Biochemical and mechanical stimuli for improved material properties and preservation of tissue-engineered cartilage
Farooque, Tanya Mahbuba
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Articular cartilage on weight-bearing joints experiences three main forces: fluid-induced shear across the surface, perfusion through the cartilage from the surrounding fluid, and compression during motion of the joint. A new bioreactor that employs two of these forces was developed in this lab to study their effect on tissue-engineered cartilage development. The focus of this research and overall hypothesis is that bioreactors that employ both perfusion and shear will improve chondrogenesis and preservation to produce functionally relevant cartilage by modulating shear stress and introducing exogenous preservation factors. Applying both a low shear stress across the surface of cell-seeded scaffolds and perfusion through them in a perfusion concentric cylinder (PCC) bioreactor may stimulate chondrocytes to undergo chondrogenesis. Experimental data showed that the PCC bioreactor stimulated cartilage growth over the course of four weeks, supported by the appearance of glycosaminoglycan (GAG) and collagen type II, which are markers for articular cartilage. Computational fluid dynamics modeling showed that shear stress across the face of the construct was heterogeneous, and that only the center experienced a relatively uniform shear stress of 0.4 dynes/cm^2 when the outer cup of the bioreactor rotated at 38 rpm. When compared to a concentric cylinder (CC) bioreactor that employed only shear stress, the PCC bioreactor caused a significant increase in cellular proliferation, which resulted in a 12-fold increase in cell number per construct compared to 7-fold increase within the CC bioreactor. However, the PCC bioreactor had a less pronounced effect on glycosaminoglycan and collagen content with 1.3 mg of GAG and 1.8 mg of collagen per construct within the CC bioreactor and 0.7 mg of GAG and 0.8 mg of collagen per construct within the PCC bioreactor after 28 days in culture (p < 0.05). Our results led to an important observation that the PCC bioreactor affected cellular proliferation significantly but not extracellular matrix synthesis. The next objective of this study focused on the PCC bioreactor to evaluate the direct role of perfusion and shear on chondrogenesis in vitro and in vivo.