Factors affecting the survival of mouse embryos cryopreserved by vitrification

The adverse effects of vitrification on mouse embryo development and metabolic phenotype in offspring

Embryo vitrification is a standard procedure in assisted reproductive technology. Previous studies have shown that frozen embryo transfer is associated with an elevated risk of adverse maternal and neonatal outcomes. This study aimed to explore the effects of mouse blastocyst vitrification on the phenotype of vitrified-warmed blastocysts, their intrauterine and postnatal development, and the long-term metabolic health of the derived offspring. The vitrified-warmed blastocysts (IVF + VT group) exhibited reduced mitochondrial activity, increased apoptotic levels, and decreased cell numbers when compared to the fresh blastocysts (IVF group). Implantation rates, live pup rates, and crown-rump length at E18.5 were not different between the two groups. However, there was a significant decrease in fetal weight and fetal/placental weight ratio in the IVF + VT group. Furthermore, the offspring of the IVF + VT group at an age of 36 weeks had reduced whole energy consumption, impaired glucose and lipid metabolism when compared with the IVF group. Notably, RNA-seq results unveiled disturbed hepatic gene expression in the offspring from vitrified-warmed blastocysts. This study revealed the short-term negative impacts of vitrification on embryo and fetal development and the long-term influence on glucose and lipid metabolism that persist from the prenatal stage into adulthood in mice.

Cryopreservation of rat embryos at all developmental stages by small-volume vitrification procedure and rapid warming in cryotubes

Intracellular ice formation during cryopreservation is lethal to the cell, including during warming. Here, we examined the effect of sample volume and warming rate on the cryopreservation success of 1-cell rat embryos based on successful development into blastocysts in vitro and to term in vivo following embryo transfer. Embryos were equilibrated in 5% propylene glycol solution for 10 min, held for 40 s at 0 °C in cryopreservation solution (5%PG + PEPeS), and cooled by immersion in liquid nitrogen. When 1-cell embryos were cryopreserved in a volume of 30-100 μL at a cooling rate of 5830-7160 °C/min and warmed at 35,480-49,400 °C/min by adding 1 mL of 0.3 M sucrose solution at 50 °C, 17.3-28.8% developed into blastocysts, compared with 57.0% of untreated embryos. However, when 1-cell embryos were cryopreserved in a smaller volume of 15 μl at 7950 °C/min and warmed at 68,850 °C/min, 58.8 ± 10.6% developed into blastocysts and 50.0 ± 7.4% developed to term, comparable to that of non-treated embryos (57.0 ± 5.4% and 51.4 ± 3.1%, respectively). Cryopreserved embryos at other developmental stages also showed high in vitro culture potential similar to that of the control. Using a conventional cryotube and a small-volume vitrification procedure with rapid warming, we achieved high levels of subsequent rat embryonic development at all developmental stages.

Osmotic response during kidney perfusion with cryoprotectant in isotonic or hypotonic vehicle solution

Organ cryopreservation would revolutionize transplantation by overcoming the shelf-life limitations of conventional organ storage. To prepare an organ for cryopreservation, it is first perfused with cryoprotectants (CPAs). These chemicals can enable vitrification during cooling, preventing ice damage. However, CPAs can also cause toxicity and osmotic damage. It is a major challenge to find the optimal balance between protecting the cells from ice and avoiding CPA-induced damage. In this study, we examined the organ perfusion process to shed light on phenomena relevant to cryopreservation protocol design, including changes in organ size and vascular resistance. In particular, we compared perfusion of kidneys (porcine and human) with CPA in either hypotonic or isotonic vehicle solution. Our results demonstrate that CPA perfusion causes kidney mass changes consistent with the shrink-swell response observed in cells. This response was observed when the kidneys were relatively fresh, but disappeared after prolonged warm and/or cold ischemia. Perfusion with CPA in a hypotonic vehicle solution led to a significant increase in vascular resistance, suggesting reduced capillary diameter due to cell swelling. This could be reversed by switching to perfusion with CPA in isotonic vehicle solution. Hypotonic vehicle solution did not cause notable osmotic damage, as evidenced by low levels of lactate dehydrogenase (LDH) in the effluent, and it did not have a statistically significant effect on the delivery of CPA into the kidney, as assessed by computed tomography (CT). Overall, our results show that CPA vehicle solution tonicity affects organ size and vascular resistance, which may have important implications for cryopreservation protocol design.

Kinetic vitrification: concepts and perspectives in animal sperm cryopreservation

Sperm cryopreservation is an important tool for genetic diversity management programs and the conservation of endangered breeds and species. The most widely used method of sperm conservation is slow freezing, however, during the process, sperm cells suffer from cryoinjury, which reduces their viability and fertility rates. One of the alternatives to slow freezing is vitrification, that consist on rapid freezing, in which viable cells undergo glass-like solidification. This technology requires large concentrations of permeable cryoprotectants (P- CPA's) which increase the viscosity of the medium to prevent intracellular ice formation during cooling and warming, obtaining successful results in vitrification of oocytes and embryos. Unfortunately, this technology failed when applied to vitrification of sperm due to its higher sensitivity to increasing concentrations of P-CPAs. Alternatively, a technique termed 'kinetic sperm vitrification' has been used and consists in a technique of permeant cryoprotectant-free cryopreservation by direct plunging of a sperm suspension into liquid nitrogen. Some of the advantages of kinetic vitrification are the speed of execution and no rate-controlled equipment required. This technique has been used successfully and with better results for motility in human (50-70% motility recovery), dog (42%), fish (82%) and donkey (21.7%). However, more studies are required to improve sperm viability after devitrification, especially when it comes to motility recovery. The objective of this review is to present the principles of kinetic vitrification, the main findings in the literature, and the perspectives for the utilization of this technique as a cryopreservation method.

An all-37 °C thawing method improves the clinical outcomes of vitrified frozen-thawed embryo transfer: a retrospective study using a case-control matching analysis

PURPOSE

The purpose of this study is to assess the impact of different temperatures and incubation times on the clinical outcomes of FET cycles during the thawing procedure and to select a better thawing method to improve clinical outcomes.

METHODS

This retrospective study included 1734 FET cycles from January 1, 2020, to January 30, 2022. Embryos vitrified using a KITAZATO Vitrification Kit were thawed at 37 °C in all steps (the case group, denoted the "all-37 °C" group) or at 37 °C and then at room temperature (RT; the control group, denoted the "37 °C-RT" group), according to the kit instructions. The groups were matched 1:1 to avoid confounding.

RESULTS

After case-control matching, 366 all-37 °C cycles and 366 37 °C-RT cycles were included. The baseline characteristics were similar (all P > 0.05) between the two groups after matching. FET of the all-37 °C group yielded a higher clinical pregnancy rate (CPR; P = 0.009) and implantation rate (IR; P = 0.019) than FET of the 37 °C-RT group. For blastocyst transfers, the CPR (P = 0.019) and IR (P = 0.025) were significantly higher in the all-37 °C group than in the 37 °C-RT group. For D3-embryo transfers, the CPR and IR were non-significantly higher in the all-37 °C group than in the 37 °C-RT group (P > 0.05).

CONCLUSIONS

Thawing vitrified embryos at 37 °C in all steps with shortening wash time can enhance CPR and IR in FET cycles. Well-designed prospective studies are warranted to further evaluate the efficacy and safety of the all-37 °C thawing method.

