The promise of organ and tissue preservation to transform medicine

Light in evaluation of molecular diffusion in tissues: Discrimination of pathologies

The evaluation of the diffusion properties of different molecules in tissues is a subject of great interest in various fields, such as dermatology/cosmetology, clinical medicine, implantology and food preservation. In this review, a discussion of recent studies that used kinetic spectroscopy measurements to evaluate such diffusion properties in various tissues is made. By immersing ex vivo tissues in agents or by topical application of those agents in vivo, their diffusion properties can be evaluated by kinetic collimated transmittance or diffuse reflectance spectroscopy. Using this method, recent studies were able to discriminate the diffusion properties of agents between healthy and diseased tissues, especially in the cases of cancer and diabetes mellitus. In the case of cancer, it was also possible to evaluate an increase of 5% in the mobile water content from the healthy to the cancerous colorectal and kidney tissues. Considering the application of some agents to living organisms or food products to protect them from deterioration during low temperature preservation (cryopreservation), and knowing that such agent inclusion may be reversed, some studies in these fields are also discussed. Considering the broadband application of the optical spectroscopy evaluation of the diffusion properties of agents in tissues and the physiological diagnostic data that such method can acquire, further studies concerning the optimization of fruit sweetness or evaluation of poison diffusion in tissues or antidote application for treatment optimization purposes are indicated as future perspectives.

Review of Rewarming Methods for Cryopreservation

Cryopreservation is the most effective technology for the long-term preservation of biological materials, including cells, tissues, and even organs in the future. The process of cooling and rewarming is essential to the successful preservation of biological materials. One of the critical problems in the development of cryopreservation is the optimization of effective rewarming technologies. This article reviewed rewarming methods, including traditional boundary rewarming commonly used for small-volume biological materials and other advanced techniques that could be potentially feasible for organ preservation in the future. The review focused on various rewarming technique principles, typical applications, and their possible limitations for cryopreservation of biological materials. This article introduced nanowarming methods in the progressing optimization and the possible difficulties. The trends of novel rewarming methods were discussed, and suggestions were given for future development.

Quantitative Analysis of Ice Crystal Growth During Freezing of Dimethyl Sulfoxide Solutions Under Alternating Current Electric Fields

During cryopreservation, the growth of ice crystals can cause mechanical damage to samples, which is one of the important factors limiting the quality of preserved samples. To enhance the preservation quality of biological samples, scholars have tried various engineering methods. Among them, an electric field is an essential factor affecting solution freezing. Dimethyl sulfoxide, as a commonly used cryoprotectant, can cause mechanical damage to cells due to ice crystals even when freezing at the optimal freezing rate. Water is a strongly polar dielectric material, and the applied alternating current (AC) electric field will affect the water freezing performance. Therefore, a quantitative study of ice crystal nucleation and growth during freezing of dimethyl sulfoxide solutions under different AC electric field conditions is needed to try to reduce ice crystal damage. We created a liquid-film device to approximate the ice crystal growth process as a two-dimensional image. The frequency of the AC voltage was set from 0 to 50 kHz. We measured the supercooling of the dimethyl sulfoxide solution under AC electric field conditions. As an objective and accurate quantitative analysis of the ice crystal growth process, we propose a Dilated Convolutional Segmentation Transformer for semantic segmentation of ice crystal images. It is concluded that the average area and the growth rate of single ice crystals decrease with increasing electric field frequency at a certain concentration of dimethyl sulfoxide solution. Lower concentrations of dimethyl sulfoxide solution in combination with an AC electric field can achieve similar ice suppression effects as when higher concentrations of dimethyl sulfoxide solution act alone. We believe that AC electric fields are expected to be an aid to cryopreservation and provide some theoretical basis and experimental foundation for its development.

High throughput method for simultaneous screening of membrane permeability and toxicity for discovery of new cryoprotective agents

Vitrification is the most promising method for cryopreservation of complex structures such as organs and tissue constructs. However, this method requires multimolar concentrations of cell-permeant cryoprotective agents (CPAs), which can be toxic at such elevated levels. The selection of CPAs for organ vitrification has been limited to a few chemicals; however, there are numerous chemicals with properties similar to commonly used CPAs. In this study, we developed a high-throughput method that significantly increases the speed of cell membrane permeability measurement, enabling ~100 times faster permeability measurement than previous methods. The method also allows assessment of CPA toxicity using the same 96-well plate. We tested five commonly used CPAs and 22 less common ones at both 4 °C and room temperature, with 23 of them passing the screening process based on their favorable toxicity and permeability properties. Considering its advantages such as high throughput measurement of membrane permeability along with simultaneous toxicity assessment, the presented method holds promise as an effective initial screening tool to identify new CPAs for cryopreservation.

Awareness and Willingness towards Organ Donation among Riyadh Residents: A Cross-Sectional Study

BACKGROUND

The increasing prevalence of chronic diseases in Saudi Arabia has heightened the need for organ transplantation; however, the donor pool remains insufficient. This study explored awareness and willingness towards organ donation among Riyadh residents and examined the sociodemographic factors influencing these attitudes.

METHODS

A cross-sectional survey using convenience sampling was conducted among adults in Riyadh. The survey assessed demographic characteristics, awareness, willingness to donate, and sociodemographic factors. Statistical analyses included descriptive statistics and logistic regression.

RESULTS

Among the 645 respondents, 56.4% were willing to donate organs, with females showing a higher propensity than males (OR 2.9, 95% CI 1.7-5.1, p < 0.001). Awareness of organ donation centers was linked to increased willingness to donate (OR 1.5, 95% CI 1.1-2.5, p < 0.001). Higher educational level was strongly associated with donor registration (OR 36.8, 95% CI 14.7-91.9, p < 0.001). Despite their high willingness, only 9.5% were registered as donors, highlighting the gap between intention and action.

CONCLUSIONS

Riyadh residents showed a significant willingness to donate organs, influenced by gender, education, and awareness. Low registration rates suggest barriers such as religious beliefs and lack of information. Targeted educational campaigns and policy evaluations, including an opt-out system, are recommended to enhance registration rates.

Analysis of cryopreservation media thermophysical characteristics after ultra-rapid cooling through differential scanning calorimetry

Cryoprotective agents play a critical role in minimizing cell damage caused by ice formation during cryopreservation. However, high concentrations of CPAs are toxic to cells and tissues. Required concentrations of CPAs can be reduced by utilizing higher cooling and warming rates, but insight into the thermophysical properties of biological solutions in the vitrification method is necessary for the development of cryopreservation protocols. Most studies on thermophysical properties under ultra-rapid cooling conditions have been qualitatively based on visualization. Differential scanning calorimetry methods are ideal for studying the behavior of biomaterials in various freezing conditions quantitatively and accurately, though previous studies have been predominantly restricted to slower cooling rates. Here, we developed an ultra-rapid cooling method for DSC that can achieve minimal cooling rates exceeding 2000 °C/min. We investigated the thermophysical vitrification behavior of ternary solutions of phosphate buffer saline (1X), dimethyl sulfoxide or glycerol and ice blocking polymers (X-1000 or Z-1000). We quantified the impact of solute concentration on ice crystal formation during rapid cooling. Our findings support the expectation that increasing the solute concentration reduces the amount of ice formation, including devitrification. Devitrification increases from 0 % to 40 % (v/v) Me2SO and then reduces significantly. The relative amounts of devitrification to the total ice formation are 0 %, 60 %, 0 % in 20 %, 40 %, 60 % (v/v) Me2SO, and 2 %, 48 %, 49 % in 20 %, 40 %, 60 % (v/v) glycerol, respectively. The results suggest that at low concentrations, such as below 20 % (v/v) for Me2SO or glycerol, increasing the warming rate after ultra-rapid freezing is not essential to eliminate devitrification. Furthermore, ice blocking polymers do not reduce ice formation substantially and cannot eliminate devitrification under ultra-rapid cooling conditions. In conclusion, our results provide insights into the impact of solute concentration on ice formation and devitrification during rapid cooling, which can be practical for optimizing cryopreservation protocols.

