Shaping and Structuring of Polymer Gels

A special issue of Gels (ISSN 2310-2861). This special issue belongs to the section "Gel Analysis and Characterization".

Deadline for manuscript submissions: closed (31 August 2023) | Viewed by 13111

Special Issue Editor

Division of Molecular Science, Graduate School of Science and Technology, Gunma University, Gunma, Kiryu 376-8515, Japan
Interests: biorheology; physical chemistry; thermodynamics

Special Issue Information

Dear Colleagues,

The majority of industrial gels are formed as apparently isotropic and homogeneous materials from polymer solutions by preparation processes including changing temperature, exerting mechanical stress, irradiating high-energy electromagnetic waves, and mixing with gelators. Gels with spatially resolved structures and mechanical properties could, however, help functionalizing materials with high performance in diverse fields. For example, gel-based micro/nano-patterning of electrical pathways enables us to prepare sophisticated soft devices. Nonuniform internal stress of micro/nanostructures in gels is often a key to develop self-shaping and actuating materials for biosensing, micro-robotics, and optics. Anisotropic artificial organs and tissues such as nerve fibers are shaped by using degradable gel scaffolds in tissue engineering, in which the characteristic shapes and structures of gels are generated by different methods such as diffusion of gelators, 3D printing, photopatterning, and the surface-mediated multicomponent approach. This Special Issue focuses on recent research and advances in shaping and structuring of polymer gels. We welcome original researches and comprehensive reviews with topics addressing shaping and structuring of polymer gels, inclusive of fabrication of gels with defined shapes and spatially controlled structures including micro/nano-structures, theoretical and experimental approaches to anisotropic gelation dynamics, and measurements and analyses of chemical and rheological properties of anisotropic gels and their applications. Biomedical studies on gel shaping such as formation of impermeable blood coagulant and structuring anisotropic tissues such as skin and blood vessels are also welcome.

Prof. Dr. Toshiaki Dobashi
Guest Editor

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Keywords

  • gel structuring
  • gel shaping
  • anisotropy
  • nonuniformity
  • diffusion
  • patterning

Published Papers (11 papers)

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Editorial

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4 pages, 190 KiB  
Editorial
Shaping and Structuring of Polymer Gels
by Toshiaki Dobashi
Gels 2024, 10(2), 134; https://doi.org/10.3390/gels10020134 - 07 Feb 2024
Viewed by 874
Abstract
Most industrial gels are prepared as apparently isotropic and homogeneous materials through a preparation process encompassing alterations in temperature, application of isotropic mechanical stress, exposure to high-energy electromagnetic waves, and mixing with cross-linkers (gelators) [...] Full article
(This article belongs to the Special Issue Shaping and Structuring of Polymer Gels)

