# Pullulan Coating Preserves High Conductivity in Cable Bacteria Wires

## TL;DR

A pullulan coating helps preserve the conductivity of cable bacteria wires, offering a sustainable alternative for green electronics.

## Contribution

A biobased pullulan coating significantly improves the stability of cable bacteria conductivity under ambient conditions.

## Key findings

- Cable bacteria coated with pullulan showed a 10-fold increase in conduction stability.
- Reducing ambient moisture also preserved conductivity, highlighting humidity's role in deterioration.
- The findings support the development of biobased coatings for O2-sensitive materials in electronics.

## Abstract

The greening of electronics
remains a grand societal challenge,
with no radical improvement within sight. Sustainable solutions for
electronics, such as biobased and transient materials, are hence receiving
growing attention. Presently, there are no biobased alternatives to
conventional conductors such as metals and organic polymers, as their
conductivity is too low. The discovery of cable bacteria, which are
filamentous microorganisms capable of conducting electricity over
centimeter-scale distances, has the potential to change this. In cable
bacteria, conductivity occurs through thin wires embedded in the cell
envelope, displaying conductivities comparable to those of the best
highly doped organic polymers. However, exposure to ambient air leads
to a gradual loss of their conductivity. To enhance stability, a bioderived
protective coating could be useful, thus retaining a fully biobased
system. To this end, we investigated pullulan, a polysaccharide polymer
primarily used in food packaging that is known for its excellent oxygen-barrier
properties. Cable bacterium filaments protected with a film derived
from a 10 wt % pullulan solution exhibited a 10-fold increase in conduction
stability under ambient conditions compared to uncoated controls.
Reducing ambient moisture also preserved the long-term conductivity
of the cable bacteria, even in the absence of a protective coating,
indicating that humidity plays a critical role in conductance deterioration.
Our findings provide an important step toward further technological
implementation of the highly conductive wires of cable bacteria and
offer practical guidelines for developing biobased coatings for O2-sensitive materials in electronics, thus contributing to
the advancement of next-generation green technologies.