  We derive the flow field disturbance produced by point viscosity variations
in a heterogeneous fluid when subject to a background flow while neglecting
fluid inertia. The disturbance flow field is found to be identical to that
generated by a force-dipole called stresslet. Using a combination of theory and
numerical simulations, we show how the hydrodynamics of an active rigid
particle is altered due to the presence of point viscosity variations, and how
this can be exploited to manipulate and steer them in microfluidic
environments.
