Diffusion kinetics and perfusion times in tissue models obtained by bioorthogonal Raman µ-spectroscopy.

The penetration kinetics of small-molecule compounds like nutrients, drugs, and cryoprotective agents into artificial cell aggregates are of pivotal relevance in many applications, from stem cell differentiation and drug screening through to cryopreservation. Depending on compound and tissue properties as well as aggregate size and shape, the penetration behavior can differ vastly. Here, we introduce bioorthogonal Raman microspectroscopy as a contactless technique to investigate the penetration of various compounds into spheroids, organoids, and other tissue models in terms of diffusion coefficients and perfusion times. We showcase the potential of the method by applying it to the radial perfusion of neural stem cell spheroids with the prevalent cryopreservation additive dimethyl sulfoxide. Employing a diffusion model for spherical bodies, the spectroscopic data were quantitatively analyzed. Perfusion times were obtained for spheroids in the sub-mm region, and interesting findings about the spheroid-size dependence of the diffusion coefficient are reported.

Application-Oriented Bulk Cryopreservation of Human iPSCs in Cryo Bags Followed by Direct Inoculation in Scalable Suspension Bioreactors for Expansion and Neural Differentiation.

Stem cell-based therapies are promising tools for regenerative medicine and require bulk numbers of high-quality cells. Currently, cells are produced on demand and have a limited shelf-life as conventional cryopreservation is primarily designed for stock keeping. We present a study on bulk cryopreservation of the human iPSC lines UKKi011-A and BIONi010-C-41. By increasing cell concentration and volume, compared to conventional cryopreservation routines in cryo vials, one billion cells were frozen in 50 mL cryo bags. Upon thawing, the cells were immediately seeded in scalable suspension-based bioreactors for expansion to assess the stemness maintenance and for neural differentiation to assess their differentiation potential on the gene and protein levels. Both the conventional and bulk cryo approach show comparative results regarding viability and aggregation upon thawing and bioreactor inoculation. Reduced performance compared to the non-frozen control was compensated within 3 days regarding biomass yield. Stemness was maintained upon thawing in expansion. In neural differentiation, a delay of the neural marker expression on day 4 was compensated at day 9. We conclude that cryopreservation in cryo bags, using high cell concentrations and volumes, does not alter the cells' fate and is a suitable technology to avoid pre-cultivation and enable time- and cost-efficient therapeutic approaches with bulk cell numbers.

Translation of hyaluronic acid-based vitreous substitutes towards current regulations for medical devices.

PURPOSE: Hydrogel-based vitreous substitutes have the potential to overcome the limitations of current clinically used endotamponades. With the goal of entering clinical trials, the present study aimed to (I) transfer the material synthesis of hyaluronic acid-based hydrogels into a routine, pharmaceutical-appropriate production and (II) evaluate the properties of the vitreous substitutes in terms of the current regulations for medical devices (MDR/ISO standards). METHODS: The multistep manufacturing process of the vitreous substitutes, including the modification of hyaluronic acid with glycidyl methacrylate, photocopolymerization with N-vinylpyrrolidone, and successive hydrogel purification, was developed under laboratory conditions, characterized using 1 H-NMR, FT-IR and UV/Vis spectroscopies and HPLC, and transferred towards a pharmaceutical production environment considering GMP standards. The optical and viscoelastic characteristics of the hyaluronic acid-based hydrogels were compared with those of extracted human vitreous and silicone oil. The effect of the hydrogels on the metabolic activity, proliferation and apoptosis of fibroblast (MRC-5, BJ, L929), retinal pigment epithelial (ARPE-19, hiPSC-derived RPE) and photoreceptor cells (661W) was studied as well as their mucosal tolerance via a HET-CAM assay. RESULTS: Hyaluronic acid-based hydrogels having a suitable purity, sterility, high transparency (>90%), appropriate refractive index (1.3365) and viscoelasticity (G' > G″) were prepared in a standardized manner under controlled process conditions. The metabolic activity, proliferation and apoptosis of various cell types as well as egg choroid were unaffected by the hyaluronic acid-based vitreous substitutes, demonstrating their biocompatibility. CONCLUSIONS: The present study demonstrates the successful transferability of the crucial synthesis steps of hyaluronic acid-based hydrogels into a routine, GMP-compliant production process while achieving the optical and viscoelastic properties, biocompatibility and purity required for their clinical use as vitreous substitutes.

