Janus effect of antifreeze proteins on ice nucleation

On-demand imidazolidinyl urea-based tissue-like, self-healable, and antibacterial hydrogels for infectious wound care

Bacterial wound infections are a growing challenge in healthcare, posing severe risks like systemic infection, organ failure, and sepsis, with projections predicting over 10 million deaths annually by 2050. Antibacterial hydrogels, with adaptable extracellular matrix-like features, are emerging as promising solutions for treating infectious wounds. However, the antibacterial properties of most of these hydrogels are largely attributed to extrinsic agents, and their mechanisms of action remain poorly understood. Herein we introduce for the first time, modified imidazolidinyl urea (IU) as the polymeric backbone for developing tissue-like antibacterial hydrogels. As-designed hydrogels behave tissue-like mechanical features, outstanding antifreeze behavior, and rapid self-healing capabilities. Molecular dynamics (MD) simulation and density functional theory (DFT) calculation were employed to well-understand the extent of H-bonding and metal-ligand coordination to finetune hydrogels' properties. In vitro studies suggest good biocompatibility of hydrogels against mouse fibroblasts & human skin, lung, and red blood cells, with potential wound healing capacity. Additionally, the hydrogels exhibit good 3D printability and remarkable antibacterial activity, attributed to concentration dependent ROS generation, oxidative stress induction, and subsequent disruption of bacterial membrane. On top of that, in vitro biofilm studies confirmed that developed hydrogels are effective in preventing biofilm formation. Therefore, these tissue-mimetic hydrogels present a promising and effective platform for accelerating wound healing while simultaneously controlling bacterial infections, offering hope for the future of wound care.

Insight into the structure-activity relationship of thermal hysteresis activity of cod collagen peptides through peptidomics and bioinformatics approaches

To elucidate the correlation between variations in thermal hysteresis activity (THA) and the physicochemical properties and structure, antifreeze peptides (AFPs) of isolated fractions (CCP-1 and CCP-2) were characterized on based peptidomics and bioinformatics. The results revealed a positive correlation between the THA of cod collagen antifreeze peptide (CCAFP) and peptide chain length, isoelectric point, and hydrophobic amino acid content. Notably, the THA of CCP-1, which has higher alkaline amino acid content, was 2.60 °C at a concentration of 10 mg/mL, significantly higher than CCP (1.90 °C) and CCP-2 (2.27 °C). Glycine, proline, and valine were the vital amino acids to the formation of hydrogen bonds. Conversely, aspartic and glutamic acids at terminal regions of AFPs tended to introduce kinks in their structures. This distortion reduced binding sites for ice crystals, thereby decreasing their THA, providing a theory for understanding the physicochemical properties and structure of AFPs that influence their THA.

Instability of natural deep eutectic solvents (NADESs) induced by Amadori rearrangement and its effects on cryopreservation of yeast cells

Natural deep eutectic solvents (NADESs) showing higher cryoprotective effects are attracting concerns, because during the storage, system browning always occurs in aldose/amino acid-based NADESs, which generated brown substances remarkably weaken the cryoprotective effects. In this study, proline/glucose-based (PG) and proline/sorbitol-based (PS) NADESs were prepared, of which storage stability, browning profile, brown substance, and cryoprotective effects were investigated. Results showed that PG at molar ratios of 1:1, 2:1, and 3:1, as well as PS at 1:1, and 2:1 can form NADESs, among which only the PG-based ones could get browning after storage. The predominant brown substance was identified as 1-deoxy-1-L-proline-d-fructose (C11H19O7N, 278 m/z), which was subsequently verified to show cytotoxicity and decrease Saccharomyces cerevisiae cells viability after cryopreservation, suggesting that the brown substance could take a negative effect on cryopreservation. This study may help to attract more concerns to the storage and cryopreservation stabilities of the NADESs in food-related applications.

Scalable robust photothermal superhydrophobic coatings for efficient anti-icing and de-icing in simulated/real environments

Photothermal superhydrophobic coatings are supposed promising to prevent ice accumulation on infrastructures but often experience significant performance degradation in real icing conditions and lack mechanical robustness. Here, we report design of robust photothermal superhydrophobic coatings with three-tier hierarchical micro-/nano-/nanostructures by deposition of nanosized MOFs on natural attapulgite nanorods, fluorination, controlled phase separation of a hydrophobic adhesive and spraying assembly. Phase separation degree and adhesive content significantly influence the coatings' properties by regulating the structural parameters and morphology. In simulated/real icing environments, the coatings simultaneously show (i) high superhydrophobicity and stable Cassie-Baxter states due to their low-surface-energy, three-tier micro-/nano-/nanostructure, (ii) excellent photothermal effect primarily due to nanosized MOFs, and (iii) good mechanical robustness by the phase-separated adhesive, reinforcement with attapulgite and the coatings' self-similar structure. Accordingly, combined with low thermal conductivity, the coatings exhibit remarkable anti-icing/frosting (e.g., no freezing in at least 150 min and almost free of frost in 25 min) and de-icing/frosting performances (e.g., fast de-icing in 12.7 min and fast de-frosting in 16.7 min) in such environments. Furthermore, we realize large-scale preparation of the coatings at reasonable costs. The coatings have great application potential for anti-icing and de-icing in the real world by efficiently using natural sunlight.

Efficient Inhibition of Ice Recrystallization During Frozen Storage: Based on the Diffusional Suppression Effect of Silk Fibroin

Effectively controlling ice recrystallization (IR) during the frozen storage of food remains highly challenging. Inspired by the structural characteristics of antifreeze proteins in nature, silk fibroin (SF) derived from silk fibers has been developed. Through dual validation using the "splat" assay and "sucrose sandwich" assay, the IR inhibition activity of SF at various concentrations was confirmed, revealing that its regular alternating hydrophilic/hydrophobic domains endow SF with the potential to inhibit the axial growth of single ice crystal and significantly reduce the average maximum crystal size by approximately 67%. Additionally, the quality stability of frozen muscle foods treated with SF was comprehensively evaluated. In stark contrast to traditional commercial antifreeze agents (4% sucrose and 4% sorbitol), prepared steaks with the addition of 2% SF maintained rich juiciness and excellent color acceptability over a three-month frozen storage period. Thus, SF holds promise as a potential protective agent for frozen muscle foods, enhancing their quality during storage.

Development of Macromolecular Cryoprotectants for Cryopreservation of Cells

Cryopreservation is a common way for long-term storage of therapeutical proteins, erythrocytes, and mammalian cells. For cryoprotection of these biosamples to keep their structural integrity and biological activities, it is essential to incorporate highly efficient cryoprotectants. Currently, permeable small molecular cryoprotectants such as glycerol and dimethyl sulfoxide dominate in cryostorage applications, but they are harmful to cells and human health. As acting in the extracellular space, membrane-impermeable macromolecular cryoprotectants, which exert remarkable membrane stabilization against cryo-injury and are easily removed post-thaw, are promising candidates with biocompatibility and feasibility. Water-soluble hydroxyl-containing polymers such as poly(vinyl alcohol) and polyol-based polymers are potent ice recrystallization inhibitors, while polyampholytes, polyzwitterions, and bio-inspired (glyco)polypeptides can significantly increase post-thaw recovery with reduced membrane damages. In this review, the synthetic macromolecular cryoprotectants are systematically summarized based on their synthesis routes, practical utilities, and cryoprotective mechanisms. It provides a valuable insight in development of highly efficient macromolecular cryoprotectants with valid ice recrystallization inhibition activity for highly efficient and safe cryopreservation of cells.

