Testing Stressed Viruses

LK13179 - One of the big questions about materials at the nanoscale is whether macroscopic theories can be applied to nano-sized systems. To answer this question, we focus on self-assembling, viral nanoparticles to test the predictions of elasticity theory. Of all known viruses those with icosahedral symmetry are the most common. Their structure can be described by folding a hexagonal lattice into a sphere-like configuration. By doing so defects with 5-fold symmetry are created at the icosahedral vertices.  According to elasticity theory these vertices should be under a permanent pre-stress, a prediction which never has been verified experimentally. Here we compare naturally occurring viruses with those that have missing proteins at their vertices, and test the hypothesis that the latter particles are stress-free. Deforming the viruses by Atomic Force Microscopy and comparing our results to detailed simulations has verified our hypothesis about pre-stress. This is the first time that the predictions about pre-stressed vertices in viral particles has been demonstrated experimentally and is a huge support for the use of continuum elasticity to describe nanometer sized objects.