Vitrification of mouse and human blastocysts using a novel cryoloop container-less technique

One-step warming of vitrified human cleavage and blastocyst stage embryos does not adversely impact embryo survivability and subsequent developmental potential

STUDY QUESTION

Does one-step warming (OW), a simplified embryo warming protocol, adversely affect survival and developmental potential in vitrified cleavage or blastocyst stage embryos compared to standard multi-step warming (SW)?

SUMMARY ANSWER

OW showed no detrimental effects on survival and developmental potential compared to SW in cleavage and blastocyst stage embryos.

WHAT IS KNOWN ALREADY

While standard embryo warming protocols involve a multi-step procedure using a stepwise osmotic solution to avoid a rapid influx of water into the embryo, recent studies suggest that eliminating the stepwise warming process does not reduce embryo survival and embryo transfer outcomes. However, previous reports have focused primarily on pregnancy rates, and a more detailed analysis of the effects of rapid osmotic pressure changes on embryos is necessary to standardize the protocol.

STUDY DESIGN, SIZE, DURATION

This preliminary study includes donated 377 vitrified human embryos (177 cleavage and 200 blastocyst stage) from 210 patients approved for discard at the patient's consent. The embryos were randomly allocated and warmed using either SW or OW protocols. In the SW protocol, embryos were rinsed with a stepwise osmotic solution (thawing, dilution, and washing solutions), and the process was completed with a 13-min warming period. In the OW protocol, embryos were only rinsed in a single solution (thawing solution) for 1 min.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Post-warming embryos were cultured using a time-lapse incubator. Survival rate and developmental potential, including the occurrence of abnormal morphokinetics and the time required for blastocyst formation after warming of cleavage stage embryos, were compared between SW and OW. Embryos that developed into the blastocyst stage were morphologically evaluated. In the warming of blastocyst stage embryos, the survival rate was determined by the presence of blastocoel expansion, and the proportion of full re-expanded blastocysts was observed at 3- and 24-h post-warming. An in vitro adhesion assay was also performed on blastocysts after culture, and adhesion rate and outgrowth area were measured 24, 48, and 72 h after culture with fibronectin-precoated dishes.

MAIN RESULTS AND THE ROLE OF CHANCE

OW did not negatively impact survival rates in either cleavage (100% in both OW and SW groups) or blastocyst stage embryos (99% in both groups). Cleavage stage embryos warmed by OW had superior or comparable rates of morulation (96 vs 85%, P = 0.0387), blastulation (78 vs 73%, P = 0.4044), full-blastocyst formation (60 vs 53%, P = 0.3196), and expanded-blastocyst formation (56 vs 49%, P = 0.4056) compared to those warmed by SW. Time-lapse monitoring analysis revealed that the frequency of collapses was reduced in OW (30 vs 50%, P = 0.0410). Additionally, all other abnormal morphokinetics were equivalent between OW and SW (P > 0.05); moreover, the time required for blastocyst formation (P > 0.05) and the morphological quality after development into the blastocyst stage (P > 0.05) were not significantly different between OW and SW. In warming of blastocyst stage embryos, the time required for full re-expansion was longer with OW (3.20 ± 3.03 h vs 2.14 ± 2.17 h, P = 0.0008), but there was no significant difference in the proportion of full re-expanded blastocysts at 3- (67 vs 75%, P = 0.2417) and 24-h (98 vs 97%, P = 1.0000) post-warming. The in vitro adhesion assay showed no significant differences in adhesion rate and outgrowth area at all observation points (P > 0.05).

LIMITATIONS, REASONS FOR CAUTION

This study was carried out as a preliminary trial using discarded embryos, which limited the number of embryos analyzed. Additionally, the impact on embryo transfer outcomes, such as clinical pregnancy and livebirth rates, remains unclear.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings suggest that OW is a safe and efficient alternative to SW protocols and may improve the efficiency of IVF laboratory workflow without impairing embryo potentials.

STUDY FUNDING/COMPETING INTEREST(S)

No funding was obtained for this study. The authors have no conflicts of interest to declare related to this study.

TRIAL REGISTRATION NUMBER

N/A.

Ultra-Fast Warming Procedure of Vitrified Blastocysts Results in Maintained Embryology and Clinical Outcomes

Vitrification has revolutionized embryo cryopreservation, but represents a significant workload in the IVF lab. We evaluated here an ultrafast blastocyst warming procedure in order to improve workflow while maintaining clinical outcome. We first evaluated the expression of main markers of lineage specification in a subset of blastocysts donated to research warmed with ultrafast protocol. We then performed a prospective pseudo-randomized pilot study comparing blastocyst survival, reexpansion and live birth rates between standard (3 steps, 15 min), and ultrafast warming protocol (1 step, 2 min). Finally, survival, reexpansion and live birth rates (LBR) obtained with ultrafast warming protocol were prospectively collected during 3 months and compared with previous indicators. Immunofluorescence experiments showed that staining and spatial organization of cell fate markers were conserved with ultrafast protocol. Survival, reexpansion and LBR were strictly comparable between standard (n = 47 cycles) and ultrafast (n = 39 cycles) groups in the pilot study (100 vs 100%, 80 vs 76% and 29.8 vs 30.7% in standard and simplified groups respectively). Survival, expansion and LBR obtained with the ultrafast warming protocol over the next 3-month period (321 cycles, 336 embryos) were comparable with those obtained with the standard protocol throughout the 6 months (547 FBT cycles, 578 embryos) preceding shifting protocol (97.6 and 29.6% vs 97.8 and 28.3% respectively, p > 0.05 for both). In conclusion, using an ultrafast blastocyst warming procedure results in similar embryology and clinical outcomes compared with standard protocol, but significantly shortens the technical procedure, ultimately improving the overall lab's workflow.

Cryopreservation of human kidney organoids

Recent advances in stem cell research have led to the creation of organoids, miniature replicas of human organs, offering innovative avenues for studying diseases. Kidney organoids, with their ability to replicate complex renal structures, provide a novel platform for investigating kidney diseases and assessing drug efficacy, albeit hindered by labor-intensive generation and batch variations, highlighting the need for tailored cryopreservation methods to enable widespread utilization. Here, we evaluated cryopreservation strategies for kidney organoids by contrasting slow-freezing and vitrification methods. 118 kidney organoids were categorized into five conditions. Control organoids followed standard culture, while two slow-freezing groups used 10% DMSO (SF1) or commercial freezing media (SF2). Vitrification involved V1 (20% DMSO, 20% Ethylene Glycol with sucrose) and V2 (15% DMSO, 15% Ethylene Glycol). Assessment of viability, functionality, and structural integrity post-thawing revealed notable differences. Vitrification, particularly V1, exhibited superior viability (91% for V1, 26% for V2, 79% for SF1, and 83% for SF2 compared to 99.4% in controls). 3D imaging highlighted distinct nephron segments among groups, emphasizing V1's efficacy in preserving both podocytes and tubules in kidney organoids. Cisplatin-induced injury revealed a significant reduction in regenerative capacities in organoids cryopreserved by flow-freezing methods, while the V1 method did not show statistical significance compared to the unfrozen controls. This study underscores vitrification, especially with high concentrations of cryoprotectants, as an effective approach for maintaining kidney organoid viability and structure during cryopreservation, offering practical approaches for kidney organoid research.

