Cryoprotectants: A review of the actions and applications of cryoprotective solutes that modulate cell recovery from ultra-low temperatures

Immature mDA neurons ameliorate motor deficits in a 6-OHDA Parkinson's disease mouse model and are functional after cryopreservation

Parkinson's disease is associated with the loss of dopaminergic neurons in the midbrain. Clinical studies investigating replacement of these neurons with in vitro-generated neurons are currently underway. However, this approach has been limited by difficulties in scaling up on-demand production of midbrain dopaminergic (mDA) neurons from pluripotent stem cells. Cryo-preservation may offer a solution, as it allows for banking of quality controlled mDA neurons. In this study, we tested different freezing conditions and found that optimal cryopreservation of immature human mDA neurons at an early differentiation time point was achieved in STEM-CELLBANKER medium using a controlled freezing program.

Using natural honey as an anti-oxidant and thermodynamically efficient cryoprotectant in embryo vitrification

Embryo cryopreservation is a common practice in reproductive biology and infertility treatments. Despite major improvements over years, the cryoprotectant solutions are still a major source of concern, mostly due to their chemical toxicity and suboptimal protection against cryoinjuries. In this work, we introduced natural honey as a non-permeating cryoprotectant to replace traditionally used sucrose in embryo vitrification. The proposed media were compared with conventional ones by evaluating vitrified/warmed mouse embryos based on their re-expansion, hatching rate and transcription pattern of selected genes involved in heat-shock response, apoptosis and oxidative stress. Despite the similar high re-expansion rate, molecular fingerprint of the cryopreservation is remarkably reduced when honey is used instead of sucrose. The biological response of the proposed media was explained from a fundamental point of view using antioxidant analysis, DSC and GC techniques. It was found that the proposed honey-based medium is less thermodynamically prone to ice formation, which along with its antioxidant capacity can control the production of oxygen radicals and minimize the stress-induced transcriptional response. Furthermore, this work tries to correlate the physico-chemical properties of the vitrification solutions with the cellular and molecular aspects of the cryopreservation and proposes the application of natural cryoprotectants in cryobiology.

Transcriptional analysis of insect extreme freeze tolerance

Few invertebrates can survive cryopreservation in liquid nitrogen, and the mechanisms by which some species do survive are underexplored, despite high application potential. Here, we turn to the drosophilid Chymomyza costata to strengthen our fundamental understanding of extreme freeze tolerance and gain insights about potential avenues for cryopreservation of biological materials. We first use RNAseq to generate transcriptomes of three C. costata larval phenotypic variants: those warm-acclimated in early or late diapause (weak capacity to survive cryopreservation), and those undergoing cold acclimation after diapause entry (extremely freeze tolerant, surviving cryopreservation). We identify mRNA transcripts representing genes and processes that accompany the physiological transition to extreme freeze tolerance and relate cryopreservation survival to the transcriptional profiles of select candidate genes using extended sampling of phenotypic variants. Enhanced capacity for protein folding, refolding and processing appears to be a central theme of extreme freeze tolerance and may allow cold-acclimated larvae to repair or eliminate proteins damaged by freezing (thus mitigating the toxicity of denatured proteins, endoplasmic reticulum stress and subsequent apoptosis). We also find a number of candidate genes (including both known and potentially novel, unannotated sequences) whose expression profiles tightly mirror the change in extreme freeze tolerance status among phenotypic variants.

Cryoprotectants synergy improve zebrafish sperm cryopreservation and offspring skeletogenesis

The synergy obtained by the combination of cryoprotectants is a successful strategy that can be beneficial on the optimization of zebrafish sperm cryopreservation. Recently, a protocol was established for this species using an electric ultrafreezer (-150 °C) performing cooling rate (-66 °C/min) and storage within one step. The ultimate objective of sperm cryopreservation is to generate healthy offspring. Therefore, the objective of this study was to select the most adequate cryoprotectant combination, for the previously established protocol, that generate high quality offspring with normal skeletogenesis. Among the permeating cryoprotectant concentrations studied 12.5% and 15% of N,N-dimethylformamide (DMF) yielded high post-thaw sperm quality and hatching rates. For these two concentrations, the presence of bovine serum albumin (10 mg/mL), egg yolk (10%), glycine (30 mM) and bicine (50 mM) was evaluated for post-thaw sperm motility, viability, in vitro fertilization success and offspring skeletal development (30 days post fertilization). Higher concentration of permeating cryoprotectant (15%) decreased the incidence of deformed arches and severe skeletal malformations, which suggests higher capacity to protect the cell against cold stress and DNA damage. Extender containing 15% DMF with Ctrl, Bicine and egg yolk were the non-permeating cryoprotectants with higher post-thaw quality. The use of these compounds results in a reduction in vertebral fusions, compressions and severity of skeletal malformations in the offspring. Therefore, these extender compositions are beneficial for the quality of zebrafish offspring sired by cryopreserved sperm with -66 °C/min freezing rate. To the best of our knowledge, this is the first report on skeletal development of the offspring sired by cryopreserved sperm performed with different freezing media compositions in zebrafish.

