Desiccation tolerance in human cells

Freeze-Dried Mesenchymal Stem Cells: From Bench to Bedside. Review

This review describes the freeze-dried mesenchymal stem cells (MSCs) and their ability to restore damaged tissues and organs. An analysis of the literature shows that after the lyophilization MSCs retain >80% of paracrine factors and that the mechanism of their action on the restoration of damaged tissues and organs is similar to the mechanism of action of paracrine factors in fresh and cryopreserved mesenchymal stem cells. Based on the own materials, the use of paracrine factors of freeze-dried MSCs in vivo and in vitro for the treatment of various diseases of organs and tissues has shown to be effective. The study also discusses about the advantages and disadvantages of freeze-dried MSCs versus cryopreserved MSCs. However, for the effective use of freeze-dried MSCs in clinical practice, a more detailed study of the mechanism of interaction of paracrine factors of freeze-dried MSCs with target cells and tissues is required. It is also necessary to identify possible other specific paracrine factors of freeze-dried MSCs. In addition, develop new therapeutic strategies for the use of freeze-dried MSCs in regenerative medicine and tissue bioengineering.

Industrial Biotechnology Conservation Processes: Similarities with Natural Long-Term Preservation of Biological Organisms

Cryopreservation and lyophilization processes are widely used for conservation purposes in the pharmaceutical, biotechnological, and food industries or in medical transplantation. Such processes deal with extremely low temperatures (e.g., -196 °C) and multiple physical states of water, a universal and essential molecule for many biological lifeforms. This study firstly considers the controlled laboratory/industrial artificial conditions used to favor specific water phase transitions during cellular material cryopreservation and lyophilization under the Swiss progenitor cell transplantation program. Both biotechnological tools are successfully used for the long-term storage of biological samples and products, with reversible quasi-arrest of metabolic activities (e.g., cryogenic storage in liquid nitrogen). Secondly, similarities are outlined between such artificial localized environment modifications and some natural ecological niches known to favor metabolic rate modifications (e.g., cryptobiosis) in biological organisms. Specifically, examples of survival to extreme physical parameters by small multi-cellular animals (e.g., tardigrades) are discussed, opening further considerations about the possibility to reversibly slow or temporarily arrest the metabolic activity rates of defined complex organisms in controlled conditions. Key examples of biological organism adaptation capabilities to extreme environmental parameters finally enabled a discussion about the emergence of early primordial biological lifeforms, from natural biotechnology and evolutionary points of view. Overall, the provided examples/similarities confirm the interest in further transposing natural processes and phenomena to controlled laboratory settings with the ultimate goal of gaining better control and modulation capacities over the metabolic activities of complex biological organisms.

Concise Review: Considering Optimal Temperature for Short-Term Storage of Epithelial Cells

Transplantation of novel tissue-engineered products using cultured epithelial cells is gaining significant interest. While such treatments can readily be provided at centralized medical centers, delivery to patients at geographically remote locations requires the establishment of suitable storage protocols. One important aspect of storage technology is temperature. This paper reviews storage temperature for above-freezing point storage of human epithelial cells for regenerative medicine purposes. The literature search uncovered publications on epidermal cells, retinal pigment epithelial cells, conjunctival epithelial cells, corneal/limbal epithelial cells, oral keratinocytes, and seminiferous epithelial cells. The following general patterns were noted: (1) Several studies across different cell types inclined toward 4 and 16°C being suitable short-term storage temperatures. Correspondingly, almost all studies investigating 37°C concluded that this storage temperature was suboptimal. (2) Cell death typically escalates rapidly following 7–10 days of storage. (3) The importance of the type of storage medium and its composition was highlighted by some of the studies; however, the relative importance of storage medium vs. storage temperature has not been investigated systematically. Although a direct comparison between the included investigations is not reasonable due to differences in cell types, storage media, and storage duration, this review provides an overview, summarizing the work carried out on each cell type during the past two decades.

Collagen Bioinks for Bioprinting: A Systematic Review of Hydrogel Properties, Bioprinting Parameters, Protocols, and Bioprinted Structure Characteristics

Bioprinting is a modern tool suitable for creating cell scaffolds and tissue or organ carriers from polymers that mimic tissue properties and create a natural environment for cell development. A wide range of polymers, both natural and synthetic, are used, including extracellular matrix and collagen-based polymers. Bioprinting technologies, based on syringe deposition or laser technologies, are optimal tools for creating precise constructs precisely from the combination of collagen hydrogel and cells. This review describes the different stages of bioprinting, from the extraction of collagen hydrogels and bioink preparation, over the parameters of the printing itself, to the final testing of the constructs. This study mainly focuses on the use of physically crosslinked high-concentrated collagen hydrogels, which represents the optimal way to create a biocompatible 3D construct with sufficient stiffness. The cell viability in these gels is mainly influenced by the composition of the bioink and the parameters of the bioprinting process itself (temperature, pressure, cell density, etc.). In addition, a detailed table is included that lists the bioprinting parameters and composition of custom bioinks from current studies focusing on printing collagen gels without the addition of other polymers. Last but not least, our work also tries to refute the often-mentioned fact that highly concentrated collagen hydrogel is not suitable for 3D bioprinting and cell growth and development.

Optimized Manufacture of Lyophilized Dermal Fibroblasts for Next-Generation Off-the-Shelf Progenitor Biological Bandages in Topical Post-Burn Regenerative Medicine

Cultured fibroblast progenitor cells (FPC) have been studied in Swiss translational regenerative medicine for over two decades, wherein clinical experience was gathered for safely managing burns and refractory cutaneous ulcers. Inherent FPC advantages include high robustness, optimal adaptability to industrial manufacture, and potential for effective repair stimulation of wounded tissues. Major technical bottlenecks in cell therapy development comprise sustainability, stability, and logistics of biological material sources. Herein, we report stringently optimized and up-scaled processing (i.e., cell biobanking and stabilization by lyophilization) of dermal FPCs, with the objective of addressing potential cell source sustainability and stability issues with regard to active substance manufacturing in cutaneous regenerative medicine. Firstly, multi-tiered FPC banking was optimized in terms of overall quality and efficiency by benchmarking key reagents (e.g., medium supplement source, dissociation reagent), consumables (e.g., culture vessels), and technical specifications. Therein, fetal bovine serum batch identity and culture vessel surface were confirmed, among other parameters, to largely impact harvest cell yields. Secondly, FPC stabilization by lyophilization was undertaken and shown to maintain critical functions for devitalized cells in vitro, potentially enabling high logistical gains. Overall, this study provides the technical basis for the elaboration of next-generation off-the-shelf topical regenerative medicine therapeutic products for wound healing and post-burn care.

