Articular cartilage has limited capacity to self-repair once damaged. Contact stresses and strains in areas of cartilage near the edges of a focal defect are altered during compression and articulation. To prevent further damage to the surrounding cartilage, cartilage defects can be repaired with a biomaterial or tissue with properties similar to those of normal cartialge to provide mechanical support and restore normal mechanical environment. Understanding structural and functional changes of native cartilage during maturation in response to chemical and mechanical stimuli is useful to fabricate cartilage tissues with properties approaching those of normal adult cartilage. Characterization of the restoration of biomechanical properties of cartilage defect with a repair material will provide valuable insights into the development of appropriate constructs to repair and restore cartilage function.

To facilitate a study of cartilage mechanobiology, a novel material and biomechanical testing system that can induce a range of shear stress and strain in cartilage was developed and fully characterized. Such biomechanical testing system can be used as a framework to study cartilage responses to a mechanical stimulus that mimics certain aspects of articulating cartilage. The mechano-biological responses of immature articular cartilage were investigated by examining the structural and functional changes of cartilage in response to chemical and mechanical stimuli. Biochemical treatments of immature articular cartilage increased GAG release, reduced tissue GAG content, and increased tensile properties of immature articular cartilage. Dynamic compression, superimposed on biochemical treatment induced organization of collagen network to variable extents. The results suggest that cartilage maturation is a complex process that may involve metabolic processes in addition to matrix consolidation at the surface.

The extent to which biomechanical environment of cartilage defect was restored with a biomaterials was elucidated using poly(ethylene glycol)- (PEG) hydrogels. PEG hydrogels with cartilage-like mechanical properties were fabricated, characterized, and inserted into a focal defect. The overall and local strains elevated in cartilage near the edge of an empty defect was returned to levels similar to intact cartilage when the defect was filled with PEG hydrogels. This suggests that a biomaterial or tissue with mechanical properties comparable to surrounding cartilage could be used to treat cartilage focal defects and restore its function.