Research

15 pages, 7788 KiB

Open AccessArticle

Effect of Composition and Freeze-Thaw on the Network Structure, Porosity and Mechanical Properties of Polyvinyl-Alcohol/Chitosan Hydrogels

by Fernando Soto-Bustamante, Gavino Bassu, Emiliano Fratini and Marco Laurati

Gels 2023, 9(5), 396; https://doi.org/10.3390/gels9050396 - 09 May 2023

Cited by 3 | Viewed by 1996

Abstract

We report the synthesis and characterization of poly (vinyl alcohol) (PVA)/Chitosan (CT) cryogels for applications involving the uptake and entrapment of particulate and bacterial colonies. In particular, we systematically investigated the network and pore structures of the gels as a function of CT [...] Read more.

We report the synthesis and characterization of poly (vinyl alcohol) (PVA)/Chitosan (CT) cryogels for applications involving the uptake and entrapment of particulate and bacterial colonies. In particular, we systematically investigated the network and pore structures of the gels as a function of CT content and for different freeze-thaw times, combining Small Angle X-Ray Scattering (SAXS), Scanning Electron Microscopy (SEM), and confocal microscopy. The nanoscale analysis obtained from SAXS shows that while the characteristic correlation length of the network is poorly affected by composition and freeze-thaw time, the characteristic size of heterogeneities associated with PVA crystallites decreases with CT content. SEM investigation evidences a transition to a more homogeneous network structure induced by the incorporation of CT that progressively builds a secondary network around the one formed by PVA. A detailed analysis of confocal microscopy image stacks allows to characterize the 3D porosity of the samples, revealing a significantly asymmetric shape of the pores. While the average volume of single pores increases with increasing CT content, the overall porosity remains almost unchanged as a result of the suppression of smaller pores in the PVA network with the progressive incorporation of the more homogeneous CT network. Increasing the freezing time in the FT cycles also results in a decrease of porosity, which can be associated with a growth in the crosslinking of the network due to PVA crystallization. The linear viscoelastic moduli measured by oscillatory rheology show a qualitatively comparable frequency-dependent response in all cases, with a moderate reduction with increasing CT content. This is attributed to changes in the structure of the strands of the PVA network. Full article

(This article belongs to the Special Issue Polymer Networks and Gels 2022)

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24 pages, 2576 KiB

Open AccessArticle

Biomanufacturing Recombinantly Expressed Cripto-1 Protein in Anchorage-Dependent Mammalian Cells Growing in Suspension Bioreactors within a Three-Dimensional Hydrogel Microcarrier

by Rachel Lev, Orit Bar-Am, Yoni Lati, Ombretta Guardiola, Gabriella Minchiotti and Dror Seliktar

Gels 2023, 9(3), 243; https://doi.org/10.3390/gels9030243 - 18 Mar 2023

Cited by 1 | Viewed by 1763

Abstract

Biotherapeutic soluble proteins that are recombinantly expressed in mammalian cells can pose a challenge when biomanufacturing in three-dimensional (3D) suspension culture systems. Herein, we tested a 3D hydrogel microcarrier for a suspension culture of HEK293 cells overexpressing recombinant Cripto-1 protein. Cripto-1 is an [...] Read more.

Biotherapeutic soluble proteins that are recombinantly expressed in mammalian cells can pose a challenge when biomanufacturing in three-dimensional (3D) suspension culture systems. Herein, we tested a 3D hydrogel microcarrier for a suspension culture of HEK293 cells overexpressing recombinant Cripto-1 protein. Cripto-1 is an extracellular protein that is involved in developmental processes and has recently been reported to have therapeutic effects in alleviating muscle injury and diseases by regulating muscle regeneration through satellite cell progression toward the myogenic lineage. Cripto-overexpressing HEK293 cell lines were cultured in microcarriers made from poly (ethylene glycol)-fibrinogen (PF) hydrogels, which provided the 3D substrate for cell growth and protein production in stirred bioreactors. The PF microcarriers were designed with sufficient strength to resist hydrodynamic deterioration and biodegradation associated with suspension culture in stirred bioreactors for up to 21 days. The yield of purified Cripto-1 obtained using the 3D PF microcarriers was significantly higher than that obtained with a two-dimensional (2D) culture system. The bioactivity of the 3D-produced Cripto-1 was equivalent to commercially available Cripto-1 in terms of an ELISA binding assay, a muscle cell proliferation assay, and a myogenic differentiation assay. Taken together, these data indicate that 3D microcarriers made from PF can be combined with mammalian cell expression systems to improve the biomanufacturing of protein-based therapeutics for muscle injuries. Full article

