Methods for cryopreservation
The present invention relates to methods of cryopreservation and compositions for use in such methods where the methods utilise non-Newtonian fluid properties of the cryopreservation medium to modulate the viscosity of that medium to deliver an improved cryopreservation process.
1. A method for cryopreservation of a biological sample using a non-Newtonian fluid as a cryopreservation medium, wherein the method comprises applying a shear stress to control viscosity of the cryopreservation medium during a cryopreservation process, the process comprises the steps of:
a) contacting the biological sample with the non-Newtonian fluid to produce a contacted biological sample;
b) a first phase comprising applying the shear stress at a first shear rate to the contacted biological sample to produce a shear thinning stress to allow the cryopreservation medium to perfuse into the contacted biological sample to produce a perfused biological sample; and
c) a second phase comprising cooling the perfused biological sample and applying the shear stress at a second shear rate to the perfused biological sample to produce a shear thickening stress to prevent formation of ice crystals during cooling of the perfused biological sample;
wherein the method produces a cryopreserved biological sample;
wherein the non-Newtonian fluid consists essentially of an aqueous suspension or an aqueous solution containing 2 wt % to 60 wt % of a non-Newtonian additive that is a particulate material with a mean particle size of 10 μm or less; and from 10 wt % to 40 wt % of a cryoprotective agent.
2. The method for cryopreservation of a biological sample according to claim 1 , wherein applying the shear stress comprises applying a stress by mechanical, sonic, magnetic or electromagnetic field means thereto.
3. The method according to claim 1 , wherein the shear stress is applied at a first amplitude during the first phase and the shear stress is applied at a different amplitude during the second phase.
4. The method according to claim 1 , wherein the cryopreservation process comprises maintaining the shear thickening stress while cooling the sample to a temperature below the glass transition temperature of the biological sample.
5. The method according claim to claim 1 , wherein the cooling occurs at a rate of 50° C. per minute or less.
6. The method according to claim 1 , wherein the biological sample is maintained at a temperature below its glass transition temperature during the cooling of the biological sample.
7. The method according to claim 1 , wherein the particulate material used as the non-Newtonian additive is selected from silica (SiO 2 ), glass, titanium dioxide, calcium carbonate, alumina, quartz, iron oxide, a synthetic polymer, a starch or a biologically derived starch, or a mixture of two or more of these materials.
8. The method according to claim 1 , wherein the cryoprotective agent is present at 10 wt % to 40 wt % in the cryopreservation medium, wherein the cryoprotective agent is selected from the group comprising dimethyl sulfoxide, formamide, acetamide, C 1 -C 3 alcohols, 1,2-isopropyldiol, 1,2-propanediol, ethylene glycol, propylene glycol, glycerol, glucose, mono-saccharides, disaccharides, polysaccharides, ficoll, polyethylene glycol, polyvinylpyrollidine or a combination of two or more of these agents.
9. The method according to claim 7 , wherein the non-Newtonian additive is a biologically derived polymer that is hydroxyethyl starch (HES) at a concentration of 45 wt % to 55 wt % in the cryopreservation medium.
10. A method for reconstituting a cryopreserved biological sample cryopreserved by the method according to claim 1 , comprising the step of warming the cryopreserved biological sample to its glass transition point and applying a shear thickening stress at a temperature from below or at the glass transition temperature until the temperature of the cryopreserved biological sample rises above its freezing point.
11. The method of claim 1 , wherein the first shear rate is between 10 −4 s −1 to 0.5 s −1 .
12. The method of claim 1 , wherein the second shear rate is between 1 s −1 to 6 s −1 .
13. A cryopreservation medium with non-Newtonian fluid properties, consisting essentially of an aqueous solution or an aqueous suspension containing between 50 wt % and 60 wt % by weight of a particulate material with a mean particle size of 10 μm or less, and between 10 wt % to 40 wt % of a cryoprotective agent.
14. The cryopreservation medium according to claim 13 wherein the cryoprotective agent is selected from the group consisting of dimethyl sulfoxide, formamide, acetamide, C 1 -C 3 alcohols, 1,2-isopropyldiol, 1,2-propanediol, ethylene glycol, propylene glycol, glycerol, glucose, mono-saccharides, disaccharides, polysaccharides, ficoll, polyethylene glycol, polyvinylpyrollidine or a combination of two or more of these agents.
15. The cryopreservation medium according to claim 13 consisting of 50 wt % to 55 wt % hydroxyethyl starch (HES) as the particulate material, 5 wt % to 20 wt % of cryoprotective agent and water.
16. The cryopreservation medium according to claim 13 , wherein the cryoprotective agent is selected from dimethylsulphoxide (DMSO) or a combination of DMSO and one or more of sucrose, glucose, glycerol, raffinose, fructose or lactose.