, 425–426, 30–39. [Google Scholar] [CrossRef]
  80. Jin, H.; Nayeem, M.O.G.; Lee, S.; Matsuhisa, N.; Inoue, D.; Yokota, T.; Hashizume, D.; Someya, T. Highly Durable Nanofiber-Reinforced Elastic Conductors for Skin-Tight Electronic Textiles. ACS Nano 2019, 13, 7905–7912. [Google Scholar] [CrossRef]
  81. He, Z.; Rault, F.; Lewandowski, M.; Mohsenzadeh, E.; Salaun, F. Electrospun PVDF Nanofibers for Piezoelectric Applications: A Review of the Influence of Electrospinning Parameters on the β Phase and Crystallinity Enhancement. Polymers 2021, 13, 174. [Google Scholar] [CrossRef] [PubMed]
  82. Castkova, K.; Kastyl, J.; Sobola, D.; Petrus, J.; Stastna, E.; Riha, D.; Tofel, P. Structure-Properties Relationship of Electrospun PVDF Fibers. Nanomaterials 2020, 10, 1221. [Google Scholar] [CrossRef] [PubMed]
  83. Al-Dhahebi, A.M.; Jose, R.; Mustapha, M.; Saheed, M.S.M. Ultrasensitive aptasensor using electrospun MXene/polyvinylidene fluoride nanofiber composite for Ochratoxin A detection. Food Chem. 2022, 390, 133105. [Google Scholar] [CrossRef] [PubMed]
  84. Lee, C.-G.; Javed, H.; Zhang, D.; Kim, J.-H.; Westerhoff, P.; Li, Q.; Alvarez, P.J.J. Porous Electrospun Fibers Embedding TiO2 for Adsorption and Photocatalytic Degradation of Water Pollutants. Environ. Sci. Technol. 2018, 52, 4285–4293. [Google Scholar] [CrossRef]
  85. Oh, T.I.; Yoon, S.; Kim, T.E.; Wi, H.; Kim, K.J.; Woo, E.J.; Sadleir, R.J. Nanofiber web textile dry electrodes for long-term biopotential recording. IEEE Trans. Biomed. Circuits Syst. 2013, 7, 204–211. [Google Scholar]
  86. Li, H.; Zhang, W.; Ding, Q.; Jin, X.; Ke, Q.; Li, Z.; Wang, D.; Huang, C. Facile Strategy for Fabrication of Flexible, Breathable, and Washable Piezoelectric Sensors via Welding of Nanofibers with Multiwalled Carbon Nanotubes (MWCNTs). ACS Appl. Mater. Interfaces 2019, 11, 38023–38030. [Google Scholar] [CrossRef]
  87. Lee, J.C.; Suh, I.W.; Park, C.H.; Kim, C.S. Polyvinylidene fluoride/silk fibroin-based bio-piezoelectric nanofibrous scaffolds for biomedical application. J. Tissue Eng. Regen. Med. 2021, 15, 869–877. [Google Scholar] [CrossRef]
  88. Kaspar, P.; Sobola, D.; Castkova, K.; Knapek, A.; Burda, D.; Orudzhev, F.; Dallaev, R.; Tofel, P.; Trcka, T.; Grmela, L.; et al. Characterization of Polyvinylidene Fluoride (PVDF) Electrospun Fibers Doped by Carbon Flakes. Polymers 2020, 12, 2766. [Google Scholar] [CrossRef]
  89. Sengupta, A.; Das, S.; Dasgupta, S.; Sengupta, P.; Datta, P. Flexible Nanogenerator from Electrospun PVDF-Polycarbazole Nanofiber Membranes for Human Motion Energy-Harvesting Device Applications. ACS Biomater. Sci. Eng. 2021, 7, 1673–1685. [Google Scholar] [CrossRef]
  90. Borrego, M.; Martin-Alfonso, J.E.; Sanchez, M.C.; Valencia, C.; Franco, J.M. Electrospun lignin-PVP nanofibers and their ability for structuring oil. Int. J. Biol. Macromol. 2021, 180, 212–221. [Google Scholar] [CrossRef]
  91. Wang, S.; Shao, H.-Q.; Liu, Y.; Tang, C.-Y.; Zhao, X.; Ke, K.; Bao, R.-Y.; Yang, M.-B.; Yang, W. Boosting piezoelectric response of PVDF-TrFE via MXene for self-powered linear pressure sensor. Compos. Sci. Technol. 2021, 202, 108600. [Google Scholar] [CrossRef]
  92. Luo, Y.; Zhao, L.; Luo, G.; Li, M.; Han, X.; Xia, Y.; Li, Z.; Lin, Q.; Yang, P.; Dai, L.; et al. All electrospun fabrics based piezoelectric tactile sensor. Nanotechnology 2022, 33, 415502. [Google Scholar] [CrossRef]
  93. Rana, S.M.S.; Rahman, M.T.; Salauddin, M.; Sharma, S.; Maharjan, P.; Bhatta, T.; Cho, H.; Park, C.; Park, J.Y. Electrospun PVDF-TrFE/MXene Nanofiber Mat-Based Triboelectric Nanogenerator for Smart Home Appliances. ACS Appl. Mater. Interfaces 2021, 13, 4955–4967. [Google Scholar] [CrossRef] [PubMed]
  94. Zheng, X.; Liu, Y.; Liu, X.; Li, Q.; Zheng, Y. A novel PVDF-TiO(2)@g-C(3)N(4) composite electrospun fiber for efficient photocatalytic degradation of tetracycline under visible light irradiation. Ecotoxicol. Environ. Saf. 2021, 210, 111866. [Google Scholar] [CrossRef] [PubMed]
  95. Venkatesan, M.; Chen, W.-C.; Cho, C.-J.; Veeramuthu, L.; Chen, L.-G.; Li, K.-Y.; Tsai, M.-L.; Lai, Y.-C.; Lee, W.-Y.; Chen, W.-C.; et al. Enhanced piezoelectric and photocatalytic performance of flexible energy harvester based on CsZn0.75Pb0.25I3/CNC–PVDF composite nanofibers. Chem. Eng. J. 2022, 433, 133620. [Google Scholar] [CrossRef]
  96. Bhatta, T.; Maharjan, P.; Cho, H.; Park, C.; Yoon, S.H.; Sharma, S.; Salauddin, M.; Rahman, M.T.; Rana, S.M.S.; Park, J.Y. High-performance triboelectric nanogenerator based on MXene functionalized polyvinylidene fluoride composite nanofibers. Nano Energy 2021, 81, 105670. [Google Scholar] [CrossRef]
  97. Deng, W.; Yang, T.; Jin, L.; Yan, C.; Huang, H.; Chu, X.; Wang, Z.; Xiong, D.; Tian, G.; Gao, Y.; et al. Cowpea-structured PVDF/ZnO nanofibers based flexible self-powered piezoelectric bending motion sensor towards remote control of gestures. Nano Energy 2019, 55, 516–525. [Google Scholar] [CrossRef]
  98. Shi, L.; Jin, H.; Dong, S.; Huang, S.; Kuang, H.; Xu, H.; Chen, J.; Xuan, W.; Zhang, S.; Li, S.; et al. High-performance triboelectric nanogenerator based on electrospun PVDF-graphene nanosheet composite nanofibers for energy harvesting. Nano Energy 2021, 80, 105599. [Google Scholar] [CrossRef]
