A highly active mineral-based ice nucleating agent supports in situ cell cryopreservation in a high throughput format

Induced Extracellular Ice Nucleation Protects Cocultured Spheroid Interior and Exterior during Cryopreservation

Spheroids and other 3D cellular models more accurately recapitulate physiological responses when compared to 2D models and represent potential alternatives to animal testing. The cryopreservation of spheroids remains challenging, limiting their wider use. Standard DMSO-only cryopreservation results in supercooling to low subzero temperatures, reducing viability, shedding surface cells, and perforating spheroid interiors. Here, cocultured spheroids with differentially labeled outer cell layers allow spatial evaluation of the protective effect of macromolecular ice nucleators by microscopy and histology. Extracellular nucleation is shown to reduce damage to both interior and exterior regions of the spheroids, which will support the development of "off-the-shelf" 3D models.

The presence of nanoparticles in aqueous droplets containing plant-derived biopolymers plays a role in heterogeneous ice nucleation

Organic matter can initiate heterogeneous ice nucleation in supercooled water droplets, thereby influencing atmospheric cloud glaciation. Predicting the ice nucleation ability of organic matter-containing cloud droplets is challenging due to the unknown mechanism for templating ice. Here, we observed the presence of nanoparticles in aqueous samples of known ice-nucleating biopolymers cellulose and lignin, as well as in newly identified ice-nucleating biopolymers xylan and laminarin. Using our drop Freezing Ice Nuclei Counter (FINC), we measured the median ice nucleation temperature (T50) of xylan and of laminarin droplets of 2 μl to be -14.2 and -20.0 °C, respectively. Next, we characterized these samples using nanoparticle tracking analysis, and we detected and quantified nanoparticles with mean diameters between 132 and 267 nm. Xylan contained the largest nanoparticles and froze at higher temperatures. Xylan also dictated the freezing in a 1:1:1:1 mixture with cellulose, lignin, laminarin, and xylan. Filtration experiments down to 300 kDa with the xylan sample indicated that the presence of nanoparticles triggered freezing. Overall, only samples with mean diameters above 150 nm froze above -20 °C. Furthermore, we determined the ice-active site densities normalized to particle concentrations, surface area, and mass of the nanoparticles to show that the samples' nucleation site densities are similar to sea spray aerosols and nanometer-sized dust. The identification and characterization of xylan and laminarin as nanometer-sized ice-nucleating substances expands the growing list of organic matter capable of impacting cloud formation and thus climate.

Cryopreserved Kidney Epithelial (Vero) Cell Monolayers for Rapid Viral Quantification, Enabled by a Combination of Macromolecular Cryoprotectants

Plaque assays quantify the amount of active, replicating virus to study and detect infectious diseases by application of samples to monolayers of cultured cells. Due to the time taken in thawing, propagating, plating, counting, and then conducting the assay, the process can take over a week to gather data. Here, we introduce assay-ready cryopreserved Vero monolayers in multiwell plates, which can be used directly from the freezer with no cell culture to accelerate the process of plaque determination. Standard dimethyl sulfoxide cryopreservation resulted in just 25% recovery, but addition of polyampholytes (macromolecular cryoprotectants) increased post-thaw recovery and viability in 12- and 24-well plate formats. Variability between individual wells was reduced by chemically induced ice nucleation to prevent supercooling. Cryopreserved cells were used to determine influenza viral plaques in just 24 h, matching results from nonfrozen controls. This innovation may accelerate viral detection and quantification and facilitate automation by eliminating extensive cell culturing.

Cryopreservation and Rapid Recovery of Differentiated Intestinal Epithelial Barrier Cells at Complex Transwell Interfaces Is Enabled by Chemically Induced Ice Nucleation

Cell-based models, such as organ-on-chips, can replace and inform in vivo (animal) studies for drug discovery, toxicology, and biomedical science, but most cannot be banked "ready to use" as they do not survive conventional cryopreservation with DMSO alone. Here, we demonstrate how macromolecular ice nucleators enable the successful cryopreservation of epithelial intestinal models supported upon the interface of transwells, allowing recovery of function in just 7 days post-thaw directly from the freezer, compared to 21 days from conventional suspension cryopreservation. Caco-2 cells and Caco-2/HT29-MTX cocultures are cryopreserved on transwell inserts, with chemically induced ice nucleation at warmer temperatures resulting in increased cell viability but crucially retaining the complex cellular adhesion on the transwell insert interfaces, which other cryoprotectants do not. Trans-epithelial electrical resistance measurements, confocal microscopy, histology, and whole-cell proteomics demonstrated the rapid recovery of differentiated cell function, including the formation of tight junctions. Lucifer yellow permeability assays confirmed that the barrier functions of the cells were intact. This work will help solve the long-standing problem of transwell tissue barrier model storage, facilitating access to advanced predictive cellular models. This is underpinned by precise control of the nucleation temperature, addressing a crucial biophysical mode of damage.

