Ice-recrystallization inhibiting polymers protect proteins against freeze-stress and enable glycerol-free cryostorage

Trehalose and mannitol based lyoprotection of Taq DNA polymerase for cold-chain-free long-term storage

Polymerase chain reactions (PCR) are most reliable and precise means for nucleic acid analysis of biological samples. A cold-chain system with temperature at around -20 °C is generally necessary for storage and transportation of PCR-related reagents. In order to facilitate ambient temperature storage and transportation, this study prepared Taq DNA polymerase and 5 × HS-Taq Mix (as low as 0.5 U/sample) into stable solid formulations using an optimized freeze-drying process and lyoprotectant formulations comprising trehalose dihydrate (3.3∼5%, w/v) and mannitol (10%, w/v). The lyocakes were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). In the optimized freeze-drying process, trehalose dihydrate mainly formed an amorphous structure and acted as both cryoprotectant and lyoprotectant, while mannitol crystallized to serve as a bulking agent. The enzyme activities of Taq and 5 × HS-Taq Mix samples were measured via real-time quantitative PCR (qPCR). Long-term storage stability test demonstrated that freeze-dried samples with optimized formulations showed no remarkable reduction in amplification efficiencies for target sequence compared to freshly prepared corresponding samples after being stored at 37 °C and 55% relative humidity (RH) for 0, 1, 4, 8 and 12 weeks.

PVAylation: precision end-functionalized poly(vinyl alcohol) for site-selective bioconjugation

The (bio)conjugation of polymers onto proteins enhances their pharmacokinetics and stability, most commonly using PEG (polyethylene glycol), but there is a need for alternatives. Poly(vinyl alcohol), PVA, is a water-soluble, biocompatible and environmentally degradable polymer, which also has the unique function of ice recrystallisation inhibition (IRI) which can aid the cryopreservation of biologics. Site-specific PVA bioconjugation ("PVAylation") is underexplored due to the challenge of obtaining homogenous mono end-functional PVA. Here we show that following deprotection of the acetate (from the precursor poly(vinyl acetate)), the concurrent xanthate end-group reduction leads to a diversity of ambiguous end-groups which prevented precision conjugation. This is overcome by using a photo-catalyzed reduction of the omega-terminal xanthates to C-H, which is orthogonal to active-ester bioconjugation functionality at the alpha-chain terminus, demonstrated by MALDI-TOF mass spectrometry. This strategy enabled the preparation of well-defined mono-functional PVA displaying alkyne, biotin and O6-benzylguanine chain-end functionalities, which are each then used for covalent or non-covalent site-specific modification of three model proteins, introduce ice-binding function. These results will enable the synthesis of new bioconjugates containing PVA and be of particular benefit for low-temperature applications.

Thermo-sensitive polycaprolactone coacervates for preventing protein aggregation under thermal stress

Inspired from heat shock proteins (HSPs), a thermo-sensitive coacervate-forming polycaprolactone (CPCL) was designed as a natural chaperone mimic to protect proteins from thermal stress. Unlike the coil-globule polymers of poly(N-isopropyl acrylamide) (PNIPAM), the as-designed CPCL underwent a partial dehydration during heating, characterizing it as a coacervate-forming polymer. With its ability to transform between the coil and coacervate states in response to temperature, theCPCL spontaneously captured and released targeted proteins, thereby behaving like a natural chaperone of HSPs. Remarkably, compared with the PNIPAM homopolymer, the CPCL provided more efficient protection for proteins by inhibiting heat-induced aggregation above the melting temperature (Tm). Taken together, we envision that the CPCL with excellent biodegradability and biocompatibility could be a safe excipient for protein protection against thermal damage without separation.

Design and Mechanistic Insights into α-Helical p-Terphenyl Guanidines as Potent Small-Molecule Antifreeze Agents

Ice formation is a critical challenge across multiple fields, from industrial applications to biological preservation. Inspired by natural antifreeze proteins, we designed and synthesized a new class of small-molecule antifreezes based on α-helical p-terphenyl scaffolds with guanidine side chains. These p-terphenyl guanidines 1, among the smallest molecules that mimic α-helical structures, exhibit potent ice recrystallization inhibition (IRI) activity, similar to that of existing large α-helical antifreeze compounds. The most effective compound, 1a, with four C1-carbon guanidine moieties, demonstrated a superior IRI activity of 0.46 (1 mg/mL). Using molecular dynamics simulations with density-functional theory and separate pKa calculations, we elucidated the mechanisms underlying their antifreeze properties.

Cellular Applications of DNP Solid-State NMR - State of the Art and a Look to the Future

Sensitivity enhanced dynamic nuclear polarization solid-state NMR is emerging as a powerful technique for probing the structural properties of conformationally homogenous and heterogenous biomolecular species irrespective of size at atomic resolution within their native environments. Herein we detail advancements that have made acquiring such data, specifically within the confines of intact bacterial and eukaryotic cell a reality and further discuss the type of structural information that can presently be garnered by the technique's exploitation. Subsequently, we discuss bottlenecks that have thus far curbed cellular DNP-ssNMR's broader adoption namely due a lack of sensitivity and spectral resolution. We also explore possible solutions ranging from utilization of new pulse sequences, design of better performing polarizing agents, and application of additional biochemical/ cell biological methodologies.

Removal of plant endogenous proteins from tobacco leaf extract by freeze-thaw treatment for purification of recombinant proteins

Plants are useful as a low-cost source for producing biopharmaceutical proteins. A significant hurdle in the production of recombinant proteins in plants, however, is the complicated process of removing plant-derived components. Removing endogenous plant proteins, including ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), a major photosynthetic plant enzyme that catalyzes photosynthesis through carboxylation and oxygenation, is important for the purification of recombinant plant proteins. In particular, RuBisCO accounts for 50% of the soluble leaf protein; thus, the removal of RuBisCO is critical for the purification of recombinant proteins from plant materials. An effective conventional method, known as freeze-thaw treatment, was developed for the removal of RuBisCO from Nicotiana benthamiana, which expresses recombinant green fluorescent protein (GFP). Crude extracts or supernatants were frozen at - 30 °C. Upon thawing, most of the RuBisCO was precipitated by centrifugation without significant inactivation and/or yield reduction of GFP. Based on the proteomics analysis, using this method, RuBisCO large and small subunits were reduced to approximately 10% and 20% of those of the unfrozen supernatant solutions, respectively, without the need for specific reagents or equipment. The proteomic analysis also revealed that many ribosomal proteins were removed from the extracts. This method improves the purification process of recombinant proteins from plant materials. Prolonged freezing damaged recombinant β-glucuronidase (GUS), suggesting that the applicability of this treatment should be carefully considered for each recombinant protein.

