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

Current State and Challenges of Tissue and Organ Cryopreservation in Biobanking

Recent years have witnessed significant advancements in the cryopreservation of various tissues and cells, yet several challenges persist. This review evaluates the current state of cryopreservation, focusing on contemporary methods, notable achievements, and ongoing difficulties. Techniques such as slow freezing and vitrification have enabled the successful preservation of diverse biological materials, including embryos and ovarian tissue, marking substantial progress in reproductive medicine and regenerative therapies. These achievements highlight improved post-thaw survival and functionality of cryopreserved samples. However, there are remaining challenges such as ice crystal formation, which can lead to cell damage, and the cryopreservation of larger, more complex tissues and organs. This review also explores the role of cryoprotectants and the importance of optimizing both cooling and warming rates to enhance preservation outcomes. Future research priorities include developing new cryoprotective agents, elucidating the mechanisms of cryoinjury, and refining protocols for preserving complex tissues and organs. This comprehensive overview underscores the transformative potential of cryopreservation in biomedicine, while emphasizing the necessity for ongoing innovation to address existing challenges.

Structural investigation, computational analysis, and theoretical cryoprotectant approach of antifreeze protein type IV mutants

Antifreeze proteins (AFPs) have unique features to sustain life in sub-zero environments due to ice recrystallization inhibition (IRI) and thermal hysteresis (TH). AFPs are in demand as agents in cryopreservation, but some antifreeze proteins have low levels of activity. This research aims to improve the cryopreservation activity of an AFPIV. In this in silico study, the helical peptide afp1m from an Antarctic yeast AFP was modeled into a sculpin AFPIV, to replace each of its four α-helices in turn, using various computational tools. Additionally, a new linker between the first two helices of AFPIV was designed, based on a flounder AFPI, to boost the ice interaction activity of the mutants. Bioinformatics tools such as ExPASy Prot-Param, Pep-Wheel, SOPMA, GOR IV, Swiss-Model, Phyre2, MODFOLD, MolPropity, and ProQ were used to validate and analyze the structural and functional properties of the model proteins. Furthermore, to evaluate the AFP/ice interaction, molecular dynamics (MD) simulations were executed for 20, 100, and 500 ns at various temperatures using GROMACS software. The primary, secondary, and 3D modeling analysis showed the best model for a redesigned antifreeze protein (AFP1mb, with afp1m in place of the fourth AFPIV helix) with a QMEAN (Swiss-Model) Z score value of 0.36, a confidence of 99.5%, a coverage score of 22%, and a p value of 0.01. The results of the MD simulations illustrated that AFP1mb had more rigidity and better ice interactions as a potential cryoprotectant than the other models; it also displayed enhanced activity in limiting ice growth at different temperatures.

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.

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.

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.

Preparation of Peptoid Antifreeze Agents and Their Structure-Property Relationship

The development of nontoxic and efficient antifreeze agents for organ cryopreservation is crucial. However, the research remains highly challenging. In this study, we designed and synthesized a series of peptoid oligomers using the solid-phase submonomer synthesis method by mimicking the amphiphilic structures of antifreeze proteins (AFPs). The obtained peptoid oligomers showed excellent antifreeze properties, reducing the ice crystal growth rate and inhibiting ice recrystallization. The effects of the hydrophobicity and sequence of the peptoid side chains were also studied to reveal the structure-property relationship. The prepared peptoid oligomers were detected as non-cytotoxic and considered to be useful in the biological field. We hope that the peptoid oligomers presented in this study can provide effective strategies for the design of biological cryoprotectants for organ preservation in the future.

A Low-Cost, Tabletop LOD-EPR System for Nondestructive Quantification of Iron Oxide Nanoparticles in Tissues

Iron oxide nanoparticles (IONPs) have wide utility in applications from drug delivery to the rewarming of cryopreserved tissues. Due to the complex behavior of IONPs (e.g., uneven particle distribution and aggregation), further developments and clinical translation can be accelerated by having access to a noninvasive method for tissue IONP quantification. Currently, there is no low-cost method to nondestructively track IONPs in tissues across a wide range of concentrations. This work describes the performance of a low-cost, tabletop, longitudinally detected electron paramagnetic resonance (LOD-EPR) system to address this issue in the field of cryopreservation, which utilizes IONPs for rewarming of rat kidneys. A low-cost LOD-EPR system is realized via simultaneous transmit and receive using MHz continuous-wave transverse excitation with kHz modulation, which is longitudinally detected at the modulation frequency to provide both geometric and frequency isolation. The accuracy of LOD-EPR for IONP quantification is compared with NMR relaxometry. Solution measurements show excellent linearity (R2 > 0.99) versus Fe concentration for both measurements on EMG308 (a commercial nanoparticle), silica-coated EMG308, and PEG-coated EMG308 in water. The LOD-EPR signal intensity and NMR longitudinal relaxation rate constant (R1) of water are affected by particle coating, solution viscosity, and particle aggregation. R1 remains linear but with a reduced slope when in cryoprotective agent (CPA) solution, whereas the LOD-EPR signal is relatively insensitive to this. R1 does not correlate well with Fe concentration in rat kidney sections (R2 = 0.3487), while LOD-EPR does (R2 = 0.8276), with a linear regression closely matching that observed in solution and CPA.

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.

