Spatial Manipulation and Integration of Supramolecular Filaments on Hydrogel Substrates towards Advanced Soft Devices

Bilayer Hydrogels by Reactive-Induced Macrophase Separation

Bilayer hydrogels encoded with smart functions have emerged as promising soft materials for engineered biological tissues and human-machine interfaces, due to the versatility and flexibility in designing their mechanical and chemical properties. However, conventional fabrication strategies often require multiple complicated steps to create an anisotropic bilayer structure with poor interfaces, which significantly limit the scope of bilayer hydrogel applications. Here, we reported a general, one-pot, macrophase separation strategy to fabricate a family of bilayer hydrogels made of vinyl and styryl monomers with a seamless interface and a controllable layer separation efficiency (20-99%). The working principle of a macrophase separation strategy allows for the decoupling of the two gelation processes to form distinct vinyl- and styryl-enriched layers by manipulating competitive polymerization reactions between vinyl and styryl monomers. This work presents a straightforward approach and a diverse range of radical monomers, which can be utilized to create next-generation bilayer hydrogels, beyond a few available today.

Strong underwater adhesion of injectable hydrogels triggered by diffusion of small molecules

It is challenging for injectable hydrogels to achieve high underwater adhesiveness. Based on this concern, we report a fully physically crosslinked injectable hydrogel composed of gelatin, tea polyphenols and urea, capable of realising smart adhesion to various materials, like glass and porcine skin, in diverse aqueous environments. The urea molecules are designed as crosslinking disruptors for interfering with the formation of hydrogen bonds in the hydrogel, therefore modulating its crosslinking density and mechanical properties such as tensile strength, toughness and adhesive strength. Triggered by physical diffusion of the urea molecules towards the surrounding liquid environment, the hydrogel can achieve efficient (∼10 s), self-strengthening and long-lasting (>2 weeks) underwater adhesion. Remarkably, for fresh porcine skin, the instantaneous underwater adhesive strength is 10.4 kPa whereas the peak strength is as high as 152.9 kPa with the aid of the self-strengthening effect. More interestingly, it can simultaneously form controllable underwater non-adhesive surfaces, regulated by changes in the diffusion-triggered local concentration of urea. Further, it is also biocompatible, antibacterial, biodegradable and 3D printable in water, which offers great convenience for various applications concerning smart interfacial adhesion, like biomedicine and flexible electronics. Likewise, the physical diffusion-mediated mechanism represents an innovative strategy for developing next-generation smart hydrogels.