Video analysis of osmotic cell response during cryopreservation

Is post-hypertonic lysis of human red blood cells caused by excessive cell volume regulation?

Human red blood cells (RBC) exposed to hypertonic media are subject to post-hypertonic lysis - an injury that only develops during resuspension to an isotonic medium. The nature of post-hypertonic lysis was previously hypothesized to be osmotic when cation leaks were observed, and salt loading was suggested as a cause of the cell swelling upon resuspension in an isotonic medium. However, it was problematic to account for the salt loading since the plasma membrane of human RBCs was considered impermeable to cations. In this study, the hypertonicity-related behavior of human RBCs is revisited within the framework of modern cell physiology, considering current knowledge on membrane ion transport mechanisms - an account still missing. It is recognized here that the hypertonic behavior of human RBCs is consistent with the acute regulatory volume increase (RVI) response - a healthy physiological reaction initiated by cells to regulate their volume by salt accumulation. It is shown by reviewing the published studies that human RBCs can increase cation conductance considerably by activating cell volume-regulated ion transport pathways inactive under normal isotonic conditions and thus facilitate salt loading. A simplified physiological model accounting for transmembrane ion fluxes and membrane voltage predicts the isotonic cell swelling associated with increased cation conductance, eventually reaching hemolytic volume. The proposed involvement of cell volume regulation mechanisms shows the potential to explain the complex nature of the osmotic response of human RBCs and other cells. Cryobiological implications, including mechanisms of cryoprotection, are discussed.

Real-time computer assisted measurement of oocyte and embryo volume for assessment of transport parameters

Cryopreservation of gametes has revolutionized both animal agriculture and human reproductive medicine. Although many new technologies have tremendously improved the cryopreservation of oocytes and embryos, osmotic stress encountered during the equilibration process can cause their loss of function. Rational cryoprotective agent (CPA) equilibration strategies can be used to minimize this stress but require trained personnel to monitor the process in individual oocytes or embryos or require the use of suboptimal average transport parameter values in mathematically guided protocols. To enable individually optimized equilibration of CPAs in individual cells, here we establish experimental and computational techniques to track the osmotic behavior of individual bovine oocytes and embryos during CPA equilibration in real time. We designed a microfluidic device to provide a controlled flow of CPA and modified standard image analysis techniques to estimate real-time cell volume changes. In particular, we used a level-set method to define a boundary within a contour plot which could automate the image analysis process. A colour based level set algorithm coupled with contour smoothing not only provided the best fit but also reduced the segmentation time to well under a second per image. The accuracy of the automated method was comparable to human segmented images for both oocytes and embryos. This technology should enable both rapid evaluation of key biophysical parameters in oocytes and embryos undergoing CPA equilibration and the development of real-time feedback-control of CPA equilibration, enabling individual oocyte- and embryo-specific optimal protocols.

Particles in Biopharmaceutical Formulations, Part 2: An Update on Analytical Techniques and Applications for Therapeutic Proteins, Viruses, Vaccines and Cells

Particles in biopharmaceutical formulations remain a hot topic in drug product development. With new product classes emerging it is crucial to discriminate particulate active pharmaceutical ingredients from particulate impurities. Technical improvements, new analytical developments and emerging tools (e.g., machine learning tools) increase the amount of information generated for particles. For a proper interpretation and judgment of the generated data a thorough understanding of the measurement principle, suitable application fields and potential limitations and pitfalls is required. Our review provides a comprehensive overview of novel particle analysis techniques emerging in the last decade for particulate impurities in therapeutic protein formulations (protein-related, excipient-related and primary packaging material-related), as well as particulate biopharmaceutical formulations (virus particles, virus-like particles, lipid nanoparticles and cell-based medicinal products). In addition, we review the literature on applications, describe specific analytical approaches and illustrate advantages and drawbacks of currently available techniques for particulate biopharmaceutical formulations.

Controlled Release of Cryoprotectants by Near-Infrared Irradiation for Improved Cell Cryopreservation

Cryopreservation is essential to store living cells and tissues for future use while maintaining the proper levels of cell functions. The use of cryoprotective agents (CPAs) to inhibit intracellular ice formation during cryopreservation is vital for cell survival, but the addition and removal of CPAs and ice recrystallization during rewarming will cause fatal injury to cells. The conventional CPA loading and unloading methods generate osmotic shocks and cause mechanical injury to biological samples, and the conventional method of rewarming using a water bath also leads to ice recrystallization and devitrification. A new CPA-loaded microparticle-based method for loading and photothermal rewarming under near-infrared (NIR) laser irradiation was proposed to overcome these difficulties. We have successfully achieved the controlled release of CPAs (2 M EG, 2 M PG, and 0.5 M trehalose) with a graphene oxide (GO, 0.04% w/v) core from a 1.5% (w/v) sodium alginate shell to the human umbilical vein endothelial cells (HUVECs) within 60 s using NIR laser irradiation (808 nm Lasever at 5000 mW/cm²) and successfully recovered the CPA-loaded cells with 0.04% (w/v) GO in 8-10 s using the same NIR irradiation. The results show that this method achieved 25% higher viability of HUVECs compared to the conventional method. In short, this study proposes a new approach for achieving controlled CPA loading to cells with a photothermal-induced strategy for cell cryopreservation.