From Nature to Innovation: The Uncharted Potential of Natural Deep Eutectic Solvents

This review discusses the significance of natural deep eutectic solvents (NaDESs) as a promising green extraction technology. It employs the consolidated meta-analytic approach theory methodology, using the Web of Science and Scopus databases to analyze 2091 articles as the basis of the review. This review explores NaDESs by examining their properties, challenges, and limitations. It underscores the broad applications of NaDESs, some of which remain unexplored, with a focus on their roles as solvents and preservatives. NaDESs' connections with nanocarriers and their use in the food, cosmetics, and pharmaceutical sectors are highlighted. This article suggests that biomimicry could inspire researchers to develop technologies that are less harmful to the human body by emulating natural processes. This approach challenges the notion that green science is inferior. This review presents numerous successful studies and applications of NaDESs, concluding that they represent a viable and promising avenue for research in the field of green chemistry.

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.

Thermomechanical stress analyses of nanowarming-assisted recovery from cryopreservation by vitrification in human heart and rat heart models

This study investigates thermomechanical stress in cryopreservation by vitrification of the heart, while exploring the effects of nanowarming-assisted recovery from cryogenic storage. This study expands upon a recently published study, combining experimental investigation and thermal analysis of cryopreservation on a rat heart model. Specifically, this study focuses on scenarios with variable concentrations of silica-coated iron-oxide nanoparticles (sIONPs), while accounting for loading limitations associated with the heart physiology, as well as the properties of cryoprotective agent (CPA) solution and the geometry of the container. Results of this study suggest that variable sIONP concentration based on the heart physiology will elevate mechanical stresses when compared with the mathematically simplified, uniform distribution case. The most dangerous part of rewarming is below glass transition and at the onset of nanowarming past the glass transition temperature on the way for organ recovery from cryogenic storage. Throughout rewarming, regions that rewarm faster, such as the chambers of the heart (higher sIONP concentration), undergo compressive stresses, while the slower rewarming regions, such as the heart myocardium (low sIONP concentration), undergo tension. Being a brittle material, the vitrified organ is expected to fail under tension in lower stresses than in compression. Unfortunately, the location and magnitude of the maximum stress in the investigated cases varied, while general rules were not identified. This investigation demonstrates the need to tailor the thermal protocol of heart cryopreservation on a case-by-case basis, since the location, orientation, magnitude, and instant at which the maximum mechanical stress is found cannot be predicted a priori. While thermomechanical stress poses a significant risk to organ integrity, careful design of the thermal protocol can be instrumental in reducing the likelihood of structural damage, while taking full advantage of the benefits of nanowarming.

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.

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.

Sound waves for solving the problem of recrystallization in cryopreservation

Organ biobanking is the pending subject of cryopreservation. Although the problem is multifaceted, advances in recent decades have largely related it to achieving rapid and uniform rewarming of cryopreserved samples. This is a physical challenge largely investigated in past in addition to cryoprotectant toxicity studies, which have also shown a great amount of advancement. This paper presents a proof-of-principle, based on the nematode Caenorhabditis elegans, of a technology capable of performing such a function: high intensity focused ultrasound. Thus, avoiding the problem of recrystallization, this worm, in its adult state, preserved at - [Formula: see text], has been systematically brought back to life after being heated with High Intensity Focused Ultrasound (HIFU) waves. The great advantage of this technology is that it is scalable; in addition, rewarming can be monitored in real time by MRI thermography and can be controlled by acoustic interferometry. We anticipate that our findings are the starting point for a possible approach to rewarming that can be used for cryopreservation of millimeter scale systems: either alone or in combination with other promising ways of heating, like nanowarming or dielectric heating, the present technology provides new ways of solving the physical aspects of the problem of recrystallization in cryopreservation, opening the door for the long-term storage of larger samples.

Nanowarming and ice-free cryopreservation of large sized, intact porcine articular cartilage

Successful organ or tissue long-term preservation would revolutionize biomedicine. Cartilage cryopreservation enables prolonged shelf life of articular cartilage, posing the prospect to broaden the implementation of promising osteochondral allograft (OCA) transplantation for cartilage repair. However, cryopreserved large sized cartilage cannot be successfully warmed with the conventional convection warming approach due to its limited warming rate, blocking its clinical potential. Here, we develope a nanowarming and ice-free cryopreservation method for large sized, intact articular cartilage preservation. Our method achieves a heating rate of 76.8 °C min-1, over one order of magnitude higher than convection warming (4.8 °C min-1). Using systematic cell and tissue level tests, we demonstrate the superior performance of our method in preserving large cartilage. A depth-dependent preservation manner is also observed and recapitulated through magnetic resonance imaging and computational modeling. Finally, we show that the delivery of nanoparticles to the OCA bone side could be a feasible direction for further optimization of our method. This study pioneers the application of nanowarming and ice-free cryopreservation for large articular cartilage and provides valuable insights for future technique development, paving the way for clinical applications of cryopreserved cartilage.

Control strategies of ice nucleation, growth, and recrystallization for cryopreservation

The cryopreservation of biomaterials is fundamental to modern biotechnology and biomedicine, but the biggest challenge is the formation of ice, resulting in fatal cryoinjury to biomaterials. To date, abundant ice control strategies have been utilized to inhibit ice formation and thus improve cryopreservation efficiency. This review focuses on the mechanisms of existing control strategies regulating ice formation and the corresponding applications to biomaterial cryopreservation, which are of guiding significance for the development of ice control strategies. Herein, basics related to biomaterial cryopreservation are introduced first. Then, the theoretical bases of ice nucleation, growth, and recrystallization are presented, from which the key factors affecting each process are analyzed, respectively. Ice nucleation is mainly affected by melting temperature, interfacial tension, shape factor, and kinetic prefactor, and ice growth is mainly affected by solution viscosity and cooling/warming rate, while ice recrystallization is inhibited by adsorption or diffusion mechanisms. Furthermore, the corresponding research methods and specific control strategies for each process are summarized. The review ends with an outlook of the current challenges and future perspectives in cryopreservation. STATEMENT OF SIGNIFICANCE: Ice formation is the major limitation of cryopreservation, which causes fatal cryoinjury to cryopreserved biomaterials. This review focuses on the three processes related to ice formation, called nucleation, growth, and recrystallization. The theoretical models, key influencing factors, research methods and corresponding ice control strategies of each process are summarized and discussed, respectively. The systematic introduction on mechanisms and control strategies of ice formation is instructive for the cryopreservation development.