Synergistic Effects of the Superhydrophilic and Superhydrophobic Components on the Antifreezing Performances of Latex Particles and Anti-Icing Properties of Latex Films

The development of new materials for antifreezing and anti-icing applications is a big challenge in industry and academic area. Inspired by the antifreeze proteins, latex particles with superhydrophilic zwitterionic shells and superhydrophobic cores are synthesized by reversible addition-fragmentation chain transfer emulsion polymerization, and the applications of the latex particles in antifreezing and anti-icing applications are investigated. In antifreezing study, the critical aggregate temperature (CAT) of the latex particles decreases, and the separation of the melting and freezing temperature of ice increases with the particle concentration. Enzyme molecules can be cryopreserved in the particle solution, and their bioactivities are well maintained. Latex particles are casted into latex films with dynamic surfaces. Anti-icing performances, including antifrosting properties, freezing delay time, and ice adhesion strengths, are studied; and the water-treated latex films present stronger anti-icing properties than other films, due to the synergistic effects of the superhydrophilic and superhydrophobic components. In addition, latex particles with zwitterionic shells and poly(n-butyl methacrylate) cores, and latex particles with small molecular surfactant on the surfaces are synthesized. The antifreezing performances of the latex particles and anti-icing properties of the latex films are compared.

Biophysical evidence that frostbite is triggered on nanocrystals of biogenic magnetite in garlic cloves (Allium sativum)

Trace levels of biologically precipitated magnetite (Fe3O4) nanocrystals are present in the tissues of many living organisms, including those of plants. Recent work has also shown that magnetite nanoparticles are powerful ice nucleation particles (INPs) that can initiate heterogeneous freezing in supercooled water just below the normal melting temperature. Hence there is a strong possibility that magnetite in plant tissues might be an agent responsible for triggering frost damage, even though the biological role of magnetite in plants is not understood. To test this hypothesis, we investigated supercooling and freezing mortality in cloves of garlic (Allium sativum), a species which is known to have moderate frost resistance. Using superconducting magnetometry, we detected large numbers of magnetite INPs within individual cloves. Oscillating magnetic fields designed to torque magnetite crystals in situ and disturb the ice nucleating process produced significant effects on the temperature distribution of supercooling, thereby confirming magnetite's role as an INP in vivo. However, weak oscillating fields increased the probability of freezing, whereas stronger fields decreased it, a result that predicts the presence of magnetite binding agents that are loosely attached to the ice nucleating sites on the magnetite crystals.

Higher molecular weight pectin inhibits ice crystal growth and its effect on the microstructural and physical properties of pectin cryogels

Understanding the formation of ice crystals is essential for tailoring the microstructure and physical properties of cryogels. This study investigated the effects and mechanisms of pectin molecular weight (Mw) on impacting ice crystal formation. Pectin fractions various Mw (10.13-212.20 kDa) were prepared by hydrothermal method. The solution of high Mw pectin fractions exhibited higher contact angle, lower water freedom, and stronger adsorption of water molecules. The splat experiment and molecular dynamic (MD) results confirmed that higher Mw pectin have stronger ice crystal growth inhibition activity than lower Mw pectin. Furthermore, the pore size distribution of the cryogel increased from 98-203 μm to 105-267 μm as the molecular weight decreased from 212.2 kDa to 121.0 kDa. Additionally, in the higher Mw pectin cryogel, stronger mechanical strength was observed. These findings suggested that changing the molecular weight of pectin has the potential to regulate the ice crystal growth, microstructure and physical properties of frozen products.

Characterizing the Orderliness of Interfacial Water through Stretching Vibrations

Spatial orderliness, which is the orderly structure of molecules, differs significantly between interfacial water and bulk water. Understanding this property is essential for various applications in both natural and engineered environments. However, the subnanometer thickness of interfacial water presents challenges for direct and rapid characterization of its structural orderliness. Herein, through molecular dynamics simulations and infrared spectral analysis of interfacial water in a graphene slit pore, we reveal a hyperbolic tangent relationship between the water ordering and its O-H stretching information in the infrared spectrum. Specifically, O-H symmetric stretching dominated in the highly ordered water structure, while a transition to the asymmetric stretching corresponded to an increase in the degree of disorder. Thus, the O-H stretching behavior could serve as a useful and quick assessment of the orderliness of interfacial water. This work provided insights into interfacial water's unique molecular network and structural dynamics and identified the stretching vibrations' key role in its degree of order, providing insight for fields such as nanotechnology, biology, and material science.

Interfacial Ice Density Fluctuations Inform Surface Ice-Philicity

The propensity of a surface to nucleate ice or bind to ice is governed by its ice-philicity─its relative preference for ice over liquid water. However, the relationship between the features of a surface and its ice-philicity is not well understood, and for surfaces with chemical or topographical heterogeneity, such as proteins, their ice-philicity is not even well-defined. In the analogous problem of surface hydrophobicity, it has been shown that hydrophobic surfaces display enhanced low water-density (vapor-like) fluctuations in their vicinity. To interrogate whether enhanced ice-like fluctuations are similarly observed near ice-philic surfaces, here we use molecular simulations and enhanced sampling techniques. Using a family of model surfaces for which the wetting coefficient, k, has previously been characterized, we show that the free energy of observing rare interfacial ice-density fluctuations decreases monotonically with increasing k. By utilizing this connection, we investigate a set of fcc systems and find that the (110) surface is more ice-philic than the (111) or (100) surfaces. By additionally analyzing the structure of interfacial ice, we find that all surfaces prefer to bind to the basal plane of ice, and the topographical complementarity of the (110) surface to the basal plane explains its higher ice-philicity. Using enhanced interfacial ice-like fluctuations as a measure of surface ice-philicity, we then characterize the ice-philicity of chemically heterogeneous and topologically complex systems. In particular, we study the spruce budworm antifreeze protein (sbwAFP), which binds to ice using a known ice-binding site (IBS) and resists engulfment using nonbinding sites of the protein (NBSs). We find that the IBS displays enhanced interfacial ice-density fluctuations and is therefore more ice-philic than the two NBSs studied. We also find the two NBSs are similarly ice-phobic. By establishing a connection between interfacial ice-like fluctuations and surface ice-philicity, our findings thus provide a way to characterize the ice-philicity of heterogeneous surfaces.

The Valence-Dependent Activity of Colloidal Molecules as Ice Recrystallization Inhibitors

Inspired by advances in cryopreservation techniques, which are essential for modern biomedical applications, there is a special interest in the ice recrystallization inhibition (IRI) of the antifreeze protein (AFPs) mimics. There are in-depth studies on synthetic materials mimicking AFPs, from simple molecular structure levels to complex self-assemblies. Herein, we report the valence-dependent IRI activity of colloidal organic molecules (CMs). The CMs were prepared through polymerization-induced particle-assembly (PIPA) of the ABC-type triblock terpolymer of poly(acryloxyethyl trimethylammonium chloride)-b-poly(benzyl acrylate)-b-poly(diacetone acrylamide) (PATAC-b-PBzA-b-PDAAM) at high monomer conversions. Stabilized by the cationic block of PATAC, the strong intermolecular H-bonding and incompatibility of the PDAAM block with PBzA contributed to the in situ formation of Janus particles (AX1) beyond the initial spherical seed particles (AX0), as well as the high valency clusters of linear AX2 and trigonal AX3. Their distribution was controlled mainly by the polymerization degrees (DPs) of PATAC and PDAAM blocks. IRI activity results of the CMs suggest that the higher fraction of AX1 results in the better IRI activity. Increasing the fraction of AX1 from 27% to 65% led to a decrease of the mean grain size from 39.8% to 10.9% and a depressed growth rate of ice crystals by 58%. Moreover, by replacing the PDAAM block with the temperature-responsive one of poly(N-isopropylacrylamide) (PNIPAM), temperature-adjustable IRI activity was observed, which is well related to the reversible transition of AX0 to AX1, providing a new idea for the molecular design of amphiphilic polymer nanoparticle-based IRI activity materials.