  99. Shi, K.; Sun, B.; Huang, X.; Jiang, P. Synergistic effect of graphene nanosheet and BaTiO3 nanoparticles on performance enhancement of electrospun PVDF nanofiber mat for flexible piezoelectric nanogenerators. Nano Energy 2018, 52, 153–162. [Google Scholar] [CrossRef]
  100. Lee, J.; Kim, S.; Lee, J.; Yang, D.; Park, B.C.; Ryu, S.; Park, I. A stretchable strain sensor based on a metal nanoparticle thin film for human motion detection. Nanoscale 2014, 6, 11932–11939. [Google Scholar] [CrossRef]
  101. Zhang, M.; Wang, W.L.; Xia, G.T.; Wang, L.C.; Wang, K. Self-Powered Electronic Skin for Remote Human-Machine Synchronization. ACS Appl. Electron. Mater. 2023, 5, 498–508. [Google Scholar] [CrossRef]
  102. Liu, M.-Y.; Hang, C.-Z.; Zhao, X.-F.; Zhu, L.-Y.; Ma, R.-G.; Wang, J.-C.; Lu, H.-L.; Zhang, D.W. Advance on flexible pressure sensors based on metal and carbonaceous nanomaterial. Nano Energy 2021, 87, 106181. [Google Scholar] [CrossRef]
  103. Dong, K.; Peng, X.; Wang, Z.L. Fiber/Fabric-Based Piezoelectric and Triboelectric Nanogenerators for Flexible/Stretchable and Wearable Electronics and Artificial Intelligence. Adv. Mater. 2020, 32, e1902549. [Google Scholar] [CrossRef]
  104. Peng, Y.; Yang, N.; Xu, Q.; Dai, Y.; Wang, Z. Recent advances in flexible tactile sensors for intelligent systems. Sensors 2021, 21, 5392. [Google Scholar] [CrossRef] [PubMed]
  105. Liu, Z.; Zhu, T.; Wang, J.; Zheng, Z.; Li, Y.; Li, J.; Lai, Y. Functionalized Fiber-Based Strain Sensors: Pathway to Next-Generation Wearable Electronics. Nanomicro. Lett. 2022, 14, 61. [Google Scholar] [CrossRef]
  106. Liu, X.; Miao, J.; Fan, Q.; Zhang, W.; Zuo, X.; Tian, M.; Zhu, S.; Zhang, X.; Qu, L. Recent Progress on Smart Fiber and Textile Based Wearable Strain Sensors: Materials, Fabrications and Applications. Adv. Fiber Mater. 2022, 4, 361–389. [Google Scholar] [CrossRef]
  107. Ji, G.; Chen, Z.; Li, H.; Awuye, D.E.; Guan, M.; Zhu, Y. Electrospinning-Based Biosensors for Health Monitoring. Biosensors 2022, 12, 876. [Google Scholar] [CrossRef]
  108. Cai, C.; Gong, H.; Li, W.; Gao, F.; Jiang, Q.; Cheng, Z.; Han, Z.; Li, S. A flexible and highly sensitive pressure sensor based on three-dimensional electrospun carbon nanofibers. RSC Adv. 2021, 11, 13898–13905. [Google Scholar] [CrossRef]
  109. Lu, L.; Wei, X.; Zhang, Y.; Zheng, G.; Dai, K.; Liu, C.; Shen, C. A flexible and self-formed sandwich structure strain sensor based on AgNW decorated electrospun fibrous mats with excellent sensing capability and good oxidation inhibition properties. J. Mater. Chem. C 2017, 5, 7035–7042. [Google Scholar] [CrossRef]
  110. Someya, T.; Kato, Y.; Sekitani, T.; Iba, S.; Noguchi, Y. Murase, networks of pressure and thermal sensors with organic transistor active matrixes. Proc. Natl. Acad. Sci. USA 2005, 102, 12321–12325. [Google Scholar] [CrossRef]
  111. Baur, C.; DiMaio, J.R.; McAllister, E.; Hossini, R.; Wagener, E.; Ballato, J.; Priya, S.; Ballato, A.; Smith, D.W. Enhanced piezoelectric performance from carbon fluoropolymer nanocomposites. J. Appl. Phys. 2012, 112, 124104. [Google Scholar]
  112. Zhu, P.; Zhang, B.; Wang, H.; Wu, Y.; Cao, H.; He, L.; Li, C.; Luo, X.; Li, X.; Mao, Y. 3D printed triboelectric nanogenerator as self-powered human-machine interactive sensor for breathing-based language expression. Nano Res. 2022, 15, 7460–7467. [Google Scholar] [CrossRef]
  113. Zhang, N.; Qin, C.; Feng, T.; Li, J.; Yang, Z.; Sun, X.; Liang, E.; Mao, Y. Non-contact cylindrical rotating triboelectric nanogenerator for harvesting kinetic energy from hydraulics. Nano Res. 2020, 13, 1903–1907. [Google Scholar] [CrossRef]
  114. Mao, Y.; Zhang, N.; Tang, Y.; Wang, M.; Chao, M.; Liang, E. A paper triboelectric nanogenerator for self-powered electronic systems. Nanoscale 2017, 9, 14499–14505. [Google Scholar] [CrossRef] [PubMed]
  115. Sun, H.; Fang, X.; Fang, Z.; Zhao, L.; Tian, B.; Verma, P.; Maeda, R.; Jiang, Z. An ultrasensitive and stretchable strain sensor based on a microcrack structure for motion monitoring. Microsyst. Nanoeng. 2022, 8, 111. [Google Scholar] [CrossRef]
  116. Li, P.; Zhao, L.; Jiang, Z.; Yu, M.; Li, Z.; Li, X. Self-Powered Flexible Sensor Based on the Graphene Modified P(VDF-TrFE) Electrospun Fibers for Pressure Detection. Macromol. Mater. Eng. 2019, 304, 1900504. [Google Scholar] [CrossRef]
  117. Wang, P.; Sun, G.; Yu, W.; Li, G.; Meng, C.; Guo, S. Wearable, ultrathin and breathable tactile sensors with an integrated all-nanofiber network structure for highly sensitive and reliable motion monitoring. Nano Energy 2022, 104, 107883. [Google Scholar] [CrossRef]
  118. Zhou, B.; Li, C.; Liu, Z.; Zhang, X.; Li, Q.; He, H.; Zhou, Y.; Jiang, L. A Highly Sensitive and Flexible Strain Sensor Based on Dopamine-Modified Electrospun Styrene-Ethylene-Butylene-Styrene Block Copolymer Yarns and Multi Walled Carbon Nanotubes. Polymers 2022, 14, 3030. [Google Scholar] [CrossRef]
  119. Ghosh, R.; Pin, K.Y.; Reddy, V.S.; Jayathilaka, W.A.D.M.; Ji, D.; Serrano-García, W.; Bhargava, S.K.; Ramakrishna, S.; Chinnappan, A. Micro/nanofiber-based noninvasive devices for health monitoring diagnosis and rehabilitation. Appl. Phys. Rev. 2020, 7, 41309. [Google Scholar] [CrossRef]
  120. Sardana, S.; Singh, Z.; Sharma, A.K.; Kaur, N.; Pati, P.K.; Mahajan, A. Self-powered biocompatible humidity sensor based on an electrospun anisotropic triboelectric nanogenerator for non-invasive diagnostic applications. Sens. Actuators B Chem. 2022, 371, 132507. [Google Scholar] [CrossRef]
