Gibson Group News
Degradable PVA's Published In ACSMacroLetters
Our latest work has been published in ACS MacroLetters, in collaboration with the Dove Group. In this work we reported the synthesis of degradable poly(vinyl alcohol) and its application as an inhibitor of ice growth. Like most vinyl-derived polymers PVA is not biodegradable (except by some environmental organisms) due to its all carbon backbone. Here we make use of the monomer MDO (2-methylene-1,3-dioxepane) which undergoes radical (co)polymerization but results in main-chain ester linkages, rather than C-C bonds, and hence makes the resulting polymers biodegradable. To enable copolymerization, chloro vinyl acetate was used, rather than vinyl acetate, enabling us to selectively remove the protecting groups rather than the backbone esters.
Using this strategy we made a panel of PVAs and showed that the esters were incoporated into the backbone. We then used these to inhibit ice growth, which we have found to be a useful tool to improve the cryopreservation of cells. A key finding was the amount of MDO (and hence esters) which was incorprorated was a crucial factor with too much MDO leading to know ice growth inhibition activity.
Read the paper here
Paper Identifying 'lost' microplastics in Ocean Samples Published
The first paper from our collaboration with Joseph Christie-Oleza in the School of Life Sciences has been published in ACS Envirnomental Science and Technology. There is a huge, and growing problem of plastic (intractable polymer) waste in the environment, especially in oceans. This plastic waste causes huge environmental damage, but there is still a problem identifying the material in ocean water samples. Current methods involve a net, which captures large pieces of plastic, but the smaller microplastic (which could enter the food chain, for example) are often missed. In this work, a protocal for identifying the microplastics using a simple fluorescent dye and image analysis is introduced.
Read the paper here
Antifreeze Protein Mimetics Published in Nature Communications
Our review article highlighting recent progress in the field of macromolecular mimics of antifreeze proteins has been published in Nature Communications. Our last review on this topic was in 2010, (and was the first independant paper from the group!) when the field had not yet emerged and it was not clear what role synthetic polymers would play. Since then, there has been an increase in interest in this field including our own important contributions.
In this review we summarise the background to antifreeze proteins and some models of how they function. We then detail small molecule mimics, but mainly focus on polymeric (or supramolecular) mimics which are emerging as potent ice growth inhibitors as well as new cryoprotectants. The article was a real team effort by 'Team Cryo'.
Read the article here
Paper Published in ACS MacroLetters
Our latest work in collaboration with the O'Reilly Group, undertaken by Lewis (about to start PDRA at CSIRO, Australia) has been published in ACS Macroletters. In this work, we used polymerization-induced self assembly (PISA) to encapsulate proteins within the core of polymer vesicles. PISA has several advantages include that the hydrophobic block is formed in situ from a water soluble monomer; this means that it is easy to encase the protein in the luman (core) compared to traditional methods. However, during the course of this work, we observed that the hydrophobic core (poly(hydroxylpropyl methacrylate), which is actually quite hydrated) did not form a permanent barrier. It was found to actually be permeable. Using this observation we were able to show that enzymes encapsulated within the core could catalyse reactions of externally added reagents, which could cross inside, react, and the subseqently diffuse back out. The importance of this work is it verstility; we used multiple enzymes to prove that this effect is real and also show there is some size selectivity, and these can be considered to be 'molecular sieves'.
Read the paper here
Permeable Protein-Loaded Polymersome Cascade Nanoreactors by Polymerization-Induced Self-Assembly
Paper Published in Angewandte Chemie
Our latest developments in new materials to enable the cryopreservation of donor cells and tissues has been pubished in the leading chemistry journal, Angewandte Chemie! We have a major research program into addressing the challenge of how can we enable the distribution, storage and application of therapeutic cells; simply put, donor cells (e.g. for bone marrow, transplant) cannot be stored for long at room temperature, meaning they must be frozen - cryopreserved. However, cells simply dont like being frozen, and current methods involve adding organic solvents as 'antifreeze', which is a very useful method, but is not suitable for all cell types, 100 % cell recovery is not achieved and there are some toxicity issues.