On the engulfment of antifreeze proteins by ice

Antifreeze proteins (AFPs) are remarkable biomolecules that suppress ice formation at trace concentrations. To inhibit ice growth, AFPs must not only bind to ice crystals, but also resist engulfment by ice. The highest supercooling, [Formula: see text], for which AFPs are able to resist engulfment is widely believed to scale as the inverse of the separation, [Formula: see text], between bound AFPs, whereas its dependence on the molecular characteristics of the AFP remains poorly understood. By using specialized molecular simulations and interfacial thermodynamics, here, we show that in contrast with conventional wisdom, [Formula: see text] scales as [Formula: see text] and not as [Formula: see text]. We further show that [Formula: see text] is proportional to AFP size and that diverse naturally occurring AFPs are optimal at resisting engulfment by ice. By facilitating the development of AFP structure-function relationships, we hope that our findings will pave the way for the rational design of AFPs.

Glycosylated Polyhydroxyproline Is a Potent Antifreeze Molecule

Molecules that inhibit the growth of ice crystals are highly desirable for applications in building materials, foods, and agriculture. Antifreezes are particularly essential in biomedicine for tissue banking, yet molecules currently in use have known toxic effects. Antifreeze glycoproteins have evolved naturally in polar fish species living in subzero climates, but practical issues with collection and purification have limited their commercial use. Here, we present a synthetic strategy using polymerization of amino acid N-carboxyanhydrides to produce polypeptide mimics of these potent natural antifreeze proteins. We investigated a set of mimics with varied structural properties and identified a glycopolypeptide with potent ice recrystallization inhibition properties. We optimized for molecular weight, characterized their conformations, and verified their cytocompatibility in a human cell line. Overall, we present a material that will have broad applications as a biocompatible antifreeze.

Two rhombic ice phases from aqueous salt solutions under graphene confinement

Water exhibits rich ice phases depending upon its respective formation conditions, and in particular, the two-dimensional ice with nonhexagonal symmetry adsorbed on solids relates to the exceptional arrangement of water molecules. Despite extensive reporting of two-dimensional ice on various solid surfaces, the geometry and thermodynamics of ice formation from an aqueous salt solution are still unknown. In this Letter, we show the formation of single- and two-phase mixed two-dimensional rhombic ice from aqueous salt solutions with different concentrations under strong compressed confinement of graphene at ambient temperature by using classical molecular dynamics simulations and first-principles calculations. The two rhombic ice phases exhibit identical geometry and thermodynamic properties, but different projections of the oxygen atoms against solid surface symmetry, where they relate to the stable and metastable arrangements of water molecules confined between two graphene layers. A single-phase rhombic ice would grow from the confined saturated aqueous solutions since the previously stable rhombic molecular arrangement becomes an unstable high-energy state by introducing salt ions nearby. Our result reveals different rhombic ice phases growing from pure water and aqueous solutions, highlighting the deciding role of salt ions in the ice formation process due to their common presence in liquids.

Facile Preparation of Impalement Resistant, Mechanically Robust and Weather Resistant Photothermal Superhydrophobic Coatings for Anti-/De-icing

Photothermal superhydrophobic coatings hold great promise in addressing the limitations of conventional superhydrophobic anti-icing coatings. However, developing such coatings with excellent impalement resistance, mechanical robustness and weather resistance remains a significant challenge. Here, we report facile preparation of robust photothermal superhydrophobic coatings with all the above advantages. The coatings were prepared by spraying a dispersion consisting of fluorinated silica nanoparticles, a silicone-modified polyester adhesive and photothermal carbon black nanoparticles onto Al alloy plates followed by thermal curing. Thermal curing caused migration of perfluorodecyl polysiloxane from within the coatings to the surface, effectively maintaining a low surface energy despite the presence of the adhesive. Therefore, combined with the hierarchical micro-/nanostructure, dense yet rough nanostructure, adhesion of the adhesive and chemically inert components, the coatings exhibited remarkable superhydrophobicity, impalement resistance, mechanical robustness and weather resistance. Furthermore, the coatings demonstrated excellent photothermal effect even in the -10 °C, 80 % relative humidity and weak sunlight (0.2 sun) environment. Consequently, the coatings showed excellent passive anti-icing and active de-icing performance. Moreover, the coatings have good generalizability and scalability. We are confident that this study will accelerate the practical implementation of photothermal superhydrophobic coatings.

Controlled condensation by liquid contact-induced adaptations of molecular conformations in self-assembled monolayers

Surface condensation control strategies are crucial but commonly require relatively tedious, time-consuming, and expensive techniques for surface-chemical and topographical engineering. Here we report a strategy to alter surface condensation behavior without resorting to any molecule-type or topographical transmutations. After ultrafast contact of liquids with and removal from surfaces, the condensation rate and density of water droplets on the surfaces decrease, the extent of which is positively correlated with the polarity of the liquid and the duration of contact. The liquid contact-induced condensation rate/density decrease (LCICD) can be attributed to the decrease of nucleation site density resulted from the liquid contact-induced adaption of surface molecular conformation. Based on this, we find that LCICD is applicable to various surfaces, on condition that there are flexible segments capable of shielding at least part of nucleation sites through changing the conformation under liquid contact induction. Leveraging the LCICD effect, we achieve erasable information storage on diverse substrates. Furthermore, our strategy holds promise for controlling condensation of other substances since LCICD is not specific to the water condensation process.

Extended Temperature Range of the Ice-Binding Protein Activity

Ice-binding proteins (IBPs) are expressed in various organisms for several functions, such as protecting them from freezing and freeze injuries. Via adsorption on ice surfaces, IBPs depress ice growth and recrystallization and affect nucleation and ice shaping. IBPs have shown promise in mitigating ice growth under moderate supercooling conditions, but their functionality under cryogenic conditions has been less explored. In this study, we investigate the impact of two types of antifreeze proteins (AFPs): type III AFP from fish and a hyperactive AFP from an insect, the Tenebrio molitor AFP, in vitrified dimethylsulfoxide (DMSO) solutions. We report that these AFPs depress devitrification at -80 °C. Furthermore, in cases where devitrification does occur, AFPs depress ice recrystallization during the warming stage. The data directly demonstrate that AFPs are active at temperatures below the regime of homogeneous nucleation. This research paves the way for exploring AFPs as potential enhancers of cryopreservation techniques, minimizing ice-growth-related damage, and promoting advancements in this vital field.

Synthetic Antifreeze Glycoproteins with Potent Ice-Binding Activity

Antifreeze glycoproteins (AFGPs) are produced by extremophiles to defend against tissue damage in freezing climates. Cumbersome isolation from polar fish has limited probing AFGP molecular mechanisms of action and limited development of bioinspired cryoprotectants for application in agriculture, foods, coatings, and biomedicine. Here, we present a rapid, scalable, and tunable route to synthetic AFGPs (sAFGPs) using N-carboxyanhydride polymerization. Our materials are the first mimics to harness the molecular size, chemical motifs, and long-range conformation of native AFGPs. We found that ice-binding activity increases with chain length, Ala is a key residue, and the native protein sequence is not required. The glycan structure had only minor effects, and all glycans examined displayed antifreeze activity. The sAFGPs are biodegradable, nontoxic, internalized into endocytosing cells, and bystanders in cryopreservation of human red blood cells. Overall, our sAFGPs functioned as surrogates for bona fide AFGPs, solving a long-standing challenge in accessing natural antifreeze materials.