Freezing Biological Time: A Modern Perspective on Organ Preservation

Transporting tissues and organs from the site of donation to the patient in need, while maintaining viability, is a limiting factor in transplantation medicine. One way in which the supply chain of organs for transplantation can be improved is to discover novel approaches and technologies that preserve the health of organs outside of the body. The dominant technologies that are currently in use in the supply chain for biological materials maintain tissue temperatures ranging from a controlled room temperature (+25 °C to +15 °C) to cryogenic (-120 °C to -196 °C) temperatures (reviewed in Criswell et al. Stem Cells Transl Med. 2022). However, there are many cells and tissues, as well as all major organs, that respond less robustly to preservation attempts, particularly when there is a need for transport over long distances that require more time. In this perspective article, we will highlight the current challenges and advances in biopreservation aimed at "freezing biological time," and discuss the future directions and requirements needed in the field.

Multiple cryoprotectant toxicity model for vitrification solution optimization

Vitrification is a promising cryopreservation technique for complex specimens such as tissues and organs. However, it is challenging to identify mixtures of cryoprotectants (CPAs) that prevent ice formation without exerting excessive toxicity. In this work, we developed a multi-CPA toxicity model that predicts the toxicity kinetics of mixtures containing five of the most common CPAs used in the field (glycerol, dimethyl sulfoxide (DMSO), propylene glycol, ethylene glycol, and formamide). The model accounts for specific toxicity, non-specific toxicity, and interactions between CPAs. The proposed model shows reasonable agreement with training data for single and binary CPA solutions, as well as ternary CPA solution validation data. Sloppy model analysis was used to examine the model parameters that were most important for predictions, providing clues about mechanisms of toxicity. This analysis revealed that the model terms for non-specific toxicity were particularly important, especially the non-specific toxicity of propylene glycol, as well as model terms for specific toxicity of formamide and interactions between formamide and glycerol. To demonstrate the potential for model-based design of vitrification methods, we paired the multi-CPA toxicity model with a published vitrification/devitrification model to identify vitrifiable CPA mixtures that are predicted to have minimal toxicity. The resulting optimized vitrification solution composition was a mixture of 7.4 molal glycerol, 1.4 molal DMSO, and 2.4 molal formamide. This demonstrates the potential for mathematical optimization of vitrification solution composition and sets the stage for future studies to optimize the complete vitrification process, including CPA mixture composition and CPA addition and removal methods.

Temperature-pressure correlations of cryoprotective additives for the design of constant volume cryopreservation protocols

In the recent years, the use of constant volume (isochoric) cryopreservation, in medicine and biotechnology has captured more attention from the research community and now there is an increasing interest in the use of this new technology. It has been established that the thermodynamics of isochoric freezing is different from that of isobaric (constant pressure) freezing. This study provides researchers in the field experimental results for various compositions of cryoprotectants commonly used in isobaric cryopreservation, in terms of temperature-pressure-molar concentration correlation. It also reveals experimental isochoric thermodynamic data for the following cryoprotectants, commonly used in isobaric cryopreservation: dimethyl sulfoxide, trehalose, ethylene glycol and diethylene glycol. Currently, the data on the pressure-temperature correlation in an isochoric system of cryoprotectants used in isobaric cryopreservation is not available. Our new experimental results indicate that the studied concentrations for each of the CPAs, lower and expands the range of temperatures in which cryopreservation by isochoric freezing can be safely practiced. We consider that these experiments will aid researchers developing new isochoric cryopreservation protocols.

Single-Mode Electromagnetic Resonance Rewarming for the Cryopreservation of Samples with Large Volumes: A Numerical and Experimental Study

Rapid and uniform rewarming has been proved to be beneficial, and sometimes indispensable for the survival of cryopreserved biomaterials, inhibiting ice-recrystallization-devitrification and thermal stress-induced fracture (especially in large samples). To date, the convective water bath remains the gold standard rewarming method for small samples in the clinical settings, but it failed in the large samples (e.g., cryopreserved tissues and organs) due to damage caused by the slow and nonuniform heating. A single-mode electromagnetic resonance (SMER) system was developed to achieve ultrafast and uniform rewarming for large samples. In this study, we investigated the heating effects of the SMER system and compared the heating performance with water bath and air warming. A numerical model was established to further analyze the temperature change and distribution at different time points during the rewarming process. Overall, the SMER system achieved rapid heating at 331.63 ± 8.59°C min^-1 while limiting the maximum thermal gradient to <9°C min^-1, significantly better than the other two warming methods. The experimental results were highly consistent, indicating SMER is a promising rewarming technology for the successful cryopreservation of large biosamples.