Hydrogel encapsulation as a handling and vitrification tool for zebrafish ovarian tissue

Zebrafish is an important animal model, thousands lines have been developed, thus having a great need for their preservation. However, the cryopreservation of fish oocytes is still limited and needs improvement. The sodium alginate hydrogel, in addition to providing support for the cells, has been shown to be a potential cryoprotectant. Therefore, the aim of this study was to evaluate the sodium alginate hydrogel encapsulation technique efficiency during zebrafish ovarian tissue vitrification. The encapsulation methodology was standardized in the first experiment. In Experiment 2, we evaluated four vitrified groups: standard protocol without encapsulation (VS); encapsulated with cryoprotectants (VS1-A); encapsulated with half the cryoprotectants concentration (VS2-A); encapsulated without cryoprotectants (VA). VS treatment (54.6 ± 12.3%; 23.7 ± 9.9%; 12.6 ± 5.0%) did not differ from the VS1-A and VA showed a lower membrane integrity percentage (1.2 ± 1.4%; 0.3 ± 0.6%; 0.5 ± 1.5%). Mitochondrial activity was significantly greater in non-encapsulated treatment (VS) when compared to the encapsulated treatments. VS1-A and VS obtained the lowest lipid peroxidation (39.4 ± 4.4 and 40.5 ± 3.3 nmol MDA/mg respectively) in which VS was not significantly different from the VS2-A treatment (63.6 ± 3.1 nmol MDA/mg), unlike, VA obtained the highest lipid peroxidation level (124.7 ± 7.9 nmol MDA/mg). The results obtained in this study demonstrate that the sodium alginate hydrogel encapsulation technique did not have a cryoprotective action, but maintained the membrane integrity when used the standard concentration of cryoprotectants. However, halving the cryoprotectant concentration of fragments encapsulated in alginate hydrogel did not cause an increase in lipid peroxidation. In addition, it provided support and prevented the oocytes from loosening from the tissue during the vitrification process, being an interesting alternative for later in vitro maturation.

The Open Cryotop System Is Effective for the Simultaneous Vitrification of a Large Number of Porcine Embryos at Different Developmental Stages

The Superfine Open Pulled Straw (SOPS) system is the most commonly used method for vitrification of pig embryos. However, this system only allows the vitrification of four to seven embryos per straw. In this study, we investigated the effectiveness of the open (OC) and closed (CC) Cryotop^® systems to simultaneously vitrify a larger number of porcine embryos. Morulae, early blastocysts and full blastocysts were vitrified with the open Cryotop^® (n = 250; 20 embryos per device) system, the closed Cryotop^® (n = 158; 20 embryos per device) system and the traditional superfine open pulled straw (SOPS; n = 241; 4–7 embryos per straw) method. Fresh embryos from each developmental stage constituted the control group (n = 132). Data expressed as percentages were compared with the Fisher's exact test. The Kruskal-Wallis test was used to analyze the effect of the different vitrification systems on the embryo quality parameters and two-by-two comparisons were accomplished with the Mann-Whitney U test. Differences were considered statistically significant when p < 0.05. Vitrified and control embryos were incubated for 24 h and examined for viability and quality. At the warming step, the embryo recovery rate for the CC system was 51%, while all embryos were recovered when using OC and SOPS. There were no differences between the vitrification and control groups in the postwarming viability of full blastocysts. In contrast, morulae and early blastocysts that were vitrified-warmed with the SOPS system had lower viability (p < 0.01) compared to those from the OC, CC and control groups. The embryonic viability was similar between the OC and control groups, regardless of the developmental stage considered. Moreover, the embryos from the OC group had comparable total cell number and cells from the inner cell mass and apoptotic index than the controls. In conclusion, the OC system is suitable for the simultaneous vitrification of 20 porcine embryos at different developmental stages and provides comparable viability and quality results to fresh embryos subjected to 24 h of in vitro culture.

Cryopreservation Competence of Chicken Oocytes as a Model of Endangered Wild Birds: Effects of Storage Time and Temperature on the Ovarian Follicle Survival

For the conservation of endangered avian species, developing gamete preservation technologies is essential. However, studies in oocytes have not been widely conducted. In this study, assuming that the ovaries are transported to a research facility after death, we investigated the effect of ovary storage on oocytes for the purpose of cryopreserving avian female gametes by using a chicken as a model of endangered avian species. After excision, the ovaries were stored at either a low temperature (4 °C) or room temperature for 1–3 days. Ovarian follicles stored under different conditions for each period were examined by neutral red staining, histology, and gene and protein expression analysis. In addition, the pH of the storage medium after preserving the ovaries was measured. Then, ovarian tissues were vitrified to determine the cryopreservation competence. Storing the ovarian tissues at 4 °C kept the follicles viable and morphologically normal for 3 days with slow decline. In contrast, although different storage temperature did not influence follicle viability and morphology after only 1 day of storage, ovarian tissues stored at room temperature rapidly declined in structurally normal follicles, and viable follicles were rarely seen after 3 days of storage. Gene and protein expression analysis showed that apoptosis had already started on the first day, as shown by the higher expression of CASP9 under room temperature conditions. Furthermore, high expression of SOD1 and a rapid decline of pH in the storage medium under room temperature storage suggested the influence of oxidative stress associated with low pH in this condition on the follicle survivability in hen ovarian tissues. Our cryopreservation study also showed that ovarian tissues stored at 4 °C could recover after cryopreservation even after 3 days of storage. The described storage conditions and cryopreservation methods, which preserve chicken follicle survival, will lay the foundation of ovarian tissue preservation to preserve the fertility of wild female birds.

Vitrification Solutions for Plant Cryopreservation: Modification and Properties

Many plants cannot vitrify themselves because they lack glassy state-inducing substances and/or have high water content. Therefore, cryoprotectants are used to induce vitrification. A cryoprotectant must have at least the following primary abilities: high glass-forming property, dehydration strength on a colligative basis to dehydrate plant cells to induce the vitrification state, and must not be toxic for plants. This review introduces the compounds used for vitrification solutions (VSs), their properties indicating a modification of different plant vitrification solutions, their modifications in the compounds, and/or their concentration. An experimental comparison is listed based on the survival or regeneration rate of one particular species after using more than three different VSs or their modifications. A brief overview of various cryopreservation methods using the Plant Vitrification Solution (PVS) is also included. This review can help in alert researchers to newly introduced PVSs for plant vitrification cryoprotocols, their properties, and the choice of their modifications in the compounds and/or their concentration.

Semi-automated versus manual embryo vitrification: inter-operator variability, time-saving, and clinical outcomes

PURPOSE

Does semi-automated vitrification have lower inter-operator variability and better clinical outcomes than manual vitrification?

METHODS

Retrospective analyses of 282 patients whose embryos had been cryopreserved, manually with Irvine®-CBS® (MV) or semi-automatically vitrified with the GAVI® method (AV) (from November 2017 to September 2020). Both techniques were performed during the same period by 5 operators. Inter-operator variability was statistically analyzed between operators who performed the vitrification and those who performed the warming process to compare the intact survival rate (% embryos with 100% intact blastomeres) and the positive survival rate (at least 50% intact blastomeres). Additionally, the complete vitrification time was assessed for the 2 techniques according to the number of vitrified embryos.

RESULTS

Manual vitrification involved warming 338 embryos in 266 cycles for 181 couples compared to 212 embryos in 162 AV cycles for 101 patients. The positive survival rate was higher (p < 0.05) after MV (96%; 323/338) than after AV (90%; 191/212). The intact survival rate (86 vs 84%) and the clinical pregnancy rate (27 vs 22%) were not significantly different between MV and AV. Regarding the inter-operator variability, no significant difference in positive and intact survival rate was evident between the 5 technicians, neither by vitrification nor by warming steps with MV and AV. Concerning time-saving, the MV technique proved to be quicker than AV (minus 11 ± 9 min).

CONCLUSIONS

Manual vitrification exhibited favorable total survival rates and was more time efficient, while both MV and AV cooling and warming treatments showed little operator variability.