Tailoring microstructure and mechanical properties of pectin cryogels by modulate intensity of ionic interconnection

Porous morphology and mechanical properties determine the applications of cryogels. To understand the influence of the ionic network on the microstructure and mechanical properties of pectin cryogels, we prepared low-methoxyl pectin (LMP) cryogels with different Ca2+ concentrations (measured as R-value, ranging from 0 to 2) through freeze-drying (FD). Results showed that the R-values appeared to be crucial parameters that impact the pore morphology and mechanical characteristics of cryogels. It is achieved by altering the network stability and water state properties of the cryogel precursor. Cryogel precursors with a saturated R-value (R = 1) produced a low pore diameter (0.12 mm) microstructure, obtaining the highest crispness (15.00 ± 1.85) and hardness (maximum positive force and area measuring 2.36 ± 0.31 N and 12.30 ± 1.57 N·s respectively). Hardness showed a negative correlation with Ca2+ concentration when R ≤ 1 (-0.89), and a similar correlation with the porosity of the gel network when R ≥ 1 (-0.80). Given the impacts of crosslinking on the pore structure, it is confirmed that the pore diameter can be designed between 56.24 and 153.58 μm by controlling R-value in the range of 0-2.

Advances in single ice crystal shaping materials: From nature to synthesis and applications in cryopreservation

Antifreeze (glyco) proteins [AF(G)Ps], which are widely present in various extreme microorganisms, can control the formation and growth of ice crystals. Given the significance of cryogenic technology in biomedicine, climate science, electronic energy, and other fields of research, scientists are quite interested in the development and synthesis high-efficiency bionic antifreeze protein materials, particularly to reproduce their dynamic ice shaping (DIS) characteristics. Single ice crystal shaping materials, a promising class of ice-controlling materials, can alter the morphology and growth rate of ice crystals at low temperatures. This review aims to highlight the development of single ice crystal shaping materials and provide a brief comparison between a series of natural and bionic synthetic materials with DIS ability, which include AF(G)Ps, polymers, salts, and nanomaterials. Additionally, we summarize their applications in cryopreservation. Finally, this paper presents the current challenges and prospects encountered in developing high-efficiency and practical single ice crystal shaping materials. STATEMENT OF SIGNIFICANCE: The formation and growth of ice crystals hold a significant importance to an incredibly broad range of fields. Therefore, the design and fabrication of the single ice crystal shaping materials have gained the increasing popularity due to its key role in dynamic ice shaping (DIS) characteristics. Especially, single ice crystal shaping materials are considered one of the most promising candidates as ice inhibitors, presenting tremendous prospects for enhancing cryopreservation. In this work, we focus on the molecular characteristics, structure-function relationships, and DIS mechanisms of typical natural and biomimetic synthetic materials. This review may provide inspiration for the design and preparation of single ice crystal shaping materials and give guidance for the development of effective cryopreservation agent.

Probing the critical nucleus size in tetrahydrofuran clathrate hydrate formation using surface-anchored nanoparticles

Controlling the formation of clathrate hydrates is crucial for advancing hydrate-based technologies. However, the microscopic mechanism underlying clathrate hydrate formation through nucleation remains poorly elucidated. Specifically, the critical nucleus, theorized as a pivotal step in nucleation, lacks empirical validation. Here, we report uniform nanoparticles, e.g., graphene oxide (GO) nanosheets and gold or silver nanocubes with controlled sizes, as nanoprobes to experimentally measure the size of the critical nucleus of tetrahydrofuran (THF) clathrate hydrate formation. The capability of the nanoparticles in facilitating THF clathrate hydrate nucleation displays generally an abrupt change at a nanoparticle-size-determined specific supercooling. It is revealed that the free-energy barrier shows an abrupt change when the nanoparticles have an approximately the same size as that of the critical nucleus. Thus, it is inferred that THF clathrate hydrate nucleation involves the creation of a critical nucleus with its size being inversely proportional to the supercooling. By proving the existence and determining the supercooling-dependent size of the critical nucleus of the THF clathrate hydrates, this work brings insights in the microscopic pictures of the clathrate hydrate nucleation.

Paradoxical effects on ice nucleation are intrinsic to a small winter flounder antifreeze protein

Antifreeze proteins (AFPs) bind to ice in solutions, resulting in non-colligative freezing point depression; however, their effects on ice nucleation are not well understood. The predominant plasma AFP of winter flounder (Pseudopleuronectes americanus) is AFP6, which is an amphiphilic alpha helix. In this study, AFP6 and modified constructs were produced as fusion proteins in Escherichia coli, subjected to proteolysis when required and purified prior to use. AFP6 and its recombinant fusion precursor generated similar thermal hysteresis and bipyramidal ice crystals, whereas an inactive mutant AFP6 produced hexagonal crystals and no hysteresis. Circular dichroism spectra of the wild-type and mutant AFP6 were consistent with an alpha helix. The effects of these proteins on ice nucleation were investigated alongside non-AFP proteins using a standard droplet freezing assay. In the presence of nucleating AgI, modest reductions in the nucleation temperature occurred with the addition of mutant AFP6, and several non-AFPs, suggesting non-specific inhibition of AgI-induced ice nucleation. In these experiments, both AFP6 and its recombinant precursor resulted in lower nucleation temperatures, consistent with an additional inhibitory effect. Conversely, in the absence of AgI, AFP6 induced ice nucleation, with no other proteins showing this effect. Nucleation by AFP6 was dose-dependent, reaching a maximum at 1.5 mM protein. Nucleation by AFP6 also required an ice-binding site, as the inactive mutant had no effect. Furthermore, the absence of nucleation by the recombinant precursor protein suggested that the fusion moiety was interfering with the formation of a surface capable of nucleating ice.

Ice nucleation proteins self-assemble into large fibres to trigger freezing at near 0 °C

In nature, frost can form at a few degrees below 0 °C. However, this process requires the assembly of tens of thousands of ice-like water molecules that align together to initiate freezing at these relatively high temperatures. Water ordering on this scale is mediated by the ice nucleation proteins (INPs) of common environmental bacteria like Pseudomonas syringae and Pseudomonas borealis. However, individually, these 100 kDa proteins are too small to organize enough water molecules for frost formation, and it is not known how giant, megadalton-sized multimers, which are crucial for ice nucleation at high sub-zero temperatures, form. The ability of multimers to self-assemble was suggested when the transfer of an INP gene into Escherichia coli led to efficient ice nucleation. Here, we demonstrate that a positively charged subdomain at the C-terminal end of the central β-solenoid of the INP is crucial for multimerization. Truncation, relocation, or change of the charge of this subdomain caused a catastrophic loss of ice nucleation ability. Cryo-electron tomography of the recombinant E. coli showed that the INP multimers form fibres that are ~5 nm across and up to 200 nm long. A model of these fibres as an overlapping series of antiparallel dimers can account for all their known properties and suggests a route to making cell-free ice nucleators for biotechnological applications.

