In vivo evaluation of a multiphased scaffold designed for orthopaedic interface tissue engineering and soft tissue-to-bone integration

Achieving functional graft integration with subchondral bone poses a significant challenge for orthopaedic soft tissue repair and reconstruction. Soft tissues such as the anterior cruciate ligament (ACL) integrate with bone through a fibrocartilage interface, which minimizes stress concentrations and mediates load transfer between soft and hard tissues. We propose that biological fixation can be achieved by regenerating this fibrocartilage interface on biological or synthetic ACL grafts. This study focuses on the in vivo evaluation of a stratified scaffold predesigned to mimic the multitissue transition found at the ACL-to-bone interface. Specifically, the scaffold consists of three distinct yet continuous phases: Phase A for ligament formation, Phase B for the interface, and Phase C for the bone region. Interface-relevant cell types, specifically fibroblasts, chondrocytes, and osteoblasts, will be tri-cultured on this scaffold, and the formation of cell type- and phase-specific matrix heterogeneity as well as fibrocartilage formation will be evaluated over 8 weeks in a subcutaneous athymic rat model. Acellular scaffolds as well as scaffolds co-cultured with fibroblasts and osteoblasts will serve as controls. It was found that the triphasic scaffold supported multilineage cellular interactions as well as tissue infiltration and abundant matrix production in vivo. In addition, controlled phase-specific matrix heterogeneity was induced on the scaffold, with distinct mineral and fibrocartilage-like tissue regions formed in the tri-cultured group. Cell seeding had a positive effect on both host infiltration and matrix elaboration, which also translated into increased mechanical properties in the seeded groups compared to the acellular controls. In summary, the biomimetic and multiphasic design coupled with spatial control of cell distribution enables multitissue regeneration on the stratified scaffold, and demonstrates the potential for regenerating the interface between soft tissue grafts and bone.