Partial freezing of rat livers extends preservation time by 5-fold

The limited preservation duration of organs has contributed to the shortage of organs for transplantation. Recently, a tripling of the storage duration was achieved with supercooling, which relies on temperatures between -4 and -6 °C. However, to achieve deeper metabolic stasis, lower temperatures are required. Inspired by freeze-tolerant animals, we entered high-subzero temperatures (-10 to -15 °C) using ice nucleators to control ice and cryoprotective agents (CPAs) to maintain an unfrozen liquid fraction. We present this approach, termed partial freezing, by testing gradual (un)loading and different CPAs, holding temperatures, and storage durations. Results indicate that propylene glycol outperforms glycerol and injury is largely influenced by storage temperatures. Subsequently, we demonstrate that machine perfusion enhancements improve the recovery of livers after freezing. Ultimately, livers that were partially frozen for 5-fold longer showed favorable outcomes as compared to viable controls, although frozen livers had lower cumulative bile and higher liver enzymes.

Ice Control during Cryopreservation of Heart Valves and Maintenance of Post-Warming Cell Viability

Heart valve cryopreservation was employed as a model for the development of complex tissue preservation methods based upon vitrification and nanowarming. Porcine heart valves were loaded with cryoprotectant formulations step wise and vitrified in 1−30 mL cryoprotectant formulations ± Fe nanoparticles ± 0.6 M disaccharides, cooled to −100 °C, and stored at −135 °C. Nanowarming was performed in a single ~100 s step by inductive heating within a magnetic field. Controls consisted of fresh and convection-warmed vitrified heart valves without nanoparticles. After washing, cell viability was assessed by metabolic assay. The nanowarmed leaflets were well preserved, with a viability similar to untreated fresh leaflets over several days post warming. The convection-warmed leaflet viability was not significantly different than that of the nanowarmed leaflets immediately after rewarming; however, a significantly higher nanowarmed leaflet viability (p < 0.05) was observed over time in vitro. In contrast, the associated artery and fibrous cardiac muscle were at best 75% viable, and viability decreased over time in vitro. Supplementation of lower concentration cryoprotectant formulations with disaccharides promoted viability. Thicker tissues benefited from longer-duration cryoprotectant loading steps. The best outcomes included a post-warming incubation step with α-tocopherol and an apoptosis inhibitor, Q-VD-OPH. This work demonstrates progress in the control of ice formation and cytotoxicity hurdles for the preservation of complex tissues.

Gluconate-Lactobionate-Dextran Perfusion Solutions Attenuate Ischemic Injury and Improve Function in a Murine Cardiac Transplant Model

Static cold storage is the cheapest and easiest method and current gold standard to store and preserve donor organs. This study aimed to compare the preservative capacity of gluconate-lactobionate-dextran (Unisol) solutions to histidine-tryptophan-ketoglutarate (HTK) solution. Murine syngeneic heterotopic heart transplantations (Balb/c-Balb/c) were carried out after 18 h of static cold storage. Cardiac grafts were either flushed and stored with Unisol-based solutions with high-(UHK) and low-potassium (ULK) ± glutathione, or HTK. Cardiac grafts were assessed for rebeating and functionality, histomorphologic alterations, and cytokine expression. Unisol-based solutions demonstrated a faster rebeating time (UHK 56 s, UHK + Glut 44 s, ULK 45 s, ULK + Glut 47 s) compared to HTK (119.5 s) along with a better contractility early after reperfusion and at the endpoint on POD 3. Ischemic injury led to a significantly increased leukocyte recruitment, with similar degrees of tissue damage and inflammatory infiltrate in all groups, yet the number of apoptotic cells tended to be lower in ULK compared to HTK. In UHK- and ULK-treated animals, a trend toward decreased expression of proinflammatory markers was seen when compared to HTK. Unisol-based solutions showed an improved preservative capacity compared with the gold standard HTK early after cardiac transplantation. Supplemented glutathione did not further improve tissue-protective properties.

Ice Recrystallization Inhibition by Amino Acids: The Curious Case of Alpha- and Beta-Alanine

Extremophiles produce macromolecules which inhibit ice recrystallization, but there is increasing interest in discovering and developing small molecules that can modulate ice growth. Realizing their potential requires an understanding of how these molecules function at the atomistic level. Here, we report the discovery that the amino acid l-α-alanine demonstrates ice recrystallization inhibition (IRI) activity, functioning at 100 mM (∼10 mg/mL). We combined experimental assays with molecular simulations to investigate this IRI agent, drawing comparison to β-alanine, an isomer of l-α-alanine which displays no IRI activity. We found that the difference in the IRI activity of these molecules does not originate from their ice binding affinity, but from their capacity to (not) become overgrown, dictated by the degree of structural (in)compatibility within the growing ice lattice. These findings shed new light on the microscopic mechanisms of small molecule cryoprotectants, particularly in terms of their molecular structure and overgrowth by ice.

Magnetic particle imaging: tracer development and the biomedical applications of a radiation-free, sensitive, and quantitative imaging modality

Magnetic particle imaging (MPI) is an emerging tracer-based modality that enables real-time three-dimensional imaging of the non-linear magnetisation produced by superparamagnetic iron oxide nanoparticles (SPIONs), in the presence of an external oscillating magnetic field. As a technique, it produces highly sensitive radiation-free tomographic images with absolute quantitation. Coupled with a high contrast, as well as zero signal attenuation at-depth, there are essentially no limitations to where that can be imaged within the body. These characteristics enable various biomedical applications of clinical interest. In the opening sections of this review, the principles of image generation are introduced, along with a detailed comparison of the fundamental properties of this technique with other common imaging modalities. The main feature is a presentation on the up-to-date literature for the development of SPIONs tailored for improved imaging performance, and developments in the current and promising biomedical applications of this emerging technique, with a specific focus on theranostics, cell tracking and perfusion imaging. Finally, we will discuss recent progress in the clinical translation of MPI. As signal detection in MPI is almost entirely dependent on the properties of the SPION employed, this work emphasises the importance of tailoring the synthetic process to produce SPIONs demonstrating specific properties and how this impacts imaging in particular applications and MPI's overall performance.

