Microscopy 101
Figure 7: Experimental workflow of TASC, as used to measure drug-polymer miscibility as a function of temperature.
However, the shelf life of RBCs stored in this way is limited to 42 days, potentially resulting in shortages of blood when high numbers of emergency blood transfusions are required. Cryo- preservation of RBC units can extend storage time to ten years, but this preservation method is not routinely used in transfu- sion medicine because current cryopreservation protocols do not permit the direct transfusion of RBCs immediately aſter thawing. Current cryopreservation protocols rely on glycerol and
controlled cooling rates prior to storage at −80°C. Aſter thaw- ing and prior to transfusion, glycerol must be removed to avoid intravascular hemolysis. Tis is a time-consuming pro- cess requiring specialized equipment. Much interest has been shown in small molecule ice recrystallization inhibitors (IRIs) such as β-PMP-Glc and β-pBrPh-Glc. Tese inhibitors can prevent ice recrystallization, a process that contributes to cel- lular injury and decreased cell viability aſter cryopreservation. Researchers at the University of Ottawa and Canadian
Blood Services have used dynamic imaging to follow the prog- ress of the ice front, monitoring and measuring events in real time. In their work, cryomicroscopy was performed using a Linkam FDCS196 cryostage with a Nikon microscope [5]. Ice was nucleated using a liquid nitrogen-cooled probe. Results show that the addition of 110 mM β-PMP-Glc or
30 mM β-pBrPh-Glc to a 15% glycerol solution increases post- thaw RBC integrity by 30–50% using slow cooling rates. Tey were able to conclude that small molecule IRIs show significant potential to preserve RBCs.
48 4. Termal analysis by structural characterization.
Termal analysis by structural characterization (TASC) is a new thermal technique based on image analysis combined with hot-stage microscopy (HSM, also known as thermo-micros- copy). TASC was invented by Professor Mike Reading, work- ing in the Department of Chemical Sciences at the University of Huddersfield in the UK, in 2017 [6]. Subsequent studies, with co-workers in the School of Pharmacy at the University of East Anglia in Norwich, Norfolk, UK, reported how TASC could be applied successfully to estimating drug-polymer miscibility and to the screening of drug-polymer combinations [7,8]. Te use of amorphous solid dispersions (ASDs), where a
polymer is used to stabilize the amorphous form of the drug, is a key way of preparing pharmaceutical compounds in order to improve drug solubility—something that can be a problem- atic step in as many as 60–70% of potential new drugs. To suc- cessfully formulate such products, the drug needs to be highly miscible with the polymer, and “drug-polymer miscibility” is a critical parameter that has been shown to affect, for example, physical stability during storage, and dissolution rate of the final formulated product. Te ability to conduct in situ struc- tural analysis of the miscibility of these compounds is a vital tool in screening potential new drugs. In this work by researchers from the school of Pharmacy
at the University of East Anglia, TASC was used in direct com- parison to the current common analytical approach of differ- ential scanning calorimetry (DSC). Changes in the features of crystalline drug particles as they are heated on a microscope
www.microscopy-today.com • 2020 November
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