A biomechanical environment constructed exploiting the mechanical property of the extracellular matrix and external loading is essential for cell behaviour. Building suitable mechanical stimuli using feasible scaffold material and moderate mechanical loading is critical in bone tissue engineering for bone repair. However, the detailed mechanism of the mechanical regulation remains ambiguous. In addition, TRPV4 is involved in bone development. Therefore, this study aims to construct a viscoelastic hydrogel combined with dynamic compressive loading and investigate the effect of the dynamic mechanical environment on the osteogenic differentiation of stem cells and bone repair in vivo. The role of TRPV4 in the mechanobiology process was also assessed. A sodium alginate-gelatine hydrogel with adjustable viscoelasticity and good cell adhesion ability was obtained. The osteogenic differentiation of BMSCs was obtained using the fast stress relaxation hydrogel and a smaller compression strain of 1.5%. TRPV4 was activated in the hydrogel with fast stress relaxation time, followed by the increase in intracellular Ca²⁺ level and the activation of the Wnt/β-catenin pathway. The inhibition of TRPV4 induced a decrease in the intracellular Ca²⁺ level, down-regulation of β-catenin, and reduced osteogenesis differentiation of BMSCs, suggesting that TRPV4 might be the key mechanism in the regulation of BMSC osteogenic differentiation in the viscoelastic dynamic mechanical environment. The fast stress relaxation hydrogel also showed a good osteogenic promotion effect in the rat femoral defect model. The dynamic viscoelastic mechanical environment significantly induced the osteogenic differentiation of BMSCs and bone regeneration, which TRPV4 being involved in this mechanobiological process. Our study not only provided important guidance for the mechanical design of new biomaterials, but also provided a new perspective for the understanding of the interaction between cells and materials, the role of mechanical loading in tissue regeneration, and the use of mechanical regulation in tissue engineering.

Nucleus pulposus (NP) tissue engineering brings new hope in the repair of intervertebral disc degeneration (IVDD). IVDD is often accompanied by multiscale changes in the mechanical microenvironment, including the changes of mechanical property of collagen fibril, NP tissue, and mechanical instability of spine. In this study, a multiscale mechanically-adapted strategy is proposed to promote NP repair. To achieve this goal, a viscoelastic-adapted dual-network hydrogel (PVA-DN) is constructed. The hydrogel with multiscale tunable viscoelasticity and dynamic compression condition is used to meet the multiscale mechanical requirements of NP regeneration. The results show that the viscoelastic hydrogel promotes the proliferation, migration and adhesion of nucleus pulposus cell (NPC) as well as the secretion of NP-specific extracellular matrix. RNA-seq results show that it attenuates the inflammatory microenvironment by inhibiting the IL-17 signaling pathway. Appropriate dynamic compression applied to the viscoelastic scaffold further promotes the physiological function of NPC, and the viscoelasticity of hydrogel protects against NPC damage induced by excessive compression. Animal experiments demonstrate that the viscoelastic hydrogel effectively restores disc mechanical function and delays disc degeneration in rats. Findings from this study highlight that the multiscale mechanically-adapted strategy is effective in the repair of IVDD.