Cryopreservation of whole murine and porcine livers

Current Techniques and Indications for Machine Perfusion and Regional Perfusion in Deceased Donor Liver Transplantation

Since the advent of University of Wisconsin preservation solution in the 1980s, clinicians have learned to work within its confines. While affording improved outcomes, considerable limitations still exist and contribute to the large number of livers that go unused each year, often for fear they may never work. The last 10 years have seen the widespread availability of new perfusion modalities which provide an opportunity for assessing organ viability and prolonged organ storage. This review will discuss the role of in situ normothermic regional perfusion for livers donated after circulatory death. It will also describe the different modalities of ex situ perfusion, both normothermic and hypothermic, and discuss how they are thought to work and the opportunities afforded by them.

Long-Term Survival and Functional Recovery of Cryopreserved Vascularized Groin Flap and Below-the-Knee Rat Limb Transplants

Effective cryopreservation of large tissues, limbs, and organs has the potential to revolutionize medical post-trauma reconstruction options and organ preservation and transplantation procedures. To date, vitrification and directional freezing are the only viable methods for long-term organ or tissue preservation, but are of limited clinical relevance. This work aimed to develop a vitrification-based approach that will enable the long-term survival and functional recovery of large tissues and limbs following transplantation. The presented novel two-stage cooling process involves rapid specimen cooling to subzero temperatures, followed by gradual cooling to the vitrification solution (VS) and tissue glass transition temperature. Flap cooling and storage were only feasible at temperatures equal to or slightly lower than the VS Tg (i.e., -135°C). Vascularized rat groin flaps and below-the-knee (BTK) hind limb transplants cryopreserved using this approach exhibited long-term survival (>30 days) following transplantation to rats. BTK-limb recovery included hair regrowth, normal peripheral blood flow, and normal skin, fat, and muscle histology. Above all, BTK limbs were reinnervated, enabling rats to sense pain in the cryopreserved limb. These findings provide a strong foundation for the development of a long-term large-tissue, limb and organ preservation protocol for clinical use.

Effect of early vs. late time-restricted high-fat feeding on circadian metabolism and weight loss in obese mice

Time-restricted feeding (TRF) limits the time and duration of food availability without calorie reduction. Although a high-fat (HF) diet leads to disrupted circadian rhythms, TRF can prevent metabolic diseases, emphasizing the importance of the timing component. However, the question of when to implement the feeding window and its metabolic effect remains unclear, specifically in obese and metabolically impaired animals. Our aim was to study the effect of early vs. late TRF-HF on diet-induced obese mice in an 8:16 light-dark cycle. C57BL male mice were fed ad libitum a high-fat diet for 14 weeks after which they were given the same food during the early (E-TRF-HF) or late (L-TRF-HF) 8 h of the dark phase for 5 weeks. The control groups were fed ad libitum either a high-fat (AL-HF) or a low-fat diet (AL-LF). Respiratory exchange ratio (RER) was highest for the AL-LF group and the lowest for the AL-HF group. E-TRF-HF led to lower body weight and fat depots, lower glucose, C-peptide, insulin, cholesterol, leptin, TNFα, and ALT levels compared with L-TRF-HF- and AL-HF-fed mice. TRF-HF regardless whether it was early or late led to reduced inflammation and fat accumulation compared with AL-HF-fed mice. E-TRF-HF led to advanced liver circadian rhythms with higher amplitudes and daily expression levels of clock proteins. In addition, TRF-HF led to improved metabolic state in muscle and adipose tissue. In summary, E-TRF-HF leads to increased insulin sensitivity and fat oxidation and decreased body weight, fat profile and inflammation contrary to AL-HF-fed, but comparable to AL-LF-fed mice. These results emphasize the importance of timed feeding compared to ad libitum feeding, specifically to the early hours of the activity period.

Vitrification and nanowarming enable long-term organ cryopreservation and life-sustaining kidney transplantation in a rat model

Banking cryopreserved organs could transform transplantation into a planned procedure that more equitably reaches patients regardless of geographical and time constraints. Previous organ cryopreservation attempts have failed primarily due to ice formation, but a promising alternative is vitrification, or the rapid cooling of organs to a stable, ice-free, glass-like state. However, rewarming of vitrified organs can similarly fail due to ice crystallization if rewarming is too slow or cracking from thermal stress if rewarming is not uniform. Here we use "nanowarming," which employs alternating magnetic fields to heat nanoparticles within the organ vasculature, to achieve both rapid and uniform warming, after which the nanoparticles are removed by perfusion. We show that vitrified kidneys can be cryogenically stored (up to 100 days) and successfully recovered by nanowarming to allow transplantation and restore life-sustaining full renal function in nephrectomized recipients in a male rat model. Scaling this technology may one day enable organ banking for improved transplantation.

