  Nanoindentation of viral capsids provides an efficient tool in order to probe
their elastic properties. We investigate in the present work the various
sources of stiffness heterogeneity as observed in Atomic Force Microscopy (AFM)
experiments. By combining experimental results with both numerical and
analytical modeling, we first show that for small viruses a position-dependent
stiffness is observed. This effect is strong and has not been properly taken
into account previously. Moreover, we show that a geometrical model is able to
reproduce this effect quantitatively. Our work suggests alternative ways of
measuring stiffness heterogeneities on small viral capsids. This is illustrated
on two different viral capsids: Adeno Associated Virus serotype 8 (AAV8) and
Hepatitis B Virus (HBV with T=4). We discuss our results in the light of
continuous elasticity modeling.
