Stanford Advisors

All Publications

  • Large-Scale Production of Wholly-Cellular Bioinks via the Optimization of Human Induced Pluripotent Stem Cell Aggregate Culture in Automated Bioreactors. Advanced healthcare materials Ho, D. L., Lee, S., Du, J., Weiss, J. D., Tam, T., Sinha, S., Klinger, D., Devine, S., Hamfeldt, A., Leng, H. T., Herrmann, J. E., He, M., Fradkin, L. G., Tan, T. K., Traul, D., Vicard, Q., Katikireddy, K., Skylar-Scott, M. A. 2022: e2201138


    Combining the sustainable culture of billions of human cells and the bioprinting of wholly-cellular bioinks offers a pathway towards organ-scale tissue engineering. Traditional 2D culture methods are not inherently scalable due to cost, space, and handling constraints. Here, we optimize the suspension culture of human induced pluripotent stem cell-derived aggregates using an automated 250 mL stirred tank bioreactor system. Cell yield, aggregate morphology, and pluripotency marker expression are maintained over three serial passages in two distinct cell lines. Furthermore, we demonstrate that the same optimized parameters can be scaled to an automated 1 L stirred tank bioreactor system. Our 4-day culture resulted in a 16.6- to 20.4-fold expansion of cells, we generate approximately 4 billion cells per vessel, while maintaining > 94% expression of pluripotency markers. The pluripotent aggregates can be subsequently differentiated into derivatives of the three germ layers, including cardiac aggregates, and vascular, cortical and intestinal organoids. Finally, the aggregates are compacted into a wholly-cellular bioink for rheological characterization and 3D bioprinting. The printed hAs are subsequently differentiated into neuronal and vascular tissue. This work demonstrates an optimized suspension culture-to-3D bioprinting pipeline that enables a sustainable approach to billion cell-scale organ engineering. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1002/adhm.202201138

    View details for PubMedID 36314397

  • Understanding the Dynamics of Cellulose Dissolved in an Ionic Liquid Solvent Under Shear and Extensional Flows. Biomacromolecules Owens, C. E., Du, J., Sánchez, P. B. 2022


    Ionic liquids (ILs) hold great potential as solvents to dissolve, recycle, and regenerate cellulosic fabrics, but the dissolved cellulose material system requires greater study in conditions relevant to fiber spinning processes, especially characterization of nonlinear shear and extensional flows. To address this gap, we aimed to disentangle the effects of the temperature, cellulose concentration, and degree of polymerization (DOP) on the shear and extensional flows of cellulose dissolved in an IL. We have studied the behavior of cellulose from two sources, fabric and filter paper, dissolved in 1-ethyl-3-methylimidazolium acetate ([C2C1Im][OAc]) over a range of temperatures (25 to 80 °C) and concentrations (up to 4%) that cover both semidilute and entangled regimes. The linear viscoelastic (LVE) response was measured using small-amplitude oscillatory shear techniques, and the results were unified by reducing the temperature, concentration, and DOP onto a single master curve using time superposition techniques. The shear rheological data were further fitted to a fractional Maxwell liquid (FML) model and were found to satisfy the Cox-Merz rule within the measurement range. Meanwhile, the material response in the non-LVE (NLVE) regime at large strains and strain rates has special relevance for spinning processes. We quantified the NLVE behavior using steady shear flow tests alongside uniaxial extension using a customized capillary breakup extensional rheometer. The results for both shear and extensional NLVE responses were described by the Rolie-Poly model to account for flow-dependent relaxation times and nonmonotonic viscosity evolution with strain rates in an extensional flow, which primarily arise from complex polymer interactions at high concentrations. The physically interpretable model fitting parameters were further compared to describe differences in material response to different flow types at varying temperatures, concentrations, and DOP. Finally, the fitting parameters from the FML and Rolie-Poly models were connected under the same superposition framework to provide a comprehensive description within the wide measured parameter window for the flow and handling of cellulose in [C2C1Im][OAc] in both linear and nonlinear regimes.

    View details for DOI 10.1021/acs.biomac.1c01623

    View details for PubMedID 35442676