Glass polymorphism and liquid-liquid phase transition in aqueous solutions: experiments and computer simulations

One of the most intriguing anomalies of water is its ability to exist as distinct amorphous ice forms (glass polymorphism or polyamorphism). This resonates well with the possible first-order liquid-liquid phase transition (LLPT) in the supercooled state, where ice is the stable phase. In this Perspective, we review experiments and computer simulations that search for LLPT and polyamorphism in aqueous solutions containing salts and alcohols. Most studies on ionic solutes are devoted to NaCl and LiCl; studies on alcohols have mainly focused on glycerol. Less attention has been paid to protein solutions and hydrophobic solutes, even though they reveal promising avenues. While all solutions show polyamorphism and an LLPT only in dilute, sub-eutectic mixtures, there are differences regarding the nature of the transition. Isocompositional transitions for varying mole fractions are observed in alcohol but not in ionic solutions. This is because water can surround alcohol molecules either in a low- or high-density configuration whereas for ionic solutes, the water ion hydration shell is forced into high-density structures. Consequently, the polyamorphic transition and the LLPT are prevented near the ions, but take place in patches of water within the solutions. We highlight discrepancies and different interpretations within the experimental community as well as the key challenges that need consideration when comparing experiments and simulations. We point out where reinterpretation of past studies helps to draw a unified, consistent picture. In addition to the literature review, we provide original experimental results. A list of eleven open questions that need further consideration is identified.

The Impact of Salts on the Ice Recrystallization Inhibition Activity of Antifreeze (Glyco)Proteins

Antifreeze (glyco)proteins (AF(G)Ps) have received increasing attention as potential cryopreservation agents since their discovery in the 1970s. While cryopreservation strategies for specific cells (such as red blood cells) are successful and widely implemented, preservation of other cell types, tissues and whole organs remains challenging. This is due to the multifactorial nature of the freeze-thaw damage, the complexity of preserving biological matter and the (country-to-country) variability of the employed procedures and regulations. AF(G)Ps are well-known for their ability to modulate ice crystal growth morphology and ice recrystallization inhibition (IRI), both of which are considered key contributors to freeze-thaw damage. To date, however, the impact of AF(G)Ps on cell survival remains at best partially understood as conflicting results on the benefits or disadvantages of including AF(G)P in cryopreservation strategies remain unelucidated. We hypothesize that variability in the additives in the cryopreservation media contributes to the observed discrepancies. To critically examine this idea, we monitored the inhibition of ice recrystallization by AF(G)P in the presence of various salts using a quantitative analysis of optical microscopy images via the Lifshitz-Slyozov-Wagner (LSW) theory for Oswald ripening. We found that the addition of salts, which are used in culture and cryopreservation media, enhances the IRI activity of AF(G)Ps, and that the magnitude of the enhancement was in line with the Hofmeister series. The size of ice crystals grown in AFGP_1–5 and type III AFP samples containing chloride, phosphate and citrate ions were statistically smaller after 90 min of incubation than crystals grown in the absence of these salts. The ice recrystallization rates (k_d) of AFGP_1–5 and type III AFP samples prepared at a fixed overall ionic strength of 100 mM progressively decreased following the Hofmeister series for anions. Our results demonstrate that the performance of AF(G)Ps is significantly influenced by additives present in common cryopreservation media. It is thus important to conduct excipient compatibility experiments to identify potential incompatibilities between additives and AF(G)Ps in cryopreservation formulations.

Semen cryopreservation for the Mediterranean brown trout of the Biferno River (Molise-Italy): comparative study on the effects of basic extenders and cryoprotectants

This study was designed to optimize the semen freezing protocol of the native Mediterranean brown trout inhabiting the Molise rivers through two experiments: an in vitro analysis of the effects of two basic extenders combined with three cryoprotectants on post-thaw semen quality; and an in vivo test to assess the fertilization and hatching rate. Semen was diluted at a ratio of 1:3 in a freezing medium composed of a glucose extender (A) or mineral extender (B). Each basic component contained 10% dimethylsulfoxide, dimethylacetamide or methanol. The post-semen quality was evaluated considering motility, duration of motility, viability and DNA integrity. The basic extender and cryoprotectant were shown to have significant effects on these variables, and the best results were obtained using extender A or B combined with dimethylsulfoxide (P < 0.05). These freezing protocols were selected for fertilization trials in vivo. Fertilization and hatching rates were significantly higher in fresh semen. No significant differences were observed in frozen semen using extender A or B, although higher percentages of eyed eggs and hatching rates were recorded using extender A. According to our in vitro and in vivo results, the glucose-based extender and dimethylsulfoxide emerged as the best combination for an effective cryopreservation protocol for semen of this trout.

FTIR Analysis of Molecular Changes Associated with Warming Injury in Cryopreserved Leukocytes

In this article, we explored the effects of cooling rate, dimethyl sulfoxide (DMSO) concentration, and thawing protocol on the post-thaw viability of frozen human white blood cells (WBCs). Different cooling rates (1, 2, 5, 10, 20, and 50 °C/min) at two DMSO concentrations (5 and 10% v/v) were tested as the samples were cooled to -120 °C. Frozen samples were thawed following either a fast (100 °C/min) or slow (2 °C/min) warming protocol applied in either a single stage or in two stages interrupted by a 6 min hold at -40, -50, -60, -70, or -80 °C. The highest post-thaw viability was obtained when WBCs were cooled at 2 °C/min in a 5% DMSO solution and warmed at the fastest rate (100 °C/min) without any interruption. Post-thaw viability decreased when the warming rate was reduced or when rapid warming was interrupted by a hold at a temperature below -60 °C. To elucidate the mechanisms of warming injury in addition to the biological response, several key interfacial and molecular phenomena require greater understanding; thus, we used Fourier transform infrared (FTIR) spectroscopy to investigate the roles of molecular structure and conformation in damage to cryopreserved WBCs during warming. During warming, FTIR spectra revealed the accumulation of cellular protein and lipid membrane damage below -60 °C if the samples were thawed slowly at 2 °C/min. The results presented here suggest that irreversible alterations of biomolecular structure are correlated with cell injury during warming; these deleterious effects appeared to be caused by one or more low-temperature kinetic processes, consistent with eutectic formation/melting and/or devitrification in the intracellular milieu.

