The cryopreservation of composite tissues: Principles and recent advancement on cryopreservation of different type of tissues

Effect of rapid cooling, frozen storage, and thawing on the passive viscoelastic properties and structure of the rat aorta

Biological tissues decay over time after harvesting, which alters their biomechanical properties. This poses logistical challenges for studies investigating passive arterial biomechanics as tissues need to be characterized shortly after excision. Freezing and cryopreservation methods can help alleviate the need for biomechanical testing of fresh tissue in human ex vivo studies. However, these methods tend to eliminate or reduce arterial cell functionality and affect passive biomechanics. Furthermore, their impact on dynamic arterial biomechanics remains unknown despite arterial viscoelastic properties being an integral component contributing to arterial stiffness under in vivo loading conditions. The present study aims to investigate the impact of rapid cooling and subsequent storage at -80 °C on the passive viscoelastic properties of arterial tissue and aid in ascertaining whether this is a suitable method to delay tissue analysis for studies investigating passive arterial biomechanics. Control and frozen abdominal rat aorta segments were quasi-statically and dynamically tested using a biaxial testing set-up. The results were modeled using a constituent-based quasi-linear viscoelastic modeling framework, yielding directional stiffness parameters, individual constituent biomechanical contributions, and a quantification of viscoelastic stiffening under dynamic pressurization conditions. Frozen samples displayed significantly decreased wall thickness, viscoelastic dissipation, viscoelastic stiffening, and significantly decreased circumferential deformation with changes in luminal pressure. Furthermore, frozen samples displayed significantly increased circumferential stiffness, pulse wave velocity, and collagen load bearing. Consequently, these changes should be considered when utilizing this tissue preservation method to delay biomechanical characterization of rat aortic tissue.

The effect of epididymosomes on the development of frozen-thawed mouse spermatogonial stem cells after culture in a decellularized testicular scaffold and transplantation into azoospermic mice

PURPOSE

This study examined SSC proliferation on an epididymosome-enriched decellularized testicular matrix (DTM) hydrogel and spermatogenesis induction in azoospermic mice.

METHODS

Epididymosomes were extracted and characterized using SEM and western blotting. After cryopreservation, thawed SSCs were cultured in a hydrogel-based three-dimensional (3D) culture containing 10 ng/mL GDNF or 20 µg/mL epididymosomes. SSCs were assessed using the MTT assay, flow cytometry, and qRT-PCR after two weeks of culture. The isolated SSCs were microinjected into the efferent ducts of busulfan-treated mice. DiI-labeled SSCs were followed, and cell homing was assessed after two weeks. After 8 weeks, the testes were evaluated using morphometric studies and immunohistochemistry.

RESULTS

The expression of PLZF, TGF-β, and miR-10b did not increase statistically significantly in the 3D + GDNF and 3D + epididymosome groups compared to the 3D group. Among the groups, the GDNF-treated group exhibited the highest expression of miR-21 (*P < 0.05). Caspase-3 expression was lower in the epididymosome-treated group than in the other groups (***P < 0.001). Compared to the 3D and negative control groups, the 3D + epididymosomes and 3D + GDNF groups showed an increase in spermatogenic cells. Immunohistochemical results confirmed the growth and differentiation of spermatogonial cells into spermatids in the treatment groups.

CONCLUSION

The DTM hydrogel containing 20 µg/mL epididymosomes or 10 ng/mL GDNF is a novel and safe culture system that can support SSC proliferation in vitro to obtain adequate SSCs for transplantation success. It could be a novel therapeutic agent that could recover deregulated SSCs in azoospermic patients.

Cryopreservation-induced delayed injury and cell-type-specific responses during the cryopreservation of endothelial cell monolayers

The cryopreservation of endothelial cell monolayers is an important step that bridges the cryopreservation of cells in suspension to that of tissues. Previous studies have identified clear distinctions in freezing mechanisms between cells in suspension and in monolayers, as well as developed novel protocols for monolayer cryopreservation. Recently, our group has shown that human umbilical vein endothelial cell (HUVEC) and porcine corneal endothelial cell (PCEC) monolayers grown on Rinzl plastic substrate can be cryopreserved in 5% dimethyl sulfoxide, 6% hydroxyethyl starch, and 2% chondroitin sulfate, following a slow-cooling protocol (-1 °C/min) with rapid plunge into liquid nitrogen from -40 °C. However, membrane integrity assessments were done immediately post thaw, which may result in an overestimation of cell viability due to possible delayed injury responses. Here, we show that for the optimal protocol condition of plunge at the -40 °C interrupt temperature, HUVEC and PCEC monolayers exhibited no significant immediate post-thaw injuries nor delayed injury responses during the 24-h post-thaw overnight culture period. HUVEC monolayers experienced no significant impact to their natural growth rate during the post-thaw culture, while PCEC monolayers experienced significantly higher growth than the unfrozen controls. The difference in the low-temperature responses between HUVEC and PCEC monolayers was further shown under high temperature plunge conditions. At these suboptimal plunge temperatures, HUVEC monolayers exhibited moderate immediate membrane injury but a pronounced delayed injury response during the 24-h post-thaw culture, while PCEC monolayers showed significant immediate membrane injury but no additional delayed injury response during the same period. Therefore, we provide further validation of our group's previously designed endothelial monolayer cryopreservation protocol for HUVEC and PCEC monolayers, and we identify several cell-type-specific responses to the freezing process.

A Method to Freeze Skin Samples for Cryobanks: A Test of Some Cryoprotectants for an Endangered Deer

The genetic diversity of endangered deer species, such as Mazama jucunda, can be preserved with the help of somatic cell cryopreservation. This procedure allows obtaining several cells from the individual even after its death, which is very important for applications in reproductive biotechnologies. This study's objective was to test cryopreservation protocols of skin fragments of M. jucunda, using different cryoprotectants in slow freezing. We evaluated four treatments, composed of three cryoprotectants, dimethyl sulfoxide (DMSO), polyvinylpyrrolidone (PVP), and ethylene glycol (EG), used alone and in combination. There was also a control group where the tissue did not undergo cryopreservation. Skin fragments were collected from the medial region of the pelvic limbs of three individuals. Each fragment was divided into 10 equal parts, standardized by weight, making two pieces for each treatment and control from each animal. The collected fragments were evaluated in culture, based on the speed of occupation of the free spaces of the cell culture flask. Cell viability was also evaluated using Trypan Blue dye and the mitotic index to understand the effect of toxicity and freezing on cell membrane integrity and cell division capacity, respectively. The treatments that used association with PVP proved to be more damaging to the cells, taking longer to reach confluence. EG alone showed better results than DMSO in the slow-freezing protocol. Clinical Trial Registration Number is 1390/21.

Impact of cryopreservation on elastomuscular artery mechanics

Low temperatures slow or halt undesired biological and chemical processes, protecting cells, tissues, and organs during storage. Cryopreservation techniques, including controlled media exchange and regulated freezing conditions, aim to mitigate the physical consequences of freezing. Dimethyl sulfoxide (DMSO), for example, is a penetrating cryoprotecting agent (CPA) that minimizes ice crystal growth by replacing intracellular water, while polyvinyl alcohol (PVA) is a nonpenetrating CPA that prevents recrystallization during thawing. Since proteins and ground substance dominate the passive properties of soft biological tissues, we studied how different freezing rates, storage temperatures, storage durations, and the presence of cryoprotecting agents (5% [v/v] DMSO + 1 mg/mL PVA) impact the histomechanical properties of the internal thoracic artery (ITA), a clinically relevant blood vessel with both elastic and muscular characteristics. Remarkably, biaxial mechanical analyses failed to reveal significant differences among the ten groups tested, suggesting that mechanical properties are virtually independent of the cryopreservation technique. Scanning electron microscopy revealed minor CPA-independent delamination in rapidly frozen samples, while cryoprotected ITAs had better post-thaw viability than their unprotected counterparts using methyl thiazole-tetrazolium (MTT) metabolic assays, especially when frozen at a controlled rate. These results can be used to inform ongoing and future studies in vascular engineering, physiology, and mechanics.

