Electric fish inspire biomimetic membranes

Scientists from the Adolphe Merkle Institute’s BioPhysics group, together with research teams across Europe, have developed a novel membrane that takes its cue from the electric organs of rays and eels. This ultra-thin, self-repairing material combines several useful properties that could find applications in sustainable energy, water treatment, and medical devices.

Biological cell membranes do two jobs: they keep cells together and let the right tiny particles, ions, pass through. Nature strikes a perfect balance of strength and openness, but human-made membranes have always forced a trade-off: tough but leaky, or tight but fragile. The new membranes break that rule.

They are assembled at the interface between two immiscible, water-based solutions. A carefully chosen block copolymer — a polymer made of two segments with different affinities for water — accumulates at this boundary. By gently replacing an organic solvent with a second aqueous solution, the polymer chains align to form a continuous film just 35 nanometers thick, while covering areas up to 10 square centimeters. This method avoids complex equipment and can be adapted by varying the container shape and size. “This approach takes advantage of favorable interactions to stabilize ultra-thin self-assembled structures that are at least one thousand-fold larger than was previously possible,” adds Assistant Prof. Alessandro Ianiro, a former group leader in AMI’s Biophysics lab.

Once formed, the membranes exhibit a degree of fluidity that allows them to close small punctures on their own. Tests showed that tiny defects heal within seconds, restoring the barrier function, because its molecules flow and reseal, just like a droplet of mercury.  This resilience stems from the mobility of polymer segments within the bilayer, which flow to seal gaps without external intervention.

Electric rays stack thousands of cell membranes to shock prey. The researchers copied this by adding a natural molecule called valinomycin, which only lets potassium ions pass through. When one side has potassium salt and the other sodium salt, ions rush across, creating about 60 millivolts per layer. Stacking multiple films increases the output proportionally. Published in the prestigious journal Nature, the results showed low power densities — around 0.04 mW/m² — but improvements in ion-channel design could boost performance in the future.

Potential Applications

The researchers have suggested several potential applications.  By controlled mixing of freshwater and seawater across these membranes, it should be possible to generate renewable power on a small scale, complementing existing salinity-gradient technologies. Their selective ion-separation capability could also lead to membranes that remove salt from water more efficiently than current polymer filters, with less energy input. Finally, as materials for dialysis or implantable sensors, the membranes’ thinness and biocompatibility could yield gentler filtration and the possibility of devices powered by the body’s own ion gradients.

“This advancement takes our previous aspirations to develop fish-inspired artificial electric organs a significant step closer towards biocompatible power sources.  Ultimately, our goal is that these human-made systems will closely mimic, and interact with the complex functions of biological organisms,” says AMI’s Chair of Biophysics, Prof. Michael Mayer.

This work brought together AMI’s Biophysics, Polymer Chemistry, and Soft Matter Physics groups with partners at TU Darmstadt, the University of Paris-Saclay, and EPFL. Future research will focus on integrating more efficient ion channels — both natural proteins and synthetic analogues — to raise ion-transport rates by orders of magnitude. The long-term goal is to develop membranes fueled by biological molecules (such as ATP, which powers virtually every cellular activity) for non-stop operation, narrowing the gap between laboratory prototypes and practical devices.