Making freezing cells safer and easier

Materials World magazine
29 Aug 2019

A new polymer is helping to make freezing cells safer. Idha Valeur takes a look.

A cryoprotectant polymer has been found to boost the longevity of frozen cells, by researchers at the University of Warwick, UK. Controlled freezing cells, known as cryopreservation, is vital for cell transfusions and other cell-based therapy methods.

In the paper, A synthetically scalable poly(ampholyte) which dramatically enhances cellular cryopreservation, published in Biomacromolecules, the researchers outline how the new polymer can protect the cells when they are frozen, enabling more to be recovered and reducing the need to use solvents during defrosting.

University of Warwick Professor, Matthew Gibson, told Materials World the main driver for the new polymer gel is to ensure scalability. ‘The polymer we invented is made in one step from a commodity polymer poly (methyl vinyl ether-co-maleic anhydride), which is available on a large scale and has been used as a bio-adhesive. We converted this into our desired polymer in a simple one-step reaction,’ he said.

Using fewer solvents when de-freezing is beneficial as it allows for higher recovery numbers. ‘Current cell cryopreservation strategies use dimethyl sulphoxide (DMSO), typically, which is a remarkable cryoprotectant and is used around the world. But it is not perfect. In our current work we looked at cell monolayers – cells attached to tissue culture plastic which is the standard format for testing and growing cells. If you try to freeze cells just using DMSO in this format, you get very few cells back, but we could increase that, in some cases, to 90% cell recovery by using our polymer, which is a major benefit in the workflow of using cells,’ Gibson explained.

‘Secondly, DMSO does have an impact on cells and if left in contact with them for too long post-thaw, it can cause problems. By adding our polymer, we could lower the DMSO concentration four-fold, but still get good recovery of cells, therefore reducing the potential side effects.

‘Finally, there are some cells which you cannot store well with DMSO, and we think the polymers could really have an impact there.’

Gibson said this study is not the first into using polyampholytes in cryopreservation, but that the process’ simplicity and scaleability makes it preferable to using a multi-step, challenging or expensive one.

‘Our material was optimised for cryopreservation benefit, and this is the most active material we have yet used in our lab, and it seems to give very significant benefits,’ he added.

Surprisingly, the new material is less effective at hindering ice growth – a function the team set out to understand. The new polymer from the current study has a more subtle mechanism that the team is examining as they ‘have evidence that they may interact with the cell membrane to protect that during cold stress’, Gibson said.

So far, the team has created tens of grams of the polymer gel in the lab, with the same result reported from an external partner. They are engaging with industry partners to put the system into real-world cryopreservation applications.