Three live births after human embryo vitrification with the use of aluminum oxide as an intermediate cooling agent: a case report

Objective

To study the possibility of increasing the cooling rates of the vitrification procedure in a closed system with the use of aluminum oxide as an intermediate coolant.

Design

Case report.

Subjects

Six patients undergoing procedures for assisted reproduction.

Intervention

Comparative studies of cryopreservation of donor embryos with aluminum oxide as an intermediate cooling agent (experimental group) and without it (control group) have been performed. After thawing, the embryo morphology and its potential to develop to the blastocyst stage have been assessed. The methodology was then applied to clinical practice.

Main Outcome Measures

Twenty embryos of 6 patients have been vitrified on day 4 after fertilization with the use of aluminum oxide as an intermediate coolant. Fourteen of them have been thawed. All have displayed normal morphology and 10 have formed blastocysts after 24 hours of culture. Four of the patients received embryo transfer with 2 embryos and the other 2 with single embryos.

Results

After preliminary comparative studies of embryos frozen with aluminum oxide and a control group, the results showed no statistically significant difference between their quality and potential to reach to blastocyst stage. That gave us ground to apply the methodology in clinical practice. After the embryo transfer, 3 clinical pregnancies with successful live births have been obtained.

Conclusions

Our experience shows that preimplantation embryos can be cryopreserved aseptically, in closed systems, with the help of aluminum oxide as an intermediate coolant.

Recent advances of oocyte/embryo vitrification in mammals from rodents and large animals

Vitrification is a valuable technology that enables semipermanent preservation and long-distance or international transportation of genetically modified and native animals. In laboratory mice, vitrification maintains and transports embryos, and many institutions and companies sell vitrified embryos. In contrast, despite numerous papers reporting on vitrification in livestock over the past decade, practical implementation has yet to be achieved. However, with advances in genome editing technology, it is anticipated that the number of genetically modified domestic animals will increase, leading to a rise in demand for vitrification of oocytes and embryos. Here, we provide an objective overview of recent advancements in vitrification technology for livestock, drawing a comparison with the current developments in laboratory animals. Additionally, we explore the future prospects for vitrification in livestock, focusing on its potential benefits and drawbacks.

Comparative Assessment of Survival and Clinical Outcome Between Two Commercial Vitrification Kits with Different Warming Protocols After Blastocyst Culture: Potential Perspectives Toward Simplified Warming Procedures

This study investigates whether there is an effect on laboratory results and clinical outcome using commercial kits with similar vitrification but different warming procedures for blastocysts vitrified on day 5 or day 6. A single-center retrospective cohort study was performed between 2011 and 2020. A change from a stage-specific kit (Kit 1) to a universal kit (Kit 2) was undertaken in 2017. A total of 1845 untested blastocysts were warmed for single vitrified-warmed blastocyst transfers (SVBT). Eight hundred and twenty-five blastocysts were vitrified with Kit 1 and 1020 with Kit 2. Blastocyst survival was not different (96.1% versus 97.3%). Seven hundred seventy-seven SVBT were performed from Kit 1 and 981 from Kit 2. Overall clinical pregnancy and live birth rates were not different (35.4% versus 34.1% and 30.9% versus 30.5% for Kit 1 and 2, respectively). Subgroup analysis for live birth rates in relation to the day of blastocyst vitrification showed no differences (36.1% and 36.1% for day 5 and 25.4% and 23.5% for day 6 blastocysts, respectively). For both kits, the mean gestational age was not different (38.8 ± 2.5 weeks versus 38.8 ± 2.0 weeks) with a singleton birth weight of 3413 ± 571 g and 3410 ± 528 g for Kit 1 and Kit 2, respectively. Differences in warming procedures do not affect laboratory performance or clinical outcome after blastocyst vitrification. The plasticity of a human blastocyst may allow for further investigation on simplification of blastocyst warming procedures.

Oocyte and embryo cryopreservation in assisted reproductive technology: past achievements and current challenges

Cryopreservation has revolutionized the treatment of infertility and fertility preservation. This review summarizes the milestones that paved the way to the current routinary clinical implementation of this game-changing practice in assisted reproductive technology. Still, evidence to support "the best practice" in cryopreservation is controversial and several protocol adaptations exist that were described and compared here, such as cumulus-intact vs. cumulus-free oocyte cryopreservation, artificial collapse, assisted hatching, closed vs. open carriers, and others. A last matter of concern is whether cryostorage duration may impact oocyte/embryo competence, but the current body of evidence in this regard is reassuring. From social and clinical perspectives, oocyte and embryo cryopreservation has evolved from an afterthought when assisted reproduction was intended for immediate pregnancy with supernumerary embryos of secondary interest to its current purpose, which primarily is to preserve fertility long-term and more comprehensively allow for family planning. However, the initial consenting process, which still is geared to short-term fertility care, may no longer be relevant when the individuals that initially preserved the tissues have completed their reproductive journey. A more encompassing counseling model is required to address changing patient values over time.

Novel Long-Term Cryo-Storage Using Vitrification and Laser Warming Techniques

Vitrification and laser warming have gained popularity over the traditional convective warming techniques in cryopreservation. Laser warming is rapid with uniform effects, thus preventing ice crystal formation in samples. Contemporary laser warming studies have focused on proof-of-concept experiments. Yet, no protocols or techniques have been developed to address the problem of warming samples from long-term storage. Herein, a new approach to laser warming samples without exposing the samples to ambient temperature is introduced. The new device presented has a mean laser-hitting accuracy of 76% ± 16% and a rewarming rate of 59% ± 25% on samples with <1 μL in volume. Although these rates depend on the choice of vitrification solution and mastery of the technique, the approach described represents a successful first step toward laser warming samples from long-term cryo-storage.

A comprehensive review and update on human fertility cryopreservation methods and tools

The broad conceptualization of fertility preservation and restoration has become already a major concern in the modern western world since a large number of individuals often face it in the everyday life. Driven by different health conditions and/or social reasons, a variety of patients currently rely on routinely and non-routinely applied assisted reproductive technologies, and mostly on the possibility to cryopreserve gametes and/or gonadal tissues for expanding their reproductive lifespan. This review embraces the data present in human-focused literature regarding the up-to-date methodologies and tools contemporarily applied in IVF laboratories' clinical setting of the oocyte, sperm, and embryo cryopreservation and explores the latest news and issues related to the optimization of methods used in ovarian and testicular tissue cryopreservation.

