Our recent work into how macromolecular antifreeze agents interact with ice was recently published in ACS Macroletters.
Enhancement of Macromolecular Ice Recrystallisation Inhibition Activity by Exploiting Depletion Forces
We have shown that the ice recrystallisation inhibition of poly(vinyl alcohol) can be improved by the addition of other, inactive macromolecules, in this case poly(ethylene glycol). The additive causes a depletant effect in the liquid channels between ice grains, driving PVA out of solution and on to the the ice crystal surface.
These results give greater insight into the mechanism behind poly(vinyl alcohol)'s antifreeze activity and open up a new suite of tools we can use to make potent antifreeze/cryopreservation agents.
Our perspective article on polyampholytes as emerging macromolecular cryoprotectants has been published in Biomacromolecules.
Polyampholytes as Emerging Macromolecular Cryoprotectants
This perspective is the first review type article on polyampholytes as cryoprotectants and it covers important contributions from both our group and other global leaders in this area.In this perspective we summarise typical methods of cryopreservation for mammalian cells and highlight some of the specific challenges. We then discuss the synthesis and properties of polyampholytes as macromolecular cryoprotectants and detail ways in which polyampholytes have been used to enhance mammalian cell cryopreservation. We further hypothesise about their specific function and how this exciting new field will develop.
Freezing cells made safer thanks to new polymer made at University of Warwick
- A new polymer that's a cryoprotectant dramatically improves the freezing of cells, has been discovered by Gibson Group researchers at the University of Warwick
- The new polymers can reduce the amount of organic solvent required in cryopreservation (freezing cells) as well as giving more and healthier cells after thawing.
- Findings may help reduce cost and improve distribution of cells for cell-based therapies, diagnostics and research.
Cell freezing (cryopreservation) – which is essential in cell transfusions as well as basic biomedical research – can be dramatically improved using a new polymeric cryoprotectant, discovered at the University of Warwick, which reduces the amount of ‘anti-freeze’ needed to protect cells.
The ability to freeze and store cells for cell-based therapies and research has taken a step forward in the paper ‘A synthetically scalable poly(ampholyte) which dramatically Enhances Cellular Cryopreservation.’ published by the University of Warwick’s Department of Chemistry and Medical School in the journal Biomacromolecules. The new polymer material protects the cells during freezing, leading to more cells being recovered and less solvent-based antifreeze being required.
Cryopreservation of cells is an essential process, enabling banking and distribution of cells, which would otherwise degrade. The current methods rely on adding traditional ‘antifreezes’ to the cells to protect them from the cold stress, but not all the cells are recovered and it is desirable to lower the amount of solvent added.
The new Warwick material was shown to allow cryopreservation using less solvent. In particular, the material was very potent at protecting cell monolayers – cells which are attached to a surface, which is the format of how they are grown and used in most biomedical research.
Having more, and better quality cells, is crucial not just for their use in medicine, but to improve the quality and accessibility of cells for the discovery of new drugs for example.
Cell-based therapies are emerging as the “fourth pillar” of chemo-therapy. New methods to help distribute and bank these cells will help make them more accessible and speed up their roll-out, and this new material may aid this process.
Our latest paper is ACS Editors' Choice Article
Optimization and Stability of Cell-Polymer Hybrids Obtained by ‘Clicking’ Synthetic Polymers to Metabolically-Labeled Cell Surface Glycans
Re-engineering of mammalian cell surfaces with polymers enables the introduction of functionality including imaging agents, drug cargoes or antibodies for cell-based therapies, without resorting to genetic techniques. Glycan metabolic labeling has been reported as a tool for engineering cell surface glycans with synthetic polymers through the installation of biorthogonal handles, such as azides. Quantitative assessment of this approach and the robustness of the engineered coatings has yet to be explored. Here, we graft poly(hydroxyethyl acrylamide) onto azido-labeled cell surface glycans using strain-promoted azide-alkyne ‘click’ cycloaddition and, using a combination of flow cytometry and confocal microscopy, evaluate the various parameters controlling the outcome of this ‘grafting to’ process. In all cases, homogenous cell coatings were formed with > 95% of the treated cells being covalently modified, superior to non-specific ‘grafting to’ approaches. Controllable grafting densities could be achieved through modulation of polymer chain length and/ or concentration, with longer polymers having lower densities. Cell surface bound polymers were retained for at least 72 hours, persisting through several mitotic divisions during this period. Furthermore, we postulate that glycan/membrane recycling is slowed by the steric bulk of the polymers, demonstrating robustness and stability even during normal biological processes. This cytocompatible, versatile and simple approach shows potential for re-engineering of cell surfaces with new functionality for future use in cell tracking or cell-based therapies.