Application of Formulation Principles to Stability Issues Encountered During Processing, Manufacturing, and Storage of Drug Substance and Drug Product Protein Therapeutics

The field of formulation and stabilization of protein therapeutics has become rather extensive. However, most of the focus has been on stabilization of the final drug product. Yet, proteins experience stress and degradation through the manufacturing process, starting with fermentaition. This review describes how formulation principles can be applied to stabilize biopharmaceutical proteins during bioprocessing and manufacturing, considering each unit operation involved in prepration of the drug substance. In addition, the impact of the container on stabilty is discussed as well.

Does freezing induce self-assembly of polymers? A molecular dynamics study

This work investigates the freezing-induced self-assembly (FISA) of polyvinyl alcohol (PVA) and PVA-like polymers using molecular dynamics simulations. In particular, the effect of the degree of supercooling, degree of polymerization, polymer type, and initial local concentration on the FISA was studied. It was found that the preeminent factor responsible for FISA is not the diffusion of the polymers away from the nucleating ice front, but the increase in the polymer's local concentration upon freezing of the solvent (water). At a higher degree of supercooling, the polymers are engulfed by the growing ice front, impeding their diffusion into the supercooled solution and finally inhibiting their self-assembly. Conversely, at a relatively lower degree of supercooling, the rate of diffusion of the polymers into the supercooled solution is higher, which increases their local concentration and results in FISA. FISA was also observed to depend on the polymer-solvent interactions. Strongly favorable solute-solvent interactions hinder the self-assembly, whereas unfavorable solute-solvent interactions promote the self-assembly. The polymer and aggregate morphology were investigated using the radius of gyration, end-to-end distance, and asphericity analysis. This study brings molecular insights into the quintessential factors governing self-assembly via freezing of the solvent, which is a novel self-assembly technique especially suitable for biomedical applications.

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

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

Trehalose counteracts the dissociation of tetrameric rabbit lactate dehydrogenase induced by acidic pH conditions

The lactate dehydrogenase from rabbit skeletal muscle (rbLDH) is a tetrameric enzyme, known to undergo dissociation when exposed to acidic pH conditions. Moreover, it should be mentioned that this dissociation translates into a pronounced loss of enzyme activity. Notably, among the compounds able to stabilize proteins and enzymes, the disaccharide trehalose represents an outperformer. In particular, trehalose was shown to efficiently counteract quite a number of physical and chemical agents inducing protein denaturation. However, no information is available on the effect, if any, exerted by trehalose against the dissociation of protein oligomers. Accordingly, we thought it of interest to investigate whether this disaccharide is competent in preventing the dissociation of rbLDH induced by acidic pH conditions. Further, we compared the action of trehalose with the effects triggered by maltose and cellobiose. Surprisingly, both these disaccharides enhanced the dissociation of rbLDH, with maltose being responsible for a major effect when compared to cellobiose. On the contrary, trehalose was effective in preventing enzyme dissociation, as revealed by activity assays and by Dynamic Light Scattering (DLS) experiments. Moreover, we detected a significant decrease of both K_0.5 and V_max when the rbLDH activity was tested (at pH 7.5 and 6.5) as a function of pyruvate concentration in the presence of trehalose. Further, we found that trehalose induces a remarkable increase of V_max when the enzyme is exposed to pH 5. Overall, our observations suggest that trehalose triggers conformational rearrangements of tetrameric rbLDH mirrored by resistance to dissociation and peculiar catalytic features.

Polyampholyte-Based Polymer Hydrogels for the Long-Term Storage, Protection and Delivery of Therapeutic Proteins

Protein storage and delivery are crucial for biomedical applications such as protein therapeutics and recombinant proteins. Lack of proper protocols results in the denaturation of proteins, rendering them inactive and manifesting undesired side effects. In this study, polyampholyte-based (succinylated ε-poly-l-lysine) hydrogels containing polyvinyl alcohol and polyethylene glycol polymer matrices to stabilize proteins are developed. These hydrogels facilitated the loading and release of therapeutic amounts of proteins and withstood thermal and freezing stress (15 freeze-thaw cycles and temperatures of -80 °C and 37 °C), without resulting in protein denaturation and aggregation. To the best of our knowledge, this strategy has not been applied to the design of hydrogels constituting polymers, (in particular, polyampholyte-based polymers) which have inherent efficiency to stabilize proteins and protect them from denaturation. Our findings can open up new avenues in protein biopharmaceutics for the design of materials that can store therapeutic proteins long-term under severe stress and safely deliver them.

Rediscovery of poly(ethylene glycol)s as a cryoprotectant for mesenchymal stem cells

BACKGROUND

A medium containing dimethyl sulfoxide (DMSO) (10% v/v) is most widely used for cell cryopreservation at -196 °C. However, residual DMSO consistently raises concerns because of its toxicity; thus, its complete removal process is required.

METHOD

As biocompatible polymers approved by the Food and Drug Administration for various biomedical applications for humans, poly(ethylene glycol)s (PEGs) with various molecular weights (400, 600, 1 K, 1.5 K, 5 K, 10 K, and 20 K Da) were studied as a cryoprotectant of mesenchymal stem cells (MSCs). Considering the cell permeability difference of PEGs depending on their molecular weight, the cells were preincubated for 0 h (no incubation), 2 h, and 4 h at 37 °C in the presence of PEGs at 10 wt.% before cryopreservation at -196 °C for 7 days. Then, cell recovery was assayed.

RESULTS

We found that low molecular weight PEGs (400 and 600 Da) exhibit excellent cryoprotecting properties by 2 h preincubation, whereas intermediate molecular weight PEGs (1 K, 1.5 K, and 5 K Da) exhibit their cryoprotecting properties without preincubation. High molecular weight PEGs (10 K and 20 K Da) were ineffective as cryoprotectants for MSCs. Studies on ice recrystallization inhibition (IRI), ice nucleation inhibition (INI), membrane stabilization, and intracellular transport of PEGs suggest that low molecular weight PEGs (400 and 600 Da) exhibit excellent intracellular transport properties, and thus the internalized PEGs during preincubation contribute to the cryoprotection. Intermediate molecular weight PEGs (1 K, 1.5 K, and 5 K Da) worked by extracellular PEGs through IRI, INI, as well as partly internalized PEGs. High molecular weight PEGs (10 K and 20 K Da) killed the cells during preincubation and were ineffective as cryoprotectants.

