In this project, we demonstrate a hybrid biological photovoltaic device by forming a 3D cooperative biofilm of cyanobacteria and heterotrophic bacteria. A 3D bioprinting technique was applied to engineer cyanobacterial encapsulation in hydrogels over the heterotrophic bacteria. The device continuously generated bioelectricity from heterotrophic bacterial respiration, with organic biomass supplied by cyanobacterial photosynthesis. This innovative platform can serve as a practical power source for unattended sensors, especially those deployed in remote and resource-limited field locations.
3D bioprinting is most notably used in diagnostic and medical applications for tissue and organ printing. Relatively little research has been devoted to printing three-dimensional microbial biofilms because, until recently, less was known about the details of microbial interactions. This bioprinting process requires careful control of the sol-gel transition of the bio-ink so that the material is fluid enough to be extruded while still retaining its patterned shape on a substrate. At the same time, bacterial cell viability must be preserved by minimizing shear stress during printing. In this work, alginate hydrogels for cyanobacterial cells were prepared through ionic crosslinking of alginate with calcium ions. The concentrations of alginate and calcium crosslinker were critical for forming a sophisticated structure. We selected 6% (w/v) alginate in DI water with 0.5 M calcium chloride. At higher calcium concentrations, the diffusion time required for sol-gel transition increased, leading to greater shear stress on the cells. Under the selected condition, various multilayered patterns could be printed because the reaction rate was slow enough to deposit partially uncrosslinked alginate on the crosslinked layer, while still enabling excellent cell viability.
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