DYNAMIC WATER SORPTION IN TREHALOSE-SALT MIXTURES: EFFECT OF COMPOSITION ON RETENTION OF THE AMORPHOUS STATE
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University of North Carolina at Charlotte
The disaccharide trehalose has received considerable attention in the bio-preservation field due to its outstanding properties as a glass former, and it is widely used in the pharmaceutical and food industries to stabilize dried products. In part, due to the high viscosity and low molecular mobility in the amorphous glass state, trehalose can preserve the life activities of biomaterials in severe conditions, such as desiccation or freezing. The glassy amorphous state is a meta-stable state that will convert to a crystal eventually, with a rate dependent on the temperature and moisture content. It is well known that amorphous trehalose crystallizes at 44% RH and higher, yet sugar crystallization can have a detrimental effect on preserved materials. In this study, a series of phosphate salts were explored as additives to trehalose compositions in order to understand their effectiveness at suppressing crystallization and retaining the desired glassy amorphous form. To study these phenomena, a Dynamic Vapor Sorption (DVS) experimental set-up was established, which employed containers with constant relative humidity achieved using supersaturated salt solutions. Microwave-assisted processing was used to reach a dry amorphous state in a series of salt-trehalose compositions. These samples were then evaluated for water uptake characteristics and the visual onset of crystallization. Four salts were studied, with choline or sodium as the cation, and monohydrogen phosphate (〖HPO〗_4) or dihydrogen phosphate (H_2 〖PO〗_4) as the anion. It was shown that the crystal suppression efficacy increased with increasing concentration of salt in the mixture, with the exception of compositions containing sodium dihydrogen phosphate, in which samples at all sugar:salt molar ratios crystallized within the same time period as pure trehalose. Of the salts evaluated, choline hydrogen phosphate was found to be most effective for suppressing crystallization. No crystals were observed in choline hydrogen phosphate:trehalose samples after 15 days (1:0.7 molar ratio) at 61% RH, whereas pure trehalose samples had crystallized at day 1. The magnitude of water sorption in salt-trehalose samples also increased with rising salt fraction for all combinations studied. Although avoidance of crystals is desirable, further studies are needed to understand the effect of increased water uptake on the glass transition temperature and the ability to preserve biomaterials in this matrix.
Keanini, RussellTrammell, Susan
Thesis (M.S.)--University of North Carolina at Charlotte, 2014.
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