Effects of biochemical and mechanical stimulation of articular chondrocytes in collagen-GAG scaffolds : extracellular matrix biosynthesis and scaffold stiffness

Abstract

As the incidence of osteoarthritis and other degenerative joint conditions continues to grow, rehabilitation via tissue engineering is becomingly increasingly attractive as an alternative to traditional surgical interventions. Chapters 2 and 3 of this thesis are specifically concerned with cartilage tissue engineering, while chapter 4 is relevant to bone and osteochondral tissue engineering. The cartilage tissue engineering sections focus on the effects of two different classes of regulators of chondrocyte behavior: chemical growth factors and mechanical loading. In chapter 2, FGF-2, a chemical regulator, was supplied to chondrocyte-seeded constructs over a 4 week culture period. Afterward, these constructs were subjected to sequential ramp and hold compressive strains on a Dynastat mechanical testing apparatus, and the unconfined elastic moduli were calculated. These data were compared to the values for scaffolds receiving no FGF. The results indicate that FGF-2 induced a significant increase in the modulus of chondrocyte-seeded scaffolds. Numerous reports indicate that certain types of mechanical loading can increase chondrocytes' ECM biosynthesis in particular cell-scaffold systems in vitro. Few if any loading experiments have been done, however, with type II collagen-GAG scaffolds cultured in serum-free medium. Chapter 3 describes a series of experiments in which chondrocyte-seeded scaffolds were subjected to dynamic compression and the effects of this treatment on the proliferation of the chondrocytes, their synthesis of ECM, and the stiffness of the scaffolds were measured. The results of these experiments were inconclusive. Analysis indicated that very few chondrocytes were retained in the scaffolds.

(cont.) A post hoc investigation of the scaffolds revealed that they were biologically inactive due to their oversize pores. The low cell density was reflected in unusually low biosynthesis values and no significant differences in stiffness post-loading. The mechanical properties of implantable constructs such as stiffness and compressive strength are likely to significantly affect the clinical outcome. The fourth chapter describes measurements of the elastic modulus and ultimate compressive strength of a bone scaffold material. Five different scaffold formulations were tested, and the mechanical properties correlated with the variations in their composition.