title: Pore closing and opening in biodegradable polymers and their effect on the controlled release of proteins.
abstract: The purpose of this paper was to investigate the phenomena of pore closing and opening in microspheres of poly(lactic-co-glycolic acid) (PLGA) and PLGA-glucose star copolymer (PLGA-Glu) and their effects on protein release. We used scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) to visually characterize the pore state and the uptake of dextran labeled with pH-insensitive probes by microspheres, as an indicator of pore connectivity. The effect of temperature on initial protein release from microspheres was also investigated. It was found that (1) pore closing occurs in both PLGA and PLGA-Glu; (2) pore closing can take place at later time during incubation at physiological condition (37 degrees C) as well as during the initial stage; (3) pore closing is much more significant at elevated temperatures; (4) previously isolated pores can become open by, for example, osmotic-mediated events; and (5) pore closing/opening correlates with the release rate of biomacromolecules from PLGA or PLGA-Glu microspheres. The pore closing/opening appeared potentially a universal event throughout the release period dictating the kinetics of protein release from PLGA microspheres. Hence, these results strongly suggest that open and isolated pores are able to toggle back-and-forth periodically during PLGA degradation while controlling protein release; these observations imply a novel new hypothesis concerning erosion-controlled release of biomacromolecules from PLGA and related polymers.
authors.affiliation: Department of Pharmaceutical Sciences, The University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Jichao
authors.initials: J
authors.lastname: Kang
authors.forename: Steven P
authors.initials: SP
authors.lastname: Schwendeman
mesh_terms: D000818:Animals; D002417:Cattle; D003911:Dextrans / Q000378:metabolism / Q000648:ultrastructure; D019344:Lactic Acid / Q000378:metabolism*; D008855:Microscopy, Electron, Scanning; D008863:Microspheres; D011100:Polyglycolic Acid / Q000378:metabolism*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000378:metabolism*; D016062:Porosity; D012710:Serum Albumin, Bovine / Q000378:metabolism*; D012995:Solubility; D013696:Temperature
chemical_list: D003911:Dextrans; D011108:Polymers; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D012710:Serum Albumin, Bovine; D019344:Lactic Acid