Identification of an Ultrathin Osteochondral Interface Tissue with Specific Nanostructure at the 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 conferring fatigue damage over a lifetime of
load cycles. However, the fine structure and mechanical properties
of the osteochondral interface tissue remain unclear. Here, we identified
an ultrathin ∼20–30 μm graded calcified region
with two-layered micronano structures of osteochondral interface tissue
in the human knee joint, which exhibited characteristic biomolecular
compositions and complex nanocrystals assembly. Results from finite
element simulations revealed that within this region, an exponential
increase of modulus (3 orders of magnitude) was conducive to force
transmission. Nanoscale heterogeneity in the hydroxyapatite, coupled
with enrichment of elastic-responsive protein-titin, which is usually
present in muscle, endowed the osteochondral tissue with excellent
mechanical properties. Collectively, these results provide novel insights
into the potential design for high-performance interface materials
for osteochondral interface regeneration.