Coexisting with Ice Crystals: Cryogenic Preservation of Muscle Food─Mechanisms, Challenges, and Cutting-Edge Strategies

Cryopreservation, one of the most effective preservation methods, is essential for maintaining the safety and quality of food. However, there is no denying the fact that the quality of muscle food deteriorates as a result of the unavoidable production of ice. Advancements in cryoregulatory materials and techniques have effectively mitigated the adverse impacts of ice, thereby enhancing the standard of freezing preservation. The first part of this overview explains how ice forms, including the theoretical foundations of nucleation, growth, and recrystallization as well as the key influencing factors that affect each process. Subsequently, the impact of ice formation on the eating quality and nutritional value of muscle food is delineated. A systematic explanation of cutting-edge strategies based on nucleation intervention, growth control, and recrystallization inhibition is offered. These methods include antifreeze proteins, ice-nucleating proteins, antifreeze peptides, natural deep eutectic solvents, polysaccharides, amino acids, and their derivatives. Furthermore, advanced physical techniques such as electrostatic fields, magnetic fields, acoustic fields, liquid nitrogen, and supercooling preservation techniques are expounded upon, which effectively hinder the formation of ice crystals during cryopreservation. The paper outlines the difficulties and potential directions in ice inhibition for effective cryopreservation.

Calixarene-based cryoprotectants for ice recrystallization inhibition and cell cryopreservation

The development of new cryoprotectants for cryopreservation of cells has attracted considerable interest. Herein, five calixarene-based CPAs (SC4A, S-S-C4A, S-SO2-C4A, SBAC4A, and CAC4A) were developed, and their IRI activity, DIS property and cryoprotective effect were studied. SBAC4A with a sulphobetaine zwitterion and SC4A with sulfo group modification possessed better cryoprotective effects than the other calixarene-based CPAs, especially for SBAC4A with the enhanced cell viabilities of 16.16 ± 1.78%, 12.60 ± 1.15% and 14.90 ± 1.66% against MCF-7, hucMSCs and A549 cells, respectively. This result provides a supramolecular principle for developing novel CPAs with consideration of the factors of hydrogen bonding, the macromolecular crowding principle and the three-dimensional (3D) structure.

Uniformly Hybrid Surface Containing Adjustable Hydrophobic/Hydrophilic Components Obtained by Programmed Strain for Synergistic Anti-Icing

Sufficient efforts have been put into the design of anti-icing materials to eliminate the icing hazard. Among the currently approved anti-icing concepts, hydrophilic/hydrophobic hybrid anti-icing materials inspired by antifreeze proteins show excellent properties in inhibiting ice nucleation, inhibiting ice crystal growth, and reducing ice adhesion. However, it is still a great challenge to accurately regulate the hydrophilic and hydrophobic hybrid components of the coating surface to clarify the synergistic mechanism. This work proposes a strain-manipulated surface modification strategy, and an anti-icing coating with adjustable hydrophilic/hydrophobic hybrid components prepared by combining chemical vapor deposition and siloxane chemistry is obtained. According to the ice resistance experiment at -15 °C, the performance of anti-icing is closely related to the proportion of hydrophilic and hydrophobic hybrids. The icing delay time and ice adhesion strength of the material with the optimal hydrophilic/hydrophobic components are 280 s and 18.6 kPa, respectively. These unique properties can be attributed to the synergistic effect of hydrophilic and hydrophobic structures on the regulation of interfacial water.

Core-Shell Microfiber Encapsulation Enables Glycerol-Free Cryopreservation of RBCs with High Hematocrit

Cryopreservation of red blood cells (RBCs) provides great potential benefits for providing transfusion timely in emergencies. High concentrations of glycerol (20% or 40%) are used for RBC cryopreservation in current clinical practice, which results in cytotoxicity and osmotic injuries that must be carefully controlled. However, existing studies on the low-glycerol cryopreservation of RBCs still suffer from the bottleneck of low hematocrit levels, which require relatively large storage space and an extra concentration process before transfusion, making it inconvenient (time-consuming, and also may cause injury and sample lose) for clinical applications. To this end, we develop a novel method for the glycerol-free cryopreservation of human RBCs with a high final hematocrit by using trehalose as the sole cryoprotectant to dehydrate RBCs and using core-shell alginate hydrogel microfibers to enhance heat transfer during cryopreservation. Different from previous studies, we achieve the cryopreservation of human RBCs at high hematocrit (> 40%) with high recovery (up to 95%). Additionally, the washed RBCs post-cryopreserved are proved to maintain their morphology, mechanics, and functional properties. This may provide a nontoxic, high-efficiency, and glycerol-free approach for RBC cryopreservation, along with potential clinical transfusion benefits.

Ice nucleation proteins self-assemble into large fibres to trigger freezing at near 0 °C

In nature, frost can form at a few degrees below 0 °C. However, this process requires the assembly of tens of thousands of ice-like water molecules that align together to initiate freezing at these relatively high temperatures. Water ordering on this scale is mediated by the ice nucleation proteins of common environmental bacteria like Pseudomonas syringae and P. borealis. However, individually, these 100-kDa proteins are too small to organize enough water molecules for frost formation, and it is not known how giant, megadalton-sized multimers, which are crucial for ice nucleation at high sub-zero temperatures, form. The ability of multimers to self-assemble was suggested when the transfer of an ice nucleation protein gene into Escherichia coli led to efficient ice nucleation. Here we demonstrate that a positively-charged sub-domain at the C-terminal end of the central beta-solenoid of the ice nucleation protein is crucial for multimerization. Truncation, relocation, or change of the charge of this subdomain caused a catastrophic loss of ice nucleation ability. Cryo-electron tomography of the recombinant E. coli showed that the ice nucleation protein multimers form fibres that are ~ 5 nm across and up to 200 nm long. A model of these fibres as an overlapping series of antiparallel dimers can account for all their known properties and suggests a route to making cell-free ice nucleators for biotechnological applications.

Natural deep eutectic solvent: A promising eco-friendly food bio-inspired antifreezing

Bio-antifreezing is a green and highly effective strategy to inhibit ice nucleation. Bio-inspired antifreezing faces the severe challenges of significant toxicity and complex manufacturing procedures. Bio-inspired antifreezing natural deep eutectic solvent (Ba-NADES) could be an efficient and low or no-toxicity approach for the frozen food industry. Ba-NADES form a strong hydrogen bond network system under cold conditions, capably reducing the melting point of the system below the freezing point and effectively inhibiting ice growth. It has efficaciously alleviated freeze injury by Ba-NADES. The review highlights the current strategies of bio-inspired antifreezing, cold resistance behavior in organisms, and the existing applications of Ba-NADES. It updated information concerning their mechanisms for antifreezing. It emphasizes that the role of water on the antifreezing quality of NADES is worthy of further investigation for more extensive food applications. This work will provide a comprehensive overview of NADES antifreezing.