Droplet Generation, Vitrification, and Warming for Cell Cryopreservation: A Review

Cryopreservation is currently a key step in translational medicine that could provide new ideas for clinical applications in reproductive medicine, regenerative medicine, and cell therapy. With the advantages of a low concentration of cryoprotectant, fast cooling rate, and easy operation, droplet-based printing for vitrification has received wide attention in the field of cryopreservation. This review summarizes the droplet generation, vitrification, and warming method. Droplet generation techniques such as inkjet printing, microvalve printing, and acoustic printing have been applied in the field of cryopreservation. Droplet vitrification includes direct contact with liquid nitrogen vitrification and droplet solid surface vitrification. The limitations of droplet vitrification (liquid nitrogen contamination, droplet evaporation, gas film inhibition of heat transfer, frosting) and solutions are discussed. Furthermore, a comparison of the external physical field warming method with the conventional water bath method revealed that better applications can be achieved in automated rapid warming of microdroplets. The combination of droplet vitrification technology and external physical field warming technology is expected to enable high-throughput and automated cryopreservation, which has a promising future in biomedicine and regenerative medicine.

A 3D-Printed Large Holding Capacity Device for Minimum Volume Cooling Vitrification of Embryos in Prolific Livestock Species

Although many devices have been developed to reduce sample volume, with an explosion of methods appearing in the literature over the last decade, commercially available devices with simultaneous vitrification of a larger number of embryos are scarce, with the apparent gap for their use in prolific livestock species. In this study, we investigated the effectiveness of a new three-dimensional (3D)-printed device that combines minimum volume cooling vitrification with simultaneous vitrification of a larger number of rabbit embryos. Late morulae/early blastocysts were vitrified with the open Cryoeyelet^® device (n = 175; 25 embryos per device), the open Cryotop^® device (n = 175; 10 embryos per device), and the traditional closed French mini-straw device (n = 125; 25 embryos per straw) and compared in terms of in vitro development and reproductive performance after transfer to adoptive mothers. Fresh embryos constituted the control group (n = 125). In experiment 1, there was no difference in the development rate to the blastocyst hatching stage between the CryoEyelet^® and the other devices. In experiment 2, the CryoEyelet^® device showed a higher implantation rate compared with the Cryotop^® (6.3% unit of SD, p = 0.87) and French mini-straw^® (16.8% unit of SD, p = 1.00) devices. In terms of offspring rate, the CryoEyelet^® device was similar to the Cryotop^® device but superior to the French straw device. Regarding embryonic and fetal losses, the CryoEyelet^® showed lower embryonic losses compared to other vitrification devices. The analysis of bodyweight showed that all devices showed a similar outcomes-a higher birthweight but a lower body weight at puberty than those in the fresh transfer embryos group. In summary, the CryoEyelet^® device can be used for the vitrification of many late morulae or early blastocyst stage rabbit embryos per device. Further studies should be performed to evaluate the CryoEyelet^® device in other polytocous species for the simultaneous vitrification of a large number of embryos.

Vitrification and in-straw warming do not affect pregnancy rates of biopsied bovine embryos

In the cattle industry, in vivo or in vitro embryo production combined with genotyping and cryopreservation technologies allows the selection and conservation of embryos carrying genes for desirable traits. This study aimed to assess the efficiency of a vitrification method suitable for in-straw warming of biopsied in vivo derived (IVD) bovine embryos. Three experiments were carried out using two methodologies: the Cryotop®, the gold standard vitrification and 3-step warming methodology, or the VitTrans, a vitrification/in-straw 1-step warming method that enables direct embryo transfer to the uterus. In experiment 1, intact and biopsied in vitro produced (IVP) day 7 expanded blastocysts were vitrified using the Cryotop® and warmed in 1- or 3-steps. No differences in survival rates were recorded at 24 h after warming for intact or biopsied IVP blastocysts irrespective of the warming procedure. In experiment 2, the effect of the time from trophectoderm (TE) biopsy to vitrification/in-straw warming on post-warming survival rate was assessed. No significant differences in survival were observed when blastocysts were vitrified/in-straw warmed immediately after biopsy or after 3 h in culture when compared to intact blastocysts. In experiment 3, IVD embryos were vitrified 3 h after biopsy using the Cryotop® or the VitTrans method and pregnancy rates were assessed at day 60 after transfer. Fresh, biopsied embryos served as control. Similar pregnancy rates were observed when IVD biopsied embryos were transferred fresh or vitrified/warmed by the Cryotop® or VitTrans method. No significant effect of the embryo quality or developmental stage was detected on the percentage of pregnant recipients when IVD biopsied embryos were transferred fresh or after vitrification. While fresh female IVD embryos produced significantly higher pregnancy rates than male embryos, there were no differences in pregnancy rates when male or female vitrified/warmed embryos were transferred. About 81% from the biopsies analyzed successfully determined the embryo sex, confirming that DNA was there, and it was efficiently amplified. To conclude, our findings indicate that both vitrification methodologies produced similar post-warming outcomes for both intact and biopsied IVP embryos. Besides, vitrification/in-straw warming of biopsied IVD bovine embryos did not affect the viability to originate pregnancy, being a useful option for their direct transfer in field conditions.

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.

Vitrification of mouse two-cell and blastocyst stage embryos in simplified closed system using either a hemi-straw or a hollow fiber device

Two-cell stage and blastocyst stage mouse embryos were equilibrated in a medium containing 7.5% ethylene glycol (EG) and 7.5% dimethyl sulfoxide (DMSO) for 8-15 min. Vitrification was performed in a medium containing 0.5 M sucrose and either 15% EG + 15% DMSO, 17.5% EG + 17.5% DMSO, or 20% EG + 20% DMSO for 30 s. They were then placed either on a hemi-straw (HS) or a hollow fiber vitrification (HFV) device and vitrified by cooled air inside a 0.5-ml straw. In two-cell embryos, a 100% survival rate was obtained from all groups except the 20% HS group (P > .05). All vitrified two-cell groups showed similar rates of blastocyst development to that of fresh control group (P > .05), except 17.5% and 20% HFV groups, which were significantly lower than the other groups (P < .05). In the blastocyst embryos, the HFV groups were divided into two subgroups (non-collapsed; HFV-NC and collapsed; HFV-C blastocyst). Re-expansion rate in 15% HFV-NC, 17.5% HFV-NC, and 15% HFV-C groups was reduced (P < .05), whereas the rest were similar to control. In conclusion, we established a simplified, reliable, and closed system for HFV vitrification applying hemi-straw, which does not require skilled practitioners.

