As I have stated in my answer to a similar question here the cosmological model is not about bound states, and even galaxies are bound states by the gravitational attraction. Certainly bound states are presumed to overcome any distortions of space time; if it were not so all our cosmological observations of velocities which depend on identifying the Doppler shifted spectra of known elements come into doubt. Also the standard Big Bang model becomes nonsense: if space between bound particles expanded, with the cosmological constant , we would not be able to measure the expansion.
At the local level in order of strength, a proton is bound by the strong force, the hydrogen atom by the electromagnetic, the earth to the sun by gravitation. A look at the relative contribution to the space curvature by Λ (equation 1 here ) shows that Λ is order of 10^20 smaller than the contribution of the gravitational constant.
At the quantum level of the interactions binding atoms and molecules, Λ would appear as an extra dispersing potential, modifying the quantum levels measured . The smallness of the number locally ( look at the answer by Ben Crowell here) assures that within the widths of the bound states the effect is infinitesimal. It is similar to not considering the gravitational attraction between electron and proton when calculating the bound states of hydrogen. For the reason that the effect of changes in gravitational attraction are not seen , see this answer by Ben Crowel, .
So it is only at cosmological levels that the expansion driven by Λ can have a measurable effect, not at a local one.