| Free radical species have been found to be essential to many biological systems. One of the most known free radical species involved in the biological processes that are regarded as the cause of several pathological phenomena is the superoxide ion, {dollar}rmcdot Osb2sp-.{dollar} It was well known that there were many different reactivities of this free radical anion species in an aqueous and/or aprotic solvent system. In particular, the superoxide ion could act as an oxygen nucleophile in aprotic solvents, which can participate in the hydrolysis of simple esters. Although the role of superoxide ion in the simple organic ester hydrolysis has been known since 1970s, its role in the hydrolytic degradation of synthetic polyester-based biomaterials has remained largely unknown. Thus, one of the objectives of this research was to examine the reactivity of the superoxide ion towards biodegradable aliphatic polyester biomaterials at different reaction conditions, such as temperature, time, and superoxide ion concentration.; Due to the extreme reactivity of superoxide ion, we observed that the effect of superoxide ion induced hydrolytic degradation on the molecular weights and the thermal properties of poly (D,L-lactide) and poly (L-lactide) was significant. We also examined the effect of the reactivity of superoxide ion on commercially available 2-0 size absorbable sutures (Dexon{dollar}rmspcircler, Vicrylspcircler, Monocrylspcircler, Maxonspcircler, and PDS IIspcircler).{dollar} These absorbable sutures are also based on linear aliphatic polyesters that were composed of either homopolymer or copolymers. We found that the superoxide ion had a profound effect on the mechanical, thermal, And surface morphological properties of these five absorbable sutures.; Another interesting stable free radical substance, Tempamine (4-amino-2,2,6,6-tetra methylpiperidine-1-oxy) nitroxyl radical has been recently revealed to have many critical biological activities. This nitroxyl radical was subsequently chemically incorporated into a variety of biodegradable polymeric materials, such as polyglycolide, poly (L-lactide), poly (D,L-lactide), poly (glycolide-L-lactide) copolymer (90:10 glycolide and lactide monomer ratio), and poly (glycolide-L-lactide) copolymer (50:50 glycolide and lactide monomer ratio) for a controlled delivery of nitroxyl radical for the therapeutic purpose. The rate and mechanism of in vitro hydrolytic release of Tempamine nitroxyl radical from the parent biodegradable polymer (polyglycolide) in buffered media at 37{dollar}sp0{dollar}C was studied by EPR spectroscopy.; A preliminary in vitro cell culture study of this new generation of biologically active biodegradable polymers indicated that it was able to retard the proliferation of smooth muscle cells (SMC) as pure nitric oxide does. |
