Journal articles: 'Ultra-Soft Hydrogels'

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Xie, Beixin, Peidong Xu, Liqun Tang, Yongrou Zhang, Kejia Xu, Hong Zhang, Zejia Liu, Licheng Zhou, Yiping Liu, and Zhenyu Jiang. "Dynamic Mechanical Properties of Polyvinyl Alcohol Hydrogels Measured by Double-Striker Electromagnetic Driving SHPB System." International Journal of Applied Mechanics 11, no. 02 (March 2019): 1950018. http://dx.doi.org/10.1142/s1758825119500182.

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As an ultra-soft material (elastic modulus in magnitude of kPa), polyvinyl alcohol (PVA) hydrogels have the potential to substitute articular cartilage, but the measurement of the dynamic stress–strain relations of ultra-soft materials is still challenging. In this paper, a double-striker electromagnetic driving split-Hopkinson pressure bar (SHPB) system was developed, in which all the bars were made of polycarbonate, and the polycarbonate striker was pushed by a metal striker driven electromagnetically to ensure the precise control of impact velocity. With the new SHPB system, well design of the size of hydrogel specimen and rational processing of the signal data, the stress–strain relations of hydrogels with varied PVA contents at different strain rates were measured successfully. Experimental results indicate that PVA hydrogels are a positive strain rate sensitive material with different strain-rate effects at low and high strain rates. Finally, based on the latest quasi-static constitution of the PVA hydrogel, a rate-dependent constitutive equation was recommended, which may well depict the mechanical behaviors of hydrogels with different fiber contents at varied strain rates. It also derives that the contributions of strain rate and fiber content on the mechanical behaviors of the hydrogel are relatively independent.

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Xu, Zhenyu, Yongsen Zhou, Baoping Zhang, Chao Zhang, Jianfeng Wang, and Zuankai Wang. "Recent Progress on Plant-Inspired Soft Robotics with Hydrogel Building Blocks: Fabrication, Actuation and Application." Micromachines 12, no. 6 (May 24, 2021): 608. http://dx.doi.org/10.3390/mi12060608.

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Millions of years’ evolution has imparted life on earth with excellent environment adaptability. Of particular interest to scientists are some plants capable of macroscopically and reversibly altering their morphological and mechanical properties in response to external stimuli from the surrounding environment. These intriguing natural phenomena and underlying actuation mechanisms have provided important design guidance and principles for man-made soft robotic systems. Constructing bio-inspired soft robotic systems with effective actuation requires the efficient supply of mechanical energy generated from external inputs, such as temperature, light, and electricity. By combining bio-inspired designs with stimuli-responsive materials, various intelligent soft robotic systems that demonstrate promising and exciting results have been developed. As one of the building materials for soft robotics, hydrogels are gaining increasing attention owing to their advantageous properties, such as ultra-tunable modulus, high compliance, varying stimuli-responsiveness, good biocompatibility, and high transparency. In this review article, we summarize the recent progress on plant-inspired soft robotics assembled by stimuli-responsive hydrogels with a particular focus on their actuation mechanisms, fabrication, and application. Meanwhile, some critical challenges and problems associated with current hydrogel-based soft robotics are briefly introduced, and possible solutions are proposed. We expect that this review would provide elementary tutorial guidelines to audiences who are interested in the study on nature-inspired soft robotics, especially hydrogel-based intelligent soft robotic systems.

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Juliar, Benjamin A., Jeffrey A. Beamish, Megan E. Busch, David S. Cleveland, Likitha Nimmagadda, and Andrew J. Putnam. "Cell-mediated matrix stiffening accompanies capillary morphogenesis in ultra-soft amorphous hydrogels." Biomaterials 230 (February 2020): 119634. http://dx.doi.org/10.1016/j.biomaterials.2019.119634.

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Strachota, Beata, Adam Strachota, Leana Vratović, Ewa Pavlova, Miroslav Šlouf, Samir Kamel, and Věra Cimrová. "Exceptionally Fast Temperature-Responsive, Mechanically Strong and Extensible Monolithic Non-Porous Hydrogels: Poly(N-isopropylacrylamide) Intercalated with Hydroxypropyl Methylcellulose." Gels 9, no. 12 (November 24, 2023): 926. http://dx.doi.org/10.3390/gels9120926.

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Exceptionally fast temperature-responsive, mechanically strong, tough and extensible monolithic non-porous hydrogels were synthesized. They are based on divinyl-crosslinked poly(N-isopropyl-acrylamide) (PNIPAm) intercalated by hydroxypropyl methylcellulose (HPMC). HPMC was largely extracted after polymerization, thus yielding a ‘template-modified’ PNIPAm network intercalated with a modest residue of HPMC. High contents of divinyl crosslinker and of HPMC caused a varying degree of micro-phase-separation in some products, but without detriment to mechanical or tensile properties. After extraction of non-fixed HPMC, the micro-phase-separated products combine superior mechanical properties with ultra-fast T-response (in 30 s). Their PNIPAm network was highly regular and extensible (intercalation effect), toughened by hydrogen bonds to HPMC, and interpenetrated by a network of nano-channels (left behind by extracted HPMC), which ensured the water transport rates needed for ultra-fast deswelling. Moreover, the T-response rate could be widely tuned by the degree of heterogeneity during synthesis. The fastest-responsive among our hydrogels could be of practical interest as soft actuators with very good mechanical properties (soft robotics), while the slower ones offer applications in drug delivery systems (as tested on the example of Theophylline), or in related biomedical engineering applications.

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Sanjuan-Alberte, Paola, Jayasheelan Vaithilingam, Jonathan C. Moore, Ricky D. Wildman, Christopher J. Tuck, Morgan R. Alexander, Richard J. M. Hague, and Frankie J. Rawson. "Development of Conductive Gelatine-Methacrylate Inks for Two-Photon Polymerisation." Polymers 13, no. 7 (March 26, 2021): 1038. http://dx.doi.org/10.3390/polym13071038.

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Conductive hydrogel-based materials are attracting considerable interest for bioelectronic applications due to their ability to act as more compatible soft interfaces between biological and electrical systems. Despite significant advances that are being achieved in the manufacture of hydrogels, precise control over the topographies and architectures remains challenging. In this work, we present for the first time a strategy to manufacture structures with resolutions in the micro-/nanoscale based on hydrogels with enhanced electrical properties. Gelatine methacrylate (GelMa)-based inks were formulated for two-photon polymerisation (2PP). The electrical properties of this material were improved, compared to pristine GelMa, by dispersion of multi-walled carbon nanotubes (MWCNTs) acting as conductive nanofillers, which was confirmed by electrochemical impedance spectroscopy and cyclic voltammetry. This material was also confirmed to support human induced pluripotent stem cell-derived cardiomyocyte (hPSC-CMs) viability and growth. Ultra-thin film structures of 10 µm thickness and scaffolds were manufactured by 2PP, demonstrating the potential of this method in areas spanning tissue engineering and bioelectronics. Though further developments in the instrumentation are required to manufacture more complex structures, this work presents an innovative approach to the manufacture of conductive hydrogels in extremely low resolution.

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Gori, M., S. M. Giannitelli, G. Vadalà, R. Papalia, L. Zollo, A. Rainer, and V. Denaro. "A POLY(SBMA) ZWITTERIONIC HYDROGEL COATING OF POLYIMIDE SURFACES TO REDUCE THE FOREIGN BODY REACTION TO INVASIVE NEURAL INTERFACES." Orthopaedic Proceedings 105-B, SUPP_7 (April 4, 2023): 20. http://dx.doi.org/10.1302/1358-992x.2023.7.020.

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Intraneural electrodes can be harnessed to control neural prosthetic devices in human amputees. However, in chronic implants we witness a gradual loss of device functionality and electrode isolation due to a nonspecific inflammatory response to the implanted material, called foreign body reaction (FBR). FBR may eventually lead to a fibrous encapsulation of the electrode surface. Poly(ethylene glycol) (PEG) is one of the most common low-fouling materials used to coat and protect electrode surfaces. Yet, PEG can easily undergo encapsulation and oxidative damage in long-term in vivo applications. Poly(sulfobetaine methacrylate) - poly(SBMA) - zwitterionic hydrogels may represent more promising alternatives to minimize the FBR due to their ultra-low fouling features. Here, we tested and compared the poly(SBMA) zwitterionic hydrogel coating with the PEG coating in reducing adhesion and activation of pro-inflammatory and pro-fibrotic cells to polyimide surfaces, which are early hallmarks of FBR. We aimed to coat polyimide surfaces with a hydrogel thin film and analysed the release of a model drug from the hydrogel.We performed hydrogel synthesis, mechanical characterization and biocompatibility analysis. Cell adhesion, viability and morphology of human myofibroblasts cultured on PEG- and hydrogel-coated surfaces were evaluated through confocal microscopy-based high-content analysis (HCA). Reduced activation of pro-inflammatory human macrophages cultured on hydrogels was assessed as well as the hydrogel drug release profile.Because of its high hydration, biocompatibility, low stiffness and ultra-low fouling characteristics the hydrogel enabled lower adhesion and activation of pro-inflammatory and pro-fibrotic cells vs. polystyrene controls, and showed a long-term release of the anti-fibrotic drug Everolimus. Furthermore, a polyimide surface was successfully coated with a hydrogel thin film.Our soft zwitterionic hydrogel could outperform PEG as more suitable coating material of neural electrodes for mitigating the FBR. Such poly(SBMA)-based biomaterial could also be envisioned as long-term delivery system for a sustained release of anti-inflammatory and anti-fibrotic drugs in vivo.

