Microrobot-Induced Shear-Wave Generation in Viscoelastic Microfluidic Channels

Magnetic microrobots can act as remotely driven sources of mechanical excitation in confined environments, opening a route to microscale elastography. This letter reports shear waves generated by a single vibrating microrobot inside viscoelastic hydrogel microchannels. A 1 mm spherical NdFeB microrobot is held against the wall of agarose channels and driven by combined uniform and gradient magnetic fields over 100-500 Hz, and wave propagation is reconstructed using high-speed imaging with digital image correlation. Frequency-dependent shear-wave speeds are measured for 0.4%, 0.8% and 1.2% agarose and fitted with a Kelvin-Voigt model to recover shear modulus and viscosity. A coupled framework using OpenFOAM for the fluid and microrobot dynamics, CalculiX for the viscoelastic solid and preCICE for two-way coupling reproduces the measured dispersion to within 5.4% on average, and a leave-one-frequency-out test shows that the fitted model predicts withheld measurements to within experimental scatter. A laser speckle contrast imaging demonstration shows that microrobot vibrations produce spatially resolved mechanical contrast, supporting feasibility for endoluminal diagnostics.