Heterogeneous ice nucleation of salt solution in porous media

Water ubiquitously exists with dissolved salt in both natural and engineered porous media, such as soil, rock, concrete, and tissue; therefore, its freezing temperature depression behavior is of particular interest to various scientific communities tackling with mechanics and physics of porous media. To date, it remains elusive which physical mechanism accounts for its freezing temperature depression and how dissolved ions affect it. Herein, a series of pore-scale experiments were designated to investigate the freezing temperature of salt solutions in tubes with varying pore diameters, pore solution volumes, solid-liquid interfacial areas, ion concentrations, and ion types. The results reveal two main findings: (i) the freezing temperature depression of pore solutions is governed by the heterogeneous ice nucleation (HIN) at the water-solid interface, as evidenced by the observation that the freezing temperature decreases with the decreasing solid-liquid interfacial areas, regardless of pore diameter and pore solution volume; (ii) the dissolved salts alter HIN processes via changing the osmotic potential across the ice embryo-liquid water interface, as indicated by the observation that the freezing temperature is mainly determined by the salt concentration irrespective of salt types. Furthermore, the classical nucleation theory model is adapted for the freezing behavior of pore solutions by including an osmotic potential term. The model shows excellent performance in capturing experimental data with various pore solution concentrations, further substantiating the HIN as the physical mechanism governing pore solution freezing.

Cryopreservation of organoids: Strategies, innovation, and future prospects

Organoid technology has demonstrated unique advantages in multidisciplinary fields such as disease research, tumor drug sensitivity, clinical immunity, drug toxicology, and regenerative medicine. It will become the most promising research tool in translational research. However, the long preparation time of organoids and the lack of high-quality cryopreservation methods limit the further application of organoids. Although the high-quality cryopreservation of small-volume biological samples such as cells and embryos has been successfully achieved, the existing cryopreservation methods for organoids still face many bottlenecks. In recent years, with the development of materials science, cryobiology, and interdisciplinary research, many new materials and methods have been applied to cryopreservation. Several new cryopreservation methods have emerged, such as cryoprotectants (CPAs) of natural origin, ice-controlled biomaterials, and rapid rewarming methods. The introduction of these technologies has expanded the research scope of cryopreservation of organoids, provided new approaches and methods for cryopreservation of organoids, and is expected to break through the current technical bottleneck of cryopreservation of organoids. This paper reviews the progress of cryopreservation of organoids in recent years from three aspects: damage factors of cryopreservation of organoids, new protective agents and loading methods, and new technologies of cryopreservation and rewarming.

Composite tissue xenopreservation: Preliminary results of staged VCA in rat to mouse model

BACKGROUND

The time between procurement and transplantation of composite tissues, especially regarding the limited donor pool, is a challenge effecting the outcomes of the transplantation. Current preservation techniques mainly include either cold preservation with a solution or machine perfusion using blood or certain oxygen-carrying solutions. However, none enables preservation beyond 24 h. Increasing this time to several days will provide better usage of the donor pool, safer transplantation of VCA with significant muscle content, and gives time to stabilize a patient before long surgical procedures. Herein, we described a novel strategy of xenopreservation (preservation via xenotransplantation) to preserve composite tissues for 7 days, followed by staged transplantation.

MATERIALS AND METHODS

We used two concordant species, female Sprague Dawley rats (n = 10) and female CF-1 mice (n = 10) in this study. Four of pair of animals are used for anatomical study. The groin flap of the rat was used as a xenograft and xenotransplanted to the neck area of the carrier mouse. Cyclosporine (CsA) was administered used as immunosuppressant. After 7 days of preservation on the mouse neck, xenotransplanted groin flap (called xenopreserved flap) was re-harvested, skin and vessels samples were collected for histopathological evaluation, and the xenopreserved flap was transplanted to the donor rat's opposite groin area. Anastomoses were performed between the flap's pedicle and the femoral vessels. Clinical observation regarding inflammation and tissue perfusion of the xenopreserved flap was monitored daily. Fifteen days after the second surgical procedure, the rats were euthanized, and skin and vessel samples were collected. Histologic evaluation, including inflammatory cell numbers, was performed. Wilcoxon test was used to compare the changes in inflammation severity and p < .05 was set for statistical significance.

RESULTS

All xenopreserved groin flaps except one survived. Mean lymphocyte count before the second operation (at the end of the xenopreservation procedure) was 20,22 ± 0.44 and reduced to 13,14 ± 0.47 at the end of 15 days, and the difference was statistically significant (p < .05).

CONCLUSION

This proof-of-concept study with preliminary results showed that xenotransplantation might be a novel strategy for preservation of VCA for a certain period of time. However, additional translational studies are needed to modulate the tissue changes following xenopreservation.

Cryopreservation Alters Tissue Structure and Improves Differentiation of Engineered Skeletal Muscle

Tissue-engineered skeletal muscle can play an important role in regenerative medicine, disease modeling, drug testing, as well as the actuation of biohybrid machines. As the applications of engineered muscle tissues expand, there exists a growing need to cryopreserve and store these tissues without impairing function. In a previous study, we developed a cryopreservation protocol in which engineered skeletal muscle tissues are frozen before myogenic differentiation. In that study, we found that this cryopreservation process led to a three-fold increase in the force generation of the differentiated muscle. Here, we perform further testing to determine the mechanisms by which cryopreservation enhances engineered skeletal muscle function. We found that cryopreservation alters the microstructure of the tissue by increasing pore size and decreasing elastic modulus of the extracellular matrix (ECM), which leads to increased expression of genes related to cell migration, cell-matrix adhesion, ECM secretion, and protease activity. Specifically, cryopreservation leads to the upregulation of many ECM proteins, including laminin, fibronectin, and several types of collagens, as well as integrins and matrix metalloproteinases. These changes to ECM structure and composition were associated with enhanced myogenic differentiation, as evidenced by the upregulation of late-stage myogenic markers and increased force generation. These results highlight the need to understand the effects of cryopreservation on the ECM of other tissues as we strive to advance tissue and organ cryopreservation protocols for regenerative medicine.

Swiss Vascular Biobank: Evaluation of Optimal Extraction Method and Admission Solution for Preserving RNA from Human Vascular Tissue

Proper biobanking is essential for obtaining reliable data, particularly for next-generation sequencing approaches. Diseased vascular tissues, having extended atherosclerotic pathologies, represent a particular challenge due to low RNA quality. In order to address this issue, we isolated RNA from vascular samples collected in our Swiss Vascular Biobank (SVB); these included abdominal aortic aneurysm (AAA), peripheral arterial disease (PAD), healthy aorta (HA), and muscle samples. We used different methods, investigated various admission solutions, determined RNA integrity numbers (RINs), and performed expression analyses of housekeeping genes (ACTB, GAPDH), ribosomal genes (18S, 28S), and long non-coding RNAs (MALAT1, H19). Our results show that RINs from diseased vascular tissue are low (2-4). If the isolation of primary cells is intended, as in our SVB, a cryoprotective solution is a better option for tissue preservation than RNAlater. Because RNA degradation proceeds randomly, controls with similar RINs are recommended. Otherwise, the data might convey differences in RNA degradation rather than the expressions of the corresponding genes. Moreover, since the 18S and 28S genes in the diseased vascular samples were degraded and corresponded with the low RINs, we believe that DV200, which represents the total RNA's disintegration state, is a better decision-making aid in choosing samples for omics analyses.