Supercooled preservation of cultured primary rat hepatocyte monolayers

Supercooled preservation (SCP) is a technology that involves cooling a substance below its freezing point without initiating ice crystal formation. It is a promising alternative to prolong the preservation time of cells, tissues, engineered tissue products, and organs compared to the current practices of hypothermic storage. Two-dimensional (2D) engineered tissues are extensively used in in vitro research for drug screening and development and investigation of disease progression. Despite their widespread application, there is a lack of research on the SCP of 2D-engineered tissues. In this study, we presented the effects of SCP at -2 and -6°C on primary rat hepatocyte (PRH) monolayers for the first time and compared cell viability and functionality with cold storage (CS, + 4°C). We preserved PRH monolayers in two different commercially available solutions: Hypothermosol-FRS (HTS-FRS) and the University of Wisconsin (UW) with and without supplements (i.e., polyethylene glycol (PEG) and 3-O-Methyl-Α-D-Glucopyranose (3-OMG)). Our findings revealed that UW with and without supplements were inadequate for the short-term preservation of PRH monolayers for both SCP and CS with high viability, functionality, and monolayer integrity. The combination of supplements (PEG and 3-OMG) in the HTS-FRS solution outperformed the other groups and yielded the highest viability and functional capacity. Notably, PRH monolayers exhibited superior viability and functionality when stored at -2°C through SCP for up to 3 days compared to CS. Overall, our results demonstrated that SCP is a feasible approach to improving the short-term preservation of PRH monolayers and enables readily available 2D-engineered tissues to advance in vitro research. Furthermore, our findings provide insights into preservation outcomes across various biological levels, from cells to tissues and organs, contributing to the advancement of bioengineering and biotechnology.

Optimized Partial Freezing Protocol Enables 10-Day Storage of Rat Livers

Preserving organs at subzero temperatures with halted metabolic activity holds the potential to prolong preservation and expand the donor organ pool for transplant. Our group recently introduced partial freezing, a novel approach in high-subzero storage at -15°C, enabling 5 days storage of rodent livers through precise control over ice nucleation and unfrozen fraction. However, increased vascular resistance and tissue edema suggested a need for improvements to extend viable preservation. Here, we describe an optimized partial freezing protocol with key optimizations including increased concentration of propylene glycol to reduce ice recrystallization and maintained osmotic balance through an increase in bovine serum albumin, all while minimizing sheer stress during cryoprotectant unloading with an acclimation period. These approaches ensured the viability during preservation and recovery processes, promoting liver function and ensuring optimal preservation. This was evidenced by increased oxygen consumption, decreased vascular resistance and edema. Ultimately, we show that using the optimized protocol, livers can be stored for 10 days with comparable vascular resistance and lactate levels to 5 days, outperforming the viability of time-matched cold stored livers as the current gold standard. This study represents a significant advancement in expanding organ availability through prolonged preservation and thereby revolutionizing transplant medicine.

A three-dimensional lattice-free agent-based model of intracellular ice formation and propagation and intercellular mechanics in liver tissues

A successful cryopreservation of tissues and organs is crucial for medical procedures and drug development acceleration. However, there are only a few instances of successful tissue cryopreservation. One of the main obstacles to successful cryopreservation is intracellular ice damage. Understanding how ice spreads can accelerate protocol development and enable model-based decision-making. Previous models of intracellular ice formation in individual cells have been extended to one-cell-wide arrays to establish the theory of intercellular ice propagation in tissues. The current lattice-based ice propagation models do not account for intercellular forces resulting from cell solidification, which could lead to mechanical disruption of tissue structures during freezing. Moreover, these models have not been expanded to include more realistic tissue architectures. In this article, we discuss the development and validation of a stochastic model for the formation and propagation of ice in small tissues using lattice-free agent-based model. We have improved the existing model by incorporating the mechanical effects of water crystallization within cells. Using information from previous research, we have also created a new model that accounts for ice growth in tissue slabs, spheroids and hepatocyte discs. Our model demonstrates that individual cell freezing can have mechanical consequences and is consistent with earlier findings.

Polyethylene glycol and caspase inhibitor emricasan alleviate cold injury in primary rat hepatocytes

Current methods of storing explanted donor livers at 4 °C in University of Wisconsin (UW) solution result in loss of graft function and ultimately lead to less-than-ideal outcomes post transplantation. Our lab has previously shown that supplementing UW solution with 35-kilodalton polyethylene glycol (PEG) has membrane stabilizing effects for cold stored primary rat hepatocytes in suspension. Expanding on past studies, we here investigate if PEG has the same beneficial effects in an adherent primary rat hepatocyte cold storage model. In addition, we investigated the extent of cold-induced apoptosis through treating cold-stored hepatocytes with pan caspase inhibitor emricasan. In parallel to storage at the current cold storage standard of 4 °C, we investigated the effects of lowering the storage temperature to -4 °C, at which the storage solution remains ice-free due to the supercooling phenomenon. We show the addition of 5 % PEG to the storage medium significantly reduced the release of lactate dehydrogenase (LDH) in plated rat hepatocytes and a combinatorial treatment with emricasan maintains hepatocyte viability and morphology following recovery from cold storage. These results show that cold-stored hepatocytes undergo multiple mechanisms of cold-induced injury and that PEG and emricasan treatment in combination with supercooling may improve cell and organ preservation.

Prolonged xenokidney graft survival in sensitized NHP recipients by expression of multiple human transgenes in a triple knockout pig

Genetic modification of porcine donors, combined with optimized immunosuppression, has been shown to improve outcomes of experimental xenotransplant. However, little is known about outcomes in sensitized recipients, a population that could potentially benefit the most from the clinical implementation of xenotransplantation. Here, five highly allosensitized rhesus macaques received a porcine kidney from GGTA1 (α1,3-galactosyltransferase) knockout pigs expressing the human CD55 transgene (1KO.1TG) and were maintained on an anti-CD154 monoclonal antibody (mAb)-based immunosuppressive regimen. These recipients developed de novo xenoreactive antibodies and experienced xenograft rejection with evidence of thrombotic microangiopathy and antibody-mediated rejection (AMR). In comparison, three highly allosensitized rhesus macaques receiving a kidney from GGTA1, CMAH (cytidine monophospho-N-acetylneuraminic acid hydroxylase), and b4GNT2/b4GALNT2 (β-1,4-N-acetyl-galactosaminyltransferase 2) knockout pigs expressing seven human transgenes including human CD46, CD55, CD47, THBD (thrombomodulin), PROCR (protein C receptor), TNFAIP3 (tumor necrosis factor-α-induced protein 3), and HMOX1 (heme oxygenase 1) (3KO.7TG) experienced significantly prolonged graft survival and reduced AMR, associated with dampened post-transplant humoral responses, early monocyte and neutrophil activation, and T cell repopulation. After withdrawal of all immunosuppression, recipients who received kidneys from 3KO.7TG pigs rejected the xenografts via AMR. These data suggest that allosensitized recipients may be suitable candidates for xenografts from genetically modified porcine donors and could benefit from an optimized immunosuppression regimen designed to target the post-transplant humoral response, thereby avoiding AMR.