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Wu, Meng, Jingsi Chen, Yuhao Ma, Bin Yan, Mingfei Pan, Qiongyao Peng, Wenda Wang, Linbo Han, Jifang Liu, and Hongbo Zeng. "Ultra elastic, stretchable, self-healing conductive hydrogels with tunable optical properties for highly sensitive soft electronic sensors." Journal of Materials Chemistry A 8, no. 46 (2020): 24718–33. http://dx.doi.org/10.1039/d0ta09735g.

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A self-healing hydrogel ionic conductor has been developed by combining dynamic covalent chemistry with nanofiller reinforcement and micelle crosslinking, and used for sensing of diverse human activities.

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Francis, Lydia, Karin V. Greco, Aldo R. Boccaccini, Judith J. Roether, Nicholas R. English, Honglei Huang, R. Ploeg, and Tahera Ansari. "Development of a novel hybrid bioactive hydrogel for future clinical applications." Journal of Biomaterials Applications 33, no. 3 (September 2018): 447–65. http://dx.doi.org/10.1177/0885328218794163.

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Three-dimensional hydrogels are ideal for tissue engineering applications due to their structural integrity and similarity to native soft tissues; however, they can lack mechanical stability. Our objective was to develop a bioactive and mechanically stable hydrogel for clinical application. Auricular cartilage was decellularised using a combination of hypertonic and hypotonic solutions with and without enzymes to produce acellular tissue. Methacryloyl groups were crosslinked with alginate and PVA main chains via 2-aminoethylmathacrylate and the entire macromonomer further crosslinked with the acellular tissue. The resultant hydrogels were characterised for its physicochemical properties (using NMR), in vitro degradation (via GPC analysis), mechanical stability (compression tests) and in vitro biocompatibility (co-culture with bone marrow-derived mesenchymal stem cells). Following decellularisation, the cartilage tissue showed to be acellular at a significant level (DNA content 25.33 ng/mg vs. 351.46 ng/mg control tissue), with good structural and molecular integrity of the retained extra cellular matrix (s-GAG= 0.19 μg/mg vs. 0.65 μg/mg ±0.001 control tissue). Proteomic analysis showed that collagen subtypes and proteoglycans were retained, and SEM and TEM showed preserved matrix ultra-structure. The hybrid hydrogel was successfully cross-linked with biological and polymer components, and it was stable for 30 days in simulated body fluid (poly dispersal index for alginate with tissue was stable at 1.08 and for PVA with tissue was stable at 1.16). It was also mechanically stable (Young’s modulus of 0.46 ± 0.31 KPa) and biocompatible, as it was able to support the development of a multi-cellular feature with active cellular proliferation in vitro. We have shown that it is possible to successfully combine biological tissue with both a synthetic and natural polymer and create a hybrid bioactive hydrogel for clinical application.

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Musgrave, Christopher, Lorcan O’Toole, Tianyu Mao, Qing Li, Min Lai, and Fengzhou Fang. "Manufacturing of Soft Contact Lenses Using Reusable and Reliable Cyclic Olefin Copolymer Moulds." Polymers 14, no. 21 (November 2, 2022): 4681. http://dx.doi.org/10.3390/polym14214681.

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We present experimental evidence of reusable, reliable cyclic olefin copolymer (COC) moulds in soft contact lens manufacturing. The moulds showed high performance surface roughness characteristics despite >20 kW exposure to 365 nm ultraviolet (UV) light from repeated use. Ultra-precision manufacturing techniques were used to fabricate transparent COC mould inserts and to produce soft contact lenses from liquid monomer compositions. Both polymer and silicone hydrogels were fabricated with more than 60 individual uses of the moulds. White light interferometry measured the surface roughness (Sa) of the COC moulds to be almost unchanged before and after repeated use (Sa 16.3 nm before vs. 16.6 nm after). The surface roughness of the prototyped lenses and that of commercially available soft contact lenses were then compared by white light interferometry. The surface roughness of the lenses was also nearly unchanged, despite undergoing more than 60 uses of the COC moulds (lens Sa 24.4 nm before vs. after Sa 26.5 nm). By comparison the roughness of the commercial lenses ranged from 9.3–28.5 nm, including conventional and silicone lenses, indicating that the reusable COC moulds produced competitive surface properties. In summary, COC moulds have potential as reusable and reliable mould inserts in the manufacturing of soft contact lenses, yet maintain high quality optical surfaces even after sustained exposure to UV light.

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Rosa, Elisabetta, Enrico Gallo, Teresa Sibillano, Cinzia Giannini, Serena Rizzuti, Eliana Gianolio, Pasqualina Liana Scognamiglio, Giancarlo Morelli, Antonella Accardo, and Carlo Diaferia. "Incorporation of PEG Diacrylates (PEGDA) Generates Hybrid Fmoc-FF Hydrogel Matrices." Gels 8, no. 12 (December 16, 2022): 831. http://dx.doi.org/10.3390/gels8120831.

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Generated by a hierarchical and multiscale self-assembling phenomenon, peptide-based hydrogels (HGs) are soft materials useful for a variety of applications. Short and ultra-short peptides are intriguing building blocks for hydrogel fabrication. These matrices can also be obtained by mixing low-molecular-weight peptides with other chemical entities (e.g., polymers, other peptides). The combination of two or more constituents opens the door to the development of hybrid systems with tunable mechanical properties and unexpected biofunctionalities or morphologies. For this scope, the formulation, the multiscale analysis, and the supramolecular characterization of novel hybrid peptide-polymer hydrogels are herein described. The proposed matrices contain the Fmoc-FF (Nα-fluorenylmethyloxycarbonyl diphenylalanine) hydrogelator at a concentration of 0.5 wt% (5.0 mg/mL) and a diacrylate α-/ω-substituted polyethylene-glycol derivative (PEGDA). Two PEGDA derivatives, PEGDA 1 and PEGDA2 (mean molecular weights of 575 and 250 Da, respectively), are mixed with Fmoc-FF at different ratios (Fmoc-FF/PEGDA at 1/1, 1/2, 1/5, 1/10 mol/mol). All the multicomponent hybrid peptide-polymer hydrogels are scrutinized with a large panel of analytical techniques (including proton relaxometry, FTIR, WAXS, rheometry, and scanning electronic microscopy). The matrices were found to be able to generate mechanical responses in the 2–8 kPa range, producing a panel of tunable materials with the same chemical composition. The release of a model drug (Naphthol Yellow S) is reported too. The tunable features, the different topologies, and the versatility of the proposed materials open the door to the development of tools for different applicative areas, including diagnostics, liquid biopsies and responsive materials. The incorporation of a diacrylate function also suggests the possible development of interpenetrating networks upon cross-linking reactions. All the collected data allow a mutual comparison between the different matrices, thus confirming the significance of the hybrid peptide/polymer-based methodology as a strategy for the design of innovative materials.

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Haraguchi, Kazutoshi. "Extraordinary Properties and New Functions of Nanocomposite Gels and Soft Nanocomposites with Unique Organic/Inorganic Network Structures." Advanced Materials Research 680 (April 2013): 65–69. http://dx.doi.org/10.4028/www.scientific.net/amr.680.65.

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New types of polymer hydrogels and nanocomposites, i.e., nanocomposite gels (NC gels) and soft, polymer nanocomposites (M-NCs), with novel organic/inorganic network structures have been fabricated. Both NC gels and M-NCs were synthesized by in-situ free-radical polymerization in the presence of exfoliated clay platelets in aqueous systems and were obtained in various forms and sizes with a wide range of clay contents. Here, disk-like inorganic clay nanoparticles act as multi-functional crosslinkers to form new types of network systems. NC gels have extraordinary optical, mechanical, and swelling/deswelling properties, as well as a number of new characteristics relating to optical anisotropy, polymer/clay morphology, biocompatibility, stimuli-sensitive surfaces, micro-patterning, self-healing, etc. The M-NCs also exhibit dramatic improvements in optical and mechanical properties including ultra-high reversible extensibility and well-defined yielding behavior, despite their high clay contents. The M-NC also showed thermoresponsive cell adhesion/detachment. Thus, the serious disadvantages (intractability, mechanical fragility, optical turbidity, poor processing ability, low stimulus sensitivity, etc.) associated with the conventional, chemically-crosslinked polymeric materials were overcome in NC gels and M-NCs.