New Alternative Mixtures of Cryoprotectants for Equine Immature Oocyte Vitrification

Simple Summary

Oocyte cryopreservation allows female gametes to be conserved for long periods, which would be of benefit for mares of high genetic merit, but its efficiency is not satisfactory yet. Therefore, the aim of this study was to optimize a vitrification protocol for equine oocytes using a systematic approach. We performed a side-by-side comparison of different cryoprotective agents (CPAs) during the vitrification and warming of equine oocytes. In the first experiment, a fixed mixture of CPAs that enter the oocyte was used, and three sugars were compared, which cannot penetrate the oocyte but provide protection through an osmotic effect. In the second experiment, one sugar from the first experiment was selected to compare three mixtures of CPAs that enter the oocyte. Overall, the embryo development was reduced after oocyte cryopreservation when compared to fresh oocytes. Yet, we were able to produce embryos with all six cryoprotective agent mixtures, and we identified one promising combination of cryoprotectants, consisting of propylene glycol, ethylene glycol, and galactose, that resulted in blastocyst rates in the same range as the fresh control group.

Abstract

Equine oocyte vitrification would benefit the growing in vitro embryo production programs, but further optimization of the protocol is necessary to reach clinical efficiency. Therefore, we aimed to perform a direct comparison of non-permeating and permeating cryoprotective agents (CPAs) during the vitrification and warming of equine immature oocytes. In the first experiment, cumulus oocytes complexes (COCs) were vitrified comparing sucrose, trehalose, and galactose in combination with ethylene glycol (EG) and dimethyl sulfoxide (DMSO). In the second experiment, the COCs were vitrified using three mixtures of permeating CPAs in a 50:50 volume ratio (ethylene glycol-dimethyl sulfoxide (ED), propylene glycol-ethylene glycol (PE), and propylene glycol-dimethyl sulfoxide (PD)) with galactose and warmed in different galactose concentrations (0.3 or 0.5 mol/L). Overall, all the treatments supported blastocyst formation, but the developmental rates were lower for all the vitrified groups in the first (4.3 to 7.6%) and the second (3.5 to 9.4%) experiment compared to the control (26.5 and 34.2%, respectively; p < 0.01). In the first experiment, the maturation was not affected by vitrification. The sucrose exhibited lower cleavage than the control (p = 0.02). Although the galactose tended to have lower maturation than trehalose (p = 0.060) and control (p = 0.069), the highest numerical cleavage and blastocyst rates were obtained with this CPA. In the second experiment, the maturation, cleavage, and blastocyst rates were similar between the treatments. Compared to the control, only the ED reached similar maturation (p = 0.02) and PE similar cleavage (p = 0.1). The galactose concentration during warming did not affect the maturation, cleavage, or blastocyst rates (p > 0.1), but the PE-0.3 exhibited the highest blastocyst rate (15.1%) among the treatments, being the only one comparable to the control (34.2%). As such, PE–galactose provides a valuable option for equine immature oocyte vitrification and should be considered for the future optimization of the protocol.

In Situ Vitrification of Lung Cancer Organoids on a Microwell Array

Three-dimensional cultured patient-derived cancer organoids (PDOs) represent a powerful tool for anti-cancer drug development due to their similarity to the in vivo tumor tissues. However, the culture and manipulation of PDOs is more difficult than 2D cultured cell lines due to the presence of the culture matrix and the 3D feature of the organoids. In our other study, we established a method for lung cancer organoid (LCO)-based drug sensitivity tests on the superhydrophobic microwell array chip (SMAR-chip). Here, we describe a novel in situ cryopreservation technology on the SMAR-chip to preserve the viability of the organoids for future drug sensitivity tests. We compared two cryopreservation approaches (slow freezing and vitrification) and demonstrated that vitrification performed better at preserving the viability of LCOs. Next, we developed a simple procedure for in situ cryopreservation and thawing of the LCOs on the SMAR-chip. We proved that the on-chip cryopreserved organoids can be recovered successfully and, more importantly, showing similar responses to anti-cancer drugs as the unfrozen controls. This in situ vitrification technology eliminated the harvesting and centrifugation steps in conventional cryopreservation, making the whole freeze–thaw process easier to perform and the preserved LCOs ready to be used for the subsequent drug sensitivity test.

Cryopreservation Protocols for Genetically Engineered Mice

Protocols for cryopreservation of mouse embryos and sperm are important for preserving genetically engineered mice (GEMs) used in research to study human development and diseases. Embryo cryopreservation is mainly carried out using either of two protocols: controlled gradual cooling or vitrification. Sperm cryopreservation protocols include two methodologies that are commonly referred to as JAX and CARD. Quality-control measures are necessary to ensure that GEMs are properly cryopreserved so that they can be retrieved for future use. An archiving system is also important in keeping proper records of frozen sperm and embryos. Frozen embryos and sperm are now preferred over live mice for shipping to distant locations. This article describes detailed protocols used in cryopreservation of mouse embryos and sperm, as well as their retrieval to live mice. © 2021 U.S. Government. Sperm cryopreservation Basic Protocol 1: JAX protocol for sperm cryopreservation Support Protocol 1: JAX protocol for making sperm cryopreservation medium Basic Protocol 2: JAX protocol for IVF of mouse sperm Alternate Protocol 1: Modified CARD protocol for sperm cryopreservation Support Protocol 2: CARD protocol for making sperm cryopreservation medium Alternate Protocol 2: CARD protocol for IVF of mouse sperm Embryo cryopreservation Basic Protocol 3: Cryopreserving and thawing 2-cell embryos Alternate Protocol 3: Cryopreserving and thawing 8-cell to morula-stage embryos Surgical transfer of embryos Basic Protocol 4: Infundibulum transfer of 2-cell to morula-stage embryos.

Winter is coming: the future of cryopreservation

The preservative effects of low temperature on biological materials have been long recognised, and cryopreservation is now widely used in biomedicine, including in organ transplantation, regenerative medicine and drug discovery. The lack of organs for transplantation constitutes a major medical challenge, stemming largely from the inability to preserve donated organs until a suitable recipient is found. Here, we review the latest cryopreservation methods and applications. We describe the main challenges-scaling up to large volumes and complex tissues, preventing ice formation and mitigating cryoprotectant toxicity-discuss advantages and disadvantages of current methods and outline prospects for the future of the field.

Principles of Ice-Free Cryopreservation by Vitrification

Vitrification is an alternative to cryopreservation by freezing that enables hydrated living cells to be cooled to cryogenic temperatures in the absence of ice. Vitrification simplifies and frequently improves cryopreservation because it eliminates mechanical injury from ice, eliminates the need to find optimal cooling and warming rates, eliminates the importance of differing optimal cooling and warming rates for cells in mixed cell type populations, eliminates the need to find a frequently imperfect compromise between solution effects injury and intracellular ice formation, and can enable chilling injury to be "outrun" by using rapid cooling without a risk of intracellular ice formation. On the other hand, vitrification requires much higher concentrations of cryoprotectants than cryopreservation by freezing, which introduces greater risks of both osmotic damage and cryoprotectant toxicity. Fortunately, a large number of remedies for the latter problem have been discovered over the past 35 years, and osmotic damage can in most cases be eliminated or adequately controlled by paying careful attention to cryoprotectant introduction and washout techniques. Vitrification therefore has the potential to enable the superior and convenient cryopreservation of a wide range of biological systems (including molecules, cells, tissues, organs, and even some whole organisms), and it is also increasingly recognized as a successful strategy for surviving harsh environmental conditions in nature. But the potential of vitrification is sometimes limited by an insufficient understanding of the complex physical and biological principles involved, and therefore a better understanding may not only help to improve present outcomes but may also point the way to new strategies that may be yet more successful in the future. This chapter accordingly describes the basic principles of vitrification and indicates the broad potential biological relevance of this alternative method of cryopreservation.

