The development of novel collagen-glycosaminoglycan scaffold for in vitro mesenchymal stem cell chondrogenesis

Articular cartilage is an incredibly tough tissue owing to its ability to withstand repetitive compressive stress throughout an individual’s lifetime. Conversely, its single greatest limitation is the inability to heal even the most minor injuries (Newman, 1998). Due to the absence of a blood supply, articular cartilage responds to damage poorly (Nelson et al., 2010; Bora et al., 1987). Consequently, this predisposes the joint to articular cartilage degeneration. The repair of damaged tissue using conventional therapies and approaches has been elusive thus far. However, the use of tissue engineered biomaterials has shown promise in cartilage defect repair.In this context, the aim of this thesis was to develop a collagen-glycosaminoglycan (CG) scaffold with optimised intrinsic physico-chemical properties that might induce mesenchymal stem cell (MSC) differentiation towards a chondrogenic lineage in vitro. In addition, the effect of environmental factors such as oxygen tension and soluble growth factors in further enhancing chondrogenesis within these highly porous CG scaffolds was investigated.

CG scaffolds developed in our laboratory have shown the potential to support MSC chondrogenesis (Farrell et al., 2006). In this thesis it was evident that different GAGs in the scaffolds elicit distinct cellular responses. In particular, hyaluronic acid stimulated enhanced migration, accelerated chondrogenic gene expression and cartilage matrix production in comparison to chondroitin sulphate. This thesis demonstrated that scaffold mean pore size plays a significant role in cellular behaviour. In particular, scaffolds with larger mean pore sizes supported significantly greater chondrogenic gene expression and accumulation of synthesised cartilage matrix in comparison to scaffolds with small mean pore sizes. In addition to the composition and micro-structure, this thesis also demonstrated that scaffold mechanical properties influence the fate of MSCs. Compliant scaffolds stimulated greater MSC chondrogenic differentiation whilst the stiffest scaffolds stimulated MSC osteogenic differentiation in the absence of differentiation factors. This further highlights the importance of scaffold physical characteristics in modulating the behaviour of progenitor cells.

This thesis also looked at the effect of environmental factors on MSC chondrogenic differentiation in the optimised porous collagen-hyaluronic acid (CHyA) scaffolds. Low oxygen environments stimulated greater MSC chondrogenic differentiation with short term exposure to hypoxia eliciting additional enhancement chondrogenesis compared to normoxia. In order to further improve the biofunctionality we developed a bioactive CHyA scaffold for the delivery of therapeutic biomolecules such as TGF-P3 in order to enhance the regenerative capacity of the scaffold. It was evident that CHyA scaffolds subsequently permitted controlled release of the growth factors. Furthermore, control over their release rates could be achieved through manipulation of scaffold degradation rates. This demonstrates the potential of using these scaffold-based systems for the delivery of chondro-inductive growth factors with great implications over local control of cellular behaviour.

Collectively, this study has led to the development of a type of CG scaffold with optimised composition, micro-architecture and mechanical properties which has significant capacity to promote cartilage regeneration. In addition, this thesis highlights the potential of using these scaffolds as templates for the development of tissue engineered constructs through enhancement of MSC-mediated chondrogenesis with environmental factors.