Liquidus tracking is a cryopreservation technique developed to cope with samples that are unsuitable for preservation by conventional means such as controlled-rate freezing and ultra-fast vitrification.
In tissues, for example, extra-cellular ice can form during conventional freezing. In contrast to cell suspensions, this extra-cellular ice can be damaging as it is contained within the system being preserved.
Conventional controlled-rate freezing only tackles the problem of inter-cellular ice, and although conventional vitrification inherently prevents the formation of ice, it typically relies on ultra-fast cooling rates of around 20 000 oC/min; these fast rates are unachievable with large samples.
By slowly increasing the concentration of cryoprotectant during the preservation process, the Liquidus Tracker prevents the formation of ice crystals within the samples, allowing vitrification without the necessity for fast cooling rates. This slow vitrification is achieved by increasing the concentration of cryoprotectant while the sample is cooled; the cytotoxicity of the cryoprotectant decreases with temperature and as such higher concentrations can be tolerated at the lower temperatures.