Current Approaches of Preservation of Cells During (freeze-) Drying

The widespread application of therapeutic cells requires a successful stabilization of cells for the duration of transport and storage. Cryopreservation is currently considered the gold standard for the storage of active cells; however, (freeze-) drying cells could enable higher shelf life stability at ambient temperatures and facilitate easier transport and storage. During (freeze-) drying, freezing, (primary and secondary) drying and also the reconstitution step pose the risk of potential cell damage. To prevent these damaging processes, a wide range of protecting excipients has emerged, which can be classified, according to their chemical affiliation, into sugars, macromolecules, polyols, antioxidants and chelating agents. As many excipients cannot easily permeate the cell membrane, researchers have established various techniques to introduce especially trehalose intracellularly, prior to drying. This review aims to summarize the main damaging mechanisms during (freeze-) drying and to introduce the most common excipients with further details on their stabilizing properties and process approaches for the intracellular loading of excipients. Additionally, we would like to briefly explain recently discovered advantages of drying microorganisms, sperm, platelets, red blood cells, and eukaryotic cells, paying particular attention to the drying technique and residual moisture content.

Principles Underlying Cryopreservation and Freeze-Drying of Cells and Tissues

Cryopreservation and freeze-drying can be used to preserve cells or tissues for prolonged periods. Vitrification, or ice-free cryopreservation, is an alternative to cryopreservation that enables cooling cells to cryogenic temperatures in the absence of ice. The processing pathways involved in (ice-free) cryopreservation and freeze-drying of cells and tissues, however, can be very damaging. In this chapter, we describe the principles underlying preservation of cells for which freezing and drying are normally lethal processes as well as for cells that are able to survive in a reversible state of suspended animation. Freezing results in solution effects injury and/or intracellular ice formation, whereas drying results in removal of (non-freezable) water normally bound to biomolecules, which is generally more damaging. Cryopreservation and freeze-drying require different types of protective agents. Different mechanistic modes of action of cryoprotective and lyoprotective agents are described including minimizing ice formation, preferential exclusion, water replacement, and vitrification. Furthermore, it is discussed how protective agents can be introduced into cells avoiding damage due to too large cell volume excursions, and how knowledge of cell-specific membrane permeability properties in various temperature regimes can be used to rationally design (ice-free) cryopreservation and freeze-drying protocols.

Dehydrated Caenorhabditis elegans Stocks Are Resistant to Multiple Freeze-Thaw Cycles

Ultracold preservation is widely used for storage of genetic stocks of Caenorhabditis elegans. Current cryopreservation protocols are vulnerable to refrigeration failures, which can result in the loss of stock viability due to damage during re-freezing. Here we present a method for preserving worms in a dehydrated and frozen form that retains viability after multiple freeze-thaw cycles. After dehydration in the presence of trehalose or glycerol, C. elegans stocks can be frozen and thawed multiple times while maintaining viability. While both dauer and non-dauer larvae survive desiccation and freezing, the dauer defective mutant daf-16 does not survive desiccation. Our technique is useful for storing stocks in a manner robust to freezer failures, and potentially for shipping strains between laboratories.

Cold-Responsive Nanoparticle Enables Intracellular Delivery and Rapid Release of Trehalose for Organic-Solvent-Free Cryopreservation

Conventional cryopreservation of mammalian cells requires the use of toxic organic solvents (e.g., dimethyl sulfoxide) as cryoprotectants. Consequently, the cryopreserved cells must undergo a tedious washing procedure to remove the organic solvents for their further applications in cell-based medicine, and many of the precious cells may be lost or killed during the procedure. Trehalose has been explored as a nontoxic alternative to traditional cryoprotectants. However, mammalian cells do not synthesize trehalose or express trehalose transporters in their membranes, and the lack of an approach for the efficient intracellular delivery of trehalose has been a major hurdle for its use in cell cryopreservation. In this study, a cold-responsive polymer (poly(N-isopropylacrylamide-co-butyl acrylate)) is utilized to synthesize nanoparticles for the encapsulation and intracellular delivery of trehalose. The trehalose-laden nanoparticles can be efficiently taken up by mammalian cells. The nanoparticles quickly and irreversibly disassemble upon cold treatment, enabling the controlled and rapid release of trehalose from the nanoparticles inside cells. The latter is confirmed by an evident increase in cell volume upon cold treatment. This rapid cold-triggered intracellular release of trehalose is crucial to developing a fast protocol to cryopreserve cells using trehalose. Cells with intracellular trehalose delivered using the nanoparticles show comparable postcryopreservation viability compared to that of cells treated with DMSO, eliminating the need for the tedious and cell-damaging washing procedure required for using the DMSO-cryopreserved cells in vivo. This cold-responsive nanoparticle may greatly facilitate the use of trehalose as a nontoxic cryoprotectant for banking cells and tissues to meet their high demand by modern cell-based medicine.

Intracellular Delivery of Trehalose for Cell Banking

Advances in stem cell technology and regenerative medicine have underscored the need for effective banking of living cells. Cryopreservation, using very low temperatures to achieve suspended animation, is widely used to store or bank cells for later use. This process requires the use of cryoprotective agents (CPAs) to protect cells against damage caused by the cooling and warming process. However, current popular CPAs like DMSO can be toxic to cells and must be thoroughly removed from cells before they can be used for research or clinical applications. Trehalose, a nontoxic sugar found in organisms capable of withstanding extreme cold or desiccation, has been explored as an alternative CPA. The disaccharide must be present on both sides of the cellular membrane to provide cryo-protection. However, trehalose is not synthesized by mammalian cells nor has the capability to diffuse through their plasma membranes. Therefore, it is crucial to achieve intracellular delivery of trehalose for utilizing the full potential of the sugar for cell banking. In this review, various methods that have been explored to deliver trehalose into mammalian cells for their banking at both cryogenic and ambient temperatures are surveyed. Among them, the nanoparticle-mediated approach is particularly exciting. Collectively, studies in the literature demonstrate the great potential of using trehalose as the sole CPA for cell banking, to facilitate the widespread use of living cells in modern medicine.

