Effect of polymer compositions on the fabrication of poly(ortho-ester) microspheres for controlled release of protein

Eight kinds of self-catalyzed poly(ortho-esters) (POEs) are used to fabrica te bovine serum albumin (BSA)-containing microspheres using a W/O/W double- emulsion solvent extraction/evaporation method. All eight kinds of POE poly mers used in this study are shown able to form microspheres under proposed fabrication conditions. The surface morphology and inner structure of the m icrospheres are analyzed using scanning electron microscopy (SEM). The micr ospheres have a size range from 64.7 to 120.2 mum. POE with a higher viscos ity leads to bigger microspheres. It was found that the POE composition has a significant effect on BSA release profiles. POEs, which are more hydroph ilic and contain a greater amount of glycolide or lactate (latent acid), yi eld higher BSA release rates. Specifically, POE containing 1,6-hexanediol d iglycolide (HD-diGL) microspheres have the highest BSA release rate after a 20-day test through a combination of surface erosion and diffusion mechani sms. POE containing a high percentage of the trans-cyclohexanedimethanol (C DM) segment tends to yield microspheres with a lower release rate because o f its hydrophobic nature. It was also found that the BSA release rate is mo re rapid at 37 degreesC than at 22 degreesC because of faster polymer degra dation and water penetration at 37 degreesC. Experimental results suggest t hat various protein release rates can be achieved by using different compos itions of POEs. (C) 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1630- 1642, 2001.