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Hygroscopicity and Shape Factor Measurements of Uric Acid Aerosol Towards the Treatment of Medical Conditions
DEWANSH RASTOGI, Kanishk Gohil, Chao Peng, Mingjin Tang, Akua Asa-Awuku, University of Maryland College Park
Abstract Number: 45
Working Group: Health-Related Aerosols
Abstract
The growth of nanocrystalline (100-200 nm) uric acid deposits in joints and tissue can lead to gout and kidney failures. Uric acid stones constitute about 4-12% of all kidney stones worldwide and form in the human body during purine metabolism. Uric acid has low water solubility (6 mg/mL), and crystallization occurs when uric acid reaches saturated concentrations. Hence, quantifying the water uptake of ultra-fine uric acid particles may contribute to new medical treatments.
In this work, we measure the physical properties of uric acid aerosols. Aerosols generated by atomization are dried and then exposed to sub-saturated and supersaturated conditions. The aerosol electrical mobility and aerodynamic diameter size are measured using Scanning Mobility Particle Sizer and Aerodynamic Aerosol Classifier, respectively. These measurements are used to calculate the shape factor for the aerosol particles at different drying rates. A Thermogravimetric Analyzer (TGA) is used to measure the mass of water adsorbed on uric acid particles exposed to sub-saturated relative humidity conditions.
Results show that the shape factor decreases from 1.4 to 1 with the increase in either particle sizes or drying rates. These shape factor measurements are used to calculate the size-independent hygroscopicity parameter measured in the supersaturated regime. The overall hygroscopicity is found to be less than 0.001. Additionally, TGA measurements show negligible water uptake by uric acid crystals at low relative humidity. Hence, uric acid particles would likely crystallize from the surrounding media even when the concentration of uric acid is low in the body. Once formed, these crystals tend to be difficult to dissolve. The traditional nanoparticle water uptake theory (Köhler theory) cannot be applied to uric acid particles, and one needs to consider adsorption theory to understand the water uptake behavior of uric acid particles.