Rapid and continuous on-chip loading of trehalose into erythrocytes

Freeze-drying is a promising approach for the long-term storage of erythrocytes at room temperature. Studies have shown that trehalose loaded into erythrocytes plays an important role in protecting erythrocytes against freeze-drying damage. Due to the impermeability of the erythrocyte membrane to trehalose, many methods have been developed to load trehalose into erythrocytes. However, these methods usually require multistep manual manipulation and long processing time; the adopted protocols are also diverse and not standardized. Thus, we develop an osmotically-based trehalose-loading microdevice (TLM) to rapidly, continuously, and automatically produce erythrocytes with loaded trehalose. In the TLM, trehalose is loaded through the erythrocyte membrane pores induced by hypotonic shock; then, the trehalose-loaded erythrocytes are rinsed to remove hemoglobin molecules and cell fragments, and the extracellular solution is restored to the isotonic state by integrating a rinsing-recovering design. First, the mixing function and the rinsing-recovering function were confirmed using a fluorescent solution. Then, the performance of the TLM was evaluated under various operating conditions with respect to the loading efficiency of trehalose, the hemolysis rate of erythrocytes (ϕ), the recovery rate of hemoglobin in erythrocytes (φ), and the separation efficiency of the TLM. Finally, the preliminary study of the freeze-drying of erythrocytes with loaded trehalose was accomplished using the TLM. The results showed that under the designated operating conditions, the loading efficiency for human erythrocytes reached ~21 mM in ~2 min with a ϕ value of ~17% and a φ value of ~74%. This study provides insights into the design of the on-chip loading of trehalose into erythrocytes and promotes the automation of life science studies on biochips.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Microvalve-based bioprinting – process, bio-inks and applications

DOD microvalve-based bioprinting system provides a highly advanced manufacturing platform that facilitates precise control over the cellular and biomaterial deposition in a highly reproducible and reliable manner. This article highlights promising directions to transform microvalve-based bioprinting into an enabling technology that will potentially drive significant advances in the field of TERM.

Experimentally Induced Repeated Anhydrobiosis in the Eutardigrade Richtersius coronifer

Tardigrades represent one of the main animal groups with anhydrobiotic capacity at any stage of their life cycle. The ability of tardigrades to survive repeated cycles of anhydrobiosis has rarely been studied but is of interest to understand the factors constraining anhydrobiotic survival. The main objective of this study was to investigate the patterns of survival of the eutardigrade Richtersius coronifer under repeated cycles of desiccation, and the potential effect of repeated desiccation on size, shape and number of storage cells. We also analyzed potential change in body size, gut content and frequency of mitotic storage cells. Specimens were kept under non-cultured conditions and desiccated under controlled relative humidity. After each desiccation cycle 10 specimens were selected for analysis of morphometric characteristics and mitosis. The study demonstrates that tardigrades may survive up to 6 repeated desiccations, with declining survival rates with increased number of desiccations. We found a significantly higher proportion of animals that were unable to contract properly into a tun stage during the desiccation process at the 5^th and 6^th desiccations. Also total number of storage cells declined at the 5^th and 6^th desiccations, while no effect on storage cell size was observed. The frequency of mitotic storage cells tended to decline with higher number of desiccation cycles. Our study shows that the number of consecutive cycles of anhydrobiosis that R. coronifer may undergo is limited, with increased inability for tun formation and energetic constraints as possible causal factors.

Recent Advances and Future Direction in Lyophilisation and Desiccation of Mesenchymal Stem Cells

Mesenchymal Stem Cells (MSCs) are a promising mammalian cell type as they can be used for the reconstruction of human tissues and organs. MSCs are shown to form bone, cartilage, fat, and muscle-like cells under specific cultivation conditions. Current technology of MSCs cryopreservation has significant disadvantages. Alternative technologies of mammalian cells preservation through lyophilisation or desiccation (air-drying) are among the upcoming domains of investigation in the field of cryobiology. Different protectants and their combinations were studied in this context. Loading of the protectant in the live cell can be a challenging issue but recent studies have shown encouraging results. This paper deals with a review of the protectants, methods of their delivery, and physical boundary conditions adopted for the desiccation and lyophilisation of mammalian cells, including MSCs. A hybrid technique combining both methods is also proposed as a promising way of MSCs dry preservation.

Freezing-induced uptake of trehalose into mammalian cells facilitates cryopreservation

The aim of this study was to investigate if membrane-impermeable molecules are taken up by fibroblasts when exposing the cells to membrane phase transitions and/or freezing-induced osmotic forces. The membrane-impermeable fluorescent dye lucifer yellow (LY) was used to visualize and quantify uptake during endocytosis, and after freezing-thawing. In addition, trehalose uptake after freezing and thawing was studied. Fourier transform infrared spectroscopic studies showed that fibroblasts display a minor non-cooperative phase transition during cooling at suprazero temperatures, whereas cells display strong highly cooperative fluid-to-gel membrane phase transitions during freezing, both in the absence and presence of protectants. Cells do not show uptake of LY upon passing the suprazero membrane phase transition at 30-10°C, whereas after freezing and thawing cells show intracellular LY equally distributed within the cell. Both, LY and trehalose are taken up by fibroblasts after freezing and thawing with loading efficiencies approaching 50%. When using 250 mM extracellular trehalose during cryopreservation, intracellular concentrations greater than 100 mM were determined after thawing. A plot of cryosurvival versus the cooling rate showed a narrow inverted-'U'-shaped curve with an optimal cooling rate of 40°C min(-1). Diluting cells cryopreserved with trehalose in isotonic cell culture medium resulted in a loss of cell viability, which was attributed to intracellular trehalose causing an osmotic imbalance. Taken together, mammalian cells can be loaded with membrane-impermeable compounds, including the protective agent trehalose, by subjecting the cells to freezing-induced osmotic stress.

