Gurav, Neelam; (1997) Biocompatibility testing of resorbable materials using improved in-vitro techniques. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Interest in degradable polymer systems for use in various biomedical applications has been increasing since their development in the 1960s. The first polymer to be used was polyglycolic acid, marketed under the trade name Dexon, as a resorbable suture. Although the success of resorbable polymers has been mainly in the form of sutures and small pins, their potential use as materials for bone fixation, bone regeneration and drug delivery vehicles is vast. These materials have obvious advantages in that retrieval of the implant can be avoided causing minimal inconvenience to the patient. Extensive in-vivo biocompatibility testing has been performed on a range of resorbable polymers but there is a lack of information available on events occurring at the cellular level specially during long term implantation. This can be investigated in depth using in-vitro assays and utilising methods which mimic the long term in-vivo degradation of polymers. The aim of this study was to determine the short and long term biocompatibility of degradable polymers using in-vitro cell culture methods. The morphology and proliferation of osteoblast-like cells and monocyte/macrophages on the polymer surfaces was investigated by light microscopy, electron microscopy and biochemical assays. Polymer degradation by enzymes and other degradation methods was investigated using gel permeation chromatography and the biocompatibility of polymers at stages of degradation was studied. The effect of the acidic pH caused by the monomers and the monomers themselves on the viability of osteoblast-like cells and monocyte/macrophages was studied. Evidence for HOS cells undergoing apoptosis was investigated by transmission electron microscopy and by utilising stains specific for apoptosis when cultured in the presence of monomers. This study demonstrated that the accelerated degradation of polymers by heat and gamma irradiation provides a good method for obtaining polymers for "long-term" biocompatibility testing. Enzyme solutions also influenced the degradation of the polymers in particular the polymer surfaces. The morphology and proliferation of osteoblast-like cells varied on the different polymer surfaces depending on surface structure, crystallinity and the release of degradation products; and in addition the presence of monomers caused a decrease in the mitochondrial activity of both the cell types tested. The monocyte/macrophages also had varying morphologies on the different polymers and were stimulated by some of the polymers to a greater extent. By using the in-vitro methods described the difficulties associated in determining the biocompatibility of many resorbable materials can be overcome.

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