Poly(D,L-lactide-co-glycolide) protein-loaded nanoparticles prepared by the double emulsion method--processing and formulation issues for enhanced entrapment efficiency.

Although extensive research in the field of biodegradable microparticles containing peptide or protein drugs has greatly advanced production know-how, the effects of critical parameters influencing successful drug entrapment have not yet been sufficiently investigated with nano-scaled carriers. This paper deals with the formulation and processing parameters of the w(1)/o/w(2) double emulsion method that can affect nanoparticle size and loading. Fluorescein isothiocyanate-labelled bovine serum albumin (FITC-BSA) was used as a model protein. Results showed that high FITC-BSA entrapment efficiencies were reached (>80%) when sonication was used for the two emulsification steps of the nanoparticle formation, independently of the mixing durations and intensities. By comparison, the use of a vortex mixer for obtaining the primary w(1)/o emulsion led to a rather poor entrapment efficiency (approximately 25%). Some inherent properties of the poly(D,L-lactic-co-glycolic acid) polymer, such as, for example, high molecular weight, high hydrophilicity or the presence of free carboxylic end groups, enhanced the drug entrapment efficiency. It was also demonstrated that a low nominal drug loading, a large volume of the inner w1 phase or the choice of methylene chloride instead of ethyl acetate as organic solvent favoured the drug entrapment, with entrapment efficiency values often reaching 100%. However, when using methylene chloride, the mean particle size was substantially increased, due to the presence of larger particles. Mean particle size increased also when the polymer concentration in the organic phase was increased.