The aim of this study was to design in vitro growth protocols that can comprehensively quantify articular cartilage structure-function relations via measurement of mechanical and biochemical properties. Newborn bovine patellofemoral groove articular cartilage explants were tested sequentially in confined compression (CC), unconfined compression (UCC), and torsional shear before (D0 i.e. day zero) and after (D14 i.e. day 14) unstimulated in vitro growth. The contents of collagen (COL), collagen-specific pyridinoline (PYR) crosslinks, glycosaminoglycan, and DNA significantly decreased during in vitro growth; consequently, a wide range of biochemical properties existed for investigating structure-function relations when pooling the D0 and D14 groups. All D0 mechanical properties were independent of compression strain while only Poisson's ratios were dependent on direction (i.e. anisotropic). Select D0 and D14 group mechanical properties were correlated with biochemical measures; including (but not limited to) results that CC/UCC moduli and UCC Poisson's ratios were correlated with COL and PYR. COL network weakening during in vitro growth due to reduced COL and PYR was accompanied by reduced CC/UCC moduli and increased UCC Poisson's ratios.

Articular cartilage (AC) serves as the major load bearing material within synovial joints and provides a low friction and wear resistant interface. As an avascular tissue, AC lacks the ability to repair structural damage or degeneration. Thus, the need for replacement tissue was a motivating factor in the development of cartilage tissue engineering. Recently, a finite element model (FEM) of cartilage growth [1] has been developed to simulate various growth conditions such as in vitro (outside the body) tissue growth experiments. In order to validate growth laws used in the FEM, empirical measurements of AC properties (mechanical and biochemical) before and after in vitro growth are needed. The goal of this study is to design protocols to comprehensively quantify the biomechanical structure-function relations of AC.