Bio-inspired cellulose reinforced anisotropic composite hydrogel with zone-dependent complex mechanical adaptability and cell recruitment characteristics

Articular cartilage, due to its avascular nature and the low cell density, is hard to regenerate once damaged, thus requiring surgical intervention. Natural cartilage exhibits a complex anisotropic feature with nonlinear and viscoelastic mechanical properties owning to complicated architecture making it attractive to mimic the structure. Here, we demonstrate a three-zone composite hydrogel with superficial, middle and deep zones incorporating into cellulose fabric, cellulose nanofiber and wood cellulose fiber respectively to prepare a stack layout composite hydrogel inspired by cartilage architecture with zone-dependent mechanical properties. The results indicate that the three-zone cellulose reinforced polyethylene glycol-based composite hydrogel demonstrates hydrogel creates native-like articular cartilage with zone-dependent, nonlinear and viscoelastic mechanical properties. The compressive moduli of the superficial, middle and deep zones are 298 kPa, 182 kPa and 9.8 MPa respectively, and the middle zone possess obvious nonlinear features. Furthermore, the highly aligned wood frame channels endow deep zone with nutrition and cell transport behaviors which are beneficial to the process of cartilage regeneration. Therefore, the bio-inspired three-zone composite hydrogel has a promising potential application for cartilage repair.