Our latest work in ACS MacroLetters
Our latest work in the design of new materials to mimic complex glycan function and to inhibit bacterial toxins has been published in ACS Macro Letters. We have previously shown that synthetic polymers bearing carbohydrates in specific orientations or densities on polymer chains can give rise to increased affinity towards bacterial lectins (toxins) and may have application as decoys to prevent infection. However, many glycopolymers are rather basic simply having lots of glycans on a flexible polymer chain. In this work, we collaborated with Prof Filip du Prez (Gent, Belgium) using their thiolactone chemistry to enable us to introduce two functional units per repeat unit of the polymer. This was advantageous as it enabled us to mimic how GM-1 - a glycolipid on our cells - presents its glycans, but in a very simple manner. Using this, we made a library of glycopolymers with either 2 glycans or a hydrophobic unit. Using a combination of inhibitory assays and biolayer interferometry we unraveled the crucial design features to obtain highly active inhibits of lectin binding. This approach shows that moving from 'boring' homo-glycopolymers to those of increased complexity may help guide the development of materials to address the spread of infection.
Read the paper here
New Glycopolymers for Toxin Inhibition is published
Our latest work into the design of new materials to inhibit toxins has been published in JPOLA. We urgently need new strategies to combat bacterial (as well as viral and fungal) infections due to the rise of antimicrobial resistance and the rapid evolution of some pathogens. Many pathogens, such as cholera or E.Coli secrete toxic proteins which bind to carbohydrates on our cell surfaces leading, which is their first step in infection. We have a major research program into the design and synthesis of new materials which can act as decoys for these toxins, preventing the infection from occurring. In this work, we evaluated a new range of polymers which instead of just having a single monosaccharide displayed multiple different ones. Our new synthetic strategy enabled this, and the rapid testing of the polymers ability to inhibit toxins. We showed that polymers bearing two difference sugars often were more potent inhibitors than those with just a single sugar, and this seemed to be linked the total capacity of binding (i.e. how many toxins the polymer can capture) rather than the actual affinity.
Read the paper here
Paper Published in Macroletters
Our latest work has been published in ACS Macro Letters. In this work we describe a new method to covalent attached synthetic polymers to cell surfaces, enabling us to bring new functionality to them, without resorting to genetic methods. There already exist many chemistry for targetting cell surfaces, such as simple NHS esters, or lipid insertion, but we wanted to form a directed, covalent bond. Glycan metabolic labeling was exploited, whereby we added an azido-functional ManNac (a sugar) to the cells, which can be processed such that it presented an azide on the cell surface as sialic acid. We then made telechelic polymers used RAFT, adding an azide reactive strained alkyne at one end, and a fluorophore or biotin at the other. We would able to show selective conjugation and coating of the cells using these polymers, with no evidence of cytoxocity nor of morphological changes (i.e. the cells looked happy). To show that we can use this method to change the functionality of the cells, we were able to recruit streptavidin to the cell surfaces, targetting the biotin units on the polymer, which did not occur without the polymer. We think this method could be broadly used to add synthetic polymers to cell surfaces to modify their function, which may have application in therapies, cell tracking and also to ask fundamental questions about how this modification affects cell function.
Read the paper here
Paper Published in Langmuir
Our latest work has been published in Langmuir, as part of a special issue focussed on Mechano- and Cryo-biology, which we were very proud to be invited to contribute too. In this work, we ask the question of 'do our antifreeze-protein mimetic polymers function the same in nanoparticle form, as in solution'. This might seem straightforward, as we know that increasing the molecular weight of our polymers, increases their activity, hence when immobilised on a nanoparticle they might be more active. We actually saw that there was no enhancement, but also no decrease (which again is a surprise as the nanoparticles have a lower molar concentration than free polymers). We made use of RAFT/MADIX polymerization to make thiol-terminated poly(vinyl alcohol) to coat gold nanoparticles for this particular work, as model nanoparticle systems, which were tunable in terms of size and composition.
Read the paper here;