New Approaches to Cryopreservation of Cells, Tissues, and Organs

In this concept article, we outline a variety of new approaches that have been conceived to address some of the remaining challenges for developing improved methods of biopreservation. This recognizes a true renaissance and variety of complimentary, high-potential approaches leveraging inspiration by nature, nanotechnology, the thermodynamics of pressure, and several other key fields. Development of an organ and tissue supply chain that can meet the healthcare demands of the 21st century means overcoming twin challenges of (1) having enough of these lifesaving resources and (2) having the means to store and transport them for a variety of applications. Each has distinct but overlapping logistical limitations affecting transplantation, regenerative medicine, and drug discovery, with challenges shared among major areas of biomedicine including tissue engineering, trauma care, transfusion medicine, and biomedical research. There are several approaches to biopreservation, the optimum choice of which is dictated by the nature and complexity of the tissue and the required length of storage. Short-term hypothermic storage at temperatures a few degrees above the freezing point has provided the basis for nearly all methods of preserving tissues and solid organs that, to date, have proved refractory to cryopreservation techniques successfully developed for single-cell systems. In essence, these short-term techniques have been based on designing solutions for cellular protection against the effects of warm and cold ischemia and basically rely upon the protective effects of reduced temperatures brought about by Arrhenius kinetics of chemical reactions. However, further optimization of such preservation strategies is now seen to be restricted. Long-term preservation calls for much lower temperatures and requires the tissue to withstand the rigors of heat and mass transfer during protocols designed to optimize cooling and warming in the presence of cryoprotective agents. It is now accepted that with current methods of cryopreservation, uncontrolled ice formation in structured tissues and organs at subzero temperatures is the single most critical factor that severely restricts the extent to which tissues can survive procedures involving freezing and thawing. In recent years, this major problem has been effectively circumvented in some tissues by using ice-free cryopreservation techniques based upon vitrification. Nevertheless, despite these promising advances there remain several recognized hurdles to be overcome before deep-subzero cryopreservation, either by classic freezing and thawing or by vitrification, can provide the much-needed means for biobanking complex tissues and organs for extended periods of weeks, months, or even years. In many cases, the approaches outlined here, including new underexplored paradigms of high-subzero preservation, are novel and inspired by mechanisms of freeze tolerance, or freeze avoidance, in nature. Others apply new bioengineering techniques such as nanotechnology, isochoric pressure preservation, and non-Newtonian fluids to circumvent currently intractable problems in cryopreservation.

Technical Considerations in the Freezing, Low-Temperature Storage and Thawing of Stem Cells for Cellular Therapies

The commercial and clinical development of cellular therapy products will invariably require cryopreservation and frozen storage of cellular starting materials, intermediates and/or final product. Optimising cryopreservation is as important as optimisation of the cell culture process in obtaining maximum yield and a consistent end-product. Suboptimal cryopreservation can lead not only to batch-to-batch variation, lowered cellular functionality and reduced cell yield, but also to the potential selection of subpopulations with genetic or epigenetic characteristics divergent from the original cell line. Regulatory requirements also impact on cryopreservation as these will require a robust and reproducible approach to the freezing, storage and thawing of the product. This requires attention to all aspects of the application of low temperatures: from the choice of freezing container and cryoprotectant, the cooling rate employed and its mode of de-livery, the correct handling of the frozen material during storage and transportation, to the eventual thawing of the product by the end-user. Each of these influences all of the others to a greater or lesser extent and none should be ignored. This paper seeks to provide practical insights and alternative solutions to the technical challenges faced during cryopreservation of cells for use in cellular therapies.

Evaluation of five additives to mitigate toxicity of cryoprotective agents on porcine chondrocytes

Cryoprotective agents (CPAs) are used in cryopreservation protocols to achieve vitrification. However, the high CPA concentrations required to vitrify a tissue such as articular cartilage are a major drawback due to their cellular toxicity. Oxidation is one factor related to CPA toxicity to cells and tissues. Addition of antioxidants has proven to be beneficial to cell survival and cellular functions after cryopreservation. Investigation of additives for mitigating cellular CPA toxicity will aid in developing successful cryopreservation protocols. The current work shows that antioxidant additives can reduce the toxic effect of CPAs on porcine chondrocytes. Our findings showed that chondroitin sulphate, glucosamine, 2,3,5,6-tetramethylpyrazine and ascorbic acid improved chondrocyte cell survival after exposure to high concentrations of CPAs according to a live-dead cell viability assay. In addition, similar results were seen when additives were added during CPA removal and articular cartilage sample incubation post CPA exposure. Furthermore, we found that incubation of articular cartilage in the presence of additives for 2 days improved chondrocyte recovery compared with those incubated for 4 days. The current results indicated that the inclusion of antioxidant additives during exposure to high concentrations of CPAs is beneficial to chondrocyte survival and recovery in porcine articular cartilage and provided knowledge to improve vitrification protocols for tissue banking of articular cartilage.

