The First Biodegradable and 3D Printed Fungal Cell

• 1
  What a 3D printed fungal cell actually is
• 2
  How the two fungi split the electron path
• 3
  Printing an electrode that keeps fungi alive
• 4
  Boundary conditions: where the cell works and where it stalls
• 5
  Where a 3D printed fungal cell fits in a real product
• 6
  Design choices and what they cost you

A 3D printed fungal cell is a microbial fuel cell built around two living organisms. One side carries a yeast that releases electrons as it digests nutrients. The other side carries a white rot fungus that produces an enzyme able to shuttle those electrons to the cathode. The two electrodes are printed, and the fungi are part of the printed structure from the start rather than added after the cell is assembled.

That last point is the real difference. In a conventional microbial fuel cell, you build the hardware and then inoculate it. Here the ink carries the organisms, so the electrode geometry is designed around living material. The cell is not a battery that happens to contain fungi. The fungi are structural members of the electrode.

The whole assembly is designed to biodegrade. Electrodes, separator and casing are meant to break down at end of life instead of going to hazardous waste. That is the claim behind the word biodegradable in the title, and it is the reason the material set is so narrow.

One caveat before anything else. Power density is low compared with lithium cells, often by orders of magnitude. A 3D printed fungal cell is a sensor power source or a research platform, not a phone battery. Read the rest of this page with that limit in mind.

The anode side runs a fermentation. Yeast consumes sugar and releases electrons plus protons. Those electrons must reach the anode surface, and the yeast does not do that efficiently on its own. The printed anode gives the colony a conductive, high-surface-area scaffold so the distance between cell and conductor stays short.

The cathode side runs an enzymatic reduction. A white rot fungus secretes an enzyme that accepts electrons from the cathode and passes them to oxygen. Without that enzyme, oxygen reduction at a plain carbon surface is slow and the cell voltage sags. The fungus is doing the job a platinum catalyst would do in a hydrogen fuel cell.

The two reactions have to be separated. If the anolyte and catholyte mix, the cell short-circuits chemically and the voltage collapses. That is why the printed separator matters as much as the electrodes. It must pass protons, block sugar and oxygen cross-over, and still be printable.

Electron transfer in these systems is mostly mediated rather than direct. The organism produces or uses a soluble shuttle molecule that carries charge between cell wall and electrode. Mediator concentration, pH and temperature all move the internal resistance. Change any one of them and the polarization curve shifts.

The ink is the hard part. It has to be extrudable through a nozzle, hold shape after deposition, conduct electrons, and stay biocompatible. Those four requirements pull against each other. More carbon loading improves conductivity but stiffens the ink and can shear the cells during extrusion.

Nozzle diameter sets a trade-off between resolution and viability. Small nozzles give fine features and higher surface area but raise shear stress at the wall. Large nozzles are gentle on the organisms and print coarse lattices. Most work lands in a middle range where the lattice struts are a few hundred micrometres wide.

Print temperature and post-processing are constrained. You cannot sinter a printed fungal electrode, because sintering kills the organism. Drying steps have to stay near ambient. Any curing must happen at conditions the fungus tolerates, which usually rules out heat and strong solvents.

Geometry is where additive manufacturing earns its place. A lattice or gyroid gives far more active surface per unit volume than a flat plate. It also fixes the distance between the current collector and the outer colony, which controls how much of the biofilm actually contributes current.

Start-up is slow. The colony has to establish itself on the printed scaffold before the current stabilizes. Expect hours to days, not minutes. During that window the cell looks dead on a meter even though the chemistry is fine.

Temperature is a narrow window. These organisms work best somewhere in the range a warm room sits in, and they slow sharply when cold. Freezing destroys the structure. Above their tolerance limit the enzymes denature and the cathode stops reducing oxygen.

Feedstock matters more than most people expect. Simple sugars ferment quickly and give a high initial current that fades. Complex feedstocks such as wastewater or plant waste give lower but steadier output. If you need a long unattended runtime, the second option usually wins.

Humidity and oxygen access control the cathode. Seal the cell too well and the cathode starves for oxygen. Leave it too open and the anolyte dries out. A printed casing with a controlled vent path is often the simplest fix.

Contamination is the quiet failure mode. A foreign bacterium that outcompetes the yeast will drop the current to near zero without any visible change. Sterile handling at assembly and a selective feedstock both reduce the risk.

The realistic near-term use is low-power, long-life sensing. Soil moisture sensors, environmental monitors and remote tags need microamps to milliamps, and a cell that runs on local nutrients and biodegrades afterward is attractive. You are trading power density for disposal and supply-chain simplicity.

The second use is research hardware. Because the electrode is printed, you can vary pore size, strut width and surface chemistry between runs and measure the effect on current. That is much harder with pressed carbon felt, where geometry is fixed by the supplier.

It does not fit high-drain applications. Anything that needs watts, fast recharge or a stable voltage rail is out of scope. Do not design a fungal cell into a product that expects lithium behavior, because the discharge curve is flat and low, and it drifts with temperature.

For teams building the non-living hardware around the cell, the printed casing, current collector and test fixture are ordinary machined and molded parts. That is the part we handle. A 3D printed fungal cell is a research platform; the fixture that holds it needs to be dimensionally stable and repeatable.

If you are prototyping that hardware, the tolerance that matters most is the electrode pocket and the seal face. A pocket held to ±0.005 mm keeps the separator compressed evenly, which directly affects internal resistance. Loose fits leak, tight fits crush the printed lattice.