Figure 1.

Schematic of experimental design. The in vitro model of microfracture consisted of articular cartilage plugs harvested from bovine knees, which were then centrally cored out to form a cylindrical defect space, followed by implantation of 1 of the following 3 experimental constructs: (1) positive control (inner plug returned to the defect), (2) negative control (fibrin only), and (3) microfracture mimic (fibrin + cells). These composite constructs were then exposed to 1 of 3 mechanical loading regimens: (1) unloaded, (2) compressive loading (MechanoActive Transduction and Evaluation bioreactor; MATE), and (3) shear loading (rotatory cell culture system; RCCS). At the end of the indicated experimental periods, some samples (n = 2 per group, per time point) were processed for histological analysis, and the remaining samples (n = 4) were evaluated by push-out test. After testing, half of the samples were processed for gene expression profiling by quantitative reverse-transcription polymerase chain reaction (n = 2) and for biochemical analysis (n = 2). TGF-β3, transforming growth factor β3.