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Li, Shengnan, Hailong Yang, Nannan Zhu, Guoqi Chen, YueYue Miao, Jingxia Zheng, Yang Cong, et al. "Biotissue‐Inspired Anisotropic Carbon Fiber Composite Hydrogels for Logic Gates, Integrated Soft Actuators, and Sensors with Ultra‐High Sensitivity (Adv. Funct. Mater. 11/2023)." Advanced Functional Materials 33, no. 11 (March 2023): 2370065. http://dx.doi.org/10.1002/adfm.202370065.

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Molchanov, V. S., M. A. Efremova, T. Yu Kiseleva, and O. E. Philippova. "Injectable ultra-soft hydrogel with natural nanoclay." Nanosystems: Physics, Chemistry, Mathematics 10, no. 1 (February 27, 2019): 76–85. http://dx.doi.org/10.17586/2220-8054-2019-10-1-76-85.

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Guo, Meiling, Yuanpeng Wu, Shishan Xue, Yuanmeng Xia, Xi Yang, Yuris Dzenis, Zhenyu Li, Weiwei Lei, Andrew T. Smith, and Luyi Sun. "A highly stretchable, ultra-tough, remarkably tolerant, and robust self-healing glycerol-hydrogel for a dual-responsive soft actuator." Journal of Materials Chemistry A 7, no. 45 (2019): 25969–77. http://dx.doi.org/10.1039/c9ta10183g.

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A novel strategy to synthesize a glycerol-hydrogel with high stretchability, ultra-toughness, remarkable tolerance, and outstanding self-healing capability has been developed. A soft actuator has been fabricated based on the glycerol-hydrogel.

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Wang, Yueyang, Qiao Wang, Xiaosai Hu, Dan He, Juan Zhao, and Guoxing Sun. "A multi-functional zwitterionic hydrogel with unique micro-structure, high elasticity and low modulus." RSC Advances 12, no. 43 (2022): 27907–11. http://dx.doi.org/10.1039/d2ra04915e.

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In this article, the authors have developed an ultra-soft and tough dual-crosslinking zwitterionic hydrogel, which possesses a unique spike-like microstructure, low modulus, excellent stretchability and compressibility with self-healing properties.

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Liu, Zhimo, Binfan Zhao, Liucheng Zhang, Shutong Qian, Jiayi Mao, Liying Cheng, Xiyuan Mao, et al. "Modulated integrin signaling receptors of stem cells via ultra-soft hydrogel for promoting angiogenesis." Composites Part B: Engineering 234 (April 2022): 109747. http://dx.doi.org/10.1016/j.compositesb.2022.109747.

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Lepo, Kelly, and Marten van Kerkwijk. "Ultra-soft Sources as Type Ia Supernovae Progenitors." Proceedings of the International Astronomical Union 7, S281 (July 2011): 136–39. http://dx.doi.org/10.1017/s1743921312014871.

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AbstractMissing from the usual considerations of nuclear burning white dwarfs as Type Ia supernovae progenitors are systems with very higher mass transfer rates, where more material than is needed for steady burning accretes on the white dwarf. This will expand the photosphere of the white dwarf, causing it to emit at longer wavelengths. Thus, we propose the name ultra-soft source (USS) for these objects.We present a VLT/FLAMES survey looking for USSs in the SMC, selected to be bright in the far UV and with blue far UV-V colors. While we find some unusual objects, and recover known planetary nebulae and WR stars, we detect no objects with strong He II lines, which should be a signature of USSs. This null result either puts an upper limit on the number of USSs in the SMC, or shows that we do not understand what the optical spectra of such objects will look like.We also discuss the unusual LMC [WN] planetary nebula LMC N66 as a possible example of a USS. It has a luminosity consistent with that expected, and its spectra show incompletely CNO-processed material — strong helium lines, some hydrogen, enhanced nitrogen and depleted carbon. It also shows periodic outbursts. USSs may resemble N66 in quiescence. However, it lacks a FUV excess, contrary to our predictions.

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Gori, Manuele, Sara Maria Giannitelli, Gianluca Vadalà, Rocco Papalia, Loredana Zollo, Massimo Sanchez, Marcella Trombetta, Alberto Rainer, Giovanni Di Pino, and Vincenzo Denaro. "A Soft Zwitterionic Hydrogel as Potential Coating on a Polyimide Surface to Reduce Foreign Body Reaction to Intraneural Electrodes." Molecules 27, no. 10 (May 13, 2022): 3126. http://dx.doi.org/10.3390/molecules27103126.

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Invasive intraneural electrodes can control advanced neural-interfaced prostheses in human amputees. Nevertheless, in chronic implants, the progressive formation of a fibrotic capsule can gradually isolate the electrode surface from the surrounding tissue leading to loss of functionality. This is due to a nonspecific inflammatory response called foreign-body reaction (FBR). The commonly used poly(ethylene glycol) (PEG)-based low-fouling coatings of implantable devices can be easily encapsulated and are susceptible to oxidative damage in long-term in vivo applications. Recently, sulfobetaine-based zwitterionic hydrogels have emerged as an important class of robust ultra-low fouling biomaterials, holding great potential to mitigate FBR. The aim of this proof-of-principle in vitro work was to assess whether the organic zwitterionic—poly(sulfobetaine methacrylate) [poly(SBMA)]—hydrogel could be a suitable coating for Polyimide (PI)-based intraneural electrodes to reduce FBR. We first synthesized and analyzed the hydrogel through a mechanical characterization (i.e., Young’s modulus). Then, we demonstrated reduced adhesion and activation of fibrogenic and pro-inflammatory cells (i.e., human myofibroblasts and macrophages) on the hydrogel compared with PEG-coated and polystyrene surfaces using cell viability assays, confocal fluorescence microscopy and high-content analysis of oxidative stress production. Interestingly, we successfully coated PI surfaces with a thin film of the hydrogel through covalent bond and demonstrated its high hydrophilicity via water contact angle measurement. Importantly, we showed the long-term release of an anti-fibrotic drug (i.e., Everolimus) from the hydrogel. Because of the low stiffness, biocompatibility, high hydration and ultra-low fouling characteristics, our zwitterionic hydrogel could be envisioned as long-term diffusion-based delivery system for slow and controlled anti-inflammatory and anti-fibrotic drug release in vivo.

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Rosenstock, D., T. Gerber, C. Castro Müller, S. Stille, and J. Banik. "Process Stability and Application of 1900 MPa Grade Press Hardening Steel with reduced Hydrogen Susceptibility." IOP Conference Series: Materials Science and Engineering 1238, no. 1 (May 1, 2022): 012013. http://dx.doi.org/10.1088/1757-899x/1238/1/012013.

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Abstract While 22MnB5 with aluminium silicon (AS) coating was established as the quasi-standard in press hardening many years ago, the need for steels that offer even higher strength is growing. These needs include corrosion protection of the automotive component and scale prevention during processing in hot forming lines. However, the processing of AS coated ultra-high strength steels involves demands for the furnace atmosphere. Reducing the hydrogen susceptibility and increasing the material strength at the same time was the driving force for the development of MBW 1900 + AS Pro. The paper focuses on the process stability of this steel concerning furnace and stamping parameters as well as the hydrogen induced cracking resistance under different dew points in the furnace atmosphere. In addition, the potential by means of different partial press hardening processes is presented. With tailored tempering, locally heated tools can be used to achieve soft areas in the part. Furthermore, the application potential of MBW 1900 + AS Pro in tailor welded blanks is shown.

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Yurakov, Yury A., Yaroslav A. Peshkov, Evelina P. Domashevskaya, Vladimir A. Terekhov, Konstantin A. Barkov, Anatoly N. Lukin, and Alexander V. Sitnikov. "A study of multilayer nanostructures [(Co45Fe45Zr10)35(Al2O3)65/a-Si:H]100 and [(Co45Fe45Zr10)35(Al2O3)65/a-Si]120 by means of XRD, XRR, IR spectroscopy, and USXES." European Physical Journal Applied Physics 87, no. 2 (August 2019): 21301. http://dx.doi.org/10.1051/epjap/2019190131.