  121. Lu, L.; Yang, B.; Liu, J. Flexible multifunctional graphite nanosheet/electrospun-polyamide 66 nanocomposite sensor for ECG, strain, temperature and gas measurements. Chem. Eng. J. 2020, 400, 125928. [Google Scholar] [CrossRef]
  122. Phadkule, S.S.; Sarma, S. High-performance flexible temperature sensor from hybrid nanocomposite for continuous human body temperature monitoring. Polym. Compos. 2022, 44, 1381–1391. [Google Scholar] [CrossRef]
  123. Ponnamma, D.; Parangusan, H.; Tanvir, A.; AlMa’adeed, M.A.A. Smart and robust electrospun fabrics of piezoelectric polymer nanocomposite for self-powering electronic textiles. Mater. Des. 2019, 184, 108176. [Google Scholar] [CrossRef]
  124. Lee, J.H.; Chen, H.; Kim, E.; Zhang, H.; Wu, K.; Zhang, H.; Shen, X.; Zheng, Q.; Yang, J.; Jeon, S.; et al. Flexible temperature sensors made of aligned electrospun carbon nanofiber films with outstanding sensitivity and selectivity towards temperature. Mater. Horiz. 2021, 8, 1488–1498. [Google Scholar] [CrossRef]
  125. Chen, X.; Zhang, D.; Tang, M.; Yang, C.; Luan, H. Microstructured Flexible Pressure Sensor Based on Nanofibrous Films for Human Motions and Physiological Detection. IEEE Sens. J. 2022, 22, 19191–19197. [Google Scholar] [CrossRef]
  126. Chen, X.; Song, Y.; Chen, H.; Zhang, J.; Zhang, H. An ultrathin stretchable triboelectric nanogenerator with coplanar electrode for energy harvesting and gesture sensing. J. Mater. Chem. A 2017, 5, 12361–12368. [Google Scholar] [CrossRef]
  127. Cheng, Y.; Wang, C.; Zhong, J.; Lin, S.; Xiao, Y.; Zhong, Q.; Jiang, H.; Wu, N.; Li, W.; Chen, S.; et al. Electrospun polyetherimide electret nonwoven for bi-functional smart face mask. Nano Energy 2017, 34, 562–569. [Google Scholar] [CrossRef]
  128. Roy, K.; Ghosh, S.K.; Sultana, A.; Garain, S.; Xie, M.; Bowen, C.R.; Henkel, K.; Schmeiβer, D.; Mandal, D. A Self-Powered Wearable Pressure Sensor and Pyroelectric Breathing Sensor Based on GO Interfaced PVDF Nanofibers. ACS Appl. Nano Mater. 2019, 2, 2013–2025. [Google Scholar] [CrossRef]
  129. Li, M.; Wang, Y.; Wen, X.; Tang, A.; Wan, C.; Sui, T.; Zhang, D.; Ju, X. A Washable, Permeable, and Ultrasensitive Sn-Based Textile Pressure Sensor for Health Monitoring. IEEE Trans. Electron Devices 2023, 70, 739–745. [Google Scholar] [CrossRef]
  130. Chen, X.; Song, Y.; Su, Z.; Chen, H.; Cheng, X.; Zhang, J.; Han, M.; Zhang, H. Flexible fiber-based hybrid nanogenerator for biomechanical energy harvesting and physiological monitoring. Nano Energy 2017, 38, 43–50. [Google Scholar] [CrossRef]
  131. Zhang, Z.; Wang, Y.; Wang, Q.; Shang, L. Smart Film Actuators for Biomedical Applications. Small 2022, 18, e2105116. [Google Scholar] [CrossRef] [PubMed]
  132. Sharma, S.; Chhetry, A.; Ko, S.; Park, J.Y. A Hybrid Ionic Nanofibrous Membrane Based Pressure Sensor with Ultra-High Sensitivity over Broad Pressure Range for Wearable Healthcare Applications. In Proceedings of the 2021 IEEE 34th International Conference on Micro Electro Mechanical Systems (MEMS), Virtual, 25–29 January 2021; pp. 55–58. [Google Scholar]
  133. Yang, M.; Yang, Z.; Lv, C.; Wang, Z.; Lu, Z.; Lu, G.; Jia, X.; Wang, C. Electrospun bifunctional MXene-based electronic skins with high performance electromagnetic shielding and pressure sensing. Compos. Sci. Technol. 2022, 221, 109313. [Google Scholar] [CrossRef]
  134. Veeralingam, S.; Priya, S.; Badhulika, S. NiO nanofibers interspersed sponge based low cost, multifunctional platform for broadband UV protection, ultrasensitive strain and robust finger-tip skin inspired pressure sensor. Chem. Eng. J. 2020, 389, 124415. [Google Scholar] [CrossRef]
  135. Lin, M.-F.; Cheng, C.; Yang, C.-C.; Hsiao, W.-T.; Yang, C.-R. A wearable and highly sensitive capacitive pressure sensor integrated a dual-layer dielectric layer of PDMS microcylinder array and PVDF electrospun fiber. Org. Electron. 2021, 98, 106290. [Google Scholar] [CrossRef]
  136. Nan, N.; He, J.; You, X.; Sun, X.; Zhou, Y.; Qi, K.; Shao, W.; Liu, F.; Chu, Y.; Ding, B. A Stretchable, Highly Sensitive, and Multimodal Mechanical Fabric Sensor Based on Electrospun Conductive Nanofiber Yarn for Wearable Electronics. Adv. Mater. Technol. 2019, 4, 1800338. [Google Scholar] [CrossRef]
  137. Cho, S.; Jang, S.; Lee, D.; Ra, Y.; Kam, D.; Kim, J.W.; Shin, D.; Seo, K.D.; Choi, D. Self-powered hybrid triboelectric–piezoelectric electronic skin based on P(VDF-TrFE) electrospun nanofibers for artificial sensory system. Funct. Compos. Struct. 2022, 4, 045005. [Google Scholar] [CrossRef]
  138. Das, R.; Zeng, W.; Asci, C.; Del-Rio-Ruiz, R.; Sonkusale, S. Recent progress in electrospun nanomaterials for wearables. APL Bioeng. 2022, 6, 021505. [Google Scholar] [CrossRef]
  139. Wang, Y.; Wang, J.; Cao, S.; Kong, D. A stretchable and breathable form of epidermal device based on elastomeric nanofibre textiles and silver nanowires. J. Mater. Chem. C 2019, 7, 9748–9755. [Google Scholar] [CrossRef]
  140. Zhou, Y.; He, J.; Wang, H.; Qi, K.; Nan, N.; You, X.; Shao, W.; Wang, L.; Ding, B.; Cui, S. Highly sensitive, self-powered and wearable electronic skin based on pressure-sensitive nanofiber woven fabric sensor. Sci. Rep. 2017, 7, 12949. [Google Scholar] [CrossRef]