Biomimetic Structural Proteins: Modular Assembly and High Mechanical Performance

Protein-based biomaterials attract growing interests due to their encoded and programmable robust mechanical properties, superelasticity, plasticity, shape adaptability, excellent interfacial behavior, etc., derived from sequence-guided backbone structures, particularly compared to chemically synthetic counterparts in materials science and biomedical engineering. For example, protein materials have been successfully fabricated as (1) artificial implants (man-made tendons, cartilages, or dental tissues), due to programmable chemistry and biocompatibility; (2) smart biodevices with temperature/light-response and self-healing effects; and (3) impact resistance materials having great mechanical performance due to biomimetics. However, the existing method of regenerating protein materials from natural sources has two critical issues, low yield and structural damage, making it unable to meet demands. Therefore, it is crucial to develop an alternative strategy for fabricating protein materials. Heterologous expression of natural proteins with a modular assembly approach is an effective strategy for material preparation. Standardized, easy-to-assemble protein modules with specific structures and functions are developed through experimental and computational tools based on natural functional protein sequences. Through recombination and heterologous expression, these artificial protein modules become keys to material fabrication. Undergoing an assembly process similar to supramolecular self-assembly of proteins in cells, biomimetic modules can be fabricated for formation of macroscopic materials such as fibers and adhesives. This strategy inspired by synthetic biology and supramolecular chemistry is important for improving target protein yields and assembly integrity. It also preserves and optimizes the mechanical functions of structural proteins, accelerating the design and fabrication of artificial protein materials.In this Account, we overview recent studies on fabricating biomimetic protein materials to elucidate the concept of modular assembly. We discuss the design of biomimetic structural proteins at the molecular level, providing a wealth of details determining the bulk properties of materials. Additinally, we describe the modular self-assembly and assembly driven by inducing molecules, and mechanical properties and applications of resulting fibers. We used these strategies to develop fiber materials with high tensile strength, high toughness, and properties such as anti-icing and high-temperature resistance. We also extended this approach to design protein-based adhesives with ultra-strong adhesion, biocompatibility, and biodegradability for surgical applications such as wound sealing and healing. Other protein materials, including films and hydrogels, have been developed through chemical assembly routes. Finally, we describe exploiting synthetic biology and chemistry to overcome bottlenecks in structural protein modular design, biosynthesis, and material assembly and our perspectives for future development in structural biomaterials.

Engineered Compounds to Control Ice Nucleation and Recrystallization

One of the greatest concerns in the subzero storage of cells, tissues, and organs is the ability to control the nucleation or recrystallization of ice. In nature, evidence of these processes, which aid in sustaining internal temperatures below the physiologic freezing point for extended periods of time, is apparent in freeze-avoidant and freeze-tolerant organisms. After decades of studying these proteins, we now have easily accessible compounds and materials capable of recapitulating the mechanisms seen in nature for biopreser-vation applications. The output from this burgeoning area of research can interact synergistically with other novel developments in the field of cryobiology, making it an opportune time for a review on this topic.

Inhibition of Defect-Induced Ice Nucleation, Propagation, and Adhesion by Bioinspired Self-Healing Anti-Icing Coatings

Anti-icing coatings on outdoor infrastructures inevitably suffer from mechanical injuries in numerous icing scenarios such as hailstorms, sandstorms, impacts of foreign objects, and icing-deicing cycles. Herein, the mechanisms of surface-defect-induced icing are clarified. At the defects, water molecules exhibit stronger adsorption and the heat transfer rate increases, accelerating the condensation of water vapor as well as ice nucleation and propagation. Moreover, the ice-defect interlocking structure increases the ice adhesion strength. Thus, a self-healing (at -20 °C) antifreeze-protein (AFP)-inspired anti-icing coating is developed. The coating is based on a design that mimics the ice-binding and non-ice-binding sites in AFPs. It enables the coating to markedly inhibit ice nucleation (nucleation temperature < -29.4 °C), prevent ice propagation (propagation rate < 0.00048 cm²/s), and reduce ice adhesion on the surface (adhesion strength < 38.9 kPa). More importantly, the coating can also autonomously self-heal at -20 °C, as a result of multiple dynamic bonds in its structure, to inhibit defect-induced icing processes. The healed coating sustains high anti-icing and deicing performance even under various extreme conditions. This work reveals the in-depth mechanism of defect-induced ice formation as well as adhesion, and proposes a self-healing anti-icing coating for outdoor infrastructures.

A Tale of Two Foulants: The Coupling of Organic Fouling and Mineral Scaling in Membrane Desalination

Membrane desalination that enables the harvesting of purified water from unconventional sources such as seawater, brackish groundwater, and wastewater has become indispensable to ensure sustainable freshwater supply in the context of a changing climate. However, the efficiency of membrane desalination is greatly constrained by organic fouling and mineral scaling. Although extensive studies have focused on understanding membrane fouling or scaling separately, organic foulants commonly coexist with inorganic scalants in the feedwaters of membrane desalination. Compared to individual fouling or scaling, combined fouling and scaling often exhibits different behaviors and is governed by foulant-scalant interactions, resembling more complex but practical scenarios than using feedwaters containing only organic foulants or inorganic scalants. In this critical review, we first summarize the performance of membrane desalination under combined fouling and scaling, involving mineral scales formed via both crystallization and polymerization. We then provide the state-of-the-art knowledge and characterization techniques pertaining to the molecular interactions between organic foulants and inorganic scalants, which alter the kinetics and thermodynamics of mineral nucleation as well as the deposition of mineral scales onto membrane surfaces. We further review the current efforts of mitigating combined fouling and scaling via membrane materials development and pretreatment. Finally, we provide prospects for future research needs that guide the design of more effective control strategies for combined fouling and scaling to improve the efficiency and resilience of membrane desalination for the treatment of feedwaters with complex compositions.

Intrinsic Anti-Freezing and Unique Phosphorescence of Glassy Hydrogels with Ultrahigh Stiffness and Toughness at Low Temperatures

Most hydrogels become frozen at subzero temperatures, leading to degraded properties and limited applications. Cryoprotectants are massively employed to improve anti-freezing property of hydrogels; however, there are accompanied disadvantages, such as varied networks, reduced mechanical properties, and the risk of cryoprotectant leakage in aqueous conditions. Reported here is the glassy hydrogel having intrinsic anti-freezing capacity and excellent optical and mechanical properties at ultra-low temperatures. Supramolecular hydrogel of poly(acrylamide-co-methacrylic acid) with moderate water content (≈50 wt.%) and dense hydrogen-bond associations is in a glassy state at room temperature. Since hydrogen bonds become strengthened as the temperature decreases, this gel becomes stronger and stiffer, yet still ductile, with Young's modulus of 900 MPa, tensile strength of 30 MPa, and breaking strain of 35% at -45 °C. This gel retains high transparency even in liquid nitrogen. It also exhibits unique phosphorescence due to presence of carbonyl clusters, which is further enhanced at subzero temperatures. Further investigations elucidate that the intrinsic anti-freezing property is related to a fact that most water molecules are tightly bound and confined in the glassy matrix and become non-freezable. This correlation, as validated in several systems, provides a roadmap to develop intrinsic anti-freezing hydrogels for widespread applications at extreme conditions.

A Synergistic Combination of AuNRs and C Dots as a Multifunctional Material for Ice Recrystallization Inhibition and Rapid Rewarming

Robust platforms and advanced biocompatible materials having diverse performances are in tremendous demand for cryopreservation of biocells, which are greatly limited by the crystallization, formation, and growth of ice crystals. The fickle structure and the arduous extraction process of modern attainable antifreezing proteins cause fatal cryoinjury of the cells making it challenging to develop anti-icing materials. Thus, designing Au colloids is an effective way to combat cell-damaging concerns during the ice freezing-thawing process. Herein, we propose an emerging biomimetic hybrid nanomaterial (AuNR@SiO₂-CDs) prepared by combining the photoheating and rewarming controlling characteristics of carbon dots (CDs) and gold nanorods (AuNRs), respectively, via a SiO₂ scaffold that has an optimal aspect ratio of ∼4.4. The performance of the material is applied in the freezing and resuscitation of Hela cells. The typical linkage between the AuNR and CDs not only retains the stable structure but also possesses the symmetric functional characteristics of affirmative cryoprotectant materials and sustained low cytotoxicity of cell viability >90%. The cell recovery rate of the Hela cell is significantly improved to ∼60%, which is propped up to >4% higher by the laser irradiation dose. The above hybrid material is paving a path toward novel bionic antifreezing proteins and is envisioned for ice recrystallization inhibition and rapid rewarming.

