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.

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.