Tough and Tunable Scaffold-Hydrogel Composite Biomaterial for Soft-to-Hard Musculoskeletal Tissue Interfaces

Biological interfaces connecting tissues with dissimilar mechanical and structural properties are ubiquitous throughout the musculoskeletal system. Tendons attach to bone via a fibrocartilaginous interface (enthesis) that reduces mechanical strain and resultant tissue failure. Despite this toughening mechanism, tears at the enthesis occur due to acute (overload) or degradative (aging) processes. Repair involves surgical fixation of the torn tendon to bone, but results in the formation of a narrow fibrovascular scar tissue with inferior biomechanical properties. Progress toward enthesis regeneration requires biomaterial approaches to protect exogenously added or endogenously recruited cells from high levels of strain at the interface between dissimilar materials. Here, we describe an innovative reinforcement strategy to address this need. We report a stratified scaffold containing collagen bone and tendon tissue compartments linked by a continuous polyethylene glycol (PEG) hydrogel interface. Tuning the gelation kinetics of the hydrogel modulates its integration with the surrounding biomaterial compartments and yields biomechanical performance advantages. Notably, the continuous hydrogel interface reduces the deleterious effects of strain concentrations that form between tissue compartments in conventional stratified biomaterials. This design of mechanically robust stratified composite biomaterials may be appropriate for a broad range of tendon and ligament-to-bone insertions.