Bacterial 3D Printing

Researchers have developed a 3D printing system that prints bacteria in an immobile gel. Bacteria can produce and modify chemicals predictably and reproducibly.  This technology will allow the creation of fully bespoke biomaterials in an environmentally friendly way, without the use of an excessive amount of chemicals or extreme conditions.

3D Printing

3D printing typically generates solid objects by the successive application of powder to a surface under computer control.  Originally, 3D printing used an inkjet nozzle; now the term Additive Manufacturing is used, encompassing binder jetting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet lamination and vat photopolymerisation.

Biological 3D printing

Applying 3D printing technologies to living cells, nature’s building blocks, is challenging because conventional techniques are inherently lethal to cells.

Several techniques have been developed with applications such as visualization, education, and transplantation; however, these are currently expensive.

Thermal inkjet bioprinting deploys fluid dots layer by layer, which solidify to a gel after a short heating phase in the extruder. Direct write bioprinting utilises mechanical or pneumatic systems and a low-melting-point scaffold material. Spheroid organ printing employs tiny tissue spheroids to assist the self-organisational and self-assembling character of real tissues.

Attempts to apply these techniques to bacterial systems have resulted in poor spatial resolution; or require laborious clean-room fabrication of microstructures that shape the printed bacteria.

By modifying an existing, commercially available 3D printer, researchers at the Delft University of Technology have produced a system that can print bacteria with high spatial resolution; microbes can be printed down to a thickness of 1mm.

Modifications to the 3D printer

• Bioink development: containing the bacteria, growth media and an alginate gel; solidifies at room temperature after contact with a calcium chloride surface and keeps bacteria viable for 48 hrs.
• The original extruder was replaced with a pipette tip and customised tubing, allowing the movement of bioink at ambient temperatures which do not destroy bacteria.
• A secondary tip was added to allow rapid switching between bioinks, allowing the production of bacterial bi-layers.

Applications

Think of bacteria as metabolic factories; they make complex molecules such as vitamins and antibiotics as well as enzymes that catalyse countless biological reactions.  In addition, the genetic amenability of model systems such as E. coli and B. subtilis make bacterial printing an attractive method to produce custom biomaterials; their enzymes can be used to modify 3D objects and their other metabolites can be used to coat them.

If this technology was adapted to print onto sheets of graphene oxide, graphene could be produced (as the bacteria metabolise the oxygen atoms) in a completely customised manner.  The more oxygen is removed from graphene oxide, the closer we arrive at pure graphene.  The ability to, essentially, print graphene onto graphene oxide with high special resolution, could revolutionise the production of graphene superconductors; allowing the carving of tiny graphene wires.

Reduced graphene is currently produced by chemical means under extreme conditions; a bacterial system, operating at ambient temperature, would be more environmentally friendly and does not require the powerful chemicals used in conventional methods.

In this preliminary work, conditions have been optimised for gelation and bacterial viability. The alginate system is compatible with numerous other chemicals which allows for the development of bacterial printing systems that use different bacteria and growth media.  The team are also looking much further afield (to the moon!) where they hope similar technology could assist in the manufacturing of solar cells and electronic devices from lunar dust.

Reference

1. Connell, J. L., Ritschdorff, E. T., Whiteley, M. & Shear, J. B. 3D printing of microscopic bacterial communities. Proc. Natl. Acad. Sci. U. S. A. 110, 18380–18385 (2013).
2. Lehner, B. A. E., Schmieden, D. T. & Meyer, A. S. A straightforward approach for 3D bacterial printing. ACS Synth. Biol. acssynbio.6b00395 (2017). doi:10.1021/acssynbio.6b00395
3. Horton, C. et al. First demonstration of photovoltaic diodes on lunar regolith-based substrate. Acta Astronaut. 56, 537–545 (2005).
4. Image Credit: Shutterstock.com/IaremenkoSergii

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