  141. Li, R.; Panahi-Sarmad, M.; Chen, T.; Wang, A.; Xu, R.; Xiao, X. Highly Sensitive and Flexible Capacitive Pressure Sensor Based on a Dual-Structured Nanofiber Membrane as the Dielectric for Attachable Wearable Electronics. ACS Appl. Electron. Mater. 2022, 4, 469–477. [Google Scholar] [CrossRef]
  142. Park, S.H.; Lee, H.B.; Yeon, S.M.; Park, J.; Lee, N.K. Flexible and Stretchable Piezoelectric Sensor with Thickness-Tunable Configuration of Electrospun Nanofiber Mat and Elastomeric Substrates. ACS Appl. Mater. Interfaces 2016, 8, 24773–24781. [Google Scholar] [CrossRef] [PubMed]
  143. Chen, G.; Chen, G.; Pan, L.; Chen, D. Electrospun flexible PVDF/GO piezoelectric pressure sensor for human joint monitoring. Diamond Relat. Mater. 2022, 129, 109358. [Google Scholar] [CrossRef]
  144. Chung, M.; Fortunato, G.; Radacsi, N. Wearable flexible sweat sensors for healthcare monitoring: A review. J. R. Soc. Interface 2019, 16, 20190217. [Google Scholar] [CrossRef] [PubMed]
  145. Zhao, X.; Chang, A.; Li, J.; Xu, J.; Hollister, J.; Che, Z.; Wan, X.; Yin, J.; Wang, S.; Lee, S.; et al. Air-Permeable Textile Bioelectronics for Wearable Energy Harvesting and Active Sensing. Adv. Mater. Technol. 2023, 2201703. [Google Scholar] [CrossRef]
  146. Hu, W.P.; Zhang, B.; Zhang, J.; Luo, W.L.; Guo, Y.; Chen, S.J.; Yun, M.J.; Ramakrishna, S.; Long, Y.Z. Ag/alginate nanofiber membrane for flexible electronic skin. Nanotechnology 2017, 28, 445502. [Google Scholar] [CrossRef]
  147. Zhao, Y.; Ren, M.; Shang, Y.; Li, J.; Wang, S.; Zhai, W.; Zheng, G.; Dai, K.; Liu, C.; Shen, C. Ultra-sensitive and durable strain sensor with sandwich structure and excellent anti-interference ability for wearable electronic skins. Compos. Sci. Technol. 2020, 200, 360–371. [Google Scholar] [CrossRef]
  148. You, X.; He, J.; Nan, N.; Sun, X.; Qi, K.; Zhou, Y.; Shao, W.; Liu, F.; Cui, S. Stretchable capacitive fabric electronic skin woven by electrospun nanofiber coated yarns for detecting tactile and multimodal mechanical stimuli. J. Mater. Chem. C 2018, 6, 12981–12991. [Google Scholar] [CrossRef]
  149. Wang, X.; Liu, X.; Schubert, D.W. Highly Sensitive Ultrathin Flexible Thermoplastic Polyurethane/Carbon Black Fibrous Film Strain Sensor with Adjustable Scaffold Networks. Nano-Micro Lett. 2021, 13, 64. [Google Scholar] [CrossRef]
  150. Wang, P.; Yu, W.; Li, G.; Meng, C.; Guo, S. Printable, flexible, breathable and sweatproof bifunctional sensors based on an all-nanofiber platform for fully decoupled pressure–temperature sensing application. Chem. Eng. J. 2023, 452, 139174. [Google Scholar] [CrossRef]
  151. Araldi da Silva, B.; de Sousa Cunha, R.; Valério, A.; De Noni Junior, A.; Hotza, D.; Gómez González, S.Y. Electrospinning of cellulose using ionic liquids: An overview on processing and applications. Eur. Polym. J. 2021, 147, 110283. [Google Scholar] [CrossRef]
  152. Mirjalali, S.; Mahdavi Varposhti, A.; Abrishami, S.; Bagherzadeh, R.; Asadnia, M.; Huang, S.; Peng, S.; Wang, C.H.; Wu, S. A Review on Wearable Electrospun Polymeric Piezoelectric Sensors and Energy Harvesters. Macromol. Mater. Eng. 2022, 308, 2200442. [Google Scholar] [CrossRef]
  153. Qiu, J.; Yu, T.; Zhang, W.; Zhao, Z.; Zhang, Y.; Ye, G.; Zhao, Y.; Du, X.; Liu, X.; Yang, L.; et al. A Bioinspired, Durable, and Nondisposable Transparent Graphene Skin Electrode for Electrophysiological Signal Detection. ACS Mater. Lett. 2020, 2, 999–1007. [Google Scholar] [CrossRef]
  154. Cho, K.W.; Sunwoo, S.H.; Hong, Y.J.; Koo, J.H.; Kim, J.H.; Baik, S.; Hyeon, T.; Kim, D.H. Soft Bioelectronics Based on Nanomaterials. Chem. Rev. 2022, 122, 5068–5143. [Google Scholar] [CrossRef]
  155. Zhi, C.; Shi, S.; Si, Y.; Fei, B.; Huang, H.; Hu, J. Recent Progress of Wearable Piezoelectric Pressure Sensors Based on Nanofibers, Yarns, and Their Fabrics via Electrospinning. Adv. Mater. Technol. 2022, 8, 2201161. [Google Scholar] [CrossRef]
  156. Huang, J.; Xie, G.; Wei, Q.; Su, Y.; Xu, X.; Jiang, Y. Degradable MXene-Doped Polylactic Acid Textiles for Wearable Biomonitoring. ACS Appl. Mater. Interfaces 2023, 15, 5600–5607. [Google Scholar] [CrossRef]
  157. Liang, F.-C.; Ku, H.-J.; Cho, C.-J.; Chen, W.-C.; Lee, W.-Y.; Chen, W.-C.; Rwei, S.-P.; Borsali, R.; Kuo, C.-C. An intrinsically stretchable and ultrasensitive nanofiber-based resistive pressure sensor for wearable electronics. J. Mater. Chem. C 2020, 8, 5361–5369. [Google Scholar] [CrossRef]
  158. Qi, K.; Wang, H.; You, X.; Tao, X.; Li, M.; Zhou, Y.; Zhang, Y.; He, J.; Shao, W.; Cui, S. Core-sheath nanofiber yarn for textile pressure sensor with high pressure sensitivity and spatial tactile acuity. J. Colloid Interface Sci. 2020, 561, 93–103. [Google Scholar] [CrossRef]
  159. Yang, J.; Zhang, Z.; Zhou, P.; Zhang, Y.; Liu, Y.; Xu, Y.; Gu, Y.; Qin, S.; Haick, H.; Wang, Y. Toward a new generation of permeable skin electronics. Nanoscale 2023, 15, 3051–3078. [Google Scholar] [CrossRef]
  160. Wang, Y.; Yokota, T.; Someya, T. Electrospun nanofiber-based soft electronics. NPG Asia Mater. 2021, 13, 22. [Google Scholar] [CrossRef]
  161. Sharifuzzaman, M.; Zahed, M.A.; Sharma, S.; Yoon, S.; Park, C.; Park, J.Y. Laser-Carbonized Mxene-Reinforced Hierarchical Nanofibers for Breathable and Reusable Electrophysiological E-Tattoos. In Proceedings of the 2021 21st International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers), Orlando, FL, USA, 20–24 June 2021; pp. 904–907. [Google Scholar]