CONCLUSIONS

PEGs can be used as cryoprotectants. However, the detailed procedures, including preincubation, should consider the effect of the molecular weight of PEGs. The recovered cells well proliferated and underwent osteo/chondro/adipogenic differentiation similar to the MSCs recovered from the traditional DMSO 10% system.

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.

Synthesis of Poly(2-(methylsulfinyl)ethyl methacrylate) via Oxidation of Poly(2-(methylthio)ethyl methacrylate): Evaluation of the Sulfoxide Side Chain on Cryopreservation

Conventional cryopreservation solutions rely on the addition of organic solvents such as DMSO or glycerol, but these do not give full recovery for all cell types, and innovative cryoprotectants may address damage pathways which these solvents do not protect against. Macromolecular cryoprotectants are emerging, but there is a need to understand their structure-property relationships and mechanisms of action. Here we synthesized and investigated the cryoprotective behavior of sulfoxide (i.e., "DMSO-like") side-chain polymers, which have been reported to be cryoprotective using poly(ethylene glycol)-based polymers. We also wanted to determine if the polarized sulfoxide bond (S⁺O^- character) introduces cryoprotective effects, as this has been seen for mixed-charge cryoprotective polyampholytes, whose mechanism of action is not yet understood. Poly(2-(methylsulfinyl)ethyl methacrylate) was synthesized by RAFT polymerization of 2-(methylthio)ethyl methacrylate and subsequent oxidation to sulfoxide. A corresponding N-oxide polymer was also prepared and characterized: (poly(2-(dimethylamineoxide)ethyl methacrylate). Ice recrystallization inhibition assays and differential scanning calorimetry analysis show that the sulfoxide side chains do not modulate the frozen components during cryopreservation. In cytotoxicity assays, it was found that long-term (24 h) exposure of the polymers was not tolerated by cells, but shorter (30 min) incubation times, which are relevant for cryopreservation, were tolerated. It was also observed that overoxidation to the sulfone significantly increased the cytotoxicity, and hence, these materials require a precision oxidation step to be deployed. In suspension cell cryopreservation investigations, the polysulfoxides did not increase cell recovery 24 h post-thaw. These results show that unlike hydrophilic backboned polysulfides, which can aid cryopreservation, the installation of the sulfoxide group onto a polymer does not necessarily bring cryoprotective properties, highlighting the challenges of developing and discovering macromolecular cryoprotectants.

Bioinspired Freeze-Tolerant Soft Materials: Design, Properties, and Applications

In nature, many biological organisms have developed the exceptional antifreezing ability to survive in extremely cold environments. Inspired by the freeze resistance of these organisms, researchers have devoted extensive efforts to develop advanced freeze-tolerant soft materials and explore their potential applications in diverse areas such as electronic skin, soft robotics, flexible energy, and biological science. Herein, a comprehensive overview on the recent advancement of freeze-tolerant soft materials and their emerging applications from the perspective of bioinspiration and advanced material engineering is provided. First, the mechanisms underlying the freeze tolerance of cold-enduring biological organisms are introduced. Then, engineering strategies for developing antifreezing soft materials are summarized. Thereafter, recent advances in freeze-tolerant soft materials for different technological applications such as smart sensors and actuators, energy harvesting and storage, and cryogenic medical applications are presented. Finally, future challenges and opportunities for the rapid development of bioinspired freeze-tolerant soft materials are discussed.

Room-Temperature Grafting from Synthesis of Protein-Polydisulfide Conjugates via Aggregation-Induced Polymerization

The reversible modification of proteins with lipoic acid (LPA)-derived polydisulfides (PDS) is an important approach toward the transient regulation and on-demand recovery of protein functions. The in situ growth of PDS from the cysteine (Cys) residue of a protein, however, has been challenging due to the near-equilibrium thermodynamics of the ring-opening polymerization of LPA. Here, we report the protein-mediated, aggregation-induced polymerization (AIP) of amphiphilic LPA-derived monomers at room temperature, which can be performed at a concentration as low as ∼2% of the equilibrium monomer concentration normally needed. The aggregation of monomers increases the effective monomer concentration in aqueous solutions to the degree that the polymerizations behave similarly to those in bulk. The PDS conjugation enhances the thermostability, protease resistance, and tolerance to freeze-thaw treatments of the target proteins. Moreover, the PDS conjugation allows rapid and convenient purification of Cys-bearing proteins by taking advantage of the liquid-liquid phase separation of the protein-PDS conjugates and the full recovery of native proteins under mild reducing conditions. This AIP effect may shed light on facilitating other polymerizations with a similar near-equilibrium character. The PDS conjugation can open up new avenues to protein delivery, dynamic and reversible protein engineering, enzyme preservation, and recycling.

Synthesis of poly(vinyl alcohol) by blue light bismuth oxide photocatalysed RAFT. Evaluation of the impact of freeze/thaw cycling on ice recrystallisation inhibition

Poly(vinyl alcohol), PVA, is the most potent polymeric ice recrystallisation inhibitor (IRI), mimicking a complex function of ice binding proteins. The IRI activity of PVA scales with its molecular weight and hence broad molecular weight distributions in free radical-derived PVAs lead to activity measurements dominated by small amounts of heavier fractions. Well-defined PVA can be prepared by thermally initiated RAFT/MADIX polymerization using xanthates by the polymerization of the less activated monomer vinyl acetate. The low conversions and molecular weights obtained during this approach, often requires feeding of additional initiator and bulk polymerization. Here we employ bismuth oxide photo-RAFT in solution, using blue light (450 nm), rather than previously reported white light, to obtain a library of PVA's. The use of blue light enabled quantitative conversion and acceptable dispersities. Purple light (380 nm) was also used, but asymmetric molecular weight distributions were obtained in some cases. High concentrations of high molecular weight PVA is known to form cryogels during freeze/thaw which has led to speculation this might limit the use of PVA in environments where the temperature cycles e.g. the construction industry. After 4 freeze/thaw cycles there was only small changes in observable IRI for all synthesised PVAs and two commercial standards. In an extended test, activity was retained after 100 freeze/thaw cycles, mitigating concerns that PVA could not be used in situations where freeze/thaw cycles occur. This work presents a convenient method to obtain well-defined PVAs for cryoscience studies compared to conventional thermal-RAFT and indicates that cryogelation concerns may not prevent their use.