Thermal Analyses of Nanowarming-Assisted Recovery of the Heart From Cryopreservation by Vitrification

This study explores thermal design aspects of nanowarming-assisted recovery of the heart from indefinite cryogenic storage, where nanowarming is the volumetric heating effect of ferromagnetic nanoparticles excited by a radio frequency electromagnet field. This study uses computational means while focusing on the human heart and the rat heart models. The underlying nanoparticle loading characteristics are adapted from a recent, proof-of-concept experimental study. While uniformly distributed nanoparticles can lead to uniform rewarming, and thereby minimize adverse effects associated with ice crystallization and thermomechanical stress, the combined effects of heart anatomy and nanoparticle loading limitations present practical challenges which this study comes to address. Results of this study demonstrate that under such combined effects, nonuniform nanoparticles warming may lead to a subcritical rewarming rate in some parts of the domain, excessive heating in others, and increased exposure potential to cryoprotective agents (CPAs) toxicity. Nonetheless, the results of this study also demonstrate that computerized planning of the cryopreservation protocol and container design can help mitigate the associated adverse effects, with examples relating to adjusting the CPA and/or nanoparticle concentration, and selecting heart container geometry, and size. In conclusion, nanowarming may provide superior conditions for organ recovery from cryogenic storage under carefully selected conditions, which comes with an elevated complexity of protocol planning and optimization.

Analysis of crystallization during rewarming in suboptimal vitrification conditions: a semi-empirical approach

Circumventing ice formation is critical to successful cryopreservation by vitrification of large organs. While ice formation during the cooling part of the cryogenic protocol is dictated by the evolving thermal conditions, ice formation during the rewarming part of the cryogenic protocol is also dependent on the history of cooling and storage conditions. Furthermore, while the exothermic effect of ice crystallization during cooling tends to adversely slow down the desired high cooling rates to ensure ice-free preservation, the same effect under some conditions tends to assist acceleration of rewarming during recovery of the specimen from cryogenic storage when limited crystallization does occur. The current study proposes a computational framework to study the thermal effects of crystallization during recovery from cryogenic storage, using a semi-empirical approach to account for the relationship between latent heat effects and the rewarming rate. This study adds another layer of computational capabilities to a recent study investigating similar effects during cooling. Results of this study demonstrate that the thermal effects of crystallization on the local cooling and rewarming rates cannot be neglected. It further explains how crystallization during rewarming helps in increasing the rewarming rate and, thereby, affects rewarming-phase crystallization. Counterintuitively, this study suggests that the fastest possible rewarming rate at the outer surface of the domain in an inwards rewarming problem is not always advantageous, while the proposed computational tool is essential to find an intermediate optimal rate.

General tissue mass transfer model for cryopreservation applications

Successful cryopreservation of complex specimens, such as tissues and organs, would greatly benefit both the medical and scientific research fields. Vitrification is one of the most promising techniques for complex specimen cryopreservation, but toxicity remains a major challenge because of the high concentration of cryoprotectants (CPAs) needed to vitrify. Our group has approached this problem using mathematical optimization to design less toxic CPA equilibration methods for cells. To extend this approach to tissues, an appropriate mass transfer model is required. Fick's law is commonly used, but this simple modeling framework does not account for the complexity of mass transfer in tissues, such as the effects of fixed charges, tissue size changes, and the interplay between cell membrane transport and transport through the extracellular fluid. Here, we propose a general model for mass transfer in tissues that accounts for all of these phenomena. To create this model, we augmented a previously published acellular model of mass transfer in articular cartilage to account for the effects of cells. We show that the model can accurately predict changes in CPA concentration and tissue size for both articular cartilage and pancreatic islets, tissue types with vastly different properties.

Vitrification and Nanowarming of Kidneys

Vitrification can dramatically increase the storage of viable biomaterials in the cryogenic state for years. Unfortunately, vitrified systems ≥3 mL like large tissues and organs, cannot currently be rewarmed sufficiently rapidly or uniformly by convective approaches to avoid ice crystallization or cracking failures. A new volumetric rewarming technology entitled "nanowarming" addresses this problem by using radiofrequency excited iron oxide nanoparticles to rewarm vitrified systems rapidly and uniformly. Here, for the first time, successful recovery of a rat kidney from the vitrified state using nanowarming, is shown. First, kidneys are perfused via the renal artery with a cryoprotective cocktail (CPA) and silica-coated iron oxide nanoparticles (sIONPs). After cooling at -40 °C min-1 in a controlled rate freezer, microcomputed tomography (µCT) imaging is used to verify the distribution of the sIONPs and the vitrified state of the kidneys. By applying a radiofrequency field to excite the distributed sIONPs, the vitrified kidneys are nanowarmed at a mean rate of 63.7 °C min-1 . Experiments and modeling show the avoidance of both ice crystallization and cracking during these processes. Histology and confocal imaging show that nanowarmed kidneys are dramatically better than convective rewarming controls. This work suggests that kidney nanowarming holds tremendous promise for transplantation.