Antioxidants increase blastocyst cryosurvival and viability post-vitrification

STUDY QUESTION

What is the effect of antioxidants acetyl-L-carnitine, N-acetyl-L-cysteine and α-lipoic acid (A3) in vitrification and warming solutions on mouse blastocyst development and viability?

SUMMARY ANSWER

The combination of three antioxidants in vitrification solutions resulted in mouse blastocysts with higher developmental potential in vitro and increased viability as assessed by both an outgrowth model in vitro and fetal development following uterine transfer.

WHAT IS KNOWN ALREADY

The antioxidant combination of acetyl-L-carnitine, N-acetyl-L-cysteine and α-lipoic acid present in IVF handling and embryo culture media has significant beneficial effects on mouse embryo and fetal development, especially under oxidative stress.

STUDY DESIGN, SIZE, DURATION

The study was a laboratory-based analysis of an animal model. Rapid cooling through vitrification was conducted on F1 mouse blastocysts, with antioxidants (A3) supplemented in vitrification and/or warming solutions, followed by culture and embryo transfer.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Pronucleate oocytes were collected and cultured in groups to Day 4 blastocysts. Expanded blastocysts were vitrified and warmed in solutions with and without the A3 antioxidants and cultured for a further 24 h. Blastocyst cell number and allocation, apoptosis and histone acetylation levels were all quantified, and viability through outgrowths and transfers assessed.

MAIN RESULTS AND THE ROLE OF CHANCE

Mouse blastocysts vitrified with no antioxidants had significantly lower cell numbers (P  < 0.001) and higher apoptotic cells (P  < 0.05) compared to non-vitrified embryos. Addition of combined A3 antioxidants to the vitrification and warming solutions resulted in a significant increase in inner cell mass cell (ICM) number (P  < 0.001) and total cell number (P  < 0.01), and an increase in outgrowth area (P < 0.05), which correlated with the increased fetal weight (P < 0.05), crown rump length (P < 0.05) and limb development (P < 0.05) determined following transfer compared to embryos with no antioxidants. Furthermore, while blastocyst vitrification significantly reduced acetylation levels (P < 0.05) compared to non-vitrified embryos, the inclusion of A3 antioxidants helped to ameliorate this.

LIMITATIONS, REASONS FOR CAUTION

Embryo development was only examined in the mouse.

WIDER IMPLICATIONS OF THE FINDINGS

Results in this study demonstrate that vitrification and warming of blastocysts have significant detrimental effects on embryo histone acetylation and subsequent viability. The presence of antioxidants in the vitrification solutions helps to alleviate the negative effects of cryopreservation. Our data indicate that antioxidants need to be present in the medium at the time of exposure to increased oxidative stress associated with vitrification and that prior exposure (i.e. during culture or IVF alone) is insufficient to protect cells against cryo-induced injury. Hence, A3 antioxidants may assist in maintaining the viability of vitrified human embryos in ART through the reduction of oxidative stress.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by a research grant from Vitrolife AB (Sweden). The authors have no conflict of interest to declare.

A review of best practices of rapid-cooling vitrification for oocytes and embryos: a committee opinion

The focus of this paper is to review best practices for rapid-cooling cryopreservation of oocytes and embryos. The discussion of best practices includes the types of cryoprotectants and cryo devices typically used. Key performance indicators of rapid-cooling vitrification success are defined.

Mitochondrial function, blastocyst development and live foals born after ICSI of immature vitrified/warmed equine oocytes matured with or without melatonin

Oocyte vitrification is considered experimental in the horse with only three live foals reported. The oxidative conditions induced by vitrification could in part explain the poor results and melatonin, a powerful antioxidant, could stimulate ROS metabolization and restore mitochondrial function in these oocytes. Our objective was to determine the oxidative status of vitrified equine oocytes and to analyze the effect of melatonin on mitochondrial-specific ROS (mROS), oocyte maturation, ICSI embryo development and viability. Immature, abattoir-derived oocytes were held for 15 h and vitrified in a final concentration of 20% EG, 20% DMSO and 0.65 M trehalose. In Experiment 1, overall ROS was determined by DCHF-DA; vitrification increased ROS production compared to non-vitrified controls (1.29 ± 0.22 vs 0.74 ± 0.25 a. u.; P = 0.0156). In Experiment 2, mROS was analyzed by MitoSOX™ in vitrified/warmed oocytes matured with (+) or without (-) supplementation of 10^-9 M melatonin; mROS decreased in vitrified and non-vitrified oocytes matured in presence of melatonin (P < 0.05). In Experiment 3, we assessed the effect of melatonin supplementation on oocyte maturation, embryo development after ICSI, and viability by pregnancy establishment. Melatonin did not improve oocyte maturation, cleavage or blastocyst rate of non-vitrified oocytes. However, vitrified melatonin (+) oocytes reached similar cleavage (61, 75 and 77%, respectively) and blastocyst rate (15, 29 and 26%, respectively) than non-vitrified, melatonin (+) and (-) oocytes. Vitrified, melatonin (-) oocytes had lower cleavage (46%) and blastocyst rate (9%) compared to non-vitrified groups (P < 0.05), but no significant differences were observed when compared to vitrified melatonin (+). Although the lack of available recipients precluded the transfer of every blastocyst produced in our study, transferred embryos from non-vitrified oocytes resulted in 50 and 83% pregnancy rates while embryos from vitrified oocytes resulted in 17 and 33% pregnancy rates, from melatonin (+) and (-) treatments respectively. Two healthy foals, one colt from melatonin (+) and one filly from melatonin (-) treatment, were born from vitrified/warmed oocytes. Gestation lengths (considering day 0 = day of ICSI) were 338 days for the colt and 329 days for the filly, respectively. Our work showed for the first time that in the horse, as in other species, intracellular reactive oxygen species are increased by the process of vitrification. Melatonin was useful in reducing mitochondrial-related ROS and improving ICSI embryo development, although the lower pregnancy rate in presence of melatonin should be further analyzed in future studies. To our knowledge this is the first report of melatonin supplementation to an in vitro embryo culture system and its use to improve embryo developmental competence of vitrified oocytes following ICSI.

Cryopreservation of single-sperm: where are we today?

BACKGROUND

Patients with severe oligospermia and nonobstructive azoospermia have very limited numbers of viable sperm in their epididymal and testicular samples. Thus, cryopreservation of their sperm is performed to avoid repeated sperm retrievals and to preserve their sperm from any side effects of any treatment regimens.