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Interatomic interactions and superstructures of multilayer nanostructures (MLNS) consisting of ferromagnetic composite layers and silicon interlayers with or without hydrogen are studied here by means of X-ray diffraction (XRD), X-ray reflectivity (XRR), IR spectroscopy, and ultra-soft X-ray emission spectroscopy (USXES). The MLNS [(Co45Fe45Zr10)35(Al2O3)65/a-Si:H]100 and [(Co45Fe45Zr10)35(Al2O3)65/a-Si]120 were deposited on the substrate Si(100) by ion-beam sputtering of two targets, where the first target was a plate of Co45Fe45Zr10 alloy with Al2O3 inserts, and the second target was a single-crystal silicon. Our results show that the iron (FeSi2) and cobalt (CoSi, CoSi2) silicides are formed at the interfaces of the composite metal-containing layer/silicon interlayer. It is demonstrated that the metal clusters of composite layers and interface silicides are partially oxidized to form iron, cobalt, and silicon oxides together with zirconium silicate. Due to the formation of silicides at the interfaces, the composition of MLNS superstructures becomes more complex, and their periods are significantly reduced (down to 5–6 nm) compared to the nominal values of bilayers of about 6.9 nm.

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Yamada, Hajime, Shiho Takahashi, Kana Yamashita, Hisashi Miyafuji, Hiroyuki Ohno, and Tatsuhiko Yamada. "High-throughput analysis of softwood lignin using tetra-n-butylphosphonium hydroxide (TBPH)." BioResources 12, no. 4 (October 30, 2017): 9396–406. http://dx.doi.org/10.15376/biores.12.4.9396-9406.

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The authors developed a high-throughput method for analyzing softwood lignin using tetra-n-butylphosphonium hydroxide (TBPH). Wood meal, TBPH, and hydrogen peroxide (H2O2) were introduced into a screw-capped glass test tube and allowed to react in a pressure cooker at 121 °C for 3 h to solubilize the wood meal. The solubilized polysaccharide was precipitated by the addition of a poor solvent such as methanol. After removal of the polysaccharide, the lignin concentration was measured via ultra-violet (UV) absorption spectroscopy. The series of operations performed was summarized as the TBPH method. The TBPH method was characterized as a simple and rapid procedure that used common equipment and was suitable for multiple-sample analysis. Softwood sample groups were prepared, and the lignin contents of these samples were measured by the TBPH method, the Klason method, and the acetyl bromide method to determine the accuracy of the proposed method. The TBPH method showed a high coefficient of determination (R2 = 0.94) when compared to the Klason method. By contrast, the acetyl bromide method showed a comparatively low correlation (R2 = 0.71) with the Klason method. This study revealed that the TBPH method presented high-throughput rapid analysis and good accuracy for soft wood lignin analysis.

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Rao, C. N. R., Ved Varun Agrawal, Kanishka Biswas, Ujjal K. Gautam, Moumita Ghosh, A. Govindaraj, G. U. Kulkarni, K. P. Kalyanikutty, Kripasindhu Sardar, and S. R. C. Vivekchand. "Soft chemical approaches to inorganic nanostructures." Pure and Applied Chemistry 78, no. 9 (January 1, 2006): 1619–50. http://dx.doi.org/10.1351/pac200678091619.

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Chemical approaches have emerged as the preferred means to synthesize nanostructures of various inorganic materials due to superior control over size, shape, and surface functionality. This article provides an overview of the contributions made in the authors' laboratory toward the synthesis of nanocrystals, nanowires, nanotubes, nanowalls, and other nanostructures of several inorganic materials. Thus, thiolized monodisperse metal nanocrystals have been obtained by a ligand exchange process and the stability of their 2D assemblies studied. Nanocrystals of pure CoO and ReO3 have been synthesized, for the first time, employing a one-pot solvothermal technique. The solvothermal method has also been used to obtain organic soluble nanocrystals of semiconducting materials such as CdS, CdSe, and GaN. Inorganic nanowires and nanotubes have been prepared by several soft chemical routes, including surfactant-assisted synthesis and hydrogel templating. A simple reaction between elemental Se and Te with NaBH4 in water has been utilized to obtain nanowires of Se and Te. We also describe the nebulized spray pyrolysis (NSP) technique to synthesize carbon nanotubes and nanowires of metals and III-V nitride semiconductors with improved yields. An important new technique for preparing nanocrystalline films of materials is by the reaction of the metal precursors in the organic layer at the interface of two immiscible liquids, with appropriate reagents. Nanocrystalline films of metals, alloys, and semiconductors and ultra-thin single-crystalline films of metal chalcogenides and oxides have been obtained by this technique. Apart from these, we discuss single precursor routes to iron sulfide, GeSe2, and III-V nitride nanostructures as well as the first synthesis of GaS and GaSe nanowalls and nanotubes obtained through exfoliation by laser irradiation and thermal treatment.

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Lomonaco, Quentin, Karine Abadie, Jean-Michel Hartmann, Christophe Morales, Paul Noël, Tanguy Marion, Christophe Lecouvey, Anne-Marie Papon, and Frank Fournel. "Soft Surface Activated Bonding of Hydrophobic Silicon Substrates." ECS Meeting Abstracts MA2023-02, no. 33 (December 22, 2023): 1601. http://dx.doi.org/10.1149/ma2023-02331601mtgabs.

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Surface Activated Bonding (SAB) is interesting for strong silicon to silicon bonding at room temperature without any annealing needed, afterwards (1). Although it is a well-known technique, the activation step, in particular, is scarcely documented. This paper offers insights about the impact of soft activation parameters on the amorphous region at the bonding interface. In addition, the adherence energy of hydrophobic silicon bonding with SAB is quantified to better understand bonding mechanisms. With very low dose and acceleration activation parameters, the surface preparation prior to bonding becomes of paramount importance. Indeed, the silicon native oxide is typically removed during the activation step. The thin amorphous silicon region is a side effect of this singular surface preparation(2). In order to work around this potential roadblock, we used instead hydrophobic surface preparation to remove the native oxide, before entering into the activation step. Two types of preparation were evaluated in this study. First, a standard “HF-Last” chemical treatment was used on standard silicon wafers. This treatment removed the silicon native oxide and passivated the surface with Si-H and, to a lesser extent, Si-F bonds (3). We otherwise used epitaxy-reconstructed silicon wafers with fully hydrophobic surfaces (4). Silicon native oxide was removed thanks to an ultra-pure H2 bake at 1100°C, 20 Torr for 2 minutes in an epitaxy chamber. Then, several tens of nm of Silicon were deposited at 950°C to obtain, after another H2 bake, a silicon surface fully passivated by hydrogen atoms with atomically smooth terraces and mono-atomic step edges. Our EVG®ComBond® bonding tool, operating under ultra-high vacuum (UHV), is equipped with an accelerated argon ion beam to perform the activation step. The softest functional settings, on our set up, are 50V (acceleration) and 26 mA (dose). After beam initialization, the two sets of substrates pass through the activation chamber. Activated substrates are then transferred to the bonding chamber within 5 minutes of handling. The exposure time in the activation chamber was evaluated, the aim being to remove adsorbed hydrogen atoms on the silicon surface without any amorphous silicon generation. Different characterization techniques such as transmission electron microscopy or FTIR-MIR were used to quantify the amorphous layer formation and the potential Si-H bonds remaining (after activation). The adherence energy of the bonded pair was measured by a double cantilever beam method under prescribed displacement control in anhydrous atmosphere (5). Figure 1 shows the adherence energy (Gc=2γc) in mJ/m² as a function of activation exposure time with soft activation parameters for both wafer preparations. The 0s reference bonding was conducted without passing through the activation module. We then had very low adherence energies, around 50 mJ/m², as expected for standard hydrophobic silicon wafer bonding under UHV (6). Upon Ar+ exposure, behaviors were very different depending on surface preparation. The adherence energy barely increased with the Ar+ exposure time for “HF-Last” surfaces. Meanwhile, even 1s of exposure to Ar+ had a definite impact on the adherence energy of epi-reconstructed, atomically smooth silicon surfaces, which was definitely higher. The maximum difference between both wafer preparations occurred for 30 up to 60 seconds exposure times. This indicate a change in the bonding mechanism as the comparatively high roughness of the “HF-Last” silicon wafer started to be counter-balanced by activation. The experimental set up, the manufacturing process, as well as further characterizations will be presented. Cross-sectional TEM imaging of the bonding interface, FTIR-MIR and AFM measurements after surface preparation will help us better understand the specificities of such soft activation process on the SAB of hydrophobic surfaces. The impact of the amorphous silicon layer on bonding will be discussed. Suga T et al. STRUCTURE OF A1-A1 A N D A1-Si3N4 INTERFACES BONDED AT ROOM TEMPERATURE BY MEANS OF THE SURFACE ACTIVATION METHOD. Acta Metallurgica et Materialia 1992. Takagi H et al. Surface activated bonding of silicon wafers at room temperature. Appl Phys Lett. 1996. Abbadie A et al. Low thermal budget surface preparation of Si and SiGe. Appl Surf Sci. 2004. Sordes D et al. Nanopackaging of Si(100)H Wafer for Atomic-Scale Investigations. 2017. Maszara WP et al. Bonding of silicon wafers for silicon‐on‐insulator. J Appl Phys. 15 nov 1988;64(10):4943-50. Tong QY et al. The Role of Surface Chemistry in Bonding of Standard Silicon Wafers. J Electrochem Soc. 1997. Figure 1

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Wang, Zhuang, Xiaoyun Xu, Renjie Tan, Shuai Zhang, Ke Zhang, and Jinlian Hu. "Hierarchically Structured Hydrogel Composites with Ultra‐High Conductivity for Soft Electronics." Advanced Functional Materials, December 31, 2023. http://dx.doi.org/10.1002/adfm.202312667.

