Hygroscopic measurements on aqueous 2-HP-b-CD droplets as aerosols for drug delivery to the lungs

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Despite the interest in CDs as medicinal agents and excipients, the physiochemical properties of CDs and CD derivatives, for example hygroscopicity, refractivity index (RI) and density are ill-defined or unknown, and there is a need to understand the underlying aerosol science impacting inhaled formulation. Qualifying and quantifying aerosol hygroscopic response is key to improving drug formulations and informing models used to predict drug deposition patterns within the lung or taken up through the olfactory system.

A poor understanding of the relationship between the physicochemical characteristics of aerosol formulation and the medicinal efficacy in the humid environment of the respiratory tract has been identified as the key barrier in optimising inhalation therapies. Recent studies have shown that the aging of the droplet as it responds to rapid changes in RH and temperature during inhalation is known to significantly impact aerosol properties.

In the measurements presented here, the RI and density of aqueous 2-HPBCD were measured with varying mass fraction of the solute (MFS) in bulk solution to infer concentrations relevant to aerosol.

On inhalation, aerosol radii of >5 microm are more likely to deposit in the mouth and throat, <5 microm will travel to the lung, and particles <1 microm are thought to be predominantly exhaled. The aerosol droplets measured with optical tweezers and discussed here range between 3–5 microm in radius.

An amorphous transition and formation of ultra-viscous aerosol has beenb identified through optical tweezers measurements. The slow water transfer observed in amorphous cyclodextrin molecules coupled with their porous nature could reveal interesting water uptake kinetics in aerosol.

C. P. F. Day, A. Miloserdov, K. Wildish-Jones, E. Pearson and A. E. Carruthers: Quantifying the hygroscopic properties of cyclodextrin containing aerosol for drug delivery to the lungs. Phys. Chem. Chem. Phys.,
2020, 22, 11327. https://doi.org/10.1039/d0cp01385d

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