Cryopreservation is the controlled freezing of biological samples to –196 °C in liquid nitrogen in order to preserve their viability for decades. At that temperature, biochemical reactions effectively stop. A cell no longer ages — it is paused.
The sentence is simple; the execution is not. Damage does not occur at –196 °C. It occurs on the way there. This article explains how cryogenic freezing works — the physics, the methods, and the equipment that holds both together.
A cell is roughly 70 % water. Water expands by about 9 % when it freezes and organises into a crystal lattice. That single fact produces the three damage mechanisms of cryopreservation:
Successful cryopreservation is therefore not a cold problem. It is a water and timing problem.
Cryoprotective agents suppress ice crystal formation. They fall into two groups:
Cryoprotectants are cytotoxic. Contact time, temperature at addition and stepwise removal during thawing are part of the protocol, not an afterthought.
The cooling rate determines where ice forms. Too fast, and intracellular water freezes before it can leave the cell — intracellular crystals. Too slow, and the cell over-dehydrates and is damaged by rising salt concentration.
Between those two failure modes lies a narrow optimum, and it differs for every cell type. For most mammalian cells, –1 °C per minute is the established starting point.
A controlled rate freezer such as the BIOFREEZE® BV45 from Consarctic® executes and records that profile. This is the real difference from a foam box in a –80 °C freezer: the box gives you an approximate rate with no evidence. A controlled rate freezer gives you a defined rate with documentation — the basic precondition for any GMP-regulated application.
During the liquid-to-solid phase transition, every sample releases latent heat of crystallisation. This heat abruptly raises sample temperature by several degrees, precisely inside the critical window.
The TC-Aktiv function in the BIOFREEZE® detects that heat release inside the sample and automatically triggers a pre-programmed shock-freeze step to dissipate it. The result is reproducibly high survival rates, independent of the operator.
The decisive value is the glass transition temperature of aqueous systems, at approximately –130 °C. Above it, water remains molecularly mobile; recrystallisation and residual enzymatic activity continue — slowly, but they continue.
That produces a clear dividing line:
If you need living cells preserved for decades, you need LN₂. Anything else is interim storage.
In liquid phase, the sample sits directly in liquid nitrogen. Temperature stability is maximal, but LN₂ can penetrate compromised closures and carry cross-contamination.
In vapour phase, the sample is stored above the LN₂ level. No direct liquid contact and therefore no contamination pathway — at the cost of a temperature gradient over tank height.
Consarctic® cryogenic tanks address that gradient structurally: the eccentric tank opening reduces the evaporation surface, lowers vapour-phase temperature and cuts LN₂ consumption by up to 30 %. In practice: vapour-phase safety without a temperature compromise.
Cryopreservation is a chain, and it is only as strong as its weakest link:
Consarctic GmbH delivers that chain from a single source — from initial planning through commissioning to ongoing support with 24/7 emergency service, 365 days a year, for customers in more than 30 countries.
The sample is treated with cryoprotectants, cooled along a defined temperature protocol, and then stored at –196 °C in liquid nitrogen. Below –130 °C all biological processes stop, so the sample remains unchanged for decades.
With uninterrupted storage below –130 °C, storage duration is theoretically unlimited, because no biochemical degradation takes place. Successful thaws after more than 25 years are clinically documented. What matters is not elapsed time but uninterrupted temperature stability.
–80 °C is above the glass transition temperature of roughly –130 °C. Water stays molecularly mobile, and recrystallisation and residual enzymatic activity slowly continue. That is acceptable for months to a few years, but not for preserving cellular viability across decades.
In liquid phase the sample sits in liquid nitrogen — maximum temperature stability, but a contamination risk from LN₂ ingress. In vapour phase it is stored above the liquid: no liquid contact and therefore no cross-contamination pathway, at the cost of a temperature gradient the tank design must control.
DMSO is a permeating cryoprotectant. It enters the cell, binds water and depresses the freezing point so that less intracellular ice forms. Typical concentration for cell suspensions is 5–10 %. Because DMSO is cytotoxic, contact time and removal during thawing must be documented.
Cryopreservation works when three things come together: the right protocol, an instrument that demonstrably holds that protocol, and storage that never rises above –130 °C for decades.
Building a cryopreservation programme, or reviewing an existing one? Consarctic GmbH supports you from concept through qualified commissioning to ongoing service. Talk to our engineers.