Cryopreservation of tissues and organs: present, bottlenecks, and future

Tissue and organ transplantation continues to be an effective measure for saving the lives of certain critically ill patients. The organ preservation methods that are commonly utilized in clinical practice are presently only capable of achieving short-term storage, which is insufficient for meeting the demand for organ transplantation. Ultra-low temperature storage techniques have garnered significant attention due to their capacity for achieving long-term, high-quality preservation of tissues and organs. However, the experience of cryopreserving cells cannot be readily extrapolated to the cryopreservation of complex tissues and organs, and the latter still confronts numerous challenges in its clinical application. This article summarizes the current research progress in the cryogenic preservation of tissues and organs, discusses the limitations of existing studies and the main obstacles facing the cryopreservation of complex tissues and organs, and finally introduces potential directions for future research efforts.

Cryopreservation of Whole Rat Livers by Vitrification and Nanowarming

Liver cryopreservation has the potential to enable indefinite organ banking. This study investigated vitrification-the ice-free cryopreservation of livers in a glass-like state-as a promising alternative to conventional cryopreservation, which uniformly fails due to damage from ice formation or cracking. Our unique "nanowarming" technology, which involves perfusing biospecimens with cryoprotective agents (CPAs) and silica-coated iron oxide nanoparticles (sIONPs) and then, after vitrification, exciting the nanoparticles via radiofrequency waves, enables rewarming of vitrified specimens fast enough to avoid ice formation and uniformly enough to prevent cracking from thermal stresses, thereby addressing the two main failures of conventional cryopreservation. This study demonstrates the ability to load rat livers with both CPA and sIONPs by vascular perfusion, cool them rapidly to an ice-free vitrified state, and rapidly and homogenously rewarm them. While there was some elevation of liver enzymes (Alanine Aminotransferase) and impaired indocyanine green (ICG) excretion, the nanowarmed livers were viable, maintained normal tissue architecture, had preserved vascular endothelium, and demonstrated hepatocyte and organ-level function, including production of bile and hepatocyte uptake of ICG during normothermic reperfusion. These findings suggest that cryopreservation of whole livers via vitrification and nanowarming has the potential to achieve organ banking for transplant and other biomedical applications.

Development of a novel ex vivo organ culture system to improve preservation methods of regenerative tissues

Recent advances in regenerative technology have made the regeneration of various organs using pluripotent stem cells possible. However, a simpler screening method for evaluating regenerated organs is required to apply this technology to clinical regenerative medicine in the future. We have developed a simple evaluation method using a mouse tooth germ culture model of organs formed by epithelial-mesenchymal interactions. In this study, we successfully established a simple method that controls tissue development in a temperature-dependent manner using a mouse tooth germ ex vivo culture model. We observed that the development of the cultured tooth germ could be delayed by low-temperature culture and resumed by the subsequent culture at 37 °C. Furthermore, the optimal temperature for the long-term preservation of tooth germ was 25 °C, a subnormothermic temperature that maintains the expression of stem cell markers. We also found that subnormothermic temperature induces the expression of cold shock proteins, such as cold-inducible RNA-binding protein, RNA-binding motif protein 3, and serine and arginine rich splicing factor 5. This study provides a simple screening method to help establish the development of regenerative tissue technology using a tooth organ culture model. Our findings may be potentially useful for making advances in the field of regenerative medicine.

Transplantation of small ovarian tissue fragments using pipelle device is effective: method evaluation and reproductive outcomes

PURPOSE

To assess the feasibility, effectiveness, and reproductive outcomes of transplantation of tiny cryopreserved ovarian pieces through a pipelle cannula during laparoscopic surgery.

METHODS

A retrospective study of patients who underwent ovarian tissue transplantation for fertility restoration between 2004 and 2022. The "pipelle group" had their ovarian cortex cut into tiny pieces of ~ 1-2 mm3 before cryopreservation. The pieces were too small to be handled and transplanted via standard laparoscopic tools. Transplantation was performed using a pipelle cannula during laparoscopic surgery. The "control group" underwent transplants of ovarian cortex pieces 1-2 mm thick, measuring approximately 25-50 mm2 pieces, using standard procedures.

RESULTS

The pipelle group consisted of 4 patients aged 19, 21, 27, and 28 years old at ovarian tissue cryopreservation (OTC). The control group consisted of 14 patients aged 21-30 years old. All pipelle patients restored their endocrine activity, and all of them conceived. FSH levels dropped during the first 3 months following the pipelle transplant. IVF cycle outcomes were similar for both groups. All patients from the pipelle group conceived, resulting in 5 pregnancies and 4 live births (one patient had 2 deliveries, and one additional pregnancy is ongoing), compared to the control group, where 8 patients achieved a total of 20 pregnancies and 18 live births.