Scalable expansion of iPSC and their derivatives across multiple lineages.

Induced pluripotent stem cell (iPSC) technology enabled the production of pluripotent stem cell lines from somatic cells from a range of known genetic backgrounds. Their ability to differentiate and generate a wide variety of cell types has resulted in their use for various biomedical applications, including toxicity testing. Many of these iPSC lines are now registered in databases and stored in biobanks such as the European Bank for induced pluripotent Stem Cells (EBiSC), which can streamline the quality control and distribution of these individual lines. To generate the quantities of cells for banking and applications like high-throughput toxicity screening, scalable and robust methods need to be developed to enable the large-scale production of iPSCs. 3D suspension culture platforms are increasingly being used by stem cell researchers, owing to a higher cell output in a smaller footprint, as well as simpler scaling by increasing culture volume. Here we describe our strategies for successful scalable production of iPSCs using a benchtop bioreactor and incubator for 3D suspension cultures, while maintaining quality attributes expected of high-quality iPSC lines. Additionally, to meet the increasing demand for "ready-to-use" cell types, we report recent work to establish robust, scalable differentiation protocols to cardiac, neural, and hepatic fate to enable EBiSC to increase available research tools.

Human iPSC-derived hepatocytes in 2D and 3D suspension culture for cryopreservation and in vitro toxicity studies.

Hepatocytes are of special interest in biomedical research for disease modelling, drug screening and in vitro toxicology. Human induced pluripotent stem cell (hiPSC)-derived hepatocytes could complement primary human hepatocytes due to their capability for large-scale expansion. In this study, we present an optimized protocol for the generation of hepatocyte-like cells (HLCs) from hiPSC in monolayer (2D) and suspension culture (3D) for production of organoids. A protocol was initially optimized in 2D using a gene edited CYP3A4 Nanoluciferase reporter hiPSC line for monitoring the maturity of HLCs and cryopreservation of definitive endoderm (DE) cells. The protocol was optimized for microwell cultures for high-throughput screening to allow for a sensitive and fast readout of drug toxicity. To meet the increasing demand of hepatic cells in biomedical research, the differentiation process was furthermore translated to scalable suspension-based bioreactors for establishment of hepatic organoids. In pilot studies, the technical settings have been optimized by adjusting the initial seeding density, rotation speed, inoculation time, and medium viscosity to produce homogeneous hepatic organoids and to maximize the biomass yield (230 organoids/ml). To speed up the production process, cryopreservation approaches for the controlled freezing of organoids were analysed with respect to cell recovery and marker expression. The results showed that cryopreserved organoids maintained their phenotype only when derived from hepatocyte progenitors (HPs) at day 8 but not from more mature stages. The establishment of robust protocols for the production of large batches of hepatocytes and hepatic organoids could substantially boost their use in biomedical and toxicology studies.

Droplet-based vitrification of adherent human induced pluripotent stem cells on alginate microcarrier influenced by adhesion time and matrix elasticity.

The gold standard in cryopreservation is still conventional slow freezing of single cells or small aggregates in suspension, although major cell loss and limitation to non-specialised cell types in stem cell technology are known drawbacks. The requirement for rapidly available therapeutic and diagnostic cell types is increasing constantly. In the case of human induced pluripotent stem cells (hiPSCs) or their derivates, more sophisticated cryopreservation protocols are needed to address this demand. These should allow a preservation in their physiological, adherent state, an efficient re-cultivation and upscaling upon thawing towards high-throughput applications in cell therapies or disease modelling in drug discovery. Here, we present a novel vitrification-based method for adherent hiPSCs, designed for automated handling by microfluidic approaches and with ready-to-use potential e.g. in suspension-based bioreactors after thawing. Modifiable alginate microcarriers serve as a growth surface for adherent hiPSCs that were cultured in a suspension-based bioreactor and subsequently cryopreserved via droplet-based vitrification in comparison to conventional slow freezing. Soft (0.35%) versus stiff (0.65%) alginate microcarriers in concert with adhesion time variation have been examined. Findings revealed specific optimal conditions leading to an adhesion time and growth surface (matrix) elasticity dependent hypothesis on cryo-induced damaging regimes for adherent cell types. Deviations from the found optimum parameters give rise to membrane ruptures assessed via SEM and major cell loss after adherent vitrification. Applying the optimal conditions, droplet-based vitrification was superior to conventional slow freezing. A decreased microcarrier stiffness was found to outperform stiffer material regarding cell recovery, whereas the stemness characteristics of rewarmed hiPSCs were preserved.