Label-Free Resistance Cytometry at the Orifice of a Nanopipette

Development of new principles and techniques at the single-cell level is significantly important since cells as basic units of living organisms always bear large heterogeneity. Herein, we demonstrate a new electrochemical principle for single-cell analysis based on an ion current blockage at the orifice of a nanopipette, defined as resistance cytometry. The amplitude and the frequency of ion current transients show strong dependence on the size and the concentration of cells, which could be used for in situ cell sizing and counting. This technique shows good ability to detect the size change of RBCs under stimulations of different pH and osmotic pressure values. More importantly, the as-presented resistance cytometry can distinguish lymphoma blood cells from normal blood cells for patient blood samples. The as-presented resistance cytometry is label-free, non-invasive, and non-destructive, which not only opens new opportunities for single-cell analysis but also provides a new platform for cell-related medical diagnostic technologies.

Effects of ectoine on behavioral, physiological and biochemical parameters of Daphnia magna exposed to dimethyl sulfoxide

DMSO is a very common solvent for hydrophobic chemicals that may pose a threat to aquatic organisms. Ectoine (ECT) is a protective amino acid produced by various strains of halophilic bacteria with high potential to alleviate detrimental effects induced by environmental stressors. This amino acid is used in many cosmetics and pharmaceuticals may enter aquatic ecosystems interacting with ions and macromolecules. Little is known on the effects of DMSO and its interaction with ECT on behavioral, physiological and biochemical endpoints of aquatic invertebrates. Therefore, the purpose of the present study was to determine protective effects of DMSO alone and in the combination with ECT on hopping frequency, swimming speed, heart rate, thoracic limb activity, catalase activity and NOx level in an animal model, Daphnia magna subjected to 0.1% and 1% DMSO alone and during combinatorial exposure to ECT (0-25 mg/L) and DMSO for 24 h and 48 h. The results showed that swimming speed, heart rate and thoracic limb activity were inhibited by both 0.1% and 1% DMSO alone however alleviating effects were observed in the combination DMSO + ECT. Thoracic limb activity was higher in the animals exposed to both solutions of DMSO alone, however the parameter was more stimulated at DMSO + ECT. The results suggest that DMSO alone may alter Daphnia behavior and physiological parameters, therefore use of the control group of non-treated animals with DMSO alone would be recommended to avoid data misinterpretation.

Automated image processing as an analytical tool in cell cryopreservation for bioprocess development

The continuous availability of cells with defined cell characteristics represents a crucial issue in the biopharmaceutical and cell therapy industry. Here, development of cell banks with a long-term stability is essential and ensured by a cryopreservation strategy. The strategy needs to be optimized for each cell application individually and usually comprises controlled freezing, storage at ultra-low temperature, and fast thawing of cells. This approach is implemented by the development of master and working cell banks. Currently, empirical cryopreservation strategy development is standard, but a knowledge-based approach would be highly advantageous. In this article, we report the development of a video-based tool for the characterisation of freezing and thawing behaviour in cryopreservation process to enable a more knowledge-based cryopreservation process development. A successful tool validation was performed with a model cryopreservation process for the β-cell line INS-1E. Performance was evaluated for two working volumes (1.0 mL and 2.0 mL), based on freezing-thawing rates (20 °C to - 80 °C) and cell recovery and increase of biomass, to determine tool flexibility and practicality. Evaluation confirmed flexibility by correctly identifying a delay in freezing and thawing for the larger working volume. Further more, a decrease in cell recovery from 0.94 (± 0.14) % using 1.0 mL working volume to 0.61 (± 0.05) % using a 2.0 mL working volume displays tool practicality. The video-based tool proposed in this study presents a powerful tool for cell-specific optimisation of cryopreservation protocols. This can facilitate faster and more knowledge-based cryopreservation process development In this study, a video-based analytical tool was developed for the characterisation of freezing and thawing behaviour in cryopreservation process development. Evaluation of the practicality and flexibility of the developed tool was done based on a scale-up case study with the cell line INS-1E. Here, the influence of sample working volume on process performance was investigated. Increasing the volume from 1to 2 mL led to a delay in freezing and thawing behaviour which caused cell recovery loss. We believe that the developed tool will facilitate more directed and systematic cryopreservation process development.

