  Adhesion interactions mediated by multiple bond types are relevant for many
biological and soft matter systems, including the adhesion of biological cells
and functionalized colloidal particles to various substrates. To elucidate
advantages and disadvantages of multiple bond populations for the stability of
heterogeneous adhesion clusters of receptor-ligand pairs, a theoretical model
for a homogeneous parallel adhesion bond cluster under constant loading is
extended to several bond types. The stability of the entire cluster can be
tuned by changing densities of different bond populations as well as their
extensional rigidity and binding properties. In particular, bond extensional
rigidities determine the distribution of total load to be shared between
different sub-populations. Under a gradual increase of the total load, the
rupture of a heterogeneous adhesion cluster can be thought of as a multistep
discrete process, in which one of the bond sub-populations ruptures first,
followed by similar rupture steps of other sub-populations or by immediate
detachment of the remaining cluster. This rupture behavior is qualitatively
independent of involved bond types, such as slip and catch bonds.
Interestingly, an optimal stability is generally achieved when the total
cluster load is shared such that loads on distinct bond populations are equal
to their individual critical rupture forces. We also show that cluster
heterogeneity can drastically affect cluster lifetime.
