Formation of extracellular and intracellular ice during warming of vitrified mouse morulae and its effect on embryo survival

Definition of protocols for cryopreservation and three-dimensional in vitro culture of prepubertal goat testicular tissue after histomorphological, ultrastructural, and functional analysis

This study aims to define the best method (slow freezing or vitrification) and fragment size (1, 5, or 9 mm³) for prepubertal goat testis cryopreservation, as well as to evaluate testicular morphological integrity after cryopreservation and in vitro culture (IVC). Initially (experiment I), 1, 5, or 9 mm³ testis fragments were cryopreserved by slow freezing using a Mr. Frosty container with 20% Dimethylsulfoxide (DMSO) or vitrified using the Ovarian Tissue Cryosystem (OTC) device, (Equilibration solution - ES: 10% DMSO and 10% ethylene glycol - EG; Vitrification solution - VS: 20% DMSO and 20% EG) and then subjected to morphological analysis, type I and III collagen quantification and gene expression (Oct4, C-kit, Bax, and Bcl-2). Subsequently, (experiment II), fresh or cryopreserved by slow freezing testis fragments were cultured in vitro and submitted to morphological analysis by scanning electron microscopy. The data from the experiment I revealed fewer morphological alterations in 1 and 5 mm³ fragments after vitrification and slow freezing, respectively. The percentage of type I collagen fibers in 5 and 9 mm³ frozen was higher than in fresh or vitrified fragments. For type III collagen, fresh or frozen fragments of 1 and 5 mm3 showed a higher percentage than fragments of 9 mm3. Gene expression for Oct4 and C-kit after slow freezing or vitrification in the 5 mm3 fragments was lower than that observed in the fresh fragments. The Bax:Bcl-2 ratio in the 1 and 9 mm³ fragments was lower than in the 5 mm³ fragments for fresh fragments or after freezing. In experiment II, fragments cultured in vitro, previously frozen or not, showed more morphological alterations than fresh or frozen fragments. We concluded that slow freezing of 5 mm³ fragments was the best protocol for cryopreserving prepubertal goat testis and although the results of IVC are encouraging, it still needs improvement to restore testicular function after cryopreservation.

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.

Recent Developments in Cell Shipping Methods

As opposed to remarkable advances in the cell therapy industry, researches reveal inexplicable difficulties associated with preserving and post-thawing cell death. Post cryopreservation apoptosis is a common occurrence that has attracted the attention of scientists to use apoptosis inhibitors. Transporting cells without compromising their survival and function is crucial for any experimental cell-based therapy. Preservation of cells allows the safe transportation of cells between distances and improves quality control testing in clinical and research applications. The vitality of transported cells is used to evaluate the efficacy of transportation strategies. For many decades, the conventional global methods of cell transfer were not only expensive but also challenging and had adverse effects. The first determination of some projects is optimizing cell survival after cryopreservation. The new generation of cryopreservation science wishes to find appropriate and alternative methods for cell transportation to ship viable cells at an ambient temperature without dry ice or in media-filled flasks. The diversity of cell therapies demands new cell shipping methodologies and cryoprotectants. In this review, we tried to summarize novel improved cryopreservation methods and alternatives to cryopreservation with safe and viable cell shipping at ambient temperature, including dry preservation, hypothermic preservation, gel-based methods, encapsulation methods, fibrin microbeads, and osmolyte solution compositions. This article is protected by copyright. All rights reserved.

Magnetic Nanoparticle-Mediated Heating for Biomedical Applications

Magnetic nanoparticles, especially superparamagnetic nanoparticles (SPIONs), have attracted tremendous attention for various biomedical applications. Facile synthesis and functionalization together with easy control of the size and shape of SPIONS to customize their unique properties, have made it possible to develop different types of SPIONs tailored for diverse functions/applications. More recently, considerable attention has been paid to the thermal effect of SPIONs for the treatment of diseases like cancer and for nanowarming of cryopreserved/banked cells, tissues, and organs. In this mini-review, recent advances on the magnetic heating effect of SPIONs for magnetothermal therapy and enhancement of cryopreservation of cells, tissues, and organs, are discussed, together with the non-magnetic heating effect (i.e., high Intensity focused ultrasound or HIFU-activated heating) of SPIONs for cancer therapy. Furthermore, challenges facing the use of magnetic nanoparticles in these biomedical applications are presented.

