Ice growth inhibition by synthetic macromolecules
Congdon, Thomas R.
Animals, plants and bacteria can survive sub-zero environments by using specialist proteins that inhibit ice growth. There has been a great deal of work into trying to understand and exploit these proteins for use in cryopreservation, but several strategies fail as the protein’s mechanism for ice growth inhibition causes ice to grow into needle-like crystals, which cause mechanical damage to the cryopreserved material. A range of studies have shown that this shaping can be removed, without affecting ice growth inhibition activity. Synthetic mimics exist, the most interesting being the simple polymer, poly(vinyl alcohol), which alone amongst other synthetic macromolecules displays ice growth inhibition behaviour. The scientific principles behind ice growth, and the molecules that can inhibit this, are detailed in Chapter 1.\ud \ud Chapter 2 examines how the molecular weight of poly(vinyl alcohol) affects ice recrystallisation inhibition activity, and the importance of hydroxyl sequence, using post-polymerisation modification and co-polymerisation. Chapter 3 details the preparation of well-defined block co-polymers of poly(vinyl alcohol), and confirms the importance of the hydroxyl sequence. These polymers maintained their ice recrystallisation inhibition activity despite the addition of large non-active blocks.\ud \ud Chapter 4 demonstrates the synthesis and utility of a novel multifunctional chain transfer agent, which is used to prepare star polymers. The resultant star-poly(vinyl alcohol) was highly active, and activity profiles of these polymers provided further evidence that the mechanism of ice recrystallisation inhibition by poly(vinyl alcohol) does not involve direct binding to ice. Chapter 5 uses the techniques and methodologies developed in Chapter 2 and applies them to another lesser-known ability of poly(vinyl alcohol); thermoresponsivity.\ud \ud In summary, controlled radical polymerisation of vinyl acetate was employed in a range of different ways to prepare poly(vinyl alcohol) and its various co-polymers. These polymers were then tested for ice recrystallisation inhibition. Due to their well defined physical properties, and advanced architectures, new insights into the nature and mechanisms of their activity were available. This mechanistic understanding, and the materials developed for this thesis, display a great deal of potential in expanding the field of cryopreservation.
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