An automated and high-throughput-screening compatible pluripotent stem cell-based test platform for developmental and reproductive toxicity assessment of small molecule compounds.

The embryonic stem cell test (EST) represents the only validated and accepted in vitro system for the detection and classification of compounds according to their developmental and reproductive teratogenic potency. The widespread implementation of the EST, however, in particular for routine application in pharmaceutical development, has not been achieved so far. Several drawbacks still limit the high-throughput screening of potential drug candidates in this format: The long assay period, the use of non-homogeneous viability assays, the low throughput analysis of marker protein expression and the compatibility of the assay procedures to automation. We have therefore introduced several advancements into the EST workflow: A reduction of the assay period, an introduction of homogeneous viability assays, and a straightforward analysis of marker proteins by flow cytometry and high content imaging to assess the impact of small molecules on differentiation capacity. Most importantly, essential parts of the assay procedure have been adapted to lab automation in 96-well format, thus enabling the interrogation of several compounds in parallel. In addition, extensive investigations were performed to explore the predictive capacity of this next-generation EST, by testing a set of well-known embryotoxicants that encompasses the full range of chemical-inherent embryotoxic potencies possible. Due to these significant improvements, the augmented workflow provides a basis for a sensitive, more rapid, and reproducible high throughput screening compatible platform to predict in vivo developmental toxicity from in vitro data which paves the road towards application in an industrial setting. Graphical abstract •The embryonic stem cell test to predict teratogenicity was made automation-compatible. •Several key improvements to the assay procedure have been introduced to increase performance. •The workflow was adapted to human iPS cells and isogenic fibroblast donor cells.

A novel human pluripotent stem cell-based assay to predict developmental toxicity.

There is a great need for novel in vitro methods to predict human developmental toxicity to comply with the 3R principles and to improve human safety. Human-induced pluripotent stem cells (hiPSC) are ideal for the development of such methods, because they are easy to retrieve by conversion of adult somatic cells and can differentiate into most cell types of the body. Advanced three-dimensional (3D) cultures of these cells, so-called embryoid bodies (EBs), moreover mimic the early developing embryo. We took advantage of this to develop a novel human toxicity assay to predict chemically induced developmental toxicity, which we termed the PluriBeat assay. We employed three different hiPSC lines from male and female donors and a robust microtiter plate-based method to produce EBs. We differentiated the cells into cardiomyocytes and introduced a scoring system for a quantitative readout of the assay-cardiomyocyte contractions in the EBs observed on day 7. Finally, we tested the three compounds thalidomide (2.3-36 µM), valproic acid (25-300 µM), and epoxiconazole (1.3-20 µM) on beating and size of the EBs. We were able to detect the human-specific teratogenicity of thalidomide and found the rodent toxicant epoxiconazole as more potent than thalidomide in our assay. We conclude that the PluriBeat assay is a novel method for predicting chemicals' adverse effects on embryonic development.

Diffraction-based technology for the monitoring of contraction dynamics in 3D and 2D tissue models.

We present a novel optical device developed for the monitoring of dynamic behavior in extended 3D-tissue models in various culture environments based on variations in their speckle patterns. The results presented point out the benefit of the technology in terms of detection, accuracy, sensitivity and a reasonable read-out speed as well as reproducibility for the measurements and monitoring of cardiac contractions. We show that the optical read-out technology is suitable for long time monitoring and for drug screening. The method is discussed and compared to other techniques, in particular calcium imaging. The device is flexible and easily adaptable to 2D and 3D-tissue model screenings using different culture environments. The technology can be parallelized for automated read-out of different multi-well-plate formats.

Quantitative analysis of F-actin alterations in adherent human mesenchymal stem cells: Influence of slow-freezing and vitrification-based cryopreservation.

