Biphasic Mechanical Properties of in vivo Repaired Cartilage

In the fast growing field of scaffold-based tissue engineering, improvement on the mechanical properties of newly formed tissues, e.g. the repaired cartilage, has always been one of the core issues. Studies on the correlations among scaffold composition, in vivo morphological changes of the construct, and the finite deformation behaviors of new tissues (e.g. creep and stress-relaxation, and equilibrium response), have attracted increasing interests. In this paper, the correlations between the compressive biphasic mechanical properties (i.e., equilibrium elastic modulus E and permeability coefficient k) of 3D printing scaffold (consisting of collagen and β-tricalcium phosphate) and the proteoglycans (PGs) concentration of the repaired cartilages after 24 weeks, 36 weeks and 52 weeks of scaffold implantation were investigated. Results indicated that the repaired cartilage covered the entire cartilage surface of large cylindrical osteochondral defects (10 mm in diameter × 15 mm in depth) on the canine trochlea grooves after 24 weeks. The equilibrium elastic modulus of the repaired cartilage reached 22.4% at 24 weeks, 70.3% at 36 weeks, and 93.4% at 52 weeks of the native cartilage, respectively. Meanwhile, the permeability coefficient decreased with time and at 52 weeks was still inferior to that of the native cartilage in one order of magnitude. In addition, the amount of glycosaminoglycans (GAGs) of repaired cartilage increased constantly with time, which at 52 weeks approached to nearly 60% of that of native cartilage. 3D printed scaffolds have potential applications in repairing large-scale cartilage defects.