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Biocompatible, biomimetic ampholyte materials

Novel ampholyte compounds mimicking one of the major components present in membranes of the natural cell such as 2-[(2-hydroxyethyl)dimethylammonio]ethyl hydrogen phosphate were designed, synthesized and incorporated into synthetic polymeric biomaterials. These materials are termed reverse-phosphorylcholine (reverse-PC) compounds as they have the ammonium group embedded into the framework of the hydrophilic unit rather than being located at the terminus. The patent describes the synthesis of the monomer units from small building blocks in a series of reactions carried out under strictly anhydrous conditions. Substantial effort was expended in optimising the final steps of the synthesis due to a competing degradative side-reaction. Structural variation of the monomer was explored to provide a series of options for subsequent polymer synthesis. Incorporation of the reverse-PC monomers into polymers of various structures was achieved, and the physical and biological performance of the subsequent materials was evaluated. The polymers were characterised using a wide range of analytical techniques, including thermal analysis. A study using XPS showed that the polymer structure varied as a function of the presence or absence of water in its environment. Surfaces coated with the materials displayed a high degree of wettability, a property highly beneficial for biomedical devices. Surfaces coated with the new polymers demonstrated very low adhesion of proteins and cells. In tests with blood, such surfaces showed virtually no cellular adhesion compared with a control surface which had substantial cell attachment. Contact lenses prepared using the new materials were compared with commercially available lenses, and protein adhesion was found to be substantially reduced in many cases. Polymers containing a high level of reverse-PC were synthesised and these displayed surprising cellular adhesion - a phenomenon ascribed to domain formation. The research was carried out under a KTP project between the University of Reading (with Mckendrick as Lead Academic) and Biointeractions Ltd.