  162. Sun, F.; Jiang, H.; Wang, H.; Zhong, Y.; Xu, Y.; Xing, Y.; Yu, M.; Feng, L.W.; Tang, Z.; Liu, J.; et al. Soft Fiber Electronics Based on Semiconducting Polymer. Chem. Rev. 2023, 123, 4693–4763. [Google Scholar] [CrossRef]
  163. Jiang, N.; Li, H.; Hu, D.; Xu, Y.; Hu, Y.; Zhu, Y.; Han, X.; Zhao, G.; Chen, J.; Chang, X.; et al. Stretchable strain and temperature sensor based on fibrous polyurethane film saturated with ionic liquid. Compos. Commun. 2021, 27, 100845. [Google Scholar] [CrossRef]
  164. Ding, S.; Lou, Y.; Niu, Z.; Wang, J.; Jin, X.; Ma, J.; Wang, B.; Li, X. A Highly Sensitive, Breathable, and Biocompatible Wearable Sensor Based on Nanofiber Membrane for Pressure and Humidity Monitoring. Macromol. Mater. Eng. 2022, 307, 2200233. [Google Scholar] [CrossRef]
  165. Li, B.; Luo, J.; Huang, X.; Lin, L.; Wang, L.; Hu, M.; Tang, L.; Xue, H.; Gao, J.; Mai, Y.-W. A highly stretchable, super-hydrophobic strain sensor based on polydopamine and graphene reinforced nanofiber composite for human motion monitoring. Compos. Part B Eng. 2020, 181, 107580. [Google Scholar] [CrossRef]
  166. Zhou, Y.; Zhan, P.; Ren, M.; Zheng, G.; Dai, K.; Mi, L.; Liu, C.; Shen, C. Significant Stretchability Enhancement of a Crack-Based Strain Sensor Combined with High Sensitivity and Superior Durability for Motion Monitoring. ACS Appl. Mater. Interfaces 2019, 11, 7405–7414. [Google Scholar] [CrossRef] [PubMed]
  167. Shi, S.; Wang, Y.; Meng, Q.; Lan, Z.; Liu, C.; Zhou, Z.; Sun, Q.; Shen, X. Conductive Cellulose-Derived Carbon Nanofibrous Membranes with Superior Softness for High-Resolution Pressure Sensing and Electrophysiology Monitoring. ACS Appl. Mater. Interfaces 2023, 15, 1903–1913. [Google Scholar] [CrossRef] [PubMed]
  168. Li, Y.; Wang, S.; Xiao, Z.-C.; Yang, Y.; Deng, B.-W.; Yin, B.; Ke, K.; Yang, M.-B. Flexible TPU strain sensors with tunable sensitivity and stretchability by coupling AgNWs with rGO. J. Mater. Chem. C 2020, 8, 4040–4048. [Google Scholar] [CrossRef]
  169. Qin, W.; Geng, J.; Lin, C.; Li, G.; Peng, H.; Xue, Y.; Zhou, B.; Liu, G. Flexible multifunctional TPU strain sensors with improved sensitivity and wide sensing range based on MXene/AgNWs. J. Mater. Sci. Mater. Electron. 2023, 34, 564. [Google Scholar] [CrossRef]
  170. Alam, M.M.; Lee, S.; Kim, M.; Han, K.S.; Cao, V.A.; Nah, J. Ultra-flexible nanofiber-based multifunctional motion sensor. Nano Energy 2020, 72, 104672. [Google Scholar] [CrossRef]
  171. Ma, Z.; Huang, Q.; Xu, Q.; Zhuang, Q.; Zhao, X.; Yang, Y.; Qiu, H.; Yang, Z.; Wang, C.; Chai, Y.; et al. Permeable superelastic liquid-metal fibre mat enables biocompatible and monolithic stretchable electronics. Nat. Mater. 2021, 20, 859–868. [Google Scholar] [CrossRef]
  172. Zhang, J.H.; Li, Z.; Xu, J.; Li, J.; Yan, K.; Cheng, W.; Xin, M.; Zhu, T.; Du, J.; Chen, S.; et al. Versatile self-assembled electrospun micropyramid arrays for high-performance on-skin devices with minimal sensory interference. Nat. Commun. 2022, 13, 5839. [Google Scholar] [CrossRef]
  173. Su, Y.; Chen, C.; Pan, H.; Yang, Y.; Chen, G.; Zhao, X.; Li, W.; Gong, Q.; Xie, G.; Zhou, Y.; et al. Muscle Fibers Inspired High-Performance Piezoelectric Textiles for Wearable Physiological Monitoring. Adv. Funct. Mater. 2021, 31, 2010962. [Google Scholar] [CrossRef]
  174. Peng, X.; Dong, K.; Ning, C.; Cheng, R.; Yi, J.; Zhang, Y.; Sheng, F.; Wu, Z.; Wang, Z.L. All-Nanofiber Self-Powered Skin-Interfaced Real-Time Respiratory Monitoring System for Obstructive Sleep Apnea-Hypopnea Syndrome Diagnosing. Adv. Funct. Mater. 2021, 31, 2103559. [Google Scholar] [CrossRef]
  175. Graham, S.A.; Patnam, H.; Manchi, P.; Paranjape, M.V.; Kurakula, A.; Yu, J.S. Biocompatible electrospun fibers-based triboelectric nanogenerators for energy harvesting and healthcare monitoring. Nano Energy 2022, 100, 107455. [Google Scholar] [CrossRef]
  176. Yang, T.; Deng, W.; Chu, X.; Wang, X.; Hu, Y.; Fan, X.; Song, J.; Gao, Y.; Zhang, B.; Tian, G.; et al. Hierarchically Microstructure-Bioinspired Flexible Piezoresistive Bioelectronics. ACS Nano 2021, 15, 11555–11563. [Google Scholar] [CrossRef]
  177. Gao, Z.; Xiao, X.; Carlo, A.D.; Yin, J.; Wang, Y.; Huang, L.; Tang, J.; Chen, J. Advances in Wearable Strain Sensors Based on Electrospun Fibers. Adv. Funct. Mater. 2023, 33, 2214265. [Google Scholar] [CrossRef]
  178. Guo, H.; Wan, J.; Wu, H.; Wang, H.; Miao, L.; Song, Y.; Chen, H.; Han, M.; Zhang, H. Self-Powered Multifunctional Electronic Skin for a Smart Anti-Counterfeiting Signature System. ACS Appl. Mater. Interfaces 2020, 12, 22357–22364. [Google Scholar] [CrossRef]
  179. Wang, M.; Wang, K.; Ma, C.; Uzabakiriho, P.C.; Chen, X.; Zhao, G. Mechanical Gradients Enable Highly Stretchable Electronics Based on Nanofiber Substrates. ACS Appl. Mater. Interfaces 2022, 14, 35997–36006. [Google Scholar] [CrossRef]
  180. Cheng, H.; Wang, B.; Yang, K.; Yang, Y.Q.; Wang, C. A high-performance piezoresistive sensor based on poly (styrene-co-methacrylic acid)@polypyrrole microspheres/graphene-decorated TPU electrospun membrane for human motion detection. Chem. Eng. J. 2021, 426, 131152. [Google Scholar] [CrossRef]
  181. Yang, G.; Tang, X.; Zhao, G.; Li, Y.; Ma, C.; Zhuang, X.; Yan, J. Highly sensitive, direction-aware, and transparent strain sensor based on oriented electrospun nanofibers for wearable electronic applications. Chem. Eng. J. 2022, 435, 135004. [Google Scholar] [CrossRef]
