Phospholipid nanoparticles: Process optimization using factorial design and atomic force microscopy

Physical properties such as particle size, polydispersity and zeta potential are important determinants of biological performance of nanoparticles. Formulation process parameters can greatly influence the physical properties of nanoparticles. The goal of the current study was to utilize a 2⁴ factorial design to understand the effect of processing conditions such as sonication energy, sonication time, homogenization energy, and homogenization time on particle size, polydispersity, and zeta potential of a phospholipid nanoparticle formulation. The main effects of the factors and interactions between them were modeled using factorial analysis. The results of the study suggest that sonication energy, sonication time, and homogenization speed are important determinants of nanoparticle size. It was observed that an increase in homogenization speed resulted in an increase in particle size; however, elimination of the homogenization step resulted in nanoparticles that were more irregular in shape and in the formation of aggregates as observed by atomic force microscopy (AFM). Zeta potential was affected only marginally by any of the process parameters. Sonication energy was the most important determinant of nanoparticle polydispersity. AFM studies suggest that although two different energy inputs may result in similar particle size, nanoparticles prepared with lower energy input exhibit less aggregation during storage. In conclusion, we have successfully used factorial design in conjunction with AFM to predict the effect of various process parameters on some of the physical properties of phospholipid nanoparticles.