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AbstractConductive hydrogels possessing high conductivity, stretchability, and biocompatibility are promising materials for underwater devices and bioelectronics. However, typical hydrogels often exhibit low electrical conductivity, which is insufficient for applications requiring high electronic communication. A common approach to increase hydrogel conductivity is to introduce conductive fillers; however, this usually implies a partial sacrifice of stretchability, biocompatibility, and water content. In addition, the electrical properties of hydrogels tend to be unstable due to rehydration in aqueous environments. In this study, a conductive hydrogel composite is fabricated from silver nanowires (AgNWs) and poly(vinyl alcohol) (PVA) employing a synergistic method of freezing and salting‐out treatments. This combined method constructs a hierarchical hydrogel structure and increases the local concentration of AgNWs by inducing continuous phase separation. The resultant conductive hydrogel composites exhibit ultra‐high electrical conductivity (≈1739 S cm−1) and electrical stability in aqueous environments while maintaining high water content (≈87%), stretchability (≈480%), and excellent biocompatibility. To illustrate the capabilities of the conductive hydrogel composites, they are applied to bionic sharks, underwater soft circuitry, and electrocardiogram electrodes.

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Jaspers, Maarten, Matthew Dennison, Mathijs F. J. Mabesoone, Frederick C. MacKintosh, Alan E. Rowan, and Paul H. J. Kouwer. "Ultra-responsive soft matter from strain-stiffening hydrogels." Nature Communications 5, no. 1 (December 2014). http://dx.doi.org/10.1038/ncomms6808.

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Ye, Yuhang, Zhangmin Wan, P. D. S. H. Gunawardane, Qi Hua, Siheng Wang, Jiaying Zhu, Mu Chiao, Scott Renneckar, Orlando J. Rojas, and Feng Jiang. "Ultra‐Stretchable and Environmentally Resilient Hydrogels Via Sugaring‐Out Strategy for Soft Robotics Sensing." Advanced Functional Materials, February 27, 2024. http://dx.doi.org/10.1002/adfm.202315184.

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AbstractThe adoption of hydrogels in most applications is hampered by their high free water content, which limits their mechanical performance and environmental resilience. Herein, this issue is simultaneously addressed by modulating the state of water and the intermolecular interactions in polyacrylamide (PAM) hydrogels. Specifically, PAM hydrogels are toughened by sugaring‐out using a monosaccharide (glucose, G). Glucose is found to facilitate PAM hydrogen bonding and interchain interactions. Meanwhile, the high hygroscopicity of glucose converts some of the free water to bound state, endowing the hydrogels with remarkable resilience to extreme environmental conditions. The PAM‐G hydrogels are demonstrated as multimodal sensors for soft robotics. Moreover, PAM‐G alcogels produced by solvent exchanging with ethanol are shown as effective opto‐mechanical sensors. Notably, all these properties are obtained by the inclusion of glucose, a green additive showing no negative health and environmental effect.

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Zhang, Qingtian, Hongda Lu, Guolin Yun, Liping Gong, Zexin Chen, Shida Jin, Haiping Du, Zhen Jiang, and Weihua Li. "A Laminated Gravity‐Driven Liquid Metal‐Doped Hydrogel of Unparalleled Toughness and Conductivity." Advanced Functional Materials, October 6, 2023. http://dx.doi.org/10.1002/adfm.202308113.

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AbstractConductive hydrogels have been promising candidates for wearable and flexible electronics due to their high flexibility and biocompatibility. However, the previously reported hydrogels with conductivity over 1000 S m−1 usually have poor mechanical properties including low tensile stress (<5 MPa) and toughness (<2 MJ m−3). Here, a liquid metal‐doped polyvinyl alcohol (PVA‐LM) hydrogel is presented, which simultaneously combines ultra‐high conductivity (maximum of 217 895 S m−1) with excellent mechanical properties, including high tensile stress (15.44 MPa), large tensile strain (704%), high toughness (43.02 MJ m−3) and excellent fatigue resistance. Such extremely high conductivity is afforded by self‐sintering behavior of LM at the bottom surface that enables the formation of conductive networks. The formation of polymer crystalline regions and polymer‐tannic acid multiple hydrogen bonds are responsible for the impressive mechanical properties of conductive hydrogels. Particularly, the electric LM filler could be recycled in the robust hydrogel by dissociation of multiple dynamic interactions. Most importantly, wearable electrodes and capacitive sensors are developed utilizing PVA‐LM hydrogel. These devices enable accurate monitoring of bioelectrical signals and human motions, highlighting their immense potential in the realm of soft electronics and wearable technology.

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Zhang, Jianhua, Jiahe Liao, Zemin Liu, Rongjing Zhang, and Metin Sitti. "Liquid Metal Microdroplet‐Initiated Ultra‐Fast Polymerization of a Stimuli‐Responsive Hydrogel Composite." Advanced Functional Materials, November 12, 2023. http://dx.doi.org/10.1002/adfm.202308238.

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AbstractRecent advances in composite hydrogels achieve material enhancement or specialized stimuli‐responsive functionalities by pairing with a functional filler. Liquid metals (LM) offer a unique combination of chemical, electrical, and mechanical properties that show great potential in hydrogel composites. Polymerization of hydrogels with LM microdroplets as initiators is a particularly interesting phenomenon that remains in its early stage of development. In this work, an LM‐hydrogel composite is introduced, in which LM microdroplets dispersed inside the hydrogel matrix have dual functions as a polymerization initiator for a polyacrylic acid‐poly vinyl alcohol (PAA/PVA) network and, once polymerized, as passive inclusion to influence its material and stimuli‐responsive characteristics. It is demonstrated that LM microdroplets enable ultra‐fast polymerization in ≈1 min, compared to several hours by conventional polymerization techniques. The results show several mechanical enhancements to the PAA/PVA hydrogels with LM‐initiated polymerization. It is found that LM ratios strongly influence stimuli‐responsive behaviors in the hydrogels, including swelling and ionic bending, where higher LM ratios are found to enhance ionic actuation performance. The dual roles of LM in this composite are analyzed using the experimental characterization results. These LM‐hydrogel composites, which are biocompatible, open up new opportunities in future soft robotics and biomedical applications.

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Zhang, Jipeng, Yang Hu, Lina Zhang, Jinping Zhou, and Ang Lu. "Transparent, Ultra-Stretching, Tough, Adhesive Carboxyethyl Chitin/Polyacrylamide Hydrogel Toward High-Performance Soft Electronics." Nano-Micro Letters 15, no. 1 (December 7, 2022). http://dx.doi.org/10.1007/s40820-022-00980-9.

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AbstractTo date, hydrogels have gained increasing attentions as a flexible conductive material in fabricating soft electronics. However, it remains a big challenge to integrate multiple functions into one gel that can be used widely under various conditions. Herein, a kind of multifunctional hydrogel with a combination of desirable characteristics, including remarkable transparency, high conductivity, ultra-stretchability, toughness, good fatigue resistance, and strong adhesive ability is presented, which was facilely fabricated through multiple noncovalent crosslinking strategy. The resultant versatile sensors are able to detect both weak and large deformations, which owns a low detection limit of 0.1% strain, high stretchability up to 1586%, ultrahigh sensitivity with a gauge factor up to 18.54, as well as wide pressure sensing range (0–600 kPa). Meanwhile, the fabrication of conductive hydrogel-based sensors is demonstrated for various soft electronic devices, including a flexible human–machine interactive system, the soft tactile switch, an integrated electronic skin for unprecedented nonplanar visualized pressure sensing, and the stretchable triboelectric nanogenerators with excellent biomechanical energy harvesting ability. This work opens up a simple route for multifunctional hydrogel and promises the practical application of soft and self-powered wearable electronics in various complex scenes.

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Ding, Baofu, Pengyuan Zeng, Ziyang Huang, Lixin Dai, Tianshu Lan, Hao Xu, Yikun Pan, et al. "A 2D material–based transparent hydrogel with engineerable interference colours." Nature Communications 13, no. 1 (March 8, 2022). http://dx.doi.org/10.1038/s41467-021-26587-z.