  182. Lu, X.; Qin, Y.; Chen, X.; Peng, C.; Yang, Y.; Zeng, Y. An ultra-wide sensing range film strain sensor based on a branch-shaped PAN-based carbon nanofiber and carbon black synergistic conductive network for human motion detection and human–machine interfaces. J. Mater. Chem. C 2022, 10, 6296–6305. [Google Scholar] [CrossRef]
  183. Roy, K.; Jana, S.; Mallick, Z.; Ghosh, S.K.; Dutta, B.; Sarkar, S.; Sinha, C.; Mandal, D. Two-Dimensional MOF Modulated Fiber Nanogenerator for Effective Acoustoelectric Conversion and Human Motion Detection. Langmuir 2021, 37, 7107–7117. [Google Scholar] [CrossRef] [PubMed]
  184. Ren, M.; Sun, Z.; Zhang, M.; Yang, X.; Guo, D.; Dong, S.; Dhakal, R.; Yao, Z.; Li, Y.; Kim, N.Y. A high-performance wearable pressure sensor based on an MXene/PVP composite nanofiber membrane for health monitoring. Nanoscale Adv. 2022, 4, 3987–3995. [Google Scholar] [CrossRef] [PubMed]
  185. Kweon, O.Y.; Lee, S.J.; Oh, J.H. Wearable high-performance pressure sensors based on three-dimensional electrospun conductive nanofibers. NPG Asia Mater. 2018, 10, 540–551. [Google Scholar] [CrossRef]
  186. Cheng, Y.; Zhu, W.; Lu, X.; Wang, C. Mechanically robust, stretchable, autonomously adhesive, and environmentally tolerant triboelectric electronic skin for self-powered healthcare monitoring and tactile sensing. Nano Energy 2022, 102, 107636. [Google Scholar] [CrossRef]
  187. Wang, S.; Shi, K.; Chai, B.; Qiao, S.; Huang, Z.; Jiang, P.; Huang, X. Core-shell structured silk Fibroin/PVDF piezoelectric nanofibers for energy harvesting and self-powered sensing. Nano Mater. Sci. 2022, 4, 126–132. [Google Scholar] [CrossRef]
  188. Wu, D.; Cheng, X.; Chen, Z.; Xu, Z.; Zhu, M.; Zhao, Y.; Zhu, R.; Lin, L. A flexible tactile sensor that uses polyimide/graphene oxide nanofiber as dielectric membrane for vertical and lateral force detection. Nanotechnology 2022, 33, 405205. [Google Scholar] [CrossRef]
  189. Wan, X.; Cong, H.; Jiang, G.; Liang, X.; Liu, L.; He, H. A Review on PVDF Nanofibers in Textiles for Flexible Piezoelectric Sensors. ACS Appl. Nano Mater. 2023, 6, 1522–1540. [Google Scholar] [CrossRef]
  190. Wang, G.; Liu, T.; Sun, X.-C.; Li, P.; Xu, Y.-S.; Hua, J.-G.; Yu, Y.-H.; Li, S.-X.; Dai, Y.-Z.; Song, X.-Y.; et al. Flexible pressure sensor based on PVDF nanofiber. Sens. Actuators A Phys. 2018, 280, 319–325. [Google Scholar] [CrossRef]
  191. Yang, X.; Wang, Y.; Qing, X. A flexible capacitive sensor based on the electrospun PVDF nanofiber membrane with carbon nanotubes. Sens. Actuators A Phys. 2019, 299, 111579. [Google Scholar] [CrossRef]
  192. Pandey, P.; Thapa, K.; Ojha, G.P.; Seo, M.-K.; Shin, K.H.; Kim, S.-W.; Sohn, J.I. Metal-organic frameworks-based triboelectric nanogenerator powered visible light communication system for wireless human-machine interactions. Chem. Eng. J. 2023, 452, 139209. [Google Scholar] [CrossRef]
  193. Jiang, C.; Li, Q.; Fan, S.; Guo, Q.; Bi, S.; Wang, X.; Cao, X.; Liu, Y.; Song, J. Hyaline and stretchable haptic interfaces based on serpentine-shaped silver nanofiber networks. Nano Energy 2020, 73, 104782. [Google Scholar] [CrossRef]
  194. Ye, G.; Wan, Y.; Wu, J.; Zhuang, W.; Zhou, Z.; Jin, T.; Zi, J.; Zhang, D.; Geng, X.; Yang, P. Multifunctional device integrating dual-temperature regulator for outdoor personal thermal comfort and triboelectric nanogenerator for self-powered human-machine interaction. Nano Energy 2022, 97, 107148. [Google Scholar] [CrossRef]
  195. Chao, M.; Di, P.; Yuan, Y.; Xu, Y.; Zhang, L.; Wan, P. Flexible breathable photothermal-therapy epidermic sensor with MXene for ultrasensitive wearable human-machine interaction. Nano Energy 2023, 108, 108201. [Google Scholar] [CrossRef]
  196. Yang, J.; Liu, S.; Meng, Y.; Xu, W.; Liu, S.; Jia, L.; Chen, G.; Qin, Y.; Han, M.; Li, X. Self-Powered Tactile Sensor for Gesture Recognition Using Deep Learning Algorithms. ACS Appl. Mater. Interfaces 2022, 14, 25629–25637. [Google Scholar] [CrossRef] [PubMed]
  197. Shen, G.; Chen, B.; Liang, T.; Liu, Z.; Zhao, S.; Liu, J.; Zhang, C.; Yang, W.; Wang, Y.; He, X. Transparent and Stretchable Strain Sensors with Improved Sensitivity and Reliability Based on Ag NWs and PEDOT:PSS Patterned Microstructures. Adv. Electron. Mater. 2020, 6, 1901360. [Google Scholar] [CrossRef]
  198. Wang, X.; Zhang, Y.; Zhang, X.; Huo, Z.; Li, X.; Que, M.; Peng, Z.; Wang, H.; Pan, C. A Highly Stretchable Transparent Self-Powered Triboelectric Tactile Sensor with Metallized Nanofibers for Wearable Electronics. Adv. Mater. 2018, 30, e1706738. [Google Scholar] [CrossRef]
  199. Kim, M.; Kaliannagounder, V.K.; Unnithan, A.R.; Park, C.H.; Kim, C.S.; Ramachandra Kurup Sasikala, A. Development of In-Situ Poled Nanofiber Based Flexible Piezoelectric Nanogenerators for Self-Powered Motion Monitoring. Appl. Sci. 2020, 10, 3493. [Google Scholar] [CrossRef]
  200. Lin, X.; Bing, Y.; Li, F.; Mei, H.; Liu, S.; Fei, T.; Zhao, H.; Zhang, T. An All-Nanofiber-Based, Breathable, Ultralight Electronic Skin for Monitoring Physiological Signals. Adv. Mater. Technol. 2022, 7, 2101312. [Google Scholar] [CrossRef]
  201. Ahmed, S.; Nauman, S.; Khan, Z.M. Electrospun nanofibrous yarn based piezoresistive flexible strain sensor for human motion detection and speech recognition. J. Thermoplast. Compos. Mater. 2022, 1–23. [Google Scholar] [CrossRef]