Melatonin reduces β-amyloid accumulation and improves short-term memory in streptozotocin-induced sporadic Alzheimer's disease model

Melatonin is a hormone secreted by the pineal gland, it can be associated with circadian rhythms, aging and neuroprotection. Melatonin levels are decreased in sporadic Alzheimer's disease (sAD) patients, which suggests a relationship between the melatonergic system and sAD. Melatonin may reduce inflammation, oxidative stress, TAU protein hyperphosphorylation, and the formation of β-amyloid (Aβ) aggregates. Therefore, the objective of this work was to investigate the impact of treatment with 10 mg/kg of melatonin (i.p) in the animal model of sAD induced by the intracerebroventricular (ICV) infusion of 3 mg/kg of streptozotocin (STZ). ICV-STZ causes changes in the brain of rats similar to those found in patients with sAD. These changes include; progressive memory decline, the formation of neurofibrillary tangles, senile plaques, disturbances in glucose metabolism, insulin resistance and even reactive astrogliosis characterized by the upregulation of glucose levels and glial fibrillary acidic protein (GFAP). The results show that ICV-STZ caused short-term spatial memory impairment in rats after 30 days of STZ infusion without locomotor impairment which was evaluated on day 27 post-injury. Furthermore, we observed that a prolonged 30-day treatment with melatonin can improve the cognitive impairment of animals in the Y-maze test, but not in the object location test. Finally, we demonstrated that animals receiving ICV-STZ have high levels of Aβ and GFAP in the hippocampus and that treatment with melatonin reduces Aβ levels but does not reduce GFAP levels, concluding that melatonin may be useful to control the progression of amyloid pathology in the brain.

Evaluation of Structural Viability of Porcine Tracheal Scaffolds after 3 and 6 Months of Storage under Three Different Protocols

Tracheal replacement with a bioengineered tracheal substitute has been developed for long-segment tracheal diseases. The decellularized tracheal scaffold is an alternative for cell seeding. It is not defined if the storage scaffold produces changes in the scaffold's biomechanical properties. We tested three protocols for porcine tracheal scaffold preservation immersed in PBS and alcohol 70%, in the fridge and under cryopreservation. Ninety-six porcine tracheas (12 in natura, 84 decellularized) were divided into three groups (PBS, alcohol, and cryopreservation). Twelve tracheas were analyzed after three and six months. The assessment included residual DNA, cytotoxicity, collagen contents, and mechanical properties. Decellularization increased the maximum load and stress in the longitudinal axis and decreased the maximum load in the transverse axis. The decellularization of the porcine trachea produced structurally viable scaffolds, with a preserved collagen matrix suitable for further bioengineering. Despite the cyclic washings, the scaffolds remained cytotoxic. The comparison of the storage protocols (PBS at 4 °C, alcohol at 4 °C, and slow cooling cryopreservation with cryoprotectants) showed no significant differences in the amount of collagen and in the biomechanical properties of the scaffolds. Storage in PBS solution at 4 °C for six months did not change the scaffold mechanics.

Characterization of Human Subcutaneous Adipose Tissue and Validation of the Banking Procedure for Autologous Transplantation

Adipose tissue (AT) is composed of a heterogeneous population which comprises both progenitor and differentiated cells. This heterogeneity allows a variety of roles for the AT, including regenerative functions. In fact, autologous AT is commonly used to repair soft tissue defects, and its cryopreservation could be a useful strategy to reduce the patient discomfort caused by multiple harvesting procedures. Our work aimed to characterize the cryopreserved AT and to validate its storage for up to three years for clinical applications. AT components (stromal vascular fraction-SVF and mature adipocytes) were isolated in fresh and cryopreserved samples using enzymatic digestion, and cell viability was assessed by immunofluorescence (IF) staining. Live, apoptotic and necrotic cells were quantified using cytometry by evaluating phosphatidylserine binding to fluorescent-labeled Annexin V. A multiparametric cytometry was also used to measure adipogenic (CD34+CD90+CD31-CD45-) and endothelial (CD34+CD31+CD45-) precursors and endothelial mature cells (CD34-CD31+CD45-). The maintenance of adipogenic abilities was evaluated using in vitro differentiation of SVF cultures and fluorescent lipid staining. We demonstrated that AT that is cryopreserved for up to three years maintains its differentiation potential and cellular composition. Given our results, a clinical study was started, and two patients had successful transplants without any complications using autologous cryopreserved AT.

Trehalose in Biomedical Cryopreservation-Properties, Mechanisms, Delivery Methods, Applications, Benefits, and Problems

Cells and tissues are the foundation of translational medicine. At present, one of the main technological obstacles is their preservation for long-term usage while maintaining adequate viability and function. Optimized storage techniques must be developed to make them safer to use in the clinic. Cryopreservation is the most common long-term preservation method to maintain the vitality and function of cells and tissues. But, the formation of ice crystals in cells and tissues is considered to be the main mechanism that could harm cells and tissues during freezing and thawing. To reduce the formation of ice crystals, cryoprotective agents (CPAs) must be added to the cells and tissues to achieve the cryoprotective effect. However, conventional cryopreservation of cells and tissues often needs to use toxic organic solvents as CPAs. As a result, cryopreserved cells and tissues may need to go through a time-consuming washing process to remove CPAs for further applications in translational medicine, and multiple valuable cells are potentially lost or killed. Currently, trehalose has been researched as a nontoxic CPA due to its cryoprotective ability and stability during cryopreservation. Nevertheless, trehalose is a nonpermeable CPA, and the lack of an effective intracellular trehalose delivery method has become the main obstacle to its use in cryopreservation. This article illustrated the properties, mechanisms, delivery methods, and applications of trehalose, summarized the benefits and limits of trehalose, and summed up the findings and research direction of trehalose in biomedical cryopreservation.

Influence of Storage Conditions on Decellularized Porcine Conjunctiva

Porcine decellularized conjunctiva (PDC) represents a promising alternative source for conjunctival reconstruction. Methods of its re-epithelialization in vitro with primary human conjunctival epithelial cells (HCEC) have already been established. However, a long-term storage method is required for a simplified clinical use of PDC. This study investigates the influence of several storage variants on PDC. PDC were stored in (1) phosphate-buffered saline solution (PBS) at 4 °C, (2) in glycerol-containing epithelial cell medium (EM/gly) at −80 °C and (3) in dimethyl sulfoxide-containing epithelial cell medium (EM/DMSO) at −196 °C in liquid nitrogen for two and six months, respectively. Fresh PDC served as control. Histological structure, biomechanical parameters, the content of collagen and elastin and the potential of re-epithelialization with primary HCEC under cultivation for 14 days were compared (n = 4–10). In all groups, PDC showed a well-preserved extracellular matrix without structural disruptions and with comparable fiber density (p ≥ 0.74). Collagen and elastin content were not significantly different between the groups (p ≥ 0.18; p ≥ 0.13, respectively). With the exception of the significantly reduced tensile strength of PDC after storage at −196 °C in EM/DMSO for six months (0.46 ± 0.21 MPa, p = 0.02), no differences were seen regarding the elastic modulus, tensile strength and extensibility compared to control (0.87 ± 0.25 MPa; p ≥ 0.06). The mean values of the epithelialized PDC surface ranged from 51.9 ± 8.8% (−196 °C) to 78.3 ± 4.4% (−80 °C) and did not differ significantly (p ≥ 0.35). In conclusion, all examined storage methods were suitable for storing PDC for at least six months. All PDC were able to re-epithelialize, which rules out cytotoxic influences of the storage conditions and suggests preserved biocompatibility for in vivo application.