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AbstractTransparent hydrogels are key materials for many applications, such as contact lens, imperceptible soft robotics and invisible wearable devices. Introducing large and engineerable optical anisotropy offers great prospect for endowing them with extra birefringence-based functions and exploiting their applications in see-through flexible polarization optics. However, existing transparent hydrogels suffer from limitation of low and/or non-fine engineerable birefringence. Here, we invent a transparent magneto-birefringence hydrogel with large and finely engineerable optical anisotropy. The large optical anisotropy factor of the embedded magnetic two-dimensional material gives rise to the large magneto-birefringence of the hydrogel in the transparent condition of ultra-low concentration, which is several orders of magnitude larger than usual transparent magnetic hydrogels. High transparency, large and tunable optical anisotropy cooperatively permit the magnetic patterning of interference colours in the hydrogel. The hydrogel also shows mechanochromic and thermochromic property. Our finding provides an entry point for applying hydrogel in optical anisotropy and colour centred fields, with several proof-of-concept applications been demonstrated.

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Chong, Jooyeun, Changhoon Sung, Kum Seok Nam, Taewon Kang, Hyunjun Kim, Haeseung Lee, Hyunchang Park, Seongjun Park, and Jiheong Kang. "Highly conductive tissue-like hydrogel interface through template-directed assembly." Nature Communications 14, no. 1 (April 18, 2023). http://dx.doi.org/10.1038/s41467-023-37948-1.

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AbstractOver the past decade, conductive hydrogels have received great attention as tissue-interfacing electrodes due to their soft and tissue-like mechanical properties. However, a trade-off between robust tissue-like mechanical properties and good electrical properties has prevented the fabrication of a tough, highly conductive hydrogel and limited its use in bioelectronics. Here, we report a synthetic method for the realization of highly conductive and mechanically tough hydrogels with tissue-like modulus. We employed a template-directed assembly method, enabling the arrangement of a disorder-free, highly-conductive nanofibrous conductive network inside a highly stretchable, hydrated network. The resultant hydrogel exhibits ideal electrical and mechanical properties as a tissue-interfacing material. Furthermore, it can provide tough adhesion (800 J/m2) with diverse dynamic wet tissue after chemical activation. This hydrogel enables suture-free and adhesive-free, high-performance hydrogel bioelectronics. We successfully demonstrated ultra-low voltage neuromodulation and high-quality epicardial electrocardiogram (ECG) signal recording based on in vivo animal models. This template-directed assembly method provides a platform for hydrogel interfaces for various bioelectronic applications.

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Pitenis, Angela A., Juan Manuel Urueña, Ryan M. Nixon, Tapomoy Bhattacharjee, Brandon A. Krick, Alison C. Dunn, Thomas E. Angelini, and W. Gregory Sawyer. "Lubricity from Entangled Polymer Networks on Hydrogels." Journal of Tribology 138, no. 4 (July 26, 2016). http://dx.doi.org/10.1115/1.4032889.

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Structural hydrogel materials are being considered and investigated for a wide variety of biotribological applications. Unfortunately, most of the mechanical strength and rigidity of these materials comes from high polymer concentrations and correspondingly low polymer mesh size, which results in high friction coefficients in aqueous environments. Recent measurements have revealed that soft, flexible, and large mesh size hydrogels can provide ultra low friction, but this comes at the expense of mechanical strength. In this paper, we have prepared a low friction structural hydrogel sample of polyhydroxyethylmethacrylate (pHEMA) by polymerizing an entangled polymer network on the surface through a solution polymerization route. The entangled polymer network was made entirely from uncrosslinked polyacrylamide (pAAm) that was polymerized from an aqueous solution and had integral entanglement with the pHEMA surface. Measurements revealed that these entangled polymer networks could extend up to ∼200 μm from the surface, and these entangled polymer networks can provide reductions in friction coefficient of almost two orders of magnitude (μ > 0.7 to μ < 0.01).

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Cafiso, Diana, Federico Bernabei, Matteo Lo Preti, Simone Lantean, Ignazio Roppolo, Candido Fabrizio Pirri, and Lucia Beccai. "DLP‐Printable Porous Cryogels for 3D Soft Tactile Sensing." Advanced Materials Technologies, February 14, 2024. http://dx.doi.org/10.1002/admt.202302041.

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AbstractThree‐Dimensional (3D) printed porous materials hold the potential for various soft sensing applications due to their remarkable flexibility, low density, and customizable geometries. However, developing versatile and efficient fabrication methods is crucial to unlock their full potential. A novel approach is introduced by combining Digital Light Processing (DLP) 3D printing and freeze‐drying to manufacture deformable cryogels featuring intricate morphologies. Photocurable hydrogels based on Poly(3,4‐ethylenedioxythiophene)Polystyrene sulfonate (PEDOT:PSS), Polyethylene glycol Diacrylate (PEGDA) and Ethylene Glycol (EG) are successfully printed and lyophilized. In this way, porous cryogels with tailorable properties are achieved. Microporosity varies from 68% to 96%, according to the chemical composition. Ultra‐soft cryogels with a compressive modulus of 0.13MPa are fabricated by adding a reactive diluent. As a result of the cryogelation process, which effectively removes water from the hydrogels, microporous structures with details as fine as 100 µm are obtained. The achieved freedom of design is exploited to fabricate resistive force sensors with a honeycomb lattice morphology. The sensitivity and the working range of the sensors can be tailored by tuning the size of the cells, paving the way for sensors with programmable architectures that can meet diverse requirements.

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Sans, Jordi, Ingrid Azevedo Gonçalves, and Robert Quintana. "Establishing Quartz Crystal Microbalance with Dissipation (QCM‐D) Coupled with Spectroscopic Ellipsometry (SE) as an Advantageous Technique for the Characterization of Ultra‐Thin Film Hydrogels." Small, March 4, 2024. http://dx.doi.org/10.1002/smll.202312041.

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AbstractDespite the considerable significance of utilizing ultra‐thin film (utf) hydrogels as multipurpose platforms for biomedical applications, there is still an important lack of adequate characterization techniques suitable for such materials. In this Perspective, the use of quartz crystal microbalance with dissipation (QCM‐D) coupled with spectral ellipsometry (SE) is presented as a potential tool for the complete characterization of utf‐hydrogels due to its nanometric sensitivity and high versatility. Herein, the fundaments for utf‐hydrogel characterization are settled down as far as the QCM‐D/SE response is explored under a wide range of different in operando wet working conditions measurements such as temperature or liquid media, among others. Therefore, the design of measuring protocols capable to perform is proposed and compiled, for the first time, complete and precise characterization of the cross‐link density, thickness variations (swelling ratio determination), stability analyses, and mechanical studies (including the simultaneous generation of stress‐strain curves and the evaluation of the viscoelastic; leading to the final determination of the Poisson's ratio) under different in operando conditions. Finally, the future challenges and implications for the general characterization of soft‐thin films are discussed.

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Yu, Xiaohui, Haopeng Zhang, Yufei Wang, Xiaoshan Fan, Zibiao Li, Xu Zhang, and Tianxi Liu. "Highly Stretchable, Ultra‐Soft, and Fast Self‐Healable Conductive Hydrogels Based on Polyaniline Nanoparticles for Sensitive Flexible Sensors." Advanced Functional Materials, June 2022, 2204366. http://dx.doi.org/10.1002/adfm.202204366.

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Li, Xin, Ruizhe Hu, Zhiqiang Xiong, Dan Wang, Zhixia Zhang, Chongbo Liu, Xiaojun Zeng, Dezhi Chen, Renchao Che, and Xuliang Nie. "Metal–Organic Gel Leading to Customized Magnetic-Coupling Engineering in Carbon Aerogels for Excellent Radar Stealth and Thermal Insulation Performances." Nano-Micro Letters 16, no. 1 (December 4, 2023). http://dx.doi.org/10.1007/s40820-023-01255-7.

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AbstractMetal–organic gel (MOG) derived composites are promising multi-functional materials due to their alterable composition, identifiable chemical homogeneity, tunable shape, and porous structure. Herein, stable metal–organic hydrogels are prepared by regulating the complexation effect, solution polarity and curing speed. Meanwhile, collagen peptide is used to facilitate the fabrication of a porous aerogel with excellent physical properties as well as the homogeneous dispersion of magnetic particles during calcination. Subsequently, two kinds of heterometallic magnetic coupling systems are obtained through the application of Kirkendall effect. FeCo/nitrogen-doped carbon (NC) aerogel demonstrates an ultra-strong microwave absorption of − 85 dB at an ultra-low loading of 5%. After reducing the time taken by atom shifting, a FeCo/Fe3O4/NC aerogel containing virus-shaped particles is obtained, which achieves an ultra-broad absorption of 7.44 GHz at an ultra-thin thickness of 1.59 mm due to the coupling effect offered by dual-soft-magnetic particles. Furthermore, both aerogels show excellent thermal insulation property, and their outstanding radar stealth performances in J-20 aircraft are confirmed by computer simulation technology. The formation mechanism of MOG is also discussed along with the thermal insulation and electromagnetic wave absorption mechanism of the aerogels, which will enable the development and application of novel and lightweight stealth coatings.

