Liquidus Tracker

The latest issue of Cryo Letters has details of a report on a new technique for long term storage of human cartilage. Alasdair Kay, lead author - shown in our photo - has been working with a novel vitrification machine, that we are pioneering, which was developed for Prof David Pegg of the University of York. Alasdair is using it at the Tissue Services laboratory in the NHS Blood and Transplant research section at Speke, Liverpool.  In his paper, which was presented recently at a meeting of the Society for Low Temperature Biology, he points out that standard cryopreservation techniques give poor post-thaw functional cell survival rates due to extracellular and intracellular crystallisation of ice in the chondrons. This impacts the ability to store transplant material,  although the need is potentially very large with some 60,000 knee replacements performed in the UK every year. Currently allograft material can be stored 3 to 4 weeks but transplants are restricted by availability of donor tissue, as cryoprotectant toxicity limits successful cryo preservation. However, the paper (co authored with Messrs Budarina, Grindley, Pegg, Kearney and Rooney) gives early positive indications that a new controlled vitrification process may work. The aim is to achieve the long-term banking of whole femoral condyles from deceased donor human knee joints and to provide them as living allografts to surgeons on demand.

In the process, increasing concentrations of cryoprotectant are supplied during cooling, sufficient to prevent freezing. Toxicity is minimised, by supplying only the concentration required to inhibit crystallisation at the actual temperature reached.  This  ‘liquidus tracking’ technique  builds on a procedure that was highly effective at maintaining cell  functionality levels at 75 – 95% in ovine articular cartilage; dimethyl sulphoxide (Me2SO) is applied to femoral condyles in progressively  increasing concentrations, whilst tissue is cooled to ultra-low  temperatures.  Data was collected in this case to ascertain the kinetics of cryoprotective agents (CPA) transport into whole femoral condyles.  Measurements of tissue CPAs were progressively taken from 0°C to -80°C and the cryo protectant concentration adjustments were made to ensure sufficient cryoprotectant was present to protect the tissue from ice formation. A reversed two stage warming procedure and structural and functional testing is currently underway to ensure the tissue is not affected by these processes.

See the report at

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