Effects of Antifreeze Protein Type I and Glycerol in Diluents on Cryopreserved Goat Epididymal Sperm

The effect of antifreeze protein (AFP) as a cryoprotectant used in different concentrations of glycerol on post-thaw quality of epididymal sperm was investigated. Sperm were isolated from 50 testicles, obtained from 25 healthy mature goat bucks, with progressive motility >80%, and total morphological abnormalities <10% were pooled in each replication. The semen samples were diluted with Tris-citrate-fructose-soybean lecithin extender containing different concentration of AFP [0 μg/mL (A0), 5 μg/mL (A5), 10 μg/mL (A10)]. Each concentration of AFP was added in an extender containing either 7% (G7) or 5% (G5) glycerol. Post-thaw total and progressive motility were found to be higher (p < 0.05) in groups A5G5 and A5G7. Plasma membrane integrity, sperm acrosome integrity, DNA integrity, acrosome intact sperm, and mitochondrial membrane potential were found to be higher (p < 0.05) in groups A5G5 and A10G5. Sperm viability was found to be higher (p < 0.05) in group A5G5, while lipid peroxidation was recorded lower (p < 0.05) in groups A5G5 and A5G7. Regarding the apoptosis occurrence, the results demonstrate higher (p < 0.05) live post-thawed spermatozoa for groups containing 5 μg/mL AFP with 5% and 7% glycerol in addition to the lowest (p < 0.05) value for groups containing 0 μg/mL AFP with 5% and 7% glycerol. Based on these results, the present study concludes that the addition of 5 μg/mL AFP in combination with 5% glycerol in freezing extender improves the post-thaw quality, structure, and function parameters for buck spermatozoa.

Principles and Protocols For Post-Cryopreservation Quality Evaluation of Stem Cells in Novel Biomedicine

Stem cell therapy is a thriving topic of interest among researchers and clinicians due to evidence of its effectiveness and promising therapeutic advantage in numerous disease conditions as presented by novel biomedical research. However, extensive clinical application of stem cells is limited by its storage and transportation. The emergence of cryopreservation technology has made it possible for living organs, tissues, cells and even living organisms to survive for a long time at deep low temperatures. During the cryopreservation process, stem cell preparations are subject to three major damages: osmotic damage, mechanical damage, and peroxidative damage. Therefore, Assessing the effectiveness and safety of stem cells following cryopreservation is fundamental to the quality control of stem cell preparations. This article presents the important biosafety and quality control parameters to be assessed during the manufacturing of clinical grade stem cell products, highlights the significance of preventing cryodamage. and provides a reference for protocols in the quality control of stem cell preparations.

The effect of glycerol as a cryoprotective agent in the cryopreservation of adipose tissue

Background

Long-term preservation of adipose tissue is crucial for clinical applications. Researchers should consider both efficiency and biosafety when choosing a cryoprotective agent (CPA) for adipose tissue preservation. Glycerol has been applied as a nontoxic CPA for multiple tissues but not adipose tissue. We aimed to evaluate the efficacy of glycerol as a CPA for adipose tissue cryopreservation.

Methods

Fresh human adipose tissues were obtained from patients who underwent liposuction and divided into 1 mL samples. Each sample was randomly mixed with 1 mL of CPA: 60–100% glycerol, 0.25 mol/L trehalose or DMSO + FBS and cryopreserved in − 196 °C liquid nitrogen for one month. After thawing and elution, the tissues were immediately evaluated for activity and structural integrity in vitro. Then, 0.2 mL of each sample was transplanted subdermally to the nude mouse dorsum and harvested after one month for histological examination to assess the effect of the cryopreserved fat in transplantation.

Results

After cryopreservation, the samples treated with DMSO + FBS, trehalose, 60% and 70% glycerol had a more integrated structure than the samples in other groups. Tissues preserved with 70% glycerol had the highest G3PDH activity of 24.41 ± 0.70, comparable to 24.76 ± 0.48 in fresh tissue (p > 0.05). Adipose-derived stem cells (ASC) viability, proliferation and differentiation capability were also better preserved in 70% glycerol group. In vivo analysis showed that tissue preserved with 70% glycerol had a retention rate of 52.37 ± 7.53%, significantly higher than other groups. Histological observation demonstrated better structural integrity and viability in 70% glycerol group. Compared to the DMSO + FBS and trehalose groups, the glycerol groups showed lower tissue inflammation.

Conclusion

Glycerol (70%) is efficient in adipose tissue cryopreservation. Glycerol-based CPAs, which are nontoxic and show biosafety, are a promising solution for clinical tissue cryopreservation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02817-z.

Cryopreservation of Tissue-Engineered Scaffold-Based Constructs: from Concept to Reality

Creation of scaffold-based tissue-engineered constructs (SB TECs) is costly and requires coordinated qualified efforts. Cryopreservation enables longer shelf-life for SB TECs while enormously enhancing their availability as medical products. Regenerative treatment with cryopreserved SB TECs prepared in advance (possibly prêt-à-porter) can be started straight away on demand. Animal studies and clinical trials indicate similar levels of safety for cryopreserved and freshly prepared SB TECs. Although cryopreservation of such constructs is more difficult than that of cell suspensions or tissues, years of research have proved the principal possibility of using ready-to-transplant SB TECs after prolonged cryostorage. Cryopreservation efficiency depends not only on the sheer viability of adherent cells on scaffolds after thawing, but largely on the retention of proliferative and functional properties by the cells, as well as physical and mechanical properties by the scaffolds. Cryopreservation protocols require careful optimization, as their efficiency depends on multiple parameters including cryosensitivity of cells, chemistry and architecture of scaffolds, conditions of cell culture before freezing, cryoprotectant formulations, etc. In this review we discuss recent achievements in SB TEC cryopreservation as a major boost for the field of tissue engineering and biobanking.

Reducing the Glucose Level in Pre-treatment Solution Improves Post-thaw Boar Sperm Quality

Frozen–thawed boar sperm was not widely used in pig artificial insemination as the sperm quality was damaged by biochemical and physical modifications during the cryopreservation process. The aim of this study was to investigate whether reduction of the glucose level in diluted medium could protect the post-thaw boar sperm or not. Boar sperm was diluted with the pre-treatment medium with different doses of glucose (153, 122.4, 91.8, 61.2, 30.6, and 0 mM) during the cooling process. The sperm motility patterns and glycolysis were evaluated during the cooling process. Meanwhile, the post-thaw sperm quality, ATP level, mitochondrial function as well as apoptosis were also measured. It was observed that 153 mM glucose treatment showed the highest glycolysis in boar sperm as the activities of hexokinase, fructose-bisphosphate aldolase A, and lactate dehydrogenase are the highest as well as the lactate level. Reduction of the glucose level from 153 to 30.6 mM suppressed sperm glycolysis. In addition, treatment with 153 mM glucose made the sperm demonstrate a circle-like movement along with a high value of curvilinear velocity and amplitude of the lateral head, while decreasing the glucose level reduced those patterns in the cooling process. Moreover, reduction of the glucose level also significantly increased the post-thaw sperm's total motility, progressive motility, straight-linear velocity, membrane integrity, and acrosome integrity. The treatment with 30.6 mM glucose showed the highest value among the treatments. Furthermore, the post-thaw sperm's succinate dehydrogenase activity, malate dehydrogenase activity, mitochondrial membrane potential as well as ATP level were increased by reducing the glucose level from 153 to 30.6 mM. Interestingly, the treatment with 30.6 mM glucose showed the lowest apoptosis of post-thaw sperm among the treatments. Those observations suggest that reduction of the glucose level in diluted medium increased the post-thaw boar sperm quality via decreasing the glycolytic metabolism. These findings provide novel insights that reduction of boar sperm activity via decreasing sperm glycolysis during the cooling process helps to improve the post-thaw sperm quality during cryopreservation.

Preoperative Cryopreservation Promotes Digital Survival after Digit Replantation

Cryopreservation has been applied in the replantation of limbs with a minimal amount of muscle tissue replanted. And small composite tissues have also been reported to be successfully replanted by preoperative cryopreservation. In this study, we aimed to study the effect of preoperative cryopreservation on digital survival after digit replantation. Accordingly, we collected and compared the demographic and clinicopathological characteristics of patients with digit injury of patients, and we observed no significant difference between the NT and CP patients of digital injury. We also investigated the records of successful digit replantation and other parameters which influenced the odds of digital survival of all recruited patients. Accordingly, we found that the number of survived digits was remarkably increased in patients in the CP group compared with that in patients in the NT group. And the number of patients requiring blood transfusion and the mean length of hospital stay were notably decreased in the CP group. And compared with other patient characteristics, the mechanism of injury (blade, crush, or avulsion) showed a remarkable difference between the two groups of digital failure. Moreover, we analyzed the correlations between patient characteristics and the odds of digit survival and found that compared with other basic characteristics of patients and their injury, the preservation temperature, especially cryopreservation, could significantly promote digital survival after replantation.

