Discipline: Biological Sciences
Subcategory: Biomedical Engineering
Tyler Gregory - FAMU-FSU College of Engineering
Co-Author(s): Prateek Benhal, FAMU-FSU College of Engineering; Annie Scutte, FAMU-FSU College of Engineering; David Quashie Jr., FAMU-FSU College of Engineering; Casey Cargill, FAMU-FSU College of Engineering; Jamel Ali, FAMU-FSU College of Engineering; Subramanian Ramakrishnan, FAMU-FSU College of Engineering
Biofabricated tissue models that closely mimic the tumor microenvironment are necessary for high throughput screening of anticancer drugs. Bioprinting of heterogeneous cell-laden hydrogels has shown promise in advancing rapid artificial tissue development. A major factor limiting the rapid production of physiologically relevant tissue models is the current limitations in printing large populations of cells effectively. However, by significantly increasing hydrogel cell-seeding densities, the time required to produce tissues can be greatly reduced. Here, we explore how increasing cell seeding densities influence the viscoelastic properties, printability, and viability of our alginate-gelatin hydrogel compositions. The initial seeding density of cells will decrease the mechanical stiffness of the various hydrogels, leading to altered printing parameters, smother filaments, and high cell viability.The two hydrogels used in this study were composed of 3% alginate (w/v) and 4% gelatin (w/v), where the alginate molecular weight was varied. The hydrogels were seeded with immortalized human embryonic kidney (HEK) cells at three seeding densities. Bulk rheological tests were conducted on the hydrogels to determine the viscoelastic behavior at varying cell densities. Hydrogels were printed at varying initial cell seeding densities to determine printing parameters for each composition. The viability of seeded hydrogels was determined over a five-day period.An inverse relationship between cell concentration and zero-shear viscosity was observed in both hydrogel compositions. We also observe that as cell seeding densities increase, the storage moduli decrease, thus lowering the required printing pressures required for gel extrusion. We also observe that increasing cell concentration can negatively impact the structural properties of the extruded material by increasing line spreading (the line width increase after the bioink leaves the nozzle). We find that hydrogels composed of higher molecular weight alginates and the highest cell-seeding densities yield high cell viability (>80%) and structural uniformity after printing. Increased cell seeding density had a softening effect on the hydrogels, allowing initially stiffer gels to be printed with smother filaments. The optimized printing parameters determined for the alginate-gelatin bioinks explored may aid in the future rapid fabrication of functional tissue models for therapeutic screening.References: Di Giuseppe, M., Law, N., Webb, B., Macrae, R. A., Liew, L. J., Sercombe, T. B., . . . Doyle, B. J. (2018). Mechanical behaviour of alginate-gelatin hydrogels for 3D bioprinting. Journal of the Mechanical Behavior of Biomedical Materials, 79, 150-157Kiyotake, E. A., Douglas, A. W., Thomas, E. E., Nimmo, S. L., & Detamore, M. S. (2019). Development and quantitative characterization of the precursor rheology of hyaluronic acid hydrogels for bioprinting. Acta Biomaterialia, 95, 176-187
Funder Acknowledgement(s): This work was funded by the National Science Foundation (No. HDR-2000202 and CMMI-2000330) and supported by the NSF FAMU CREST Center award (No. HDR-1735968). This research work was also supported by The Grainger Foundation Frontiers of Engineering Grant under the National Academy of Sciences Award Number: 2000013181 and the CaRE2 - REC Program, funded by the National Cancer Institute (NCI) of the National Institutes of Health (NIH) through the grants of NIH/NCI1U54CA233396, 1U54CA23344, and 1U54CA23346. All the work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1644779 and the State of Florida.
Faculty Advisor: Subramanian Ramakrishnan, email@example.com
Role: I developed experimental procedures, data acquisitions and analysis. This included hydrogel formulation, characterization, 3D biofabrication of scaffolds, and cell cytotoxicity assays.