Influence of PEG in PEG-PLGA microspheres on particle properties and protein release

The aim of the present study was to compare different commercial available types of Poly(d,l-lactide-co-glycolide) (PLGA), multiblock copolymers of PLGA and polyethylene gylcol (PEG) as well as blends of PLGA and PEG regarding the preparation of microparticles and the release behavior of encapsulated protein. Microspheres were prepared by the solvent evaporation technique using the same conditions for each formulation. The encapsulation rate of bovine serum albumin (BSA) was unaffected by the different polymer types, and the mean was 79±4%. Microspheres composed of blends of PLGA and PEG showed a porous structure, a higher specific surface area, an inhomogenous distribution of protein and a higher release rate of BSA than microspheres consisting of PLGA, whereas the release profiles were the same. The specific surface area of microparticle formulations composed of diblock copolymers was the highest with 8.57±0.07m(2)/g emphasized by a highly porous, sponge-like structure. The triblock copolymer formulation revealed nearly spherical particles with a slightly uneven surface. Although the triblock copolymer consists of 10% PEG, the specific surface area was the lowest of all formulations. The rapid hydration due to PEG leads to a swollen matrix, which released the protein in a slow and continuous way.