Comparison between two cryopreservation techniques of human ovarian cortex: morphological aspects and the heat shock response (HSR)

This study was tailored to compare the cryopreservation of the human ovarian cortex using closed metal container vitrification or the slow-freezing technique. Superficial ovarian cortical tissue biopsies were collected from 12 participants who underwent gynaecological videolaparoscopy. The fragmented samples were allocated to three experimental conditions: (a) fresh ovarian tissue, (b) slow-freezing, and (c) vitrification with a metal closed container. After thawing or rewarming, cellular morphological analyses were performed to determine tissue viability. The cellular response to thermal stress was measured by a putative increase in the immune quantification of the heat shock protein 70 kDa (heat shock protein 70 kDa response - HSR) after a heat challenge (2 h exposure at 42 °C). Both the total number of intact follicles and the frequency of primordial follicles were higher in fresh ovarian tissue than in the preserved samples, regardless of the technique employed. There was a trend towards an increase in the absolute number of intact follicles in the tissue preserved by vitrification. After cryopreservation, a higher HSR was obtained after slow-freezing. These results indicate that both cryopreservation techniques present advantages and may be used as alternatives to ovarian tissue cryopreservation.

Physiological responses to cryoprotectant treatment in an early larval stage of the malaria mosquito, Anopheles gambiae

The development of cryopreservation protocols for Anopheles gambiae could significantly improve research and control efforts. Cryopreservation of any An. gambiae life stage has yet to be successful. The unique properties of embryos have proven to be resistant to any practical cryoprotectant loading. Therefore, we have chosen to investigate early non-feeding first instar larvae as a potential life stage for cryopreservation. In order to determine an appropriate cryoprotective compound, larvae were treated with progressively better glass-forming cryoprotective mixtures. Toxicity evaluation in combination with calorimetry-based water content and supercooling point depression assessments were used to determine the cryoprotectants that could be used for cryostorage of viable larvae. Approximately 35-75% of the larvae were viable after reasonably high osmotic and biochemical challenge. This study provides ample evidence for an active osmoregulatory response in the Anopheles larvae to counter the permeation of cryoprotectants from the surrounding medium. The data show a strong correlation between the larval mortality and water content, indicating an osmoregulatory crisis in the larva due to certain cryoprotectants such as the higher concentrations of ethane diol (ED). The observations also indicate that the ability of the larvae to regulate permeation and water balance ceases at or within 20 min of cryoprotectant exposure, but this is strongly influenced by the treatment temperature. Among the compound cryoprotectants tested, 25% ED + 10% dimethyl sulfoxide (DMSO) and 40% ED + 0.5 M trehalose seem to present a compromise between viability, larval water content, supercooling point depression, and glass forming abilities.

Whole Ovary Cryopreservation and Transplantation: A Systematic Review of Challenges and Research Developments in Animal Experiments and Humans

Ovarian tissue cryopreservation and transplantation is the only fertility preservation option that enables both restoration of fertility and resumption of ovarian endocrine function, avoiding the morbidity associated with premature menopause. It is also the only technique available to prepubertal patients and those whose treatment cannot be delayed for life-threatening reasons. Ovarian tissue cryopreservation can be carried out in two different ways, either as ovarian cortical fragments or as a whole organ with its vascular pedicle. Although use of cortical strips is the only procedure that has been approved by the American Society for Reproductive Medicine, it is fraught with drawbacks, the major one being serious follicle loss occurring after avascular transplantation due to prolonged warm ischemia. Whole ovary cryopreservation involves vascular transplantation, which could theoretically counteract the latter phenomenon and markedly improve follicle survival. In theory, this technique should maintain endocrine and reproductive functions much longer than grafting of ovarian cortical fragments. However, this procedure includes a number of critical steps related to (A) the level of surgical expertise required to accomplish retrieval of a whole ovary with its vascular pedicle, (B) the choice of cryopreservation technique for freezing of the intact organ, and (C) successful execution of functional vascular reanastomosis upon thawing. The aim of this systematic review is to shed light on these challenges and summarize solutions that have been proposed so far in animal experiments and humans in the field of whole ovary cryopreservation and transplantation.

Meiotic Status Does Not Affect the Vitrification Effectiveness of Domestic Cat Oocytes

Simple Summary

Assisted reproduction techniques (ART) are crucial for preserving endangered animal species. Cryopreservation by vitrification can maintain gamete viability for a long time. Efforts to preserve endangered species within the Felidae family are focused on developing appropriate ART procedures. The domestic cat is a good biomedical model. Unfortunately, the current state of knowledge on vitrification of cat oocytes is inconclusive and the efficiency of ART procedures is low. A key example concerns how the meiotic status of the oocyte influences suitability for vitrification. This is the main question of this study. First, we conducted a toxicity test to make sure that the vitrification solution (VS) we proposed does not have a toxic effect on cat oocytes. Next, we performed vitrification on cat oocytes before (nonmature) and after in vitro maturation (IVM) and checked their developmental potential. There was no negative impact of the applied VS on oocyte maturation and fertilization, demonstrating a possibility to obtain embryos in vitro regardless of the meiotic status. There is a need for more research on vitrification of the domestic cat oocytes as a model species for wild cats.

Abstract

Cryopreservation is important for animal fertility and biodiversity. Unfortunately, cryopreservation of feline oocytes is still an experimental technique. The aims of this study were to analyze the potential toxicity of the cryoprotectants in the vitrification solution (VS) on cat oocytes and to investigate whether the meiotic status of oocytes influences their developmental potential after vitrification. Two experiments were conducted with the VS composed of 20% ethylene glycol, 20% dimethyl sulfoxide, 20% fetal calf serum, 1.5 M trehalose, and 10% Ficoll PM-70: (1) toxicity assessment of the VS on immature cumulus oocyte complexes (COCs), and subsequently in vitro maturation (IVM) and in vitro fertilization; (2) assessment of the influence of the meiotic status on vitrification effectiveness, where immature and in vitro matured COCs were vitrified on the Cryotop. After rewarming, vitrified oocytes were subjected to IVM (immature) and intracytoplasmic sperm injection (ICSI) with fresh epididymal sperm. The toxicity test revealed no negative effect of oocyte exposure to the applied VS on their developmental potential (p > 0.05). Although the vitrification procedure itself significantly reduced the meiotic competence of oocytes, their meiotic status before vitrification (immature vs. in vitro matured) did not influence fertilization and morula rates. The only parameter affected by vitrification was the rate of oocytes suitable for ICSI, which was significantly lower for immature oocytes. Regardless of the meiotic status of vitrified oocytes, morphologically normal morulae were obtained. Moreover, the two meiotic stages examined are suitable for vitrification, with mature oocytes being a better choice when a well-equipped laboratory is available.

Molecular Design of Polyampholytes for Vitrification-Induced Preservation of Three-Dimensional Cell Constructs without Using Liquid Nitrogen

Current slow-freezing methods are too inefficient for cryopreservation of three-dimensional (3D) tissue constructs. Additionally, conventional vitrification methods use liquid nitrogen, which is inconvenient and increases the chance of cross-contamination. Herein, we have developed polyampholytes with various degrees of hydrophobicity and showed that they could successfully vitrify cell constructs including spheroids and cell monolayers without using liquid nitrogen. The polyampholytes prevented ice crystallization during both cooling and warming, demonstrating their potential to prevent freezing-induced damage. Monolayers and spheroids vitrified in the presence of polyampholytes yielded high viabilities post-thawing with monolayers vitrified with PLL-DMGA exhibiting more than 90% viability. Moreover, spheroids vitrified in the presence of polyampholytes retained their fusibilities, thus revealing the propensity of these polyampholytes to stabilize 3D cell constructs. This study is expected to open new avenues for the development of off-the-shelf tissue engineering constructs that can be prepared and preserved until needed.

