The development of novel polyester-based polyHIPE foams as matrices for tissue engineering

Abstract

Motivations for exploring the creation of man-made tissues (cell transplantation) and the growth of artificial organs (neoorgans) are varied. Early matrices, following on from the injection of cells into other tissues, were constructed from extracellular matrix proteins, e.g. collagen. Limitations in structure and strength led to current materials that are either a composite matrix, i.e. a fibre mesh supported by a second polymer; or a monolithic sponge-like structure - foam. PolyHIPE (High bitemal Phase Emulsion) polymers are emulsion-derived foams. The product has an open-cellular macroporous morphology. Porosity can be varied between 74 and 99% and cell size from 5 - 200 μm. In this thesis, polycaprolactone and polylactide diols have been end-capped with aciylate groups to yield macro monomers. A series of novel PolyHIPE scaffolds were prepared by free-radical homopolymerisation of the macro monomers or copolymerization of macromonomers with styrene or methyl methaciylate. The PolyHIPEs produced were shown by SEM to be porous with cell sizes ranging from 5 - 100 μm and pores from 1-10 μm. The morphology of the materials was affected by diluent type, polyester content, surfactant concentration, NaCI content and the initiator used. Biodegradability has been achieved because polycaprolactone and polylactide contain weak ester linkages that can be hydrolysed in vivo. An in vitro study has shown that the PolyHIPEs demonstrated some biodegradability during a 10 week period but a longer experiment is necessary. PolyHIPEs prepared from 1 g of PCL or PL and 4 g styrene have been shown to support the growth and proliferation of human and rat skin fibroblasts and chicken embryo tissue containing various cell types. A 10 week in vivo study showed that the scaffolds did not invoke any immune or inflammatory responses and are, therefore, not toxic in the early stages after implantation.