Effect of electron beam radiation on the degradation of biopolymers

Abstract

Abstract The study of the effects of electron beam (e-beam) radiation on PLGA and PLLA and their subsequent hydrolytic degradation characteristics were reported in this thesis. The objective is to investigate the use of e-beam radiation as a means to control and fine-tune the hydrolytic degradation time of these biopolymers. The results obtained show conclusive evidence that PLGA and PLLA degrade through chain scission when exposed to e-beam irradiation in the presence of air, through two main degradation mechanisms of backbone main chain scission and hydrogen abstraction. The presence of a crystalline phase could however arrest this radiationinduced degradation process. The decrease in average molecular weights results in changes in the physiochemical properties of these biodegradable polyesters. The decrease in average molecular weights were observed to follow a linear relationship with radiation dose. Irradiated samples of PLGA and PLLA, when hydrolytically degraded, were observed to degrade faster than the non-irradiated samples. This was due to a higher water uptake, resulting from a lower Tg and the formation of more hydrophilic hydroxyl end groups, with irradiation. The increase in water uptake leads to an increase in osmotic pressure and subsequently an increase in mass loss due to microcavitation and osmotic cracking. A modeled relationship between radiation dose and the hydrolytic degradation time, through their molecular weights, was established for both PLGA and PLLA. This relationship allows for a more accurate and precise control of the rate of hydrolytic degradation of PLGA and PLLA with e-beam radiation. It is concluded that e-beam radiation could therefore be used to control the hydrolytic degradation times of PLGA and PLLA. iii ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library Acknowledgements Acknowledgements The author would like to express his sincere gratitude to the following people who have played an important role in the author’s accomplishments and completion of his PhD research and thesis: My heart felt thanks to my supervisor, Professor Freddy Boey Yin Chiang, who is also the main initiator behind this research project. His key involvement saw the materializing of this research work; and his guidance and advice rendered were indeed indispensable for the completion of my PhD research. Special thanks to my co-supervisor, Assistant Professor Ooi Chui Ping, for her relentless support, help and guidance throughout my PhD research work. Her invaluable advice and encouragement throughout my candidature is greatly appreciated. I would like to thank Ms. Tan Hui Tong for her help in printing and compiling my thesis, on my behalf, during my 3 months attachment at Mayo Clinic. Not forgetting the school manager (Ms Loreen Tan) all the technical staff (Nelson Ng, Serene Kok, Wilson Lim, Choo Yong Cheong, Samsudin), friends and colleagues of Biomaterials Lab and Advanced Materials Research Center (AMRCB3) who have in one way or other contributed to the completion of my PhD research work. iv ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library Table Of