Freeze-Dried Microfluidic Monodisperse Microbubbles as a New Generation of Ultrasound Contrast Agents

We succeeded in freeze-drying monodisperse microbubbles without degrading their performance, that is, their monodispersity in size and echogenicity. We used microfluidic technology to generate cryoprotected highly monodisperse microbubbles (coefficient of variation [CV] <5%). By using a novel retrieval technique, we were able to freeze-dry the microbubbles and resuspend them without degradation, that is, keeping their size distribution narrow (CV <6%). Acoustic characterization performed in two geometries (a centimetric cell and a millichannel) revealed that the resuspended bubbles conserved the sharpness of the backscattered resonance peak, leading to CVs ranging between 5% and 10%, depending on the geometry. As currently observed with monodisperse bubbles, the peak amplitudes are one order of magnitude higher than those of commercial ultrasound contrast agents. Our work thus solves the question of storage and transportation of highly monodisperse bubbles. This work might open pathways toward novel clinical non-invasive measurements, such as local pressure, impossible to carry out with the existing commercial ultrasound contrast agents.

Degradable Polyampholytes from Radical Ring-Opening Copolymerization Enhance Cellular Cryopreservation

Macromolecular cryoprotectants based on polyampholytes are showing promise as supplemental cryoprotectants alongside conventional DMSO-based freezing. Here we exploit radical ring-opening (ter)polymerization to access ester-containing cryoprotective polyampholytes, which were shown to be degradable. Using a challenging cell monolayer cryopreservation model, the degradable polyampholytes were found to enhance post-thaw recovery when supplemented into DMSO. This demonstrates that degradable macromolecular cryoprotectants can be developed for application in biotechnology and biomedicine.

Lipid bilayers as potential ice nucleating agents

Cellular damage is a key issue in the context of cryopreservation. Much of this damage is believed to be caused by extracellular ice formation at temperatures well above the homogeneous freezing point of pure water. Hence the question: what initiates ice nucleation during cryopreservation? In this paper, we assess whether cellular membranes could be responsible for facilitating the ice nucleation process, and what characteristics would make them good or bad ice nucleating agents. By means of molecular dynamics simulations, we investigate a number of phospholipids and lipopolysaccharide bilayers at the interface with supercooled liquid water. While these systems certainly appear to act as ice nucleating agents, it is likely that other impurities might also play a role in initiating extracellular ice nucleation. Furthermore, we elucidate the factors which affect a bilayer's ability to act as an ice nucleating agent; these are complex, with specific reference to both chemical and structural factors. These findings represent a first attempt to pinpoint the origin of extracellular ice nucleation, with important implications for the cryopreservation process.

Red Blood Cell Cryopreservation with Minimal Post-Thaw Lysis Enabled by a Synergistic Combination of a Cryoprotecting Polyampholyte with DMSO/Trehalose

From trauma wards to chemotherapy, red blood cells are essential in modern medicine. Current methods to bank red blood cells typically use glycerol (40 wt %) as a cryoprotective agent. Although highly effective, the deglycerolization process, post-thaw, is time-consuming and results in some loss of red blood cells during the washing procedures. Here, we demonstrate that a polyampholyte, a macromolecular cryoprotectant, synergistically enhances ovine red blood cell cryopreservation in a mixed cryoprotectant system. Screening of DMSO and trehalose mixtures identified optimized conditions, where cytotoxicity was minimized but cryoprotective benefit maximized. Supplementation with polyampholyte allowed 97% post-thaw recovery (3% hemolysis), even under extremely challenging slow-freezing and -thawing conditions. Post-thaw washing of the cryoprotectants was tolerated by the cells, which is crucial for any application, and the optimized mixture could be applied directly to cells, causing no hemolysis after 1 h of exposure. The procedure was also scaled to use blood bags, showing utility on a scale relevant for application. Flow cytometry and adenosine triphosphate assays confirmed the integrity of the blood cells post-thaw. Microscopy confirmed intact red blood cells were recovered but with some shrinkage, suggesting that optimization of post-thaw washing could further improve this method. These results show that macromolecular cryoprotectants can provide synergistic benefit, alongside small molecule cryoprotectants, for the storage of essential cell types, as well as potential practical benefits in terms of processing/handling.

Freeform Cell-Laden Cryobioprinting for Shelf-Ready Tissue Fabrication and Storage

One significant drawback of existing bioprinted tissues is their lack of shelf-availability caused by complications in both fabrication and storage. Here, we report a cryobioprinting strategy for simultaneously fabricating and storing cell-laden volumetric tissue constructs through seamlessly combining extrusion bioprinting and cryopreservation. The cryobioprinting performance was investigated by designing, fabricating, and storing cell-laden constructs made of our optimized cryoprotective gelatin-based bioinks using a freezing plate with precisely controllable temperature. The in situ freezing process further promoted the printability of cell-laden hydrogel bioinks to achieve freeform structures otherwise inconvenient with direct extrusion bioprinting. The effects of bioink composition on printability and cell viability were evaluated. The functionality of the method was finally investigated using cell differentiation and chick ex ovo assays. The results confirmed the feasibility and efficacy of cryobioprinting as a single-step method for concurrent tissue biofabrication and storage.

Cryopreservation of human erythrocytes through high intracellular trehalose with membrane stabilization of maltotriose-grafted ε-poly(L-lysine)

Cryopreservation of human erythrocytes via suitable cryoprotectants is essential for transfusion at emergency, but the conventional glycerolization method requires a tedious thawing-deglycerolization process. Alternatively, trehalose, a nonreducing disaccharide, has gained...

