Studies On Biodegradable Polycarbonates Containing Cholesteryl Moiety Or Cholic Acid Moiety

Biodegradable polycarbonates are a class of important biomedical materials. Because biodegradable polycarbonates have surface erosion property, good biocompatibility and favorable mechanical properties, they have been interested investigated for the applications in tissue engineering and drug controlled release. Through tailoring the main chain structures and incorporating functional pendent groups, biodegradable polycarbonates are enabled to possess versatile physiochemical and biological properties to meet the requirements in different biomedical fields.In Chapter 1, the recent development of biodegradable polycarbonates is briefly reviewed with emphasis on their structures, syntheses, properties and applications.Stimulated by the need for biomedical materials with improved properties, modification strategies have been used to optimize some specific properties such as bioactivity and biocompatibility. Incorporation of the bioactive or biocompatible compounds including lipids, vitamins, hormones, and peptides to the polymer chains is one of the most important modification strategies. Cholesterol is a fundamental composition of mammalian membranes, with high thermodynamic affinity for the cell membrane, universally important function in all eukaryotic cells, and homeostasis for cell survival. In Chapter 2, a series of biodegradable cholesteryl end-functionalized polymers/oligomers based on 2,2-dimethyltrimethylene carbonate (DTC) were studied. The functionalized polymers/oligomers, Chol-(DTC)n, were synthesized through the ring-opening polymerization initiated by cholesterol with a hydroxyl group. The end-functionalized polymers/oligomers were characterized by ~1H nuclear magnetic resonance spectroscopy (~1H NMR), Fourier transform infrared (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and polarizing light microscopy (PLM). Incorporation of cholesteryl moiety to the polymer chain results in liquid crystallinity for the resultant oligomers when their molecular weights are in a particular range. Because of the existence of cholesteryl moiety in the polymers/oligomers, the functionalized polymers/oligomers are expected to have improved properties as matrices in tissue engineering.Cholic acid is a bile acid with a role in mammalian digestion. In Chapter 3, a series of star-like biodegradable polymers/oligomers containing cholic acid moieties based on 2,2-dimethyltrimethylene carbonate (DTC) were studied. The functionalized polymers/oligomers, CA-(DTC)n, were synthesized through the ring-opening polymerization initiated by cholic acid with hydroxyl groups. The functionalized polymers/oligomers were characterized by ~1H nuclear magnetic resonance spectroscopy (~1H NMR), Fourier transform infrared (FTIR) and polarizing light microscopy (PLM). Incorporation of cholic acid moiety to the polymer chain results in liquid crystallinity for the resultant oligomers with particularmolecular weights. Using the fiinctionalized polymer with a proper transition temperature, the microsphere drug delivery system was fabricated using a convenient melting-emulsion method. The in vitro drug release property of microspheres was investigated.