Cryopreservation by vitrification: a promising approach for transplant organ banking

PURPOSE OF REVIEW

The objective of this review is to describe the physical and biological barriers to organ cryopreservation, historic approaches for conventional cryopreservation and evolving techniques for ice-free cryopreservation by vitrification.

RECENT FINDINGS

Vitrification is a process whereby a biologic substance is cooled to cryogenic temperatures without the destructive phase transition of liquid to solid ice. Recent advances in cryoprotective solutions, organ perfusion techniques and novel heating technologies have demonstrated the potential for vitrification and rewarming organs on a scale applicable for human transplantation.

SUMMARY

Successful strategies for organ cryopreservation could enable organ banking, which would recast the entire process in which organs are recovered, allocated, stored and prepared for transplant.

Thermodynamic Theory and Experimental Validation of a Multiphase Isochoric Freezing Process

Freezing of the aqueous solutions that comprise biological materials, such as isotonic physiological saline, results in the formation of ice crystals and the generation of a hypertonic solution, both of which prove deleterious to biological matter. The field of modern cryopreservation, or preservation of biological matter at subfreezing temperatures, emerged from the 1948 discovery that certain chemical additives such as glycerol, known as cryoprotectants, can protect cells from freeze-related damage by depressing the freezing point of water in solution. This gave rise to a slew of important medical applications, from the preservation of sperm and blood cells to the recent preservation of an entire liver, and current cryopreservation protocols thus rely heavily on the use of additive cryoprotectants. However, high concentrations of cryoprotectants themselves prove toxic to cells, and thus there is an ongoing effort to minimize cryoprotectant usage while maintaining protection from ice-related damage. Herein, we conceive from first principles a new, purely thermodynamic method to eliminate ice formation and hypertonicity during the freezing of a physiological solution: multiphase isochoric freezing. We develop a comprehensive thermodynamic model to predict the equilibrium behaviors of multiphase isochoric systems of arbitrary composition and validate these concepts experimentally in a simple device with no moving parts, providing a baseline from which to design tailored cryopreservation protocols using the multiphase isochoric technique.

A robust ex vivo method to evaluate the diffusion properties of agents in biological tissues

A robust method is presented for evaluating the diffusion properties of chemicals in ex vivo biological tissues. Using this method that relies only on thickness and collimated transmittance measurements, the diffusion properties of glycerol, fructose, polypropylene glycol and water in muscle tissues were evaluated. Amongst other results, the diffusion coefficient of glycerol in colorectal muscle was estimated with a value of 3.3 × 10^-7 cm² /s. Due to the robustness and simplicity of the method, it can be used in other fields of biomedical engineering, namely in organ cryoprotection and food industry.

Effects of trimethylamine oxide (TMAO) and loading duration on the shoot tip cryopreservation of loquat (Eriobotrya japonica)

Two cryoprotectant solutions, including trimethylamine oxide (TMAO) and dimethyl sulfoxide (DMSO), and several loading durations were used to evaluate the cryopreservation of the shoot tip of Eriobotrya plants. The best results for regrowth (59.91%) were obtained from 10% TMAO compared to 10% DMSO as cryoprotectant, although nonsignificant differences were found for survival between the two cryoprotectants. We detected pronounced effects of loading duration on survival and regrowth rates of shoot tips. The maximum regrowth (56.36%) was observed at 9 h of loading duration. The cryoprotectants and loading durations greatly affected the regrowth of Eriobotrya shoot tips, and TMAO could be introduced as a nontoxic and efficient cryoprotectant. These results could lay a foundation for the cryopreservation of Eriobotrya.

Synergy of orientational relaxation between bound water and confined water in ice cold-crystallization

Dehydration/rehydration of some glycerol molecules provides the optimal path for ice cold-crystallization, wherein bound- and confined-water participate in a dynamically synergetic manner.

n-Octyl (Thio)glycosides as Potential Cryoprotectants: Glass Transition Behaviour, Membrane Permeability, and Ice Recrystallization Inhibition Studies

A series of eight n-octyl (thio)glycosides (1α, β–4α, β) with d-glucose or d-galactose-configured head groups and varying anomeric configuration were synthesized and evaluated for glass transition behaviour, membrane permeability, and ice recrystallization inhibition (IRI) activity. Of these, n-octyl β-d-glucopyranoside (2β) exhibited a high glass transition temperatures (Tg), both as a neat sample and 20 wt-% aqueous solution. Membrane permeability studies of this compound revealed cellular uptake to concentrations relevant to the inhibition of intracellular ice formation, thus presenting a promising lead candidate for further biophysical and cryopreservation studies. Compounds were also evaluated as ice recrystallization inhibitors; however, no detectable activity was observed for the newly tested compounds.

A Freezing Protocol for Hematopoietic Stem Cells

Especially in the field of autologous transplantation, it has been found necessary to develop methods that ensure long-term storage with maintenance of functionality of the cells to bridge the therapy-related temporal separation of collection and application.Based on the experiences of more than 40 years, some practical considerations, especially regarding the cell concentration, final volume, and possibly other exogenous substances, should be considered when establishing a protocol for the routine cryopreservation of peripheral blood stem cells. In the following chapter, we describe a freezing protocol for cryopreservation of peripheral blood stem cells which was used and optimized over the past 8 years and was applied to the cryopreservation of more than 2000 peripheral stem cell transplants.