Cryopreservation is an essential tool to meet the increasing demand for stem cells in medical applications. To ensure maintenance of cell function upon thawing, the preservation of the actin cytoskeleton is crucial, but so far there is little quantitative data on the influence of cryopreservation on cytoskeletal structures. For this reason, our study aims to quantitatively describe cryopreservation induced alterations to F-actin in adherent human mesenchymal stem cells, as a basic model for biomedical applications. Here we have characterised the actin cytoskeleton on single-cell level by calculating the circular standard deviation of filament orientation, F-actin content, and average filament length. Cryo-induced alterations of these parameters in identical cells pre and post cryopreservation provide the basis of our investigation. Differences between the impact of slow-freezing and vitrification are qualitatively analyzed and highlighted. Our analysis is supported by live cryo imaging of the actin cytoskeleton via two photon microscopy. We found similar actin alterations in slow-frozen and vitrified cells including buckling of actin filaments, reduction of F-actin content and filament shortening. These alterations indicate limited functionality of the respective cells. However, there are substantial differences in the frequency and time dependence of F-actin disruptions among the applied cryopreservation strategies; immediately after thawing, cytoskeletal structures show least disruption after slow freezing at a rate of 1°C/min. As post-thaw recovery progresses, the ratio of cells with actin disruptions increases, particularly in slow frozen cells. After 120 min of recovery the proportion of cells with an intact actin cytoskeleton is higher in vitrified than in slow frozen cells. Freezing at 10°C/min is associated with a high ratio of impaired cells throughout the post-thawing culture.

Zooming in on Cryopreservation of hiPSCs and Neural Derivatives: A Dual-Center Study Using Adherent Vitrification.

Human induced pluripotent stem cells (hiPSCs) are an important tool for research and regenerative medicine, but their efficient cryopreservation remains a major challenge. The current gold standard is slow-rate freezing of dissociated colonies in suspension, but low recovery rates limit immediate post-thawing applicability. We tested whether ultrafast cooling by adherent vitrification improves post-thawing survival in a selection of hiPSCs and small molecule neural precursor cells (smNPCs) from Parkinson's disease and controls. In a dual-center study, we compared the results by immunocytochemistry (ICC), fluorescence-activated cell sorting analysis, and RNA-sequencing (RNA-seq). Adherent vitrification was achieved in the so-called TWIST substrate, a device combining cultivation, vitrification, storage, and post-thawing cultivation. Adherent vitrification resulted in preserved confluency and significantly higher cell numbers, and viability at day 1 after thawing, while results were not significantly different at day 4 after thawing. RNA-seq and ICC of hiPSCs revealed no change in gene expression and pluripotency markers, indicating that physical damage of slow-rate freezing disrupts cellular membranes. Scanning electron microscopy showed preserved colony integrity by adherent vitrification. Experiments using smNPCs demonstrated that adherent vitrification is also applicable to neural derivatives of hiPSCs. Our data suggest that, compared to the state-of-the-art slow-rate freezing in suspension, adherent vitrification is an improved cryopreservation technique for hiPSCs and derivatives. Stem Cells Translational Medicine 2019;8:247&259.

A complete workflow for the differentiation and the dissociation of hiPSC-derived cardiospheres.

Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) are an invaluable tool for both basic and translational cardiovascular research. The potential that these cells hold for therapy, disease modeling and drug discovery is hampered by several bottlenecks that currently limit both the yield and the efficiency of cardiac induction. Here, we present a complete workflow for the production of ready-to-use hiPSC-CMs in a dynamic suspension bioreactor. This includes the efficient and highly reproducible differentiation of hiPSCs into cardiospheres, which display enhanced physiological maturation compared to static 3D induction in hanging drops, and a novel papain-based dissociation method that offers higher yield and viability than the broadly used dissociation reagents TrypLE and Accutase. Molecular and functional analyses of the cardiomyocytes reseeded after dissociation confirmed both the identity and the functionality of the cells, which can be used in downstream applications, either as monolayers or spheroids.

Towards ready-to-use 3-D scaffolds for regenerative medicine: adhesion-based cryopreservation of human mesenchymal stem cells attached and spread within alginate-gelatin cryogel scaffolds.

