Dimethyl Sulfoxide-Free Cryopreservation of Chondrocytes Based on Zwitterionic Molecule and Polymers

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.

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.

Synthesis of Poly(allyl glycidyl ether)-Derived Polyampholytes and Their Application to the Cryopreservation of Living Cells

Through the postpolymerization modification of poly(allyl glycidyl ether) (PAGE), a functionalizable polyether with a poly(ethylene oxide) backbone, we engineered a new class of highly tunable polyampholyte materials. These polyampholytes can be synthesized to have several useful properties, including low cytotoxicity and pH-responsive coacervate formation. In this study, we used PAGE-based polyampholytes (PAGE-PAs) for the cryopreservation of mammalian cell suspensions. Typically, dimethyl sulfoxide (DMSO) is the cryoprotectant used for preserving mammalian cells, but DMSO suffers from key drawbacks including toxicity and difficult post-thaw removal that motivates the development of new materials and methods. Toxicity and post-thaw survival were dependent on PAGE-PA composition with the highest immediate post-thaw survival for normal human dermal fibroblasts occurring for the least toxic PAGE-PA at a cation/anion ratio of 35:65. With low toxicity, the PAGE-PA concentration could be increased in order to increase immediate post-thaw survival of the immortalized mouse embryonic fibroblasts (NIH/3T3). While immediate post-thaw viability was achieved using only the PAGE-PAs, long-term cell survival was low, highlighting the challenges involved with the design of cryoprotective polyampholytes. An environment utilizing both PAGE-PAs and DMSO in a cryoprotective solution offered promising post-thaw viabilities exceeding 70%, with long-term metabolic activities comparable to unfrozen cells.

Zwitterionic Biomaterials

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Development of Organogels for Live Yarrowia lipolytica Encapsulation

Encapsulation of cells/microorganisms attracts great attention in many applications, but current studies mainly focus on hydrophilic encapsulation materials. Herein, we develop a new class of hydrophobic and lipophilic organogels for highly efficient encapsulation of Yarrowia lipolytica, an oleaginous yeast, by a mild and nonsolvent photopolymerization method. The organogels allow free diffusion of hydrophobic molecules that oleaginous yeasts require to survive and function. Moreover, they are mechanically robust and possess favorable biocompatibility, thus providing a free-standing platform and an ideal survival environment for oleaginous Y. lipolytica encapsulation. By tuning monomer structures and cross-linking densities, the optimized organogel, Gel_12-1.5%, achieves the highest viability of ∼96%. Furthermore, organogels can inhibit the cryoinjuries to oleaginous yeasts in cryopreservation, exhibiting the potential for long-term storage. It is also found that with varying alkyl lengths, the organogels show different temperature-dependent phase transition properties, which enable the rapid selection of targeted yeasts for steganography. Findings in this work provide guidance for designing biocompatible, hydrophobic, and lipophilic encapsulation materials.

Skin-Adaptable, Long-Lasting Moisture, and Temperature-Tolerant Hydrogel Dressings for Accelerating Burn Wound Healing without Secondary Damage

Developing multifunctional wound dressings, possessing not only skin-like mechanical properties and adaptability, long-lasting moisture, and temperature tolerance that maximally mimics the human skin but also on-demand adhesion without unnecessary bleeding and secondary damage upon peeling, is necessary but remains a challenge. Herein, a novel dual cross-linked and multifunctional hydrogel, termed PSNC hydrogel for polymerized sulfobetaine methacrylate (SBMA), N-(2-amino-2-oxyethyl)acrylamide (NAGA), and 1-carboxy-N-methyl-N-di(2-methacryloyloxy-ethyl)methanaminium inner salt (CBMAX), was fabricated as a wound dressing for burn injuries via one-pot radical polymerization in glycerine (GLY)/H₂O solvent. The dual cross-linked network of the PSNC hydrogel combined the double hydrogen bonding of N-(2-amino-2-oxyethyl)acrylamide (NAGA) with a covalently cross-linked zwitterionic network, endowing the hydrogel with skin-like mechanical properties with a high stretchability of 1613.8 ± 79.8%, a tensile strength of 77.5 ± 1.8 kPa, and a tensile modulus of 1.9 ± 0.1 kPa. Moreover, the hydrogel with well-developed adaptability can withstand skin deformation without breaking or debonding attributed to its good tissue adhesiveness and self-healing ability. Further, the utilization of the GLY/H₂O binary solvent effectively prevented the crystallization and evaporation of free water, endowing the hydrogel with not only long-lasting moisture but also excellent temperature tolerance in a wide range from -20 to 60 °C. More importantly, the PSNC hydrogel could effectively accelerate wound healing of burn injuries and could be easily removed on-demand with saline without causing secondary damage due to intense hydration. Such a novel PSNC zwitterionic hydrogel could be a promising candidate for the treatment of burn wounds and tissue regeneration.

