Biological membranes are modeled as infinitely thin surfaces. The real membrane is five nanometers thick. Most theories of electromechanical stability ignore this difference. Ning, Omar, Shekhar, and Mandadapu show that ignoring it throws away more than 70% of the answer.
The key quantity is the traction moment — the torque generated by electric fields acting across the finite thickness of the membrane. In a zero-thickness model, the electric field creates a pressure on the membrane surface, pushing it toward instability. In a finite-thickness model, the field also creates a moment: because the charge distributions on the two leaflets are separated by a real physical distance, the forces don't simply compress the membrane — they twist it. This traction moment accounts for over 70% of the total electrostatic correction to both surface tension and bending rigidity under physiological conditions.
The practical consequence is that electroporation thresholds — the voltage at which the membrane ruptures — are different than zero-thickness models predict. And the direction of the correction depends on how charge is distributed between the two leaflets. Surface charges, which zero-thickness models treat as a minor perturbation, can actually stabilize the membrane by increasing effective tension at physiological ionic strength. The charge distribution between inner and outer leaflet becomes a design parameter for membrane stability, not a negligible detail.
The existing theories turn out to be special cases of the finite-thickness framework. Each prior result emerges by setting specific thickness or charge parameters to zero. The unified model doesn't contradict the earlier work — it reveals what it was leaving out, and the omission was the dominant term.
Five nanometers is thin. But the physics that fits inside those five nanometers carries most of the mechanical load.