(This article belongs to the Special Issue Polymer Networks and Gels 2022)

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11 pages, 4619 KiB

Open AccessArticle

Accessible Low-Cost Laser Pointers for the Reduction of Aryl Halides via Triplet-Triplet Annihilation Upconversion in Aerated Gels

by Paola Domínguez Domínguez, Sebastian Bonardd, Samuel Martín Koury, Raúl Pérez-Ruiz, M. Consuelo Jiménez and David Díaz Díaz

Gels 2022, 8(12), 800; https://doi.org/10.3390/gels8120800 - 06 Dec 2022

Cited by 1 | Viewed by 1259

Abstract

The search for economic alternatives in the use of expensive scientific equipment represents a way of providing many laboratories access to scientific developments that, otherwise, might be hampered by economic constraints. This inspired the purpose of this work, which was to demonstrate for [...] Read more.

The search for economic alternatives in the use of expensive scientific equipment represents a way of providing many laboratories access to scientific developments that, otherwise, might be hampered by economic constraints. This inspired the purpose of this work, which was to demonstrate for the first time that we can carry out the photoreduction of aryl halides via green-to-blue upconversion in an aerated gel medium, using a simple economic set-up based on easily accessible and low-cost laser pointers. The optimized set-up consists of three laser pointers connected to a switching-mode power supply. One laser should be aligned to Z-axis and separated 5 cm from the sample, while the light incidence of the other two lasers should be adjusted to 45° and separated ca. 3 cm from the sample. The results of this study were found to be reproducible in random experiments and demonstrated that the photoreduction of several aryl halides can be carry out within 24 h of irradiation with comparable yields and mass balances, to those obtained with other very expensive pulsed laser sources. An economic estimation of the expenses concludes that we can easily reduce by >98% the total cost of this type of research by using the described set-up. Our work offers many groups with limited resources a feasible alternative to work in this area without the necessity of extremely expensive devices. Full article

(This article belongs to the Special Issue Polymer Networks and Gels 2022)

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27 pages, 5089 KiB

Open AccessArticle

Comparative Insights into the Fundamental Steps Underlying Gelation of Plant and Algal Ionic Polysaccharides: Pectate and Alginate

by Sergio Paoletti and Ivan Donati

Gels 2022, 8(12), 784; https://doi.org/10.3390/gels8120784 - 29 Nov 2022

Cited by 3 | Viewed by 1040

Abstract

Pectate and alginate are among the most important biopolymers able to give rise to ionotropic gelation upon the addition of di- or multivalent counterions. The two ionic polysaccharides exhibit several common aspects of the gelation mechanism with calcium ions, the physiologically and commercially [...] Read more.

Pectate and alginate are among the most important biopolymers able to give rise to ionotropic gelation upon the addition of di- or multivalent counterions. The two ionic polysaccharides exhibit several common aspects of the gelation mechanism with calcium ions, the physiologically and commercially most relevant counterion type. The first one pertains to the role that specific Ca²⁺/polyion interactions play in the establishment of the ion-mediated chain/chain cross-links. Such interactions include both a specific affinity of the territorially condensed Ca²⁺ counterions for the polyuronate(s) and the formation of long-lasting chemical bonding (inner ion–sphere complex) of specific interchain sites accompanied by high conformational ordering. As to the first mechanism, it is dominated by the strong desolvation of the interacting ionic species, with concomitant positive variations in both enthalpy and entropy, the contribution of the latter prevailing over the former due to the favorable liberation of a very large number of water molecules of hydration. Both dilatometric and microcalorimetric data point to the higher affinity of Ca²⁺ for pectate than for alginate. The selective accumulation of calcium ions close to the polyanion(s) favors the onset of the second—chemical bonding—mode, which is associated with charge neutralization at the bonding site. This mode coincides with the largely accepted “egg-box” model for the calcium-mediated interchain junction of pectate and alginate. A new approach was devised for the calculation of the fraction of chemically bound divalent ions; it was based on the available circular dichroism data (further supported by scattering and viscosity results) and successfully tested by comparison with an independently determined fraction in the case of pectate. In detail, the strong bonding mode manifests in two sequential bonding modes. The first one (at low concentrations of added Ca²⁺ ions) entails a cross-link in which only one calcium ions is bracketed in a “twisted” egg-box between two chains; upon further counterion addition, a series of nearest-neighboring “perfect” egg-box structures develops. Both dilatometric and microcalorimetric changes associated with the latter chemical bonding modes are quantitatively larger for pectate than for alginate; clearly the latter polyuronate suffers from the relevant presence of the weakly calcium-binding mannuronic acid repeating units. Light-scattering experiments provided a clear-cut demonstration of the intermolecular bonding of calcium ions from the very beginning of the linker addition. Full article