Engineered Trehalose Permeable to Mammalian Cells

Trehalose is a naturally occurring disaccharide which is associated with extraordinary stress-tolerance capacity in certain species of unicellular and multicellular organisms. In mammalian cells, presence of intra- and extracellular trehalose has been shown to confer improved tolerance against freezing and desiccation. Since mammalian cells do not synthesize nor import trehalose, the development of novel methods for efficient intracellular delivery of trehalose has been an ongoing investigation. Herein, we studied the membrane permeability of engineered lipophilic derivatives of trehalose. Trehalose conjugated with 6 acetyl groups (trehalose hexaacetate or 6-O-Ac-Tre) demonstrated superior permeability in rat hepatocytes compared with regular trehalose, trehalose diacetate (2-O-Ac-Tre) and trehalose tetraacetate (4-O-Ac-Tre). Once in the cell, intracellular esterases hydrolyzed the 6-O-Ac-Tre molecules, releasing free trehalose into the cytoplasm. The total concentration of intracellular trehalose (plus acetylated variants) reached as high as 10 fold the extracellular concentration of 6-O-Ac-Tre, attaining concentrations suitable for applications in biopreservation. To describe this accumulation phenomenon, a diffusion-reaction model was proposed and the permeability and reaction kinetics of 6-O-Ac-Tre were determined by fitting to experimental data. Further studies suggested that the impact of the loading and the presence of intracellular trehalose on cellular viability and function were negligible. Engineering of trehalose chemical structure rather than manipulating the cell, is an innocuous, cell-friendly method for trehalose delivery, with demonstrated potential for trehalose loading in different types of cells and cell lines, and can facilitate the wide-spread application of trehalose as an intracellular protective agent in biopreservation studies.

Nanoparticle-mediated intracellular delivery enables cryopreservation of human adipose-derived stem cells using trehalose as the sole cryoprotectant

In this study, pH responsive genipin-cross-linked Pluronic F127-chitosan nanoparticles (GNPs) was synthesized to encapsulate trehalose for intracellular delivery to cryopreserve primary human adipose-derived stem cells (hADSCs). Trehalose is a disaccharide of glucose used by lower organisms to survive extreme cold in nature and has been used to cryopreserve various biomacromolecules. However, it does not enter mammalian cells because of its highly hydrophilic nature, and has only been used in combination with other cell-penetrating cryoprotectants (such as dimethyl sulfoxide, DMSO) to cryopreserve mammalian cells. Our data show that trehalose can be efficiently encapsulated in our GNPs for intracellular delivery, which enables cryopreservation of primary hADSCs using the nontoxic sugar as the sole cryoprotectant. This capability is important because the conventional approach of cryopreserving mammalian cells using highly toxic (at body temperature) cell-penetrating cryoprotectants requires multistep washing of the cryopreserved cells to remove the toxic cryoprotectant for further use, which is time-consuming and associated with significant cell loss (∼10% during each washing step). By contrast, the trehalose-cryopreserved cells can be used without washing, which should greatly facilitate the wide application of the burgeoning cell-based medicine.

Design of novel cell penetrating peptides for the delivery of trehalose into mammalian cells

Stabilization of cells in a desiccated state can significantly simplify the storage and transportation and save expenses for clinical applications. Introduction of the impermeable disaccharide, trehalose, into cells is an important step to improve the desiccation tolerance of cells. In this study, a novel cell penetrating peptide, KRKRWHW, was developed based on molecular simulations. The peptide exhibited little cytotoxicity and high penetrating efficiency into mammalian cells. The cell viability of mouse embryonic fibroblasts (MEFs) after the incubation with various concentrations of KRKRWHW from 0.01mM to 5mM at 37°C for 4h was maintained at around 100%. The peptide was able to penetrate into MEFs within 1h at 37°C with an efficiency of around 90% at 0.1mM. Trehalose, as a cargo coupled with the peptide of KRKRWHW through hydrogen bond and π-π bond, was successfully loaded into the MEFs. This novel peptide provides a novel approach for the delivery of trehalose into mammalian cells.

Molecular dynamics simulations of the interactions of DMSO, mono- and polyhydroxylated cryosolvents with a hydrated phospholipid bilayer

Molecular dynamics (MD) simulations have been used to investigate the interactions of a variety of hydroxylated cryosolvents (glycerol, propylene glycol and ethylene glycol), methanol and dimethyl sulfoxide (DMSO) in aqueous solution with a 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) bilayer in its fluid phase at 323K. Each cryosolvent induced lateral expansion of the membrane leading to thinning of the bilayer and resulting in disordering of the lipid hydrocarbon chains. Propylene glycol and DMSO were observed to exhibit a greater disordering effect on the structure of the membrane than the other three alcohols. Closer examination exposed a number of effects on the lipid bilayer as a function of the molecular size and hydrogen bonding capacity of the cryosolvents. Analyses of hydrogen bonds revealed that increased concentrations of the polyhydroxylated cryosolvents induced the formation of a cross-linked cryosolvent layer across the surface of the membrane bilayer. This effect was most pronounced for glycerol at sufficiently high concentrations, which displayed a comparatively enhanced capacity to induce cross-linking of lipid headgroups resulting in the formation of extensive hydrogen bonding bridges and the promotion of a dense cryosolvent layer across the phospholipid bilayer.

Thermostability of biological systems: fundamentals, challenges, and quantification

This review examines the fundamentals and challenges in engineering/understanding the thermostability of biological systems over a wide temperature range (from the cryogenic to hyperthermic regimen). Applications of the bio-thermostability engineering to either destroy unwanted or stabilize useful biologicals for the treatment of diseases in modern medicine are first introduced. Studies on the biological responses to cryogenic and hyperthermic temperatures for the various applications are reviewed to understand the mechanism of thermal (both cryo and hyperthermic) injury and its quantification at the molecular, cellular and tissue/organ levels. Methods for quantifying the thermophysical processes of the various applications are then summarized accounting for the effect of blood perfusion, metabolism, water transport across cell plasma membrane, and phase transition (both equilibrium and non-equilibrium such as ice formation and glass transition) of water. The review concludes with a summary of the status quo and future perspectives in engineering the thermostability of biological systems.

