Two methods dominate the cryopreservation of biological samples, and they are not interchangeable. Vitrification freezes a sample so rapidly that ice crystals never form. Slow cooling — controlled-rate freezing — lowers the temperature along a programmed profile and lets the cell dehydrate in a controlled way.
Choosing the wrong method for a given sample type costs viability, and the loss usually stays invisible until thawing. This article sets out the technical case for vitrification vs. slow cooling and shows which sample needs which method.
Vitrification is an ultra-rapid cryopreservation technique that cools a sample at rates above 10,000 °C per minute, taking it directly into a glass-like amorphous state. Because water molecules have no time to arrange into a crystal lattice, no ice crystals form — and no mechanical membrane damage occurs.
The trade-off is a high concentration of cryoprotectants, typically ethylene glycol combined with DMSO at 30–40 % total concentration. These agents are cytotoxic, so exposure time before plunging into liquid nitrogen at –196 °C is strictly limited, often to under 90 seconds.
The common factor is very small volumes in the microlitre range, handled as individual, exceptionally valuable samples.
Slow cooling is programmed controlled-rate freezing, typically at 0.3 to 3 °C per minute. A controlled rate freezer such as the BIOFREEZE® BV45 from Consarctic® runs a defined temperature profile that osmotically dehydrates the cell before intracellular ice can form.
Slow cooling is superior wherever volume and reproducibility matter:
A 250 ml cryobag cannot be vitrified. Physics does not allow it: the required cooling rate is unreachable at that volume.
As a sample transitions from liquid to solid, it releases latent heat of crystallisation. This heat surge raises sample temperature abruptly and generates ice crystals at precisely the moment the protocol is designed to prevent them. It is the most common cause of unexplained viability loss in otherwise correctly executed protocols.
The TC-Aktiv function in the BIOFREEZE® detects this heat release inside the sample itself and triggers a pre-programmed shock-freeze step that dissipates it. The result is reproducibly high survival rates — across batches, and regardless of which operator runs the equipment.
Four questions decide the method:
In practice, many facilities run both methods in parallel — a fertility clinic vitrifies oocytes and embryos while freezing testicular tissue and sperm samples in a controlled rate freezer.
Whatever the freezing method, every sample ends in the same state — at –196 °C in liquid nitrogen. That is where it is decided whether the care taken during freezing was worth anything.
Above roughly –130 °C, the glass transition temperature of aqueous systems, recrystallisation begins: microscopic ice nuclei grow together and destroy exactly the structures vitrification was meant to protect. Every temperature excursion above that threshold is irreversible.
For reproductive medicine, Consarctic® supplies the ABV+ series (aluminium cryogenic containers from 4 to 150 litres for vials, bags and straws) and the ABS+ series (stainless steel cryogenic tanks). Both feature the eccentric tank opening, which reduces the evaporation surface, lowers vapour-phase temperature and cuts LN₂ consumption by up to 30 %. The rotatable base shortens retrieval time, and with it the time neighbouring samples spend exposed to warmth.
This is complemented by the Consarctic® Monitoring System, providing continuous level and temperature surveillance with remote access and alarm forwarding.
An excellent vitrification protocol inside a poorly monitored tank is a delayed risk. Consarctic GmbH therefore plans, installs and qualifies the entire chain — from the freezing instrument through the cryogenic tank and LN₂ supply to monitoring and cryogenic transport in the ASR+ dry shipper series.
All systems are manufactured to GMP-compliant standards and certified to EN ISO 13485:2016 and ISO 9001:2015. Commissioning includes full IQ/OQ documentation by certified technicians, and the 24/7 emergency service is available 365 days a year.
More than 1,500 customers in over 30 countries — including Charité Universitätsmedizin Berlin, the Max Planck Society and Qatar Biobank — rely on this infrastructure.
Vitrification cools a sample at over 10,000 °C/min so that no ice crystals form and the sample solidifies in a glass-like state. Slow cooling lowers temperature along a programmed profile at 0.3–3 °C/min and osmotically dehydrates the cell. Vitrification suits microvolumes such as oocytes and embryos; slow cooling suits cell suspensions, bags and GMP batches.
No. Vitrification is superior for oocytes and embryos, but it fails at larger volumes because the required cooling rate is physically unattainable. For stem cell products, cryobags and regulated batch processes, controlled slow cooling with a documented protocol is the method of choice.
For most mammalian cells, –1 °C/min is the standard starting point. The optimum is cell-type specific and lies between 0.3 and 3 °C/min. The BIOFREEZE® ships with pre-installed programs and allows fully customisable protocols.
At the phase transition the sample releases heat of crystallisation, briefly raising its temperature and producing ice crystals at exactly the wrong moment. The TC-Aktiv function in the BIOFREEZE® detects this heat release and compensates with an automatic shock-freeze step.
For reproductive medicine, Consarctic® supplies the ABV+ series (aluminium, 4–150 L) and the ABS+ series (stainless steel). Both accommodate vials, straws and bags, use an eccentric tank opening for stable vapour-phase temperatures, and integrate with the Consarctic® Monitoring System.
Vitrification and slow cooling are not competitors. They are two tools for two physical problems, and the choice is made per sample type. The cryogenic infrastructure behind them has to carry both, and stay stable for decades.
Planning a new cryopreservation programme, or reviewing your existing freezing protocols? The engineers at Consarctic GmbH advise on method selection, equipment and tank configuration, and qualified commissioning. Get in touch.