Effect of ice nucleation by droplet of immobilized silver iodide on freezing of rabbit and bovine embryos

Engineered Compounds to Control Ice Nucleation and Recrystallization

One of the greatest concerns in the subzero storage of cells, tissues, and organs is the ability to control the nucleation or recrystallization of ice. In nature, evidence of these processes, which aid in sustaining internal temperatures below the physiologic freezing point for extended periods of time, is apparent in freeze-avoidant and freeze-tolerant organisms. After decades of studying these proteins, we now have easily accessible compounds and materials capable of recapitulating the mechanisms seen in nature for biopreser-vation applications. The output from this burgeoning area of research can interact synergistically with other novel developments in the field of cryobiology, making it an opportune time for a review on this topic.

A highly active mineral-based ice nucleating agent supports in situ cell cryopreservation in a high throughput format

Cryopreservation of biological matter in microlitre scale volumes of liquid would be useful for a range of applications. At present, it is challenging because small volumes of water tend to supercool, and deep supercooling is known to lead to poor post-thaw cell viability. Here, we show that a mineral ice nucleator can almost eliminate supercooling in 100 µl liquid volumes during cryopreservation. This strategy of eliminating supercooling greatly enhances cell viability relative to cryopreservation protocols with uncontrolled ice nucleation. Using infrared thermography, we demonstrate a direct relationship between the extent of supercooling and post-thaw cell viability. Using a mineral nucleator delivery system, we open the door to the routine cryopreservation of mammalian cells in multiwell plates for applications such as high throughput toxicology testing of pharmaceutical products and regenerative medicine.

Pollen derived macromolecules serve as a new class of ice-nucleating cryoprotectants

Cryopreservation of biological material is vital for existing and emerging biomedical and biotechnological research and related applications, but there remain significant challenges. Cryopreservation of cells in sub-milliliter volumes is difficult because they tend to deeply supercool, favoring lethal intracellular ice formation. Some tree pollens are known to produce polysaccharides capable of nucleating ice at warm sub-zero temperatures. Here we demonstrated that aqueous extractions from European hornbeam pollen (pollen washing water, PWW) increased ice nucleation temperatures in 96-well plates from ≈ − 13 °C to ≈ − 7 °C. Application of PWW to the cryopreservation of immortalized T-cells in 96-well plates resulted in an increase of post-thaw metabolic activity from 63.9% (95% CI [58.5 to 69.2%]) to 97.4% (95% CI [86.5 to 108.2%]) of unfrozen control. When applied to cryopreservation of immortalized lung carcinoma monolayers, PWW dramatically increased post-thaw metabolic activity, from 1.6% (95% CI [− 6.6 to 9.79%]) to 55.0% (95% CI [41.6 to 68.4%]). In contrast to other ice nucleating agents, PWW is soluble, sterile and has low cytotoxicity meaning it can be readily incorporated into existing cryopreservation procedures. As such, it can be regarded as a unique class of cryoprotectant which acts by inducing ice nucleation at warm temperatures.

Sand-mediated ice seeding enables serum-free low-cryoprotectant cryopreservation of human induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) possess tremendous potential for tissue regeneration and banking hiPSCs by cryopreservation for their ready availability is crucial to their widespread use. However, contemporary methods for hiPSC cryopreservation are associated with both limited cell survival and high concentration of toxic cryoprotectants and/or serum. The latter may cause spontaneous differentiation and/or introduce xenogeneic factors, which may compromise the quality of hiPSCs. Here, sand from nature is discovered to be capable of seeding ice above -10 °C, which enables cryopreservation of hiPSCs with no serum, much-reduced cryoprotectant, and high cell survival. Furthermore, the cryopreserved hiPSCs retain high pluripotency and functions judged by their pluripotency marker expression, cell cycle analysis, and capability of differentiation into the three germ layers. This unique sand-mediated cryopreservation method may greatly facilitate the convenient and ready availability of high-quality hiPSCs and probably many other types of cells/tissues for the emerging cell-based translational medicine.

High Sub-Zero Organ Preservation: A Paradigm of Nature-Inspired Strategies

The field of organ preservation is filled with advancements that have yet to see widespread clinical translation, with some of the more notable strategies deriving their inspiration from nature. While static cold storage (SCS) at 2 °C to 4 °C is the current state-of-the-art, it contributes to the current shortage of transplantable organs due to the limited preservation times it affords combined with the limited ability of marginal grafts (i.e. those at risk for post-transplant dysfunction or primary non-function) to tolerate SCS. The era of storage solution optimization to minimize SCS-induced hypothermic injury has plateaued in its improvements, resulting in a shift towards the use of machine perfusion systems to oxygenate organs at normothermic, sub-normothermic, or hypothermic temperatures, as well as the use of sub-zero storage temperatures to leverage the protection brought forth by a reduction in metabolic demand. Many of the rigors that organs are subjected to at low sub-zero temperatures (-80 °C to -196 °C) commonly used for mammalian cell preservation have yet to be surmounted. Therefore, this article focuses on an intermediate temperature range (0 °C to -20 °C), where much success has been seen in the past two decades. The mechanisms leveraged by organisms capable of withstanding prolonged periods at these temperatures through either avoiding or tolerating the formation of ice has provided a foundation for some of the more promising efforts. This article therefore aims to contextualize the translation of these strategies into the realm of mammalian organ preservation.