How cryoprotectants work: hydrogen-bonding in low-temperature vitrified solutions

Dimethyl sulfoxide (DMSO) increases cell and tissue viability at low temperatures and is commonly used as a cryoprotectant for cryogenic storage of biological materials. DMSO disorders the water hydrogen-bond networks and inhibits ice-crystal growth, though the specific DMSO interactions with water are difficult to characterize. In this study, we use a combination of Fourier Transform infrared spectroscopy (FTIR), molecular dynamics simulations, and vibrational frequency maps to characterize the temperature-dependent hydrogen bonding interactions of DMSO with water from 30 °C to −80 °C. Specifically, broad peaks in O–D stretch vibrational spectra of DMSO and deuterated water (HDO) cosolvent systems show that the hydrogen bond networks become increasingly disrupted compared to pure water. Simulations demonstrated that these disrupted hydrogen bond networks remain largely localized to the first hydration shell of DMSO, which explains the high DMSO concentrations needed to prevent ice crystal formation in cryopreservation applications.

Dimethyl sulfoxide (DMSO) increases cell and tissue viability at low temperatures and is commonly used as a cryoprotectant for cryogenic storage of biological materials.

Optimization of long-term cold storage of rat precision-cut lung slices with a tissue preservation solution

Precision-cut lung slices (PCLS) are used as ex vivo model of the lung to fill the gap between in vitro and in vivo experiments. To allow optimal utilization of PCLS, possibilities to prolong slice viability via cold storage using optimized storage solutions were evaluated. Rat PCLS were cold stored in DMEM/F-12 or two different preservation solutions for up to 28 days at 4°C. After rewarming in DMEM/F-12, metabolic activity, live/dead staining, and mitochondrial membrane potential was assessed to analyze overall tissue viability. Single-cell suspensions were prepared and proportions of CD45⁺, EpCAM⁺, CD31⁺, and CD90⁺ cells were analyzed. As functional parameters, TNF-α expression was analyzed to detect inflammatory activity and bronchoconstriction was evaluated after acetylcholine stimulus. After 14 days of cold storage, viability and mitochondrial membrane potential were significantly better preserved after storage in solution 1 (potassium chloride rich) and solution 2 (potassium- and lactobionate-rich analog) compared with DMEM/F-12. Analysis of cell populations revealed efficient preservation of EpCAM⁺, CD31⁺, and CD90⁺ cells. Proportion of CD45⁺ cells decreased during cold storage but was better preserved by both modified solutions than by DMEM/F-12. PCLS stored in solution 1 responded substantially longer to inflammatory stimulation than those stored in DMEM/F-12 or solution 2. Analysis of bronchoconstriction revealed total loss of function after 14 days of storage in DMEM/F-12 but, in contrast, a good response in PCLS stored in the optimized solutions. An improved base solution with a high potassium chloride concentration optimizes cold storage of PCLS and allows shipment between laboratories and stockpiling of tissue samples.

Live Imaging of Primary Neurons in Long-Term Cryopreserved Human Nerve Tissue

Tissue cryopreservation provides a convenient solution for tackling one of the major problems in neuroscience research, namely, the scarce availability of human nerve tissues, especially if needed alive. While brain tissue can be used only postmortem, live nerve tissue can reasonably well be harvested from the periphery. A valuable source of primary neurons is the intestine, which compared with brain has the advantage to be safely accessible via endoscopy. The nerve tissue innervating the intestine (the enteric nervous system; ENS) can be sampled with regular endoscopic biopsy forceps and remains viable for multiple physiological and immunohistochemical tests, as previously demonstrated. Here, we present a method to preserve, over longer periods of time, human primary neurons contained in these biopsies. The use of a cryoprotective agent and the application of controlled cooling revealed to be crucial to properly store the nerve tissue and to enable functional measurements after thawing. These primary neurons were evaluated for functionality (live imaging) and morphology (histology) up to one year after cryopreservation. Calcium (Ca²⁺) imaging indicated that human primary neurons remained viable and responded to selective stimulations (serotonergic and nicotinic agonists) after cryopreservation. Additionally, immunohistochemistry performed with specific neuronal markers showed that nerve structure and neuronal morphology were retained, with no signs of cellular damage. In this study, we demonstrate that the human ENS is a realistic source of primary neurons, which can be successfully preserved over long times and as such can be exploited both for gastrointestinal-specific as well as for general neuroscience research.

Application of Cryopreservation Technique in the Preservation of Rat Limbs

OBJECTIVE

The aim of this study was to observe the physiologic and pathologic changes of severed fingers (limbs) under different storage conditions through animal experiments, and to screen out the best preservation conditions.

METHODS

Sixty healthy adult male Sprague-Dawley rats were selected and evenly divided into 4 preservation groups, including conventional low-temperature dry (CLTD), the University of Wisconsin (UW) solution, cryopreservation, and cryopreservation + UW solution preservation group. After harvesting the limbs, were preservated for 72 hours and 7 days, respectively. Then the limbs were thawed and replanted in situ. Sciatic nerves were collected for hematoxylin & eosin (H&E) staining and observed the changes in tissue morphology.

RESULTS

Replantation was successful in 11 of 15 rats (73%) in the cryopreservation + UW group, and the walking function of the 9 (82%) rats in cryopreservation + UW group were significantly better than that of the cryopreservation preservation group. Additionally, the H&E staining results shown that the CLTD group nerve bundles were morphologically damaged, and there were more acellular structures and tissue fragments; the UW group nerve bundles were less injured and the perineurium was more complete and more orderly. The nerve bundles in the cryopreservation group and the cryopreservation + UW group are tightly arranged, and the tissue morphology is regular. Compared with the cryopreservation + UW group, the completeness of the cryopreservation group was not sufficient.

CONCLUSIONS

The cryopreservation technology combined with the UW solution is a new and effective method for preservation of severed limbs.

Antifreeze proteins for low-temperature preservation in reproductive medicine: A systematic review over the last three decades

Antifreeze proteins (AFPs) are synthesized by diverse non-mammalian species, allowing them to survive in severely cold environments. Since the 1990s, the scientific literature reports their use for low-temperature preservation of germplasm. The aim of this systematic review was to compile available scientific evidence regarding the use of AFP for low-temperature preservation of several reproductive specimens. Internet databases were consulted using the terms: "antifreeze protein" OR "AFP" OR "antifreeze glycoprotein" OR "AFGP" OR "ice-binding protein" OR "IBP" OR "thermal hysteresis protein" AND "cryopreservation". From 56 articles, 87 experiments testing AFPs in low-temperature preservation of gametes, embryos or reproductive tissues/cells were fully analyzed and outcomes were annotated. A positive outcome was considered as a statistically significant improvement on any parameter evaluated after low-temperature preservation with AFP, whereas a negative outcome included worsening of any evaluated parameter, in comparison to untreated groups or groups treated with a lower concentration of AFP. The findings indicated that research on the use of AFP as a cryoprotectant for reproductive specimens has increased markedly over the past decade. Some experiments reported both positive and negative results, which depended, on AFP concentration in the preservation media. Variation in the outcomes associated with species was also observed. Among the 66 experiments conducted in mammals, 77.3% resulted in positive, and 28.8% in negative outcomes after the use of AFP. In fishes, positive and negative outcomes were observed in 71.4% and 33.3% of 21 experiments, respectively. Most positive outcomes included preserving cell post-warming survival. The beneficial effect of AFP supports its use in cryobiological approaches used in human and veterinary medicines and animal protein industry. Moreover, combination of different AFP types, or AFP with antioxidants, or even the use of AFP-biosimilar, comprise some promising approaches to be further explored in cryopreservation.

