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Combinations of hydrogels and solids provide high level functionality for devices such as tissue engineering scaffolds and soft machines. However, the weak bonding between hydrogels and solids hampers functionality. Here, a versatile strategy to develop mechanically robust solid−hydrogel hybrid materials using surface embedded radicals generated through plasma immersion ion implantation (PIII) of polymeric surfaces is reported. Evidence is provided that the reactive radicals play a dual role: inducing surface‐initiated, spontaneous polymerization of hydrogels; and binding the hydrogels to the surfaces. Acrylamide and silk hydrogels are formed and covalently attached through spontaneous reactions with the radicals on PIII activated polymer surfaces without cross‐linking agents or initiators. The hydrogel amount increases with incubation time, monomer concentration, and temperature. Stability tests indicate that 95% of the hydrogel is retained even after 4 months in PBS solution. T‐peel tests show that failure occurs at the tape−hydrogel interface and the hydrogel‐PIII‐treated PTFE interfacial adhesion strength is over 300 N m−1. Cell assays show no adhesion to the as‐synthesized hydrogels; however, hydrogels synthesized with fibronectin enable cell adhesion and spreading. These results show that polymers functionalized with surface‐embedded radicals provide excellent solid platforms for the generation of robust solid−hydrogel hybrid structures for biomedical applications. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogels are the focus of extensive research due to their potential use in fields including biomedical, pharmaceutical, biosensors, and cosmetics. However, the general weak mechanical properties of hydrogels limit their utility. Here, pristine silk fibroin (SF) hydrogels with excellent mechanical properties are generated via a binary‐solvent‐induced conformation transition (BSICT) strategy. In this method, the conformational transition of SF is regulated by moderate binary solvent diffusion and SF/solvent interactions. β‐sheet formation serves as the physical crosslinks that connect disparate protein chains to form continuous 3D hydrogel networks, avoiding complex chemical and/or physical treatments. The Young's modulus of these new BSICT–SF hydrogels can reach up to 6.5 ± 0.2 MPa, tens to hundreds of times higher than that of conventional hydrogels (0.01–0.1 MPa). These new materials fill the “empty soft materials' space” in the elastic modulus/strain Ashby plot. More remarkably, the BSICT–SF hydrogels can be processed into different constructions through different polymer and/or metal‐based processing techniques, such as molding, laser cutting, and machining. Thus, these new hydrogel systems exhibit potential utility in many biomedical and engineering fields. [ABSTRACT FROM AUTHOR]

Elastomeric, fully degradable, and biocompatible biomaterials are rare, with current options presenting significant limitations in terms of ease of functionalization and tunable mechanical and degradation properties. A new method for covalently crosslinking tyrosine residues in silk proteins, via horseradish peroxidase and hydrogen peroxide, to generate highly elastic hydrogels with tunable properties, is reported. These materials offer tunable mechanical properties, gelation kinetics, and swelling properties. In addition, these new polymers withstand shear strains on the order of 100%, compressive strains greater than 70% and display stiffness between 200-10 000 Pa, covering a significant portion of the properties of native soft tissues. Molecular weight and solvent composition allow control of material mechanical properties over several orders of magnitude while maintaining high resilience and resistance to fatigue. Encapsulation of human bone marrow derived mesenchymal stem cells (hMSC) shows long term survival and exhibits cell-matrix interactions reflective of both silk concentration and gelation conditions. Further biocompatibility of these materials is demonstrated with in vivo evaluation. These new protein-based elastomeric and degradable hydrogels represent an exciting new biomaterials option, with a unique combination of properties, for tissue engineering and regenerative medicine. [ABSTRACT FROM AUTHOR]

There is great need for soft biomaterials that match the stiffness of human tissues for tissue engineering and regeneration. Hydrogels are frequently employed for extracellular matrix functionalization and to provide appropriate mechanical cues. It is challenging, however, to achieve structural integrity and retain bioactive molecules in hydrogels for complex tissue formation that may take months to develop. This work aims to investigate mechanical and biochemical characteristics of silk hydrogels for soft tissue engineering, specifically for the nervous system. The stiffness of 1 to 8% silk hydrogels, measured by atomic force microscopy, is 4 to 33 kPa. The structural integrity of silk gels is maintained throughout embryonic chick dorsal root ganglion (cDRG) explant culture over 4 days whereas fibrin and collagen gels decrease in mass over time. Neurite extension of cDRGs cultured on 2 and 4% silk hydrogels exhibit greater growth than softer or stiffer gels. Silk hydrogels release <5% of neurotrophin-3 (NT-3) over 2 weeks and 11-day old gels show maintenance of growth factor bioactivity. Finally, fibronectin- and NT-3-functionalized silk gels elicit increased axonal bundling suggesting their use in bridging nerve injuries. These results support silk hydrogels as soft and sustainable biomaterials for neural tissue engineering. [ABSTRACT FROM AUTHOR]