Research

Jump to: Editorial

13 pages, 5344 KiB  
Article
Additive-Free Method for Enhancing the Volume Phase Transition Rate in Light-Responsive Hydrogels: A Study of Micro-Nano Bubble Water on PNIPAM-co-AAc Hydrogels
by Saho Kuroki, Masaya Kubota, Ryota Haraguchi, Yushi Oishi and Takayuki Narita
Gels 2023, 9(11), 880; https://doi.org/10.3390/gels9110880 - 07 Nov 2023
Viewed by 962
Abstract
Light-responsive hydrogels containing light-thermal convertible pigments have received interest for their possible applications in light-responsive shutters, valves, drug delivery systems, etc. However, their utility is limited by the slow response time. In this study, we investigated the use of micro-nano bubble water as [...] Read more.
Light-responsive hydrogels containing light-thermal convertible pigments have received interest for their possible applications in light-responsive shutters, valves, drug delivery systems, etc. However, their utility is limited by the slow response time. In this study, we investigated the use of micro-nano bubble water as a preparation solvent to accelerate the volume phase transition kinetics of poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-co-AAc) hydrogels. The hydrogels were characterized by dynamic light scattering (DLS) and dissolved oxygen (DO) measurements. The mechanical properties, surface morphology, and chemical composition of the hydrogels were analyzed by Young’s modulus measurements, scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectroscopy, respectively. The results showed that hydrogels prepared with bubble water changed the volume transition rate by more than two orders of magnitude by simply changing the standing time of the bubble water for only a few hours. The cooperative diffusion coefficients obtained from the light-induced volume transition kinetics correlated linearly with Young’s modulus and metastable state swelling ratio. Our results suggest that bubbles act as efficient water channels, thereby modulating the response rate and providing a simple, additive-free method for preparing hydrogels with a wide range of response rates. Full article
(This article belongs to the Special Issue Shaping and Structuring of Polymer Gels)
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16 pages, 11798 KiB  
Article
Universal Behavior of Fractal Water Structures Observed in Various Gelation Mechanisms of Polymer Gels, Supramolecular Gels, and Cement Gels
by Shin Yagihara, Seiei Watanabe, Yuta Abe, Megumi Asano, Kenta Shimizu, Hironobu Saito, Yuko Maruyama, Rio Kita, Naoki Shinyashiki and Shyamal Kumar Kundu
Gels 2023, 9(7), 506; https://doi.org/10.3390/gels9070506 - 21 Jun 2023
Cited by 1 | Viewed by 987
Abstract
So far, it has been difficult to directly compare diverse characteristic gelation mechanisms over different length and time scales. This paper presents a universal water structure analysis of several gels with different structures and gelation mechanisms including polymer gels, supramolecular gels composed of [...] Read more.
So far, it has been difficult to directly compare diverse characteristic gelation mechanisms over different length and time scales. This paper presents a universal water structure analysis of several gels with different structures and gelation mechanisms including polymer gels, supramolecular gels composed of surfactant micelles, and cement gels. The spatial distribution of water molecules was analyzed at molecular level from a diagram of the relaxation times and their distribution parameters (τβ diagrams) with our database of the 10 GHz process for a variety of aqueous systems. Polymer gels with volume phase transition showed a small decrease in the fractal dimension of the hydrogen bond network (HBN) with gelation. In supramolecular gels with rod micelle precursor with amphipathic molecules, both the elongation of the micelles and their cross-linking caused a reduction in the fractal dimension. Such a reduction was also found in cement gels. These results suggest that the HBN inevitably breaks at each length scale with relative increase in steric hindrance due to cross-linking, resulting in the fragmentation of collective structures of water molecules. The universal analysis using τ–β diagrams presented here has broad applicability as a method to characterize diverse gel structures and evaluate gelation processes. Full article
(This article belongs to the Special Issue Shaping and Structuring of Polymer Gels)
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17 pages, 1855 KiB  
Article
Gelation and Orientation Dynamics Induced by Contact of Protein Solution with Transglutaminase Solution
by Kasumi Kakinoki, Ryuta Kurasawa, Yasuyuki Maki, Toshiaki Dobashi and Takao Yamamoto
Gels 2023, 9(6), 478; https://doi.org/10.3390/gels9060478 - 12 Jun 2023
Viewed by 782
Abstract
Gel growth induced by contact of polymer solutions with crosslinker solutions yields an emerging class of anisotropic materials with many potential applications. Here, we report the case of a study on the dynamics in forming anisotropic gels using this approach with an enzyme [...] Read more.