Effects of four disaccharides on nucleation and growth of ice crystals in concentrated glycerol aqueous solution

Devitrification has been determined to be one of the major causes of cell death in cryopreservation by vitrification method. Reliable quantification of the nucleation and growth of ice crystals of devitrification is of great importance for the optimization of the vitrification solutions. In the present study, cryomicroscopy was used to investigate the nucleation and growth of ice crystals in concentrated glycerol aqueous solution (60 wt%) in the presence of sucrose, trehalose, maltose and lactose. Results showed that sucrose rather than trehalose seems to be the most effective one to inhibit the nucleation and ice growth, despite the excellent inhibitory ability of trehalose on ice growth that has been confirmed in many researches. Hence, for ice inhibition, sucrose was a more effective disaccharide additive to suppress nucleation and growth of ice crystals that occurred during devitrification in concentrated glycerol solutions.

Science of cryopreservation in reproductive medicine - Embryos and oocytes as exemplars

The modern successes of reproductive medicine are based on the achievements in the fields of artificial fertilization and cryobiology over the last 50years. Cryopreservation of oocytes makes it possible to preserve their reproductive potential after surgical interventions, treatment of cancer, for delayed pregnancy and to use cells for donation. Cryopreservation of embryos allows not only to reduce the multiple pregnancies rate and to increase the cumulative pregnancy rate as a result of embryo transfer in the following favorable cycles of the patient, but is also a necessary procedure in case of genetic diagnosis or in the case of contraindications for embryo transfer in the stimulated cycle due to possible complications. However, the viability of cryopreserved oocytes and embryos depends on the degree of their cryo damage during the process of freeze-warming. In this regard, it is very important to develop such freezing protocols that minimize the damages caused by the intra- and extracellular ice crystal formation, toxic effect of high concentrations of cryoprotectants and osmotic stresses. The effectiveness of cryopreservation of gametes and embryos is assessed on the basis of morphological, functional and genetic changes in the cells after warming. Special attention should be paid to the ethical issues of assisted reproductive technology, including cryobiotech technologies, which in many countries remain open and in need of settlement.

To Protect and to Preserve: Novel Preservation Strategies for Extracellular Vesicles

Extracellular vesicles (EVs)-based therapeutics are based on the premise that EVs shed by stem cells exert similar therapeutic effects and these have been proposed as an alternative to cell therapies. EV-mediated delivery is an effective and efficient system of cell-to-cell communication which can confer therapeutic benefits to their target cells. EVs have been shown to promote tissue repair and regeneration in various animal models such as, wound healing, cardiac ischemia, diabetes, lung fibrosis, kidney injury, and many others. Given the unique attributes of EVs, considerable thought must be given to the preservation, formulation and cold chain strategies in order to effectively translate exciting preclinical observations to clinical and commercial success. This review summarizes current understanding around EV preservation, challenges in maintaining EV quality, and also bioengineering advances aimed at enhancing the long-term stability of EVs.

Modification of cellular membranes conveys cryoprotection to cells during rapid, non-equilibrium cryopreservation

Rapid cooling and re-warming has been shown promising to cryopreserve living cells, which cannot be preserved by conventional slow freezing methods. However, success is limited by the cytotoxicity of highly concentrated cryoprotective agents. Recent results have shown that cryoprotective agents do not need to suppress intracellular ice crystals completely to allow for survival after cryopreservation. Cryoprotective agents like DMSO or ethylene glycol can also lead to a tolerance of cells towards intracellular ice. It is however unclear by which mechanism this tolerance is achieved. These substances are also known to modulate properties of cellular membranes. It is shown here that cryoprotective DMSO and ethylene glycol have a clear influence on the mobility of lipids in the plasma membrane of HeLa cells. To isolate changes of the properties of plasma membranes from effects on ice formation, the membrane properties were modulated in absence of cryoprotective agents. This was achieved by changing their sterol content. In cells with elevated sterol content, an immobile lipid fraction was present, similar to cells treated with DMSO and ethylene glycol. These cells showed also significantly increased plasma membrane integrity after rapid freezing and thawing in the absence of classical cryoprotective agents. However, their intracellular lysosomes, which cannot be enriched with sterols, still got ruptured. These results clearly indicate that a modulation of membrane properties can convey cryoprotection. Upon slow cooling, elevated sterol content had actually an adverse effect on the plasma membranes, which shows that this effect is specific for rapid, non-equilibrium cooling processes. Unraveling this alternative mode of action of cryoprotection should help in the directed design of novel cryoprotective agents, which might be less cytotoxic than classical, empirically-found cryoprotective agents.

Thermal expansion of substrate may affect adhesion of Chinese hamster fibroblasts to surfaces during freezing

Despite success in cryopreservation of cells in suspension, cryopreservation of cells in monolayers is still challenging. One of the major problems is detachment of the cells from the substrate which occurs during cryopreservation. We hypothesized that this detachment may be due to a mismatch in the coefficient of linear thermal expansion α_L between glass and the frozen cell layer which manifests as residual stress and stress relaxation. This mismatch results in a difference between the thermal expansion of ice and glass as they undergo temperature changes. Rinzl plastic coverslips were selected as a possible substitute for glass because Rinzl has an α_L (60 × 10^-6/K) similar to that of ice (51 × 10^-6/K) whereas glass has a much lower α_L (5 × 10^-6/K). V79-4 Chinese hamster fibroblasts were cultured on both glass and Rinzl coverslips until confluent and the area of coverage was measured before and after freezing at -9 °C. The glass coverslips showed significant loss of cells (coverage = 77.9 ± 8.0%) compared with Rinzl (coverage = 97.9 ± 1.4%). We concluded that Rinzl coverslips may improve cell attachment in future monolayer cryopreservation experiments.

