In vitro degradation and release profiles for poly-dl-lactide-poly(ethylene glycol) microspheres containing human serum albumin

Poly-dl-lactide-poly(ethylene glycol) (PELA) block copolymers containing sa me the content (10%) of polyethylene glycol (PEG) were synthesized with fiv e different molecular weight of PEG by ring-opening polymerization. PELA mi crospheres containing human serum albumin (HSA) were elaborated by solvent extraction method based on the formation of double w/o/w emulsion. In vitro matrix degradation and protein release of these microspheres were performe d in phosphate buffered saline (PBS) (154 mM, pH 7.43). The degradation pro files were characterized by measuring the loss of microspheres mass, the de crease of polymer intrinsic viscosity, the decrease of pH value of degradat ion medium, the reduction of polymer number-average molecular weight (M-n) and the change of molecular weight polydispersity (M-w/M-n). The release pr ofiles were investigated From the measurement of protein presented in the r elease medium at various intervals. It showed that the matrix degradation a nd protein release profiles were highly polymer-dependent. The extent of bu rst release in the initial protein release increased with the decrease of m olecular weight of PELA copolymer. It is suggested that these matrix polyme rs may be optimized as carriers in protein (antigen) delivery system for di fferent purposes. (C) 2001 Elsevier Science B.V. All rights reserved.