Amy G Ding1, Steven P Schwendeman. 1. Department of Pharmaceutical Sciences, University of Michigan, Ann Arbor, Michigan 48109-1065, USA.
Abstract
PURPOSE: The acidic microclimate pH (micropH) distribution inside poly(lactic-co-glycolic acid) (PLGA) microspheres was monitored quantitatively as a function of several formulation variables. METHODS: A ratiometric method by confocal laser scanning microscopy with Lysosensor yellow/blue dextran was adapted from those previously reported, and micropH distribution kinetics inside microspheres was examined during incubation under physiologic conditions for 4 weeks. Effects of PLGA molecular weight (MW) and lactic/glycolic acid ratio, microspheres size and preparation method, and polymer blending with poly(ethylene glycol) (PEG) were evaluated. RESULTS: micropH kinetics was accurately sensed over a broadly acidic range (2.8 < micropH < 5.8) and was more acidic and variable inside PLGA with lower MW and lactic/glycolic acid ratio. Lower micropH was found in larger microspheres of lower MW polymers, but size effects for lactic-rich polymers were insignificant during 4 weeks. Microspheres prepared by the oil-in-oil emulsion method were less acidic than those prepared by double emulsion, and blending PLGA 50/50 with 20% PEG increased micropH significantly (micropH > 5 throughout incubation). CONCLUSIONS: Coupling this method with that previously developed (SNARF-1 dextran for micropH 5.8-8.0) should provide microclimate pH mapping over the entire useful pH range (2.8-8.0) for optimization of PLGA delivery of pH-sensitive bioactive substances.
PURPOSE: The acidic microclimate pH (micropH) distribution inside poly(lactic-co-glycolic acid) (PLGA) microspheres was monitored quantitatively as a function of several formulation variables. METHODS: A ratiometric method by confocal laser scanning microscopy with Lysosensor yellow/blue dextran was adapted from those previously reported, and micropH distribution kinetics inside microspheres was examined during incubation under physiologic conditions for 4 weeks. Effects of PLGA molecular weight (MW) and lactic/glycolic acid ratio, microspheres size and preparation method, and polymer blending with poly(ethylene glycol) (PEG) were evaluated. RESULTS: micropH kinetics was accurately sensed over a broadly acidic range (2.8 < micropH < 5.8) and was more acidic and variable inside PLGA with lower MW and lactic/glycolic acid ratio. Lower micropH was found in larger microspheres of lower MW polymers, but size effects for lactic-rich polymers were insignificant during 4 weeks. Microspheres prepared by the oil-in-oil emulsion method were less acidic than those prepared by double emulsion, and blending PLGA 50/50 with 20% PEG increased micropH significantly (micropH > 5 throughout incubation). CONCLUSIONS: Coupling this method with that previously developed (SNARF-1 dextran for micropH 5.8-8.0) should provide microclimate pH mapping over the entire useful pH range (2.8-8.0) for optimization of PLGA delivery of pH-sensitive bioactive substances.
Authors: O L Johnson; J L Cleland; H J Lee; M Charnis; E Duenas; W Jaworowicz; D Shepard; A Shahzamani; A J Jones; S D Putney Journal: Nat Med Date: 1996-07 Impact factor: 53.440
Authors: Ramprakash Govindarajan; Margaret Landis; Bruno Hancock; Larry A Gatlin; Raj Suryanarayanan; Evgenyi Y Shalaev Journal: AAPS PharmSciTech Date: 2014-10-16 Impact factor: 3.246