Fabrication of SilMA hydrogels with stiffness gradients for soft-to-hard interface tissue engineering

Native tissue interfaces exhibit continuous gradients in mechanical stiffness and extracellular matrix (ECM) composition, which are essential for effective load transmission and functional integration between adjacent tissues. However, accurately replicating these intricate biomechanical gradients in engineered biomaterials remains a significant challenge in interface tissue engineering. In this study, we present a stiffness-gradient methacrylated silk fibroin (SilMA) hydrogel designed to promote tissue interface regeneration, with a focus on mechanical cues as a critical design parameter. Silk fibroin was chemically modified into SilMA, and its concentration systematically varied to produce multilayer hydrogels exhibiting a continuous stiffness gradient ranging from 7.07 ± 4.02 kPa to 71.30 ± 0.97 kPa, effectively mimicking the native mechanical heterogeneity found at tissue interfaces. Functional assays revealed that the low-stiffness layer significantly enhanced angiogenesis, the intermediate-stiffness layer provided an optimal mechanical environment for stem cell osteogenic differentiation, and the high-stiffness layer recapitulated the biomechanical properties of native cartilage tissue. This biomimetic stiffness-gradient SilMA hydrogel scaffold offers a promising strategy for regenerating complex tissue interfaces by harnessing the instructive role of mechanical microenvironments. Our findings underscore the importance of spatially graded mechanical properties in guiding cellular responses and tissue repair, and advance the design of next-generation materials for interface tissue engineering.