Comparison of the function and structural integrity of cryopreserved pulmonary homografts versus decellularized pulmonary homografts after 180 days implantation in the juvenile ovine model

Homograft availability and durability remain big challenges. Increasing the post-mortem ischaemic harvesting time beyond 24 h increases the potential donor pool. Cryopreservation, routinely used to preserve homografts, damages the extracellular matrix (ECM), contributing to valve degeneration. Decellularization might preserve the ECM, promoting host-cell infiltration and contributing towards better clinical outcomes. This study compared the performance of cryopreserved versus decellularized pulmonary homografts in the right ventricle outflow tract (RVOT) of a juvenile ovine model. Homografts (n = 10) were harvested from juvenile sheep, subjected to 48 h post-mortem cold ischaemia, cryopreserved or decellularized and implanted in the RVOT of juvenile sheep for 180 days. Valve performance was monitored echocardiographically. Explanted leaflet and wall tissue evaluated histologically, on electron microscopical appearance, mechanical properties and calcium content. In both groups the annulus diameter increased. Cryopreserved homografts developed significant (¾) pulmonary regurgitation, with trivial regurgitation (¼) in the decellularized group. Macroscopically, explanted cryopreserved valve leaflets retracted and thickened while decellularized leaflets remained thin and pliable with good coaptation. Cryopreserved leaflets and walls demonstrated loss of interstitial cells with collapsed collagen, and decellularized scaffolds extensive, uniform ingrowth of host-cells with an intact collagen network. Calcific deposits were shown only in leaflets and walls of cryopreserved explants. Young fibroblasts, with vacuoles and rough endoplasmic reticulum in the cytoplasm, repopulated the leaflets and walls of decellularized scaffolds. Young's modulus of wall tissue in both groups increased significantly. Cryopreserved valves deteriorate over time due to loss of cellularity and calcification, while decellularized scaffolds demonstrated host-cell repopulation, structural maintenance, tissue remodelling and growth potential.

Preservation solutions for attenuation of ischemia-reperfusion injury in vascularized composite allotransplantation

Vascularized composite allotransplantation represents the final level of the reconstructive ladder, offering treatment options for severe tissue loss and functional deficiencies. Vascularized composite allotransplantation is particularly susceptible to ischemia–reperfusion injury and requires preservation techniques when subjected to extended storage times prior to transplantation. While static cold storage functions to reduce ischemic damage and is widely employed in clinical settings, there exists no consensus on the ideal preservation solution for vascularized composite allotransplantation. This review aims to highlight current clinical and experimental advances in preservation solution development and their critical role in attenuating ischemia–reperfusion injury in the context of vascularized composite allotransplantation.

Spherical depth-sensing nanoindentation of human anterior skull base bones: Establishment of a test protocol

The mechanical properties of anterior skull base (ASB) bones are not well understood due to their complex geometry and deep location. However, it is of particular interest for skull base surgeons to appraise the force range they can apply during procedures and know what kind of haptic feedback a simulation device should produce in order to be realistic for trainees. The aim of this study was to establish a measurement protocol to set the level of hydration state, temperature and curve analysis method for spherical depth sensing nanoindentation of ASB bones. A definitive screening design method was used to test the different possible combinations of these factors. Two samples of ASB bones from the heads of two human body donors (two specimens) were selected according to their microstructure as assessed by micro-CT (microtomography): low-porosity (16.87%, sphenoid bone) and high-porosity (79.85%, ethmoid bone). Depth measurement series of 36 nanoindentations (n = 288) were performed on specimen 1 according to the L8 Taguchi orthogonal array to study the effect of temperature (two levels: 20 or 37 °C), hydration state (dry or immerged in physiological saline sodium chloride), and loading curve analysis according to the Hertzian contact theory (fitting at the start or at the end). The mean values of reduced Young's (E*) modulus varied significantly depending on the hydration status and bone microstructure. In order to obtain the physiological properties of ASB bones, we thus propose performing immersion tests. To simplify the experimentation protocol, future experiments must include a room temperature level and a fit of the curve at the end of the load. A validation series was performed on the second specimen to assess the set of parameters. The E* in dry bone gave mean values of 994.68 MPa, versus 409.79 MPa in immerged bones (p < 0.00001). This is the first time a study has been carried out on ASB bones, defining the experimental parameters related to physiological conditions.

A novel method to evaluate prethawing viability of cryopreserved CD34+ hematopoietic stem cells for autologous transplantation

BACKGROUND

Cryopreservation of CD34+ hematopoietic stem cells (HSCs) is associated with variable loss of viability. Although postfreezing CD34+ cell viability can be assessed on the sampling tube (bag tail) directly connected to the main bag (mother bag), results often underestimate the actual viability observed when the mother bag is thawed and reinfused. We assessed a novel method to measure postfreezing CD34+ cell viability, based on small bag (minibag) samples; results were compared with those obtained on the corresponding mother bags and bag tails.

STUDY DESIGN AND METHODS

Sixty-one apheresis procedures of 42 patients undergoing autologous HSC transplant were analyzed. Viable CD34+ cells were quantified with flow cytometry before controlled rate freezing (ICE-CUBE14M system, SY-LAB- IceCube, SIAD), after 10 days of storage (mini-bag and bag tail), and before reinfusion (aliquot from a thawed mother bag). Results were compared using Student's t test and Spearman's rho correlation test.

RESULTS

The mean CD34+ cell viability before cryopreservation was 99.3% (confidence interval [CI], 98.94-99.65%); the mean amount of CD34+ cells, white blood cells and neutrophils in the mother bag was 0.8 ± 1.1 × 10⁹ /L, 63.4 ± 23.5 × 10⁹ /L, and 25.7 ± 15.5 × 10⁹ /L, respectively. Mother bags postthawing CD34+ cell viability was 72.3% (CI, 67.74-76.85%; p < 0.01 compared to prefreezing); no difference was observed with respect to minibags (73.7%; CI, 69.80-77.59%; p = NS), whereas significantly lower values were found for bag tails (58.6%; CI, 54.19-63.00%; p < 0.01 vs. both mini- and mother bags).

CONCLUSION

Compared to bag tails, minibags represent a more accurate tool to measure the CD34+ cell viability of the apheresis mother bag prior to reinfusion; in addition, minibags may could be of help for case-by-case calculation of the amount of apheresis to be infused to patients undergoing autologous HSC transplant.

A closed vitrification system enables a murine ovarian follicle bank for high-throughput ovotoxicity screening, which identifies endocrine disrupting activity of microcystins

Increasing evidence reveals that a broad spectrum of environmental chemicals and pharmaceutical compounds cause female ovarian toxicity (ovotoxicity). The current gold standard of ovotoxicity testing largely relies on whole laboratory animals, but in vivo models are time consuming, costly, and present animal welfare concerns. We previously demonstrated that the 3D encapsulated in vitro follicle growth (eIVFG) is a robust in vitro model for ovotoxicity testing. However, the follicle preparation process is complex and highly dependent on technical skills. Here, we aimed to use vitrification method to cryopreserve murine immature follicles for a high-content eIVFG, chemical exposure, and ovotoxicity screening. Results indicated that a closed vitrification system combined with optimized vitrification protocols preserved mouse follicle viability and functionality and vitrified follicles exhibited comparable follicle and oocyte reproductive outcomes to freshly harvested follicles during eIVFG, including follicle survival and development, ovarian steroidogenesis, and oocyte maturation and ovulation. Moreover, vitrified follicles consistently responded to ovotoxic chemical, doxorubicin (DOX). We further used vitrified follicles to test the response of microcystins (MCs), an emerging category of environmental contaminants produced by cyanobacteria associated with harmful algal blooms (HABs), and found that different congeners of MCs exhibited differential ovotoxicities. In summary, our study demonstrates that vitrification enables a long-term-storage and ready-to-use ovarian follicle bank for high-throughput ovotoxicity screening, which identifies endocrine disrupting effects of MCs.

