Development of composite electrospun scaffolds for tissue engineering.

The aim of this project was to design and evaluate biocompatible and biodegradable membranes. These membranes must be suitable for treating conditions where two tissues are required to coexist but would normally compete, and also for conditions where the target tissue must cope with distension. Two clinical conditions were considered in the design of materials -repair of major defects of the hard palate and a tissue engineered membrane for repair of the weakened pelvic floor where this tissue is subject to dynamic distension on a daily basis. Cleft palate is a condition that affects one in every 500-700 live births worldwide. Its current treatment is slow and multi-staged over at least 15 years. This is due to the difficulty of trying to replace both the fast-growing soft tissue and the much slower growing hard tissue, in the hard palate in a child. There are two immediate problems: soft tissue overgrows the area where bone is required; and the defect in the hard palate expands with the growth of the child. A scaffold/membrane is required, which supports soft tissue growth and hard tissue growth, by keeping them segregated, and which can also expand with the growth of the child. The approach undertaken was that of composite membrane production based on the use of electrospinning. First it was shown that monolayers of microfibres and nanofibres could be created in random, aligned and pseudo woven layers. These scaffolds were shown to have mechanical properties suitable for the treatment of a range of conditions, such as pelvic organ prolapse and bladder repair. These scaffolds were then further processed to produce multi-layered scaffolds, combining micro and nanofibres to make bi and trilayer membranes. Scaffolds were characterised by SEM and evaluation of mechanical properties. Cell culture was then evaluated on these scaffolds. It was demonstrated that fibroblasts can infiltrate and fill microfibrous scaffolds, while nanofibrous scaffolds were shown to act as a barrier to cell entry for up to six weeks, but were still porous enough to allow nutrients to pass through membranes. Experiments showed that co-cultures of bone forming and soft tissue forming cells were kept segregated on multi-layered microfibrous/nanofibrous scaffolds. Novel balloon collectors and fibre orientation were used to make scaffolds with low Poisson’s ratios in an attempt to create a scaffold that does not contract when distended. Finally, it was shown how proof of concept bioreactors can be used to multi-axially stress cells in culture to induce extracellular matrix production. In summary, the techniques developed in this thesis lay the foundations for the creation of complex multi-layered scaffolds for tissue engineering, with tailored and novel mechanical properties. Furthermore, the research demonstrates that cells cultured on these scaffolds will respond well to distension on these scaffolds.