Model biological systems demonstrate the inducibility of pathways that strongly reduce cryoprotectant toxicity

Cryoprotectant toxicity is a limiting factor for the cryopreservation of many living systems. We were moved to address this problem by the potential of organ vitrification to relieve the severe shortage of viable donor organs available for human transplantation. The M22 vitrification solution is presently the only solution that has enabled the vitrification and subsequent transplantation with survival of large mammalian organs, but its toxicity remains an obstacle to organ stockpiling for transplantation. We therefore undertook a series of exploratory studies to identify potential pretreatment interventions that might reduce the toxic effects of M22. Hormesis, in which a living system becomes more resistant to toxic stress after prior subtoxic exposure to a related stress, was investigated as a potential remedy for M22 toxicity in yeast, in the nematode worm C. elegans, and in mouse kidney slices. In yeast, heat shock pretreatment increased survival by 18-fold after exposure to formamide and by over 9-fold after exposure to M22 at 30 °C; at 0 °C and with two-step addition, treatment with 90% M22 resulted in 100% yeast survival. In nematodes, surveying a panel of pretreatment interventions revealed 3 that conferred nearly total protection from acute whole-worm M22-induced damage. One of these protective pretreatments (exposure to hydrogen peroxide) was applied to mouse kidney slices in vitro and was found to strongly protect nuclear and plasma membrane integrity in both cortical and medullary renal cells exposed to 75-100% M22 at room temperature for 40 min. These studies demonstrate for the first time that endogenous cellular defenses, conserved from yeast to mammals, can be marshalled to substantially ameliorate the toxic effects of one of the most toxic single cryoprotectants and the toxicity of the most concentrated vitrification solution so far described for whole organs.

27 MHz constant field dielectric warming of kidneys cryopreserved by vitrification

Organs cryopreserved by vitrification are exposed to the lowest possible concentration of cryoprotectants for the least time necessary to successfully avoid ice formation. Faster cooling and warming rates enable lower concentrations and perfusion times, reducing toxicity. Since warming rates necessary to avoid ice formation during recovery from vitrification are typically faster than cooling rates necessary for vitrification, warming speed is a major determining factor for successful vitrification. Dielectric warming uses an oscillating electric field to directly heat water and cryoprotectant molecules inside organs to achieve warming that's faster and more uniform than can be achieved by heat conduction from the organ surface. This work studied 27 MHz dielectric warming of rabbit kidneys perfused with M22 vitrification solution. The 27 MHz frequency was chosen because its long wavelength and penetration depth are suitable for human organs, because it had an anticipated favorable temperature of maximum dielectric absorption in M22, and because it's an allocated frequency for industrial and amateur use with inexpensive amplifiers available. Previously vitrified kidneys were warmed from -100 °C by placement in a 27 MHz electric field formed between parallel capacitor plates in a resonant circuit. Power was varied during warming to maintain constant electric field amplitude between the plates. Maximum power absorption occurred near -70 °C, with a peak warming rate near 150 °C/min in 50 mL total volume with approximately 500 W power. After some optimization, it was possible to warm ∼13 g vitrified kidneys with unprecedentedly little injury from medullary ice formation and a favorable serum creatinine trend after transplant. Distinct behaviors of power absorption and system tuning observed as a function of temperature during warming are promising for non-invasive thermometry and future automated control of the warming process at even faster rates with user-defined temperature dependence.

Effective cryopreservation of human brain tissue and neural organoids

Human brain tissue models and organoids are vital for studying and modeling human neurological disease. However, the high cost of long-term cultured organoids inhibits their wide-ranging application. It is therefore urgent to develop methods for the cryopreservation of brain tissue and organoids. Here, we establish a method using methylcellulose, ethylene glycol, DMSO, and Y27632 (termed MEDY) for the cryopreservation of cortical organoids without disrupting the neural cytoarchitecture or functional activity. MEDY can be applied to multiple brain-region-specific organoids, including the dorsal/ventral forebrain, spinal cord, optic vesicle brain, and epilepsy patient-derived brain organoids. Additionally, MEDY enables the cryopreservation of human brain tissue samples, and pathological features are retained after thawing. Transcriptomic analysis shows that MEDY can protect synaptic function and inhibit the endoplasmic reticulum-mediated apoptosis pathway. MEDY will enable the large-scale and reliable storage of diverse neural organoids and living brain tissue and will facilitate wide-ranging research, medical applications, and drug screening.

Parenteral nutrition emulsion inhibits CYP3A4 in an iPSC derived liver organoids testing platform

OBJECTIVES

Parenteral nutrition (PN) is used for patients of varying ages with intestinal failure to supplement calories. Premature newborns with low birth weight are at a high risk for developing PN associated liver disease (PNALD) including steatosis, cholestasis, and gallbladder sludge/stones. To optimize nutrition regimens, models are required to predict PNALD.

METHODS

We have exploited induced pluripotent stem cell derived liver organoids to provide a testing platform for PNALD. Liver organoids mimic the developing liver and contain the different hepatic cell types. The organoids have an early postnatal maturity making them a suitable model for premature newborns. To mimic PN treatment we used medium supplemented with either clinoleic (80% olive oil/20% soybean oil) or intralipid (100% soybean oil) for 7 days.

RESULTS

Homogenous HNF4a staining was found in all organoids and PN treatments caused accumulation of lipids in hepatocytes. Organoids exhibited a dose dependent decrease in CYP3A4 activity and expression of hepatocyte functional genes. The lipid emulsions did not affect overall organoid viability and glucose levels had no contributory effect to the observed results.

CONCLUSIONS

Liver organoids could be utilized as a potential screening platform for the development of new, less hepatotoxic PN solutions. Both lipid treatments caused hepatic lipid accumulation, a significant decrease in CYP3A4 activity and a decrease in the RNA levels of both CYP3A4 and CYP1A2 in a dose dependent manner. The presence of high glucose had no additive effect, while Clinoleic at high dose, caused significant upregulation of interleukin 6 and TLR4 expression.

Bridging the Gap in Cryopreservation Mechanism: Unraveling the Interplay between Structure, Dynamics, and Thermodynamics in Cryoprotectant Aqueous Solutions

Cryoprotectants play a crucial role in preserving biological material, ensuring their viability during storage and facilitating crucial applications such as the conservation of medical compounds, tissues, and organs for transplantation. However, the precise mechanism by which cryoprotectants modulate the thermodynamic properties of water to impede the formation and growth of ice crystals, thus preventing long-term damage, remains elusive. This is evident in the use of empirically optimized recipes for mixtures that typically contain DMSO, glycerol, and various sugar constituents. Here, we use terahertz calorimetry, Overhauser nuclear polarization, and molecular dynamics simulations to show that DMSO exhibits a robust structuring effect on water around its methyl groups, reaching a maximum at a DMSO mole fraction of XDMSO = 0.33. In contrast, glycerol exerts a smaller water-structuring effect, even at higher concentrations (Scheme 1). These results potentially suggest that the wrapped water around DMSO's methyl group, which can be evicted upon ligand binding, may render DMSO a more surface-active cryoprotectant than glycerol, while glycerol may participate more as a viscogen that acts on the entire sample. These findings shed light on the molecular intricacies of cryoprotectant solvation behavior and have potentially significant implications for optimizing cryopreservation protocols.

