Production of microparticles by high-pressure homogenization

A high-pressure homogenization method for the production of aqueous suspensions of poly(D,L-lactide) and poly(D,L-lactide-co-glycolide) was investigated. Depending on the production conditions it was possible to produce micro--as well as nanoparticulate systems without the use of organic solvents. The influence of different homogenization temperatures and different dispersion media on particle size and charge was investigated. Additionally, various polymer/surfactant ratios were investigated. Homogenization in phosphate buffer at temperatures above the glass transition temperature (Tg) of the polymers resulted in wide particle size distributions with a high percentage of particles in the nanometer range. The effect of a second homogenization step at a temperature below Tg was examined at two different homogenization pressures. Additional homogenization cycles at 10 degrees C led to smaller particle size distributions and the average particle sizes were smaller. The stability of the particles was affected by the concentration of surfactant as well as by the zeta potential of the particles. Phosphate buffer kept the pH of the suspension in a range that provided a high surface charge of the particles because of deprotonization of the carboxylic functions of the polymer.