(M-483) Rheological Characterization of Cell-Laden Alginate-Gelatin Hydrogels

Introduction:: The biofabrication of tissue models that closely mimic the tumor microenvironment are necessary for high throughput rapid screening of anticancer drugs. 3D bioprinting of heterogeneous cell-laden hydrogels has shown promise in advancing rapid artificial tissue development. A major bottleneck 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 effectively reduced. Here, we explore the effects of increasing cell seeding densities on the viscoelastic properties, printability, and viability of two different alginate-gelatin hydrogel compositions.

Materials and Methods:: 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 (2x10⁵. 1.5x10⁶, and 2x10⁷ cells/ml). Bulk rheological tests were conducted on the hydrogels to determine the viscoelastic behavior at varying cell densities. Hydrogels were printed at varying concentration to determine printing parameters for each seeding density variation. The viability of seeded hydrogels was determined over a period of five days.


Results, Conclusions, and Discussions:: An inverse relationship between cell concentration and zero-shear viscosity (Figure 1). We 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 amount of line width increase after the bioink leaves the nozzle post-print. We find that hydrogels composed of higher molecular weight alginates and the highest cell-seeding densities (10⁷ cells/mL) 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.


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