Cryopreservation of donkey embryos: Comparison of embryo survival rate after in vitro culture between conventional freezing and vitrification

Embryo cryopreservation ensures that genetic biodiversity is preserved over time. This study evaluates the survival of donkey embryos subjected to slow freezing and vitrification after thawing and in vitro culture. Seven-day-old in vivo produced donkey embryos were subjected to slow freezing (SF, N = 14) or vitrification (VIT, N = 22). After one year of cryopreservation, embryos were warmed, washed and placed in incubation for in vitro culture (IVC). In order to assess the embryo viability, the quality grade and developmental stage were recorded after thawing and after 24 and 48 h of IVC. Eleven embryos (SF = 4 and VIT = 7) were incubated under a time-lapse camera, for up to 68 h, in order to determine the area and growth. The survival rate was not influenced by the procedure but by the developmental stage: after 48 h of IVC blastocyst survival rate (1/8, 12.5%) was significantly lower compared to both morulas (8/12, 66.7%) and early blastocysts (11/16, 68.7%) (P < 0.05). Embryo diameter class at recovery did not significantly influence the survival rate. In terms of the embryos that were judged to be alive after 48 h of IVC, quality grade 1 was observed in 7/8 (88%) and 4/12 (33%) of the SF and VIT embryos, respectively (P < 0.05). After time-lapse analysis, the IVC embryo area as well as growth percentage were statistically higher in the SF than the VIT embryos (P < 0.05). In conclusion, no difference in survival rates was found between the two cryopreservation procedures, although embryo quality was more negatively affected by vitrification.

Successful vitrification of dromedary camel embryos using a novel embryo vitrification kit

Embryos (n = 87) collected 8 days after mating and 7 days after ovulation were vitrified using a camel-specific vitrification kit. Vitrification solutions (VS) containing 20% foetal calf serum, with or without 2% bovine serum albumin (BSA) were used to cryopreserve embryos, in three steps VS1 (5 min), VS2 (5 min) and VS3 (30-35 s) at room temperature (RT) before being loaded into open pulled straws and immediately frozen in liquid nitrogen. Embryos were subsequently thawed in warming solutions (WS) in three steps: WS1 at 37 °C (1 min), WS2 at RT (5 min) then into holding media at RT (5-60 min) prior to transfer, in pairs, into recipient camels 6 days after ovulation. There were 42 of 43 embryos viable after vitrification in media without BSA and these were subsequently transferred into 21 recipient females which resulted in ten pregnancies 60 days after transfer (48% pregnancy rate). There were 38 of 44 viable embryos vitrified in media containing BSA that were transferred in pairs into 19 recipient females which resulted in five pregnancies 60 days after transfer (26% pregnancy rate; P > 0.05). Of the total 15 foetuses that developed to 60 days of gestation after vitrification, 11 resulted from embryos of 200-499 μm diameter and four from embryos of 500-700 μm diameter (P > 0.05). There were encouraging results with use of this novel vitrification kit for the commercial application of cryopreservation of camel embryos with a diameter of 300-550 μm.

Ovarian tissue vitrification is more efficient than slow freezing to preserve ovarian stem cells in CF-1 mice

OBJECTIVE

The aim of this study was to investigate the efficacy of protocols for mice ovary cryopreservation to compare the differences in Mouse Vasa Homologue expression (a germline cell marker) and ovarian viability after vitrification or slow freezing.

METHODS

Female CF1 mice aged 40-45 days were randomly divided into three groups: Control, vitrification or slow freezing. Their ovaries were surgically removed, rinsed in saline solution and cryopreserved. For vitrification, we used a commercial protocol and for slow freeze, we used 1.5 M ethylene glycol (EG) as cryoprotectant. After that, the ovaries were processed for histological an immunohistochemical analysis, and counting of primordial, primary, pre-antral and antral follicles.

RESULTS

No significant difference was found in the proportion of high-quality primordial, primary and pre-antral follicles after thawing/warming in the slow freezing and vitrification groups. The immunohistochemistry for MVH antibody demonstrated that the slow freeze group had a higher number of unmarked cells (p=0.012), indicating a harmful effect on the MVH expression in the ovarian tissue, where the cell structure is complex.

CONCLUSION

Although both protocols indicated similar results in the histological analysis of follicular counts, the vitrification protocol was significantly better to preserve ovarian stem cells, an immature germ cell population. These cells are able to self-renew having regeneration potential, and may be effective for the treatment of ovarian failure and consequently infertility.

Vitrification of in vitro-derived bovine embryos: targeting enhancement of quality by refining technology and standardising procedures

Bovine invitro fertilisation technology has been widely exploited in commercial settings. The majority of invitro-derived cattle embryos are transferred into recipient cows as recently collected (i.e. 'fresh') embryos due to the lack of a reliable cryopreservation method that results in favourable pregnancy rates following transfer of thawed embryos. This is a primary reason for the poor industry uptake of this extreme temperature freezing process. Numerous investigations into vitrification have revealed the importance of rapid cooling and warming rates, enhancing embryo viability after cryopreservation compared with conventional slow freezing. Those studies spawned a considerable assortment of cryovessels and diversity of procedures, delivering variable rates of success, which makes performing vitrification consistently a practical challenge. Hence, further research is required in order to both optimise and standardise vitrification methodology and to design a cryovessel that enables direct transfer of vitrified embryos to recipients after warming. In parallel with improvements in vitrification, it is important to continue to raise the quality of invitro-derived cattle embryos through modifications in laboratory culture techniques. The twin goals of methodology refinement and standardisation, leading to embryo quality enhancement, are each imperative if invitro fertilisation technology is to be adopted in the field.

Human oocytes and zygotes are ready for ultra-fast vitrification after 2 minutes of exposure to standard CPA solutions

Vitrification of human oocytes and embryos in different stages of development is a key element of daily clinical practice of in vitro fertilization treatments. Despite the cooling and warming of the cells is ultra-fast, the procedure as a whole is time consuming. Most of the duration is employed in a long (8–15 minutes), gradual or direct exposure to a non-vitrifying cryoprotectant solution, which is followed by a short exposure to a more concentrated vitrifying solution. A reduction in the duration of the protocols is desirable to improve the workflow in the IVF setting and reduce the time of exposure to suboptimal temperature and osmolarity, as well as potentially toxic cryoprotectants. In this work it is shown that this reduction is feasible. In silico (MatLab program using two-parameter permeability model) and in vitro observations of the oocytes’ osmotic behaviour indicate that the dehydration upon exposure to standard cryoprotectant solutions occurs very fast: the point of minimum volume of the shrink-swell curve is reached within 60 seconds. At that point, intracellular water ejection is complete, which coupled with the permeation of low molecular weight cryoprotectants results in similar intracellular and extracellular solute concentrations. This shows that prolonging the exposure to the cryoprotectant solutions does not improve the cytosolic glass forming tendency and could be avoided. To test this finding, human oocytes and zygotes that were donated for research were subjected to a shortened, dehydration-based protocol, consisting of two consecutive exposures of one-minute to two standard cryoprotectant solutions, containing ethylene glycol, dimethyl sulfoxide and sucrose. At the end of this two-minute dehydration protocol, the critical intracellular solute concentration necessary for successful vitrification was attained, confirmed by the post-warming survival and ability to resume cytokinesis of the cells. Further studies of the developmental competency of oocytes and embryos would be necessary to determine the suitability of this specific dehydration protocol for clinical practice, but based on our results, short times of exposure to increasingly hypertonic solutions could be a more time-efficient strategy to prepare human oocytes and embryos for vitrification.

Cryopreservation of Human Ovarian Tissue: A Review

BACKGROUND

Cryopreservation of human ovarian tissue has been increasingly applied worldwide to safeguard fertility in cancer patients, notably in young girls and women who cannot delay the onset of their treatment. Moreover, it has been proposed to patients with benign pathologies with a risk of premature ovarian insufficiency. So far, more than 130 live births have been reported after transplantation of cryopreserved ovarian tissue, and almost all patients recovered their ovarian function after tissue reimplantation.