Insights into the Emerging Networks of Voids in Simulated Supercooled Water

The structural evolution of supercooled liquid water as we approach the glass transition temperature continues to be an active area of research. Here, we use molecular dynamics simulations of TIP4P/ice water to study the changes in the connected regions of empty space within the liquid, which we investigate using the Voronoi-voids network. We observe two important features: supercooling enhances the fraction of nonspherical voids and different sizes of voids tend to cluster forming a percolating network. By examining order parameters such as the local structure index (LSI), tetrahedrality and topological defects, we show that water molecules near large void clusters tend to be slightly more tetrahedral than those near small voids, with a lower population of under- and overcoordinated defects. We show further that the distribution of closed rings of water molecules around small and large void clusters maintain a balance between 6 and 7 membered rings. Our results highlight the changes of the dual voids and water network as a structural hallmark of supercooling and provide insights into the molecular origins of cooperative effects underlying density fluctuations on the subnanometer and nanometer length scale. In addition, the percolation of the voids and the hydrogen bond network around the voids may serve as useful order parameters to investigate density fluctuations in supercooled water.

Ice Binding Proteins: Diverse Biological Roles and Applications in Different Types of Industry

More than 80% of Earth’s surface is exposed periodically or continuously to temperatures below 5 °C. Organisms that can live in these areas are called psychrophilic or psychrotolerant. They have evolved many adaptations that allow them to survive low temperatures. One of the most interesting modifications is production of specific substances that prevent living organisms from freezing. Psychrophiles can synthesize special peptides and proteins that modulate the growth of ice crystals and are generally called ice binding proteins (IBPs). Among them, antifreeze proteins (AFPs) inhibit the formation of large ice grains inside the cells that may damage cellular organelles or cause cell death. AFPs, with their unique properties of thermal hysteresis (TH) and ice recrystallization inhibition (IRI), have become one of the promising tools in industrial applications like cryobiology, food storage, and others. Attention of the industry was also caught by another group of IBPs exhibiting a different activity—ice-nucleating proteins (INPs). This review summarizes the current state of art and possible utilizations of the large group of IBPs.

Eel sperm cryopreservation: An overview

The eels are teleost fishes from the order Anguilliformes that includes several species with high commercial value. Due to the high interest for aquaculture production of some eel species and for the need to restore eel species that are endangered, several research groups have directed their research toward developing protocols to cryopreserve the spermatozoa of Japanese eel (Anguilla japonica) and European eel (Anguilla anguilla). In this review, we provide an overview on the different protocols that have been developed so far. The first developed protocols used DMSO as cryoprotectant in both species with good success, obtaining sperm motilities of over 45% in Japanese eel and over 35% in European eel. Moreover, sperm cryopreserved using DMSO was successfully used in fertilization trials, although with low fertilization rates. However, recent studies show that DMSO produce epigenetic changes in eel sperm and therefore, the last developed protocols used methanol as cryoprotectant instead. Cryopreservation protocols using methanol as cryoprotectant, showed improved motility values in both Japanese and European eel. In addition, the latest protocols have been adapted to cryopreserve larger volumes of sperm of up to 5 mL, which is useful for larger scale fertilization trials. The present study introduces the state of the art and future perspectives of the eel sperm cryopreservation to be applied in aquaculture and biological conservation programs.

Hypothermic and cryogenic preservation of tissue-engineered human bone

To foster translation and commercialization of tissue-engineered products, preservation methods that do not significantly compromise tissue properties need to be designed and tested. Robust preservation methods will enable the distribution of tissues to third parties for research or transplantation, as well as banking of off-the-shelf products. We recently engineered bone grafts from induced pluripotent stem cells and devised strategies to facilitate a tissue-engineering approach to segmental bone defect therapy. In this study, we tested the effects of two potential preservation methods on the survival, quality, and function of tissue-engineered human bone. Engineered bone grafts were cultured for 5 weeks in an osteogenic environment and then stored in phosphate-buffered saline (PBS) solution at 4 °C or in Synth-a-Freeze™ at -80 °C. After 48 h, samples were warmed up in a water bath at 37 °C, incubated in osteogenic medium, and analyzed 1 and 24 h after revitalization. The results show that while storage in Synth-a-Freeze at -80 °C results in cell death and structural alteration of the extracellular matrix, hypothermic storage in PBS does not significantly affect tissue viability and integrity. This study supports the use of short-term hypothermic storage for preservation and distribution of high-quality tissue-engineered bone grafts for research and future clinical applications.

Pre-grafting histological studies of skin grafts cryopreserved in α helix antarctic yeast oriented antifreeze peptide (Afp1m)

A number of living creatures in the Antarctic region have developed characteristic adaptation of cold weather by producing antifreeze proteins (AFP). Antifreeze peptide (Afp1m) fragment have been designed in the sequence of strings from native proteins. The objectives of this study were to assess the properties of Afp1m to cryopreserve skin graft at the temperature of -10 °C and -20 °C and to assess sub-zero injuries in Afp1m cryopreserved skin graft using light microscopic techniques. In the present study, a process was developed to cryopreserve Sprague-Dawley (SD) rat skin grafts with antifreeze peptide, Afp1m, α-helix peptide fragment derived from Glaciozyma antractica yeast. Its viability assessed by different microscopic techniques. This study also described the damages caused by subzero temperatures (-10 and -20 °C) on tissue cryopreserved in different concentrations of Afp1m (0.5, 1, 2, 5 and 10 mg/mL) for 72 h. Histological scores of epidermis, dermis and hypodermis of cryopreserved skin grafts showed highly significant difference (p < 0.01) among the different concentrations at -10 and -20 °C. In conclusion, the integrity of cryopreserved skin grafts with lower concentrations of Afp1m (0.5, 1 and 2 mg/mL) or at -20 °C was not maintained. The present study attested that Afp1m is a good cryoprotective agent for the cryopreservation of skin graft. Higher Afp1m concentrations (5 and 10 mg/mL) at -10 °C found to be suitable for the future in vivo study using (SD) rat skin grafts.

Cryocornea - toward enhancing the capacity and throughput of ex vivo corneal model

Objective: The objective of this study was to investigate the effects of the concentration of two intracellular (i.e. propylene glycol and glycerol) and four extracellular (i.e. dextran, hydroxypropyl methylcellulose, polyvinylpyrolidone, trehalose) cryoprotective agents as well as the effects of freeze-thawing procedures on the corneal cryoprotection.Significance: The corneal cryopreservation may possibly become the long-term storage technique of choice for collection of animal corneas suitable for ex vivo drug testing.Methods: The integrity of corneal barrier was evaluated by measurements of transepithelial electrical resistance.Results: Under the investigated experimental conditions the best result was obtained for slow freezing (2 h at -20 °C followed by 46 h at -70 °C) and rapid thawing (0.25 h at 34 °C) procedure where 20% (w/V) trehalose in Krebs Ringer buffer solution was used as extracellular cryoprotective agent.Conclusions: The selection of corneal freeze-thawing protocol as well as the optimal type and concentration of a cryoprotective agent allows the cryostorage of porcine corneal tissues with suitable TEER properties (cryocornea).

Advances in machine perfusion, organ preservation, and cryobiology: potential impact on vascularized composite allotransplantation

PURPOSE OF REVIEW

In this review, we discuss novel strategies that allow for extended preservation of vascularized composite allografts and their potential future clinical implications for the field of vascularized composite allotransplantation (VCA).