In this work, we were inspired by the secondary structure (fold) of antifreeze glycoproteins (from polar fish), and made a mimic with the same structure, but composed of different units - poly(proline). By using a single building block, this system is very easy to obtain by various synthetic or biotechnolgoical methods. We found that this very simple structure was a (moderate) ice growth inhibitor and that it had patches of hydrophobicity, which we think is essential for activity. This new material was then used to enhance the cryopreservation of cells adhered to tissue culture plastic - this is a major advance as it is hard to store cells in this format, and they are normally stored in suspension. However, most applications and studies of cells are conducted as monolayers. Our collaborator, Dr Sylvain Deville in France, provided confocal cryomicroscopy to study how the polymers interacted with the ice crystals.
Read the paper here
Latest Work Published in ACS Macro Letters
Our latest work on antifreeze-protein mimetic polymers has been published in ACS Macro Letters. We have a major research interest in developing polymers which can mimic the function of antifreeze proteins; specifically their ability to slow the rate of ice crystal growth (recrystallisation). Ice recrystallisation is a major problem during the cryostorage of cells for medicine, transfusion, transplant and basic cell biology, hence understanding how these polymers function will help us make new, safer regenerative medicine treatments.
We have previously shown that poly(vinyl alcohol), PVA, is a remarkable ice growth inhibtor, but we do not really understand exactly how it works. Here we used column chromtography to isolate near-monodisperse fractions of PVA. The starting polymers, made by RAFT, would normally be described as being 'well defined' with a dispersity of 1.2 However, this still contains a complex mixture. This work showed that polymers with DP = 10, when monodisperse, had a lot less activity than DP 10 with more dispersity and the activity was attributed to the high molecular weight tails. This helped to us to identify how long a polymer must be, to be active (above ~12 units) and will guide our future work.
This work was conducted by an undergraduate student, Nick Vail during his MChem placement.
Graphenic Ice Nucleators Published in PCCP
Our latest work in mimicing Nature's solutions to controlling ice growth and formation has been published in Physical Chemistry, Chemical Physics. We have previously studied the use of synthetic polymers to mimic antifreeze proteins - essentially to stop ice crystals from growing larger, which has a major impact on cellular cryopreservation for regenerative medicine. However, the formation of ice (nucleation) is also an incredibly complex process which is also important in cell cryopreservation. There are few known ice nucleators and most are inorganic minerals (dust) rather than molecular systems. In this work, in collaboration with Jon Rourke, we took base washed graphene oxide (bwGO) as a scaffold to develop new nucleating agents. bwGO has epoxide groups, which we exploited to graft various thiols, including small molecules and polymers, to the surface. Using a multi-point nucleation assay we identified several candidates which were potent nucleators.
This is signifcant as it shows we can develop molecular systems to mimic ice nucleating proteins - proteins which are crucial for life, or even for making snow on ski slopes! (really..)
Read the paper here
Impact of Sequential Surface-Modification of Graphene Oxide on Ice Nucleation
Latest Work Published In J.A.C.S !
In our latest publication we describe an entirely new approach to mimicing antifreeze protein (AFP) function, using self-assembled metal complexes, in place of helical peptides. This work also provides insight into the fundemental design principles to mimic AFP function.
It is often assumed that the desirable property of IRI (ice recrystalisation inhibition), associated with AFPs, requries a specific 'match' or structure to interact with growing ice crystals. We have hypothesised that, in fact, key macromolecular features, rather than 'binding motifs' are what are required. Here we used self-assembled metal complexes which have similar dimensions and pitch to short helical antifreeze proteins as potent IRI's. Crucially, the ligands themselves are not water soluble, but the produced metal complexes are. Modelling showed that the active 'metallohelices' had 'patchy amphiphilicity'; in short, segregated domains of hydrophobic and hydrophilic character. There are not obvious ice-binding sites, and few hydrogen bond donors, confirming that amphipathicity (not amphiphilicity) is the crucial feature.
These results are exciting for both fundamental studies of ice/water interface, but to help us develop new cryoprotectants for low-temperature applications, especially cell/tissue cryopreservation.
The work was conducted in collaboration with the Scott and Fox groups, and can be found here;