New insight into the mechanism by which antifreeze peptides regulate the physiological function of Streptococcus thermophilus subjected to freezing stress

INTRODUCTION

Antifreeze peptides regulate the physiological functions of frozen cells and even their apoptosis; however, the mechanisms by which antifreeze peptides regulate these processes remain unclear, although the interactions between cell membranes and ice are well known to be important in this process.

OBJECTIVES

Our study aims to investigate how antifreeze peptides regulate cell physiological functions during the freezing process.

METHODS

We investigated the cryoprotective effect of rsfAFP on the physiological functions of S. thermophilus under freezing stress by measuring cellular metabolism activity, intracellular enzyme activity, cell membrane characterization, and cell apoptosis. The mechanism by which rsfAFP impacts S. thermophilus physiological functions under freezing stress was investigated using multispectral techniques and cryo-TEM.

RESULTS

We show that a recombinant antifreeze peptide (rsfAFP) interacts with the extracellular capsular polysaccharides and peptidoglycan of Streptococcus thermophilus and ice to cover the outer layer of the membrane, forming a dense protective layer that regulates the molecular structure of extracellular ice crystals, which results in reduced extracellular membrane damage, depressed apoptosis and increased intracellular metabolic activity. This interaction mechanism was indicated by the fact that S. thermophilus better maintained its permeability barrier, membrane fluidity, membrane structural integrity, and cytoplasmic membrane potential during freezing stress with rsfAFP treatment.

CONCLUSION

These results provide new insights into the mechanism by which rsfAFP regulates frozen cellphysiological functionsand apoptosis under freezing stress.

An Extreme-Environment-Resistant Self-Healing Anti-Icing Coating

Anti-icing coatings on outdoor infrastructures and transportations inevitably suffer from surface injuries, especially in extreme weather events (e.g., freezing weather or acid rain). The coating surface damage can result in anti-icing performance loss or even icing promotion. The development of anti-icing coatings that enables self-healing in extreme conditions is highly desired but still challenging. Herein, an extreme-environment-resistant self-healing anti-icing coating is developed by integrating fluorinated graphene (FG) into a supramolecular polymeric matrix. The coating exhibits both anti-icing and deicing performance (ice nucleation temperature is ≈-30.3 °C; ice shear strength is ≈48.7 kPa), mainly attributable to the hydrophobic FG and silicone-based supramolecular material. Notably, owing to the crosslinking polymeric network with various dynamic bonds, this coating can sustain anti-icing/deicing performance after autonomous self-healing under harsh conditions including low temperature (-20 °C), strong acid (pH = 0), and strong alkali (pH = 14) environments. This coating paves the way to meet the anti-icing demand in open air, especially for the infrastructures in polar regions or acid/alkali environments.

Inhibiting ice recrystallization by amyloid protein fibrils

Ice recrystallization is harmful to the quality of frozen foods and the cryopreservation of cells and biological tissues, requiring biocompatible materials with ice recrystallization inhibition (IRI) activity. Emerging studies have associated IRI activity with amphiphilic structures. We propose amphiphilic amyloid protein fibrils (APFs) may be IRI-active. APFs were prepared from whey protein isolate (WPI) in water (W-APFs) and in trifluoroethanol (TFE-APFs). W-APFs and TFE-APFs were more IRI-active than WPI over a concentration range of 2.5-10.0 mg/mL. Both APFs showed stronger IRI activity at pH 3.0 than at pH 5.0, 7.0, and 10.0, which was ascribed to the effect of water dispersibility and fibril length. The reduced IRI activity of the two APFs with increasing NaCl content was caused by fibril aggregation. Ice binding by APFs was absent or very weak. Ordered water was observed for the two APFs, which might be essential for IRI activity. Our findings may lead to the use of APFs as novel ice recrystallization inhibitors.

Microcurvature Controllable Metal-Organic Framework Nanoagents Capable of Ice-Lattice Matching for Cellular Cryopreservation

Ice-binding proteins (IBPs) produced by psychrophilic organisms to adapt for the survival of psychrophiles in subzero conditions have received illustrious interest as a cryopreservation agent required for cells and tissues to completely recover after freezing/thawing. Depressing water-freezing point and avoiding ice-crystal growth affect their activities which are closely related to the presence of ice crystal well-matched binding moiety. The interaction of IBPs with ice and water is critical in enhancing their freeze avoidance against cell or tissue damage. Metal-organic frameworks (MOFs) with a controllable lattice at the molecular level and a size at the nanometer scale can offer periodically ordered ice-binding sites by modifying organic linkers and controlling microcurvature at the ice surface. Herein, zirconium (Zr)-based MOF-801 nanoparticles (NPs) with good biocompatibility were used as a cryoprotectant that is well dispersed and colloidal-stable in an aqueous solution. The MOF NP size was precisely controlled, and 10, 35, 100, and 250 nm NPs were prepared. The specific IBPs-mimicking pendants (valine and threonine) were simply introduced into the MOF NP-surface through the acrylate-based functionalization to endow with hydrophilic and hydrophobic dualities. When small-sized MOF-801 NPs were attached to ice, they confined ice growth in high curvature between the adsorption sites because of the decreased radius of the convex area of the growth region, leading to highly enhanced ice recrystallization inhibition (IRI). Surface-functionalized MOF NPs could increase the number of anchored clathrate water molecules with hydrophilic/hydrophobic balance of the ice-binding moiety, effectively inhibiting ice growth. The MOF-801 NPs were biocompatible with various cell lines regardless of concentration or NP surface-functionalization, whereas the smaller-sized surface-functionalized NPs showed a good cell recovery rate after freezing/thawing by induction of IRI. This study provides a strategy for the fabrication of low-cost, high-volume antifreeze nanoagents that can extend useful applications to organ transplantation, cord blood storage, and vaccines/drugs.

Ice recrystallization inhibition activity in bile salts

Ice recrystallization inhibitors are novel cryoprotective agents that can reduce the freezing damage of cells, tissues, and organs in cryopreservation. To date, potent ice recrystallization inhibition (IRI) activity has been found on antifreeze (glyco)proteins, polymers, nanomaterials, and a limited number of chemically synthesized small molecules. This paper reports a relatively potent IRI activity on a group of small biological molecules - bile salts. The IRI activity increased as the number of hydroxyl groups decreased in bile salts. Among sodium cholate (NaC), sodium deoxycholate (NaDC), sodium chenodeoxycholate (NaCC), and sodium lithocholate (NaLC), the least hydrophilic NaLC at a concentration of 25.0 mM entirely blocked the ice growth in phosphate-buffered saline (PBS) under test conditions. The IRI activity of bile salts was not related to viscosity or gelation. No IRI activity was found below the critical micelle concentration. The IRI activity was independent of liquid crystal formation. No ice shaping and thermal hysteresis were observed on any bile salts, but NaC and NaLC could increase the ice nucleation temperature. The findings add bile salts to the existing material list of ice recrystallization inhibitors.

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.

A Dynamic Membrane-Active Glycopeptide for Enhanced Protection of Human Red Blood Cells against Freeze-Stress

Intracellular delivery of freezing-tolerant trehalose is crucial for cryopreservation of red blood cells (RBCs) and previous strategies based on membrane-disruptive activity usually generate severe hemolysis. Herein, a dynamic membrane-active glycopeptide is developed by grafting with 25% maltotriose and 50% p-benzyl alcohol for the first time to effectively facilitate entry of membrane-impermeable trehalose in human RBCs with low hemolysis. Results of the mechanism acting on cell membranes suggest that reversible adsorption of such benzyl alcohol-grafted glycopeptide on cell surfaces upon weak perturbation with phospholipids and dynamic transition toward membrane stabilization are essential for keeping cellular biofunctions. Furthermore, the functionalized glycopeptide is indicative of typical α-helical/β-sheet structure-driven regulations of ice crystals during freeze-thaw, thereby strongly promoting efficient cryopreservation. Such all-in-one glycopeptide enables achieving both high cell recovery post-thaw >85% and exceptional cryosurvival >95% in direct freezing protocols. The rationally designed benzyl alcohol-modified glycopeptide permits the development of a competent platform with high generality for protection of blood cells against freeze-stress.

