Genipin does not reduce the initiation or propagation of microcracks in collagen networks of cartilage.

Objective: We recently initiated microcracks, i.e. micron-scale cracks in the collagen networks of cartilage, using both single low-energy impacts and unconfined, cyclic compressions. We also tracked the propagation of microcracks after cyclic compressions simulating 12,000 walking strides. In this study, we aimed to determine the effect of one or more genipin treatments on: (1) the initiation of microcracks under mechanical impacts and (2) the subsequent propagation of microcracks under cyclic, unconfined compression. We hypothesized that treatments with genipin would improve the resistance of cartilage to microdamage, specifically reducing both the initiation of microcracks under impact loading and the propagation of microcracks under cyclic compression. Design: We tested 49 full-thickness, cylindrical osteochondral specimens. We incorporated one or two doses of genipin in between mechanical treatments, i.e. single low-energy mechanical impacts to initiate microcracks and unconfined, cyclic compressions to propagate microcracks. We also imaged specimens using second harmonic generation confocal microscopy, and analyzed the resulting images to quantify changes in morphologies (length, width, and depth) and orientations of microcracks. Finally, we used separate mixed-regression modeling to evaluate the effects of genipin treatments on mechanically induced microcracks. Results: Specimens treated with genipin presented significantly longer and marginally deeper microcracks after mechanical impacts. Two doses of genipin caused significantly longer and wider microcracks under propagation verses one dose. Conclusions: Our results do not support our hypothesis: unfortunately treatments with genipin, and the resulting mechanisms of cross-linking, do not provide resistance to microdamage, quantified as the initiation and propagation of microcracks.