Enhanced Adsorption of a Protein-Nanocarrier Complex onto Cell Membranes through a High Freeze Concentration by a Polyampholyte Cryoprotectant

Advances in Cryopreservatives: Exploring Safer Alternatives

Cryopreservation of cells, tissues, and organs is widely used in the biomedical and research world. There are different cryopreservatives that are used for this process; however, many of them, such as DMSO, are used despite the problems they present, mainly due to the toxicity it presents to certain types of samples. The aim of this Review is to highlight the different types of substances used in the cryopreservation process. It has been shown that some of these substances are well-known, as in the case of the families of alcohols, sugars, sulfoxides, etc. However, in recent years, other compounds have appeared, such as ionic liquids, deep eutectic solvents, or certain polymers, which open the door to new cryopreservation methods and are also less toxic to frozen samples.

Bridging polymer chemistry and cryobiology

Polymers, especially charged polymers, are the key to a sustainable future, as they have the capability to act as alternatives to plastics, reduce the impact of global warming, and offer solutions to global environmental pollution problems. Biomaterial polymers have proven to be incredibly effective in a multitude of applications, including clinical applications. In the fields of cryobiology and cryopreservation, polymers have emerged as credible alternatives to small molecules and other compounds, yielding excellent results. This review outlines the results of research in the areas of polymer chemistry and cryobiology, which have not been discussed together previously. Herein, we explain how recent polymer research has enabled the development of polymeric cryoprotectants with novel mechanisms and the development of novel methods for the intracellular delivery of substances, such as drugs, using a cryobiological technique called the freeze-concentration effect. Our findings indicate that interdisciplinary collaboration between cryobiologists and polymer chemists has led to exciting developments that will further cell biology and medical research.

Role of an Ice Surface in the Photoreaction of Coumarins

Ice affects many chemical reactions in nature, which greatly influences the atmosphere, climate, and life. However, the exact mechanism of ice in these chemical reactions remains elusive. For example, it is still an open question as to whether ice can act as a catalyst to greatly enhance the reactivity and selectivity, which is essential for the production of some natural compounds in our planet. Here, we discover that ice can lead to high efficiency and stereoselectivity of the [2 + 2] photodimerization of coumarin and its derivatives. The conversion of the [2 + 2] photodimerization of coumarins enhanced by ice is dozens of times higher than that in the unfrozen saturated solution, and the reaction displays a high syn-head-head stereoselectivity (>95%) in comparison with those in the absence of the ice. Note that almost no reaction occurs in the crystal powder and melt of the coumarins, indicating that the role of ice in the photodimerization reaction is not simply due to the usual mechanisms found in the freezing concentration. We further reveal that the reaction rate is found to be proportional to the total area of the ice surface and follows Michaelis-Menten-like kinetics, indicating that the ice surface catalyzes the reaction. Molecular dynamics simulations demonstrate that ice surfaces can induce reactants to form a two-dimensional liquid-crystal-ordered layer with a suitable intermolecular distance and unique side-by-side packing, facilitating stereoselective photodimerization for syn-head-head dimers. These findings give evidence that ice-surface-induced molecular assembly may play an important role in atmospheric heterogeneous photoreaction processes.

Biocompatibility of nanomaterials and their immunological properties

Nanomaterials (NMs) have revolutionized multiple aspects of medicine by enabling novel sensing, diagnostic, and therapeutic approaches. Advancements in processing and fabrication have also allowed significant expansion in the applications of the major classes of NMs based on polymer, metal/metal oxide, carbon, liposome, or multi-scale macro-nano bulk materials. Concomitantly, concerns regarding the nanotoxicity and overall biocompatibility of NMs have been raised. These involve putative negative effects on both patients and those subjected to occupational exposure during manufacturing. In this review, we describe the current state of testing of NMs including those that are in clinical use, in clinical trials, or under development. We also discuss the cellular and molecular interactions that dictate their toxicity and biocompatibility. Specifically, we focus on the reciprocal interactions between NMs and host proteins, lipids, and sugars and how these induce responses in immune and other cell types leading to topical and/or systemic effects.

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.

Cytosolic delivery of quantum dots mediated by freezing and hydrophobic polyampholytes in RAW 264.7 cells

Quantum dots (QDs) can be delivered efficiently inside macrophages using a freeze-concentration approach. In this study, we introduced a new, facile, high concentration-based freezing technology of low toxicity. We also developed QD-conjugated new hydrophobic polyampholytes using poly-l-lysine (PLL), a naturally derived polymer, which showed sustained biocompatibility, stability over one week, and enhanced intracellular delivery. When freeze-concentration was applied, the QD-encapsulated hydrophobic polyampholytes showed a higher tendency to adsorb onto the cell membrane than the non-frozen molecules. Interestingly, we observed that the efficacy of adsorption of QDs on RAW 264.7 macrophages was higher than that on fibroblasts. Furthermore, the intracellular delivery of QDs using hydrophobic polyampholytes was higher than those of PLL and QDs. In vitro studies revealed the efficient endosomal escape of QDs in the presence of hydrophobic polyampholytes and freeze-concentration. Collectively, these observations indicated that the promising combination of freeze-concentration and hydrophobic polyampholytes may act as an effective and versatile strategy for the intracellular delivery of QDs, which can be used for biological diagnosis and therapeutic applications.

Changes in Cryopreserved Cell Nuclei Serve as Indicators of Processes during Freezing and Thawing

The mechanisms underlying cell protection from cryoinjury are not yet fully understood. Recent biological studies have addressed cryopreserved cell survival but have not correlated the cryoprotection effectiveness with the impact of cryoprotectants on the most important cell structure, the nucleus, and the freeze/thaw process. We identified changes of cell nuclei states caused by different types of cryoprotectants and associate them with alterations of the freeze/thaw process in cells. Namely, we investigated both higher-order chromatin structure and nuclear envelope integrity as possible markers of freezing and thawing processes. Moreover, we analyzed in detail the relationship between nuclear envelope integrity, chromatin condensation, freeze/thaw processes in cells, and cryopreservation efficiency for dimethyl sulfoxide, glycerol, trehalose, and antifreeze protein. Our interdisciplinary study reveals how changes in cell nuclei induced by cryoprotectants affect the ability of cells to withstand freezing and thawing and how nuclei changes correlate with processes during freezing and thawing. Our results contribute to the deeper fundamental understanding of the freezing processes, notably in the cell nucleus, which will expand the applications and lead to the rational design of cryoprotective materials and protocols.

Hydrophobic Polyampholytes and Nonfreezing Cold Temperature Stimulate Internalization of Au Nanoparticles to Zwitterionic Liposomes

Nanomedicine relies on the effective internalization of nanoparticles combined with polymeric nanocarriers into living cells. Thus, exploration of internalization is essential for improving the efficacy of nanoparticle-based strategies in clinical practice. Here, we investigated the physicochemical internalization of gold nanoparticles (AuNPs) conjugated with hydrophobic polyampholytes into cell-sized liposomes at a low but nonfrozen temperature. The hydrophobic polyampholytes localized in the disordered phase of the membrane, and internalization of AuNPs was enhanced in the presence of hydrophobic polyampholytes together with incubation at -3 °C as compared to 25 °C. These results contribute toward a mechanistic understanding for developing a model nanomaterials-driven delivery system based on hydrophobic polyampholytes and low temperature.