Bioassembly of Region-Specific Fibrocartilage Microtissues to Engineer Zonally Defined Meniscal Grafts

Meniscal injuries are common orthopaedic problems which can impair knee function and lead to the development of osteoarthritis. While recent advances in tissue engineering have enabled the fabrication of meniscus-like grafts, these do not fully replicate the zonal structure and composition of the native meniscus. Here, fibrocartilage microtissues are used as building blocks to biofabricate zonally defined meniscal grafts. Meniscus progenitor cells (MPCs) isolated from the inner (iMPC) and outer (oMPC) regions of caprine menisci are used to engineer region-specific meniscal microtissues. Both iMPC and oMPC-derived microtissues are rich in glycosaminoglycans (GAGs) and collagen, with iMPC-derived microtissues staining more intensely for type II collagen. These microtissues are assembled into two different physically confining moulds, where they rapidly fuse and generate a fibrocartilaginous graft. The impact of the catabolic enzyme chondroitinase-ABC (cABC) on the composition and structural organization of the meniscal grafts is then explored, which is found to reduce sGAG levels but to increase collagen fiber thickness. Finally, iMPC and oMPC microtissues are spatially assembled to biofabricate a scaled-up and zonally defined meniscal construct. These findings support the use of MPC-derived microtissues as biological building blocks for the engineering of meniscal grafts.