Ice nucleating agents allow embryo freezing without manual seeding

Embryo slow freezing protocols include a nucleation induction step called manual seeding. This step is time consuming, manipulator dependent and hard to standardize. It requires access to samples, which is not always possible within the configuration of systems, such as differential scanning calorimeters or cryomicroscopes. Ice nucleation can be induced by other methods, e.g., by the use of ice nucleating agents. Snomax is a commercial preparation of inactivated proteins extracted from Pseudomonas syringae. The aim of our study was to investigate if Snomax can be an alternative to manual seeding in the slow freezing of mouse embryos. The influence of Snomax on the pH and osmolality of the freezing medium was evaluated. In vitro development (blastocyst formation and hatching rates) of fresh embryos exposed to Snomax and embryo cryopreserved with and without Snomax was assessed. The mitochondrial activity of frozen-thawed blastocysts was assessed by JC-1 fluorescent staining. Snomax didn't alter the physicochemical properties of the freezing medium, and did not affect embryo development of fresh embryos. After cryopreservation, the substitution of manual seeding by the ice nucleating agent (INA) Snomax did not affect embryo development or embryo mitochondrial activity. In conclusion, Snomax seems to be an effective ice nucleating agent for the slow freezing of mouse embryos. Snomax can also be a valuable alternative to manual seeding in research protocols in which manual seeding cannot be performed (i.e., differential scanning calorimetry and cryomicroscopy).

Cryopreservation of encapsulated liver spheroids for a bioartificial liver: reducing latent cryoinjury using an ice nucleating agent

INTRODUCTION

Acute liver failure has high mortality due to donor organ shortages. A bioartificial liver could "bridge the gap" to transplant or spontaneous recovery. Alginate encapsulation of HepG2 cells enables cell spheroid formation, thus providing sufficient functional biomass. Cryopreservation (CryoP) of these spheroids would allow an off-the-shelf capability for unpredictable emergency use. Cell death during CryoP often results from intracellular ice formation, after supercooling. An ice nucleating agent (INA), crystalline cholesterol, was trialled to reduce supercooling and subsequent cryoinjury.

MATERIALS AND METHODS

Spheroids were cooled in a controlled rate freezer in 12% dimethylsulfoxide/Celsior +/- INA, and sample temperatures were recorded throughout. Viability was assessed using fluorescent staining with image analysis, cell number by nuclei count, function using assays to detect liver-specific protein synthesis and secretion, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) reduction, and broad-spectrum cytochrome P450 activity.

RESULTS

Spheroids cryopreserved without INA displayed latent cryoinjury in the first 6 h after thawing. INA reduced supercooling during CryoP and also latent cryoinjury. Cell numbers, viability, and function as measured over 72 h post-thaw were all improved when INA was present during CryoP.

Survival of bull spermatozoa seeded and frozen at different rates in egg yolk-tris and whole milk extenders

Six factorially arranged experiments were designed to study effects of seeding, freezing, and thawing rates in whole milk and egg yolk-Tris extenders commonly used for commercial cryopreservation of bull sperm. In these extenders, semen normally is supercooled to -13 or -14 degrees C unless the sperm are seeded. When sperm were supercooled or seeded, either mechanically or with immobilized silver iodide, and frozen to -196 degrees C, the postthaw percentages of motile sperm were 59, 57, and 64%, respectively. Freezing rates of -15, -25, and -35 degrees C/min gave similar sperm survival rates and were superior to -5 degrees C/min. For milk, the critical freezing temperature extended to -75 degrees C before transfer to liquid nitrogen gave good results. For egg yolk-Tris extender, transfer to liquid nitrogen was less critical once -50 degrees C had been attained. Thawing of sperm in water baths at 25 and 45 degrees C gave similar results, and both temperatures were superior to 5 degrees C. The postthaw percentage of motile sperm in egg yolk-Tris was equal or superior to that of sperm frozen in milk. A freezing rate of -15 degrees C/min to -100 degrees C and thawing at 25 degrees C consistently gave good results.

Protein interaction with ice

Many organisms have evolved novel mechanisms to minimize freezing injury due to extracellular ice formation. This article reviews our present knowledge on the structure and mode of action of two types of proteins capable of ice interaction. The antifreeze proteins inhibit ice crystal formation and alter ice growth habits. The ice nucleation proteins, on the other hand, provide a proper template to stimulate ice growth. The potential applications of these proteins in different industries are discussed.