Non-thermal plasma induces apoptosis in melanoma cells via production of intracellular reactive oxygen species

Non-thermal atmospheric pressure dielectric barrier discharge (DBD) plasma may provide a novel approach to treat malignancies via induction of apoptosis. The purpose of this study was to evaluate the potential of DBD plasma to induce apoptosis in melanoma cells. Melanoma cells were exposed to plasma at doses that did not induce necrosis, and cell viability and apoptotic activity were evaluated by Trypan blue exclusion test, Annexin-V/PI staining, caspase-3 cleavage, and TUNEL® analysis. Trypan blue staining revealed that non-thermal plasma treatment significantly decreased the viability of cells in a dose-dependent manner 3 and 24 h after plasma treatment. Annexin-V/PI staining revealed a significant increase in apoptosis in plasma-treated cells at 24, 48, and 72 h post-treatment (p < 0.001). Caspase-3 cleavage was observed 48 h post-plasma treatment at a dose of 15 J/cm(2). TUNEL® analysis of plasma-treated cells demonstrated an increase in apoptosis at 48 and 72 h post-treatment (p < 0.001) at a dose of 15 J/cm(2). Pre-treatment with N-acetyl-L: -cysteine (NAC), an intracellular reactive oxygen species (ROS) scavenger, significantly decreased apoptosis in plasma-treated cells at 5 and 15 J/cm(2). Plasma treatment induces apoptosis in melanoma cells through a pathway that appears to be dependent on production of intracellular ROS. DBD plasma production of intracellular ROS leads to dose-dependent DNA damage in melanoma cells, detected by γ-H2AX, which was completely abrogated by pre-treating cells with ROS scavenger, NAC. Plasma-induced DNA damage in turn may lead to the observed plasma-induced apoptosis. Since plasma is non-thermal, it may be used to selectively treat malignancies.

Reinterpretation of evidence advanced for neo-oogenesis in mammals, in terms of a finite oocyte reserve

The central tenet of ovarian biology, that the oocyte reserve in adult female mammals is finite, has been challenged over recent years by proponents of neo-oogenesis, who claim that germline stem cells exist in the ovarian surface epithelium or the bone marrow. Currently opinion is divided over these claims, and further scrutiny of the evidence advanced in support of the neo-oogenesis hypothesis is warranted - especially in view of the enormous implications for female fertility and health. This article contributes arguments against the hypothesis, providing alternative explanations for key observations, based on published data. Specifically, DNA synthesis in germ cells in the postnatal mouse ovary is attributed to mitochondrial genome replication, and to DNA repair in oocytes lagging in meiotic progression. Lines purported to consist of germline stem cells are identified as ovarian epithelium or as oogonia, from which cultures have been derived previously. Effects of ovotoxic treatments are found to negate claims for the existence of germline stem cells. And arguments are presented for the misidentification of ovarian somatic cells as de novo oocytes. These clarifications, if correct, undermine the concept that germline stem cells supplement the oocyte quota in the postnatal ovary; and instead comply with the theory of a fixed, unregenerated reserve. It is proposed that acceptance of the neo-oogenesis hypothesis is erroneous, and may effectively impede research in areas of ovarian biology. To illustrate, a novel explanation that is consistent with orthodox theory is provided for the observed restoration of fertility in chemotherapy-treated female mice following bone marrow transplantation, otherwise interpreted by proponents of neo-oogenesis as involving stimulation of endogenous germline stem cells. Instead, it is proposed that the chemotherapeutic regimens induce autoimmunity to ovarian antigens, and that the haematopoietic chimaerism produced by bone marrow transplantation circumvents activation of an autoreactive response, thereby rescuing ovarian function. The suggested mechanism draws from animal models of autoimmune ovarian disease, which implicate dysregulation of T cell regulatory function; and from a surmised role for follicular apoptosis in the provision of ovarian autoantigens, to sustain self-tolerance during homeostasis. This interpretation has direct implications for fertility preservation in women undergoing chemotherapy.

Preservation protocols for human adipose tissue-derived adult stem cells

The development of simple but effective storage protocols for adult stem cells will greatly enhance their use and utility in tissue-engineering applications. There are three primary storage techniques, freezing (cryopreservation), drying (anhydrobiosis), and freeze drying (lyophilization), each with its own advantages and disadvantages. Cryopreservation has shown the most promise but is a fairly complex process, necessitating the use of chemicals called cryoprotective agents (CPAs), freezing equipment, and obviously, storage in liquid nitrogen. Preservation by desiccation is an alternative that attempts to reproduce a naturally occurring preservative technique, namely, the phenomenon of anhydrobiosis and requires the use of high (and possibly, toxic) concentration of CPAs as well as disaccharides (sugars). Lyophilization works by first cryopreserving (freezing) the material and then desiccating (drying) it by the process of sublimation or the conversion of ice (solid) to water vapor (gas phase). The purpose of this chapter is to present a general overview of these storage techniques and the optimal protocols/results obtained in our laboratory for long-term storage of adult stem cells using freezing storage and drying storage.

Preservation of differentiation and clonogenic potential of human hematopoietic stem and progenitor cells during lyophilization and ambient storage

Progenitor cell therapies show great promise, but their potential for clinical applications requires improved storage and transportation. Desiccated cells stored at ambient temperature would provide economic and practical advantages over approaches employing cell freezing and subzero temperature storage. The objectives of this study were to assess a method for loading the stabilizing sugar, trehalose, into hematopoietic stem and progenitor cells (HPC) and to evaluate the effects of subsequent freeze-drying and storage at ambient temperature on differentiation and clonogenic potential. HPC were isolated from human umbilical cord blood and loaded with trehalose using an endogenous cell surface receptor, termed P2Z. Solution containing trehalose-loaded HPC was placed into vials, which were transferred to a tray freeze-dryer and removed during each step of the freeze-drying process to assess differentiation and clonogenic potential. Control groups for these experiments were freshly isolated HPC. Control cells formed 1450+/-230 CFU-GM, 430+/-140 BFU-E, and 50+/-40 CFU-GEMM per 50 microL. Compared to the values for the control cells, there was no statistical difference observed for cells removed at the end of the freezing step or at the end of primary drying. There was a gradual decrease in the number of CFU-GM and BFU-E for cells removed at different temperatures during secondary drying; however, there were no significant differences in the number of CFU-GEMM. To determine storage stability of lyophilized HPC, cells were stored for 4 weeks at 25 degrees C in the dark. Cells reconstituted immediately after lyophilization produced 580+/-90 CFU-GM ( approximately 40%, relative to unprocessed controls p<0.0001), 170+/-70 BFU-E (approximately 40%, p<0.0001), and 41+/-22 CFU-GEMM (approximately 82%, p = 0.4171), and cells reconstituted after 28 days at room temperature produced 513+/-170 CFU-GM (approximately 35%, relative to unprocessed controls, p<0.0001), 112+/-68 BFU-E (approximately 26%, p<0.0001), and 36+/-17 CFU-GEMM ( approximately 82%, p = 0.2164) These studies are the first to document high level retention of CFU-GEMM following lyophilization and storage for 4 weeks at 25 degrees C. This type of flexible storage stability would potentially permit the ability to ship and store HPC without the need for refrigeration.