Gel growth induced by contact of polymer solutions with crosslinker solutions yields an emerging class of anisotropic materials with many potential applications. Here, we report the case of a study on the dynamics in forming anisotropic gels using this approach with an enzyme as a trigger of gelation and gelatin as the polymer. Unlike the previously studied cases of gelation, the isotropic gelation was followed by gel polymer orientation after a lag time. The isotropic gelation dynamics did not depend on concentrations of the polymer turning into gel and of the enzyme inducing gelation, whereas, for the anisotropic gelation, the square of the gel thickness was a linear function of the elapsed time, and the slope increased with polymer concentration. The gelation dynamics of the present system was explained by a combination of diffusion-limited gelation followed by free-energy-limited orientation of polymer molecules. Full article
(This article belongs to the Special Issue Shaping and Structuring of Polymer Gels)
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11 pages, 2550 KiB  
Article
Effect of UV Irradiation of Pre-Gel Solutions on the Formation of Collagen Gel Tubes
by Yu Ishibashi, Ryota Haraguchi, Shigehisa Aoki, Yushi Oishi and Takayuki Narita
Gels 2023, 9(6), 458; https://doi.org/10.3390/gels9060458 - 02 Jun 2023
Cited by 1 | Viewed by 1026
Abstract
Hollow collagen gels are promising materials for drug/cell delivery systems to promote tissue regeneration because they may be able to function as carriers for these types of loads. Controlling the cavity size and swelling suppression is essential to expand the applications and improve [...] Read more.
Hollow collagen gels are promising materials for drug/cell delivery systems to promote tissue regeneration because they may be able to function as carriers for these types of loads. Controlling the cavity size and swelling suppression is essential to expand the applications and improve the usability of such gel-like systems. We investigated the effects of UV-treated collagen solutions as a pre-gel aqueous mixture on the formation and properties of the hollow collagen gels in terms of their preparation range limits, morphology, and swelling ratio. The UV treatment thickened the pre-gel solutions, which allowed hollowing at lower collagen concentrations. This treatment also prevents the over-swelling of the hollow collagen rods in PBS buffer solutions. The UV-treated collagen solutions provided a large lumen space in the prepared collagen hollow fiber rods with a limited swelling ratio, allowing vascular endothelial cells and ectodermal cells to be cultured separately in the outer and inner lumen. Full article
(This article belongs to the Special Issue Shaping and Structuring of Polymer Gels)
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11 pages, 3343 KiB  
Article
Macroscopic Pattern Formation of Alginate Gels in a Two-Dimensional System
by Ryota Haraguchi, Yushi Oishi and Takayuki Narita
Gels 2023, 9(6), 444; https://doi.org/10.3390/gels9060444 - 26 May 2023
Viewed by 1008
Abstract
Macroscopic spatial patterns were formed in calcium alginate gels when a drop of a calcium nitrate solution was placed on the center of a sodium alginate solution on a petri dish. These patterns have been classified into two groups. One is multi-concentric rings [...] Read more.
Macroscopic spatial patterns were formed in calcium alginate gels when a drop of a calcium nitrate solution was placed on the center of a sodium alginate solution on a petri dish. These patterns have been classified into two groups. One is multi-concentric rings consisting of alternating cloudy and transparent areas observed around the center of petri dishes. The other is streaks extending to the edge of the petri dish, which are formed to surround the concentric bands between the concentric bands and the petri dish edge. We have attempted to understand the origins of the pattern formations using the properties of phase separation and gelation. The distance between two adjacent concentric rings was roughly proportional to the distance from where the calcium nitrate solution was dropped. The proportional factor p increased exponentially for the inverse of the absolute temperature of the preparation. The p also depended on the concentration of alginate. The pattern characteristics in the concentric pattern agreed with those in the Liesegang pattern. The paths of radial streaks were disturbed at high temperatures. The length of these streaks shortened with increasing alginate concentration. The characteristics of the streaks were similar to those of crack patterns resulting from inhomogeneous shrinkage during drying. Full article
(This article belongs to the Special Issue Shaping and Structuring of Polymer Gels)
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14 pages, 1404 KiB  
Article
Dielectric Study on Supramolecular Gels by Fiber Structure Formation from Low-Molecular-Weight Gelator/Water Mixtures
by Kenta Shimizu, Fumiya Abe, Yasuhiro Kishi, Rio Kita, Naoki Shinyashiki and Shin Yagihara
Gels 2023, 9(5), 408; https://doi.org/10.3390/gels9050408 - 12 May 2023