Properties of viable lyopreserved amnion are equivalent to viable cryopreserved amnion with the convenience of ambient storage

Human amniotic membrane (AM) has a long history of clinical use for wound treatment. AM serves as a wound protective barrier maintaining proper moisture. AM is anti-inflammatory, anti-microbial and antifibrotic, and supports angiogenesis, granulation tissue formation and wound re-epithelialization. These properties of AM are attributed to its native extracellular matrix, growth factors, and endogenous cells including mesenchymal stem cells. Advances in tissue preservation have helped to overcome the short shelf life of fresh AM and led to the development of AM products for clinical use. Viable cryopreserved amnion (VCAM), which retains all native components of fresh AM, has shown positive outcomes in clinical trials for wound management. However, cryopreservation requires ultra-low temperature storage and shipment that limits widespread use of VCAM. We have developed a lyopreservation technique to allow for ambient storage of living tissues. Here, we compared the structural, molecular, and functional properties of a viable lyopreserved human amniotic membrane (VLAM) with properties of VCAM using in vitro and in vivo wound models. We found that the structure, growth factors, and cell viability of VLAM is similar to that of VCAM and fresh AM. Both, VCAM and VLAM inhibited TNF-α secretion and upregulated VEGF expression in vitro under conditions designed to mimic inflammation and hypoxia in a wound microenvironment, and resulted in wound closure in a diabetic mouse chronic wound model. Taken together, these data demonstrate that VLAM structural and functional properties are equivalent to VCAM but without the constraints of ultra-low temperature storage.

Impact of vitrification on granulosa cell survival and gene expression

INTRODUCTION

Cryopreservation of ovarian tissue is an essential step in Ovarian Tissue Banking. In order to prevent the formation of ice crystals, typically the tissue is slowly frozen using a cryoprotectant. As an alternative the method of ultra-fast freezing by vitrification becomes more attention for freezing ovarian tissue because it has successfully been used for oocytes, embryos and sperm. However the impact of vitrification on granulosa cells, which are an essential part of ovarian tissue is uncertain.

AIM

In this study, we have therefore analysed the influence of vitrification on the survival rates of granulosa cells, the impact of DMSO or ethylenglycol containing vitrification protocols and investigated to what extent the gene expression of apoptosis- and temperature-sensitive genes changes.

MATERIAL AND METHODS

We used the human granulosa cell line KGN as a model for human granulosa cells and determined the survival rate and cell cycle stages by FACS analyses. The change in gene expression was determined by quantitative PCR analyses.

RESULTS

Our results show that vitrification is possible in granulosa cells but it reduces cell viability and leads to fluctuations in the cell cycle. The DMSO containing protocol results in a lower amount of dead cells than the ethylenglycol containing protocol. Gene expression analysis reveals that TNF-alpha expression is strongly increased after vitrification, while other apoptosis or temperature-related genes seem to stay unaffected.

CONCLUSION

We conclude that vitrification influences the viability of human granulosa cells. Furthermore, our results suggest that this could be mediated by a change in TNF-alpha gene expression.

Serum- and albumin-free cryopreservation of endothelial monolayers with a new solution

Cryopreservation is the only long-term storage option for the storage of vessels and vascular constructs. However, endothelial barrier function is almost completely lost after cryopreservation in most established cryopreservation solutions. We here aimed to improve endothelial function after cryopreservation using the 2D-model of porcine aortic endothelial cell monolayers. The monolayers were cryopreserved in cell culture medium or cold storage solutions based on the 4°C vascular preservation solution TiProtec^®, all supplemented with 10% DMSO, using different temperature gradients. After short-term storage at −80°C, monolayers were rapidly thawed and re-cultured in cell culture medium. Thawing after cryopreservation in cell culture medium caused both immediate and delayed cell death, resulting in 11 ± 5% living cells after 24 h of re-culture. After cryopreservation in TiProtec and chloride-poor modifications thereof, the proportion of adherent viable cells was markedly increased compared to cryopreservation in cell culture medium (TiProtec: 38 ± 11%, modified TiProtec solutions ≥ 50%). Using these solutions, cells cryopreserved in a sub-confluent state were able to proliferate during re-culture. Mitochondrial fragmentation was observed in all solutions, but was partially reversible after cryopreservation in TiProtec and almost completely reversible in modified solutions within 3 h of re-culture. The superior protection of TiProtec and its modifications was apparent at all temperature gradients; however, best results were achieved with a cooling rate of −1°C/min. In conclusion, the use of TiProtec or modifications thereof as base solution for cryopreservation greatly improved cryopreservation results for endothelial monolayers in terms of survival and of monolayer and mitochondrial integrity.

