Structural properties of biodegradable polyesters and rheological behaviour of their dispersions and films.
This paper focuses on the dependence of the rheological properties of PLA-PEG and PLGA dispersions and films on the polymer structural properties, in order to obtain useful information to predict and explain the performance of polyester films as drug-delivery systems. In this study, one PLA-PEG and three PLGA polymers of different molecular mass were synthesized and characterized by NMR, GPC, DSC and TGA-FT-IR. To characterize the viscoelastic behaviour of concentrated solutions in dichloromethane and of the films obtained by a solvent-casting technique, oscillatory shear rheometry was used. The polymer dispersions showed a characteristic Newtonian viscous behaviour, but with different consistency index depending on the nature of the polymer. Freshly prepared, PLGA and PLA-PEG films had elastic modulus (G') greater than viscous modulus (G"). The decrease in both moduli caused by an increase in temperature from 25 to 37 degrees C was especially marked for the polymers with T(g) below or around 25 degrees C (PLGA 27 kDa and PLA-PEG 27 kDa). After being immersed in pH 7.4 aqueous solution for one week, PLGA films showed a significant increase in both G' and G", due to the promotion of polymer-polymer interactions in a non-solvent medium. In contrast, the PLA-PEG film became softer and more hydrated, due to the amphiphilic character of the polymer. The water taken up by the film acted as a plasticizer and induced the softening of the system. These results suggest that the presence of PEG chains exerts a strong influence on the mechanical properties of polyesters films and, possibly, the performance as coating or matrices of drug-delivery systems.
Departamento de Ingeniería Química y Tecnología Farmacéutica, Facultad de Farmacia, Universidad de La Laguna, La Laguna 38200, Tenerife, Spain.
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Santoveña
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Alvarez-Lorenzo
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Concheiro
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Llabrés
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JB
Fariña
D001673:Biodegradation, Environmental; D004337:Drug Carriers / Q000737:chemistry*; D007773:Lactates / Q000737:chemistry*; D019344:Lactic Acid / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008970:Molecular Weight; D011091:Polyesters / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry*; D012212:Rheology; D014783:Viscosity
D004337:Drug Carriers; D007773:Lactates; D011091:Polyesters; D011108:Polymers; C088513:poly(lactic acid-ethylene glycol); D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; D011092:Polyethylene Glycols