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Zhou, Yan, Xiaoteng Jia, Daxin Pang, Shan Jiang, Meihua Zhu, Geyu Lu, Yaping Tian, Caiyun Wang, Danming Chao, and Gordon Wallace. "An integrated Mg battery-powered iontophoresis patch for efficient and controllable transdermal drug delivery." Nature Communications 14, no. 1 (January 18, 2023). http://dx.doi.org/10.1038/s41467-023-35990-7.

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AbstractWearable transdermal iontophoresis eliminating the need for external power sources offers advantages for patient-comfort when deploying epidermal diseases treatments. However, current self-powered iontophoresis based on energy harvesters is limited to support efficient therapeutic administration over the long-term operation, owing to the low and inconsistent energy supply. Here we propose a simplified wearable iontophoresis patch with a built-in Mg battery for efficient and controllable transdermal delivery. This system decreases the system complexity and form factors by using viologen-based hydrogels as an integrated drug reservoir and cathode material, eliminating the conventional interface impedance between the electrode and drug reservoir. The redox-active polyelectrolyte hydrogel offers a high energy density of 3.57 mWh cm−2, and an optimal bioelectronic interface with ultra-soft nature and low tissue-interface impedance. The delivery dosage can be readily manipulated by tuning the viologen hydrogel and the iontophoresis stimulation mode. This iontophoresis patch demonstrates an effective treatment of an imiquimod-induced psoriasis mouse. Considering the advantages of being a reliable and efficient energy supply, simplified configuration, and optimal electrical skin-device interface, this battery-powered iontophoresis may provide a new non-invasive treatment for chronic epidermal diseases.

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Li, Shengnan, Hailong Yang, Nannan Zhu, Guoqi Chen, YueYue Miao, Jingxia Zheng, Yang Cong, et al. "Biotissue‐Inspired Anisotropic Carbon Fiber Composite Hydrogels for Logic Gates, Integrated Soft Actuators, and Sensors with Ultra‐High Sensitivity." Advanced Functional Materials, December 15, 2022, 2211189. http://dx.doi.org/10.1002/adfm.202211189.

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Hussain, Ashhar, Javad Rahmannezhad, Gyeong Min Choi, Seo Gyun Kim, Wook Ryol Hwang, Jinhwan Yoon, and Heon Sang Lee. "Hyper-elastic behavior of soft-tissue like microgels in two-phase converging microchannel flow." Physics of Fluids 35, no. 12 (December 1, 2023). http://dx.doi.org/10.1063/5.0174625.

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Deformation of biological cells, tissues, and similar soft materials is often considered linearly elastic; however, the assumption is only valid in a very limited stress range and often leads to significant errors in mechanical evaluation. We demonstrated the hyper-elastic behavior of ultra-soft poly(N-isopropyl acrylamide) (PNIPAm) microgels (USPNMs) in a converging channel flow, as a representation for biological tissues. The hyper-elasticity of USPNMs in response to a broad range of deformation was characterized at the centerline of the converging flow. We introduced a carrier fluid consisting of baby hydrogels (avg. diameter, 10 μm) and oil that carried the hydrophilic USPNM sample (avg. diameter, 100 μm) on the centerline of oil background fluid. By “baby hydrogel,” we mean small PNIPAm particles obtained during USPNM synthesis, using which, enabled settling-free flow, prevented wall contact, and enhanced carrier fluid viscosity for increased stresses at lower flowrates. Furthermore, drastic reduction of interfacial tension was observed in the converging area due to contact of baby gels with USPNM particles in the carrier fluid. The shear and elongational stresses were balanced with the elastic stress and interfacial Laplace pressure. As a result, we obtained a stress–strain curve from the microscopic images during flow. The non-linear stress–strain curve was characterized by conventional hyper-elastic models. The elastic modulus of the synthesized USPNM was 24 Pa, which is as low as animal brain tissue. This method holds great potential for implementing in similar hyper-elastic systems, enabling accurate mechanical evaluations in the field of soft materials, biology, and medicine.

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Liu, Yafei, Yujie Gui, Ying Lv, Huixia Feng, Xia Zhao, Jianhui Qiu, Xuemei Ma, and Yuchen Yang. "Conductive MXene nanocomposite organohydrogels for ultra-stretchable, low-temperature resistant and stable strain sensors." Journal of Materials Chemistry C, 2024. http://dx.doi.org/10.1039/d3tc03862a.

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Hydrogels have unique flexibility and a highly efficient, low-cost manufacturing process, thus they are expected to be used in electronic skin, wearable sensors, soft robotics, and human–computer interaction.

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Chen, Qin, Xinyue Zhang, Siyu Liu, Kai Chen, Cunao Feng, Xiaowei Li, Jianwei Qi, Yong Luo, Hongtao Liu, and Dekun Zhang. "Cartilage-bone inspired the construction of soft-hard composite material with excellent interfacial binding performance and low friction for artificial joints." Friction, July 16, 2022. http://dx.doi.org/10.1007/s40544-022-0645-2.

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AbstractInspired by the cartilage-bone structure in natural joints, soft-hard integrated materials have received extensive attention, which are the most promising candidates for artificial joints due to their combination of excellent load-bearing properties and lubricating properties. The latest progress showed that the combination of hydrogel and titanium alloy can realize a bionic natural joint lubrication system on the surface of titanium alloy. However, obtaining a tough interface between the hydrogel (soft and wet) and the titanium substrate (hard and dry) is still a great challenge. Here, we designed a “soft (hydrogel)-hard (Ti6Al4V)” integrated material with outstanding combination, which simulates the structure and function of cartilage-bone in the natural joint. The load-bearing properties, binding performance, and tribological behaviors for different forms of the soft-hard integrated materials were investigated. The results showed that the hydrogel layer and Ti6Al4V substrate possess ultra-high interfacial toughness (3,900 J/m2). In addition, the combination of the hydrogel layer and Ti6Al4V substrate provided a good lubrication system to endow the “soft (hydrogel)-hard (Ti6Al4V)” integrated material with high load-bearing and excellent tribological properties. Therefore, this study provided an effective strategy for prolonging the service life of Ti6Al4V in the biomedical field.

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Shur, Michael, Outman Akouissi, Olivier Rizzo, Didier J. Colin, John M. Kolinski, and Stéphanie P. Lacour. "Revealing the complexity of ultra-soft hydrogel re-swelling inside the brain." Biomaterials, January 2023, 122024. http://dx.doi.org/10.1016/j.biomaterials.2023.122024.

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Chen, Yuewei, Yanyan Zhou, Zihe Hu, Weiying Lu, Zhuang Li, Ning Gao, Nian Liu, et al. "Gelatin-Based Metamaterial Hydrogel Films with High Conformality for Ultra-Soft Tissue Monitoring." Nano-Micro Letters 16, no. 1 (November 29, 2023). http://dx.doi.org/10.1007/s40820-023-01225-z.

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AbstractImplantable hydrogel-based bioelectronics (IHB) can precisely monitor human health and diagnose diseases. However, achieving biodegradability, biocompatibility, and high conformality with soft tissues poses significant challenges for IHB. Gelatin is the most suitable candidate for IHB since it is a collagen hydrolysate and a substantial part of the extracellular matrix found naturally in most tissues. This study used 3D printing ultrafine fiber networks with metamaterial design to embed into ultra-low elastic modulus hydrogel to create a novel gelatin-based conductive film (GCF) with mechanical programmability. The regulation of GCF nearly covers soft tissue mechanics, an elastic modulus from 20 to 420 kPa, and a Poisson's ratio from − 0.25 to 0.52. The negative Poisson's ratio promotes conformality with soft tissues to improve the efficiency of biological interfaces. The GCF can monitor heartbeat signals and respiratory rate by determining cardiac deformation due to its high conformability. Notably, the gelatin characteristics of the biodegradable GCF enable the sensor to monitor and support tissue restoration. The GCF metamaterial design offers a unique idea for bioelectronics to develop implantable sensors that integrate monitoring and tissue repair and a customized method for endowing implanted sensors to be highly conformal with soft tissues.