CONCLUSION

Pipelle transplantation for tiny cryopreserved ovarian pieces is feasible and effective. This study opens a door for patients who had their ovaries cut into small pieces and may even simplify the procedure in some instances, making ovarian transplant more accessible.

TRIAL REGISTRATION

(#6531-19-SMC) [18/09/2019].

Cryopreservation by Directional Freezing and Vitrification Focusing on Large Tissues and Organs

The cryopreservation of cells has been in routine use for decades. However, despite the extensive research in the field, cryopreservation of large tissues and organs is still experimental. The present review highlights the major studies of directional freezing and vitrification of large tissues and whole organs and describes the different parameters that impact the success rate of large tissue and organ cryopreservation. Key factors, such as mass and heat transfer, cryoprotectant toxicity, nucleation, crystal growth, and chilling injury, which all have a significant influence on whole-organ cryopreservation outcomes, are reviewed. In addition, an overview of the principles of directional freezing and vitrification is given and the manners in which cryopreservation impacts large tissues and organs are described in detail.

A Systematic Review of Ovarian Tissue Transplantation Outcomes by Ovarian Tissue Processing Size for Cryopreservation

Ovarian tissue cryopreservation (OTC) is the only pre-treatment option currently available to preserve fertility for prepubescent girls and patients who cannot undergo ovarian stimulation. Currently, there is no standardized method of processing ovarian tissue for cryopreservation, despite evidence that fragmentation of ovaries may trigger primordial follicle activation. Because fragmentation may influence ovarian transplant function, the purpose of this systematic review was (1) to identify the processing sizes and dimensions of ovarian tissue within sites around the world, and (2) to examine the reported outcomes of ovarian tissue transplantation including, reported duration of hormone restoration, pregnancy, and live birth. A total of 2,252 abstracts were screened against the inclusion criteria. In this systematic review, 103 studies were included for analysis of tissue processing size and 21 studies were included for analysis of ovarian transplantation outcomes. Only studies where ovarian tissue was cryopreserved (via slow freezing or vitrification) and transplanted orthotopically were included in the review. The size of cryopreserved ovarian tissue was categorized based on dimensions into strips, squares, and fragments. Of the 103 studies, 58 fertility preservation sites were identified that processed ovarian tissue into strips (62%), squares (25.8%), or fragments (31%). Ovarian tissue transplantation was performed in 92 participants that had ovarian tissue cryopreserved into strips (n = 51), squares (n = 37), and fragments (n = 4). All participants had ovarian tissue cryopreserved by slow freezing. The pregnancy rate was 81.3%, 45.5%, 66.7% in the strips, squares, fragment groups, respectively. The live birth rate was 56.3%, 18.2%, 66.7% in the strips, squares, fragment groups, respectively. The mean time from ovarian tissue transplantation to ovarian hormone restoration was 3.88 months, 3.56 months, and 3 months in the strips, squares, and fragments groups, respectively. There was no significant difference between the time of ovarian function' restoration and the size of ovarian tissue. Transplantation of ovarian tissue, regardless of its processing dimensions, restores ovarian hormone activity in the participants that were reported in the literature. More detailed information about the tissue processing size and outcomes post-transplant are required to identify a preferred or more successful processing method.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk], identifier [CRD42020189120].

Clinical guideline for vascularized composite tissue cryopreservation

At the Summit on Organ Banking through Converging Technologies held recently in Boston, tissue and organ cryopreservation technology was a topic of considerable interest. Although cryopreservation has been widely used in clinical practice, it currently remains limited to bloodless tissues with simple structures and functions that are small or thin, for example, ultra-thin skin, ovarian tissue slices, and other similar tissues. For whole organs, except for successful cryopreservation of rat ovaries (2002) and hind limbs (August 2002), successful cryopreservation of vascularized animal tissues or organs and their replantation have not yet been reported. We conducted histological and electron microscopic examinations on muscle after blood supply restoration to explain this problem and describe our experience with the goal of informing our colleagues to further develop the technology. To achieve broad application of vascularized tissue and organ cryopreservation, we have summarized our experience and established a clinical application scope for vascularized composite tissue cryopreservation.

Winter is coming: the future of cryopreservation

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

Recent advances in ice templating: from biomimetic composites to cell culture scaffolds and tissue engineering

We review the evolution of ice-templating process from initial inorganic materials to recent developments in shaping increasingly labile biological matter.