Improving the long-term storage of a mammalian biosensor cell line via genetic engineering

The unique properties of mammalian cells make them valuable for a variety of applications in medicine, industry, and diagnostics. However, the utility of such cells is restricted due to the difficulty in storing them non-frozen for an extended time and still maintaining their stability and responsiveness. In order to extend the active life span of a mammalian biosensor cell line at room and refrigerated temperatures, we have over expressed genes that are reported to provide protection from apoptosis, stress, or oxidation. We demonstrated that over expression of genes from the extremophile, Artemia franciscana, as well as GADD45beta, extends room-temperature storage of fully active cells 3.5-fold, while over production of several anti-apoptotic proteins extended 4 degrees C storage 2- to 3-fold. Methodologies like these that improve the stability of mammalian-cell-based technologies in the absence of freezers may enable widespread use of these tools in applications that have been considered impractical based solely on limited storage characteristics.

The encapsulation and intracellular delivery of trehalose using a thermally responsive nanocapsule

The thermally responsive wall permeability of an empty core-shell structured Pluronic nanocapsule (together with its temperature dependent size and surface charge) was successfully utilized for encapsulation, intracellular delivery, and controlled release of trehalose, a highly hydrophilic small (M(W) = 342 D) molecule (a disaccharide of glucose) that is exceptional for long-term stabilization of biologicals (particularly at ambient temperatures). It was found that trehalose can be physically encapsulated in the nanocapsule using a soaking-freeze-drying-heating procedure. The nanocapsule is capable of physically withholding trehalose with negligible release in hours for cellular uptake at 37 degrees C when its wall permeability is low. A quick release of the encapsulated sugar can be achieved by thermally cycling the nanocapsule between 37 and 22 degrees C (or lower). A significant amount of trehalose (up to 0.3 M) can be delivered into NIH 3T3 fibroblasts by incubating the cells with the trehalose-encapsulated nanocapsules at 37 degrees C for 40 min. Moreover, cytotoxicity of the nanocapsule for the purpose of intracellular delivery of trehalose was found to be negligible. Altogether, the thermally responsive nanocapsule is effective for intracellular delivery of trehalose, which is critical for the long-term stabilization of mammalian cells at ambient temperatures and the eventual success of modern cell-based medicine.

Comparison of frozen versus desiccated reference human red blood cells for hemagglutination assays

BACKGROUND

Red blood cells (RBCs) are commonly used fresh or stored in frozen format for identification of patients' antibodies and serologic specificity of such antibodies at reference laboratories. However, maintaining a large pool of fresh RBCs is impossible in a blood-banking environment and blood in frozen format poses a logistic disadvantage in terms of accessibility, maintenance cost, safety, and sample recovery. This study explores an alternative, desiccation storage method for RBCs to provide a reagent that supports greater utilization and flexibility for reference laboratories.

STUDY DESIGN AND METHODS

RBCs from five donors were used in the study. RBCs were processed and kept in either frozen or desiccated format. Study variables for either the frozen or the desiccated cells included cell recovery as quantified by cell counts, gross microscopic examination, and hemagglutination assays.

RESULTS

The mean percentage of cell recovery for thawed and washed frozen RBCs was 20% versus 50% for rehydrated and washed desiccated RBCs. Microscopic examination of thawed cells from the frozen preparation showed cells with irregular shapes, a sharp contrast when compared with rehydrated cells from the desiccated preparation, where cells are mostly intact, smooth surface, and biconcave in structure. Cells in both preparations performed well in manual agglutination tests.

CONCLUSION

Desiccation preservation of RBCs provides a somewhat better RBC recovery and cell structure stability, while maintaining the necessary antigen-antibody reactions for cell surface markers, which will allow desiccated RBCs to be archived in blood collecting and processing reference laboratories.

Further optimization of mouse spermatozoa evaporative drying techniques

It has been shown in the past that mouse spermatozoa could be dried under a stream of nitrogen gas at ambient temperature and stored at 4 degrees C or 22 degrees C for up to 3 months and was capable of generating live-born offspring. In previous desiccation work, dried sperm were stored in a vacuum-sealed plastic bag placed in a vacuum-packed Mylar bag. However, dried specimens stored in this way often lost moisture, particularly in samples stored at higher temperatures (22 degrees C) compared to lower temperatures (4 degrees C). The present report describes a method which minimizes this water loss from the dried sperm samples. Its use is described in a preliminary study on the effect of supplementing the trehalose with glycerol. The results have demonstrated that mouse sperm can be stored at 4 degrees C over saturated NaBr without the uptake of water which occurs when they are stored in Mylar packages. In addition, we were able to get some survival of sperm (9-15%) at room temperature storage after 3 months. The addition of glycerol to trehalose had little effect on the survival of dried mouse sperm stored over NaBr for 1 and 3 months.

Rhesus macaque blastocysts resulting from intracytoplasmic sperm injection of vacuum-dried spermatozoa

BACKGROUND

Sperm desiccation is an attractive approach for sperm preservation. In this study, we examined the feasibility and efficiency of intracytoplasmic sperm injection using vacuum-dried rhesus macaque sperm in CZB medium supplemented with 10% fetal bovine serum.

METHODS

A total of 109 MII oocytes were injected with 69 fresh ejaculated sperm and 40 vacuum-dried sperm.