MAIN BODY

The development of intracytoplasmic sperm injection technology has extended the therapeutic capacity of assisted reproductive technology for men with azoospermia via the surgical or percutaneous isolation of sperm from the testis/epididymis. The conventional cryopreservation techniques are inadequate for preserving individually selected sperm. The technique for freezing single sperm was first developed in 1997 and has been explored from the perspective of frozen carriers, freezing programs, and cryoprotectant formulations. Among these methods, advances in frozen carriers have directly improved single-sperm freezing technology. In this review, we evaluate the different technologies for the cryopreservation of single sperm by discussing the advantages and disadvantages of different freezing methods, their clinical applications, and the outcomes for a range of frozen carriers.

CONCLUSION

Our review article describes the latest and current technologies implemented for the cryopreservation of single sperm that could potentially benefit patients with severe oligospermia and who rarely have any sperm in their ejaculate. This review provides a platform to understand the process and pitfalls of single-sperm cryopreservation to ensure further improvements in the cryopreservation technology in future studies.

Hollow fiber vitrification allows cryopreservation of embryos with compromised cryotolerance

PURPOSE

This study aims to demonstrate vitrification methods that provide reliable cryopreservation for embryos with compromised cryotolerance.

METHODS

Two-cell stage mouse embryos and in vitro produced porcine embryos were vitrified using the hollow fiber vitrification (HFV) and Cryotop (CT) methods. The performance of these two methods was compared by the viability of the vitrified-rewarmed embryos.

RESULTS

Regardless of the method used, 100% of the mouse 2-cell embryos developed successfully after vitrification-rewarming into the blastocyst stage, whereas vitrification tests using porcine morulae with the HFV method produced significantly better results. The developmental rates of vitrified porcine morula into the blastocyst stage, as well as blastocyst cell number, were 90.3% and 112.3 ± 6.9 in the HFV group compared with 63.4% and 89.5 ± 8.1 in the CT group (P < .05). Vitrification tests using 4- to 8-cell porcine embryos resulted in development into the blastocyst stage (45.5%) in the HFV group alone, demonstrating its better efficacy. The HFV method did not impair embryo viability, even after spontaneous rewarming at room temperature for vitrified embryos, which is generally considered a contraindication.

CONCLUSION

Vitrification test using embryos with compromised cryotolerance allows for more precise determining of effective cryopreservation methods and devices.

Equivalent clinical outcome after vitrified-thawed blastocyst transfer using semi-automated embryo vitrification system compared with manual vitrification method

PURPOSE

This study compared Gavi®, an automated system for the equilibration and dehydration steps of vitrification, and a manual vitrification procedure in terms of effects on clinical outcomes.

METHODS

The authors retrospectively compared survival rate, and clinical and perinatal outcomes after vitrified-thawed single blastocyst transfer between Gavi® (G method) in 398 cases and Cryotop® (C method) in 208 cases.

RESULTS

With C and G methods, survival rates were 98.6% (208/211) and 99.3% (398/401), total pregnancy rates were 34.3% (72/208) and 33.4% (133/398), and total miscarriage rates were 22.2% (16/72) and 24.8% (33/133), respectively. Among women <35 years old, pregnancy rates were 41.1% (30/73) and 40.5% (62/153) and miscarriage rates were 13.3% (4/30) and 16.1% (10/62) with C and G methods, respectively. Among women ≥35 years old, pregnancy rates were 31.1% (42/135) and 29.0% (71/245) and miscarriage rates were 28.6% (12/42) and 32.4% (23/71) with C and G methods, respectively. C and G methods showed no significant differences in any trials, including gestational age, cesarean section rate, or birthweight (P > .05 each).

CONCLUSIONS

Gavi® showed comparable clinical outcomes to the manual vitrification method and can be considered an alternative vitrification procedure in assisted reproductive technology.

Achievements and future perspectives of embryo transfer technology in pigs

Commercial embryo transfer (ET) has unprecedented productive and economic implications for the pig sector. However, pig ET has been considered utopian for decades mainly because of the requirements of surgical techniques for embryo collection and embryo deposition into recipients, alongside challenges to preserve embryos. This situation has drastically changed in the last decade since the current technology allows non-surgical ET and short- and long-term embryo preservation. Here, we provide a brief review of the improvements in porcine ET achieved by our laboratory in the past 20 years. This review includes several aspects of non-surgical ET technology and different issues affecting ET programmes and embryo preservation systems. The future perspectives of ET technology are also considered. We will refer only to embryos produced in vivo since they are the only type of embryos with possible short-term use in pig production.

Preclinical validation of the new vitrification device possessing a feature of absorbing excess vitrification solution for the cryopreservation of human embryos

AIM

The cryopreservation of embryos is essential for assisted reproductive technology field. The aim of the present study is to examine the efficacy and ease of use of a new vitrification device, Kitasato Vitrification System (KVS), in cryopreservation of human embryos.

METHODS

Human embryos at the cleavage or blastocyst stage were vitrified and warmed by KVS or Cryotop (control device). The survival of cleavage- and blastocyst-stage embryos and the developmental competence of cleavage-stage embryos were evaluated. Four individuals inexperienced in vitrification and warming embryos tested both KVS and Cryotop. The vitrification time and the detachment time of the embryos were evaluated.

RESULTS

At the cleavage stage, there were no significant differences in the survival rate and the development rate to the blastocyst stage between KVS and Cryotop (100 vs 96.8% and 63.3 vs 61.3%, respectively). At the blastocyst stage, there was no significant difference in the re-expansion rate between KVS and Cryotop (100 vs 88.9%). The vitrification time was shorter for KVS than Cryotop. There was no significant difference in the detachment time between KVS and Cryotop.

CONCLUSION

Kitasato Vitrification System is easy to operate, even for inexperienced users, and the viability of human embryos vitrified by KVS is comparable to that of Cryotop, a widely used vitrification device.

Cumulus cells during in vitro fertilization and oocyte vitrification in sheep: Remove, maintain or add?

The objective was to evaluate the developmental competence of immature and matured ovine oocytes after removing, maintaining or adding cumulus cells (CC) associated to vitrification by Cryotop method. Three experiments were performed involving 3,144 oocytes. In Experiment 1, CC were removed from immature, matured or fertilized oocytes subjected to in vitro embryo production. In Experiment 2, oocytes were vitrified either in MI or MII stage with or without CC, while a control group with CC remained unvitrified. In Experiment 3, oocytes partially denuded from CC were vitrified either in MI or MII stage, and a co-culture of fresh CC was added or not soon after warming to complete in vitro maturation (IVM) and in vitro fertilization (IVF), or IVF, respectively, while a control group remained unvitrified. In Experiment 1, the cleavage rate, development rate on Day 6 and blastocyst rate on Day 8 were improved when CC were maintained until the end of IVF (P < 0.05). In Experiment 2, vitrification of oocytes with enclosed CC showed a tendency to increase cleavage (P = 0.06) and improved blastocyst rate (P < 0.05). In Experiment 3, adding CC as co-culture after vitrification-warming tended to improve cleavage rate (P = 0.06) and increased hatching rate (P < 0.05). Regarding oocyte stage, vitrification of in vitro matured oocytes resulted in greater developmental competence than immature stages (P < 0.05). In conclusion, CC seems to have a relevant role for in vitro embryo development in either fresh or vitrified oocytes.