The Assessment of Various Factors Affecting the Postwarming Viability and Developmental Capability of Goat Metaphase II Oocytes Vitrified by Cryotop

The effects of the equilibration time, the vitrification procedure, and the warming procedure on the quality of goat oocytes vitrified by Cryotop were assessed. In the first part of the study, oocytes were exposed to 10% dimethyl sulfoxide (DMSO) and 10% ethylene glycol (EG) for 1, 3, 5, or 10 minutes, respectively, followed by vitrification. In the second part, after equilibration in 7.5% DMSO +7.5% EG for 3 minutes, 10% DMSO +10% EG for 3 minutes, or 4% EG for 10 minutes, oocytes were equilibrated in 15% DMSO +15% EG, 20% DMSO +20% EG, or 35% EG for 30 seconds before vitrification. The vitrification procedures were designated as first vitrification procedure (VPI), second vitrification procedure (VPII), and third vitrification procedure (VPIII), respectively. In the third part, oocytes vitrified using VPIII were warmed by the three procedures (first warming procedure [TPI], second warming procedure [TPII], or third warming procedure [TPIII]) containing different concentrations of trehalose. The results showed that after equilibration for 1 or 3 minutes in 10% DMSO and 10% EG, the viability and developmental capability of vitrified oocytes were significantly superior to the groups after equilibration for over 5 minutes (p < 0.05). With the VPIII procedure, the frequencies with normal morphology, cleavage, and blastocyst formation of vitrified oocytes were 91.87% ± 4.14%, 76.51% ± 4.37%, and 39.84% ± 2.91%, respectively, demonstrating a significant increase compared to the VPI or VPII group (p < 0.05). The rates of vitrified oocytes with normal morphology and cleavage in the TPI group were higher than the TPII or TPIII group (p < 0.05). In conclusion, equilibration in 10% DMSO and 10% EG for <3 minutes benefits the viability of vitrified oocytes. EG may be more efficient for vitrification of goat oocytes compared to DMSO. Higher concentrations (more than 1 M) of trehalose enhance cryosurvival of goat oocytes when warming.

Equilibrium vitrification of mouse embryos using low concentrations of cryoprotectants

Previously, we developed a method for vitrification of mouse embryos in a near-equilibrium state using EFS35c, PB1 medium containing 35% (v/v) ethylene glycol, and 0.98 M sucrose. This method has advantages in both slow freezing and vitrification. However, since the vitrification solution in this method contains high concentrations of cryoprotectants and thus has high osmolality, the solution would injure oocytes and embryos with high sensitivity to chemical toxicity and high osmolality. In this study, we examined whether embryos could be vitrified in a near-equilibrium state using a solution containing low concentrations of cryoprotectants and thus with low osmolality. To investigate whether embryos were vitrified in a near-equilibrium state, 2-cell mouse embryos were vitrified with EDFS10/10a, PB1 medium containing 10% (v/v) ethylene glycol, 10% (v/v) DMSO, and 0.4 M sucrose, in liquid nitrogen, stored at -80 °C for 4-28 days, and warmed in water at 25 °C. The viability of the embryos was evaluated by the appearance of embryos after warming and developmental ability. When embryos were vitrified in liquid nitrogen using EDFS10/10a, the survival and developmental ability into blastocysts after storage at -80 °C for 7 days were high, indicating that embryos were vitrified in a near-equilibrium state. A high proportion of embryos vitrified with EDFS10/10a developed to term after transportation with dry ice, re-cooling in liquid nitrogen, and transfer to recipients. Therefore, new equilibrium vitrification developed in this study may be useful for oocytes and embryos that are highly sensitive to the toxicity of cryoprotectants and high osmolality.

