Preparation of amino acid nanoparticles at varying saturation conditions in an aerosol flow reactor
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Nanoparticle formation of five amino acids, glycine, l-proline, l-valine, l-phenylalanine, and l-leucine was studied. The aim was to explore factors determining nanoparticle formation and crystallinity. The amino acid nanoparticles have been prepared at different saturation conditions in the aerosol reactor. In a condensed state, the particles were formed by droplet drying. The raise in temperature induced the sublimation of amino acids from the aerosol particles. The amino acid vapor was condensed by physical vapor deposition in a rapid cooling process. The diffusion coefficients and nucleation rates of amino acids have been calculated to understand particle formation. Upon the vapor deposition, amino acids formed crystalline nanoparticles except in the case l-phenylalanine according to X-ray diffraction. The crystal polymorph of glycine in the nanoparticles depended on the applied reactor temperature. The preference of crystallographic orientation varied in both the particle formations from condensed and vapor phase. l-Valine, l-phenylalanine, and l-leucine formed leafy-looking particles. These results could be utilized in the fabrication of nano-sized asperities on drug particle surfaces to reduce forces between particles and accordingly increase particle dispersion in dry powder inhalers.