Articular Cartilage Chondrocytes in Type I and Type II Collagen-GAG Matrices Exhibit Contractile Behavior in Vitro

Natural healing of articular cartilage defects generally does not occur, and untreated lesions may predispose the joint to osteoarthritis. To promote healing of cartilage defects, many researchers are turning toward a tissue engineering approach involving cultured cells and/or porous, resorbable matrices. This study investigated the contractile behavior of cultured canine chondrocytes seeded in a porous collagen-glycosaminoglycan (GAG) scaffold. Chondrocytes isolated from the knee joints of adult canines and expanded in monolayer culture were seeded into porous collagen-GAG scaffolds. Scaffolds were of two different compositions, with the predominant collagen being either type I or type II collagen, and of varying pore diameters. Over the 4-week culture period, the seeded cells contracted all of the type I and type II collagen-based matrices, despite a wide range of stiffness (145 ± 23 Pa, for the type I scaffold, to 732 ± 35 Pa, for the type II material). Pore diameter (25-85 μm, type I; and 53-257 μm, type II) did not affect cell-mediated contraction. Immunohistochemical staining revealed the presence of α-smooth muscle actin, an isoform responsible for contraction of smooth muscle cells and myofibroblasts, in the cytoplasm of the seeded cells and in chondrocytes in normal adult canine articular cartilage.