Contrary to popular perception, ice usually does not form in liquid water at 0°C. Indeed, there is excellent evidence that even ocean-scale volumes of water can measurably supercool to temperatures below the melting point of ice (1). Small droplets of water can be cooled to temperatures below -38°C before freezing. In nature, ice is usually nucleated heterogeneously by substances in contact with supercooled water. This process plays a key role in various scientific and technological contexts, notably atmospheric science and low-temperature biology (2,3).
Many substances are known to nucleate ice well. These include mineral dusts, biological substances, inorganic crystals, alcohol monolayers and many others (2). Remarkably, we do not properly understand why one substance should nucleate ice more effectively than another. In this project you will experimentally examine the ice nucleation ability of recently discovered ice nucleating polysaccharides to generate an improved underpinning understanding of heterogeneous ice nucleation.
You will directly deploy this knowledge in the contexts of climate-relevant atmospheric science and technologically and clinically relevant cryobiology. The core of the project will involve use of novel laboratory experiments techniques to discover the spatial distribution and statistical nature of ice nucleation events caused by polysaccharides and other polymers in microlitre scale water droplets, by repurposing established experimental techniques for high-speed examination of the ice nucleation process (4). You will examine these findings using classical nucleation theory and advanced statistical models to generate a new physically grounded understanding of the heterogeneous ice nucleation process.
Your experimental work will be conducted in conjunction with the lab of Prof Matthew Gibson at the University of Manchester, who will provide expertise in polymer characterisation. Improved fundamental understanding of heterogeneous ice nucleation by polymers will allow generation of physically rooted parameterisations for ice nucleation in cloud models. At present, order of magnitude differences in ice nucleating particle effectiveness are used in these models but are not physically underpinned. Resolving this will allow more accurate representation of convective cloud systems in weather and climate modelling (5).
Cryopreservation of biological material is critical for transport and storage of emerging cell therapies, and for storage minimising the use of life animals in safety testing of medicines. The improvements in understanding of nucleation theory as applied to heterogeneous ice nucleation will be employed to improve choice and utilisation of ice nucleating polysaccharides in the context of biological cryopreservation, building on the recent discovery of the exceptional utility of ice-nucleating polysaccharides for freezing of mammalian cells (6) and cell spheroids (7). This work will be conducted in conjunction with the CASE partner for this project, Cryologyx Ltd (https://cryologyx.com/). Cryologyx Lead Development Scientist Dr Ruben Thomas will act as industrial supervisor for the project.
You will have the opportunity to work in a truly interdisciplinary manner, with freedom to explore applications of their fundamental findings in both medically and technologically relevant cell biology work and/or computer modelling of cloud processes.
Figure 1: (a) image of ice forming on a substrate under high speed cryomicroscopy, from ref. (4). (b) Schematic of ice forming on a polysaccharide. (c) confocal microscope image mammalian cell spheroid cryopreserved using ice nucleating polysaccahrides, from ref. (7). (d) Hole punch cloud over Leeds, UK. These clouds occur when ice nucleating particles cause parts of clouds to precipitate while leaving surrouding areas untouched.
(1) Haumann, F. A et al. Supercooled Southern Ocean waters. Geophysical Research Letters, (2020), 47, e2020GL090242. (2) Knopf, D.A., Alpert, P.A. Atmospheric ice nucleation. Nature Reviews Physics (2023). 5, 203–217 (3) Morris G.J and Acton E. Controlled ice nucleation in cryopreservation–a review. Cryobiology. (2013) 66(2):85-92. (4) Holden M. A. et al. High-speed imaging of ice nucleation in water proves the existence of active sites. Science Advances, (2019), 5, eaav4316 (5) Hawker, R. E. et al. The temperature dependence of ice-nucleating particle concentrations affects the radiative properties of tropical convective cloud systems, Atmospheric Chemistry and Physics, 21, 5439–5461 (6) Murray K. A. et al. Pollen derived macromolecules serve as a new class of ice-nucleating cryoprotectants Scientific Reports (2022) 12295 (7) Murray K. A. et al. Chemically Induced Extracellular Ice Nucleation Reduces Intracellular Ice Formation Enabling 2D and 3D Cellular Cryopreservation JACS Au 2023, 3, 5, 1314–1320