Development of controlled matrix heterogeneity on a triphasic scaffold for orthopedic interface tissue engineering.

Biological fixation of orthopedic soft tissue grafts to bone poses a significant clinical challenge. The clinical success of soft tissue-based grafts for anterior cruciate ligament (ACL) reconstruction is limited by the lack of functional graft integration with subchondral bone. Soft tissues such as the ACL connect to subchondral bone via a complex interface whereby three distinct tissue regions (ligament, fibrocartilage, and bone) work in concert to facilitate load transfer from soft to hard tissue while minimizing stress concentration at the interface. Although a fibrovascular tissue forms at the graft-to-bone interface following surgery, this tissue is nonphysiologic and represents a weak link between the graft and bone. We propose that the re-establishment of the native multi-tissue interface is essential for biological graft fixation. In vivo observations and our in vitro monolayer co-culture results suggest that osteoblast-fibroblast interaction is important for interface regeneration. This study focuses on the design of a triphasic scaffold system mimicking the multi-tissue organization of the native ACL-to-bone interface and the evaluation of osteoblast-fibroblast interactions during three-dimensional co-culture on the triphasic scaffold. We found that the triphasic scaffold supported cell proliferation, migration and phenotypic matrix production while maintaining distinct cellular regions and phase-specific extracellular matrix deposition over time. This triphasic scaffold is designed to guide the eventual reestablishment of an anatomically oriented and mechanically functional fibrocartilage interfacial region directly on biological and synthetic soft tissue grafts. The results of this study demonstrate the feasibility of multi-tissue regeneration on a single scaffold, and the potential of interface tissue engineering to enable the biological fixation of soft tissue grafts to bone.