128 Development of a low cost sensor system for determination of glass transition temperatures during cooling and warming

Ice nucleation and glass transition (Tg) temperatures influence cell viability during cryopreservation. Knowledge of these phase changes for cryoprotectant mixtures is an essential step in optimising cryopreservation protocols for cell survival. Differential scanning calorimetry (DSC) is the conventional device used to determine Tg, but the expensive nature of such instrumentation limits its widespread use. A cost-effective sensor system has been designed to monitor ice nucleation and Tg events in cryoprotectant solutions. Glycerol was used a test solution and Tg values were measured (with and without NaCl supplement) in cryotubes and cryostraws, using RTD temperature and screen-printed impedance sensors. The effect of changes to ice-nucleation temperature on Tg was also investigated using ice nucleators. Cooling rates of (a) 5 °C min −1 , (b) 0.1 °C min −1 and (c) direct plunge into liquid nitrogen were set using a Grant Asymptote (EF600) controlled rate freezer. Protocols (a) and (b) were run from 0 °C to −90 °C followed by rapid plunge into liquid nitrogen. The warming event of the three protocols was monitored during slow warming of the samples in air at room temperature. The Tg values during warming events compared favourably with the values obtained by DSC reported in the literature. The reported DSC derived Tg values (Morris et al., 2006) for 10% glycerol +0.15 M NaCl (−55 °C) are close to the values obtained in the current work (−52 to −57 °C). The availability of low cost sensor systems to monitor changes in impedance allows the determination of Tg of cryopreservation media during both cooling and warming cycles, and should enable such measurements to become routine in laboratories. Source of funding: University of Bedfordshire Research Development funds. Conflict of interest: None declared. jahanbeen.jahangir@beds.ac.uk