Direct comparison of isobaric and isochoric vitrification of two aqueous solutions with photon counting X-ray computed tomography

Vitrification is a promising approach for ice-free cryopreservation of biological material, but progress is hindered by the limited set of experimental tools for studying processes in the interior of the vitrified matter. Isochoric cryopreservation chambers are often metallic, and their opacity prevents direct visual observation. In this study, we introduce photon counting X-ray computed tomography (CT) to compare the effects of rigid isochoric and unconfined isobaric conditions on vitrification and ice formation during cooling of two aqueous solutions: 50 wt% DMSO and a coral vitrification solution, CVS1. Previous studies have only compared vitrification in isochoric systems with isobaric systems that have an exposed air-liquid interface. We use a movable piston to replicate the surface and thermal boundary conditions of the isochoric system yet maintain isobaric conditions. When controlling for the boundary conditions we find that similar ice and vapor volume fractions form during cooling in isochoric and isobaric conditions. Interestingly, we observe distinct ice and vapor cavity morphology in the isochoric systems, possibly due to vapor outgassing or cavitation as rapid cooling causes the pressure to drop in the confined systems. These observations highlight the array of thermal-fluid processes that occur during vitrification in confined aqueous systems and motivate the further application of imaging techniques such as photon counting X-ray CT in fundamental studies of vitrification.

CPA toxicity screening of cryoprotective solutions in rat hearts

In clinical practice, donor hearts are transported on ice prior to transplant and discarded if cold ischemia time exceeds ∼5 h. Methods to extend these preservation times are critically needed, and ideally, this storage time would extend indefinitely, enabling improved donor-to-patient matching, organ utilization, and immune tolerance induction protocols. Previously, we demonstrated successful vitrification and rewarming of whole rat hearts without ice formation by perfusion-loading a cryoprotective agent (CPA) solution prior to vitrification. However, these hearts did not recover any beating even in controls with CPA loading/unloading alone, which points to the chemical toxicity of the cryoprotective solution (VS55 in Euro-Collins carrier solution) as the likely culprit. To address this, we compared the toxicity of another established CPA cocktail (VEG) to VS55 using ex situ rat heart perfusion. The CPA exposure time was 150 min, and the normothermic assessment time was 60 min. Using Celsior as the carrier, we observed partial recovery of function (atria-only beating) for both VS55 and VEG. Upon further analysis, we found that the VEG CPA cocktail resulted in 50 % lower LDH release than VS55 (N = 4, p = 0.017), suggesting VEG has lower toxicity than VS55. Celsior was a better carrier solution than alternatives such as UW, as CPA + Celsior-treated hearts spent less time in cardiac arrest (N = 4, p = 0.029). While we showed substantial improvement in cardiac function after exposure to vitrifiable concentrations of CPA by improving both the CPA and carrier solution formulation, further improvements will be required before we achieve healthy cryopreserved organs for transplant.

Elevated fucose content enhances the cryoprotective performance of anionic polysaccharides

Biological cryopreservation often involves using a cryoprotective agent (CPA) to mitigate lethal physical stressors cells endure during freezing and thawing, but effective CPA concentrations are cytotoxic. Hence, natural polysaccharides have been studied as biocompatible alternatives. Here, a subset of 26 natural polysaccharides of various chemical composition was probed for their potential in enhancing the metabolic post-thaw viability (PTV) of cryopreserved Vero cells. The best performing cryoprotective polysaccharides contained significant fucose amounts, resulting in average PTV 2.8-fold (up to 3.1-fold) compared to 0.8-fold and 2.2-fold for all non-cryoprotective and cryoprotective polysaccharides, respectively, outperforming the optimized commercial CryoStor™ CS5 formulation (2.6-fold). Stoichiometrically, a balance between fucose (18-35.7 mol%), uronic acids (UA) (13.5-26 mol%) and high molecular weight (MW > 1 MDa) generated optimal PTV. Principal component analysis (PCA) revealed that fucose enhances cell survival by a charge-independent, MW-scaling mechanism (PC1), drastically different from the charge-dominated ice growth disruption of UA (PC2). Its neutral nature and unique properties distinguishable from other neutral monomers suggest fucose may play a passive role in conformational adaptability of polysaccharide to ice growth inhibition, or an active role in cell membrane stabilization through binding. Ultimately, fucose-rich anionic polysaccharides may indulge in polymer-ice and polymer-cell interactions that actively disrupt ice and minimize lethal volumetric fluctuations due to a balanced hydrophobic-hydrophilic character. Our research showed the critical role neutral fucose plays in enhancing cellular cryopreservation outcomes, disputing previous assumptions of polyanionicity being the sole governing predictor of cryoprotection.

Multiscale transport and 4D time-lapse imaging in precision-cut liver slices (PCLS)

Background

Monitoring cellular processes across different levels of complexity, from the cellular to the tissue scale, is important for understanding tissue structure and function. However, it is challenging to monitor and estimate these structural and dynamic interactions within three-dimensional (3D) tissue models.

Objective

The aim of this study was to design a method for imaging, tracking, and quantifying 3D changes in cell morphology (shape and size) within liver tissue, specifically a precision-cut liver slice (PCLS). A PCLS is a 3D model of the liver that allows the study of the structure and function of liver cells in their native microenvironment.

Methods

Here, we present a method for imaging liver tissue during anisosmotic exposure in a multispectral four-dimensional manner. Three metrics of tissue morphology were measured to quantify the effects of osmotic stress on liver tissue. We estimated the changes in the volume of whole precision cut liver slices, quantified the changes in nuclei position, and calculated the changes in volumetric responses of tissue-embedded cells.

Results

During equilibration with cell-membrane-permeating and non-permeating solutes, the whole tissue experiences shrinkage and expansion. As nuclei showed a change in position and directional displacement under osmotic stress, we demonstrate that nuclei could be used as a probe to measure local osmotic and mechanical stress. Moreover, we demonstrate that cells change their volume within tissue slices as a result of osmotic perturbation and that this change in volume is dependent on the position of the cell within the tissue and the duration of the exposure.

Conclusion

The results of this study have implications for a better understanding of multiscale transport, mechanobiology, and triggered biological responses within complex biological structures.

Organ procurement in forensic deaths: A retrospective analysis of the Italian context with a focus on the Puglia Region virtuous experience

Organ transplantation is one the most important contributions of modern medicine to society since it provides a unique therapy for terminal organ failure. However, the development of this therapeutic approach is hindered by the limited organ supply. In Italy, organ procurement requires a multidisciplinary medical-surgical approach in which legal medical doctors (LMDs) are generally tasked with ascertaining the reality of death. Sometimes, a medico-legal report is required when the deceased's family deny their consent to the organs and tissues removal from a potential deceased donor. LMDs can also be appointed by law to carry out post-mortem examinations of potential deceased donors. In these cases, the public prosecutors' interest in preserving the corpse integrity for forensic purposes seems to conflict with the ethical-humanitarian interest in promoting, at most, the opportunity to donate; however, a LMD can act as a mediator and allow both goals. This paper aims to illustrate the Apulia Region experience in reconciling the justice interests with those of a culture promoting deceased organ and tissue donation. It has been pursued by analyzing the virtuous regional organ procurement trend in forensic deaths before and after a crucial 2015 initiative, comparing the results with the national ones, and contextualizing them in the relevant literature to show systemic strengths and weaknesses and inform future Italian policy development.