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.

Mouse Embryo Cryopreservation by Rapid Cooling

Embryo cryopreservation has been used to archive mouse strains. Protocols have evolved over this time and now vary considerably in terms of cryoprotectant solution, cooling and warming rates, methods to add and remove cryoprotectant, container or carrier type, volume of cryoprotectant, the stage of preimplantation development, and the use of additional treatments such as blastocyst puncture and microinjection. The rapid cooling methods use concentrated solutions of cryoprotectants to reduce the water content of the cell before cooling commences, thus preventing the formation of ice crystals. Embryos are equilibrated with the cryoprotectants, loaded into a carrier, and then rapidly cooled (e.g., by being plunged directly into LN₂ or onto a surface cooled in LN₂). The rapid cooling methods eliminate the need for controlled-rate freezers and seeding procedures. However, they are much more sensitive to minor variations when performing the steps. The rapid-cooling protocol described here is suitable for use with plastic insemination straws. Because it uses relatively large volumes, it is less technically demanding than some other methods that use minivolume devices.

The analysis of viability for mammalian cells treated at different temperatures and its application in cell shipment

Mammalian cells are very important experimental materials and widely used in biological and medical research fields. It is often required that mammalian cells are transported from one laboratory to another to meet with various researches. Conventional methods for cell shipment are laborious and costive despite of maintaining high viability. In this study we aimed to develop a simple and low-cost method for cell shipment by investigating the viabilities of different cell lines treated at different temperatures. We show that the viability of mammalian cells incubated at 1°C or 5°C significantly reduced when compared with that at 16°C or 22°C. Colony formation assays revealed that preservation of mammalian cells at 1°C or 5°C led to a poorer recovery than that at 16°C or 22°C. The data from proliferation and apoptotic assays confirmed that M2 cells could continue to proliferate at 16°C or 22°C, but massive death was caused by apoptosis at 1°C or 5°C. The morphology of mammalian cells treated under hypothermia showed little difference from that of the untreated cells. Quantitative RT-PCR and alkaline phosphatase staining confirmed that hypothermic treatment did not change the identity of mouse embryonic stem cells. A case study showed that mammalian cells directly suspended in culture medium were able to be shipped for long distance and maintained a high level of viability and recovery. Our findings not only broaden the understanding to the effect of hypothermia on the viability of mammalian cells, but also provide an alternative approach for cell shipment.

The development of the cell cryopreservation protocol with controlled rate thawing

Thawing in the water bath is often considered as a standard procedure. The thermal history of samples thawed in this way is poorly controlled, but cryopreservation and banking of cell-based products require standardization, automation and safety of all the technological stages including thawing. The programmable freezers allow implementation of the controlled cooling as well as the controlled thawing. As the cell damage occurs during the phase transformation that takes place in the cryoprotectant medium in the process of freezing-thawing, the choice of warming rates within the temperature intervals of transformations is very important. The goal of the study was to investigate the influence of warming rates within the intervals of the phase transformations in the DMSO-based cryoprotectant medium on the cell recovery and to develop a cryopreservation protocol with controlled cooling and warming rates. The temperature intervals of phase transformations such as melting of the eutectic mixture of the cryoprotectant solution (MEMCS), melting of the eutectic salt solution (MESS), melting of the main ice mass (MMIM), recrystallization before MEMCS, recrystallization before MESS and recrystallization before MMIM were determined by thermo-mechanical analysis. The biological experiments were performed on the rat testicular interstitial cells (TIC). The highest levels of the cell recovery and metabolic activity after cryopreservation were obtained using the protocol with the high (20 °C/min) warming rate in the temperature intervals of crystallization of the eutectics as well as recrystallizations and the low (1 °C/min) warming rate in the temperature intervals of melting of the eutectics as well as MMIM. The total cell recovery was 65.3 ± 2.1 %, the recovery of the 3-beta-HSD-positive (Leydig) cells was 82.9 ± 1.8 %, the MTT staining was 32.5 ± 0.9 % versus 42.1 ± 1.7 %; 57.4 ± 2.1 % and 24.0 ± 1.1 % respectively, when compared to the thawing in the water bath.

