BIOREACTOR CULTURE OF CARTILAGE FROM MESENCHYMAL POPULATIONS

Abstract

Joint pain, as a consequence of cartilage degeneration or trauma results in severe pain or disability for millions of individuals worldwide. However, the potential for cartilage to regenerate is limited and there is an absence of clinically viable cartilage formation regimes. Cartilage is composed of only one cell type, is avascular and has a relatively simple composition and structure, thus cartilage tissue engineering has tremendous potential. Therefore, to address this clinical need, we have adopted a tissue engineering approach to the generation of cartilage ex vivo from mesenchymal cell populations encapsulated in polysaccharide templates form alginate and chitosan that favours chondrogenesis, and cultured within perfused or rotating bioreactor systems. To drive the chondrogenic phenotype, alginate beads were encapsulated with isolated human bone marrow cells, human articular chondrocytes or a combination of both in a 2:1 ratio, with the addition of TGF-â3, and placed in either a Synthecon rotating-wall bioreactor, perfused at a flow rate of 1ml/hour, or held in static conditions for 28 days. Alcian Blue and Sirius Red staining indicated ordered, structured and even cell distribution within capsules from the rotating bioreactor system in comparison with perfused and static conditions. Furthermore, alginate beads encapsulated with mixed cell populations that were cultured under static and rotating-wall conditions revealed positive staining for both collagen and proteoglycan, and with areas that closely resembled the formation of osteoid. Cell viability, assessed using the fluorescent dye Cell Tracker Green, indicated a higher proportion of metabolically active cells in capsules from the rotating-wall bioreactor than perfused or static under the conditions examined. Immunohistochemistry indicated the expression of type II collagen, SOX9 and C-MYC in samples from all conditions after 28 days. C-MYC is implicated in cell proliferation and differentiation and type II collagen and SOX9 are cartilage-specific markers. Biochemical analysis revealed significantly increased (p < 0.05) protein in samples encapsulated with mixed cell populations compared with alginate samples that were encapsulated with either bone marrow or chondrocytes. There was also a significant increase in protein in all samples that were cultured in the rotating-wall bioreactor in comparison with perfused or static conditions after 28 days. A significant increase in DNA was observed in the rotating-wall than perfused or static for the bone marrow cultures. Interestingly in chondrocyte cultures perfused conditions were found to result in significantly higher DNA than rotating-wall and static, and static conditions resulted in significantly higher DNA for alginate encapsulated with mixed cell populations. The current studies outline a tissue engineering approach utilising progenitor populations, bioreactors and appropriate stimuli to promote the formation of cartilage within a unique innovative polysaccharide capsule structure, and indicate the potential of rotating-wall systems to promote cartilage formation. Understanding the conditions required for the generation of functional cartilage constructs using such bioreactor systems carries significant clinical potential.