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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: On the biodegradation of biomedical polymers

Author: HEELEY, Judith

Year: 1992

Supervisor(s): Ray Smith

Poly--hydroxybutyrate (PHB) and its copolymers with polyhydroxyvalerate (PHV) are produced via a biotechnology route by Marlborough Biopolymers, a subsidiary of ICI plc. Much interest has been shown in these polymers for use in the biomedical field, for example in orthopaedics, as biodegradable fixation devices and in pharmaceutics as controlled drug delivery systems. The polymers are related to poly-alpha-hydroxy acids, a hydrolytically unstable group of compounds used in the biomedical field primarily for their degradation properties. It was thus thought that PHB and its copolymers would show a similar susceptibility to degradation. It is well known that PHB is degraded by bacteria, but there is little evidence for the degradation of these polymers in non-bacterial systems.
To ascertain whether other enzymes, not normally considered to have a role in the bacterial degradation of PHB, could affect the rate of degradation, a series of experiments was devised. Samples were incubated with an enzyme at 37^oC for periods of up to 21 days. Controls were run in parallel, omitting enzyme. The enzymes used were papain, esterase, proteinase K and alpha-chymotrypsin. Optimum enzyme activity was maintained throughout the test period. For comparison with the enzyme tests, a series of hydrolysis experiments were performed using dilute sodium hydroxide solution. All polymers and filtrates from both sets of tests were reserved for further analysis.

The degradation of the polymers was assessed by employing the following techniques: Gel Permeation Chromatography, thin Layer Chromatography, Nuclear Magnetic Resonance Spectroscopy, Fourier Transform infra-red Spectroscoy, mass spectrometry and ultra-violet spectroscopy. This study gives conclusive evidence for the degradation of PHB by certain enzyme systems.