Optimization of Deep Eutectic Solvents Enables Green and Efficient Cryopreservation

Cryopreservation presents significant opportunities for biomedical applications including cell therapy, tissue engineering, and assisted reproduction. Dimethyl sulfoxide (DMSO), the most commonly used cryoprotectant (CPA), can be added to cells to prevent cryogenic damage. However, the toxicity of cryoprotectants restrains its further development in many areas with safety concerns such as clinical treatment. Therefore, the development of low-toxicity cryoprotectants is essential for medical research. This work reports deep eutectic solvents (DES) as naturally biocompatible osmoprotectants for green and efficient cryopreservation of human umbilical cord mesenchymal stem cells (HuMSC), which may be an ideal alternative to DMSO. The six types of DESs were explored for thermal properties, toxicity, and permeability in cells. Raman spectroscopy and viscosity studies showed that DES exhibited an improved hydrogen-bonding system as the temperature decreased. By optimizing the freezing process (cooling rate, incubation time, and loading procedure) of DES, the viability of mouse embryonic fibroblast cells (NIH-3T3) after thawing was significantly improved. The HuMSC were successfully preserved with no significant difference (p > 0.05) in cell viability (94.65%) after thawing compared with DMSO, which preserved the cell differentiation function and improved the cell proliferation rate. The mechanism of DES in cryopreservation was investigated, and it was found that DES could bind water molecules and effectively inhibit the growth of ice crystals during ice recrystallization, reducing mechanical damage to cells. This study highlights the excellent performance of DES as a low-toxicity CPA for stem cell preservation, which may be a significant advance for future clinical cell therapy.

Screening of Hydrophilic Polymers Reveals Broad Activity in Protecting Phages during Cryopreservation

Bacteriophages have many biotechnological and therapeutic applications, but as with other biologics, cryopreservation is essential for storage and distribution. Macromolecular cryoprotectants are emerging for a range of biologics, but the chemical space for polymer-mediated phage cryopreservation has not been explored. Here we screen the cryoprotective effect of a panel of polymers against five distinct phages, showing that nearly all the tested polymers provide a benefit. Exceptions were poly(methacrylic acid) and poly(acrylic acid), which can inhibit phage-infection with bacteria, making post-thaw recovery challenging to assess. A particular benefit of a polymeric cryopreservation formulation is that the polymers do not function as carbon sources for the phage hosts (bacteria) and hence do not interfere with post-thaw measurements. This work shows that phages are amenable to protection with hydrophilic polymers and opens up new opportunities for advanced formulations for future phage therapies and to take advantage of the additional functionality brought by the polymers.

Generation of heart and vascular system in rodents by blastocyst complementation

Generating organs from stem cells through blastocyst complementation is a promising approach to meet the clinical need for transplants. In order to generate rejection-free organs, complementation of both parenchymal and vascular cells must be achieved, as endothelial cells play a key role in graft rejection. Here, we used a lineage-specific cell ablation system to produce mouse embryos unable to form both the cardiac and vascular systems. By mouse intraspecies blastocyst complementation, we rescued heart and vascular system development separately and in combination, obtaining complemented hearts with cardiomyocytes and endothelial cells of exogenous origin. Complemented chimeras were viable and reached adult stage, showing normal cardiac function and no signs of histopathological defects in the heart. Furthermore, we implemented the cell ablation system for rat-to-mouse blastocyst complementation, obtaining xenogeneic hearts whose cardiomyocytes were completely of rat origin. These results represent an advance in the experimentation towards the in vivo generation of transplantable organs.

Awareness, Attitudes, and Willingness: A Cross-Sectional Study of Organ Donation in Saudi Arabia

BACKGROUND

Organ transplantation is inherently dependent on the availability of organ donors. There is a noticeable paucity of literature addressing the rates of organ donation registration and the awareness of Islamic regulations (Fatwa) regarding organ donation within Saudi Arabia. Our study aimed to evaluate the level of organ donation registration, awareness of Islamic regulations, and knowledge of the Saudi Center for Organ Transplantation (SCOT) within the Saudi society.

METHODS

We conducted a cross-sectional survey from 30 March to 9 April 2023. This survey aimed to assess the awareness of Islamic (Fatwa) guidance on organ donation, the role of SCOT, and the rate of organ donation registration facilitated through the Tawakkalna app, the official health passport application in Saudi Arabia.

RESULTS

Out of 2329 respondents, 21% had registered as potential deceased organ donors, despite 87% acknowledging the importance of organ donation. Awareness of the Islamic Fatwa regarding organ donation was reported by 54.7% of respondents, and 37% recognized the Fatwa's acceptance of brain death criteria. The likelihood of registration as organ donors was higher among Saudi citizens under 45 years of age, females, healthcare workers (HCWs), individuals with higher education, relatives of patients awaiting organ donations, those informed about the Islamic Fatwas, and those willing to donate organs to friends. Conversely, being over the age of 25, Saudi nationality, employment as an HCW, awareness of SCOT, and prior organ donation registration were predictive of a heightened awareness of Islamic Fatwas. However, perceiving the importance of organ donation correlated with a lower awareness of the Fatwas. Significant positive correlations were found between awareness of SCOT, awareness of Fatwas, and registration for organ donation.

CONCLUSIONS

While the Saudi population exhibits a high regard for the importance of organ donation, this recognition is not adequately translated into registration rates. The discrepancy may be attributable to limited awareness of SCOT and the relevant Islamic Fatwas. It is imperative to initiate organ donation awareness campaigns that focus on religious authorization to boost organ donation rates and rectify prevalent misconceptions.

Disulfide-HMGB1 signals through TLR4 and TLR9 to induce inflammatory macrophages capable of innate-adaptive crosstalk in human liver transplantation

Ischemia-reperfusion injury (IRI) during orthotopic liver transplantation (OLT) contributes to graft rejection and poor clinical outcomes. The disulfide form of high mobility group box 1 (diS-HMGB1), an intracellular protein released during OLT-IRI, induces pro-inflammatory macrophages. How diS-HMGB1 differentiates human monocytes into macrophages capable of activating adaptive immunity remains unknown. We investigated if diS-HMGB1 binds toll-like receptor (TLR) 4 and TLR9 to differentiate monocytes into pro-inflammatory macrophages that activate adaptive immunity and promote graft injury and dysfunction. Assessment of 106 clinical liver tissue and longitudinal blood samples revealed that OLT recipients were more likely to experience IRI and graft dysfunction with increased diS-HMGB1 released during reperfusion. Increased diS-HMGB1 concentration also correlated with TLR4/TLR9 activation, polarization of monocytes into pro-inflammatory macrophages, and production of anti-donor antibodies. In vitro, healthy volunteer monocytes stimulated with purified diS-HMGB1 had increased inflammatory cytokine secretion, antigen presentation machinery, and reactive oxygen species production. TLR4 inhibition primarily impeded cytokine/chemokine and costimulatory molecule programs, whereas TLR9 inhibition decreased HLA-DR and reactive oxygen species production. diS-HMGB1-polarized macrophages also showed increased capacity to present antigens and activate T memory cells. In murine OLT, diS-HMGB1 treatment potentiated ischemia-reperfusion-mediated hepatocellular injury, accompanied by increased serum alanine transaminase levels. This translational study identifies the diS-HMGB1/TLR4/TLR9 axis as potential therapeutic targets in OLT-IRI recipients.

Current opinion: advances in machine perfusion and preservation of vascularized composite allografts - will time still matter?

PURPOSE OF REVIEW

A major hurdle hindering more widespread application of reconstructive transplantation is the very limited cold ischemia time (CIT) of vascularized composite allografts (VCAs). In this review, we discuss cutting edge machine perfusion protocols and preservation strategies to overcome this limitation.

RECENT FINDINGS

Several preclinical machine perfusion studies have demonstrated the multifactorial utility of this technology to extend preservation windows, assess graft viability prior to transplantation and salvage damaged tissue, yet there are currently no clinically approved machine perfusion protocols for reconstructive transplantation. Thus, machine perfusion remains an open challenge in VCA due to the complexity of the various tissue types. In addition, multiple other promising avenues to prolong preservation of composite allografts have emerged. These include cryopreservation, high subzero preservation, vitrification and nanowarming. Despite several studies demonstrating extended preservation windows, there are several limitations that must be overcome prior to clinical translation. As both machine perfusion and subzero preservation protocols have rapidly advanced in the past few years, special consideration should be given to their potential complementary utilization.