Cultivation and proliferation of stem cells in three-dimensional (3-D) scaffolds is a promising strategy for regenerative medicine. Mesenchymal stem cells with their potential to differentiate in various cell types, cryopreserved adhesion-based in fabricated scaffolds of biocompatible materials can serve as ready-to-use transplantation units for tissue repair, where pores allow a direct contact of graft cells and recipient tissue without further preparation. A successful cryopreservation of adherent cells depends on attachment and spreading processes that start directly after cell seeding. Here, we analyzed different cultivation times (0.5, 2, 24 h) prior to adhesion-based cryopreservation of human mesenchymal stem cells within alginate-gelatin cryogel scaffolds and its influence on cell viability, recovery and functionality at recovery times (0, 24, 48 h) in comparison to non-frozen control. Analysis with confocal laser scanning microscopy and scanning electron microscopy indicated that 2 h cultivation time enhanced cryopreservation success: cell number, visual cell contacts, membrane integrity, motility, as well as spreading were comparable to control. In contrast, cell number by short cultivation time (0.5 h) reduced dramatically after thawing and expanded cultivation time (24 h) decreased cell viability. Our results provide necessary information to enhance the production and to store ready-to-use transplantation units for application in bone, cartilage or skin regenerative therapy.

The individual-cell-based cryo-chip for the cryopreservation, manipulation and observation of spatially identifiable cells. II: functional activity of cryopreserved cells.

BACKGROUND: The cryopreservation and thawing processes are known to induce many deleterious effects in cells and might be detrimental to several cell types. There is an inherent variability in cellular responses among cell types and within individual cells of a given population with regard to their ability to endure the freezing and thawing process. The aim of this study was to evaluate the fate of cryopreserved cells within an optical cryo apparatus, the individual-cell-based cryo-chip (i3C), by monitoring several basic cellular functional activities at the resolution of individual cells. RESULTS: In the present study, U937 cells underwent the freezing and thawing cycle in the i3C device. Then a panel of vital tests was performed, including the number of dead cells (PI staining), apoptotic rate (Annexin V staining), mitochondrial membrane potential (TMRM staining), cytoplasm membrane integrity and intracellular metabolism (FDA staining), as well as post-thawing cell proliferation assays. Cells that underwent the freezing - thawing cycle in i3C devices exhibited the same functional activity as control cells. Moreover, the combination of the multi-parametric analysis at a single cell resolution and the optical and biological features of the device enable an accurate determination of the functional status of individual cells and subsequent retrieval and utilization of the most valuable cells. CONCLUSIONS: The means and methodologies described here enable the freezing and thawing of spatially identifiable cells, as well as the efficient detection of viable, specific, highly biologically active cells for future applications.

The individual-cell-based cryo-chip for the cryopreservation, manipulation and observation of spatially identifiable cells. I: methodology.

BACKGROUND: Cryopreservation is the only widely applicable method of storing vital cells for nearly unlimited periods of time. Successful cryopreservation is essential for reproductive medicine, stem cell research, cord blood storage and related biomedical areas. The methods currently used to retrieve a specific cell or a group of individual cells with specific biological properties after cryopreservation are quite complicated and inefficient. RESULTS: The present study suggests a new approach in cryopreservation, utilizing the Individual Cell-based Cryo-Chip (i3C). The i3C is made of materials having appropriate durability for cryopreservation conditions. The core of this approach is an array of picowells, each picowell designed to maintain an individual cell during the severe conditions of the freezing--thawing cycle and accompanying treatments. More than 97% of cells were found to retain their position in the picowells throughout the entire freezing--thawing cycle and medium exchange. Thus the comparison between pre-freezing and post-thawing data can be achieved at an individual cell resolution. The intactness of cells undergoing slow freezing and thawing, while residing in the i3C, was found to be similar to that obtained with micro-vials. However, in a fast freezing protocol, the i3C was found to be far superior. CONCLUSIONS: The results of the present study offer new opportunities for cryopreservation. Using the present methodology, the cryopreservation of individual identifiable cells, and their observation and retrieval, at an individual cell resolution become possible for the first time. This approach facilitates the correlation between cell characteristics before and after the freezing--thawing cycle. Thus, it is expected to significantly enhance current cryopreservation procedures for successful regenerative and reproductive medicine.