Cryopreservation as a Key Element in the Successful Delivery of Cell-Based Therapies-A Review

Cryopreservation is a key enabling technology in regenerative medicine that provides stable and secure extended cell storage for primary tissue isolates and constructs and prepared cell preparations. The essential detail of the process as it can be applied to cell-based therapies is set out in this review, covering tissue and cell isolation, cryoprotection, cooling and freezing, frozen storage and transport, thawing, and recovery. The aim is to provide clinical scientists with an overview of the benefits and difficulties associated with cryopreservation to assist them with problem resolution in their routine work, or to enable them to consider future involvement in cryopreservative procedures. It is also intended to facilitate networking between clinicians and cryo-researchers to review difficulties and problems to advance protocol optimization and innovative design.

Optimizing ovarian tissue quality before cryopreservation: comparing outcomes of three decortication methods on stromal and follicular viability

OBJECTIVE

To evaluate whether specific ovarian decortication techniques vary in promoting ovarian cortex cryopreservation and transplant outcomes.

DESIGN

Experimental design.

SETTING

University hospital.

ANIMAL(S)

Nonobese diabetic (NOD)/severe combined immunodeficiency (SCID) female mice.

INTERVENTION(S)

Human ovarian biopsy samples allocated to one of the following decortication procedures: scratching with scalpel blade (B), cutting with microsurgical scissors (M), separation with slicer (S), or no-separation (control, C). Parallel, in vivo experiment: decortication techniques combined with slow freezing (SF) and vitrification (VT) before xenograft into immunodeficient mice.

MAIN OUTCOME MEASURE(S)

Follicular counts, apoptosis, shear stress, Hippo pathway and inflammation. In vivo: recovered grafts analyzed for follicular counts, angiogenesis, proliferation, and fibrosis.

RESULT(S)

There were no differences in follicular density or number of damaged follicles between the decortication techniques in the in vitro study. Nevertheless, the M samples showed statistically significantly increased stromal damage compared with the controls and S samples, and up-regulation of Hsp60 shear stress gene expression. Decortication by both M and S inhibited the Hippo pathway, promoting gene expression changes. In the 21-day xenograft, total follicular density statistically significantly decreased compared with the nongrafted controls in all groups. Nevertheless, no differences were observed between the decortication techniques. Ovarian stroma vascularization was increased in the vitrified samples, but among the slow-freezing samples, the B samples had the lowest microvessel density. The M decorticated xenografts had increased fibrosis.

CONCLUSION(S)

Decortication with a slicer causes less damage to ovarian tissue than other commonly used methods although microsurgical scissors seem to preserve slightly increased follicular numbers. Nevertheless, blade decortication seems to be a reliable technique for maintaining acceptable follicular conditions without inducing serious stromal impairment.

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

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

Unveiling Cells' Local Environment during Cryopreservation by Correlative In Situ Spatial and Thermal Analyses

Cryopreservation is the only fully established procedure to extend the lifespan of living cells and tissues, a key to activities spanning from fundamental biology to clinical practice. Despite its prevalence and impact, the central aspects of cryopreservation, such as the cell's physicochemical environment during freezing, remain elusive. Here we address that question by coupling in situ microscopic directional freezing to visualize cells and their surroundings during freezing with the freezing-medium phase diagram. We extract the freezing-medium spatial distribution in cryopreservation, providing a tool to describe the cell vicinity at any point during freezing. We show that two major events define the cells' local environment over time: the interaction with the moving ice front and the interaction with the vitreous moving front, a term we introduce here. Our correlative strategy may be applied to cells relevant to clinical research and practice and may help in the design of new cryoprotective media based on local physicochemical cues.

Evaluation of ovarian tissue transplantation: results from three clinical centers

OBJECTIVE

To report ovarian tissue autotransplantation (AT) results and describe the relationship between technical and clinical factors and outcomes.

DESIGN

Multicenter retrospective cohort study.

SETTING

Tertiary medical centers.

PATIENT(S)

Infertile patients who had stored ovarian tissue before sterilizing treatment and returned for AT with the aim of conceiving.

INTERVENTIONS(S)

Ovarian tissue cryopreservation (OTC) and AT, endocrine monitoring, in vitro fertilization.

MAIN OUTCOME MEASURE(S)

Endocrine performance, pregnancy and live-birth rates.

