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Biodegradable block copolymers Abstract :Recently, block copolymers have got tremendous impetus on the ongoing research in the area of drug delivery technology, due to their capability to provide a biomaterial having a broad range of amphiphilic characteristics, as well as targeting the drugs to specific site. This article is an attempt to review applications of block copolymers in surface modification, drug targeting, nano and microparticles, hydrogels, micelles etc. The physicochemical properties of block copolymers and various synthetic routes for block copolymers are also discussed. Introduction Biodegradable polymers are the youngest members of the materials family with increasing applications in pharmaceutical, medical and biomedical engineering [1–5]. Biodegradable polymers are not limited to release of drugs, peptides or proteins at the characteristic rates and specific site target, but are also extended to medical devices [6] and wound dressing [7], as well as for fabricating scaffold in tissue engineering [8,9]. To meet these demands, biodegradable block copolymers have been found as promising biomaterials by virtue of their ability to manipulate their amphiphilic behavior, mechanical and physical properties by adjusting the ratio of the constituting block or adding new blocks of desired properties. The recent developments in this field are the subject of this review, which addresses the types of biodegradable block copolymers, synthetic routes, properties and their uses as different carriers for delivery of various drugs, peptide and proteins, as targeted agents for target specific delivery. D egradation of and drug release from a novel 2,2-bis(2-oxazoline) linked poly(lactic acid) polymer Abstract The degradation rate of poly(lactic acid) (PLA) is typically modified by copolymerization of the glycolide with lactide. In the present study, the degradation rate of PDLLA was modified by a novel linking of PLA with 2,29-bis(2-oxazoline). This modification resulted in formation of a more rapidly degrading poly(ester amide) (PEA) for controlled drug release. The hydrolytic degradation of PDLLA and PEA films was studied in PBS (pH 7.4, USP XXIV, 37 8C); the resulting decrease in molecular weight was determined by size exclusion chromatography and the weight loss of films was measured. Drug releases of guaifenesin (mw 198.2), timolol (mw 332.4), sodium salicylate (mw 160.1) and FITC–dextran (mw 4400) from PDLLA and PEA films and microspheres were examined in PBS (pH 7.4, 37 8C). The degradation rate of PEA was substantially greater than that of PDLLA. The release profiles of all small model drugs (mw ,332.4) from PDLLA films were biphasic or triphasic, while the release profiles of small model drugs from PEA films varied extensively. Due to the faster weight loss of PEA, FITC–dextran (mw 4400) was released substantially more rapidly from PEA microspheres than from PDLLA microspheres. In conclusion, all model drugs, except guaifenesin, were released faster from PEA preparations than from PDLLA preparations. Conclusion In conclusion,the addition of 2,29-bis(2-oxazoline) as a chain extender to PLA increased the hydrolytic degradation rate of the polymer.The release profiles of all small model drugs from PDLLA films were biphasic or triphasic, while release profiles of small model drugs from PEA films varied extensively.In particular,PEA enhanced the release of a macromolecule from microspheres due to the faster degradation rate of PEA.The present results suggest that PEA provides an alternative to existing biodegradable lactic acid-based polymers for controlled drug delivery. [ Last edited by zzgyb on 2009-1-17 at 09:18 ] |
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