Equilibrium vitrification of mouse embryos at various developmental stages

Previously, we developed a new method by which 2-cell mouse embryos can be vitrified in liquid nitrogen in a near-equilibrium state, and then kept at -80°C for several days. In the present study, we examined whether or not the method was effective for mouse embryos at other developmental stages. Eight-cell embryos, morulae, and expanded blastocysts of ICR mice were vitrified with ethylene glycol-based solutions, named EFSc because of their composition of ethylene glycol (30-40%, v/v) and FSc solution. The FSc solution was PB1 medium containing 30% (w/v) Ficoll PM-70 plus 1.5 M sucrose. The extent of equilibrium was assessed by examining how well vitrified embryos survived after being kept at -80°C. When 8-cell embryos and morulae were vitrified with EFS35c or EFS40c and then kept at -80°C, the survival rate was high even after 4 days in storage and remained high after re-cooling in liquid nitrogen. On the other hand, the survival of vitrified-expanded blastocysts kept at -80°C was low. Therefore, 8-cell embryos and morulae can be vitrified in a near-equilibrium state using the same method as for 2-cell embryos. A high proportion of C57BL/6J embryos at the 2-cell, 8-cell, and morula stages vitrified with EFS35c developed to term after transportation on dry ice, re-cooling in liquid nitrogen, and transfer to recipients. In conclusion, the near-equilibrium vitrification method, which is effective for 2-cell mouse embryos, is also effective for embryos at the 8-cell and morula stages. The method would enable handy transportation of vitrified embryos using dry ice.

Effects of different cryopreservation methods on post-thaw culture conditions of in vitro produced bovine embryos

The aim of this work was to evaluate the effect of cryopreservation protocols on subsequent development of in vitro produced bovine embryos under different culture conditions. Expanded in vitro produced blastocysts (n = 600) harvested on days 7-9 were submitted to controlled freezing [slow freezing group: 10% ethylene glycol (EG) for 10 min and 1.2°C/min cryopreservation]; quick-freezing [rapid freezing group: 10% EG for 10 min, 20% EG + 20% glycerol (Gly) for 30 s]; or vitrification [vitrification group: 10% EG for 10 min, 25% EG + 25% Gly for 30 s] protocols. Control group embryos were not exposed to cryoprotectant or cryopreservation protocols and the hatching rate was evaluated on day 12 post-insemination. In order to evaluate development, frozen-thawed embryos were subjected to granulosa cell co-culture in TCM199 or SOFaa for 4 days. Data were analyzed by PROC MIXED model using SAS Systems for Windows®. Values were significant at p < 0.05. The hatching rate of the control group was 46.09%. In embryos cultured in TCM199, slow freezing and vitrification group hatching rates were 44.65 ± 5.94% and 9.43 ± 6.77%, respectively. In embryos cultured in SOFaa, slow freezing and vitrification groups showed hatching rates of 11.65 ± 3.37 and 8.67 ± 4.47%, respectively. In contrast, the rapid freezing group embryos did not hatch, regardless of culture medium. The slow freezing group showed higher hatching rates than other cryopreservation groups. Under such conditions, controlled freezing (1.2°C/min) can be an alternative to cryopreservation of in vitro produced bovine embryos.