Development of Icephilic ACTIVE Glycopeptides for Cryopreservation of Human Erythrocytes

Ice formation and recrystallization exert severe impairments to cellular cryopreservation. In light of cell-damaging washing procedures in the current glycerol approach, many researches have been devoted to the development of biocompatible cryoprotectants for optimal bioprotection of human erythrocytes. Herein, we develop a novel ACTIVE glycopeptide of saccharide-grafted ε-poly(L-lysine), that can be credited with adsorption on membrane surfaces, cryopreservation with trehalose, and icephilicity for validity of human erythrocytes. Then, by Borch reductive amination or amidation, glucose, lactose, maltose, maltotriose, or trehalose was tethered to ε-polylysine. The synthesized ACTIVE glycopeptides with intrinsic icephilicity could localize on the membrane surface of human erythrocytes and improve cryopreservation with trehalose, so that remarkable post-thaw cryosurvival of human erythrocytes was achieved with a slight variation in cell morphology and functions. Human erythrocytes (∼50% hematocrit) in cryostores could maintain high cryosurvival above 74%, even after plunged in liquid nitrogen for 6 months. Analyses of differential scanning calorimetry, Raman spectroscopy, and dynamic ice shaping suggested that this cryopreservation protocol combined with the ACTIVE glycopeptide and trehalose could enhance the hydrogen bond network in nonfrozen solutions, resulting in inhibition of recrystallization and growth of ice. Therefore, the ACTIVE glycopeptide can be applied as a trehalose-associated "chaperone", providing a new way to serve as a candidate in glycerol-free human erythrocyte cryopreservation.

Polymer-Mediated Cryopreservation of Bacteriophages

Bacteriophages (phages, bacteria-specific viruses) have biotechnological and therapeutic potential. To apply phages as pure or heterogeneous mixtures, it is essential to have a robust mechanism for transport and storage, with different phages having very different stability profiles across storage conditions. For many biologics, cryopreservation is employed for long-term storage and cryoprotectants are essential to mitigate cold-induced damage. Here, we report that poly(ethylene glycol) can be used to protect phages from cold damage, functioning at just 10 mg·mL-1 (∼1 wt %) and outperforms glycerol in many cases, which is a currently used cryoprotectant. Protection is afforded at both -20 and -80 °C, the two most common temperatures for frozen storage in laboratory settings. Crucially, the concentration of the polymer required leads to frozen solutions at -20 °C, unlike 50% glycerol (which results in liquid solutions). Post-thaw recoveries close to 100% plaque-forming units were achieved even after 2 weeks of storage with this method and kill assays against their bacterial host confirmed the lytic function of the phages. Initial experiments with other hydrophilic polymers also showed cryoprotection, but at this stage, the exact mechanism of this protection cannot be concluded but does show that water-soluble polymers offer an alternative tool for phage storage. Ice recrystallization inhibiting polymers (poly(vinyl alcohol)) were found to provide no additional protection, in contrast to their ability to protect proteins and microorganisms which are damaged by recrystallization. PEG's low cost, solubility, well-established low toxicity/immunogenicity, and that it is fit for human consumption at the concentrations used make it ideal to help translate new approaches for phage therapy.

Design of an Ice Recrystallization-Inhibiting Polyampholyte-Containing Graft Polymer for Inhibition of Protein Aggregation

Freezing-induced damage to proteins, through osmotic stress and ice recrystallization, during protein processing and long-term storage is a serious concern and may lead to loss of protein activity owing to denaturation. In this study, graft copolymers composed of a cryoprotective polymer (capable of preventing osmotic stress) and poly(vinyl alcohol) (PVA; known for its high ice recrystallization inhibition (IRI) property) were developed. The polymers had high IRI activity, albeit slightly lower than that of PVA alone, but substantially higher than that of succinylated ε-poly-l-lysine (PLLSA) alone. The graft polymers showed an efficiency higher than that of PVA or PLLSA alone in protecting proteins from multiple freeze-thaw cycles, as well as during prolonged freezing, indicating a synergy between PVA and PLLSA. The PLLSA-based graft polymer is a promising material for use in protein biopharmaceutics for the long-term storage of proteins under freezing conditions.

Synthesis, self-aggregation and cryopreservation effects of perylene bisimide-glycopeptide conjugates

Three perylene bisimide-glycopeptide conjugates (PBI-AFF-Man, PBI-AFF-Glu and PBI-AFF-Gal) were synthesized, which showed moderate activity in the control of ice crystal growth. Furthermore, the cellular cryopreservation effects of PBI-AFF-Man, PBI-AFF-Glu and PBI-AFF-Gal showed enhancements in cell viabilities, especially for PBI-AFF-Glu with values of 22.77 ± 3.33% (HeLa cells), 19.43 ± 1.90% (A549 cells) and 16.63 ± 1.76% (GES-1 cells) at a dose of 1.0 mg mL^-1. This work will help guide the development of self-assembled cryoprotectants.

Approaches for manufacture, formulation, targeted delivery and controlled release of phage-based therapeutics

A future successful bacteriophage industry requires development of robust scalable manufacturing platforms for upstream production of high phage titres and their downstream purification and concentration whilst achieving processing yields en route. Development of a broadly applicable process flow sheet employing well-characterised unit operations with knowledge of their critical process parameters is beginning to emerge. A quality-by-design approach is advocated for the development of cost-effective phage production platforms. The use of on-line and at-line process analytical tools for process monitoring, control and quality assurance are discussed. Phage biophysical characterisation tools allowing rational development of liquid formulations and dry powder forms are presented. Recent innovations in phage encapsulation methods highlight the potential innovation opportunities in this research space that could have significant impact on the future prospects of this industry.

Integrated Graphene Oxide with Noble Metal Nanoparticles to Develop High-Sensitivity Fiber Optic Particle Plasmon Resonance (FOPPR) Biosensor for Biomolecules Determination

In this research, a direct, simple and ultrasensitive fiber optic particle plasmon resonance (FOPPR) biosensing platform for immunoglobulin G (IgG) detection was developed using a gold nanoparticle/graphene oxide (AuNP/GO) composite as signal amplification element. To obtain the best analytical performance of the sensor, experimental parameters including the surface concentration of GO on the AuNPs, formation time of the GO, the concentration of the anti-IgG and incubation time of anti-IgG were optimized. The calibration plots displayed a good linear relationship between the sensor response (ΔI/I₀) and the logarithm of the analyte concentrations over a linear range from 1.0 × 10⁻¹⁰ to 1.0 × 10⁻⁶ g/mL of IgG under the optimum conditions. A limit of detection (LOD) of 0.038 ng/mL for IgG was calculated from the standard calibration curve. The plot has a linear relationship (correlation coefficient, R = 0.9990). The analytical performance of present work’s biosensor was better than that of our previously reported mixed self-assembled monolayer of 11-mercaptoundecanoic acid/6-mercapto-1-hexanol (MUA/MCH = 1:4) method by about three orders of magnitude. The achieved good sensitivity may be attributed to the synergistic effect between GO and AuNPs in this study. In addition, GO could immobilize more antibodies due to the abundant carboxylic groups on its surface. Furthermore, we also demonstrated that the results from this sensor have good reproducibility, with coefficients of variation (CVs) < 8% for IgG. Therefore, the present strategy provides a novel and convenient method for chemical and biochemical quantification and determination.

