Li Lei, Schwendeman Steven P
Department of Pharmaceutical Sciences, University of Michigan, Ann Arbor, MI 48019-1065, USA.
J Control Release. 2005 Jan 3;101(1-3):163-73. doi: 10.1016/j.jconrel.2004.07.029.
A quantitative ratiometric method based on laser scanning confocal microscopic imaging was developed to create a pixel-by-pixel neutral microclimate pH (5.8-8.0) map inside poly(lactic-co-glycolic acid) (PLGA) microspheres. The method was accurate to within +/-0.2 pH units. PLGA microspheres with encapsulated bovine serum albumin and the pH-sensitive dye, SNARF-1(R) dextran (MW=10 kDa), were prepared by a water-in-oil-in-water solvent evaporation method. The imaging method was used to monitor the pH changes in PLGA microspheres with or without co-encapsulation of acid-neutralizing MgCO3, and for three different microsphere sizes (2.0+/-0.3, 40+/-10 and 137+/-32 microm) during incubation under physiological conditions. The pH of microspheres was significantly higher with co-encapsulated base compared to base-free microspheres, whose microclimate pH was predominantly below the dye detection limit of pH=5.8. The small microspheres displayed a more neutral pH during incubation probably due to their much shorter diffusion path for polymer-dissolved acids compared with medium- and large-size microspheres. The pH mapping technique discussed here may be useful in routine formulation development and for elucidation of mechanisms of microclimate pH development and polymer erosion.
基于激光扫描共聚焦显微镜成像技术开发了一种定量比率法，用于在聚乳酸 - 乙醇酸共聚物（PLGA）微球内部逐像素创建中性微环境pH值（5.8 - 8.0）图谱。该方法的精度在±0.2 pH单位以内。通过水包油包水溶剂蒸发法制备了包封牛血清白蛋白和pH敏感染料SNARF-1®葡聚糖（分子量 = 10 kDa）的PLGA微球。该成像方法用于监测在生理条件下孵育期间，有无共包封酸中和剂碳酸镁的PLGA微球以及三种不同微球尺寸（2.0±0.3、40±10和137±32微米）的pH变化。与无微球相比，共包封碱的微球的pH值显著更高，无微球的微环境pH值主要低于染料检测极限pH = 5.8。与中、大尺寸微球相比，小尺寸微球在孵育过程中显示出更中性的pH值，这可能是因为聚合物溶解酸在其中的扩散路径短得多。本文讨论的pH测绘技术可能有助于常规制剂开发以及阐明微环境pH值形成和聚合物侵蚀的机制。