Stability of mouse oocytes at -80 °C: the role of the recrystallization of intracellular ice

The germplasm of mutant mice is stored as frozen oocytes/embryos in many facilities worldwide. Their transport to and from such facilities should be easy and inexpensive with dry ice at -79 °C. The purpose of our study was to determine the stability of mouse oocytes with time at that temperature. The metaphase II oocytes were cryopreserved with a vitrification solution (EAFS10/10) developed by M Kasai and colleagues. Two procedures were followed. In one, the samples were cooled at 187 °C/min to -196 °C, warmed to -80 °C, held at -80 °C for 1 h to 3 months, and warmed to 25 °C at one of three rates. With the highest warming rate (2950 °C/min), survival remained at 75% for the first month, but then slowly declined to 40% over the next 2 months. With the slowest warming (139 °C/min), survival was only ∼ 5% even at 0 time at -80 °C. In the second procedure, the samples were cooled at 294 °C/min to -80 °C (without cooling to -196 °C) and held for up to 3 months before warming at 2950 °C/min. Survival was ∼ 90% after 7 days and dropped slowly to 35% after 3 months. We believe that small non-lethal quantities of intracellular ice formed during the cooling and that the intracellular crystals increased to a damaging size by recrystallization during the 3 month's storage at -80 °C. From the practical point of view, this protocol yields sufficient stability to make it feasible to ship oocytes worldwide in dry ice.

The dominance of warming rate over cooling rate in the survival of mouse oocytes subjected to a vitrification procedure

The formation of more than trace amounts of ice in cells is lethal. The two contrasting routes to avoiding it are slow equilibrium freezing and vitrification. The cryopreservation of mammalian oocytes by either method continues to be difficult, but there seems a slowly emerging consensus that vitrification procedures are somewhat better for mouse and human oocytes. The approach in these latter procedures is to load cells with high concentrations of glass-inducing solutes and cool them at rates high enough to induce the glassy state. Several devices have been developed to achieve very high cooling rates. Our study has been concerned with the relative influences of warming rate and cooling rate on the survival of mouse oocytes subjected to a vitrification procedure. Oocytes suspended in an ethylene glycol-acetamide-Ficoll-sucrose solution were cooled to -196 degrees C at rates ranging from 37 to 1827 degrees C/min between 20 and -120 degrees C, and for each cooling rate, warmed at rates ranging from 139 to 2950 degrees C/min between -70 and -35 degrees C. The results are unambiguous. If the samples were warmed at the highest rate, survivals were >80% over cooling rates of 187-1827 degrees C/min. If the samples were warmed at the lowest rate, survivals were near 0% regardless of the cooling rate. We interpret the lethality of slow warming to be a consequence of it allowing time for the growth of small intracellular ice crystals by recrystallization.

Effect of warming rate on the survival of vitrified mouse oocytes and on the recrystallization of intracellular ice

Successful cryopreservation demands there be little or no intracellular ice. One procedure is classical slow equilibrium freezing, and it has been successful in many cases. However, for some important cell types, including some mammalian oocytes, it has not. For the latter, there are increasing attempts to cryopreserve them by vitrification. However, even if intracellular ice formation (IIF) is prevented during cooling, it can still occur during the warming of a vitrified sample. Here, we examine two aspects of this occurrence in mouse oocytes. One took place in oocytes that were partly dehydrated by an initial hold for 12 min at -25 degrees C. They were then cooled rapidly to -70 degrees C and warmed slowly, or they were warmed rapidly to intermediate temperatures and held. These oocytes underwent no IIF during cooling but blackened from IIF during warming. The blackening rate increased about 5-fold for each five-degree rise in temperature. Upon thawing, they were dead. The second aspect involved oocytes that had been vitrified by cooling to -196 degrees C while suspended in a concentrated solution of cryoprotectants and warmed at rates ranging from 140 degrees C/min to 3300 degrees C/min. Survivals after warming at 140 degrees C/min and 250 degrees C/min were low (<30%). Survivals after warming at > or =2200 degrees C/min were high (80%). When warmed slowly, they were killed, apparently by the recrystallization of previously formed small internal ice crystals. The similarities and differences in the consequences of the two types of freezing are discussed.