Asymptote Ltd.

Asymptote launches liquid nitrogen free controlled rate freezer

Asymptote will be launching an innovative liquid nitrogen-free controlled rate freezer at MEDICA 2006.

Their controlled-rate freezer successfully freezes embryos, stem cells and sperm without the need for potentially contaminating liquid nitrogen, reports a study accepted for publication in the journal Reproductive Bio Medicine Online.


The EF600 freezer is the first piece of controlled rate equipment which does not use liquid nitrogen to freeze cells used in IVF.

Although conventional liquid nitrogen freezers accurately control cooling, samples are placed at risk of contamination from liquid nitrogen-borne bacteria and are unsuitable for use in sterile environments. Laboratories which operate under sterile conditions, or require high air quality, should avoid the use of liquid nitrogen freezers, for example laboratories freezing cells for use in cell therapy.

Asymptote’s liquid nitrogen-free freezer removes the risk of samples being contaminated during freezing. It does not compromise sterility and can be used in cleanrooms.

The freezer relies on technology more commonly found in aerospace applications: a Stirling Cycle Cryocooler. The Cryocooler is an electrically-powered cooler that reaches temperatures below -100ºC in the freezer, low enough to cryopreserve cells. It provides a highly reliable alternative to liquid nitrogen based freezers, having a backup (UPS) power supply and no dependence on cryogens.

Although alternative refrigeration methods are potentially available, such as Peltier modules and mechanical compressors, they either lack the cooling ability or are too large and cumbersome to be suitable for use as laboratory scale cryopreservation equipment.

Embryos and stem cells need to follow precisely controlled cooling profiles to ensure a high survival on thawing. The study showed that mouse embryos, human embryonic stem cells and human sperm frozen in the nitrogen-free freezer all had a good survival rate on thawing. The survival rate was similar to samples frozen in a conventional liquid nitrogen freezer.

The freezer is small and simple to operate. It does not have the problems associated with storing and handling liquid nitrogen, and the running cost of the nitrogen-free freezer is estimated to be just 1% of a liquid nitrogen freezer.

Studies are also being carried out on horse sperm and have shown the freezer’s ability to freeze larger volumes of cell suspensions in bags. The freezer can be used either in the laboratory or as a portable device powered from a car battery. This makes it ideal for veterinary and conservation work where the need for large amounts of liquid nitrogen has previously hindered collections and experiments in the field.