Gear-based 3D-printed Micromachines Actuated by Optical Tweezers

The miniaturization of mechanical mechanisms is crucial to enable the development of compact, high-performance micromachines. However, the downscaling actuation of conventional gears and micromotors has remained limited by the inherent challenges of implementing mechanical/electrical powering. Here, we present the design, fabrication, and characterization of an optomechanical, gear-driven micromachine realized through two-photon polymerization 3D printing. The actuation is achieved using optical tweezers. The device integrates a microgear transmission system with an optically actuated part, enabling light-controlled micromachines. When illuminated by a highly focused laser source, the first gear generates rotational torque within the gear assembly, converting optical energy into directional mechanical work that can be transmitted to the coupled gear. We demonstrate the fabrication of micromachines using two-photon polymerization (2PP) laser writing, enabling the fabrication of spur gear trains and bevel gears that can produce out-of-plane rotations, which is not achievable with traditional micromachining fabrication techniques. The micromachines are composed of a single gear or a train of two or three gears without any unwanted adhesion between the components, leading to functioning systems. Experimentally, the fabricated micromachines were actuated using optical tweezers, demonstrating continuous gear rotation, effective motion transmission in gear trains, out-of-plane rotations, and the ability to amplify velocity or torque. Optical-tweezer actuation broadens the potential applications of these micromachines, particularly in biomedical and lab-on-a-chip systems, where precise, minimally invasive control at the microscale is essential.

💡 Research Summary

This paper introduces a novel approach to microscale mechanical actuation by integrating 3D‑printed microgears with optical tweezers. Using two‑photon polymerization (2PP) direct laser writing, the authors fabricate both spur‑gear trains and bevel‑gear pairs with sub‑micron precision. Each gear incorporates four 5 µm spherical “optical handles” that serve as trapping sites for tightly focused laser beams. By time‑multiplexing four traps and moving them along a circular trajectory, a controlled rotational torque is applied to a driver gear, which then transmits motion to coupled gears.

Theoretical analysis employs a T‑matrix method (implemented via the Optical Tweezers Toolbox) to calculate the normalized trapping efficiency Q for the dielectric spheres. With Q_max ≈ 0.42, a 100 mW laser yields ≈185 pN of force and ≈1.85 nN·µm of torque on the small gear. Gear ratios are exploited to amplify torque (≈2.4×) when the small gear drives the large one, and to amplify angular velocity (≈1.33×) when the large gear drives the small one. In the bevel‑gear configuration, the planar rotation of the lower gear is converted into out‑of‑plane rotation of the upper gear, achieving a velocity amplification of ≈4.17× with a modest torque ratio of ≈1.34.

Fabrication challenges such as unwanted adhesion between closely spaced parts are addressed by using a dual‑ring rotor design, sacrificial support pillars, and post‑processing steps including careful solvent washing and supercritical CO₂ drying. Scanning electron microscopy confirms the integrity of single gears, two‑gear trains, three‑gear assemblies, and bevel‑gear pairs.

Experimental validation demonstrates continuous gear rotation, efficient torque transmission, and the predicted amplification effects. The system operates entirely contactlessly, minimizing thermal and photonic damage, which makes it attractive for biomedical and lab‑on‑a‑chip applications where precise, minimally invasive manipulation is essential. The work establishes the first optical‑tweezer‑driven gear train and out‑of‑plane rotating bevel gear at the microscale, opening pathways for optically powered micro‑electromechanical systems, microfluidic pumps, and microrobotic manipulators.