Vitrified embryo transfer in Merino sheep under extensive conditions

The aim was to evaluate pregnancy success after transfer of embryos vitrified in micropipette tips in Merino sheep under extensive conditions. A second objective was to evaluate the influence of embryo stage in such pregnancy rate. One hundred and twenty-seven embryos were rewarmed and transferred into recipient ewes. On rewarming, the embryos were placed into three-step cryoprotectant dilutions. Finally, prior to transfer to recipient females, embryos were maintained in Basic Medium for 5 min at 25ºC and were re-evaluated by morphological criteria; all degenerated embryos were eliminated. Recipient ewes (n = 150) were treated for estrus with sponges placed for 14 days and 300 IU of eCG. At embryo transfer, three experimental groups were defined: morulae transferred on Day 7, blastocysts transferred on Day 7 and blastocysts transferred on Day 8 after sponge removal. In all groups, semi-laparoscopic transfer of one rewarmed embryo per recipient was performed. Pregnancy was diagnosed by ultrasonography on day 28 after embryo transfer. The embryo selection rate after rewarming was higher for blastocysts (89.3% - 67/75) compared to morulae (65.9% - 60/91) (P < 0.05). Pregnancy diagnosis showed a 38.3% (23/60) of success after morula transfer on Day 7 post progestagen removal. The day of transfer showed a significant influence on pregnancy rate after blastocyst transfer (Day 8, 55.9% - 19/34 vs Day 7, 21.2% - 7/33) (P < 0.05). Blastocysts transfer on Day 8 showed the highest global efficiency (pregnancies/total embryos after rewarming) (47.5% - 19/40) (P < 0.05). In conclusion, reproductive efficiency obtained by vitrified embryo transfer allows its recommendation for embryo transfer programs under extensive conditions. The importance of considering the synchrony between the embryo age and the recipient uterus stage is emphasized.

Embryo competence and cryosurvival: Molecular and cellular features

Global cattle genetic market is experiencing a change of strategy, large genetic companies, traditionally recognized in the artificial insemination field, have also begun to operate in the embryo market. Consequently, the demand for in vitro produced (IVP) embryos has grown. However, the overall efficiency of the biotechnology process remains low. Additionally, the lack of homogeneity of post-cryopreservation survival results of IVP embryos still impairing a massive dissemination of this biotechnology in the field. A great challenge for in vitro production labs is to increase the amount of embryos produced with exceptional quality after each round of in vitro fertilization. Herein, we discuss the molecular and cellular features associated with the competence and cryosurvival of IVP embryos. First, morphofunctional, cellular and molecular competence of the embryos were addressed and a relationship between embryo developmental ability and quality were established with cryosurvival and pregnancy success. Additionally, determinant factors of embryo competence and cryosurvival were discussed including the following effects: genotype, oocyte quality and follicular microenvironment, in vitro production conditions, and lipids and other determining molecules. Finally, embryo cryopreservation aspects were addressed and an embryo-focused approach to improve cryosurvival was presented.

New idea for hair transplantation to preserve more donor hair follicles

Higher risk of rapid progression in alopecia or male pattern baldness was observed in men who had family history. This could result from accumulation of DHT in hair follicles. Hair follicles on frontal region are more vulnerable to DHT. With development of minimal invasive hair transplantation surgery, hair follicles transplantation could be performed from frontal or occipital region to frontal region. However, limited hair follicles remained a problem. With development of technology of vitrification, we suggested extracting hair follicles from frontal region without affecting the appearance and preserving them with vitrification when the patient was young. When alopecia progressively developed, these extracted hair follicles would increase the donor number of hair follicles used for transplantation, which could extend longer dense hair appearance.

A new vitrification device that absorbs excess vitrification solution adaptable to a closed system for the cryopreservation of mouse embryos

Several closed vitrification devices that avoid contact with liquid nitrogen have been reported. Recently, based on the Kitasato Vitrification System (KVS), we developed the Closed-KVS, which is a closed vitrification device. The KVS is an open vitrification device that can absorb excess vitrification solution. In this study, we performed two experiments to evaluate the efficacy of the Closed-KVS as a vitrification device for the cryopreservation of mouse embryos at the blastocyst and two-cell stage. In the first experiment, the blastocysts were vitrified using either the Closed-KVS or the KVS (control device). The survival, re-expansion, and hatching rates were not significantly different between embryos vitrified using the Closed-KVS and those vitrified using the KVS. In the second experiment, we evaluated the embryonic development of the two-cell stage embryos vitrified using the Closed-KVS. There were no significant differences in the survival, blastocyst formation, or hatching rates between vitrified or non-vitrified embryos. Additionally, we evaluated the cooling and warming rates of these devices using a numerical simulation method. The cooling rates of the Closed-KVS were similar regardless of whether the outer cap was pre-cooled and were lower than those of the KVS. However, the warming rates of the Closed-KVS (irrespective of cap pre-cooling) were the same as those of the KVS (612,000 °C/min). In summary, the Closed-KVS is a novel closed vitrification device for the cryopreservation of mouse embryos at the blastocyst and two-cell stage.

Blastocoele expansion: an important parameter for predicting clinical success pregnancy after frozen-warmed blastocysts transfer

OBJECTIVE

To assess the predictive value of each individual morphological parameter: blastocoele expansion degree, inner cell mass (ICM), and trophectoderm (TE) grades on the clinical pregnancy outcome in frozen-warmed embryo transfer (FET) cycles.

METHODS

This is a retrospective cohort study, including 1154 FET cycles receiving vitrified-warmed one or two blastocysts transfer from August 2011 through to May 2018. The correlation between blastocyst morphology parameters and clinical outcome after FET was assessed.

RESULTS

In the subgroup analysis based on clinical pregnancy, the patients who achieved clinical pregnancy had a significantly higher degree of blastocyst expansion (3.69 ± 0.68 vs. 3.53 ± 0.78, P = 0.000) and had a thicker endometrium (9.65 ± 1.63 vs. 9.28 ± 1.64) compared with those with non-clinical pregnancy. The logistic regression analysis showed that among the three blastocyst morphology parameters, only the blastocoele expansion degree was significantly correlated with the clinical pregnancy outcome and had ability to predict the outcome after FET cycles with one or two vitrified-warmed blastocysts transferred. Both ICM and TE stages were not associated with pregnancy outcomes.

