High Resolution Nanostructure with Two-stages of Exponential Energy Dissipation at the Ultrathin Osteochondral Interface Tissue of Human Knee Joint

Cartilage adheres to subchondral bone via a specific osteochondral interface tissue where forces are transferred from soft cartilage to hard bone without fatigue damage over a lifetime of load cycles. However, the fine structure and mechanical properties of osteochondral interface tissue remain unclear. Here, we identified an ultrathin ∼20-30 μm calcified region with two-layered micro-nano structures of osteochondral interface tissue in human knee joint, which exhibited characteristic biomolecular compositions and complex nanocrystals assembly. Within this region, an exponential increase of modulus (3 orders of magnitude) was conducive to the force transmission which was verified by finite element simulations. The nanoscale heterogeneity of hydroxyapatite, along with enrichment of elastic-responsive protein-titin which is usually present in muscle, endowed the osteochondral tissue with excellent energy dissipation and fatigue resistance properties. Our results provide potential design for high-performance interface materials for osteochondral interface regeneration and functional coatings. ### Competing Interest Statement The authors have declared no competing interest.