  202. He, J.; Guo, X.; Yu, J.; Qian, S.; Hou, X.; Cui, M.; Yang, Y.; Mu, J.; Geng, W.; Chou, X. A high-resolution flexible sensor array based on PZT nanofibers. Nanotechnology 2020, 31, 155503. [Google Scholar] [CrossRef]
  203. Sengupta, D.; Romano, J.; Kottapalli, A.G.P. Electrospun bundled carbon nanofibers for skin-inspired tactile sensing, proprioception and gesture tracking applications. npj Flex. Electron. 2021, 5, 29. [Google Scholar] [CrossRef]
  204. Khan, H.; Razmjou, A.; Ebrahimi Warkiani, M.; Kottapalli, A.; Asadnia, M. Sensitive and Flexible Polymeric Strain Sensor for Accurate Human Motion Monitoring. Sensors 2018, 18, 418. [Google Scholar] [CrossRef] [PubMed]
  205. Zheng, K.; Gu, F.; Wei, H.; Zhang, L.; Chen, X.; Jin, H.; Pan, S.; Chen, Y.; Wang, S. Flexible, Permeable, and Recyclable Liquid-Metal-Based Transient Circuit Enables Contact/Noncontact Sensing for Wearable Human-Machine Interaction. Small Methods 2023, 7, e2201534. [Google Scholar] [CrossRef]
  206. Wang, X.; Liu, J.; Zheng, Y.; Shi, B.; Chen, A.; Wang, L.; Shen, G. Biocompatible liquid metal coated stretchable electrospinning film for strain sensors monitoring system. Sci. China Mater. 2022, 65, 2235–2243. [Google Scholar] [CrossRef]
  207. Zhou, H.; Huang, W.; Xiao, Z.; Zhang, S.; Li, W.; Hu, J.; Feng, T.; Wu, J.; Zhu, P.; Mao, Y. Deep-Learning-Assisted Noncontact Gesture-Recognition System for Touchless Human-Machine Interfaces. Adv. Funct. Mater. 2022, 32, 2208271. [Google Scholar] [CrossRef]
  208. Cao, J.; Liang, F.; Li, H.; Li, X.; Fan, Y.; Hu, C.; Yu, J.; Xu, J.; Yin, Y.; Li, F.; et al. Ultra-robust stretchable electrode for e-skin: In situ assembly using a nanofiber scaffold and liquid metal to mimic water-to-net interaction. InfoMat 2022, 4, e12302. [Google Scholar] [CrossRef]
  209. Chao, M.; He, L.; Gong, M.; Li, N.; Li, X.; Peng, L.; Shi, F.; Zhang, L.; Wan, P. Breathable Ti(3)C(2)T(x) MXene/Protein Nanocomposites for Ultrasensitive Medical Pressure Sensor with Degradability in Solvents. ACS Nano 2021, 15, 9746–9758. [Google Scholar] [CrossRef]
  210. Lu, L.; Jiang, C.; Hu, G.; Liu, J.; Yang, B. Flexible Noncontact Sensing for Human-Machine Interaction. Adv. Mater. 2021, 33, e2100218. [Google Scholar] [CrossRef]
  211. Gong, M.; Wan, P.; Ma, D.; Zhong, M.; Liao, M.; Ye, J.; Shi, R.; Zhang, L. Flexible Breathable Nanomesh Electronic Devices for On-Demand Therapy. Adv. Funct. Mater. 2019, 29, 1902127. [Google Scholar] [CrossRef]
  212. Cao, L.; Liu, Q.; Ren, J.; Chen, W.; Pei, Y.; Kaplan, D.L.; Ling, S. Electro-Blown Spun Silk/Graphene Nanoionotronic Skin for Multifunctional Fire Protection and Alarm. Adv. Mater. 2021, 33, e2102500. [Google Scholar] [CrossRef]
Figure 1. Summary of electrospun-based bionic artificial skin, which includes the material selection, working mechanism, and related applications.
Figure 1. Summary of electrospun-based bionic artificial skin, which includes the material selection, working mechanism, and related applications.
Biomimetics 08 00223 g001
Figure 2. Illustration of electrospinning apparatus [23]. Copyright 2017 American Chemical Society.
Figure 2. Illustration of electrospinning apparatus [23]. Copyright 2017 American Chemical Society.
Biomimetics 08 00223 g002
Figure 3. (a) SEM images of PVDF-HFP nanofibers with MWCNTs added after annealing treatment under 120, 130, and 140 °C for ten minutes, respectively [86]. Copyright 2019 American Chemical Society. (b) SEM images of PVDF/SF fibers added with 0%, 10%, and 20% filament protein nanofibers [87]. Copyright 2021 John Wiley & sons.
Figure 3. (a) SEM images of PVDF-HFP nanofibers with MWCNTs added after annealing treatment under 120, 130, and 140 °C for ten minutes, respectively [86]. Copyright 2019 American Chemical Society. (b) SEM images of PVDF/SF fibers added with 0%, 10%, and 20% filament protein nanofibers [87]. Copyright 2021 John Wiley & sons.
Biomimetics 08 00223 g003
Figure 4. (a) Schematic illustration of electrospinning of solution doped with additives [97]. Copyright 2018 Elsevier. FE-SEM image (b), TEM image (c), (d,e) confocal fluorescent spectrum of PPNG pad with 1 v/v% IPQDs added [95]. Copyright 2021 Elsevier. (f) FE-SEM image of PMC nanofibers (inset shows the roughness on the fibers at the nanoscale). (g,h) TEM images of PMC nanofibers at different scales, showing the insertion of MXene nanosheets in PVDF substrate [96]. Copyright 2020 Elsevier.
Figure 4. (a) Schematic illustration of electrospinning of solution doped with additives [97]. Copyright 2018 Elsevier. FE-SEM image (b), TEM image (c), (d,e) confocal fluorescent spectrum of PPNG pad with 1 v/v% IPQDs added [95]. Copyright 2021 Elsevier. (f) FE-SEM image of PMC nanofibers (inset shows the roughness on the fibers at the nanoscale). (g,h) TEM images of PMC nanofibers at different scales, showing the insertion of MXene nanosheets in PVDF substrate [96]. Copyright 2020 Elsevier.
Biomimetics 08 00223 g004
Figure 5. (a) SEM images for different GNS density (0–2.0 wt%) of electrospun PVDF/G composite nanofibers [98]. Copyright 2020 Elsevier. (b) SEM image of pure PVDF fibers. (c) SEM image of Graphene-BT/PVDF nanocomposite fibers with graphene concentration of 0.15 wt%. (d) TEM image of Graphene-BT/PVDF nanocomposite fibers with graphene concentration of 0.15 wt% [99]. Copyright 2018 Elsevier.