CONCLUSIONS

The blastocoele expansion degree may be essential for successful pregnancy and should be given priority when selecting frozen blastocyst for transfer.

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.

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.

Efficient vitrification of mouse embryos using the Kitasato Vitrification System as a novel vitrification device

BACKGROUND

Currently, the cryopreservation of embryos and oocytes is essential for assisted reproductive technology (ART) laboratories worldwide. This study aimed to evaluate the efficacy of the Kitasato Vitrification System (KVS) as a vitrification device for the cryopreservation of mouse embryos to determine whether this novel device can be adapted to the field of ART.

METHODS

In Experiment 1, blastocysts were vitrified using the KVS. Vitrified blastocysts were warmed and subsequently cultured for 72 h. In Experiment 2, 2-cell-stage embryos were vitrified using the KVS, and vitrified embryos were warmed and subsequently cultured for 96 h. In Experiment 3, we evaluated the in vivo developmental potential of vitrified 2-cell-stage embryos using the KVS, and in Experiment 4, we evaluated the cooling and warming rates for these devices using a numerical simulation.

RESULTS

In Experiment 1, there were no significant differences between the survival rates of the KVS and a control device. However, re-expanded (100%) and hatching (91.8%) rates were significantly higher for blastocysts vitrified using the KVS. In Experiment 2, there were no significant differences between the survival rates, or rates of development to the blastocyst stage, of vitrified and fresh embryos. In Experiment 3, after embryo transfer, 41% of the embryos developed into live offspring. In Experiment 4, the cooling and warming rates of the KVS were 683,000 and 612,000 °C/min, respectively, exceeding those of the control device.

CONCLUSIONS

Our study clearly demonstrates that the KVS is a novel vitrification device for the cryopreservation of mouse embryos at the blastocyst and 2-cell stage.

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.

Direct comparison of Cryotop® vitrification and Bicell® freezing on recovery of functional rat pancreatic islets

Two protocols, Bicell^® freeze-thawing and Cryotop^® vitrification-warming, were compared for suitability in cryopreserving rat pancreatic islets (101-150 μm in mean diameter). Immediate survival rates of post-thaw and post-warm islets (50 and 57%, respectively), assessed by FDA/PI double staining, were lower than that of fresh control islets (90%). Most of the PI-positive dead cells were detected in peripheral area of post-warm islets, and were removed after subsequent 24 h culture (survival rate; 85% vs 59% in post-thaw islets). Quantitative PCR analysis showed that Bicell^® freeze-thawing compromised expression of genes relating to β-cell function (Pdx1 and Glut2), but not to one of apoptotic pathways (Bax/Bcl2 ratio). Expression of these genes was maintained in islets before and after the Cryotop^® vitrification-warming. Values of stimulus index (SI) for 20 mM/3 mM glucose-stimulated insulin secretion were 6.7, 1.9 and 3.9 in fresh control, post-thaw and post-warm islets, respectively. The SI values after 24 h culture were 4.1, 1.9 and 3.1, respectively. Larger islets (>150 μm in diameter) had comparable survival rates, but lower SI values after Cryotop^® vitrification-warming when compared to smaller counterparts. These results suggest that rat pancreatic islets can be cryopreserved by Cryotop^® vitrification-warming rather than Bicell^® freeze-thawing, without considerable loss of in vitro β-cell function.

Application of hollow fiber vitrification for cryopreservation of bovine early cleavage stage embryos and porcine morula-blastomeres

A novel hollow fiber vitrification (HFV) method was applied to materials that have previously been difficult to cryopreserve, thereby expanding the potential application of this method. The results showed that zona-free porcine morulae and their isolated blastomeres remained viable even after vitrification. The rate of development to blastocysts after vitrification was similar for zona-free and zona-intact morulae (21/23, 91.3% for both). Vitrified blastomeres had a developmental potential equal to that of non-vitrified blastomeres (blastocyst formation rate after reaggregation: 16/17, 94.1% for both). The HFV method was also effective for the cryopreservation of in vitro matured/fertilized bovine embryos at the 2- to 4-cell, 8- to 16-cell and morula stages. The blastocyst formation rates of vitrified embryos (66.1–82.5%) were similar to those of non-vitrified embryos (74.5–82.5%). These results indicate that this novel HFV method is an effective tool for embryo cryopreservation that can enhance current practices in reproductive biology.

The effect of artificial shrinkage and assisted hatching on the development of mouse blastocysts and cell number after vitrification

Objective

The goal of this study was to ascertain optimal assisted hatching (AH) method in frozen embryo transfer. We compared the effect of depending on whether mechanical or laser-AH was performed before or after the vitrification of embryo development rate and blastocyst cell numbers.

Methods

In order to induce superovulation, pregnant mare's serum gonadotropin followed by human chorionic gonadotropin were injected into 4- to 5-week-old female mice. 2-cell embryos were then collected by flushing out the oviducts. The Expanded blastocysts were recovered after the collected embryos were incubated for 48 hours, and were then subjected to artificial shrinkage (AS) and cross-mechanical AH (cMAH) or quarter-laser zona thinning-AH (qLZT-AH) were carried out using the expanded blastocysts before or after vitrification. After 48 hours of incubation, followed by vitrification and thawing (V-T), and blastocysts were fluorescence stained and observed.

Results

The rate of formation of hatched blastocysts after 24 and 72 hours of incubation was significantly higher in the AS/qLZT-AH/V-T group than in the other groups (p<0.05). The cell number of the inner cell mass was higher in AS/V-T/non-AH and AS/V-T/cMAH groups than those of others (p<0.05). In the control group, the number of trophectoderm and the total cell number were higher than in the AS-AH group (p<0.05).

Conclusion

The above results suggest that AS and AH in vitrification of expanded blastocysts lead to the more efficient formation of hatched blastocysts in mice.

High throughput cryopreservation of cells by rapid freezing of sub-μl drops using inkjet printing--cryoprinting

We have successfully used inkjet printing to cryopreserve 3T3 mouse fibroblast cells and human neuroprogenitor cells (NPCs) derived from human embryonic stem cells (hESCs). Sessile drops of volume 114 nl were formed by printing cell suspensions containing dimethyl sulphoxide (DMSO) as a cryoprotection agent (CPA) at rates in the region 100 Hz-20 kHz, from individual droplets of 380 pl. After printing and a freeze/thaw cycle (with a minimum 24 hours hold period at liquid N2 temperature), 3T3 cells showed an average viability of >90% with CPA concentration <0.8 M at all drop deposition rates. This is a significantly lower CPA concentration than normally used with conventional cryopreservation methods. Cell viability shows a small variation with the polymer substrates used, with the best results obtained using a polyimide substrate. The viability of 3T3 cells after 2 months storage at liquid nitrogen temperature was slightly reduced compared to the cells held for 24 hours but there was no significant further deterioration after 4 or 6 months storage. The viability of NPCs after an identical freeze/thaw cycle were only 55% but this is comparable with conventional cryopreservation methods that use much higher CPA concentrations. A parallel series of experiments printing cells onto substrates held at 195 K or directly into liquid N2 showed considerable variation in cell survival rate with drop deposition rate. Cell suspensions required higher levels of CPA than when printing followed by freezing. At low deposition rates a combination of DMSO and polyethylene glycol (PEG) was needed to allow cell viability after freezing. These results show that inkjet printing provides a practical high throughput method for the cryopreservation of cells with lower CPA concentrations than are required for current low volume cryopreservation methods.