(This article belongs to the Special Issue Polymer Networks and Gels 2022)

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17 pages, 2842 KiB

Open AccessArticle

A Sustainable Hydroxypropyl Cellulose-Nanodiamond Composite for Flexible Electronic Applications

by Elena Palmieri, Francesca Pescosolido, Luca Montaina, Rocco Carcione, Greta Petrella, Daniel Oscar Cicero, Emanuela Tamburri, Silvia Battistoni and Silvia Orlanducci

Gels 2022, 8(12), 783; https://doi.org/10.3390/gels8120783 - 29 Nov 2022

Cited by 4 | Viewed by 1644

Abstract

Designing fully green materials for flexible electronics is an urgent need due to the growing awareness of an environmental crisis. With the aim of developing a sustainable, printable, and biocompatible material to be exploited in flexible electronics, the rheological, structural and charge transport [...] Read more.

Designing fully green materials for flexible electronics is an urgent need due to the growing awareness of an environmental crisis. With the aim of developing a sustainable, printable, and biocompatible material to be exploited in flexible electronics, the rheological, structural and charge transport properties of water-based hydroxypropyl cellulose (HPC)-detonation nanodiamond (DND) viscous dispersions are investigated. A rheological investigation disclosed that the presence of the DND affects the orientation and entanglement of cellulose chains in the aqueous medium. In line with rheological analyses, the NMR diffusion experiments pointed out that the presence of DND modifies the hydrodynamic behavior of the cellulose molecules. Despite the increased rigidity of the system, the presence of DND slightly enhances the ionic conductivity of the dispersion, suggesting a modification in the charge transport properties of the material. The electrochemical analyses, performed through Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS), revealed that the HPC-DND system is remarkably stable in the explored voltage range (−0.1 to +0.4 V) and characterized by a lowered bulk resistance with respect to HPC. Such features, coupled with the printability and filmability of the material, represent good requirements for the exploitation of such systems in flexible electronic applications. Full article

(This article belongs to the Special Issue Polymer Networks and Gels 2022)

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13 pages, 11660 KiB

Open AccessArticle

Prestressed Composite Polymer Gels as a Model of the Extracellular-Matrix of Cartilage

by Alexandros Chremos, Jack F. Douglas, Peter J. Basser and Ferenc Horkay

Gels 2022, 8(11), 707; https://doi.org/10.3390/gels8110707 - 02 Nov 2022

Cited by 2 | Viewed by 1293

Abstract

Articular cartilage is a composite hydrogel found in animal and human joints, which exhibits unique load-bearing properties that have been challenging to reproduce in synthetic materials and model in molecular dynamics (MD) simulations. We computationally investigate a composite hydrogel that mimics key functional [...] Read more.

Articular cartilage is a composite hydrogel found in animal and human joints, which exhibits unique load-bearing properties that have been challenging to reproduce in synthetic materials and model in molecular dynamics (MD) simulations. We computationally investigate a composite hydrogel that mimics key functional properties of articular cartilage as a potential biomimetic model to investigate its unique load-bearing properties. Specifically, we find that the emergence of prestress in composite gels derives primarily from the stiffness of the polymer matrix and the asymmetry in the enthalpic interactions of the embedded particles and polymer matrix. Our MD simulations of the development of prestress agree qualitatively with osmotic pressure measurements observed in our model composite hydrogel material. Full article