Strong Hydration Ability of Silk Fibroin Suppresses Formation and Recrystallization of Ice Crystals During Cryopreservation

The cryopreservation (CP) of cell/tissue is indispensable in medical science. However, the formation of ice during cooling and ice recrystallization/growth in time of thawing present significant risk of cell/tissue damage upon analysis of CP process. Herein, the natural and biocompatible silk fibroin (SF) with regular hydrophobic and hydrophilic domains, were first employed as a cryoprotectant (CPA), to the CP of human bone-derived mesenchymal stem cells (hBMSCs), which has been routinely cyropreserved for cell-based therapies. Addtion of SF can regulate the formation of ice crystals during cooling process because of its strong hydration ability in the comparation to the cryopreservation medium (CM) without SF. Moreover, the devitrification-induced recrystallization/growth of ice during the thawing process is suppressed. Most importantly, the addition of 10 mg mL^-1 SF can achieve 81.28% cell viability of cryopreserved hBMSCs as similar as those with the addition of 180 mg mL^-1 Ficoll 70 (commercial CPA), and the functions of the cryopreserved hBMSCs are maintained as good as that of the fresh ones. This work is not only significant for meeting the ever-increasing demand of cell therapy, but also trailblazing for designing materials in controlling ice formation and growth during the CP of other cells and tissues.

Dimethyl Sulfoxide-Free Cryopreservation of Human Umbilical Cord Mesenchymal Stem Cells Based on Zwitterionic Betaine and Electroporation

The effective cryopreservation of mesenchymal stem cells (MSCs) is indispensable to the operation of basic research and clinical transplantation. The prevalent protocols for MSC cryopreservation utilize dimethyl sulfoxide (DMSO), which is easily permeable and able to protect MSCs from cryo-injuries, as a primary cryoprotectant (CPA). However, its intrinsic toxicity and adverse effects on cell function remain the bottleneck of MSC cryopreservation. In this work, we cryopreserved human umbilical cord mesenchymal stem cells (UCMSCs) using zwitterionic betaine combined with electroporation without any addition of DMSO. Betaine was characterized by excellent compatibility and cryoprotective properties to depress the freezing point of pure water and balance the cellular osmotic stress. Electroporation was introduced to achieve intracellular delivery of betaine, intending to further provide comprehensive cryoprotection on UCMSCs. Compared with DMSO cryopreservation, UCMSCs recovered from the protocol we developed maintained the normal viability and functions and reduced the level of reactive oxygen species (ROS) that are harmful to cell metabolism. Moreover, the in vivo distribution of thawed UCMSCs was consistent with that of fresh cells monitored by a bioluminescence imaging (BLI) system. This work opens a new window of opportunity for DMSO-free MSC cryopreservation using zwitterionic compounds like betaine combined with electroporation.

Solid Composite Material for Delivering Viable Cells into Skin Tissues via Detachable Dissolvable Microneedles

Delivering cells to desired locations in the body is needed for disease treatments, tissue repairs, and various scientific investigations such as animal models for drug development. Here, we report the solid composite material that when embedded with viable cells, can temporarily keep cells alive. Using the material, we also show the fabrication of detachable dissolvable microneedles (DMNs) that can instantly deliver viable cells into skin tissue. B16-F10-murine-melanoma (B16-F10) and human-embryonic-kidney-293T (HEK293T) cells embedded in the solid matrix of the hyaluronic/polyvinylpyrolidone/maltose (HA/PVP/maltose) mixture show 50.6 ± 12.0 and 71.0 ± 5.96% survivals, respectively, when kept at 4 °C for 24 h. Detachable DMNs made of the HA/PVP/maltose mixture and loaded with B16-F10-cells were constructed, and the obtained DMN patches could detach the cell-loaded needles into the skin within 1 min of patch application. In vivo intradermal tumorgrafting mice with the DMNs containing 800 cells of B16-F10 developed tumors 10 times bigger in volume than tumors induced by hypodermic needle injection of suspension containing 100,000 cells. We anticipate this work to be a starting point for viable cell encapsulation in the solid matrix and viable cell delivery via DMNs.