RESULT(S)

From 2004 to 2018, 70 patients underwent 87 ATs. Sixty patients undergoing 70 ATs met the inclusion criteria. After AT, menses returned in 94% of patients and median FSH dropped from 68 to 19 IU/mL. Fifty pregnancies and 44 deliveries were attained, with 50% of women achieving at least one pregnancy and 41.6% at least one delivery. Twelve patients underwent AT more than once and had their endocrine activity restored in case menses recurred after the first transplantation. Repeated transplantations yielded five live births in three patients, two of whom had already given birth after the first transplantation. Preharvesting chemotherapy was not associated with inferior outcomes. Of seven patients whose pelvis was exposed to radiation before AT, four conceived and delivered. Neither tissue dimensions nor surgical approach affected fertility outcomes.

CONCLUSION(S)

OTC is highly effective at restoring fertility in sterilized patients, and prior exposure to chemotherapy should not be considered a contraindication. Repeated AT should be contemplated in case of graft malfunction, especially if previous transplantation was successful. In selected cases, conception and delivery may be feasible after pelvic exposure to radiation.

Techniques of Cryopreservation for Ovarian Tissue and Whole Ovary

Cryopreservation of ovarian tissue has been considered experimental for many years, but very recently the American Society of Reproductive Medicine is reviewing the process and perhaps soon will remove the label of “experimental” and recognize it as an established method for preserving female fertility when gonadotoxic treatments cannot be delayed or in patients before puberty or when there is desire to cryopreserve more than just few oocytes. This article discusses in detail the 3 methodologies used for cryopreservation: (a) slow freezing, (b) directional freezing, and (c) vitrification.

Systems engineering the organ preservation process for transplantation

Improving organ preservation and extending the preservation time would have game-changing effects on the current practice of organ transplantation. Machine perfusion has emerged as an improved preservation technology to expand the donor pool, assess graft viability and ensure adequate graft function. However, its efficacy in extending the preservation time is limited. Subzero organ preservation does hold the promise to significantly extend the preservation time and recent advances in cryobiology bring it closer to clinical translation. In this review, we aim to broaden the perspective in the field from a focus on these individual technologies to that of a systems engineering. This would enable the creation of a preservation process that integrates the benefits of machine perfusion with those of subzero preservation, with the ultimate goal to provide on demand availability of donor organs through organ banking.

Rat Hindlimb Cryopreservation and Transplantation: A Step Toward "Organ Banking"

In 2016, over 5 million reconstructive procedures were performed in the United States. The recent successes of clinical vascularized composite allotransplantations, hand and face transplantations included, established the tremendous potential of these life-enhancing reconstructions. Nevertheless, due to limited availability and lifelong immunosuppression, application is limited. Long-term banking of composite transplants may increase the availability of esthetically compatible parts with partial or complete HLA matching, reducing the risk of rejection and the immunosuppressive burden. The study purpose was to develop efficient protocols for the cryopreservation and transplantation of a complete rodent limb. Directional freezing is a method in which a sample is cooled at a constant-velocity linear temperature gradient, enabling precise control of the process and ice crystal formation. Vitrification is an alternative cryopreservation method in which the sample solidifies without the formation of ice crystals. Testing both methods on a rat hindlimb composite tissue transplantation model, we found reliable, reproducible, and stable ways to preserve composite tissue. We believe that with further research and development, cryopreservation may lead to composite tissue "banks." This may lead to a paradigm shift from few and far apart emergent surgeries to wide-scale, well-planned, and better-controlled elective surgeries.

Expectations and limitations of ovarian tissue transplantation

Constant progress in the diagnosis and treatment of cancer disease has increased the number and prognosis of cancer survivors. However, the toxic effects of chemotherapy and radiotherapy on ovarian function have resulted in premature ovarian failure. Patients are, therefore, still expecting methods to be developed to preserve their fertility successfully. Several potential options are available to preserve fertility in patients who face premature ovarian failure, including immature or mature oocyte and embryo cryopreservation. However, for children or prepubertal women needing immediate chemotherapy, cryopreservation of ovarian tissue is the only alternative. The ultimate aim of this strategy is to implant ovarian tissue into the pelvic cavity (orthotopic site) or in a heterotopic site once oncological treatment is completed and the patient is disease free. Transplantation of ovarian tissue with sufficiently large numbers of follicles could potentially restore endocrine function and allow multiple cycles for conception. However, the success of ovarian tissue transplantation still has multiple challenges, such as the low number of follicles in the graft that may affect their longevity as well as the survival of the tissue during ex vivo processing and subsequent transplantation. Therefore, this review aims to summarize the achievements of ovary grafting and the potential techniques that have been developed to improve ovarian graft survival.

