Adult mesenchymal stem cells (MSCs) offer great potential in tissue engineering applications as they can be directed to differentiate along numerous lineages to produce a range of skeletal tissues, including the chondrogenic lineage. The importance of mechanical loading for the maintenance of skeletal tissues is well reported. The aim of this thesis was to dem onstrate that the application of cyclic tensile strain to MSC-seeded collagen-GAG scaffolds regulates the chondrogenic differentiation process, in the presence of chondrogenic growth factors.

A custom -designed multistation bioreactor was developed to apply cyclic uniaxial tensile strain to 3D constructs. Firstly, the chondrogenic differentiation of the MSCs using TGF-|31 was demonstrated. To apply cyclic tensile strain, the cell-seeded scaffolds were uniaxially clam ped between stainless steel grips. This allowed for an investigation into the importance of cell-m ediated contraction for the differentiation process. Inhibition of contraction through clamping resulted in a reduction in the rate of GAG synthesis. The application of physiological loading of 10% strain at 1 Hz reversed this process and resulted in an increase in the rate of GAG synthesis. An investigation into the mechanotransduction process dem onstrated that stretch-activated ion channels were involved in mediating the differentiation process.

A computational model was developed to investigate the biophysical stimuli developed within the scaffold during cyclic loading. The results demonstrated that the magnitudes of fluid flow and strain developed were sim ilar to those previously reported to regulate chondrogenic differentiation, therefore indicating that these stimuli were the main regulators of in the m echanoregulation of the differentiation process.

Characterisation of intracellular signalling pathways involved in TGF-pl and IGF-1-induced chondrogenic differentiation dem onstrated the differential involvem ent of the MAPK and PI3-kinase in involved in the chondrogenic differentiation of adult MSCs, in 2D and in the 3D collagen-GAG scaffold. These intracellular studies provide further knowledge of possible downstream pathways of mechanosensitive mem brane receptors involved in the mechanotransduction and mechanoregulation of MSC differentiation.

In summary, this thesis demonstrates that the collagen-GAG scaffold is suitable for the induction of the chondrogenic differentiation of MSCs. Furthermore, the effects of mechanical constraint and mechanical stimulation on matrix synthesis has implications for tissue engineering strategies used in the clinical repair of articular cartilage defects. Investigations into mechanotransduction and intracellular signalling provide new knowledge on pathways involved in mechanical and growth-factor-induced chondrogenic differentiation in adult MSCs.