Bioinspired materials and technology for advanced cryopreservation

Cryopreservation can help to meet the demand for biosamples of high medical value. However, it remains difficult to effectively cryopreserve some sensitive cells, tissues, and reproductive organs. A coordinated effort from the perspective of the whole frozen biological system is necessary to advance cryopreservation technology. Animals that survive in cold temperatures, such as hibernators and cold-tolerant insects, offer excellent natural models. Their anti-cold strategies, such as programmed suppression of metabolism and the synthesis of cryoprotectants (CPAs), warrant systematic study. Furthermore, the discovery and synthesis of metabolism-regulating and cryoprotective biomaterials, combined with biotechnological breakthroughs, can also promote the development of cryopreservation. Further advances in the quality and duration of biosample storage inspired by nature will promote the application of cryopreserved biosamples in clinical therapy.

A Roadmap to Cardiac Tissue-Engineered Construct Preservation: Insights from Cells, Tissues, and Organs

Worldwide, over 26 million patients suffer from heart failure (HF). One strategy aspiring to prevent or even to reverse HF is based on the transplantation of cardiac tissue-engineered (cTE) constructs. These patient-specific constructs aim to closely resemble the native myocardium and, upon implantation on the diseased tissue, support and restore cardiac function, thereby preventing the development of HF. However, cTE constructs off-the-shelf availability in the clinical arena critically depends on the development of efficient preservation methodologies. Short- and long-term preservation of cTE constructs would enable transportation and direct availability. Herein, currently available methods, from normothermic- to hypothermic- to cryopreservation, for the preservation of cardiomyocytes, whole-heart, and regenerative materials are reviewed. A theoretical foundation and recommendations for future research on developing cTE construct specific preservation methods are provided. Current research suggests that vitrification can be a promising procedure to ensure long-term cryopreservation of cTE constructs, despite the need of high doses of cytotoxic cryoprotective agents. Instead, short-term cTE construct preservation can be achieved at normothermic or hypothermic temperatures by administration of protective additives. With further tuning of these promising methods, it is anticipated that cTE construct therapy can be brought one step closer to the patient.

Zebrafish as a New Tool in Heart Preservation Research

Heart transplantation became a reality at the end of the 1960s as a life-saving option for patients with end-stage heart failure. Static cold storage (SCS) at 4-6 °C has remained the standard for heart preservation for decades. However, SCS only allows for short-term storage that precludes optimal matching programs, requires emergency surgeries, and results in the unnecessary discard of organs. Among the alternatives seeking to extend ex vivo lifespan and mitigate the shortage of organs are sub-zero or machine perfusion modalities. Sub-zero approaches aim to prolong cold ischemia tolerance by deepening metabolic stasis, while machine perfusion aims to support metabolism through the continuous delivery of oxygen and nutrients. Each of these approaches hold promise; however, complex barriers must be overcome before their potential can be fully realized. We suggest that one barrier facing all experimental efforts to extend ex vivo lifespan are limited research tools. Mammalian models are usually the first choice due to translational aspects, yet experimentation can be restricted by expertise, time, and resources. Instead, there are instances when smaller vertebrate models, like the zebrafish, could fill critical experimental gaps in the field. Taken together, this review provides a summary of the current gold standard for heart preservation as well as new technologies in ex vivo lifespan extension. Furthermore, we describe how existing tools in zebrafish research, including isolated organ, cell specific and functional assays, as well as molecular tools, could complement and elevate heart preservation research.

Winter is coming: the future of cryopreservation

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

Ice Inhibition for Cryopreservation: Materials, Strategies, and Challenges

Cryopreservation technology has developed into a fundamental and important supporting method for biomedical applications such as cell-based therapeutics, tissue engineering, assisted reproduction, and vaccine storage. The formation, growth, and recrystallization of ice crystals are the major limitations in cell/tissue/organ cryopreservation, and cause fatal cryoinjury to cryopreserved biological samples. Flourishing anti-icing materials and strategies can effectively regulate and suppress ice crystals, thus reducing ice damage and promoting cryopreservation efficiency. This review first describes the basic ice cryodamage mechanisms in the cryopreservation process. The recent development of chemical ice-inhibition molecules, including cryoprotectant, antifreeze protein, synthetic polymer, nanomaterial, and hydrogel, and their applications in cryopreservation are summarized. The advanced engineering strategies, including trehalose delivery, cell encapsulation, and bioinspired structure design for ice inhibition, are further discussed. Furthermore, external physical field technologies used for inhibiting ice crystals in both the cooling and thawing processes are systematically reviewed. Finally, the current challenges and future perspectives in the field of ice inhibition for high-efficiency cryopreservation are proposed.

The Use of High-Intensity Focused Ultrasound for the Rewarming of Cryopreserved Biological Material

High-intensity focused ultrasound (HIFU) has been used in different medical applications in the last years. In this work, we present for the first time the use of HIFU in the field of cryopreservation, the preservation of biological material at low temperatures. An HIFU system has been designed with the objective of achieving a fast and uniform rewarming in organs, key to overcome the critical problem of devitrification. The finite-element simulations have been carried out using COMSOL Multiphysics software. An array of 26 ultrasonic transducers was simulated, achieving an HIFU focal area in the order of magnitude of a model organ (ovary). A parametric study of the warming rate and temperature gradients, as a function of the frequency and power of ultrasonic waves, was performed. An optimal value for these parameters was found. The results validate the appropriateness of the technique, which is of utmost importance for the future creation of cryopreserved organ banks.