SUMMARY

This review aims to summarize the recent results described in the literature regarding human ovarian tissue cryopreservation in terms of methods and main results obtained so far. To cryopreserve human ovarian tissue, most studies describe a slow freezing/rapid thawing protocol, which is usually an adaptation of a protocol developed for sheep ovarian tissue. Since freezing has been shown to have a deleterious effect on ovarian stroma and granulosa cells, various research groups have been vitrifying ovarian tissue. Despite promising results, only 2 babies have been born after transplantation of vitrified/warmed ovarian tissue. Optimization of both cryopreservation strategies as well as thawing/warming protocols is therefore necessary to improve the survival of follicles in cryopreserved ovarian tissue.

KEY MESSAGES

Human ovarian tissue cryopreservation has been successfully applied worldwide to preserve fertility in patients with malignant or nonmalignant pathologies that have a detrimental effect on fertility. Human ovarian tissue cryopreservation could also be applied as an alternative to postpone pregnancy or menopause in healthy women. Slow freezing and vitrification procedures have been applied to cryopreserve human ovarian tissue, but both alternatives require optimization.

Vitrification of canine ovarian tissues with polyvinylpyrrolidone preserves the survival and developmental capacity of primordial follicles

Ovarian tissue cryopreservation combined with immature follicle development can preserve female fertility in wildlife, regardless of age or reproductive timing. To investigate the effects of different cryopreservation methods and cryoprotectants on follicular survival and developmental capacity, ovarian cortical pieces from 15 dogs were cryopreserved by slow freezing or vitrification with different additional cryoprotectants as follows: dimethyl sulfoxide (DMSO), polyvinylpyrrolidone (PVP), combined DMSO and PVP (each at half the concentration of when used independently), or none (control). Cryopreserved ovarian tissues were evaluated by neutral red staining, histology, and xenotransplantation assays. Among cryopreservation conditions tested, vitrification with combined DMSO and PVP significantly improved the maintenance of follicular morphology compared to that in control. Furthermore, ovarian tissues vitrified using this condition maintained follicle morphology and developmental capacity 9 weeks after grafting, as shown by an increased percentage of primary and secondary follicles and a significant decrease in the transition stage from primordial to primary stage follicles 5 and 9 weeks after grafting. In contrast, slow freezing and control groups lost intact follicles by 5 weeks after grafting. The described cryopreservation techniques, which preserve canine follicle development, will build the foundation of ovarian tissue cryopreservation to preserve female fertility in wild canids.

Cryopreservation and microfluidics: a focus on the oocyte

Cryopreservation of gametes and embryos has played a critical role in successful assisted reproductive technologies in rodents, domestic farm species, endangered species and humans. With improved success, and changing needs, the utility of gamete or embryo cryopreservation has escalated. In this review we address some of the foundational history of mammalian cryobiology, species-specific utilities, fundamental understandings of cryoprotectant agents and their use in slow-rate freezing and vitrification, and expand on the recent success and uses of oocyte vitrification and warming. In the area of female gamete cryopreservation, emphasis will be placed on not just cell survival, but also perceived and measured affects of cryopreservation on intracellular structures and functions that affect subsequent completion of meiosis with chromatin segregation fidelity, normal fertilisation and embryonic developmental competence. We compare and contrast data from cow, mouse and humans with a focus on using species-comparative developmental biology to guide future studies for improving methodologies for all species. The application of the relatively new technology microfluidics is discussed in relation to moving gradually (i.e. changing the solution over cells in an automated fashion) compared with the stepwise manual movement of cells through changing solution currently used. This use of microfluidics to change the way cells are exposed to cryoprotectant agents can provide new insights into the effects of osmotic stress and cellular strain rates previously unappreciated, precise methods of computational and biological data acquisition and appreciation of morphometric changes to cellular structure in response to different osmotic stresses and strain rates achieved with varying cryoprotectant exposures. Collectively, these devices and methodologies provide a means of achieving incremental improvement of oocyte and zygote cryopreservation with normalised and improved developmental competence. Finally, we look to the past and the future to acknowledge the accomplishment of leaders in the field of mammalian gamete and embryo cryobiology, their inspirational works, their tireless dissemination of information and the potential of new technologies in bioengineering to improve the efficiency and safety of gamete and embryo cryopreservation.

Cryoprotectant-Free Freezing of Cells Using Liquid Marbles Filled with Hydrogel

Cryopreservation without cryoprotectant remains a significant challenge for the re-establishment of cell culture after freeze-thaw. Thus, finding an alternative and a simple cryopreservation method is necessary. Liquid marble (LM)-based digital microfluidics is a promising approach for cryoprotectant-free cryopreservation. However, the use of this platform to efficiently preserve samples with low cell density and well-controlled serum concentrations has not been investigated. We addressed this issue by embedding an agarose-containing fetal bovine serum (FBS) inside the LM. A low density of 500 cells/μL of murine 3T3 cells was selected for evaluating the postcryogenic survivability. The effects on the post-thaw cell viability of the concentration of agarose, the amount of FBS inside the agarose, and the volume of the LM were investigated systematically. This paper also presents an analysis on the changes in shape and crack size of post-thawed agarose. The results revealed that the embedded agarose gel serves as a controlled release mechanism of FBS and significantly improves cell viability. Post-thaw recovery sustains major cellular features, such as viability, cell adhesion, and morphology. The platform technology reported here opens up new possibilities to cryopreserve rare biological samples without the toxicity risk of cryoprotectants.

Evaluation of cryopreservation efficiency on embryo growth after exposing them in intracellular cryoprotectant ethylene glycol or glycerol and replacing them by trehalose

The present study was conducted to see whether toxicity could be reduced by replacing some of the penetrating cryoprotectant (intracellular cryoprotectant) with a disaccharide as well as finding out the optimum equilibration time in a vitrification solution before rapid cooling. Goat ovaries (1,685) were aspirated and 1,761 culturable oocytes (COC) were recovered. The recovered COCs were matured in maturation medium and evaluated on the basis of cumulus expansion. The matured oocytes were coincubated with fresh semen capacitated in TALP media, for 18 h. The inseminated oocytes were further cultured in mSOF for in vitro embryo development. The cleavage rate was 11.76% and the development rate of embryos to 4–8 and 8–16 cells morulae was 55.6% and 42.4%, respectively. In vitro produced goat embryos (132), 4–16 cell stages, were used for cryopreservation using different protocols. In protocol- 1, 2, 3 and 4, there was no survivability of embryos. In protocol- 5, 6, 7 and 8, the survivability of embryo after freezing was 10, 25, 35.7 and 72.2%, respectively. In protocol- 8, the percentage of live embryos was significantly higher than other protocols. Also it was found that the survivability rate of embryos in protocol 6 and 7 were significantly higher as compared to protocol 1, 2, 3, 4 and 5. However, non-significant differences were found among protocol 1, 2, 3, 4 and 5, and between 6 and 7. From our results, it can be concluded that cryopreservation using 20% ethylene glycol and 0.9 M trehalose for 30 min gives significantly higher post thaw (72.2%) survivability of embryos.

Comparison of two closed carriers for vitrification of human blastocysts in a donor program

The survival of human blastocysts to vitrification with two different carriers is compared. Both vitrification carriers used in this study are in the category of closed carriers, as they completely isolate the samples from direct contact with liquid nitrogen or its vapours during cooling and storage, until warming. This characteristic is appealing because it reduces or eliminates the theoretical risk of cross-contamination during that period of time. The two closed vitrification systems used present very different design and features: in the High Security Vitrification device, the carrier straw containing the embryos is encapsulated inside an external straw before plunging in liquid nitrogen, resulting in thermal insulation during cooling. On the other hand, in the SafeSpeed carrier embryos are loaded in a thin-walled, narrow capillary designed to maximize the thermal transference. Both closed carriers achieved comparable outcomes in terms of survival of blastocysts to the vitrification process, with 97.5% vs. 96.1% survival with HSV and SafeSpeed, respectively. In conclusion, the cooling and warming rates at which these carriers operate, in combination with the cytosolic solute concentration in the cells of the cryopreserved blastocysts attained after a cryoprotectant-loading protocol, result in successful vitrification of human blastocysts for human assisted reproduction.

