Dear Colleagues,

Many papers have been published on the science and technology of gel materials. Recently, gel materials with ultra-high strength, self-healing properties, and biocompatibility have been developed, and new gels are also being developed, including structures that degrade in nature. These gel materials are used as electrolytes in lithium secondary batteries, sensor probes, cushioning materials, and low-friction materials. A wide range of research is being conducted, from basic research to applied research to practical materials. In this context, this Special Issue welcomes papers on gel materials that are aimed at or have been put into practical use. The practical use of gels requires great ingenuity, not only in the chemical composition and molecular structure of the gel but also in its engineering, including thinning, molding, bonding with different materials, dimensional stability, heat resistance, and durability. This Special Issue welcomes papers that focus not only on the basic chemistry of gels with new functions, but also on the engineering for practical application of gels.

Prof. Dr. Takaya Sato
Dr. Katsuhiko Sato
Prof. Dr. Toshio Kamijo
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Gels is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• hydrophilic- and lipophilic-gels
• polymers for gels
• electrochemistry of gels
• biosensing application of gels
• self-remediation of gels
• chemistry and engineering of gels
• battery and capacitor application of gels
• biocompatibility and biodegradability of gels
• film and coating of gels
• ionic liquids application for gels
• 3D-printing of gels
• manufacturing of gels
• target drug and cosmetics application of gels
• structure and cross linkage of gels
• industrial application of gels

Title: Temperature-Sensitive Breathable Film Based on High Ther-mal-Expansion Gel Particles
Authors: Kohei Sakai; Koh Yoshida; Jin Gong; Kosei Sato; Kazuhiro Hamada; Hiroshi Ito
Affiliation: 1 Department of Mechanical Systems Engineering, Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan; tmf62483@st.yamagata-u.ac.jp (K.S.) 2 Department of Polymer Science & Engineering, Graduate School of Organic Materials Science, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan; t221034m@st.yamagata-u.ac.jp (K.Y.); jin-gong@yz.yamagata-u.ac.jp (J.G.); ihiroshi@yz.yamagata-u.ac.jp (H.I.) 3 Kohjin Film & Chemicals Co., Ltd., 1-1 Koukokumachi, Yatsushiro, Kumamoto 866-8686, Japan; k_sato@kohjin.co.jp (K.S.); kazuhiro_hamada@kohjin.co.jp (K.H.)

Title: A biomimetic Bacterial Cellulose/ Gelatin composite Scaffold with Suture-free biological hydrogel for urethral tissue engi-neering
Authors: Xiangguo Lv; Lin Wang; Zhe Li; Baoxiu Wang; Shiyan Chen; Ranxing Yang; Yidong Liu
Affiliation: 1 Department of Urology, Renji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China; chnlvsc@163.com 2 State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai , China. 3 Department of Urology, Shanghai Jiaotong University Affiliated Sixth People's Hospital, Shanghai, China;
Abstract: This study focused on the challenges of epithelialization and vascularization encountered in urethral repair. Us-ing the ultrastructure of biomimetic urethral extracellular matrix as a foundation, a bioscaffold with distinct struc-tural layers of dense and porous regions was constructed. Here we describe the design considerations for urethral tissues and study the use of cellulose nanofibers combined with macroporous gelatin sponge to make biocompatible bilayer scaffolds with microstructure and nanotexture for urethral tissue engineering through the application of three-dimensional porous architecture technology and nanofiber in-situ self-assembly techniques. At the nanoscale, both the dense and porous layers of the scaffold were covered with nanofibers. The study also optimized the pa-rameters of nanofiber diameter and pore size to explore the mechanism of how the micro-nano structure of the composite material induces cell and tissue regeneration. Additionally, an innovative approach combining in-situ hydrogel technology with a "photocoupling reaction" was proposed. This aimed to promote suture-free physiologi-cal repair of the bioscaffold within the body. By creating hydrogels modified with methacrylated gelatin (GelMA) and nitrobenzyl-based photo-trigger molecules (NB) decorating hyaluronic acid (HA-NB), which possess strong biological adhesion to tissues/cells both in vivo and in vitro, the study explored their mechanism of cell and tissue adsorption. Through animal experiments, it was confirmed that the hydrogel-modified biomimetic material pro-moted rapid epithelialization and sufficient vascularization in vivo , providing new ideas and methods for the treatment of urethral stricture.

Title: Influence of drying method and vulcanisation on mechanical properties of polyvinylsilsesquioxane aerogels
Authors: Aleksandra M. Pisarek; Bartosz Nowak; Max Zinke; Kai Steffens; Danny Bialuschewski; Barbara Milow; Jakub M. Gac
Affiliation: 1 Faculty of Chemical and Process Engineering, Warsaw University of Technology, Waryńskiego 1, 00-645 Warsaw, Poland 2 Institute of Inorganic Chemistry, University of Cologne, Greinstrasse 6, 50939 Cologne, Germany 3 Institute of Materials Research, German Aerospace Center, Linder Höhe, 51147 Cologne, Germany
Abstract: Silica aerogels obtained from organosilicon precursors, due to their unique properties, such as high porosity and specific surface area as well as low density, have become increasingly widely used in various industrial fields in recent decades. Unfortunately, in addition to the interesting features mentioned above, they also have some disadvantages, including their mechanical fragility and the high cost of the supercritical drying process that is usually used to produce them. In the case of aerogels made from vinyltrimethoxysilane, a solution may be free radical vulcanization using double bonds present in the non-hydrolysable functional group. Such additional cross-linking helps to strengthen the aerogel structure. Moreover, it limits the collapse of the structure during ambient pressure drying and thus enables the synthesis of this material using this cheaper method. The test results show that vulcanized aerogels, regardless of the drying method, are generally characterized by a higher Young's modulus and inelastic range during compression tests. Vulcanization also af-fects the amount of energy dissipated per cycle during cyclic loading-unloading compression tests. The mechanical properties of aerogels are also influenced by the heterogeneous surface layer ("wall"), the thickness of which depends on the drying method and the composition of the reaction mixture.