Thermomechanical stress analysis of rabbit kidney and human kidney during cryopreservation by vitrification with the application of radiofrequency heating

This study presents a computational framework for thermomechanical stress analysis in a specimen undergoing cryopreservation, with emphasis on radiofrequency (RF) heating for recovering from cryogenic storage. In particular, this study addresses cryopreservation by vitrification, where the specimen is stored in the amorphous phase (vitreous means glassy). In broad terms, the relatively high cooling and rewarming rates necessary for vitrification result in differential thermal expansion in the specimen, which is the driving force for thermo-mechanical stress. Thermomechanical stress can lead to structural damage, such as fractures or plastic deformation, rendering the specimen useless. Not without technical difficulties, those hazardous effects during the rewarming phase of the protocol can be mitigated by applying volumetric heating, with RF heating as an attractive means. The proposed computational framework in this study addresses the coupled electromagnetic, thermal and solid mechanics fields, using commercially available solvers. This study advances from a spherical-case benchmark to realistic models of the rabbit kidney and the human kidney. Results of this study suggest that structural damage to the brittle material can be prevented when stress relaxation is facilitated around the glass transition temperature. Furthermore, this study suggests that volumetric heating is necessary to surpass the critical rewarming rate, while benefiting from lowering the overall thermomechanical stress during recovery from cryogenic storage. More broadly, the computational framework presented here can be used for the optimization of the RF heating parameters, chamber specifics, specimen container shape, and the thermal protocol in order to preserve structural integrity in the specimen.

Perfusion, cryopreservation, and nanowarming of whole hearts using colloidally stable magnetic cryopreservation agent solutions

Nanowarming of cryopreserved organs perfused with magnetic cryopreservation agents (mCPAs) could increase donor organ utilization by extending preservation time and avoiding damage caused by slow and nonuniform rewarming. Here, we report formulation of an mCPA containing superparamagnetic iron oxide nanoparticles (SPIONs) that are stable against aggregation in the cryopreservation agent VS55 before and after vitrification and nanowarming and that achieve high-temperature rise rates of up to 321°C/min under an alternating magnetic field. These SPIONs and mCPAs have low cytotoxicity against primary cardiomyocytes. We demonstrate successful perfusion of whole rat hearts with the mCPA and removal using Custodiol HTK solution, even after vitrification, cryostorage in liquid nitrogen for 1 week, and nanowarming under an alternating magnetic field. Quantification of SPIONs in the hearts using magnetic particle imaging demonstrates that the formulated mCPAs are suitable for perfusion, vitrification, and nanowarming of whole organs with minimal residual iron in tissues.

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

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

Rapid quantification of multi-cryoprotectant toxicity using an automated liquid handling method

Cryopreservation in a vitrified state has vast potential for long-term storage of tissues and organs that may be damaged by ice formation. However, the toxicity imparted by the high concentration of cryoprotectants (CPAs) required to vitrify these specimens remains a hurdle. To address this challenge, we previously developed a mathematical approach to design less toxic CPA equilibration methods based on the minimization of a toxicity cost function. This approach was used to design improved methods for equilibration of bovine pulmonary artery endothelial cells (BPAEC) with glycerol. To fully capitalize on the toxicity cost function approach, it is critical to describe the toxicity kinetics of additional CPAs, including multi-CPA mixtures that are commonly used for vitrification. In this work, we used automated liquid handling to characterize the toxicity kinetics of five of the most common CPAs (glycerol, dimethyl sulfoxide (DMSO), propylene glycol, ethylene glycol, and formamide), along with their binary and ternary mixtures for BPAEC. In doing so, we developed experimental methods that can be used to determine toxicity kinetics more quickly and accurately. Our results highlight some common CPA toxicity trends, including the relatively low toxicity of ethylene glycol and a general increase in toxicity as the CPA concentration increases. Our results also suggest potential new approaches to reduce toxicity, including a surprising toxicity neutralization effect of glycerol on formamide. In the future, this dataset will serve as the basis to expand our CPA toxicity model, enabling application of the toxicity cost function approach to vitrification solutions containing multiple CPAs.

Scaling Effects on the Residual Thermomechanical Stress During Ice-Free Cooling to Storage Temperature

Cryopreservation via vitrification (glass formation) is a promising approach for long-term preservation of large-size tissues and organs. Unfortunately, thermomechanical stress, which is driven by the tendency of materials to change size with temperature, may lead to structural failure. This study focuses on analysis of thermomechanical stress in a realistic, pillow-like shape cryobag as it is cooled to cryogenic storage, subject to sufficiently high cooling rates to facilitate vitrification. Contrary to common perception, it is demonstrated in this study that the maximum stress in the specimen does not necessarily increase with increasing size of the specimen. In fact, the maximum stress is affected by the combination of two competing effects, associated with the extent of the temperature gradients within the specimen and its overall volume. On one hand, the increase in specimen size gives rise to more prominent temperature gradients, which can intensify the thermomechanical stress. On the other hand, the temperature distribution at the core of larger specimens is more uniform, which leads to a larger portion of the specimen transitioning from fluid to a glassy material almost instantaneously, which carries a moderating effect on the overall mechanical stress at the glassy state (i.e., lower residual stress). In conclusion, this study demonstrates the role of container shape optimization in reducing the thermomechanical stress during cooling.

Control of ice recrystallization in liver tissues using small molecule carbohydrate derivatives

Minimizing ice recrystallization injury in tissues and organs has historically been sought using biological antifreeze proteins. However, the size of these compounds can limit permeation and their potential immunogenicity disqualifies them from use in several cryopreservation applications. Novel small molecule carbohydrate-derived ice recrystallization inhibitors (IRIs) are not subject to these constraints, and thus we sought to evaluate the ability of a highly active IRI to permeate liver tissue and control recrystallization. Rat liver tissue blocks (0.5 mm²) were incubated with the IRI for 6 h at 22 °C and subsequently plunged in liquid nitrogen. Ice crystals within the tissue were fixed using a formal acetic alcohol fixative as it was rewarmed from -80 °C to 22 °C over the course of 48 h. The untreated control demonstrated a gradient of increasing crystal size from the exterior to the interior region of the tissue; however, the IRI-treated condition had no such gradient and exhibited small crystals throughout. Threshold segmentation confirmed a significant reduction in the ice crystal size within the interior region of the IRI-treated condition, suggesting the IRI permeated throughout and effectively controlled recrystallization within the tissue.

