Putting cells on ice: Science-facts not science-fiction

A woman wakes to find that she’s trapped inside a cryogenic chamber. She has no recollection of who she is or how she got there. It’s been decades since her last breath.

The notion of “cryogenically” freezing someone to preserve their body far into the future has long been a science-fiction staple: in this case, I’m describing the opening scene of the 2021 Netflix thriller “Oxygen”, although I could be referencing “Alien”, “Futurama”, or a number of other TV classics. Far from fiction, however, the need to store human cells is a genuine concern for biomedical research and, increasingly, for society too.

When “cryogenics” is mentioned in popular media, what’s usually meant is cryopreservation – the scientific process of using sub-zero temperatures to preserve living organisms or biological materials. At these low temperatures (often approaching –200ºC) chemical reactions are drastically slowed, putting metabolism and natural aging processes on pause. When the need arises, the frozen material can then be warmed and its function restored without experiencing damage or decay. At least, that’s the idea.

This is an essential step used in many current medical treatments to extend the shelf-life of chemical ingredients or cells. Vaccines, including those which prevent COVID-19, are shipped and stored in this way. The freezing of reproductive cells like eggs and sperm is also a common method for preserving fertility. But it’s becoming even more important as scientific advancements change the way we treat diseases.

While traditional drugs can be manufactured in pill-form and stored in a medicine cabinet for months, new treatments for diseases including cancer involve fragile materials like cells or antibodies, requiring a more considered approach. Because they’re not stable for long periods of time outside of the body, cryopreservation is often required to transport these materials between patients and medical facilities. Unfortunately, things are rarely as easy as they appear on TV, and cryopreservation is no different. The underlying process is complex and fraught with danger, meaning that most things don’t make it out of a deep freeze in one piece. The source of all the problems: ice.

When biological matter is cooled below zero, ice formation is almost inevitable. Ice first appears as tiny crystals which then amass and grow over time. If you have a sweet tooth, you might have experienced this: it’s the same process that gives ice cream an unpleasant, grainy texture if it’s left out for too long. It’s not good for cells either. Ice can draw out water from cells causing severe dehydration, as well as squashing internal structures and rupturing the membranes which hold a cell together. For larger tissues and organs, blood vessels may be punctured, and the supply of oxygen and essential nutrients cut off. The outcome is irreversible and deadly internal damage.

Thankfully, teams of researchers all over the world are working together on this, and my team is one of them. The aim of my PhD is to identify new chemical additives, known as cryoprotectants, that can control ice growth and reduce the injury it causes.

I should point out that this strategy isn’t new. In fact, it’s been used for millennia, just not by humans. For many species living in harsh environments, cryoprotectants are their key to survival, enabling some truly remarkable feats. Take the Canadian wood frog, or Rana Sylvatica. While most animals seek refuge from winter’s chill in warmer spaces like burrows or nests, this wood frog has a different strategy. It spends the winter frozen, literally. As the temperature drops, ice fills the frogs’ internal cavities; their hearts stop beating and they stop breathing. For months they appear, as one researcher describes, like “hard icy stones carved in the shape of a frog”. Yet, when spring arrives the frogs waste no time. Within hours they thaw, perfectly unharmed, and hop away in search of a mate or food. They’ve cracked cryopreservation.

To accomplish this, the frogs accumulate cryoprotectants in their blood before entering their “popsicle” phase. Some of these cryoprotectants are natural antifreezes that lower the freezing temperature and prevent vital fluids from turning to ice. Others have been found to stick to ice directly, preventing the growth of larger, more harmful ice crystals. It’s this particular trick that we’re copying and engineering into synthetic cryoprotectants that can be used to safely freeze human cells. The trouble is we don’t understand exactly how this works, so my project is trying to fill in the gaps.

Given everything I’ve described, you might have started to picture the lab I work in: an icy-cold room flanked with deep freezers and frogs peering out from glass tanks. At least, these were my friends’ impressions.

The room I call a lab doesn’t actually look that different from most offices: computers whirring away, a smell of coffee lingering in the air, emails announcing their arrival. Despite appearances, we’re doing the same thing as our experimental counterparts are doing – clad in goggles and gloves – just down the hall: running experiments, collecting data and testing hypotheses. Welcome to the field of computational chemistry.

As a computational chemist, much of my PhD involves creating experiments in a computer using molecular simulations, a tool that allows you to peer into the mysterious world of atoms and molecules, and study their precise movement over time. The technique has been around for a while, but with recent technological advancements we can now run more complex experiments with greater ease and accuracy.

Like a virtual microscope, I’ve been using these simulations to understand and visualise how cryoprotectants can slow ice growth, mostly (thanks to COVID) from the comfort of my bedroom. Crucially, this computational work doesn’t happen in isolation, but in tandem with traditional experiments, reflecting the broader interdisciplinary approach that’s required to solve the most challenging scientific problems.

Our work has revealed important insights that should aid the discovery of new cryoprotectants that can control ice growth more effectively. Our hope is that this translates into improved cryopreservation outcomes that will one day transform cell cryopreservation from science-fiction into science-fact.