Catalytic Synthesis and Characterization of Biodegradable ...

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Chapter 6 Figure 6.6 Cyclic voltammograms of (A) MPEG-b-PTAm and (B) MPEG-b-PLA-b-PTAm micelles in 0.1 M HCl aqueous solution. 6.5 EPR study of the micelles in PBS containing ascorbic acid It is known that a reducing environment is necessary for biological systems. The antioxidants such as ascorbic acid (Vc) and glutathione (GSH) are important to keep the redox status in living cells and exist in most of parts in vivo. Thus, we evaluated the reduction resistance of the micelles in the presence of antioxidants. Since the reduction of nitroxyl radical into hydroxylamine group by GSH is much slower than Vc and there is higher concentration of Vc in the blood stream, 22, 23 we selected antioxidant Vc for our study. The EPR measurements were conducted in the presence of Vc at concentration of 5.0 mM which is 50 times more than the concentration of Vc in the blood. As shown in Figure 6.7 A, the EPR signal decreased over time in PBS solution containing Vc, ascribing to the reduction of nitroxyl radicals. And the EPR signal pattern of both MPEG-b-PTAm and MPEG-b-PLA-b-PTAm micelles were broad single, which is distinct from typical triplet signal of free TEMPOL radical in diluted solution, due to the spin-spin interaction of TEMPO in the side chains. 19, 24, 25 Furthermore, we observed that the EPR signal in aqueous media is broader than in chloroform, which is consisted with previous report. 18 These results indicated that the polymer segment containing nitroxyl radicals had been incorporated into micelles in aggregated state in the hydrophobic core. By virtue of the micelle structure, the nitroxyl radicals in the core could resist reduction for a longer time than free TEMPOL radical even in the presence of higher concentration of Vc (Figure 6.7 B). The half-life time for both MPEG-b-PTAm and MPEG-b-PLA-b-PTAm micelles were about 8 ‐ 120 ‐
Synthesis of Amphiphilic Triblock Copolymers of Acrylamide, Lactate, and Ethyleneoxide min, however, the time for free TEMPOL radical was less than 1 min. The prolonging time for both MPEG-b-PTAm and MPEG-b-PLA-b-PTAm micelles in the reducing environment would endow the systems have the promising application as the stable EPR probes. Figure 6.7 (A) EPR spectra of MPEG-b-PTAm and MPEG-b-PLA-b-PTAm micelles in PBS containing 5.0 mM ascorbic acid over time; (B) Dependence of EPR signal intensity on the time. 6.6 Cytotoxicity assay MTT cell toxicity assay was used to determine the cytoxicity of the synthesized block copolymers MEPG-b-PTAm and MPEG-b-PLA-b-PTAm. The results shown in Figure 6.8 revealed that both MEPG-b-PTAm and MPEG-b-PLA-b-PTAm had as low cytotoxicity as the MPEG5K and MPEG-b-PLA. The good biocompatibility of the MEPG-b-PTAm and MPEG-b-PLA-b-PTAm, presumably ascribing to the hydrophiphic shell of the MPEG segment in aqueous solution, would make these materials suitable for applications in vivo. In ‐ 121 ‐
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Catalytic Synthesis and Characteriz
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Preface Biodegradable polyesters ha
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Chapter 3 Polymerization of Lactic
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Chapter 1 Polymerization and Applic
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1.2.2 Aluminum Catalysts - 7 - Poly
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1.3 Polylactide 1.3.1 Introduction
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1.3.4 Application of PLA Figure 1.3
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initialization of the device by app
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182. R. B. Weller, J. Invest. Derma
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Synthesis and Electrochemistry of S
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