Cited by 2 | Viewed by 1266
Abstract
There are various types of gel materials used in a wide range of fields, and their gelation mechanisms are extremely diverse. Furthermore, in the case of hydrogels, there exist some difficulties in understanding complicated molecular mechanisms especially with water molecules interacting through hydrogen [...] Read more.
There are various types of gel materials used in a wide range of fields, and their gelation mechanisms are extremely diverse. Furthermore, in the case of hydrogels, there exist some difficulties in understanding complicated molecular mechanisms especially with water molecules interacting through hydrogen bonding as solvents. In the present work, the molecular mechanism of the structural formation of fibrous super-molecular gel by the low molecular weight gelator, N-oleyl lactobionamide/water mixture was elucidated using the broadband dielectric spectroscopy (BDS) method. The dynamic behaviors observed for the solute and water molecules indicated hierarchical structure formation processes in various time scales. The relaxation curves obtained at various temperatures in the cooling and heating processes showed relaxation processes respectively reflecting the dynamic behaviors of water molecules in the 10 GHz frequency region, solute molecules interacting with water in MHz region, and ion-reflecting structures of the sample and electrode in kHz region. These relaxation processes, characterized by the relaxation parameters, showed remarkable changes around the sol–gel transition temperature, 37.8 °C, determined by the falling ball method and over the temperature range, around 53 °C. The latter change suggested a structure formation of rod micelles appearing as precursors before cross-linking into the three-dimensional network of the supramolecular gels. These results clearly demonstrate how effective relaxation parameter analysis is for understanding the gelation mechanism in detail. Full article
(This article belongs to the Special Issue Shaping and Structuring of Polymer Gels)
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15 pages, 2239 KiB  
Article
Relationship between Rate-Limiting Process and Scaling Law in Gel Growth Induced by Liquid-Liquid Contact
by Takao Yamamoto
Gels 2023, 9(5), 359; https://doi.org/10.3390/gels9050359 - 24 Apr 2023
Viewed by 768
Abstract
Gelation through the liquid-liquid contact between a polymer solution and a gelator solution has been attempted with various combinations of gelator and polymer solutions. In many combinations, the gel growth dynamics is expressed as Xt, where X is the gel [...] Read more.
Gelation through the liquid-liquid contact between a polymer solution and a gelator solution has been attempted with various combinations of gelator and polymer solutions. In many combinations, the gel growth dynamics is expressed as Xt, where X is the gel thickness and t is the elapsed time, and the scaling law holds for the relationship between X and t. In the blood plasma gelation, however, the crossover of the growth behavior from Xt in the early stage to Xt in the late stage was observed. It was found that the crossover behavior is caused by a change in the rate-limiting process of growth from the free-energy-limited process to the diffusion-limited process. How, then, would the crossover phenomenon be described in terms of the scaling law? We found that the scaling law does not hold in the early stage owing to the characteristic length attributable to the free energy difference between the sol-gel phases, but it does in the late stage. We also discussed the analysis method for the crossover in terms of the scaling law. Full article
(This article belongs to the Special Issue Shaping and Structuring of Polymer Gels)
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13 pages, 1779 KiB  
Article
Mesoscopic Characterization of the Early Stage of the Glucono-δ-Lactone-Induced Gelation of Milk via Image Analysis Techniques
by Kento Sekiguchi, Morimasa Tanimoto and Shuji Fujii
Gels 2023, 9(3), 202; https://doi.org/10.3390/gels9030202 - 06 Mar 2023
Viewed by 1187
Abstract
We provide a method for quantifying the kinetics of gelation in milk acidified with glucono-δ-lactone (GDL) using image analysis techniques, particle image velocimetry (PIV), differential variance analysis (DVA) and differential dynamic microscopy (DDM). The gelation of the milk acidified with GDL [...] Read more.