Vitrification of bovine embryos followed by in vitro hatching and expansion

The objective of this study was to assess the effects of bovine embryo vitrification by applying three different vitrification solutions containing ethylene glycol (EG) and dimethylsulphoxide (DMSO) at different concentrations (10, 20 or 25% each) combined with 1.0 M glucose or 1.0 M sucrose, on the in vitro hatching and expansion rates. Healthy oocytes were selected for in vitro maturation and fertilization from 200 bovine ovaries, and subsequently cultured up to the blastocyst stage (n = 800). Control (n = 200) and vitrified cells (n = 100 per treatment; 600 in total) were cultured for an extra 24 or 48 h to evaluate hatching and expansion, respectively. Vitrification significantly decreased embryonic re-expansion and hatching rates independently of the tested solution when compared with control embryos, but solutions with 25% EG + 25% DMSO resulted in the highest re-expansion (75%) and hatching (70%) rates, independently of the added sugar. The addition of sucrose resulted in higher rates of re-expanded and hatched embryos when compared with glucose addition. We concluded that the combination of 25% EG + 25% DMSO and 1.0 M sucrose allowed hatching and expansion of vitrified-warmed bovine embryos produced in vitro.

Successful pregnancies from vitrified embryos in the dromedary camel: Avoidance of a possible toxic effect of sucrose on embryos

Successful embryo cryopreservation facilitates the wider application of assisted reproduction technologies and also provides a useful method for gene banking of valuable genetics. Unfortunately attempts to establish an effective cryopreservation protocol for camelid embryos have been unsuccessful. In the current study, a modified vitrification protocol with three steps was investigated, whereby embryos were exposed to solutions containing increasing amounts of glycerol and ethylene glycol for fixed time periods. Embryos were then loaded into an Open Pull Straw (OPS) and plunged directly into liquid nitrogen for storage. Three experiments were designed to investigate the effect of 1) artificial shrinkage (AS) of embryos, 2) the addition of sucrose to the vitrification solutions, and 3) the replacement of sucrose by galactose in the warming solution, on the outcome of vitrification. The results showed that neither AS of hatched embryos prior to vitrification, nor the addition of sucrose into vitrification solutions improves the outcome of vitrification, while replacement of sucrose with galactose in warming solution increases the survival and developmental rates of vitrified embryos in culture. Transfer of vitrified embryos that were warmed in galactose resulted in a pregnancy rate of 42.8% per embryo or 46.1% per recipient. Collectively, these results suggest a possible species-specific toxic effect of sucrose on camel embryos, and that avoiding its use either in vitrification or warming solution is critical for establishing an effective protocol. This study may also be applicable to the vitrification of embryos of other camelid species including alpaca and llamas.

Noninvasive embryo assessment technique based on buoyancy and its association with embryo survival after cryopreservation

Embryo cryopreservation offers many benefits by allowing genetic preservation, genetic screening, cost reduction, global embryo transport and single embryo transfer. However, freezing of embryos decreases embryo viability, as intracellular ice crystal formation often damages embryos. Success rates of frozen embryo transfer are expected to be 15-20% less than fresh embryo transfer. We have developed a noninvasive embryo assessment technique (NEAT) which enables us to predict embryo viability based on buoyancy. The purpose of this research was twofold. First was to determine if a NEAT, through a specific gravity device can detect embryo survival of cryopreservation. Second, it was to relate embryo buoyancy to embryo viability for establishing pregnancies in sheep. Blastocysts descent times were measured on one-hundred sixty-nine mice blastocysts before cryopreservation, according to standard protocol and post-thawing blastocysts descent times were measured again. There was a significant difference in blastocyst post-thaw descent times with NEAT in those blastocysts which demonstrated viability from those that did not (P < 0.05). This suggests NEAT is successful in determining blastocysts viability in cryopreserved mice blastocysts. At a commercial ovine facility, NEAT was performed on fourteen frozen and thawed ovine blastocysts. Blastocysts of similar descent times were paired and transferred into recipient ewes as twins. Pregnancy was later confirmed by blood test and multiple gestation outcomes were determined at lambing. Six of seven recipient ewes were pregnant and all pregnant ewes delivered lambs without complication. Four ewes delivered twin lambs and two ewes delivered singletons, which totals ten of the fourteen (71%) blastocysts surviving to term. This pregnancy rate is comparable to expected to pregnancy rates in a commercial setting. The blastocysts which did not establish pregnancy demonstrated less buoyancy versus those blastocysts which established pregnancies which survived to term (P < 0.05). These results suggest NEAT can identify which blastocysts survive cryopreservation, thus significantly reduce the transfer of non-viable embryos. Further studies on a larger scale commercial setting will evaluate the efficacy of NEAT.

Modified MicroSecure Vitrification: A Safe, Simple and Highly Effective Cryopreservation Procedure for Human Blastocysts

Clinical embryo vitrification evolved with the development of unique vitrification devices in the 21^st century and with the misconception that ultra-rapid cooling in an "open" system (i.e., direct LN₂ contact) was a necessity to optimize vitrification success. The dogma surrounding the importance of cooling rates led to unsafe practices subject to technical variation and to the creation of vitrification devices that disregarded important quality-control factors (e.g., ease of use, repeatability, reliability, labeling security, and storage safety). Understanding the quality-control flaws of other devices allowed for the development of a safe, secure, repeatable, and reliable µS-VTF method aimed to minimize intra- and inter-technician variation. Equally important, it combined the availability of two existing FDA-compliant devices: 1) a 0.3-mL ionomeric resin embryo straw with internalized, dual-colored, tamper-proof labeling with repeatable weld seal potential; and 2) shortened, commonly-used, 300-µm ID sterile flexipettes to directly load the embryo(s) in order to create a highly-effective global vitrification device. Like other aseptic, closed vitrification systems (e.g., High Security Vitrification (HSV), Rapid-i, and VitriSafe) effectively used in reproductive medicine, microSecure Vitrification (µS-VTF) has proven that it can achieve high post-warming survival and pregnancy outcomes with its attention to simplicity, and reduced technical variation. Although the 0.3-mL embryo straw containing an internal hydrophobic plug was commercially replaced with a standard semen straw possessing cotton-polyvinyl pyrrolidone (PVP) plugs, it maintained its ionomeric resin composition to ensure weld sealing. However, the cotton plugs can wick out the fluid-embryo contents of the flexipettes upon contact. A modified µS-VTF method was adapted to include an additional internal weld seal before the plug on the device loading side. The added technical step to the µS-VTF procedure has not affected its successful application, as high survival rates (> 95%) and pregnancy rates continue today.

Synergistic Development of Biochips and Cell Preservation Methodologies: A Tale of Converging Technologies

PURPOSE OF THE REVIEW

Over the past several decades, cryopreservation has been widely used to preserve cells during long term storage, but advances in stem cell therapies, regenerative medicine, and miniaturized cell-based diagnostics and sensors are providing new targets of opportunity for advancing preservation methodologies. The advent of microfluidics-based devices is an interesting case in which the technology has been used to improve preservation processing, but as the devices have evolved to also include cells, tissues, and simulated organs as part of the architecture, the biochip itself is a desirable target for preservation. In this review, we will focus on the synergistic co-development of preservation methods and biochip technologies, while identifying where the challenges and opportunities lie in developing methods to place on-chip biologics on the shelf, ready for use.

RECENT FINDINGS

Emerging studies are demonstrating that the cost of some biochips have been reduced to the extent that they will have high utility in point-of-care settings, especially in low resource environments where diagnostic capabilities are limited. Ice-free low temperature vitrification and anhydrous vitrification technologies will likely emerge as the preferred strategy for long-term preservation of bio-chips.

