Complex instability of axially compressed tubular lipid membrane with controlled spontaneous curvature.

Tubular lipid membranes (TLMs) are formed by an external pulling force from artificial or biological bilayer vesicles and can be subsequently stabilized by incorporating proteins or amphiphilic polymers into the lipid bilayer. The arising spontaneous curvature of the lipid sheet allows switching off the pulling force without TLM destabilization. However, here we show that during this process two different thermal fluctuation modes drastically increase their amplitudes making fluctuations of the TLM much greater than its radius. Due to the system's proximity to the critical fluctuation point, a weak axial compressive force is sufficient to destabilize the TLM. Its absolute value is shown to be much smaller than that of the pulling force required for the initial lipid nanotube formation. Induced complex instability was studied in the frame of Landau phase transition theory. The process involves two consecutive second-order phase transitions and leads to the tube deformation combining annular corrugation with completely unconventional chiral buckling.