Storage stability of liposomes stored at elevated subzero temperatures in DMSO/sucrose mixtures

Cryopreservation of biological materials is predominantly done using liquid nitrogen, and its application involves high maintenance costs and the need for periodical refilling of liquid nitrogen. Stable storage in mechanical freezers at −80°C would eliminate these issues and allow for shipment of frozen specimens using dry ice. In this work, the possibility of increasing the storage temperature of cryopreserved samples to −80°C by using combinations of DMSO and sucrose has been studied. Preservation efficacy was studied by measuring stability of liposomes encapsulated with carboxyfluorescein during storage at −150, −80 and −25°C for up to three months. Thermal and molecular mobility properties of the different DMSO-sucrose formulations were measured using differential scanning calorimetry, whereas hydrogen bonding interactions of the formulations were probed by Fourier transform infrared spectroscopy. It was found that addition of sucrose to DMSO solutions increases the T_g, and decreases molecular mobility in the glassy state at a particular temperature. Although it was expected that storage above or close to T_g at −80°C would affect liposome stability, stability was found to be similar compared to that of samples stored at −150°C. Higher molecular mobility in the glassy state could not be associated with faster CF-leakage rates. Distinct differences in storage stability at −25°C, far above T_g, were found among the sucrose/DMSO formulations, which were explained by the differences in permeability of sucrose and DMSO resulting in different levels of osmotic stress in the formulations.

Ultrarapid Inductive Rewarming of Vitrified Biomaterials with Thin Metal Forms

Arteries with 1-mm thick walls can be successfully vitrified by loading cryoprotective agents (CPAs) such as VS55 (8.4 M) or less concentrated DP6 (6 M) and cooling at or beyond their critical cooling rates of 2.5 and 40 °C/min, respectively. Successful warming from this vitrified state, however, can be challenging. For example, convective warming by simple warm-bath immersion achieves 70 °C/min, which is faster than VS55's critical warming rate of 55 °C/min, but remains far below that of DP6 (185 °C/min). Here we present a new method that can dramatically increase the warming rates within either a solution or tissue by inductively warming commercially available metal components placed within solutions or in proximity to tissues with non-invasive radiofrequency fields (360 kHz, 20 kA/m). Directly measured warming rates within solutions exceeded 1000 °C/min with specific absorption rates (W/g) of 100, 450 and 1000 for copper foam, aluminum foil, and nitinol mesh, respectively. As proof of principle, a carotid artery diffusively loaded with VS55 and DP6 CPA was successfully warmed with high viability using aluminum foil, while standard convection failed for the DP6 loaded tissue. Modeling suggests this approach can improve warming in tissues up to 4-mm thick where diffusive loading of CPA may be incomplete. Finally, this technology is not dependent on the size of the system and should therefore scale up where convection cannot.

Advances in the slow freezing cryopreservation of microencapsulated cells

Over the past few decades, the use of cell microencapsulation technology has been promoted for a wide range of applications as sustained drug delivery systems or as cells containing biosystems for regenerative medicine. However, difficulty in their preservation and storage has limited their availability to healthcare centers. Because the preservation in cryogenic temperatures poses many biological and biophysical challenges and that the technology has not been well understood, the slow cooling cryopreservation, which is the most used technique worldwide, has not given full measure of its full potential application yet. This review will discuss the different steps that should be understood and taken into account to preserve microencapsulated cells by slow freezing in a successful and simple manner. Moreover, it will review the slow freezing preservation of alginate-based microencapsulated cells and discuss some recommendations that the research community may pursue to optimize the preservation of microencapsulated cells, enabling the therapy translate from bench to the clinic.

Recent progress in tissue optical clearing for spectroscopic application

This paper aims to review recent progress in optical clearing of the skin and over naturally turbid biological tissues and blood using this technique in vivo and in vitro with multiphoton microscopy, confocal Raman microscopy, confocal microscopy, NIR spectroscopy, optical coherence tomography, and laser speckle contrast imaging. Basic principles of the technique, its safety, advantages and limitations are discussed. The application of optical clearing agent on a tissue allows for controlling the optical properties of tissue. Optical clearing-induced reduction of tissue scattering significantly facilitates the observation of deep-located tissue regions, at the same time improving the resolution and image contrast for a variety of optical imaging methods suitable for clinical applications, such as diagnostics and laser treatment of skin diseases, mucosal tumor imaging, laser disruption of pathological abnormalities, etc.

The enhancement and suppression of immersion mode heterogeneous ice-nucleation by solutes

Heterogeneous nucleation of ice from aqueous solutions is an important yet poorly understood process in multiple fields, not least the atmospheric sciences where it impacts the formation and properties of clouds. In the atmosphere ice-nucleating particles are usually, if not always, mixed with soluble material. However, the impact of this soluble material on ice nucleation is poorly understood. In the atmospheric community the current paradigm for freezing under mixed phase cloud conditions is that dilute solutions will not influence heterogeneous freezing. By testing combinations of nucleators and solute molecules we have demonstrated that 0.015 M solutions (predicted melting point depression <0.1 °C) of several ammonium salts can cause suspended particles of feldspars and quartz to nucleate ice up to around 3 °C warmer than they do in pure water. In contrast, dilute solutions of certain alkali metal halides can dramatically depress freezing points for the same nucleators. At 0.015 M, solutes can enhance or deactivate the ice-nucleating ability of a microcline feldspar across a range of more than 10 °C, which corresponds to a change in active site density of more than a factor of 105. This concentration was chosen for a survey across multiple solutes-nucleant combinations since it had a minimal colligative impact on freezing and is relevant for activating cloud droplets. Other nucleators, for instance a silica gel, are unaffected by these 'solute effects', to within experimental uncertainty. This split in response to the presence of solutes indicates that different mechanisms of ice nucleation occur on the different nucleators or that surface modification of relevance to ice nucleation proceeds in different ways for different nucleators. These solute effects on immersion mode ice nucleation may be of importance in the atmosphere as sea salt and ammonium sulphate are common cloud condensation nuclei (CCN) for cloud droplets and are internally mixed with ice-nucleating particles in mixed-phase clouds. In addition, we propose a pathway dependence where activation of CCN at low temperatures might lead to enhanced ice formation relative to pathways where CCN activation occurs at higher temperatures prior to cooling to nucleation temperature.