The Grand Challenges of Organ Banking: Proceedings from the first global summit on complex tissue cryopreservation

The first Organ Banking Summit was convened from Feb. 27 - March 1, 2015 in Palo Alto, CA, with events at Stanford University, NASA Research Park, and Lawrence Berkeley National Labs. Experts at the summit outlined the potential public health impact of organ banking, discussed the major remaining scientific challenges that need to be overcome in order to bank organs, and identified key opportunities to accelerate progress toward this goal. Many areas of public health could be revolutionized by the banking of organs and other complex tissues, including transplantation, oncofertility, tissue engineering, trauma medicine and emergency preparedness, basic biomedical research and drug discovery - and even space travel. Key remaining scientific sub-challenges were discussed including ice nucleation and growth, cryoprotectant and osmotic toxicities, chilling injury, thermo-mechanical stress, the need for rapid and uniform rewarming, and ischemia/reperfusion injury. A variety of opportunities to overcome these challenge areas were discussed, i.e. preconditioning for enhanced stress tolerance, nanoparticle rewarming, cyroprotectant screening strategies, and the use of cryoprotectant cocktails including ice binding agents.

Dissolved Gases and Ice Fracturing During the Freezing of a Multicellular Organism: Lessons from Tardigrades

Three issues are critical for successful cryopreservation of multicellular material: gases dissolved in liquid, thermal conductivity of the tissue, and localization of microstructures. Here we show that heat distribution is controlled by the gas amount dissolved in liquids and that when changing the liquid into solid, the dissolved gases either form bubbles due to the absence of space in the lattice of solids and/or are migrated toward the concentrated salt and sugar solution at the cost of amount of heat required to be removed to complete a solid-state transition. These factors affect the heat distribution in the organs to be cryopreserved. We show that the gas concentration issue controls fracturing of ice when freezing. There are volumetric changes not only when changing the liquid into solid (volume increases) but also reduction of the volume when reaching lower temperatures (volume decreases). We discuss these issues parallel with observations of the cryosurvivability of multicellular organisms, tardigrades, and discuss their analogy for cryopreservation of large organs.

Directional freezing for large volume cryopreservation

Cryopreservation is currently the method of choice when it comes to long-term preservation of viable biological samples. The process, and consequently the volume of the sample, however, is limited by the ability to achieve homogenous and efficient heat removal. When this cannot be properly managed, ice crystals will grow uncontrollably resulting in extensive damage to the cryopreserved cells or tissues. Directional freezing is a technique that can be used to precisely control heat dissipation and ice crystal growth and morphology even when freezing large volumes. The technique has been used over the years to cryopreserve spermatozoa, oocytes, embryos, tissue slices and whole organs from a wide variety of domestic and wild species. In this chapter a protocol for directional freezing of spermatozoa is described and its benefits and shortcomings are discussed.

Directional freezing of spermatozoa and embryos

Directional freezing is based on a simple thermodynamic principle whereby the sample is moved through a predetermined temperature gradient at a velocity that determines the cooling rate. Directional freezing permits a precise and uniform cooling rate in small- and large-volume samples. It avoids supercooling and reduces mechanical damage caused by crystallisation. Directional solidification was used to date for slow and rapid freezing, as well as for vitrification of oocytes and embryos by means of the minimum drop size technique: small drops are placed on a microscope slide that is moved at high velocity from the hot base to the cold base. Sperm samples from a wide range of domestic and wild animals were successfully cryopreserved using the directional freezing method. The bovine sexed semen industry may benefit from the increased survival of spermatozoa after directional freezing.

Advances in the management of the explanted donor liver

Liver transplantation is the best therapy in end-stage liver disease. Donor organ shortage and efforts to expand the donor organ pool are permanent issues given that advances in perioperative management and immunosuppressive therapy have brought the procedure into widespread clinical use. The management of organ procurement, including donor preconditioning and adequate organ storage, has a key role in transplantation. However, the organ procurement process can differ substantially between transplant centres, depending on local and national preferences. Advances in the field have come from experimental and clinical research on dynamic storage systems, such as machine perfusion devices, as an alternative to static cold storage. Determination of the clinical significance of these new systems is a topic worthy of future investigations.

Cryopreservation and replantation of amputated rat hind limbs

BACKGROUND

In spite of the relatively high success rate of limb replantation, many patients cannot undergo replantation surgery because the preservation time of an amputated limb is only about six hours. In addition, although allotransplantation of composite tissues is being performed more commonly with increasingly greater success rates, the shortage of donors limits the number of patients that can be treated. So the purpose of this study is to examine the feasibility of cryopreservation and replantation of limbs in a rat model.

METHODS

Twelve five-month-old Sprague-Dawley rats were divided evenly into group A (above-knee amputation) and group B (Syme's amputation). One hind limb was amputated from each rat. The limbs were irrigated with cryoprotectant, cooled in a controlled manner to -140°C, and placed in liquid nitrogen. Thawing and replantation were performed 14 days later.

