Fig. 2: Design, Fabrication and characterization of ant microbot.

a The ant body is fabricated by femtosecond laser direct writing in magnetic photoresist. b Thermal stimuli-responsive hydrogel joints are integrated into the body via TPP. The joint consists of two parts with distinct cross-link densities, where dark red and light red portions indicate high and low cross-link density, respectively. c Site-selective photo-reduced Ag NPs are used for photothermal conversion, where the Ag NPs are reduced from silver ammonium ions absorbing photons. The area with Ag NPs in the SEM image is marked in yellow. d The laser is used to trigger the ant mandibles to open, and the radius of the focused spot under the 5 × objective lens is ~3.3 μm. When Ag NPs are irradiated by NIR light, strong photothermal conversion induces the temperature increase in hydrogel joints. The portion of the asymmetric joint with low cross-link density produces larger shrinkage deformation than the portion with high cross-link density, causing the hydrogel joints to drive the mandibles open. Scale bars, (a–d) 10 μm. e Simulation results show that the heat converted from light absorbed by the Ag NPs induces the hydrogel joints to deform driving the mandibles to open. f Dynamic light-responsive properties of the mandibles, where the response time is ~8 ms. Scale bar, 10 μm. g Bending angle of the joints over 1000 cycles of on-off switch of laser with actuation power of 20 mW. h The mass magnetization curve of the magnetic ant microbot measured with VSM, which indicates the superparamagnetism of the magnetic ant microbot. i If there is an angle between the ant microbot axis and magnetic direction, a magnetic torque is generated on the ant microbot, which induces a rotational motion of the ant microbot to align along the magnetic field. j Optical images show the ant microbot rotation with the rotation of an external magnetic field (B).