  Friction, the resistive force between two surfaces sliding past each other,
is at the core of a wide diversity of locomotion schemes. While such schemes
are somewhat understood for homogeneous environments, locomotion based on
friction in inhomogeneous environments has not received much attention. Here,
we introduce and demonstrate the concept of tribotaxis by utilizing
microwalkers that detect gradients in the friction coefficient controlled by
the density of biological receptors on the substrate. When actuated
stochastically, these microwalkers migrate to regions of higher friction,
effectively performing chemotaxis. Simulations and theory based on biased
random walks are in excellent agreement with experiments. Our results may have
important implications in artificial and natural locomotion in biological
environments because interfaces are a prominent motif in nature.
