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A study of structure-property relationships and potential biomaterial application for doubly crosslinked microgels

Milani, Amirhossein

[Thesis]. Manchester, UK: The University of Manchester; 2014.

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Abstract

Thesis abstractThis thesis presents a study of doubly crosslinked microgels (DXMs) and their application in restoring mechanical properties of degenerated intervertebral discs (IVDs). The DXMs were prepared from inter-crosslinking of singly crosslinked microgel (SXM) particles. The SXMs were prepared via emulsion polymerisation of a structural monomer (either methyl methacrylate or ethyl acrylate), methacrylic acid, and a crosslinking monomer (either ethylene glycol dimethacrylate or 1,4-butanediol diacrylate). The presence of methacrylic acid (carboxylic acid group) in the microgel composition caused the microgels to become pH-responsive, and also enabled the microgels to be functionalised with other groups such as vinyl group. In this work, the double crosslinking of swollen microgel particles occurred via free radical polymerisation of vinyl groups that were attached to the surface of the microgels. The attachment of vinyl groups was conducted by using glycidyl methacrylate (GMA). The carboxylic acid groups on the microgels were able to react with the epoxide group of GMA. The major effect of double crosslinking was to avoid microgel particles migration during the application of meaningful load. This caused the DXMs to show superior physical and mechanical properties in comparison to their parents SXMs.The DXMs were designed to be injectable and then cured in-vivo. Bio-mechanical tests were performed on natural, degenerated and DXM injected bovine intervertebral discs (IVD). The results showed a significant improvement on mechanical properties of degenerated IVDs after injection of DXMs. Biocompatibility tests were also conducted on DXMs, and the results showed that they could be classified as biocompatible material.The effect of length and structure of functional group on DXMs physical and mechanical properties were investigated. For this purpose a hydrophobic glycidylised oligo acrylate (GOA) was synthesised and used instead of GMA. It was observed that using a longer molecule as a functional group could increase the ductility of DXMs significantly.