RESULTS

In group A, the limbs became swollen after restoration of blood flow resulting in blood vessel compression and all replantations failed. In group B, restoration of blood flow was noted in all limbs after replantation. In one case, the rat chewed the replanted limb and replantation failed. The other five rats were followed for three months with no abnormalities noted in the replanted limbs.

CONCLUSIONS

Limbs with a minimal amount of muscle tissue can be successfully cryopreserved and replanted.

Follicle activation and 'burn-out' contribute to post-transplantation follicle loss in ovarian tissue grafts: the effect of graft thickness

STUDY QUESTION

What are the effects of thin ovarian grafts compared with grafts of the standard thickness on follicle loss post-transplantation?

SUMMARY ANSWER

Transplantation of reduced-thickness ovarian grafts led to intense activation and 'burn-out' a short time after transplantation resulting in significant folllicle loss.

WHAT IS KNOWN ALREADY

Transplantation of fresh and frozen-thawed ovarian tissue has been proved successful, but techniques vary and are not optimised, often resulting in significant follicular loss. Follicle loss is mostly related to the freezing-thawing process and to post-transplantation hypoxia.

STUDY DESIGN, SIZE, DURATION

Bovine ovarian tissue strips (n = 55) were prepared in two groups of conventional-thickness strips (1-2 mm) or thin strips (0.5-0.9 mm). Fresh or frozen-thawed samples were xenotransplanted into sterilized immune-deficient mice (n = 49). Non-transplanted conventional size fresh samples were used as controls (n = 6). Grafts from all study groups were recovered after 7 days for analysis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Morphometric differential counting of follicle classes was performed by two observers. Immunohistochemistry was conducted for proliferation (Ki67), cortical fibrosis (Masson tri-chrome) and blood-vessel density (CD31). Results were expressed as the mean number of dormant or growing follicle (GF) type per section or total follicle counts per graft. Blood-vessel density was calculated per mm(2). P-values <0.05 were considered statistically significant.

MAIN RESULTS AND THE ROLE OF CHANCE

The loss of all follicle types, and most noteably of primordial follicles (PMFs), was observed 7 days post-transplantation (P < 0.05). The relatively high number of GFs and the positive Ki67 staining in all recovered grafts indicated that follicle activation was depleting the resting follicle pool. The reduced graft thickness had an adverse effect on the number of recovered follicles, especially on the resting non-GFs in the fresh, and more so in the frozen-thawed, samples (P < 0.05). Extensive stromal fibrosis and high blood-vessel density were observed in all grafts with no advantage in the thin prepared grafts.

LIMITATIONS, REASONS FOR CAUTION

This study used only one species of ovaries (bovine) for xenotransplantation. The immediate post-transplantation events were not visualized directly nor were the molecules involved in follicle activation studied.

WIDER IMPLICATIONS OF THE FINDINGS

Follicle activation and 'burn-out' appear to be important in follicle loss after transplantation. Reducing graft thickness in an attempt to improve freezing conditions and reduce post-transplantation ischemia has adverse effects on the graft follicle pool due to increased activation and loss. Agents which prevent 'burn-out' will potentially improve follicle pool survival.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by research grants from the Israeli Science Foundation (No. 1675/10), the Israeli Jack Craps foundation and the Israel Cancer Research Fund (ICRF No. 12-3081). The authors have no competing interest to declare.

Effect of a magnetic field on Drosophila under supercooled conditions

Under subzero degree conditions, free water contained in biological cells tends to freeze and then most living things die due to low temperatures. We examined the effect of a variable magnetic field on Drosophila under supercooled conditions (a state in which freezing is not caused even below the freezing point). Under such supercooled conditions with the magnetic field at 0°C for 72 hours, -4°C for 24 hours and -8°C for 1 hour, the Drosophila all survived, while all conversely died under the supercooled conditions without the magnetic field. This result indicates a possibility that the magnetic field can reduce cell damage caused due to low temperatures in living things.

