  Measurement of the life time of attachments formed by a single microtubule
(MT) with a single kinetochore (kt) {\it in-vitro} under force-clamp conditions
had earlier revealed a catch-bond-like behavior. In the past the physical
origin of this apparently counter-intuitive phenomenon was traced to the nature
of the force-dependence of the (de-)polymerization kinetics of the MTs. Here
first the same model MT-kt attachment is subjected to external tension that
increases linearly with time until rupture occurs. In our {\it force-ramp}
experiments {\it in-silico}, the model displays the well known `mechanical
signatures' of a catch-bond probed by molecular force spectroscopy. Exploiting
this new evidence, we have further strengthened the analogy between MT-kt
attachments and common ligand-receptor bonds in spite of the crucial
differences in their underlying physical mechanisms. We then extend the
formalism to model the stochastic kinetics of an attachment formed by a bundle
of multiple parallel microtubules with a single kt considering the effect of
rebinding under force-clamp and force-ramp conditions. From numerical studies
of the model we predict the trends of variation of the mean life time and mean
rupture force with the increasing number of MTs in the bundle. Both the mean
life time and the mean rupture force display nontrivial nonlinear dependence on
the maximum number of MTs that can attach simultaneously to the same kt.
