Muscle-Inspired Self-Growing Anisotropic Hydrogels with Mechanical Training-Promoting Mechanical Properties.

Muscles are highly anisotropic, force-bearing issues. They form via a process involving nutrient absorption for matrix growth and mechanical training for matrix toughening, in which cyclic disassembly-reconstruction of muscle fibers plays a critical role in generating strong anisotropic structures. Inspired by this process, a mechanical training-associated growing strategy is developed for preparing tough anisotropic hydrogels. Using anisotropic hydrogels made from polyvinyl alcohol (PVA)/tannic acid (TA) as an example, it is demonstrated that the hydrogels can absorb poly(ethylene glycol) diacrylate (PEGDA) via disassembling their aligned nanofibrillar structures. Incorporation of PEGDA within the hydrogels induces PVA to form crystal domains while subsequent mechanical training can restore the aligned fibrillar structures. Such a combining process results in expansion in materials' size (≈2 times) and significant enhancement in their mechanical properties (Young's modulus: from 2.4 to 2.85 MPa; ultimate tensile strength: from 8.2 to 14.1 MPa; toughness: from 335 to 465 MJ m). With a high energy dissipation efficiency (≈90%), potential applications for these tough and adaptable hydrogels are envisioned in impact-protective materials, surgical sutures, etc.