The application of convolution neural network based cell segmentation during cryopreservation

For most of the cells, water permeability and plasma membrane properties play a vital role in the optimal protocol for successful cryopreservation. Measuring the water permeability of cells during subzero temperature is essential. So far, there is no perfect segmentation technique to be used for the image processing task on subzero temperature accurately. The ice formation and variable background during freezing posed a significant challenge for most of the conventional segmentation algorithms. Thus, a robust and accurate segmentation approach that can accurately extract cells from extracellular ice that surrounding the cell boundary is needed. Therefore, we propose a convolutional neural network (CNN) architecture similar to U-Net but differs from those conventionally used in computer vision to extract all the cell boundaries as they shrank in the engulfing ice. The images used was obtained from the cryo-stage microscope, and the data was validated using the Hausdorff distance, means ± standard deviation for different methods of segmentation result using the CNN model. The experimental results prove that the typical CNN model extracts cell borders contour from the background in its subzero state more coherent and effective as compared to other traditional segmentation approaches.

Analysis of polarized-light effects in glass-promoting solutions with applications to cryopreservation and organ banking

This study presents experimental results and an analysis approach for polarized light effects associated with thermomechanical stress during cooling of glass promoting solutions, with applications to cryopreservation and tissue banking in a process known as vitrification. Polarized light means have been previously integrated into the cryomacroscope-a visualization device to detect physical effects associated with cryopreservation success, such as crystallization, fracture formation, and contamination. The experimental study concerns vitrification in a cuvette, which is a rectangular container. Polarized light modeling in the cuvette is based on subdividing the tridimensional (3D) domain into a series of planar (2D) problems, for which a mathematical solution is available in the literature. The current analysis is based on tracking the accumulated changes in light polarization and magnitude, as it passes through the sequence of planar problems. Results of this study show qualitative agreement in light intensity history and distribution between experimental data and simulated results. The simulated results help explaining differences between 2D and 3D effects in photoelasticity, most notably, the counterintuitive observation that high stress areas may correlate with low light intensity regions based on the particular experimental conditions. Finally, it is suggested that polarized-light analysis must always be accompanied by thermomechanical stress modeling in order to explain 3D effects.

Insights on Cryopreserved Sheep Fibroblasts by Cryomicroscopy and Gene Expression Analysis

Cryopreservation includes a set of techniques aimed at storing biological samples and preserving their biochemical and functional features without any significant alterations. This study set out to investigate the effects induced by cryopreservation on cultured sheepskin fibroblasts (CSSF) through cryomicroscopy and gene expression analysis after subsequent in vitro culture. CSSF cells were cryopreserved in a cryomicroscope (CM) or in a straw programmable freezer (SPF) using a similar thermal profile (cooling rate -5°C/min to -120°C, then -150°C/min to -196°C). CSSF volume and intracellular ice formation (IIF) were monitored by a CM, while gene expression levels were investigated by real-time polymerase chain reaction in SPF-cryopreserved cells immediately after thawing (T0) and after 24 or 48 hours (T24, T48) of post-thaw in vitro culture. No significant difference in cell viability was observed at T0 between CM and SPF samples, while both CM and SPF groups showed lower viability (p < 0.05) compared to the untreated control group. Gene expression analysis of cryopreserved CSSF 24 and 48 hours post-thawing showed a significant upregulation of the genes involved in protein folding and antioxidant mechanisms (HPS90b and SOD1), while a transient increase (p < 0.05) in the expression levels of OCT4, BCL2, and GAPDH was detected 24 hours post-thawing. Overall, our data suggest that cryostored CSSF need at least 24 hours to activate specific networks to promote cell readaptation.

Polarized light scanning cryomacroscopy, part I: Experimental apparatus and observations of vitrification, crystallization, and photoelasticity effects

