Synergistic Organic-Inorganic Assembly Enhances Condylar Osteochondral Interface Mechanics

The condylar osteochondral interface is a unique biomechanical junction where organic and inorganic components synergistically enhance mechanical performance. This study aimed to elucidate how organic-inorganic assembly and residual stress contribute to interfacial mechanical integrity. Porcine temporomandibular joint condyles underwent demineralization, remineralization, deproteinization, and annealing. Structural and mechanical changes were assessed using Raman spectroscopy, nanoindentation, scanning/transmission electron microscopy, X-ray diffraction, and compressive testing. Residual stresses were evaluated through collagen contraction, hydroxyapatite (HAP) lattice alterations, and mineral-collagen interactions. Mechanical integrity depended on balanced organic-inorganic interactions. Demineralization reduced adhesion strength and modulus, while remineralization partially restored them without fully recovering residual stress. Raman mapping and nanoindentation revealed increasing mineralization from cartilage to bone, with highly mineralized regions showing superior stiffness and toughness due to residual stress from HAP compression of collagen fibrils. High-temperature annealing and collagenase treatment confirmed that collagen contraction generated compressive stresses influencing the HAP lattice. TEM and indentation demonstrated that inorganic assembly further enhanced residual stress through physical interlocks with collagen. Residual stress arising from synergistic organic-inorganic interactions is a key toughening mechanism of the osteochondral interface. The degree of mineralization and collagen content jointly determine stiffness and toughness. Although remineralization restores mineral structures, incomplete recovery of residual stress highlights the critical role of intact organic-inorganic synergy. These findings provide mechanistic insights into interfacial biomechanics and suggest strategies for osteochondral repair.