A Computational Model of Osteochondral Defect Repair Following Implantation of Stem Cell-Laden Multiphase Scaffolds

Developing successful tissue engineering strategies requires an understanding of how cells within an implanted scaffold interact with the host environment. The objective of this study was to use a computational mechanobiological model to explore how the design of a cell-laden scaffold influences the spatial formation of cartilage and bone within an osteochondral defect. Tissue differentiation was predicted using a previously developed model, in which cell fate depends on the local oxygen tension and the mechanical environment within a damaged joint. This model was first updated to include a rule through which mature cartilage was resistant to both terminal differentiation and vascularization, and then used to simulate osteochondral defect repair following the implantation of various cell-free and cell-laden scaffolds. While delivery of a cell-free scaffold led to only marginal improvements in joint repair, implantation of a cell-laden bilayered scaffold was predicted to significantly increase cartilage formation in the chondral phase of the scaffold. Despite these improvements, bone still progressed into the chondral regions of these engineered implants by means of endochondral ossification during the later stages of repair. This led to thinning of the cartilage tissue, which in turn resulted in a prediction of increased tissue strain and, eventually, increases in fibrocartilage formation as a result of this altered mechanical stimulus. In contrast to this, the model predicted that implantation of a trilayered scaffold, which included a compact layer to confine angiogenesis to the osseous phase of the defect, further improves joint regeneration. This is achieved by allowing chondrogenically primed mesenchymal stem cells, which are seeded into the chondral phase of the implant, to form stable cartilage, which was ultimately resistant to both vascularization and endochondral ossification. These models provide a framework for exploring how environmental factors impact bone, cartilage, and joint regeneration and can be used to inform the design of new tissue engineering strategies for use in orthopedic medicine.