Strong and tough liquid crystal hydrogels from chitin whiskers with multiscale dynamic bonds guide osteogenic differentiation.

Liquid crystal (LC) state and viscoelasticity with rapid stress relaxation of osteoid are crucial for cell behavior regulation, but mimicking these features in bone repair materials through a facile approach is challenging. Here, harnessing the innate LC characteristic and nanoscale rigidity of chitin whiskers (CHWs), we develop novel CHWs/polyvinyl alcohol (CHWs/PVA) LC hydrogels with multiple osteoid-like features through a facile dual-physical crosslinking strategy. The self-assembly of CHWs, accompanying with PVA chains, enable the hydrogels with osteoid-like LC state and viscoelasticity. Freeze-thawing-induced microcrystalline domains (sacrificial bonds) and Hofmeister-enhanced hydrogen bonds can serve as multiscale hierarchical energy dissipation motors to endow the hydrogels with rapid stress relaxation rate, as well as high and adjustable modulus. We found that YAP-dependent mechanotransduction and LC state-mediated protein clustering can synergistically boost the osteogenic differentiation of bone mesenchymal stem cells, moreover, this positive effect can be flexibly regulated by adjusting the modulus, stress relaxation and LC characteristics of the hydrogels. This study provides new insights for designing osteoid-like biomimetic materials, and further elucidates the strengthening and toughening as well as osteogenic differentiation mechanisms.