Revealing the Mechanism of Irreversible Binding of Antifreeze Glycoproteins to Ice

Antifreeze glycoproteins (AFGPs) are a special kind of antifreeze proteins with strong flexibility. Whether their antifreeze activity is achieved by reversibly or irreversibly binding to ice is widely debated, and the molecular mechanism of irreversible binding remains unclear. In this work, the antifreeze mechanism of the smallest AFGP isoform, AFGP8, is investigated at the atomic level. The results indicate that AFGP8 can bind to ice both reversibly through its hydrophobic methyl groups (peptide binding) and irreversibly through its hydrophilic disaccharide moieties (saccharide binding). Although peptide binding occurs faster than saccharide binding, free-energy calculations indicate that the latter is energetically more favorable. In saccharide binding, at least one disaccharide moiety is frozen in the grown ice, resulting in irreversible binding, while the other moieties significantly perturb the water hydrogen-bonding network, thus inhibiting ice growth more effectively. The present study reveals the coexistence of reversible and irreversible bindings of AFGP8, both contributing to the inhibition of ice growth and further provides molecular mechanism of irreversible binding.

Microencapsulation and nanowarming enables vitrification cryopreservation of mouse preantral follicles

Preantral follicles are often used as models for cryopreservation and in vitro culture due to their easy availability. As a promising approach for mammalian fertility preservation, vitrification of preantral follicles requires high concentrations of highly toxic penetrating cryoprotective agents (up to 6 M). Here, we accomplish low-concentration-penetrating cryoprotective agent (1.5 M) vitrification of mouse preantral follicles encapsulated in hydrogel by nanowarming. We find that compared with conventional water bath warming, the viability of preantral follicles is increased by 33%. Moreover, the cavity formation rate of preantral follicles after in vitro culture is comparable to the control group without vitrification. Furthermore, the percentage of MII oocytes developed from the vitrified follicles, and the birth rate of offspring following in vitro fertilization and embryo transfer are also similar to the control group. Our results provide a step towards nontoxic vitrification by utilizing the synergistic cryoprotection effect of microencapsulation and nanowarming.

Molecular Factors of Ice Growth Inhibition for Hyperactive and Globular Antifreeze Proteins: Insights from Molecular Dynamics Simulation

The molecular mechanism behind the ice growth inhibition by antifreeze proteins (AFPs) is yet to be understood completely. Also, what physical parameters differentiate between the AFP and non-AFP are largely unknown. Thus, to get an atomistic overview of the differential antifreeze activities of different classes of AFPs, we have studied ice growth from different ice surfaces in the presence of a moderately active globular type III AFP and a hyperactive spruce budworm (sbw) AFP. Results are compared with the observations of ice growth simulations in the presence of topologically similar non-AFPs using all-atom molecular dynamics simulations. Simulation data suggest that the ice surface coverage is a critical factor in ice growth inhibition. Due to the presence of an ice binding surface (IBS), AFPs form a high affinity complex with ice, accompanied by a transition of hydration water around the IBS from clathrate-like to ice-like. Several residues around the periphery of the IBS anchor the AFP to the curved ice surface mediated by multiple strong hydrogen bonds, stabilizing the complex immensely. In the high surface coverage regime, the slow unbinding kinetics dominates over the ice growth kinetics and thus facilitates the ice growth inhibition. Due to the non-availability of a proper IBS, non-AFPs form a low-affinity complex with the growing ice surface. As a result, the non-AFPs are continuously repelled by the surface. If the concentration of AFPs is low, then the effective surface coverage is reduced significantly. In this low surface coverage regime, AFPs can also behave like impurities and are engulfed by the growing ice crystal.

Identification of Novel Antifreeze Peptides from Takifugu obscurus Skin and Molecular Mechanism in Inhibiting Ice Crystal Growth

Foodborne hydrolyzed antifreeze peptides have been widely used in the food industry and the biomedical field. However, the components of hydrolyzed peptides are complex and the molecular mechanism remains unclear. This study focused on identification and mechanism analysis of novel antifreeze peptides from Takifugu obscurus skin by traditional methods and computer-assisted techniques. Results showed that three peptides (EGPRAGGAPG, GDAGPSGPAGPTG, and GEAGPAGPAG) possessed cryoprotection via reducing the freezing point and inhibiting ice crystal growth. Molecular docking confirmed that the cryoprotective property was related to peptide structure, especially α-helix, and hydrogen bond sites. Moreover, the antifreeze peptides were double-faces, which controlled ice crystals while affecting the arrangement of surrounding water molecules, thus exhibiting a strong antifreeze activity. This investigation deepens the comprehension of the mechanism of antifreeze peptides at molecular scale, and the novel efficient antifreeze peptides can be developed in antifreeze materials design and applied in food industry.

Research progress on quality deterioration mechanism and control technology of frozen muscle foods

Freezing can prolong the shelf life of muscle foods and is widely used in their preservation. However, inevitable quality deterioration can occur during freezing, frozen storage, and thawing. This review explores the eating quality deterioration characteristics (color, water holding capacity, tenderness, and flavor) and mechanisms (irregular ice crystals, oxidation, and hydrolysis of lipids and proteins) of frozen muscle foods. It also summarizes and classifies the novel physical-field-assisted-freezing technologies (high-pressure, ultrasound, and electromagnetic) and bioactive antifreeze (ice nucleation proteins, antifreeze proteins, natural deep eutectic solvents, carbohydrate, polyphenol, phosphate, and protein hydrolysates), regulating the dynamic process from water to ice. Moreover, some novel thermal and nonthermal thawing technologies to resolve the loss of water and nutrients caused by traditional thawing methods were also reviewed. We concluded that the physical damage caused by ice crystals was the primary reason for the deterioration in eating quality, and these novel techniques promoted the eating quality of frozen muscle foods under proper conditions, including appropriate parameters (power, time, and intermittent mode mentioned in ultrasound-assisted techniques; pressure involved in high-pressure-assisted techniques; and field strength involved in electromagnetic-assisted techniques) and the amounts of bioactive antifreeze. To obtain better quality frozen muscle foods, more efficient technologies and substances must be developed. The synergy of novel freezing/thawing technology may be more effective than individual applications. This knowledge may help improve the eating quality of frozen muscle foods.

Janus regulation of ice growth by hyperbranched polyglycerols generating dynamic hydrogen bonding

In this study, a new phenomenon describing the Janus effect on ice growth by hyperbranched polyglycerols, which can align the surrounding water molecules, has been identified. Even with an identical polyglycerol, we not only induced to inhibit ice growth and recrystallization, but also to promote the growth rate of ice that is more than twice that of pure water. By investigating the polymer architecture and population, we found that the stark difference in the generation of quasi-structured H2O molecules at the ice/water interface played a crucial role in the outcome of these opposite effects. Inhibition activity was induced when polymers at nearly fixed loci formed steady hydrogen bonding with the ice surface. However, the formation-and-dissociation dynamics of the interfacial hydrogen bonds, originating from and maintained by migrating polymers, resulted in an enhanced quasi-liquid layer that facilitated ice growth. Such ice growth activity is a unique property unseen in natural antifreeze proteins or their mimetic materials.