RECENT FINDINGS

The current gold standard in tissue preservation - static cold preservation on ice - is insufficient to preserve VCA grafts for more than a few hours. Advancements in the field of VCA regarding matching and allocation, desensitization, and potential tolerance induction are all within reasonable reach to achieve; these are, however, constrained by limited preservation time of VCA grafts. Although machine perfusion holds many advantages over static cold preservation, it currently does not elongate the preservation time. More extreme preservation techniques, such as cryopreservation approaches, are, however, specifically difficult to apply to composite tissues as the susceptibility to ischemia and cryoprotectant agents varies greatly by tissue type.

SUMMARY

In the current scope of extended preservation protocols, high subzero approaches of VCA grafts will be particularly critical enabling technologies for the implementation of tolerance protocols clinically. Ultimately, advances in both preservation techniques and tolerance induction have the potential to transform the field of VCA and eventually lead to broad applications in reconstructive transplantation.

Mechanical process prior to cryopreservation of lipoaspirates maintains extracellular matrix integrity and cell viability: evaluation of the retention and regenerative potential of cryopreserved fat-derived product after fat grafting

Background

Cryopreservation of fat grafts facilitates reinjection for later use. However, low temperature and thawing can disrupt tissues and cause lipid leakage, which raises safety concerns. Here, we compared the cryopreservation potential of stromal vascular fraction (SVF) gel processed from lipoaspirate with that of fat.

Methods

Human SVF gel and fat were cryopreserved at − 20 °C without cryoprotectant for 1 month. Fresh SVF gel and fat were used as controls. Tissue viability, adipose-derived stem cell (ASC) function, and the extracellular content were evaluated. At 3 months after transplanting the specimens to immunocompromised mice subcutaneously, the grafts were examined for retention, tissue engraftment, and inflammatory levels. The regenerative effect of cryopreserved SVF gel was evaluated in a murine ischemic wound healing model.

Results

At 1 month, the cell death rate in the SVF gel group was 36 ± 2%. The survived ASCs not only could be isolated via explant culture but also preserved colony-forming and differentiation. However, prolonged cryopreservation exacerbated apoptosis. Assessment of recovered tissues showed that the morphology, cell viability, and extracellular protein enrichment were better in SVF gel-preserved tissues than in frozen fat. At 3 months after lipotransfer, the retention ability of 1-month cryopreserved fat was 41.1 ± 9% compared to that of 1-month cryopreserved SVF gel. Immunostaining results showed that adipose tissue regeneration and integrity in the 1-month cryopreserved SVF gel group were superior to those of the cryopreserved fat group. The cryopreserved SVF gel also accelerated healing of the ischemic wound, compared with cryopreserved fat.

Conclusion

Cryopreserved SVF gel maintained tissue integrity and cell viability and resulted in a better long-term retention rate than that of cryopreserved fat. Cryopreserved SVF gel also showed superior regenerative potential and improved ischemic wound healing.

Numerical solution of inward solidification of a dilute ternary solution towards a semi-permeable spherical cell

Modeling a cell's response to encroaching ice has informed the development of cryopreservation protocols for four decades. It has been well documented that knowledge of the cellular state as a function of media and cooling rate faciliate informed cryopreservation protocol design and explain mechanisms of damage. However, previous efforts have neglected the interaction between solutes and the encroaching ice front and their effects on the cell state. To address this, here we examine the cryobiologically relevant setting of a spherically-symmetric model of a biological cell separated by a ternary fluid mixture from an encroaching solid-liquid interface. The cell and liquid regions contain cell membrane impermeable intracellular and extracellular salts, respectively, a cell membrane permeable solute commonly used in cryopreservation protocols known as a cryoprotective agent (CPA), and water as a membrane permeable solvent. As cooling and solidification proceed the extracellular chemical environment evolves and leads to mass transport across the cell membrane. Consequently, both the solidification front and the cell membrane are free boundaries whose dynamics are coupled through transport processes in the solid, liquid and cell regions. We describe a numerical procedure to solve this coupled free-boundary problem based on a domain transformation and method of lines approach. We also investigate how the thermal and chemical states inside the cell are influenced by different cooling protocols at the external boundary. Finally, we observe that the previously unaccounted-for partial solute rejection at the advancing solid-liquid interface increases the CPA and salt concentrations in the extracellular liquid as a function of the interface speed and segregation coefficients, suggesting that previous model predictions of the cell state during cryopreservation were inaccurate.

Ultrastructural morphology is distinct among primary progenitor cell isolates from normal, inflamed, and cryopreserved equine hoof tissue and CD105+K14+ progenitor cells

The equine hoof dermal-epidermal interface requires progenitor cells with distinct characteristics. This study was designed to provide accurate ultrastructural depictions of progenitor cells isolated from inflamed tissue and normal tissue before and after cryopreservation and following selection of cells expressing both keratin (K) 14 (ectodermal) and cluster of differentiation (CD) 105 (mesodermal). Passage 3 cell ultrastructure was assessed following 2D culture and after 3D culture on decellularized hoof tissue scaffolds. Outcome measures included light, transmission electron, and scanning electron microscopy, immunocytochemistry, and CD105⁺K14⁺ cell trilineage plasticity. Cells from normal tissue had typical progenitor cell characteristics. Those from inflamed tissue had organelles and morphology consistent with catabolic activities including lysosomes, irregular rough endoplasmic reticulum, and fewer vacuoles and early endosomes than those from normal tissue. Cryopreserved tissue cells appeared apoptotic with an irregular cell membrane covered by cytoplasmic protrusions closely associated with endocytic and exocytic vesicles, chromatin aggregated on the nuclear envelop, abundant, poorly organized rough endoplasmic reticulum, and plentiful lysosomes. Cells that were CD105⁺K14⁺ were distinguishable from heterogenous cells by infrequent microvilli on the cell surface, sparse endosomes and vesicles, and desmosomes between cells. Cells expressed ectodermal (K15) and mesodermal (CD105) proteins in 2D and 3D cultures. Inflamed and cryopreserved tissue isolates attached poorly to tissue scaffold while normal tissue cells attached well, but only CD105⁺K14⁺ cells produced extracellular matrix after 4 d. The CD105⁺K14⁺ cells exhibited osteoblastic, adipocytic, and neurocytic differentiation. Ultrastructural information provided by this study contributes to understanding of equine hoof progenitor cells to predict their potential contributions to tissue maintenance, healing, and damage as well post-implantation behavior.

Emerging technologies in organ preservation, tissue engineering and regenerative medicine: a blessing or curse for transplantation?

Since the beginning of transplant medicine in the 1950s, advances in surgical technique and immunosuppressive therapy have created the success story of modern organ transplantation. However, today more than ever, we are facing a huge discrepancy between organ supply and demand, limiting the potential for transplantation to save and improve the lives of millions. To address the current limitations and shortcomings, a variety of emerging new technologies focusing on either maximizing the availability of organs or on generating new organs and organ sources hold great potential to eventully overcoming these hurdles. These advances are mainly in the field of regenerative medicine and tissue engineering. This review gives an overview of this emerging field and its multiple sub-disciplines and highlights recent advances and existing limitations for widespread clinical application and potential impact on the future of transplantation.

Cryostorage of testicular tissue and retransplantation of spermatogonial stem cells in the infertile male

Transplantation of own cryostored spermatogonial stem cells (SSCs) is a promising technique for fertility restoration when the SSC pool has been depleted. In this regard, cryopreservation of pre-pubertal testicular tissue or SSCs suspensions before gonadotoxic therapies is ethically accepted and increasingly proposed. SSC transplantation has also been considered to treat other causes of infertility relying on the possibility of propagating SSCs retrieved in the testes of infertile men before autologous re-transplantation. Although encouraging results were achieved in animals and in preclinical experiments, clinical perspectives are still limited by a number of unresolved technical and safety issues, such as the risk of cancer cell contamination of cells intended for transplantation and the genetic and epigenetic stability of SCCs when cultured before re-transplantation. Moreover, while genome editing techniques raise the hope of modifying the SSCs genome before re-transplantation, their application for reproductive purposes might be a step too far for the moment.