Design of suspension culture system with bubble sparging for human induced pluripotent stem cells in a plastic fluid

Application of bacterial-derived long cellulose nanofiber to suspension culture of mammalian cells as a shear protectant

Nanofibrillated bacterial cellulose (NFBC) is a bio-compatible long-fiber nanocellulose produced by cellulose-synthesizing bacteria. It forms an entangled network structure in the suspension state, thereby imparting greater viscosity than conventional media additives. In this study, we examined its application as a shear protectant in the suspension culture of mammalian cells to mitigate hydrodynamic stress imposed on the cells. The media supplemented with hydroxypropyl cellulose-adsorbed NFBC (HP-NFBC) exhibited an increase in shear viscosity according to rheometric analysis, similar to FP003, a commercially available medium additive. Suspension culture of Chinese hamster ovary cells in HP-NFBC-containing media under a high stirring rate (120 rpm) demonstrated higher cell growth and lower cell death compared to those in the medium without additives and in FP003. A 0.10 (w/v)% concentration of HP-NFBC showed the highest viable cell number among the tested concentrations. Computational fluid dynamics simulation revealed a decrease in shear rate and flow velocity within the spinner flask owing to the addition of HP-NFBC or FP003. It is suggested that the decline of these parameters in high-viscosity media suppresses the hydrodynamic stress on cells. This study highlights the potential of HP-NFBC as a shear protectant in mammalian cell suspension culture.

The impact of repeated temperature cycling on cryopreserved human iPSC viability stems from cytochrome redox state changes

Human induced pluripotent stem cells (hiPSCs) are an attractive cell source for regenerative medicine. For its widespread use as a starting material, a robust storage and distribution system in the frozen state is necessary. For this system, managing transient warming during storage and transport is essential, but how transient warming affects cells and the mechanisms involved are not yet fully understood. This study examined the influence of temperature cyclings (from -80°C to -150°C) on cryopreserved hiPSCs using a custom-made cryo Raman microscope, flow cytometry, and performance indices to assess viability. Raman spectroscopy indicated the disappearance of mitochondrial cytochrome signals after thawing. A reduction in the mitochondrial membrane potential was detected using flow cytometry. The performance indices indicated a decrease in attachment efficiency with an increase in the number of temperature cycles. This decrease was observed in the temperature cycle range above the glass transition temperature of the cryoprotectant. Raman observations captured an increase in the signal intensity of intracellular dimethyl sulfoxide (DMSO) during temperature cycles. Based on these results, we proposed a schematic illustration for cellular responses to temperature fluctuations, suggesting that temperature fluctuations above the glass-transition temperature trigger the movement of DMSO, leading to cytochrome c oxidation, mitochondrial damage, and caspase-mediated cell death. This enhances our understanding of the key events during cryopreservation and informs the development of quality control strategies for hiPSC storage and transport.

Growth prolongation of human induced pluripotent stem cell aggregate in three-dimensional suspension culture system by addition of botulinum hemagglutinin

Human induced pluripotent stem cells (hiPSCs) can be used in regenerative therapy as an irresistible cell source, and so the development of scalable production of hiPSCs for three-dimensional (3D) suspension culture is required. In this study, we established a simple culture strategy for improving hiPSC aggregate growth using botulinum hemagglutinin (HA), which disrupts cell-cell adhesion mediated by E-cadherin. When HA was added to the suspension culture of hiPSC aggregates, E-cadherin-mediated cell-cell adhesion was temporarily disrupted within 24 h, but then recovered. Phosphorylated myosin light chain, a contractile force marker, was also recovered at the periphery of hiPSC aggregates. The cell aggregates were suppressed the formation of collagen type I shell-like structures at the periphery by HA and collagen type I was homogenously distributed within the cell aggregates. In addition, these cell aggregates retained the proliferation marker Ki-67 throughout the cell aggregates. The apparent specific growth rate with HA addition was maintained continuously throughout the culture, and the final cell density was 1.7-fold higher than that in the control culture. These cells retained high expression levels of pluripotency markers. These observations indicated that relaxation of cell-cell adhesions by HA addition induced rearrangement of the mechanical tensions generated by actomyosin in hiPSC aggregates and suppression of collagen type I shell-like structure formation. These results suggest that this simple and readily culture strategy is a potentially useful tool for improving the scalable production of hiPSCs for 3D suspension cultures.