RESULTS

Cleavage occurred in 97% of oocytes injected with fresh, motile sperm and in 88% of oocytes injected with vacuum-dried sperm. Of the cleaved oocytes, 68% fresh sperm-injected oocytes and 74% of dried sperm-injected oocytes developed to the compact morula stage. Blastocyst development was comparable between fresh-injected (16%) and vacuum-dried-injected (17%) oocytes. Differences between treatment groups were not significant. Transmission electron microscopic observation of the blastocysts indicated no detectable differences between fresh sperm and dried sperm-derived embryos.

CONCLUSIONS

We conclude that vacuum-dried rhesus macaque sperm are capable of inducing fertilization and development of pre-implantation embryos when sperm were dried under vacuum and microinjected into normal viable oocytes.

Evaluation of toxicity of commercial ophthalmic fluoroquinolone antibiotics as assessed on immortalized corneal and conjunctival epithelial cells

PURPOSE

To evaluate the toxicity of a variety of the fluoroquinolone antibiotics on the ocular surface by using tissue culture models of corneal epithelial cells and conjunctival epithelial cells.

METHODS

Immortalized conjunctival (CCC) and human corneal (HCE) epithelial cells were grown and when confluent the cells allowed to air dry for 1 hour. Medium was then replaced with 100 microL of one of the following: 1) Vigamox [moxifloxacin (0.5%: MX)]; (2) Zymar [gatifloxacin (0.3%: GA)]; 3) Quixin [levofloxacin (0.5%: LE)]; 4) Ocuflox [ofloxacin (0.3%: OF)]; 5) Ciloxan [ciprofloxacin (0.3%: CP)]; 6) medium (viable control); 7) "normal"/physiologic saline; 8) formalin (dead control). After one hour, 150 microL of MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazonium bromide was added and incubated for 4 hours. After decanting, precipitate was dissolved in 150 microL of isopropanol. Absorbance was determined at 572 nm.

RESULTS

The lowest amount of cell death was associated with the viable control. All ophthalmic preparations showed both corneal and conjunctival cell toxicity. Aside from the viable control, normal saline showed the next lowest amount of toxicity. Of the topical ocular antibiotics tested, MX showed the least amount of toxicity. All of the other antibiotics tested were statistically indistinguishable from each other.

CONCLUSIONS

All of the topical ocular antibiotics tested showed evidence of both corneal and conjunctival toxicity (MX < OF < or = LE < or = CP < or = GA), although only MX was statistically significant. Whether this finding reflects on in vivo wound healing remains to be determined. This model provides a rapid and cost-effective method to screen for surface toxicity of topical agents.

Trehalose and trehalose-based polymers for environmentally benign, biocompatible and bioactive materials

Trehalose is a non-reducing disaccharide that is found in many organisms but not in mammals. This sugar plays important roles in cryptobiosis of selaginella mosses, tardigrades (water bears), and other animals which revive with water from a state of suspended animation induced by desiccation. The interesting properties of trehalose are due to its unique symmetrical low-energy structure, wherein two glucose units are bonded face-to-face by 1→1-glucoside links. The Hayashibara Co. Ltd., is credited for developing an inexpensive, environmentally benign and industrial-scale process for the enzymatic conversion of α-1,4-linked polyhexoses to α,α-d-trehalose, which made it easy to explore novel food, industrial, and medicinal uses for trehalose and its derivatives. Trehalose-chemistry is a relatively new and emerging field, and polymers of trehalose derivatives appear environmentally benign, biocompatible, and biodegradable. The discriminating properties of trehalose are attributed to its structure, symmetry, solubility, kinetic and thermodynamic stability and versatility. While syntheses of trehalose-based polymer networks can be straightforward, syntheses and characterization of well defined linear polymers with tailored properties using trehalose-based monomers is challenging, and typically involves protection and deprotection of hydroxyl groups to attain desired structural, morphological, biological, and physical and chemical properties in the resulting products. In this review, we will overview known literature on trehalose’s fascinating involvement in cryptobiology; highlight its applications in many fields; and then discuss methods we used to prepare new trehalose-based monomers and polymers and explain their properties.

Spectrophotometric measurement of intraliposomal trehalose

Trehalose, a non-reducing glucose disaccharide found at high concentrations in many species of anhydrobiotic organisms, shows significant promise in protecting cellular viability and structural integrity during freezing and desiccation. As mammalian cell membranes are impermeable to trehalose, extensive efforts have been taken to introduce trehalose into mammalian cells. In this study, we report on the characterization of trehalose-containing liposomes, with focus on the entrapment of trehalose inside liposomes, as the first step in establishing liposomes as a delivery system in the biopreservation field. Liposomes were synthesized by hydrating a phospholipid/cholesterol lipid bilayer with 200-400 mM trehalose buffer and repeatedly extruding the lipid suspension to form unilamellar vesicles. The trehalose content of the liposomal lysate was determined spectrophotometrically using a commercial kit Megazyme and confirmed with HPLC measurements. The number of liposomes was calculated from the phosphate content of the liposomal preparation and an estimated number of lipid molecules in a 401+/-8 nm liposome. Based on an intraliposomal trehalose content, the calculated liposomal encapsulation efficiency of 200 mM trehalose liposomes was of 92+/-0.7%. This value was in agreement with the 300 and 400 mM trehalose liposomes (91.1+/-8.2% and 102.1+/-9.4%, respectively). The Megazyme method for trehalose measurement is an inexpensive and sensitive technique that does not require specialized instrumentation or extensive technical expertise. Therefore, it can be used to enhance current efforts in the development of alternative strategies for the cryo- and lyoprotection of mammalian cells.

