Protein spray-freeze drying. Effect of atomization conditions on particle size and stability

Purpose. To investigate the effect of atomization conditions on particle si ze and stability of spray-freeze dried protein. Methods. Atomization variables were explored for excipient-frree (no zinc a dded) and zinc-complexed bovine serum albumin (BSA). Particle size was meas ured by laser diffraction light scattering following sonication in organic solvent containing poly(lactide-co-glycolide) (PLG). Powder surface area wa s determined from the N, vapor sorption isotherm. Size-exclusion chromatogr aphy (SEC) was used to assess decrease in percent protein monomer. Fourier- transform infrared (FTIR) spectroscopy was employed to estimate protein sec ondary structure. PLG microspheres were made using a non-aqueous, cryogenic process and release of spray-freeze dried BSA was assessed in vitro. Results. The most significant atomization parameter affecting particle size was the mass now ratio (mass of atomization N, relative to that for Liquid feed). Particle size was inversely related to specific surface area and th e amount of protein aggregates formed. Zinc-complexation reduced the specif ic surface area and stabilized the protein against aggregation. FTIR data i ndicated perturbations in secondary structure upon spray-freeze drying for both excipient-free and zinc-complexed protein. Conclusions. Upon sonication, spray-freeze dried protein powders exhibited friability, or susceptibility towards disintegration. For excipient-free pr otein, conditions where the mass flow ratio was > similar to0.3 yielded sub -micron powders with relatively large specific surface areas. Reduced parti cle size was also linked to a decrease in the percentage of protein monomer upon drying. This effect was ameliorated by zinc-complexation, via a mecha nism involving reduction in specific surface area of the powder rather than stabilization of secondary structure. Reduction of protein particle size w as beneficial in reducing the initial release (burst) of the protein encaps ulated in PLG microspheres.