A comparison of different vitrification devices and the effect of blastocoele collapse on the cryosurvival of in vitro produced porcine embryos

The aim of this study was to determine the optimum conditions for vitrifying in vitro produced day 7 porcine embryos using different vitrification devices and blastocoele collapse methods. Firstly embryos were collapsed by micro-pipetting, needle puncture and sucrose with and without conducting vitrification. In the next experiment, non-collapsed embryos were vitrified in an open device using either superfine open-pulled straws (SOPS) or the CryoLoop^TM system, or vitrified in a closed device using either the CryoTip^TM or Cryo Bio^TM’s high security vitrification system (HSV). The post-thaw survival of embryos vitrified in the open devices did not differ significantly (SOPS: 37.3%; CryoLoop^TM: 37.3%) nor did the post-thaw survival of embryos vitrified in the closed devices (CryoTip™: 38.5%; HSV: 42.5%). The re-expansion rate of embryos that were collapsed via micro-pipetting (76.0%) did not differ from those that were punctured (75.0%) or collapsed via sucrose (79.6%) when vitrification was not performed. However, embryos collapsed via sucrose solutions (24.5%) and needle puncture (16.0%) prior to vitrification were significantly less likely to survive vitrification than the control (non-collapsed) embryos (53.6%, P < 0.05). The findings show that both open and closed vitrification devices were equally effective for the vitrification of porcine blastocysts. Collapsing blastocysts prior to vitrification did not improve survival, which is inconsistent with the findings of studies in other species. This may be due to the extremely sensitive nature of porcine embryos, and/or the invasiveness of the collapsing procedures.

Comparison of Cryotop and micro volume air cooling methods for cryopreservation of bovine matured oocytes and blastocysts

This study was designed to compare the efficiency of the Cryotop method and that of two methods that employ a micro volume air cooling (MVAC) device by analyzing the survival and development of bovine oocytes and blastocysts vitrified using each method. In experiment I, in vitro-matured (IVM) oocytes were vitrified using an MVAC device without direct contact with liquid nitrogen (LN₂; MVAC group) or directly plunged into LN₂ (MVAC in LN₂ group). A third group of IVM oocytes was vitrified using a Cryotop device (Cryotop group). After warming, vitrified oocytes were fertilized in vitro. There were no significant differences in cleavage and blastocyst formation rates among the three vitrified groups, with the rates ranging from 53.1% to 56.6% and 20.0% to 25.5%, respectively; however, the rates were significantly lower (P < 0.05) than those of the fresh control group (89.3% and 43.3%, respectively) and the solution control group (87.3% and 42.0%, respectively). In experiment II, in vitro-produced (IVP) expanded blastocysts were vitrified using the MVAC, MVAC in LN₂ and Cryotop methods, warmed and cultured for survival analysis and then compared with the solution control group. The rate of development of vitrified-warmed expanded blastocysts to the hatched blastocyst stage after 24 h of culture was lower in the MVAC in LN₂ group than in the solution control group; however, after 48–72 h of culture, the rates did not significantly differ between the groups. These results indicate that the MVAC method without direct LN₂ contact is as effective as the standard Cryotop method for vitrification of bovine IVM oocytes and IVP expanded blastocysts.

Efficient cryopreservation of mouse embryos by modified droplet vitrification (MDV)

The aim of this study was to assess modified droplet vitrification (MDV) for the cryopreservation of early developmental mouse embryos. Mouse embryos were equilibrated in holding solution for 3 min followed by immersion in vitrification solution for 30-45 s, and then three embryos per 3-μL vitrification droplet were directly dropped into liquid nitrogen. Vitrified embryos were warmed to examine their developmental potential both in vitro and in vivo. The results demonstrated that MDV vitrified and warmed embryos had a survival rate of 98.1-99.6% (P>0.05); however, blastocyst development post warming and culture in vitro demonstrated that vitrified 4-celled, 8-celled, 16-celled, morulae, and blastocyst embryos had significant higher developmental potentials (94.7-99.5%) than those from zygotes (9.2%) and 2-celled embryos (85.7%) (P<0.05). Compared to CryoLoop and CryoTech vitrification, MDV showed similar results with regards to rates of survival, blastocyst development, but with the higher hatching rate (76.1% vs. 64.0-67.3%) (P<0.05). Cryopreservation by MDV resulted in a similar blastocyst developmental potential in 4-celled and 16 celled embryos from ICR (94.7-99.5%), C57BL/6J (94.7-96.4%), and their crossbred F1 strain (97.9-98.9%) (P>0.05). After embryo transfer of vitrified ICR embryos from 4-celled, 16-celled, morulae and blastocyst stage, 40.7-43.7% of the embryos developed into live offspring (P>0.05), but MDV vitrification resulted in the highest birth rate (43.8%) compared to CryoLoop (38.3%) and CryoTech (35.4%) (P<0.05), when 4-celled mouse embryos were used for vitrification. Our study clearly demonstrated that MDV is the most efficient vitrification to cryopreserve embryos at least 4-celled and advanced stages, which can be used to preserve important mouse genomes from different strains and different developmental stages.

Preserving human cells for regenerative, reproductive, and transfusion medicine

Cell cryopreservation maintains cellular life at sub-zero temperatures by slowing down biochemical processes. Various cell types are routinely cryopreserved in modern reproductive, regenerative, and transfusion medicine. Current cell cryopreservation methods involve freezing (slow/rapid) or vitrifying cells in the presence of a cryoprotective agent (CPA). Although these methods are clinically utilized, cryo-injury due to ice crystals, osmotic shock, and CPA toxicity cause loss of cell viability and function. Recent approaches using minimum volume vitrification provide alternatives to the conventional cryopreservation methods. Minimum volume vitrification provides ultra-high cooling and rewarming rates that enable preserving cells without ice crystal formation. Herein, we review recent advances in cell cryopreservation technology and provide examples of techniques that are utilized in oocyte, stem cell, and red blood cell cryopreservation.