Cryomacroscopy is an effective means to observe physical events affecting cryopreservation success in large-size specimens. The current study aims at integrating polarized-light in the study of large-size cryopreservation, using the scanning cryomacroscope as a development platform. Results of this study demonstrate polarized light as a visualization enhancement means, including the following effects: contaminants in the CPA solution, crystallization, fracture formation, thermal contraction, and solute precipitation. In addition, photoelasticity effects are used to demonstrate the development of residual stresses and the potential for stress relaxation above the glass transition temperature. Furthermore, this study suggests that the ability to periodically switch between non-polarized light and polarized light is an essential feature of investigation. When using polarized light for example, a dark region may represent a free-of-stress and free-of-crystals material, or fully crystallized material, which may potentially experience mechanical stress; switching to a non-polarized light would help to distinguish between the different cases. The analysis of thermo-mechanical stress in cryopreservation is essentially based on four key elements: identification of physical events, knowledge of physical properties, thermal analysis of the specimen, and description of the mechanical behavior of the cryopreserved material (also known as the constitutive law). With the above knowledge, one can investigate the conditions to preserve structural integrity. While the current study aims at identification of physical events, critical knowledge on physical properties and mechanical behavior has already been developed in previous studies. The companion manuscript (Part II) aims at providing means for thermal analysis in the specimen, which will serve as the basis for a multi-scale analysis of thermo-mechanical stress in large-size specimens.

Adaptive responses of cell hydration to a low temperature arrest

Slow cooling leads to a passive dehydration of cells, whereas rehydration during warming reflects the active regain of functionality. The ability to modulate such an energy demanding process could be instrumental in optimizing the cryo-arrest of living systems. In the present study, various levels of hypertonic stress were used to disturb the water content of cells and to define the energy profiles of aquaporins and (Na(+) conducting) cation channels during rehydration. Na(+) import was found to be the rate-limiting step in water restoration, whereas aquaporins merely played a permissive role. Indeed, regulated Na(+) import was increased 2-fold following cryo-arrests, thus facilitating the osmotic rehydration of cells. Freezing temperatures increased cell viscosity with a remarkable hysteresis and viscosity was a trigger of cation channels. The peptide hormone vasopressin was a further activator of channels, increasing the viability of post-cryo cells considerably. Hence, the hormone opens the path for a novel class of cryo-protectants with an intrinsic biological activity.

Active control of the nucleation temperature enhances freezing survival of multipotent mesenchymal stromal cells

Cryopreservation is a technique that has been extensively used for storage of multipotent mesenchymal stromal cells (MSCs) in regenerative medicine. Therefore, improving current cryopreservation procedures in terms of increasing cell viability and functionality is important. In this study, we optimized the cryopreservation protocol of MSCs derived from the common marmoset Callithrix jacchus (cj), which can be used as a non-human primate model in various pathological and transplantation studies and have a great potential for regenerative medicine. We have investigated the effect of the active control of the nucleation temperature using induced nucleation at a broad range of temperatures and two different dimethylsulfoxide concentrations (Me2SO, 5% (v/v) and 10%, (v/v)) to evaluate the overall effect on the viability, metabolic activity and recovery of cells after thawing. Survival rate and metabolic activity displayed an optimum when ice formation was induced at -10 °C. Cryomicroscopy studies indicated differences in ice crystal morphologies as well as differences in intracellular ice formation with different nucleation temperatures. High subzero nucleation temperatures resulted in larger extracellular ice crystals and cellular dehydration, whereas low subzero nucleation temperatures resulted in smaller ice crystals and intracellular ice formation.

The Scanning Cryomacroscope - A Device Prototype for the Study of Cryopreservation

A new cryomacroscope prototype-a visualization device for the in situ analysis of cryopreserved biological samples-is presented in the current study. In order to visualize samples larger than the field of view of the optical setup, a scanning mechanism is integrated into the system, which represents a key improvement over previous cryomacroscope prototypes. Another key feature of the new design is in its compatibility with available top-loading controlled-rate cooling chambers, which eliminates the need for a dedicated cooling mechanism. The objective for the current development is to create means to generate a single digital movie of an experimental investigation, with all relevant data overlaid. The visualization capabilities of the scanning cryomacroscope are demonstrated in the current study on the cryoprotective agent dimethyl sulfoxide and the cryoprotective cocktail DP6. Demonstrated effects include glass formation, various regimes of crystallization, thermal contraction, and fracture formation.

Storage of human biospecimens: selection of the optimal storage temperature

Millions of biological samples are currently kept at low tempertures in cryobanks/biorepositories for long-term storage. The quality of the biospecimen when thawed, however, is not only determined by processing of the biospecimen but the storage conditions as well. The overall objective of this article is to describe the scientific basis for selecting a storage temperature for a biospecimen based on current scientific understanding. To that end, this article reviews some physical basics of the temperature, nucleation, and ice crystal growth present in biological samples stored at low temperatures (-20°C to -196°C), and our current understanding of the role of temperature on the activity of degradative molecules present in biospecimens. The scientific literature relevant to the stability of specific biomarkers in human fluid, cell, and tissue biospecimens is also summarized for the range of temperatures between -20°C to -196°C. These studies demonstrate the importance of storage temperature on the stability of critical biomarkers for fluid, cell, and tissue biospecimens.