Effect of water content on the glass transition temperature of mixtures of sugars, polymers, and penetrating cryoprotectants in physiological buffer

Long-term storage of viable mammalian cells is important for applications ranging from in vitro fertilization to cell therapy. Cryopreservation is currently the most common approach, but storage in liquid nitrogen is relatively costly and the requirement for low temperatures during shipping is inconvenient. Desiccation is an alternative strategy with the potential to enable viable cell preservation at more convenient storage temperatures without the need for liquid nitrogen. To achieve stability during storage in the dried state it is necessary to remove enough water that the remaining matrix forms a non-crystalline glassy solid. Thus, the glass transition temperature is a key parameter for design of cell desiccation procedures. In this study, we have investigated the effects of moisture content on the glass transition temperature (T_g) of mixtures of sugars (trehalose or raffinose), polymers (polyvinylpyrrolidone or Ficoll), penetrating cryoprotectants (ethylene glycol, propylene glycol, or dimethyl sulfoxide), and phosphate buffered saline (PBS) solutes. Aqueous solutions were dried to different moisture contents by equilibration with saturated salt solutions, or by baking at 95°C. The glass transition temperatures of the dehydrated samples were then measured by differential scanning calorimetry. As expected, T_g increased with decreasing moisture content. For example, in a desiccation medium containing 0.1 M trehalose in PBS, T_g ranged from about 360 K for a completely dry sample to about 220 K at a water mass fraction of 0.4. Addition of polymers to the solutions increased T_g, while addition of penetrating cryoprotectants decreased T_g. Our results provide insight into the relationship between relative humidity, moisture content and glass transition temperature for cell desiccation solutions containing sugars, polymers and penetrating cryoprotectants.

Simple multimodal optical technique for evaluation of free/bound water and dispersion of human liver tissue

The optical dispersion and water content of human liver were experimentally studied to estimate the optical dispersions of tissue scatterers and dry matter. Using temporal measurements of collimated transmittance [Tc(t)] of liver samples under treatment at different glycerol concentrations, free water and diffusion coefficient (Dgl) of glycerol in liver were found as 60.0% and 8.2×10-7  cm2/s, respectively. Bound water was calculated as the difference between the reported total water of 74.5% and found free water. The optical dispersion of liver was calculated from the measurements of refractive index (RI) of tissue samples made for different wavelengths between 400 and 1000 nm. Using liver and water optical dispersions at 20°C and the free and total water, the dispersions for liver scatterers and dry matter were calculated. The estimated dispersions present a decreasing behavior with wavelength. The dry matter dispersion shows higher RI values than liver scatterers, as expected. Considering 600 nm, dry matter has an RI of 1.508, whereas scatterers have an RI of 1.444. These dispersions are useful to characterize the RI matching mechanism in optical clearing treatments, provided that [Tc(t)] and thickness measurements are performed during treatment. The knowledge of Dgl is also important for living tissue cryoprotection applications.

Pressure in isochoric systems containing aqueous solutions at subzero Centigrade temperatures

OBJECTIVE

Preservation of biological materials at subzero Centigrade temperatures, cryopreservation, is important for the field of tissue engineering and organ transplantation. Our group is studying the use of isochoric (constant volume) systems of aqueous solution for cryopreservation. Previous studies measured the pressure-temperature relations in aqueous isochoric systems in the temperature range from 0°C to - 20°C. The goal of this study is to expand the pressure-temperature measurement beyond the range reported in previous publications.

MATERIALS AND METHODS

To expand the pressure-temperature measurements beyond the previous range, we have developed a new isochoric device capable of withstanding liquid nitrogen temperatures and pressures of up to 413 MPa. The device is instrumented with a pressure transducer than can monitor and record the pressures in the isochoric chamber in real time. Measurements were made in a temperature range from - 5°C to liquid nitrogen temperatures for various solutions of pure water and Me2SO (a chemical additive used for protection of biological materials in a frozen state and for vitrification (glass formation) of biological matter). Undissolved gaseous are is carefully removed from the system.

RESULTS

Temperature-pressure data from - 5°C to liquid nitrogen temperature for pure water and other solutions are presented in this study. Following are examples of some, temperature-pressure values, that were measured in an isochoric system containing pure water: (- 20°C, 187 MPa); (-25°C, 216 MPa); (- 30°C, 242.3 MPa); (-180°C, 124 MPa). The data is consistent with the literature, which reports that the pressure and temperature at the triple point, between ice I, ice III and water is, - 21.993°C and 209.9 MPa, respectively. It was surprising to find that the pressure in the isochoric system increases at temperatures below the triple point and remains high to liquid nitrogen temperatures. Measurements of pressure-temperature relations in solutions of pure water and Me2SO in different concentrations show that, for concentrations in which vitrification is predicted, no increase in pressure was measured during rapid cooling to liquid nitrogen temperatures. However, ice formation either during cooling or warming to and from liquid nitrogen temperatures produced an increase in pressure.

CONCLUSIONS

The data obtained in this study can be used to aid in the design of isochoric cryopreservation protocols. The results suggest that the pressure measurement is important in the design of "constant volume" systems and can provide a simple means to gain information on the occurrence of vitrification and devitrification during cryopreservation processes of aqueous solutions in an isochoric system.