2D and 3D inkjet printing of biopharmaceuticals - A review of trends and future perspectives in research and manufacturing

There is an ongoing global shift in pharmaceutical business models from small molecule drugs to biologics. This increase in complexity is in response to advancements in our diagnoses and understanding of diseases. With the more targeted approach coupled with its inherently more costly development and manufacturing, 2D and 3D printing are being explored as suitable techniques to deliver more personalised and affordable routes to drug discovery and manufacturing. In this review, we explore first the business context underlying this shift to biopharmaceuticals and provide an update on the latest work exploring discovery and pharmaceutics. We then draw on multiple disciplines to help reveal the shared challenges facing researchers and firms aiming to develop biopharmaceuticals, specifically when using the most commonly explored manufacturing routes of drop-on-demand inkjet printing and pneumatic extrusion. This includes separating out how to consider mechanical and chemical influences during manufacturing, the role of the chosen hardware and the challenges of aqueous formulation based on similar challenges being faced by the printing industry. Together, this provides a review of existing work and guidance for researchers and industry to help with the de-risking and rapid development of future biopharmaceutical products.

Synergistic Ice Inhibition Effect Enhances Rapid Freezing Cryopreservation with Low Concentration of Cryoprotectants

Despite recent advances in controlling ice formation and growth, it remains a challenge to design anti-icing materials in various fields from atmospheric to biological cryopreservation. Herein, tungsten diselenide (WSe2)-polyvinyl pyrrolidone (PVP) nanoparticles (NPs) are synthesized through one-step solvothermal route. The WSe2-PVP NPs show synergetic ice regulation ability both in the freezing and thawing processes. Molecularly speaking, PVP containing amides group can form hydrogen bonds with water molecules. At a macro level, the WSe2-PVP NPs show adsorption-inhibition and photothermal conversation effects to synergistically restrict ice growth. Meanwhile, WSe2-PVP NPs are for the first time used for the cryopreservation of human umbilical vein endothelial cell (HUVEC)-laden constructs based on rapid freezing with low concentrations of cryoprotectants (CPAs), the experimental results indicate that a minimal concentration (0.5 mg mL-1) of WSe2-PVP NPs can increase the viabilities of HUVECs in the constructs post cryopreservation (from 55.8% to 83.4%) and the cryopreserved constructs can also keep good condition in vivo within 7 days. Therefore, this work provides a novel strategy to synergistically suppress the formation and growth of the ice crystalsfor the cryopreservation of cells, tissues, or organs.

Ice Inhibition for Cryopreservation: Materials, Strategies, and Challenges

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

The atomistic details of the ice recrystallisation inhibition activity of PVA

Understanding the ice recrystallisation inhibition (IRI) activity of antifreeze biomimetics is crucial to the development of the next generation of cryoprotectants. In this work, we bring together molecular dynamics simulations and quantitative experimental measurements to unravel the microscopic origins of the IRI activity of poly(vinyl)alcohol (PVA)-the most potent of biomimetic IRI agents. Contrary to the emerging consensus, we find that PVA does not require a "lattice matching" to ice in order to display IRI activity: instead, it is the effective volume of PVA and its contact area with the ice surface which dictates its IRI strength. We also find that entropic contributions may play a role in the ice-PVA interaction and we demonstrate that small block co-polymers (up to now thought to be IRI-inactive) might display significant IRI potential. This work clarifies the atomistic details of the IRI activity of PVA and provides novel guidelines for the rational design of cryoprotectants.

The Formation and Control of Ice Crystal and Its Impact on the Quality of Frozen Aquatic Products: A Review

Although freezing has been used to delay the deterioration of product quality and extend its shelf life, the formation of ice crystals inevitably destroys product quality. This comprehensive review describes detailed information on the effects of ice crystals on aquatic products during freezing storage. The affecting factors (including nucleation temperature, freezing point, freezing rate, and temperature fluctuation) on the size, number, distribution, and shape of ice crystals are also elaborated in detail. Meanwhile, the corresponding technologies to control ice crystals have been developed based on these affecting factors to control the formation of ice crystals by inhibiting or inducing ice crystallization. In addition, the effects of ice crystals on the water, texture, and protein of aquatic products are comprehensively discussed, and the paper tries to describe their underlying mechanisms. This review can provide an understanding of ice crystallization in the aquatic products during freezing and contribute more clues for maintaining frozen food quality.

Enhancing the preservation of liposomes: The role of cryoprotectants, lipid formulations and freezing approaches

In the last decades, liposomes acquired a striking success in the biomedical field thanks to their biocompatibility and drug delivery ability. Many liposomal drug formulations have been already approved by the Food and Drug Administration (FDA) and used for the treatment of a wide range of pathologies with or without further engineering. Their clinical application requires strict compliance with high standard quality rules, and it is crucial to employ storage methods that do not affect the integrity of the vesicles and preventing the leakage of their cargo. In this work, the design of a suitable formulation for freeze-drying had been investigated for two different liposomes, DOPC-DOTAP and the PEGylated counterpart, DOPC-DOTAP-DSPE-PEG. The role of various cryoprotectants was evaluated paying attention to their ability to preserve the structural integrity of liposomes. At first, the study was focused on freezing and two methodologies were investigated, quenching in liquid nitrogen and shelf-ramped freezing. This analysis showed that the disaccharides (cellobiose, glucose, lactose, sucrose, and trehalose) and the polyol (mannitol) protected successfully the integrity of liposomes, while during the process, in the presence of a surfactant, liposomes were strongly damaged and fragmented by the ice crystals. Furthermore, the choice of the rate of freezing depended on the different compositions of the lipid bilayer. Finally, the effects of lyophilization on liposomes with and without additives were studied; cellobiose, lactose and trehalose showed encouraging results for the maintenance of the morpho-functional parameters of liposomes during the entire freeze-drying process.

