(682c) Chemical and Mechanical Actuation of Bent-Rod Microparticles Near a Wall

In this work, we investigate hybrid propulsion in slender bent-rod actuators that simultaneously employ mechanical and chemical modes of swimming. Using a combination of slender body theory and Lorentz’s reciprocal theorem, we analyze how these bent rods move under both hinge articulation and surface reaction-driven self-diffusiophoresis.

While prior studies have treated mechanical and chemical propulsion separately, our work presents a single framework for analyzing their coupled effects. For the mechanical mode of swimming, our calculations reveal that the bent rod actuator experiences a zero net displacement performing reciprocal strokes, validating Purcell’s scallop theorem. Further, we obtain trajectories of such bent rods under a non-reciprocal hinge articulation. We find that the particle trajectories are influenced by the amplitude of the hinge articulation, geometric asymmetry, and the angular velocity between the two arms of the bent rod actuator. Similarly, we find that chemical propulsion in isolation leads to characteristically circular trajectories. The speed of propulsion and the radius of curvature of the trajectories depend on the geometric and chemical asymmetries arising out of a prescribed surface flux and the position of the hinge along the particle. When both mechanisms are combined, we uncover rich dynamics: hinge actuation modifies the effective phoretic force and torque, either enhancing or counteracting chemical propulsion. Notably, even reciprocal hinge actuation—ineffective in the mechanical-only case—can result in net displacement when combined with self-diffusiophoresis.

Experimental studies, both in vivo and in vitro, often examine such microswimmers near boundaries, where wall-induced hydrodynamic and chemical interactions play a significant role. However, most existing theoretical models assume unbounded fluids. To address this gap, we are extending our framework to incorporate particle–wall interactions, allowing us to predict trajectory modifications near boundaries and validate our results against experimental data. In summary, our findings provide a theoretical foundation for designing microscale swimmers that exploit synchronized mechanical and chemical propulsion, with direct implications for navigation in complex, confined, and biologically relevant environments.