Fabrication and testing of a tool for thermodynamic characterization of microsamples
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Cryopreservation utilizes very low temperatures to preserve living cells and tissues. Successfully cryopreservation protocols for a limited number of cell types have been developed experimentally. To develop generalized protocols an accurate measurement of thermodynamic properties such as heat capacity, latent heat, and the physical phase change temperatures is imperative. In thermal analysis, frequently used to quantitatively measure such thermodynamic properties are the differential scanning calorimeter (DSC) and differential thermal analyzer (DTA). However, commercially available DSC and DTA are macroscopic in nature requiring samples to be multi-cellular. Therefore, the measurements acquired effectively average the behavior of the cell sample, concealing individual cell behavior. It is hypothesized that the evaluation of thermodynamic properties on a single cell level will allow for more fundamental understanding of cell-level transport, and effectively lead to more successful cryopreservation protocols. Compton developed a sample holder via MEMS technology on the order of a prototypical mouse oocyte cell ([aboout]100 m) in size to detect phase change and reduce relative thermal mass ultimately improving measurement sensitivity.  Armes developed a control software capable of providing any desired heating or cooling profile within a humidity controlled environment where repeatable scans using water samples have been demonstrated.  This DTA apparatus developed successful characterized nano-liter (nL) samples; however, assembling the DTA proved to be challenging. To improve the practicality of the DTA, a thin film platinum resistance temperature detector (TFPRTD) calorimeter has been developed via lift-off technology. In this project, we fabricated and tested thin-film calorimeter RTD sizes ranges from 100m to 500m. The objective of the thin-film RTD apparatus is to successfully obtain characteristic temperatures of single cell fish eggs that range from 100 m to 500m in size and various other biological cells on the single cell level, whilst investigating intracellular ice formation (IIF). The thin-film DTA has been shown to measure the freezing point of water samples and fish eggs, with samples volumes on a micro-liter scale. The specific heat capacity for single cell fish egg has also been experimentally determined and characterized. Repeatable scans using water, onion epidermal cells, and fish eggs have been demonstrated.
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