Size, Shape, and Phase of Nanoscale Uric Acid Particles

Uric acid particles are formed due to hyperuricemia, and previous works have focused on understanding the surface forces, crystallization, and growth of micron- and supermicron-sized particles. However, little to no work has furthered our understanding about uric acid nanonuclei that precipitate during the initial stages of kidney stone formation. In this work, we generate nanosized uric acid particles by evaporating saturated solution droplets of uric acid. Furthermore, we quantify the effects of drying rate on the morphology of uric acid nanonuclei. An aerosol droplet drying method generates uric acid nanoparticles in the size range of 20-200 nm from aqueous droplets (1-6 μm). Results show that uric acid nanonuclei are non-spherical with a shape factor value in the range of 1.1-1.4. The shape factor values change with drying rate and indicate that the nanoparticle morphology is greatly affected by drying kinetics. The nanonuclei are amorphous but can grow to form crystalline micron-sized particles. Indeed, a pre-crystallization phase was observed for heterogeneous nucleation of uric acid particles in the size range of a few hundred nanometers. Our findings show that the morphology of uric acid nanonuclei is significantly different from that of crystalline supermicron-sized particles. These new findings imply that the dissolution characteristics, surface properties, elimination, and medical treatment of uric acid nanonuclei formed during the initial stages of nucleation must be reconsidered.