Effects of trehalose co-incubation on in vitro matured prepubertal ovine oocyte vitrification

Our aim was to evaluate if loading prepubertal ovine oocyte with trehalose would impact on their further developmental potential in vitro and if it would improve their survival to vitrification procedures. COCs matured in vitro with (TRH) or without (CTR) 100mM trehalose were tested for developmental potential after in vitro fertilization and culture. Trehalose uptake was measured by the antrone spectrophotometric assay. No differences were recorded between the two experimental groups in fertilization rates (91.1 CTR vs 92.5% TRH), cleavage rates calculated on fertilized oocytes (96.1 CTR vs 95.4% TRH), first cleavage kinetic (56.1 CTR vs 51% TRH), and blastocyst rates (14.3 CTR vs 13.0% TRH). Anthrone assay revealed that in TRH group trehalose concentration/oocyte was 2.6microM. MII oocytes were then vitrified using cryoloops in TCM 199 containing 20% FCS, sucrose 0.5M, 16.5% Me(2)SO, 16.5% EG and plunged in LN(2). After warming, oocytes from TRH and CTR groups were tested for membrane integrity using the propidium iodide (PI)/Hoechst differential staining, and for developmental ability after in vitro fertilization. Trehalose in maturation medium affected membrane resistance (P<0.01) to vitrification/warming but not fertilization and cleavage rates. The differential staining showed a lower number of PI positive cells in TRH group compared to CTR one (14.3 vs 24.7%, respectively). Fertilization rates and cleavage rates did not differ between the two groups (55.3 and 41% for TRH and 47.7 and 41.7% for CTR, respectively). In conclusion trehalose in maturation medium stabilizes cell membranes during vitrification/warming of prepubertal ovine oocytes but does not affect fertilization and cleavage rates after warming.

Effects of freeze-drying on cytology, ultrastructure, DNA fragmentation, and fertilizing ability of bovine sperm

Freeze-drying sperm is an alternative to cryopreservation. Although sperm from various species has been freeze-dried, there are few reports for bovine sperm. The primary objective of this study was to evaluate the protective effect of various freeze-drying media on the structural and functional components of bovine sperm. The media tested were composed of TCM 199 with Hanks salts supplemented with 10% fetal calf serum (FCS) and TCM 199 with Hanks salts supplemented with 10% FCS and 0.2 M trehalose and EGTA solution. The efficiency of each medium on the preservation of freeze-dried sperm structures was evaluated with conventional and electron microscopy, DNA integrity was analyzed by a TUNEL assay, and fertilizing ability of lyophilized sperm was determined with ICSI. Although the plasma membrane was damaged in all media tested, mitochondria were similarly preserved in all freeze-drying treatments. The acrosome was best preserved in the media that contained trehalose (other treatments also conserved this structure). In contrast, media containing EGTA or trehalose most effectively preserved the nuclei in freeze-dried sperm, with only 2 and 5%, respectively, of cells with fragmented DNA. Furthermore, sperm conserved with these media also had higher (P<0.05) rates of sperm head decondensation (32.5 and 27.5%), pronucleus formation (37.5 and 45.0%) and blastocyst formation (19.4 and 18.3%) than medium supplemented with FCS (15.0, 20.0 and 10.2%, respectively). In conclusion, media with EGTA and trehalose adequately protected bovine sperm during freeze-drying by preserving the viability of their nuclei.

Trehalose effects on α-crystallin aggregates

alpha-Crystallin in its native state is a large, heterogeneous, low-molecular weight (LMW) aggregate that under certain conditions may progressively became part of insoluble high-molecular weight (HMW) systems. These systems are supposed to play a relevant role in eye lens opacification and vision impairment. In this paper, we report the effects of trehalose on alpha-crystallin aggregates. The role of trehalose in alpha-crystallin stress tolerance, chaperone activity and thermal stability is studied. The results show that trehalose stabilizes the alpha-crystallin native structure, inhibits alpha-crystallin aggregation, and disaggregates preformed LMW systems not affecting its chaperone activity.

3-O-methyl-D-glucose improves desiccation tolerance of keratinocytes

Transplantation of autologous skin grafts and tissue engineered skin replacements for the treatment of burns, trauma, and ulcerative wounds has been shown to restore a protective barrier to infection and fluid loss, reduce heat loss, provide mechanical strength, diminish pain, and dampen the hypermetabolic stress response to thermal injury. Patencies of these grafts depend mainly on the high viability and sustained function of the enmeshed keratinocytes. With growing demand in tissue replacement therapies, development of successful and economical preservation techniques for skin grafts and replacements becomes essential. In this regard, if attained, desiccated state storage offers an economical solution to availability, storage, and transportation problems. Recent studies indicate that carbohydrates are very efficient in stabilizing mammalian cells against various types of stresses, including those associated with cryopreservation and desiccation. In this study we introduce the use of 3-O-methyl-D-glucose (3-OMG), a nonmetabolizable glucose derivative, as a new means of providing protection for keratinocytes undergoing desiccation. We show that with decreasing water contents, viability of the cells decreases; however, at the same water content the immediate post-rehydration viability and long-term survival of the cells exposed to 3-OMG are much higher than those of controls.

Transfusion and transplantation of cryopreserved cells and tissues

The modern era of cryomedicine began in 1949 in London and developed world-wide in the second half of the 20th century based on the first report of a novel method of cryopreservation of sperm and erythrocytes using glycerol that was reported in 1949 and 1950 by Polge and Smith. In 1951 at Hradec Kralove, Czech. Klen initiated a "tissue bank" using his unique freeze-drying system. In 1964, the initial meeting of the Society for Cryobiology was organized by its first president. B. J. Luyet in Washington, DC. Cryobiology including cryopreservation and cryosurgery, contributed immense advances for clinical medicine. Cryomedicine will realize the goals of the New Millennium medicine: regeneration, plasticity, and minimally invasive therapy. I explained the first one, regeneration in this paper in detail. Cryomedicine involved subzero-temperatures to freeze the biological objects either for preservation or for destruction. Cryopreservation involves the cooling of the target biological materials to below the temperature of solidification by consumption of energy, through continuously supplying inert cryogens to attain the necessary cryo-temperatures by Joule-Thompson's effect. Therefore biological materials for cryopreservation should be carefully selected and once frozen purposefully kept in the frozen state to be used later to regenerate human cells, tissues and organs, and also to relaize "plasticity". Recently, lyophilization of human cells and tissues came back to the main street of cryopreservation to provide low cost economical and ecological banking of cells and tissues as a hope of the New Millennium. The first attempt of that was made by Prof. Dr. Rudolf Klen and his colleagues.Finally, physicians and related scientists who are going to be interested in cryomedicine should not worry about "freezing and thawing" as being time consuming and labor intensive, otherwise they will not share in the crucial benefits of cryomedicine.