SUMMARY

The development of preservation methodologies for partially or fully assembled biochips would enable the widespread distribution of these technologies and enhance their application.

Which Stage of Mouse Embryos Is More Appropriate for Vitrification?

Background

Vitrification has been shown as one of the most effective methods of cryopreservation for mammalian embryos. However, there is no consensus which stage of embryonic development is the most appropriate for vitrification with subsequent maximal development after thawing. This study was carried out to explore and compare the effect(s) of vitrification on mouse 2-cell, 4-cell, 8-cell, morula and blastocyst stage embryos and subsequent blast formation and hatching after thawing.

Materials and Methods

In this experimental study, 2-cell embryos were obtained from the oviducts of super ovulated female NMRI mice. Some embryos were randomly selected and vitrified through a two-step media protocol and cryotop. Other embryos were cultured to assess their development. During the ensuing days, some of these cultured embryos were vitrified at 4-cell, 8-cell, morula and blastocyst stages. After 10 to 14 days, the embryos were thawed to assess their survival and also cultured to determine the rate of blastocyst formation and hatching. The results were analyzed using one-way ANOVA and Tukey’s post-hoc tests.

Results

There was no significant difference in the survival rates of vitrified embryos at 2-cell, 4-cell, 8-cell, morula and blastocyst stages after thawing (P>0.05). The blastocyst formation rate of vitrified 8-cell embryos was significantly higher than that of 2-cell embryos (P<0.05). The hatching rate of vitrified 4-cell, 8-cell and blastocysts were significantly higher than that of 2-cell embryos (P<0.05).

Conclusion

Vitrification is suitable for cryopreservation of all stages of mouse embryonic development. However, the best tolerance for vitrification was observed at 4and 8-cell stages of development. Accordingly, the development of vitrified embryos to blastocysts, following thawing, was most efficacious for 4 and 8-cell embryos. Compared to mouse 2-cell embryos, embryos vitrified as blastocysts had the highest rate of hatching.

Cryopreservation: Vitrification and Controlled Rate Cooling

Cryopreservation is the application of low temperatures to preserve the structural and functional integrity of cells and tissues. Conventional cooling protocols allow ice to form and solute concentrations to rise during the cryopreservation process. The damage caused by the rise in solute concentration can be mitigated by the use of compounds known as cryoprotectants. Such compounds protect cells from the consequences of slow cooling injury, allowing them to be cooled at cooling rates which avoid the lethal effects of intracellular ice. An alternative to conventional cooling is vitrification. Vitrification methods incorporate cryoprotectants at sufficiently high concentrations to prevent ice crystallization so that the system forms an amorphous glass thus avoiding the damaging effects caused by conventional slow cooling. However, vitrification too can impose damaging consequences on cells as the cryoprotectant concentrations required to vitrify cells at lower cooling rates are potentially, and often, harmful. While these concentrations can be lowered to nontoxic levels, if the cells are ultra-rapidly cooled, the resulting metastable system can lead to damage through devitrification and growth of ice during subsequent storage and rewarming if not appropriately handled.The commercial and clinical application of stem cells requires robust and reproducible cryopreservation protocols and appropriate long-term, low-temperature storage conditions to provide reliable master and working cell banks. Though current Good Manufacturing Practice (cGMP) compliant methods for the derivation and banking of clinical grade pluripotent stem cells exist and stem cell lines suitable for clinical applications are available, current cryopreservation protocols, whether for vitrification or conventional slow freezing, remain suboptimal. Apart from the resultant loss of valuable product that suboptimal cryopreservation engenders, there is a danger that such processes will impose a selective pressure on the cells selecting out a nonrepresentative, freeze-resistant subpopulation. Optimizing this process requires knowledge of the fundamental processes that occur during the freezing of cellular systems, the mechanisms of damage and methods for avoiding them. This chapter draws together the knowledge of cryopreservation gained in other systems with the current state-of-the-art for embryonic and induced pluripotent stem cell preservation in an attempt to provide the background for future attempts to optimize cryopreservation protocols.

Cryopreservation of feline oocytes by vitrification using commercial kits and slush nitrogen technique

Assisted reproductive techniques are a valuable tool for conservation breeding of endangered species. Cryopreservation methods are the basis of gamete banks, supporting genetic diversity preservation. Unfortunately, cryopreservation of feline oocytes is still considered an experimental technique. The aim of this study was to compare two commercial kits, with our protocol for vitrification of cat oocytes (IZW), which comprises a three-step method with ethylene glycol, DMSO, fetal calf serum, trehalose and Ficoll PM-70. Furthermore, we applied slush nitrogen (SN₂ ) for ultra-rapid freezing to improve survival rates. Cumulus-oocyte complexes were collected from domestic cat ovaries by slicing and vitrified at immature stage using Cryotop as storage device. Vit Kit^® Freeze/Thaw (n = 89) showed the lowest maturation percentage obtained after warming (10.1%). A significant difference in maturation percentage of oocytes was found between Kitazato^® kit (38.7%, n = 137) and IZW protocol (24.5%, n = 143). The cleavage after ICSI of warmed and matured oocytes (20.7% and 28.6%, respectively) and the morula percentage (18. 2% and 22.5%, respectively), however, did not reveal any significant difference between the two methods. Application of SN₂ did not result in any improvement of oocytes' cryopreservation. Maturation percentage of the oocytes vitrified by IZW method with SN₂ (n = 144) decreased until 6.1%, without any cleavage after fertilization. For Kitazato^® (n = 62), only 17.7% were able to undergo maturation and cleavage percentage dropped to 18.2%, not reaching morula stage. These data demonstrate that feline oocytes can be vitrified either by our IZW method or by commercial Kitazato^® kit, but the use of SN₂ is improving neither maturation nor cleavage percentages when combined with these procedures.

Cryopreservation of whole bovine ovaries: comparisons of different thawing protocols

OBJECTIVE

The aim of this study was to perform a comparative investigation of several different thawing protocols and to determine an appropriate protocol for thawing whole bovine frozen ovaries.

STUDY DESIGN

Bovine ovaries were slowly frozen and then thawed by applying different protocols. Ultrastructural change, follicle viability, and the hormone levels of culture supernatant were measured.

RESULTS

The percentage of morphologically normal primordial follicles and the hormone levels of culture supernatant in group D (two-step, thawing in water at 39°C) were significantly higher than those in any other group. Moreover, the ultrastructural alteration of oocyte in group D (two-step, thawing in water at 39°C) was slighter than those in any other group.

CONCLUSIONS

The two-step protocol involving short-term exposure to water at a moderately high temperature (39°C) proved to be a suitable for thawing bovine whole ovaries.

Thermal and clinical performance of a closed device designed for human oocyte vitrification based on the optimization of the warming rate

Although it was qualitatively pointed out by Fahy et al. (1984), the key role of the warming rates in non-equillibrium vitrification has only recently been quantitatively established for murine oocytes by Mazur and Seki (2011). In this work we study the performance of a closed vitrification device designed under the new paradigm, for the vitrification of human oocytes. The vitrification carrier consists of a main straw in which a specifically designed capillary is mounted and where the oocytes are loaded by aspiration. It can be hermetically sealed before immersion in liquid nitrogen for vitrification, and it is warmed in a sterile water bath at 37 °C. Measured warming rates achieved with this design were of 600.000 ºC/min for a standard DMEM solution and 200.000 ºC/min with the vitrification solution for human oocytes. A cohort of 143 donor MII sibling human oocytes was split into two groups: control (fresh) and vitrified with SafeSpeed device. Similar results were found in both groups: survival (97.1%), fertilization after ICSI (74.7% in control vs. 77.3% in vitrified) and good quality embryos at day three (54.3% in control vs. 58.1% in vitrified) were settled as performance indicators. The pregnancy rate was 3/6 (50%) for the control, 2/3 (66%) for vitrified and 4/5 (80%) for mixed transfers.