SUMMARY

Current and emerging machine perfusion and preservation technologies in VCA have great promise to transform the field of reconstructive transplantation, as every extra hour of CIT helps ease the complexities of the peri-transplant workflow. Amongst the many advantages, longer preservation windows may allow for elective procedures, improved matching, establishment of novel immunomodulatory protocols and global transport of grafts, ultimately enabling us the ability to offer this life changing procedure to more patients.

Polyethylene Glycol and Caspase Inhibitor Emricasan Alleviates Cold Injury in Primary Rat Hepatocytes

Current methods of storing explanted donor livers at 4°C in University of Wisconsin (UW) solution result in loss of graft function and ultimately leads to less-than-ideal outcomes post transplantation. Our lab has previously shown that supplementing UW solution with 35-kilodalton polyethylene glycol (PEG) has membrane stabilizing effects for cold stored primary rat hepatocytes in suspension. Expanding on past studies, we here investigate if PEG has the same beneficial effects in an adherent primary rat hepatocyte cold storage model. In addition, we investigated the extent of cold-induced apoptosis through treating cold-stored hepatocytes with pan caspase inhibitor emricasan. In parallel to storage at the current cold storage standard of 4°C, we investigated the effects of lowering the storage temperature to -4°C, at which the storage solution remains ice-free due to the supercooling phenomenon. We show the addition of 5% PEG to the storage medium significantly reduced the release of lactate dehydrogenase (LDH) in plated rat hepatocytes and a combinatorial treatment with emricasan maintains hepatocyte viability and morphology following recovery from cold storage. These results show that cold-stored hepatocytes undergo multiple mechanisms of cold-induced injury and that PEG and emricasan treatment in combination with supercooling may improve cell and organ preservation.

Mass spectrometry-based proteomics for advancing solid organ transplantation research

Scarcity of high-quality organs, suboptimal organ quality assessment, unsatisfactory pre-implantation procedures, and poor long-term organ and patient survival are the main challenges currently faced by the solid organ transplant (SOT) field. New biomarkers for assessing graft quality pre-implantation, detecting, and predicting graft injury, rejection, dysfunction, and survival are critical to provide clinicians with invaluable prediction tools and guidance for personalized patients' treatment. Additionally, new therapeutic targets are also needed to reduce injury and rejection and improve transplant outcomes. Proteins, which underlie phenotypes, are ideal candidate biomarkers of health and disease statuses and therapeutic targets. A protein can exist in different molecular forms, called proteoforms. As the function of a protein depends on its exact composition, proteoforms can offer a more accurate basis for connection to complex phenotypes than protein from which they derive. Mass spectrometry-based proteomics has been largely used in SOT research for identification of candidate biomarkers and therapeutic intervention targets by so-called "bottom-up" proteomics (BUP). However, such BUP approaches analyze small peptides in lieu of intact proteins and provide incomplete information on the exact molecular composition of the proteins of interest. In contrast, "Top-down" proteomics (TDP), which analyze intact proteins retaining proteoform-level information, have been only recently adopted in transplantation studies and already led to the identification of promising proteoforms as biomarkers for organ rejection and dysfunction. We anticipate that the use of top-down strategies in combination with new technological advancements in single-cell and spatial proteomics could drive future breakthroughs in biomarker and therapeutic target discovery in SOT.

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

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

Engineered Test Tissues: A Model for Quantifying the Effects of Cryopreservation Parameters

Engineered tissues are showing promise as implants to repair or replace damaged tissues in vivo or as in vitro tools to discover new therapies. A major challenge of the tissue engineering field is the sample preservation and storage until their transport and desired use. To successfully cryopreserve tissue, its viability, structure, and function must be retained post-thaw. The outcome of cryopreservation is impacted by several parameters, including the cryopreserving agent (CPA) utilized, the cooling rate, and the storage temperature. Although a number of CPAs are commercially available for cell cryopreservation, there are few CPAs designed specifically for tissue cryostorage and recovery. In this study, we present a flexible, relatively high-throughput method that utilizes engineered tissue rings as test tissues for screening the commercially available CPAs and cryopreservation parameters. Engineered test tissues can be fabricated with low batch-to-batch variability and characteristic morphology due to their endogenous extracellular matrix, and they have mechanical properties and a ring format suitable for testing with standard methods. The tissues were grown for 7 days in standard 48-well plates and cryopreserved in standard cryovials. The method allowed for the quantification of metabolic recovery, tissue apoptosis/necrosis, morphology, and mechanical properties. In addition to establishing the method, we tested different CPA formulations, freezing rates, and freezing points. Our proposed method enables timely preliminary screening of CPA formulations and cryopreservation parameters that may improve the storage of engineered tissues.

Zinc Cations Uniquely Stabilize Cell Membrane for Cell Cryopreservation

We report, for the first time, merely using a small amount of (0.039% w/w) Zn(II) instead of very high concentration (25%-50% w/w) of conventional cryoprotective agents (CPAs), i.e., glycerol, during the cryopreservation of red blood cells (RBCs) can lead to a comparable post-thaw recovery rate of ∼95% while avoiding the tedious gradient washout process for the removal of CPA afterward. The result is remarkable, since Zn(II) does not have the ice-controlling ability reported to be critical for CPA. It benefits from its moderate interaction with lipid molecules, facilitating the formation of small and dynamic lipid clusters. Consequently, the membrane fluidity is maintained, and the cells are resilient to osmotic and mechanical stresses during cryopreservation. This study first reports the ion-specific effect on stabilizing the cell membrane; meanwhile, reversibly tuning the structure of biological samples against injuries during the cooling and rewarming provides a new strategy for cryopreservation.

Inequities in kidney health and kidney care

Health inequity refers to the existence of unnecessary and unfair differences in the ability of an individual or community to achieve optimal health and access appropriate care. Kidney diseases, including acute kidney injury and chronic kidney disease, are the epitome of health inequity. Kidney disease risk and outcomes are strongly associated with inequities that occur across the entire clinical course of disease. Insufficient investment across the spectrum of kidney health and kidney care is a fundamental source of inequity. In addition, social and structural inequities, including inequities in access to primary health care, education and preventative strategies, are major risk factors for, and contribute to, poorer outcomes for individuals living with kidney diseases. Access to affordable kidney care is also highly inequitable, resulting in financial hardship and catastrophic health expenditure for the most vulnerable. Solutions to these injustices require leadership and political will. The nephrology community has an important role in advocacy and in identifying and implementing solutions to dismantle inequities that affect kidney health.

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.

Zebrafish as a high throughput model for organ preservation and transplantation research

Despite decades of effort, the preservation of complex organs for transplantation remains a significant barrier that exacerbates the organ shortage crisis. Progress in organ preservation research is significantly hindered by suboptimal research tools that force investigators to sacrifice translatability over throughput. For instance, simple model systems, such as single cell monolayers or co-cultures, lack native tissue structure and functional assessment, while mammalian whole organs are complex systems with confounding variables not compatible with high-throughput experimentation. In response, diverse fields and industries have bridged this experimental gap through the development of rich and robust resources for the use of zebrafish as a model organism. Through this study, we aim to demonstrate the value zebrafish pose for the fields of solid organ preservation and transplantation, especially with respect to experimental transplantation efforts. A wide array of methods were customized and validated for preservation-specific experimentation utilizing zebrafish, including the development of assays at multiple developmental stages (larvae and adult), methods for loading and unloading preservation agents, and the development of viability scores to quantify functional outcomes. Using this platform, the largest and most comprehensive screen of cryoprotectant agents (CPAs) was performed to determine their toxicity and efficiency at preserving complex organ systems using a high subzero approach called partial freezing (i.e., storage in the frozen state at -10°C). As a result, adult zebrafish cardiac function was successfully preserved after 5 days of partial freezing storage. In combination, the methods and techniques developed have the potential to drive and accelerate research in the fields of solid organ preservation and transplantation.