Figure 5. (a) SEM images for different GNS density (0–2.0 wt%) of electrospun PVDF/G composite nanofibers [98]. Copyright 2020 Elsevier. (b) SEM image of pure PVDF fibers. (c) SEM image of Graphene-BT/PVDF nanocomposite fibers with graphene concentration of 0.15 wt%. (d) TEM image of Graphene-BT/PVDF nanocomposite fibers with graphene concentration of 0.15 wt% [99]. Copyright 2018 Elsevier.
Biomimetics 08 00223 g005
Figure 6. The illustration of four typical sensing mechanisms: (a) piezoresistive, (b) capacitive, (c) piezoelectric, (d) triboelectric sensing [104]. Copyright 2021 MDPI.
Figure 6. The illustration of four typical sensing mechanisms: (a) piezoresistive, (b) capacitive, (c) piezoelectric, (d) triboelectric sensing [104]. Copyright 2021 MDPI.
Biomimetics 08 00223 g006
Figure 7. (a) The manufacturing procedure illustration of LMFM. (b) Impedance change of EGaln-SBS against tensile strain; the insets in b show EGaIn-SBS at 0% and 1000% strain, respectively. (c) ECG signal from ECG electrodes made by EGlan-SBS [171]. Copyright 2021 Springer Nature. (d) Schematic diagram of the manufacture and structure of EMPAs. (e) SEM image of EMPAs; the inset shows an enlarged SEM image of a single electrospun micropyramid. (f) LCM image of an electrospun micropyramid. (g) Sensors based on EMPAs manufactured to monitor a driver’s fingertip pulses for extended periods of time; the insets show magnified fingertip pulse waveforms. Copyright 2022 Springer Nature. (h) Schematic of muscle fibers in human leg [172]. (i) SEM image of electrospun fibers via dopamine coating. (j) Real-time pulse signals for static and after motion states [173]. Copyright 2021 Wiley-VCH.
Figure 7. (a) The manufacturing procedure illustration of LMFM. (b) Impedance change of EGaln-SBS against tensile strain; the insets in b show EGaIn-SBS at 0% and 1000% strain, respectively. (c) ECG signal from ECG electrodes made by EGlan-SBS [171]. Copyright 2021 Springer Nature. (d) Schematic diagram of the manufacture and structure of EMPAs. (e) SEM image of EMPAs; the inset shows an enlarged SEM image of a single electrospun micropyramid. (f) LCM image of an electrospun micropyramid. (g) Sensors based on EMPAs manufactured to monitor a driver’s fingertip pulses for extended periods of time; the insets show magnified fingertip pulse waveforms. Copyright 2022 Springer Nature. (h) Schematic of muscle fibers in human leg [172]. (i) SEM image of electrospun fibers via dopamine coating. (j) Real-time pulse signals for static and after motion states [173]. Copyright 2021 Wiley-VCH.
Biomimetics 08 00223 g007
Figure 8. (a) An illustration of the structure of TENG-based SANES. (b) The sleep respiratory state judgment based on the OSAH diagnosis system [174]. Copyright 2021 Wiley-VCH. (c) Circuit diagram of health monitoring system connecting various TEHS devices to the monitor. (d) Integration of multiple TEHS in a wheelchair, nursing bed, and body for building health monitoring systems [175]. Copyright 2022 Elsevier.
Figure 8. (a) An illustration of the structure of TENG-based SANES. (b) The sleep respiratory state judgment based on the OSAH diagnosis system [174]. Copyright 2021 Wiley-VCH. (c) Circuit diagram of health monitoring system connecting various TEHS devices to the monitor. (d) Integration of multiple TEHS in a wheelchair, nursing bed, and body for building health monitoring systems [175]. Copyright 2022 Elsevier.
Biomimetics 08 00223 g008
Figure 9. (a) Schematic illustration of NHSE-based electronic skin preparation and photos of the e-skin sensing array and wireless control module. (b) E-skin human-computer interaction system based on NHSE for playing computer games [208]. Copyright 2022 Wiley-VCH. (c) Images of pressure-sensing arrays based on MXene/protein composite nanofibers pressed by different numbers of fingers. (d) Concept illustration of wireless transmission [209]. Copyright 2021 American Chemical Society.
Figure 9. (a) Schematic illustration of NHSE-based electronic skin preparation and photos of the e-skin sensing array and wireless control module. (b) E-skin human-computer interaction system based on NHSE for playing computer games [208]. Copyright 2022 Wiley-VCH. (c) Images of pressure-sensing arrays based on MXene/protein composite nanofibers pressed by different numbers of fingers. (d) Concept illustration of wireless transmission [209]. Copyright 2021 American Chemical Society.
Biomimetics 08 00223 g009
Figure 10. (a) Schematic diagram of manufacturing MPHS. (b) Photos of MPHS sensor array and smart cart driven by non-contact gestures [210]. Copyright 2021 Wiley-VCH. (c) Photographs of grasping and releasing a beaker, and the change in resistance and temperature signals obtained by the flexible heater when grasping and releasing a beaker containing hot water by hand. Copyright 2019 Wiley-VCH. (d) Images of the temperature distribution of the flexible heater when the applied voltage is 2.5 V and the temperature distribution attached to the human hand back before and after the DC voltage is applied [211]. (e) Schematic concept illustration for high temperature triggered protection system [212]. Copyright 2021 Wiley-VCH.
Figure 10. (a) Schematic diagram of manufacturing MPHS. (b) Photos of MPHS sensor array and smart cart driven by non-contact gestures [210]. Copyright 2021 Wiley-VCH. (c) Photographs of grasping and releasing a beaker, and the change in resistance and temperature signals obtained by the flexible heater when grasping and releasing a beaker containing hot water by hand. Copyright 2019 Wiley-VCH. (d) Images of the temperature distribution of the flexible heater when the applied voltage is 2.5 V and the temperature distribution attached to the human hand back before and after the DC voltage is applied [211]. (e) Schematic concept illustration for high temperature triggered protection system [212]. Copyright 2021 Wiley-VCH.
Biomimetics 08 00223 g010
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Chen, X.; Li, H.; Xu, Z.; Lu, L.; Pan, Z.; Mao, Y. Electrospun Nanofiber-Based Bioinspired Artificial Skins for Healthcare Monitoring and Human-Machine Interaction. Biomimetics 2023, 8, 223. https://doi.org/10.3390/biomimetics8020223

AMA Style

Chen X, Li H, Xu Z, Lu L, Pan Z, Mao Y. Electrospun Nanofiber-Based Bioinspired Artificial Skins for Healthcare Monitoring and Human-Machine Interaction. Biomimetics. 2023; 8(2):223. https://doi.org/10.3390/biomimetics8020223

Chicago/Turabian Style

Chen, Xingwei, Han Li, Ziteng Xu, Lijun Lu, Zhifeng Pan, and Yanchao Mao. 2023. "Electrospun Nanofiber-Based Bioinspired Artificial Skins for Healthcare Monitoring and Human-Machine Interaction" Biomimetics 8, no. 2: 223. https://doi.org/10.3390/biomimetics8020223

Article Metrics

Back to TopTop