Polymeric nanoparticles as drug controlled release systems: a new formulation strategy for drugs with small or large molecular weight.

We report a study evaluating the encapsulation and release modalities from poly(D,L lactic acid) (PLA) or poly(D,L-lactide-co-glicolide) (PLGA) micro- and nano-particles of the antiischemic drug N6-cyclopentyladenosine (CPA) and bovine serum albumin (BSA), chosen as protein model. The results obtained by classical preparation methods (nanoprecipitation, single or double emulsion/solvent evaporation) of the particles were compared with those obtained by their formulation with a novel method, employing a thermosensible gel of Pluronic F-127, whose aqueous solutions can be liquid when refrigerated, but gel upon warming. Our results indicate that CPA-loaded nanoparticles, obtained by classical methods, drastically reduce their drug content showing, moreover, any control of the drug release with respect to CPA-loaded microparticles. The novel preparation method allowed us to obtain, instead, CPA encapsulation values in nanoparticles similar to those obtained for microparticles, achieving also a weak control of the drug release. Any drastic reduction of BSA particle content was obtained by decreasing their size from micro- to nano-scales, independently on the employment of classical or novel preparation methods. Moreover, the size reduction induced only a weak increase of the BSA release rate. The patterns of protein released from micro- and nano-particles obtained by the same formulation method were similar. In particular, the micro- and nano-spheres prepared by double emulsion technique showed an incomplete BSA release, characterized by an elevated burst effect followed by a very slow phase. On the other hand, the release from micro- and nano-particles obtained by the novel method was complete and quite regular, being characterized by a little burst release followed by a fast phase. These results have been related to the strong BSA distribution (observed by confocal laser scanning microscope) in the surface or in the core of microparticles obtained by the classical or novel methods, respectively.