A Reversibly Thermoresponsive, Theranostic Nanoemulgel for Tacrolimus Delivery to Activated Macrophages: Formulation and In Vitro Validation

Despite long-term immunosuppression, organ transplant recipients face the risk of immune rejection and graft loss. Tacrolimus (TAC, FK506, Prograf®) is an FDA-approved keystone immunosuppressant for preventing transplant rejection. However, it undergoes extensive first-pass metabolism and has a narrow therapeutic window, which leads to erratic bioavailability and toxicity. Local delivery of TAC directly into the graft, instead of systemic delivery, can improve safety, efficacy, and tolerability. Macrophages have emerged as promising therapeutic targets as their increased levels correlate with an increased risk of organ rejection and a poor prognosis post-transplantation. Here, we present a locally injectable drug delivery platform for macrophages, where TAC is incorporated into a colloidally stable nanoemulsion and then formulated as a reversibly thermoresponsive, pluronic-based nanoemulgel (NEG). This novel formulation is designed to undergo a sol-to-gel transition at physiological temperature to sustain TAC release in situ at the site of local application. We also show that TAC-NEG mitigates the release of proinflammatory cytokines and nitric oxide from lipopolysaccharide (LPS)-activated macrophages. To the best of our knowledge, this is the first TAC-loaded nanoemulgel with demonstrated anti-inflammatory effects on macrophages in vitro.

Xenogeneic cross-circulation for physiological support and recovery of ex vivo human livers

BACKGROUND AND AIMS

The scarcity of suitable donor livers highlights a continuing need for innovation to recover organs with reversible injuries in liver transplantation.

APPROACH AND RESULTS

Explanted human donor livers (n = 5) declined for transplantation were supported using xenogeneic cross-circulation of whole blood between livers and xeno-support swine. Livers and swine were assessed over 24 hours of xeno-support. Livers maintained normal global appearance, uniform perfusion, and preservation of histologic and subcellular architecture. Oxygen consumption increased by 75% ( p = 0.16). Lactate clearance increased from -0.4 ± 15.5% to 31.4 ± 19.0% ( p = 0.02). Blinded histopathologic assessment demonstrated improved injury scores at 24 hours compared with 12 hours. Vascular integrity and vasoconstrictive function were preserved. Bile volume and cholangiocellular viability markers improved for all livers. Biliary structural integrity was maintained.

CONCLUSIONS

Xenogeneic cross-circulation provided multisystem physiological regulation of ex vivo human livers that enabled functional rehabilitation, histopathologic recovery, and improvement of viability markers. We envision xenogeneic cross-circulation as a complementary technique to other organ-preservation technologies in the recovery of marginal donor livers or as a research tool in the development of advanced bioengineering and pharmacologic strategies for organ recovery and rehabilitation.

Temperature-Controlled 3D Cryoprinting Inks Made of Mixtures of Alginate and Agar

Temperature-controlled 3D cryoprinting (TCC) is an emerging tissue engineering technology aimed at overcoming limitations of conventional 3D printing for large organs: (a) size constraints due to low print rigidity and (b) the preservation of living cells during printing and subsequent tissue storage. TCC addresses these challenges by freezing each printed voxel with controlled cooling rates during deposition. This generates a rigid structure upon printing and ensures cell cryopreservation as an integral part of the process. Previous studies used alginate-based ink, which has limitations: (a) low diffusivity of the CaCl2 crosslinker during TCC's crosslinking process and (b) typical loss of print fidelity with alginate ink. This study explores the use of an ink made of agar and alginate to overcome TCC protocol limitations. When an agar/alginate voxel is deposited, agar first gels at above-freezing temperatures, capturing the desired structure without compromising fidelity, while alginate remains uncrosslinked. During subsequent freezing, both frozen agar and alginate maintain the structure. However, agar gel loses its gel form and water-retaining ability. In TCC, alginate crosslinking occurs by immersing the frozen structure in a warm crosslinking bath. This enables CaCl2 diffusion into the crosslinked alginate congruent with the melting process. Melted agar domains, with reduced water-binding ability, enhance crosslinker diffusivity, reducing TCC procedure duration. Additionally, agar overcomes the typical fidelity loss associated with alginate ink printing.

An extreme value statistics model of heterogeneous ice nucleation for quantifying the stability of supercooled aqueous systems

The propensity of water to remain in a metastable liquid state at temperatures below its equilibrium melting point holds significant potential for cryopreserving biological material such as tissues and organs. The benefits conferred are a direct result of progressively reducing metabolic expenditure due to colder temperatures while simultaneously avoiding the irreversible damage caused by the crystallization of ice. Unfortunately, the freezing of water in bulk systems of clinical relevance is dominated by random heterogeneous nucleation initiated by uncharacterized trace impurities, and the marked unpredictability of this behavior has prevented the implementation of supercooling outside of controlled laboratory settings and in volumes larger than a few milliliters. Here, we develop a statistical model that jointly captures both the inherent stochastic nature of nucleation using conventional Poisson statistics as well as the random variability of heterogeneous nucleation catalysis through bivariate extreme value statistics. Individually, these two classes of models cannot account for both the time-dependent nature of nucleation and the sample-to-sample variability associated with heterogeneous catalysis, and traditional extreme value models have only considered variations of the characteristic nucleation temperature. We conduct a series of constant cooling rate and isothermal nucleation experiments with physiological saline solutions and leverage the statistical model to evaluate the natural variability of kinetic and thermodynamic nucleation parameters. By quantifying freezing probability as a function of temperature, supercooled duration, and system volume while accounting for nucleation site variability, this study also provides a basis for the rational design of stable supercooled biopreservation protocols.

Isochoric Supercooling Organ Preservation System

This technical paper introduces a novel organ preservation system based on isochoric (constant volume) supercooling. The system is designed to enhance the stability of the metastable supercooling state, offering potential long-term preservation of large biological organs at subfreezing temperatures without the need for cryoprotectant additives. Detailed technical designs and usage protocols are provided for researchers interested in exploring this field. The paper also presents a control system based on the thermodynamics of isochoric freezing, utilizing pressure monitoring for process control. Sham experiments were performed using whole pig liver sourced from a local food supplier to evaluate the system's ability to sustain supercooling without ice nucleation for extended periods. The results demonstrated sustained supercooling without ice nucleation in pig liver tissue for 24 and 48 h. These findings suggest the potential of this technology for large-volume, cryoprotectant-free organ preservation with real-time control over the preservation process. The simplicity of the isochoric supercooling device and the design details provided in the paper are expected to serve as encouragement for other researchers in the field to pursue further research on isochoric supercooling. However, final evidence that these preserved organs can be successfully transplanted is still lacking.

Advanced cryopreservation engineering strategies: the critical step to utilize stem cell products

With the rapid development of stem cell-related therapies and regenerative medicine, the clinical application of stem cell products is on the rise. However, ensuring the effectiveness of these products after storage and transportation remains a challenge in the transformation to clinical trials. Cryopreservation technology allows for the long-term storage of cells while ensuring viability, making it a top priority for stem cell preservation. The field of cryopreservation-related engineering technologies is thriving, and this review provides an overview of the background and basic principles of cryopreservation. It then delves into the main bioengineering technologies and strategies used in cryopreservation, including photothermal and electromagnetic rewarming, microencapsulation, and synergetic ice inhibition. Finally, the current challenges and future prospects in the field of efficient cryopreservation of stem cells are summarized and discussed.