Porcine uterus cryopreservation: an analysis of contractile function using different uterotonics

Cryopreservation of whole organs has become increasingly successful in recent years, and establishing reliable methods for confirming the success of specific cryopreservation procedures has therefore become extremely important. On the assumption that methods such as histological evaluation do not provide definitive evidence of long-term cryopreservation and that clear signs of conserved function in an organ are good evidence of its viability, contractile function was analysed in porcine uteri (n=60), either after long-term (group A) or short-term (group B) cryopreservation and post-thaw treatment with three different uterotonics. A slow freezing protocol was used to preserve the organs. Fifteen fresh uteri were analysed similarly for contractile function, which was evaluated by measuring intrauterine pressure after administration of oxytocin, prostaglandin E(1) (PGE(1)), and carbachol. After cryopreservation, all but three uteri (95%) showed rhythmic contractions similar to those in fresh uteri except for differences in the heights of contraction peaks, with lower contractions in PGE(1) subgroup B (P<0.05). With the exception of three nonresponsive uteri in group A, there were no differences in contractility between uteri after long-term cryopreservation and fresh uteri. The results of this study thus contribute to the debate on whether slow freezing or vitrification techniques are best for whole-organ cryopreservation. In summary, (1) preservation of muscular function in porcine uteri is feasible with a slow freezing protocol; (2) measurement of contractile function following administration of uterotonics is a useful method of confirming functionality; and (3) long-term cryopreservation does not significantly impair post-thaw contractibility in comparison with fresh uteri.

Organ Preservation: Current Concepts and New Strategies for the Next Decade

SUMMARY: Organ transplantation has developed over the past 50 years to reach the sophisticated and integrated clinical service of today through several advances in science. One of the most important of these has been the ability to apply organ preservation protocols to deliver donor organs of high quality, via a network of organ exchange to match the most suitable recipient patient to the best available organ, capable of rapid resumption of life-sustaining function in the recipient patient. This has only been possible by amassing a good understanding of the potential effects of hypoxic injury on donated organs, and how to prevent these by applying organ preservation. This review sets out the history of organ preservation, how applications of hypothermia have become central to the process, and what the current status is for the range of solid organs commonly transplanted. The science of organ preservation is constantly being updated with new knowledge and ideas, and the review also discusses what innovations are coming close to clinical reality to meet the growing demands for high quality organs in transplantation over the next few years.

Ovarian function 6 years after cryopreservation and transplantation of whole sheep ovaries

Whole ovary cryopreservation and transplantation has been proposed as a method for preserving long-term ovarian function. This work reports ovarian function 6years post transplantation of frozen-thawed whole sheep ovaries. Three 9-month-old Assaf sheep underwent unilateral oophorectomy to provide organs for the experiments. After perfusing with cold University of Wisconsin solution supplemented with 10% dimethyl sulphoxide, ovaries were cryopreserved using unidirectional solidification freezing technology. After thawing, ovaries were re-perfused and re-transplanted orthotopically by microvascular re-anastomosis, to the contralateral ovarian pedicle after removing the remaining ovary. Six years following transplantation and after inducing superovulation, the sheep were killed and the ovaries analysed. Two ovaries had normal size and shape showing some recent corpora lutea, while the third showed atrophic changes. A total of 36 antral follicles were counted by transillumination and four germinal vesicle oocytes were aspirated and matured in vitro to metaphase II. Serum progesterone concentrations were indicative of ovulatory activity in one of the three sheep. Histological evaluations revealed normal tissue architecture, intact blood vessels and follicles at various stages. Currently, this is the longest recorded ovarian function after cryopreservation and re-transplantation. Cryopreservation of whole ovaries, using directional freezing combined with microvascular anastomosis, is a promising method for preserving long-term reproductive capacity and endocrine function.

Freeze-drying of mononuclear cells derived from umbilical cord blood followed by colony formation

BACKGROUND

We recently showed that freeze-dried cells stored for 3 years at room temperature can direct embryonic development following cloning. However, viability, as evaluated by membrane integrity of the cells after freeze-drying, was very low; and it was mainly the DNA integrity that was preserved. In the present study, we improved the cells' viability and functionality after freeze-drying.

METHODOLOGY/PRINCIPAL FINDINGS

We optimized the conditions of directional freezing, i.e. interface velocity and cell concentration, and we added the antioxidant EGCG to the freezing solution. The study was performed on mononuclear cells (MNCs) derived from human umbilical cord blood. After freeze-drying, we tested the viability, number of CD34(+)-presenting cells and ability of the rehydrated hematopoietic stem cells to differentiate into different blood cells in culture. The viability of the MNCs after freeze-drying and rehydration with pure water was 88%-91%. The total number of CD34(+)-presenting cells and the number of colonies did not change significantly when evaluated before freezing, after freeze-thawing, and after freeze-drying (5.4 x 10(4)+/-4.7, 3.49 x 10(4)+/-6 and 6.31 x 10(4)+/-12.27 cells, respectively, and 31+/-25.15, 47+/-45.8 and 23.44+/-13.3 colonies, respectively).

CONCLUSIONS

This is the first report of nucleated cells which have been dried and then rehydrated with double-distilled water remaining viable, and of hematopoietic stem cells retaining their ability to differentiate into different blood cells.