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Sharma, Vinay, Xinfeng Shi, George Yao, George M. Pharr, and James Yuliang Wu. "Surface characterization of an ultra-soft contact lens material using an atomic force microscopy nanoindentation method." Scientific Reports 12, no. 1 (November 21, 2022). http://dx.doi.org/10.1038/s41598-022-24701-9.

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AbstractAs new ultra-soft materials are being developed for medical devices and biomedical applications, the comprehensive characterization of their physical and mechanical properties is both critical and challenging. To characterize the very low surface modulus of the novel biomimetic lehfilcon A silicone hydrogel contact lens coated with a layer of a branched polymer brush structure, an improved atomic force microscopy (AFM) nanoindentation method has been applied. This technique allows for precise contact-point determination without the effects of viscous squeeze-out upon approaching the branched polymer. Additionally, it allows individual brush elements to be mechanically characterized in the absence of poroelastic effects. This was accomplished by selecting an AFM probe with a design (tip size, geometry, and spring constant) that was especially suited to measuring the properties of soft materials and biological samples. The enhanced sensitivity and accuracy of this method allows for the precise measurement of the very soft lehfilcon A material, which has an extremely low elastic modulus in the surface region (as low as 2 kPa) and extremely high elasticity (nearly 100%) in an aqueous environment. The surface-characterization results not only reveal the ultra-soft nature of the lehfilcon A lens surface but also demonstrate that the elastic modulus exhibits a 30 kPa/200 nm gradient with depth due to the disparity between the modulus of the branched polymer brushes and the SiHy substrate. This surface-characterization methodology may be applied to other ultra-soft materials and medical devices.

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Zhong, Shihao, Zhengyuan Xin, Yaozhen Hou, Yang Li, Hen-Wei Huang, Tao Sun, Qing Shi, and Huaping Wang. "Double-Modal Locomotion of a Hydrogel Ultra-Soft Magnetic Miniature Robot with Switchable Forms." Cyborg and Bionic Systems, November 21, 2023. http://dx.doi.org/10.34133/cbsystems.0077.

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Oh, Byungkook, Young-Soo Lim, Kun Woo Ko, Hyeonyeob Seo, Dong Jun Kim, Dukyoo Kong, Jae Min You, et al. "Ultra-soft and highly stretchable tissue-adhesive hydrogel based multifunctional implantable sensor for monitoring of overactive bladder." Biosensors and Bioelectronics, January 2023, 115060. http://dx.doi.org/10.1016/j.bios.2023.115060.

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Liu, Hui, Weiyi Zhao, Yunlei Zhang, Xiaoduo Zhao, Shuanhong Ma, Michele Scaraggi, and Feng Zhou. "Robust Super‐Lubricity for Novel Cartilage Prototype Inspired by Scallion Leaf Architecture." Advanced Functional Materials, January 4, 2024. http://dx.doi.org/10.1002/adfm.202310271.

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AbstractThe simultaneous achievement ‐under physiologically high contact pressures‐ of ultra‐low friction, nearly zero surface wear, and long lifetime in the development of human cartilage prosthetics is still a big challenge. In this work, inspired by the unique lubrication mechanism of scallion leaves resulting from the synergy of oriented surface micro‐topography and mucus hydration, a novel layered soft hydrogel as cartilage prototype is developed by chemically embedding thick hydrophilic polyelectrolyte brush chains into the sub‐surface of a high strength anisotropic hydrogel bulk. It exhibits an anisotropic polymer network with unique mechanical properties (tensile strength: 8.3 to 23.7 MPa; elastic modulus 20.0 to 30.0 MPa), anisotropic hydrated surface texture, super‐lubricity, and excellent wear resistance. Thydrogel architecture can exhibit low coefficient of friction (COF) less than ≈0.01 under a wide range of contact stresses (0.2 to 2.4 MPa) and maintain cartilage‐like long‐lasting (50k sliding cycles) robust super‐lubricity (COF ≈ 0.006) and nearly‐zero wear under high contact pressure (≈2.4 MPa) condition. Theoretical underpinning reveals how multiscale surface anisotropy, mechanics, and hydration regulate super‐low friction generation. This work provides a novel design paradigm for the fabrication of robust soft materials with extraordinary lubricity as implantable prototypes and coatings.

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Zhao, Lianjia, Hao Xu, Lingchen Liu, Yiqiang Zheng, Wei Han, and Lili Wang. "MXene‐Induced Flexible, Water‐Retention, Semi‐Interpenetrating Network Hydrogel for Ultra‐Stable Strain Sensors with Real‐Time Gesture Recognition." Advanced Science, September 6, 2023. http://dx.doi.org/10.1002/advs.202303922.

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AbstractAs water‐saturated polymer networks, hydrogels are a growing family of soft materials that have recently become promising candidates for flexible electronics application. However, it remains still difficult for hydrogel‐based strain sensors to achieve the organic unity of mechanical properties, electrical conductivity, and water retention. To address this challenge, based on the template, the excellent properties of MXene nanoflakes (rich surface functional groups, high specific surface area, hydrophilicity, and conductivity) are fully utilized in this study to prepare the P(AA‐co‐AM)/MXene@PDADMAC semi‐interpenetrating network (semi‐IPN) hydrogel. The proposed hydrogel continues to exhibit excellent strain response and flexibility after 30 days of storage at room temperature, and its performance do not decrease after 1100 cycles. Considering these characteristics, a hydrogel‐based device for converting sign language into Chinese characters is successfully developed and optimized using machine learning. Therefore, this study provides novel insight and application directions for hydrogel families.

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Xue, Kai, Changyou Shao, Jie Yu, Hongmei Zhang, Bing Wang, Wenfeng Ren, Yabin Cheng, et al. "Initiatorless Solar Photopolymerization of Versatile and Sustainable Eutectogels as Multi‐Response and Self‐Powered Sensors for Human–Computer Interface." Advanced Functional Materials, September 8, 2023. http://dx.doi.org/10.1002/adfm.202305879.

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AbstractEutectogels are emerging as an appealing soft conductor for self‐powered sensing and the next generation of flexible human–computer interactive devices owing to their inherent mechanical elasticity and high ionic conductivity. However, it still remains a challenge to simultaneously achieve multi‐functional and multi‐response integrations through a facile and sustainable approach. Herein, a self‐healing, environment tolerant, intrinsically conductive, and recyclable eutectogel with multiple responses is developed via one‐step solar‐initiated polymerization of deep eutectic solvents (DESs) and ionic liquids (ILs). Abundant hydrogen bonds and ion‐dipole interactions impart eutectogels with high mechanical strength (8.8 MPa), ultra‐stretchability (>1100%), strong self‐adhesion (≈12 MPa), recyclability, and autonomously self‐healing ability. Furthermore, the intrinsically conductive eutectogels with appealing versatile sensations on strain, temperature, and humidity can serve as wearable sensors for wireless motion recognition and human–computer interaction control. More importantly, the eutectogel‐assembled single‐electrode triboelectric nanogenerator (TENG) exhibits extreme environment‐tolerant and fast self‐healable properties that contribute to maintaining excellent and stable electrical outputs in a wide work temperature range (approximately −40–60 °C), which appear to be promising in self‐powered flexible electronics with high environmental adaptability.

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Wang, Xue, Liguo Wang, Chen Liu, Yan Cao, Peng He, Yu Cui, and Huiquan Li. "Self‐Healing Polyurethane Elastomers with Superior Tensile Strength and Elastic Recovery Based on Dynamic Oxime‐Carbamate and Hydrogen Bond Interactions." Macromolecular Rapid Communications, May 9, 2024. http://dx.doi.org/10.1002/marc.202400022.

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AbstractThe preparation of self‐healing polyurethane elastomers (PUEs) incorporating dynamic bonds is of considerable practical significance. However, developing a PUE with outstanding mechanical properties and high self‐healing efficiency poses a significant challenge. Herein, this work has successfully developed a series of self‐healing PUEs with various outstanding properties through rational molecular design. These PUEs incorporate m‐xylylene diisocyanate and reversible dimethylglyoxime as hard segment, along with polytetramethylene ether glycol as soft segment. A significant amount of dynamic oxime‐carbamate and hydrogen bonds are formed in hard segment. The microphase separated structure of the PUEs enables them to be colorless with a transparency of >90%. Owing to the chemical composition and multiple dynamic interactions, the PUEs are endowed with ultra‐high tensile strength of 34.5 MPa, satisfactory toughness of 53.9 MJ m−3, and great elastic recovery both at low and high strains. The movement of polymer molecular chains and the dynamic reversible interactions render a self‐healing efficiency of 101% at 70 °C. In addition, this self‐healing polyurethane could still maintain high mechanical properties after recycling. This study provides a design strategy for the preparation of a comprehensive polyurethane with superior overall performance, which holds wide application prospects in the fields of flexible displays and solar cells.

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Journal articles on the topic 'Ultra-Soft Hydrogels'

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