Nataša Jovanović

Stabilization of Proteins in Dry Powder Formulations Using Supercritical Fluid Technology

Therapeutic proteins have become essential in the treatment of many diseases. Their formulation in dry form is often required to improve their stability. Traditional freeze-drying or spray-drying processes are often harmful to labile proteins and could be replaced by supercritical fluid (SCF) drying to produce particles with defined physicochemical characteristics in a mild single step. A survey of the current SCF drying processes for proteins is presented to give insight into the effect of SCF drying on protein stability and to identify issues that need further investigation. Methods used for drying aqueous and organic protein solutions are described. In particular, effects of process and formulation parameters on particle formation and protein stability are discussed. Although SCF methodology for drying proteins is still in its infancy, it can provide a serious alternative to existing drying methods for stabilizing proteins.

Effect of the spraying conditions and nozzle design on the shape and size distribution of particles obtained with supercritical fluid drying

In the perspective of production of dry therapeutic protein formulations, spray drying of lysozyme (as a model protein) into supercritical carbon dioxide was studied. The effects of the nozzle (i.e., co-current coaxial converging and converging-diverging, and T-mixer impinging) and process conditions (i.e., flow rates, pressure) on the drying of the lysozyme prepared in aqueous solution dried with supercritical carbon dioxide enriched with ethanol were investigated. The particle size distribution, width of particle size distribution and morphology were used to determine the effect of the various parameters assessed. Particles with a median size of approximately 1.5, approximately 5 or approximately 25 microns were produced depending of the nozzle selected. A basic comparative study of the nozzle was done by computational fluid dynamics, but the differences in particle size could not be depicted by these computations. The proportional increase of the flow rates (up to fivefold) caused a decrease in particle size (7- to 12-fold), and doubling the pressure caused a moderate decrease of the size (5-20%). The individual effect of the supercritical carbon dioxide, ethanol and solution streams was explained with a mass transfer model. Changing the ratio between flow rates slightly affected the particle size in various ways because of the swelling and shrinking stages of the drying droplet in supercritical carbon dioxide enriched with ethanol.