Engineering articular cartilage-like grafts by self-assembly of infrapatellar fat pad-derived stem cells

Well documented limitations associated with primary chondrocytes for cartilage tissue engineering applications have led to increased interest in the use of multi-potent stem/progenitor cells. The objective of this study was to firstly investigate if infrapatellar fat pad-derived stem cells (FPSCs) could be used to engineer cartilage-like tissues through a self-assembly (SA) process, and secondly to compare the properties of such grafts to those engineered by agarose hydrogel encapsulation (AE). Self-assembled cartilaginous tissues were first engineered by geometrically confining FPSCs on tissue culture plastic, and then either continuously or transiently supplementing these constructs with transforming growth factor-b3 (TGF-b3). Transient supplementation with TGF-b3 (for the first 21 days of culture) enhanced the development of self-assembled grafts, with sGAG accumulation reaching levels of 8.4 ± 1.5% w/w after 6 weeks of culture. While overall levels of matrix synthesis were higher with AE compared to SA, when normalized to tissue wet weight, ECM accumulation was significantly greater in the lighter SA constructs. A potential drawback with the SA approach on tissue culture plastic was that it often led to the development of contracted,geometrically inconsistent tissues.We therefore next explored if SA on polyethylene terephthalate (PET) transwell membranes would lead to the development of more morphologically stable and homogenous tissues. At high seeding densities, SA on such transwell membranes led to the formation of geometrically uniform constructs that underwent minimal contraction during culture. In conclusion, the results of this study demonstrate the potential of SA using FPSCs for cartilage tissue engineering, with grafts attaining relatively high levels of sGAG content within clinically relevant timeframes. Such an approach is easily scalable and may lend itself to treating large, full thickness cartilage defects.