  Single-molecule mechanical manipulation has enabled the quantitative
understanding of the kinetics of bond ruptures as well as protein unfolding
mechanism. Single-molecule experiments with theoretical models have allowed one
to gain insight into free energy landscape for chemical bond and/or protein
folding. For mechanically induced bond rupture, the bond-rupture kinetics may
be governed by loading device. However, the role of loading device on the
kinetics of mechanical rupture has been rarely received much attention until
recently. In this work, we have theoretically and/or computationally studied
the effect of loading-device stiffness on the kinetics of mechanical unfolding.
Specifically, we have considered a one-dimensional model for a bond rupture
whose kinetics is depicted by Kramers' theory. It is elucidated that the
kinetics of bond rupture is determined by force constant of loading device. The
Brownian dynamics simulation of a bond rupture is considered in order to
validate our theory. It is illustrated that the mean rupture force is dependent
on the force constant of a loading device, such that increase in the
loading-device stiffness leads to the higher bond rupture force. Moreover, we
have taken into account the computational simulation of mechanical unfolding of
a small protein, i.e. {\beta}-hairpin. Our simulation shows that unfolding
force is highly correlated with the stiffness of a loading device. Our
numerical and theoretical studies highlight the significance of a loading
device on the kinetics of mechanical unfolding of a chemical bond and/or a
folded domain in the single-molecule mechanical experiments.