(This article belongs to the Special Issue Polymer Networks and Gels 2022)

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14 pages, 3934 KiB

Open AccessArticle

Green In Situ Synthesis of Silver Nanoparticles-Peptide Hydrogel Composites: Investigation of Their Antibacterial Activities

by Roya Binaymotlagh, Alessandra Del Giudice, Silvano Mignardi, Francesco Amato, Andrea Giacomo Marrani, Francesca Sivori, Ilaria Cavallo, Enea Gino Di Domenico, Cleofe Palocci and Laura Chronopoulou

Gels 2022, 8(11), 700; https://doi.org/10.3390/gels8110700 - 29 Oct 2022

Cited by 11 | Viewed by 1711

Abstract

The present paper investigated the synthesis of peptide-based hydrogel composites containing photo-generated silver nanoparticles (AgNPs) obtained in the presence and absence of honey as tensile strength enhancer and hydrogel stabilizer. Fmoc-Phe and diphenylalanine (Phe₂) were used as starting reagents for the [...] Read more.

The present paper investigated the synthesis of peptide-based hydrogel composites containing photo-generated silver nanoparticles (AgNPs) obtained in the presence and absence of honey as tensile strength enhancer and hydrogel stabilizer. Fmoc-Phe and diphenylalanine (Phe₂) were used as starting reagents for the hydrogelator synthesis via an enzymatic method. In particular, we developed an in situ one-pot approach for preparing AgNPs inside peptide hydrogels using a photochemical synthesis, without any toxic reducing agents, with reaction yields up to 30%. The structure and morphology of the nanohybrids were characterized with different techniques such as FESEM, UV-Vis, DLS, SAXS and XPS. Moreover, the antibacterial activity of these hybrid biomaterials was investigated on a laboratory strain and on a clinical isolate of Staphylococcus aureus. Results demonstrated that honey increased both swelling ability and also mechanical stability of the hydrogel. Finally, a higher antibacterial effect of AgNPs in the hybrid was observed in the presence of honey. In particular, AgNPs/hgel and AgNPs/hgel-honey showed an enhanced antibacterial activity (3.12 mg/L) compared to the free form of AgNPs, alone or in combination with honey (6.25 mg/L) for both S. aureus strains. Full article

(This article belongs to the Special Issue Polymer Networks and Gels 2022)

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16 pages, 2713 KiB

Open AccessArticle

External Stimuli-Responsive Characteristics of Poly(N,N′-diethylacrylamide) Hydrogels: Effect of Double Network Structure

by Julie Šťastná, Vladislav Ivaniuzhenkov and Lenka Hanyková

Gels 2022, 8(9), 586; https://doi.org/10.3390/gels8090586 - 15 Sep 2022

Cited by 2 | Viewed by 1363

Abstract

Swelling experiments and NMR spectroscopy were combined to study effect of various stimuli on the behavior of hydrogels with a single- and double-network (DN) structure composed of poly(N,N′-diethylacrylamide) and polyacrylamide (PAAm). The sensitivity to stimuli in the DN hydrogel was found [...] Read more.

Swelling experiments and NMR spectroscopy were combined to study effect of various stimuli on the behavior of hydrogels with a single- and double-network (DN) structure composed of poly(N,N′-diethylacrylamide) and polyacrylamide (PAAm). The sensitivity to stimuli in the DN hydrogel was found to be significantly affected by the introduction of the second component and the formation of the double network. The interpenetrating structure in the DN hydrogel causes the units of the component, which is insensitive to the given stimulus in the form of the single network (SN) hydrogel, to be partially formed as globular structures in DN hydrogel. Due to the hydrophilic PAAm groups, temperature- and salt-induced changes in the deswelling of the DN hydrogel are less intensive and gradual compared to those of the SN hydrogel. The swelling ratio of the DN hydrogel shows a significant decrease in the dependence on the acetone content in acetone–water mixtures. A certain portion of the solvent molecules bound in the globular structures was established from the measurements of the ¹H NMR spin–spin relaxation times T₂ for the studied DN hydrogel. The time-dependent deswelling and reswelling kinetics showed a two-step profile, corresponding to the solvent molecules being released and absorbed during two processes with different characteristic times. Full article

(This article belongs to the Special Issue Polymer Networks and Gels 2022)

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