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, an d 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 mat rices. 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. Scaffold s were of two different compositions, with the predominant collagen being e ither type I or type TI collagen, and of varying pore diameters, Over the 4 -week culture period, the seeded cells contracted all of the type I and typ e 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 mum, type I; and 53-257 mum, type II) did not affect c ell-mediated contraction. Immunohistochemical staining revealed the presenc e of alpha -smooth muscle actin, an isoform responsible for contraction of smooth muscle cells and myofibroblasts, in the cytoplasm of the seeded cell s and in chondrocytes in normal adult canine articular cartilage.