We provide a method for quantifying the kinetics of gelation in milk acidified with glucono-δ-lactone (GDL) using image analysis techniques, particle image velocimetry (PIV), differential variance analysis (DVA) and differential dynamic microscopy (DDM). The gelation of the milk acidified with GDL occurs through the aggregation and subsequent coagulation of the casein micelles as the pH approaches the isoelectric point of the caseins. The gelation of the acidified milk with GDL is an important step in the production of fermented dairy products. PIV qualitatively monitors the average mobility of fat globules during gelation. The gel point estimated by PIV is in good agreement with that obtained by rheological measurement. DVA and DDM methods reveal the relaxation behavior of fat globules during gelation. These two methods make it possible to calculate microscopic viscosity. We also extracted the mean square displacement (MSD) of the fat globules, without following their movement, using the DDM method. The MSD of fat globules shifts to sub-diffusive behavior as gelation progresses. The fat globules used as probes show the change in matrix viscoelasticity caused by the gelling of the casein micelles. Image analysis and rheology can be used complementarily to study the mesoscale dynamics of the milk gel. Full article
(This article belongs to the Special Issue Shaping and Structuring of Polymer Gels)
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13 pages, 7739 KiB  
Article
Construction of Engineered Muscle Tissue Consisting of Myotube Bundles in a Collagen Gel Matrix
by Kazuya Furusawa, Yuuki Kawahana and Ryoya Miyashita
Gels 2023, 9(2), 141; https://doi.org/10.3390/gels9020141 - 08 Feb 2023
Viewed by 1926
Abstract
Tissue engineering methods that aim to mimic the hierarchical structure of skeletal muscle tissue have been widely developed due to utilities in various fields of biology, including regenerative medicine, food technology, and soft robotics. Most methods have aimed to reproduce the microscopical morphology [...] Read more.
Tissue engineering methods that aim to mimic the hierarchical structure of skeletal muscle tissue have been widely developed due to utilities in various fields of biology, including regenerative medicine, food technology, and soft robotics. Most methods have aimed to reproduce the microscopical morphology of skeletal muscles, such as the orientation of myotubes and the sarcomere structure, and there is still a need to develop a method to reproduce the macroscopical morphology. Therefore, in this study, we aim to establish a method to reproduce the macroscopic morphology of skeletal muscle by constructing an engineered muscle tissue (EMT) by culturing embryonic chicken myoblast-like cells that are unidirectionally aligned in collagen hydrogels with micro-channels (i.e., MCCG). Whole mount fluorescent imaging of the EMT showed that the myotubes were unidirectionally aligned and that they were bundled in the collagen gel matrix. The myotubes contracted in response to periodic electrostimulations with a frequency range of 0.5–2.0 Hz, but not at 5.0 Hz. Compression tests of the EMT showed that the EMT had anisotropic elasticity. In addition, by measuring the relaxation moduli of the EMTs, an anisotropy of relaxation strengths was observed. The observed anisotropies could be attributed to differences in maturation and connectivity of myotubes in the directions perpendicular and parallel to the long axis of the micro-channels of the MCCG. Full article
(This article belongs to the Special Issue Shaping and Structuring of Polymer Gels)
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15 pages, 2363 KiB  
Article
Fabrication and Characterization of Chicken- and Bovine-Derived Chondroitin Sulfate/Sodium Alginate Hybrid Hydrogels
by Yaqi Zhao, Yan Li, Tianchan Lan, Baowei Wang, Ming Huang, He Huang, Changming Qiao and Jingxin Sun
Gels 2022, 8(10), 620; https://doi.org/10.3390/gels8100620 - 28 Sep 2022
Viewed by 1488
Abstract
The physicochemical properties and microstructure of hybrid hydrogels prepared using sodium alginate (SA) and chondroitin sulfate (CS) extracted from two animal sources were investigated. SA-based hybrid hydrogels were prepared by mixing chicken- and bovine-derived CS (CCS and BCS, respectively) with SA at 1/3 [...] Read more.
The physicochemical properties and microstructure of hybrid hydrogels prepared using sodium alginate (SA) and chondroitin sulfate (CS) extracted from two animal sources were investigated. SA-based hybrid hydrogels were prepared by mixing chicken- and bovine-derived CS (CCS and BCS, respectively) with SA at 1/3 and 2/3 (w/w) ratios. The results indicated that the evaporation water loss rate of the hybrid hydrogels increased significantly upon the addition of CS, whereas CCS/SA (2/3) easily absorbed moisture from the environment. The thermal stability of the BCS/SA (1/3) hybrid hydrogel was higher than that of CCS/SA (1/3) hybrid hydrogel, whereas the hardness and adhesiveness of the CCS/SA (1/3) hybrid hydrogel were lower and higher, respectively, than those of the BCS/SA (1/3) hybrid hydrogel. Low-field nuclear magnetic resonance experiments demonstrated that the immobilized water content of the CCS/SA (1/3) hybrid hydrogel was higher than that of the BCS/SA (1/3) hybrid hydrogel. FTIR showed that S=O characteristic absorption peak intensity of BCS/SA (2/3) was obviously higher, suggesting that BCS possessed more sulfuric acid groups than CCS. SEM showed that the hybrid hydrogels containing CCS have more compact porous microstructure and better interfacial compatibility compared to BCS. Full article
(This article belongs to the Special Issue Shaping and Structuring of Polymer Gels)
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