Cryopreservation of organoids: Strategies, innovation, and future prospects

Organoid technology has demonstrated unique advantages in multidisciplinary fields such as disease research, tumor drug sensitivity, clinical immunity, drug toxicology, and regenerative medicine. It will become the most promising research tool in translational research. However, the long preparation time of organoids and the lack of high-quality cryopreservation methods limit the further application of organoids. Although the high-quality cryopreservation of small-volume biological samples such as cells and embryos has been successfully achieved, the existing cryopreservation methods for organoids still face many bottlenecks. In recent years, with the development of materials science, cryobiology, and interdisciplinary research, many new materials and methods have been applied to cryopreservation. Several new cryopreservation methods have emerged, such as cryoprotectants (CPAs) of natural origin, ice-controlled biomaterials, and rapid rewarming methods. The introduction of these technologies has expanded the research scope of cryopreservation of organoids, provided new approaches and methods for cryopreservation of organoids, and is expected to break through the current technical bottleneck of cryopreservation of organoids. This paper reviews the progress of cryopreservation of organoids in recent years from three aspects: damage factors of cryopreservation of organoids, new protective agents and loading methods, and new technologies of cryopreservation and rewarming.

Investigation of Rapid Rewarming Chips for Cryopreservation by Joule Heating

Rapid and uniform rewarming is critical to cryopreservation. Current rapid rewarming methods require complex physical field application devices (such as lasers or radio frequencies) and the addition of nanoparticles as heating media. These complex devices and nanoparticles limit the promotion of the rapid rewarming method and pose potential biosafety concerns. In this work, a joule heating-based rapid electric heating chip (EHC) was designed for cryopreservation. Uniform and rapid rewarming of biological samples in different volumes can be achieved through simple operations. EHC loaded with 0.28 mL of CPA solution can achieve a rewarming rate of 3.2 × 105 °C/min (2.8 mL with 2.3 × 103 °C/min), approximately 2 orders of magnitude greater than the rewarming rates observed with an equal capacity straw when combined with laser nanowarming or magnetic induction heating. In addition, the degree of supercooling can be significantly reduced without manual nucleation during the cooling of the EHC. Subsequently, the results of cryopreservation validation of cells and spheroids showed that the cell viability and spheroid structural integrity were significantly improved after cryopreservation. The viability of human lung adenocarcinoma (A549) cells postcryopreservation was 97.2%, which was significantly higher than 93% in the cryogenic vials (CV) group. Similar results were seen in human mesenchymal stem cells (MSCs), with 93.18% cell survival in the EHC group, significantly higher than 86.83% in the CV group, and cells in the EHC group were also significantly better than those in the CV group for further apoptosis and necrosis assays. This work provides an efficient rewarming protocol for the cryopreservation of biological samples, significantly improving the quantity and quality of cells and spheroids postcryopreservation.

Advanced cryopreservation engineering strategies: the critical step to utilize stem cell products

With the rapid development of stem cell-related therapies and regenerative medicine, the clinical application of stem cell products is on the rise. However, ensuring the effectiveness of these products after storage and transportation remains a challenge in the transformation to clinical trials. Cryopreservation technology allows for the long-term storage of cells while ensuring viability, making it a top priority for stem cell preservation. The field of cryopreservation-related engineering technologies is thriving, and this review provides an overview of the background and basic principles of cryopreservation. It then delves into the main bioengineering technologies and strategies used in cryopreservation, including photothermal and electromagnetic rewarming, microencapsulation, and synergetic ice inhibition. Finally, the current challenges and future prospects in the field of efficient cryopreservation of stem cells are summarized and discussed.

Chemically Induced Extracellular Ice Nucleation Reduces Intracellular Ice Formation Enabling 2D and 3D Cellular Cryopreservation

3D cell assemblies such as spheroids reproduce the in vivo state more accurately than traditional 2D cell monolayers and are emerging as tools to reduce or replace animal testing. Current cryopreservation methods are not optimized for complex cell models, hence they are not easily banked and not as widely used as 2D models. Here we use soluble ice nucleating polysaccharides to nucleate extracellular ice and dramatically improve spheroid cryopreservation outcomes. This protects the cells beyond using DMSO alone, and with the major advantage that the nucleators function extracellularly and hence do not need to permeate the 3D cell models. Critical comparison of suspension, 2D and 3D cryopreservation outcomes demonstrated that warm-temperature ice nucleation reduces the formation of (fatal) intracellular ice, and in the case of 2/3D models this reduces propagation of ice between adjacent cells. This demonstrates that extracellular chemical nucleators could revolutionize the banking and deployment of advanced cell models.