Thrust Symmetry Engineering in Lithographically Defined Bubble-Propelled Micromotors via Multi-Orifice Exhaust-Port...

Bubble-driven catalytic micromotors generate thrust through gas-liquid interfacial processes at the inner surfaces of the catalyst; however, systematic control over the thrust-vector symmetry through the geometric design of the exhaust port layout has not been demonstrated. Here, we report a lithographic fabrication platform that produces stacked Au/Pt hollow micromotors with independently programmable catalytic exhaust-port configurationssingle, two, and three orificeswhich enable a direct experimental investigation of the extent to which the interface-defined port geometry strongly influences the propulsion behavior. Using a single-orifice trapezoidal micromotor as the baseline system, we establish concentration-dependent propulsion at 73 μm s^-1 (5 wt % H₂O₂) and 636 μm s^-1 (15 wt % H₂O₂). Extending the platform to a two-orifice design reveals persistent curved trajectories (∼450 μm s^-1, 15 wt % H₂O₂), indicating that even small geometric asymmetries in exhaust-port placement can produce measurable and persistent torque. A three-orifice design incorporating a central forward-thrust port and two lateral steering ports enables the straight-line motion to be recovered under uniform fuel conditions, consistent with improved thrust-vector balance for the mirror-symmetric port placement. In a nonuniform fuel environment imposed by a H₂O₂ gel source, the three-orifice micromotor exhibits directional motion toward the low-concentration region, consistent with differential bubble generation across the lateral ports. These results establish that, within the present platform and under the same material and catalytic conditions, the number, placement, and symmetry of exhaust ports strongly affect the observed propulsion state, providing an interface-programmable geometric route to activate micromotor behavior without changing the material composition or fuel chemistry.