Development of supercooling preservation method of adherent cultured human cells

Cryopreservation of mammalian cells is an important technology; however, freezing damage due to osmotic pressure differences and ice crystal formation is inevitable. In addition, cryopreserved cells cannot be used immediately after thawing in many cases. Therefore, in this study, we developed a method for supercooling and preserving adherent cells using a precision temperature-controlled CO2 incubator. The effects of the cooling rate from 37 to -4°C, the warming rate from -4 to 37°C and a preservation solution on cell viability after storage were examined. Human hepatocarcinoma-derived cell line HepG2 cells, preserved with HypoThermosol FRS at -4°C with a cooling rate of -0.028°C/min (24 h from 37°C to -4°C) and warming to 37°C at a rate of +1.0°C/min (40 min from -4 to 37°C), displayed high cell viability after 14 days of preservation. The superiority of supercooling preservation at -4°C was demonstrated by comparing the obtained results with that of refrigerated preservation at +4°C. Cells preserved for 14 days under optimal conditions showed no cell shape abnormalities and may be used for experiments immediately after thawing. The optimized supercooling preservation method determined in this study is suitable for the temporary preservation of adherent cultured cells.

Advances in Gelatin Bioinks to Optimize Bioprinted Cell Functions

Gelatin is a widely utilized bioprinting biomaterial due to its cell-adhesive and enzymatically cleavable properties, which improve cell adhesion and growth. Gelatin is often covalently cross-linked to stabilize bioprinted structures, yet the covalently cross-linked matrix is unable to recapitulate the dynamic microenvironment of the natural extracellular matrix (ECM), thereby limiting the functions of bioprinted cells. To some extent, a double network bioink can provide a more ECM-mimetic, bioprinted niche for cell growth. More recently, gelatin matrices are being designed using reversible cross-linking methods that can emulate the dynamic mechanical properties of the ECM. This review analyzes the progress in developing gelatin bioink formulations for 3D cell culture, and critically analyzes the bioprinting and cross-linking techniques, with a focus on strategies to optimize the functions of bioprinted cells. This review discusses new cross-linking chemistries that recapitulate the viscoelastic, stress-relaxing microenvironment of the ECM, and enable advanced cell functions, yet are less explored in engineering the gelatin bioink. Finally, this work presents the perspective on the areas of future research and argues that the next generation of gelatin bioinks should be designed by considering cell-matrix interactions, and bioprinted constructs should be validated against currently established 3D cell culture standards to achieve improved therapeutic outcomes.

Current practice and novel approaches in organ preservation

Organ transplantation remains the only treatment option for patients with end-stage organ failure. The last decade has seen a flurry of activity in improving organ preservation technologies, which promise to increase utilization in a dramatic fashion. They also bring the promise of extending the preservation duration significantly, which opens the doors to sharing organs across local and international boundaries and transforms the field. In this work, we review the recent literature on machine perfusion of livers across various protocols in development and clinical use, in the context of extending the preservation duration. We then review the next generation of technologies that have the potential to further extend the limits and open the door to banking organs, including supercooling, partial freezing, and nanowarming, and outline the opportunities arising in the field for researchers in the short and long term.

Speeding up the Production of Clinical-Grade Skin Substitutes Using Off-the-shelf Decellularized Self-Assembled Dermal Matrices

Patients with deep and extensive wounds need urgent skin coverage to re-establish the cutaneous barrier that prevents life-threatening infections and dehydration. However, the current clinically-available skin substitutes intended for permanent coverage are limited in number, and a trade-off between production time and quality must be made. Here, we report the use of decellularized self-assembled dermal matrices to reduce by half the manufacturing process time of clinical-grade skin substitutes. These decellularized matrices can be stored for over 18 months and recellularized with patients' cells in order to generate skin substitutes that show outstanding histological and mechanical properties in vitro. Once grafted in mice, these substitutes persist over weeks with high graft take, few contraction events, and high stem cell content. These next-generation skin substitutes constitute a substantial advancement in the treatment of major burn patients, combining, for the first time, high functionality, rapid manufacturability and easy handling for surgeons and healthcare practitioners. Future clinical trials will be conducted to assess the advantages of these substitutes over existing treatments. STATEMENT OF SIGNIFICANCE: The number of patients in need for organ transplantation is ever-growing and there is a shortage in tissue and organ donors. In this study, we show for the first time that we can preserve decellularized self-assembled tissues and keep them in storage. Then, in only three weeks we can use them to produce bilayered skin substitutes that have properties very close to those of the native human skin. These findings therefore represent a major step forward in the field of tissue engineering and organ transplantation, paving the way toward a universal off-the-shelf biomaterial for tissue reconstruction and surgery that will be beneficial for many clinicians and patients.

Exceeding the Limits of Static Cold Storage in Limb Transplantation Using Subnormothermic Machine Perfusion

BACKGROUND

 For 50 years, static cold storage (SCS) has been the gold standard for solid organ preservation in transplantation. Although logistically convenient, this preservation method presents important constraints in terms of duration and cold ischemia-induced lesions. We aimed to develop a machine perfusion (MP) protocol for recovery of vascularized composite allografts (VCA) after static cold preservation and determine its effects in a rat limb transplantation model.

METHODS

 Partial hindlimbs were procured from Lewis rats and subjected to SCS in Histidine-Tryptophan-Ketoglutarate solution for 0, 12, 18, 24, and 48 hours. They were then either transplanted (Txp), subjected to subnormothermic machine perfusion (SNMP) for 3 hours with a modified Steen solution, or to SNMP + Txp. Perfusion parameters were assessed for blood gas and electrolytes measurement, and flow rate and arterial pressures were monitored continuously. Histology was assessed at the end of perfusion. For select SCS durations, graft survival and clinical outcomes after transplantation were compared between groups at 21 days.

RESULTS

 Transplantation of limbs preserved for 0, 12, 18, and 24-hour SCS resulted in similar survival rates at postoperative day 21. Grafts cold-stored for 48 hours presented delayed graft failure (p = 0.0032). SNMP of limbs after 12-hour SCS recovered the vascular resistance, potassium, and lactate levels to values similar to limbs that were not subjected to SCS. However, 18-hour SCS grafts developed significant edema during SNMP recovery. Transplantation of grafts that had undergone a mixed preservation method (12-hour SCS + SNMP + Txp) resulted in better clinical outcomes based on skin clinical scores at day 21 post-transplantation when compared to the SCS + Txp group (p = 0.01613).

CONCLUSION

 To date, VCA MP is still limited to animal models and no protocols are yet developed for graft recovery. Our study suggests that ex vivo SNMP could help increase the preservation duration and limit cold ischemia-induced injury in VCA 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.

A new paradigm in transplant immunology: At the crossroad of synthetic biology and biomaterials

Solid organ transplant (SOT) recipients require meticulously tailored immunosuppressive regimens to minimize graft loss and mortality. Traditional approaches focus on inhibiting effector T cells, while the intricate and dynamic immune responses mediated by other components remain unsolved. Emerging advances in synthetic biology and material science have provided novel treatment modalities with increased diversity and precision to the transplantation community. This review investigates the active interface between these two fields, highlights how living and non-living structures can be engineered and integrated for immunomodulation, and discusses their potential application in addressing the challenges in SOT clinical practice.