Protection of Alcohol Dehydrogenase against Freeze-Thaw Stress by Ice-Binding Proteins Is Proportional to Their Ice Recrystallization Inhibition Property

Ice-binding proteins (IBPs) have ice recrystallization inhibition (IRI) activity. IRI property has been extensively utilized for the cryopreservation of different types of cells and tissues. Recent reports demonstrated that IRI can also play a significant role in protecting proteins from freezing damage during freeze-thaw cycles. In this study, we hypothesized that the protective capability of IBPs on proteins against freeze-thaw damage is proportional to their IRI activity. Hence we used two IBPs: one with higher IRI activity (LeIBP) and the other with lower activity (FfIBP). Yeast alcohol dehydrogenase (ADH) was used as a freeze-labile model protein. IBPs and ADH were mixed, frozen at -20 °C, and thawed repeatedly. The structure of ADH was assessed using fluorescence emission spectra probed by 1-anilinonaphthalene-8-sulfonate over the repeated freeze-thaw cycles. The activity was monitored at 340 nm spectrophotometrically. Fluorescence data and activity clearly indicated that ADH without IBP was freeze-labile. However, ADH maintained about 70% residual activity after five repeated cycles at a minimal concentration of 0.1 mg mL^-1 of high IRI-active LeIBP, but only 50% activity at 4 mg mL^-1 of low active FfIBP. These results showed that the protection of proteins from freeze-thaw stress by IBPs is proportional to their IRI activity.

Ice recrystallisation inhibiting polymers prevent irreversible protein aggregation during solvent-free cryopreservation as additives and as covalent polymer-protein conjugates

Protein storage and transport is essential to deliver therapies (biologics), enzymes for biotechnological applications, and underpins fundamental structural and molecular biology. To enable proteins to be stored and transported it is often essential to freeze them, requiring cryoprotectants such as glycerol or trehalose. Here we explore the mechanisms by which poly(vinyl alcohol), PVA, a potent ice recrystallisation inhibitor protects proteins during freeze/thaw to enable solvent-free cryopreservation with a focus on comparing mixing, verses polymer-protein conjugation. A panel of poly(vinyl alcohol)s are investigated including commercial, well-defined (from RAFT), and PVA-protein conjugates, to map out PVA's efficacy. Enzymatic activity recovery of lactate dehydrogenase was found to correlate with post-thaw aggregation state (less aggregated protein had greater activity), which was modulated by PVA's ice recrystallisation inhibition activity. This macromolecular cryoprotectant matched the performance of glycerol, but at lower additive concentrations (as low as 1 mg.mL-1). It was also demonstrated that storage at -20 °C, rather than -80 °C was possible using PVA as a cryoprotectant, which is not possible with glycerol storage. A second protein, green-fluorescent protein (GFP), was used to enable screening of molecular weight effects and to obtain PVA-GFP bioconjugates. It was observed that covalent attachment of RAFT-derived PVA showed superior cryoprotectant activity compared to simple mixing of the polymer and protein. These results show that PVA is a real alternative to solvent-based protein storage with potential in biotechnology, food and therapeutics. PVA is already approved for many biomedical applications, is low cost and available on a large scale, making it an ideal cryoprotectant formulation enhancer.

Post-Thaw Culture and Measurement of Total Cell Recovery Is Crucial in the Evaluation of New Macromolecular Cryoprotectants

The storage and transport of cells is a fundamental technology which underpins cell biology, biomaterials research, and emerging cell-based therapies. Inspired by antifreeze and ice-binding proteins in extremophiles, macromolecular (polymer) cryoprotectants are emerging as exciting biomaterials to enable the reduction and/or replacement of conventional cryoprotective agents such as DMSO. Here, we critically study post-thaw cellular outcomes upon addition of macromolecular cryoprotectants to provide unambiguous evidence that post-thaw culturing time and a mixture of assays are essential to claim a positive outcome. In particular, we observe that only measuring the viability of recovered cells gives false positives, even with non-cryoprotective polymers. Several systems gave apparently high viability but very low total cell recovery, which could be reported as a success but in practical applications would not be useful. Post-thaw culture time is also shown to be crucial to enable apoptosis to set in. Using this approach we demonstrate that polyampholytes (a rapidly emerging class of cryoprotectants) improve post-thaw outcomes across both measures, compared to poly(ethylene glycol), which can give false positives when only viability and short post-thaw time scales are considered. This work will help guide the discovery of new macromolecular cryoprotectants and ensure materials which only give positive results under limited outcomes can be quickly identified and removed.

Ice recrystallisation inhibiting polymer nano-objects via saline-tolerant polymerisation-induced self-assembly

Chemical tools to modulate ice formation/growth have great (bio)-technological value, with ice binding/antifreeze proteins being exciting targets for biomimetic materials. Here we introduce polymer nanomaterials that are potent inhibitors of ice recrystallisation using polymerisation-induced self-assembly (PISA), employing a poly(vinyl alcohol) graft macromolecular chain transfer agent (macro-CTA). Crucially, engineering the core-forming block with diacetone acrylamide enabled PISA to be conducted in saline, whereas poly(2-hydroxypropyl methacrylate) cores led to coagulation. The most active particles inhibited ice growth as low as 0.5 mg mL-1, and were more active than the PVA stabiliser block alone, showing that the dense packing of this nanoparticle format enhanced activity. This provides a unique route towards colloids capable of modulating ice growth.

A Multiparametric Fluorescence Probe to Understand the Physicochemical Properties of Small Unilamellar Lipid Vesicles in Poly(ethylene glycol)-Water Medium

FDAPT (2-formyl-5-(4'-N,N-dimethylaminophenyl)thiophene) efficiently senses the minimum alteration of lipid bilayer microenvironment with all six different fluorescence parameters namely emission wavelength, fluorescence intensity, steady-state anisotropy, and their corresponding time-dependent parameters (Sahu et al., J. Phys. Chem. B 2018, 122, 7308-7318). In the present work, the effect of poly(ethylene glycol) on the small unilamellar vesicle is demonstrated with the emission behavior of the FDAPT probe. A medium and a high molecular weight PEG were chosen to perturb the lipid vesicles. The alteration of the bilayer polarity, water content inside bilayer, lipid packing density in the perturbed vesicles reflect significant changes in different fluorescence parameters of FDAPT probe. The effect of PEG on the unilamellar vesicle was rationalized with the alteration of the emission behavior, fluorescence lifetime, steady-state anisotropy and anisotropy decay of the probe. The simple and convenient fluorescence measurements provide new insights into the effect of PEG on the packing density, water volume, micro polarity, and microviscosity of the small unilamellar vesicle. The physiological understanding was extended to rationalize the cryoprotecting behavior of PEG.