Thermal conductivity of cryoprotective agents loaded with nanoparticles, with application to recovery of preserved tissues and organs from cryogenic storage

The objective of this study is to provide thermal conductivity data for CPA-based nanofluids for the benefit of the analyses of cryopreservation by vitrification. Thermal conductivity measurements were conducted using a hot-wire technique on an experimentation platform of the cryomacroscope, to correlate measurements with observed physical effects such as crystallization and fracturing. Tested materials in this study include the CPA cocktails M22, VS55, DP6, and DP6+sucrose. Nanofluids in this study include the above CPA cocktails as base solutions, when mixed with either iron-oxide nanoparticles (IONP) or silica-coated iron-oxide nanoparticles (sIONP). Results of this study demonstrated the addition of sIONP to any of the CPA cocktails tested did not significantly affect its thermal conductivity, its tendency to vitrify or, conversely, its tendency to form rewarming phase crystallization (RPC). Fractures were observed with cryomacroscopy at the onset of rewarming for DP6+sIONP under carefully controlled rewarming conditions without RF activation, despite the inherent opacity of the sIONP solutions. It is likely that using RF heating in order to accelerate rewarming while unifying the temperature distribution would prevent fracture and RPC. However, sIONP were not activated in this study, as the RF heating mechanism would interfere with thermal conductivity measurements. The addition of IONP to DP6 appears to hinder the tendency of the CPA to vitrify, which is a detrimental effect. But it is unlikely that uncoated nanoparticle solutions will be used in practical applications.

Repeated Freezing Procedures Preserve Structural and Functional Properties of Amniotic Membrane for Application in Ophthalmology

For decades, the unique regenerative properties of the human amniotic membrane (hAM) have been successfully utilized in ophthalmology. As a directly applied biomaterial, the hAM should be available in a ready to use manner in clinical settings. However, an extended period of time is obligatory for performing quality and safety tests. Hence, the low temperature storage of the hAM is a virtually inevitable step in the chain from donor retrieval to patient application. At the same time, the impact of subzero temperatures carries an increased risk of irreversible alterations of the structure and composition of biological objects. In the present study, we performed a comprehensive analysis of the hAM as a medicinal product; this is intended for a novel strategy of application in ophthalmology requiring a GMP production protocol including double freezing–thawing cycles. We compared clinically relevant parameters, such as levels of growth factors and extracellular matrix proteins content, morphology, ultrastructure and mechanical properties, before and after one and two freezing cycles. It was found that epidermal growth factor (EGF), transforming growth factor beta 1 (TGF-β1), hepatocyte growth factor (HGF), basic fibroblast growth factor (bFGF), hyaluronic acid, and laminin could be detected in all studied conditions without significant differences. Additionally, histological and ultrastructure analysis, as well as transparency and mechanical tests, demonstrated that properties of the hAM required to support therapeutic efficacy in ophthalmology are not impaired by dual freezing.

Liquid-Liquid Phase Separation Produces Fast H-Bond Dynamics in DMSO-Water Mixtures

Liquid-liquid phase separation is common in complex mixtures, but the behavior of nanoconfined liquids is poorly understood from a physical perspective. Dimethyl sulfoxide (DMSO) is an amphiphilic molecule with unique concentration-dependent bulk properties in mixtures with water. Here, we use ultrafast two-dimensional infrared (2D IR) spectroscopy to measure the H-bond dynamics of two probe molecules with different polarities: formamide (FA) and dimethylformamide (DMF). Picosecond H-bond dynamics are fastest in the intermediate concentration regime (20-50 mol % DMSO), because such confined water exhibits bulk-like dynamics. Each vibrational probe experiences a unique microscopic environment as a result of nanoscale phase separation. Molecular dynamics simulations show that the dynamics span multiple time scales, from femtoseconds to nanoseconds. Our studies suggest a previously unknown liquid environment, which we label "local bulk", in which despite the local heterogeneity, the ultrafast H-bond dynamics are similar to bulk water.

Preparation of Scalable Silica-Coated Iron Oxide Nanoparticles for Nanowarming

Cryopreservation technology allows long-term banking of biological systems. However, a major challenge to cryopreserving organs remains in the rewarming of large volumes (>3 mL), where mechanical stress and ice formation during convective warming cause severe damage. Nanowarming technology presents a promising solution to rewarm organs rapidly and uniformly via inductive heating of magnetic nanoparticles (IONPs) preloaded by perfusion into the organ vasculature. This use requires the IONPs to be produced at scale, heat quickly, be nontoxic, remain stable in cryoprotective agents (CPAs), and be washed out easily after nanowarming. Nanowarming of cells and blood vessels using a mesoporous silica-coated iron oxide nanoparticle (msIONP) in VS55, a common CPA, has been previously demonstrated. However, production of msIONPs is a lengthy, multistep process and provides only mg Fe per batch. Here, a new microporous silica-coated iron oxide nanoparticle (sIONP) that can be produced in as little as 1 d while scaling up to 1.4 g Fe per batch is presented. sIONP high heating, biocompatibility, and stability in VS55 is also verified, and the ability to perfusion load and washout sIONPs from a rat kidney as evidenced by advanced imaging and ICP-OES is demonstrated.