Polyampholytes as Emerging Macromolecular Cryoprotectants

Cellular cryopreservation is a platform technology which underpins cell biology, biochemistry, biomaterials, diagnostics, and the cold chain for emerging cell-based therapies. This technique relies on effective methods for banking and shipping to avoid the need for continuous cell culture. The most common method to achieve cryopreservation is to use large volumes of organic solvent cryoprotective agents which can promote either a vitreous (ice free) phase or dehydrate and protect the cells. These methods are very successful but are not perfect: not all cell types can be cryopreserved and recovered, and the cells do not always retain their phenotype and function post-thaw. This Perspective will introduce polyampholytes as emerging macromolecular cryoprotective agents and demonstrate they have the potential to impact a range of fields from cell-based therapies to basic cell biology and may be able to improve, or replace, current solvent-based cryoprotective agents. Polyampholytes have been shown to be remarkable (mammalian cell) cryopreservation enhancers, but their mechanism of action is unclear, which may include membrane protection, solvent replacement, or a yet unknown protective mechanism, but it seems the modulation of ice growth (recrystallization) may only play a minor role in their function, unlike other macromolecular cryoprotectants. This Perspective will discuss their synthesis and summarize the state-of-the-art, including hypotheses of how they function, to introduce this exciting area of biomacromolecular science.

Peptidic Antifreeze Materials: Prospects and Challenges

Necessitated by the subzero temperatures and seasonal exposure to ice, various organisms have developed a remarkably effective means to survive the harsh climate of their natural habitats. Their ice-binding (glyco)proteins keep the nucleation and growth of ice crystals in check by recognizing and binding to specific ice crystal faces, which arrests further ice growth and inhibits ice recrystallization (IRI). Inspired by the success of this adaptive strategy, various approaches have been proposed over the past decades to engineer materials that harness these cryoprotective features. In this review we discuss the prospects and challenges associated with these advances focusing in particular on peptidic antifreeze materials both identical and akin to natural ice-binding proteins (IBPs). We address the latest advances in their design, synthesis, characterization and application in preservation of biologics and foods. Particular attention is devoted to insights in structure-activity relations culminating in the synthesis of de novo peptide analogues. These are sequences that resemble but are not identical to naturally occurring IBPs. We also draw attention to impactful developments in solid-phase peptide synthesis and 'greener' synthesis routes, which may aid to overcome one of the major bottlenecks in the translation of this technology: unavailability of large quantities of low-cost antifreeze materials with excellent IRI activity at (sub)micromolar concentrations.

Bioinspired Ice Growth Inhibitors Based on Self-Assembling Peptides

Antifreeze proteins (AFPs) are widely found in organisms living in subzero environments. Their strong ability to inhibit ice growth and recrystallization have inspired considerable bioinspired efforts to engineer artificial ice growth inhibitors for cryopreservation. However, it remains challenging to engineer biocompatible and cost-effective synthetic ice growth inhibitors to meet the increasing needs of cryoprotectants in biomedical research and industry. Here we report the design of artificial ice growth inhibitors based on self-assembling peptides. We demonstrate the importance of threonine residues as well as their spatial arrangement for effective ice binding. The engineered self-assembling ice growth inhibiting peptides show moderate ice inhibiting activity including suppression of ice growth rates and retardation of recrystallization of ice crystals. The applications of these peptides in cryopreservation of enzymes and cells were also demonstrated.

Enhancement of Macromolecular Ice Recrystallization Inhibition Activity by Exploiting Depletion Forces

Antifreeze (glyco) proteins (AF(G)Ps) are potent inhibitors of ice recrystallization and may have biotechnological applications. The most potent AF(G)Ps function at concentrations a thousand times lower than synthetic mimics such as poly(vinyl alcohol), PVA. Here, we demonstrate that PVA’s ice recrystallization activity can be rescued at concentrations where it does not normally function, by the addition of noninteracting polymeric depletants, due to PVA forming colloids in the concentrated saline environment present between ice crystals. These depletants shift the equilibrium toward ice binding and, hence, enable PVA to inhibit ice growth at lower concentrations. Using theory and experiments, we show this effect requires polymeric depletants, not small molecules, to enhance activity. These results increase our understanding of how to design new ice growth inhibitors, but also offer opportunities to enhance activity by exploiting depletion forces, without re-engineering ice-binding materials. It also shows that when screening for IRI activity that polymer contaminants in buffers may give rise to false positive results.

Mimicking the Ice Recrystallization Activity of Biological Antifreezes. When is a New Polymer "Active"?

Antifreeze proteins and ice-binding proteins have been discovered in a diverse range of extremophiles and have the ability to modulate the growth and formation of ice crystals. Considering the importance of cryoscience across transport, biomedicine, and climate science, there is significant interest in developing synthetic macromolecular mimics of antifreeze proteins, in particular to reproduce their property of ice recrystallization inhibition (IRI). This activity is a continuum rather than an "on/off" property and there may be multiple molecular mechanisms which give rise to differences in this observable property; the limiting concentrations for ice growth vary by more than a thousand between an antifreeze glycoprotein and poly(vinyl alcohol), for example. The aim of this article is to provide a concise comparison of a range of natural and synthetic materials that are known to have IRI, thus providing a guide to see if a new synthetic mimic is active or not, including emerging materials which are comparatively weak compared to antifreeze proteins, but may have technological importance. The link between activity and the mechanisms involving either ice binding or amphiphilicity is discussed and known materials assigned into classes based on this.

Efficient synthesis of amino acid polymers for protein stabilization

Poly-l-glutamate exerts substantial protein stabilization during lyophilization by preventing protein aggregation.

Trehalose-functional glycopeptide enhances glycerol-free cryopreservation of red blood cells

Arginine- and trehalose-modified ε-polylysine (ε-PL) demonstrated a high synergistic function with trehalose for RBC cryopreservation.