In this study, a biological microactuator was demonstrated by closed-loop motion control of the front leg of an insect (Mecynorrhina torquata, beetle) via electrical stimulation of the leg muscles. The three antagonistic pairs of muscle groups in the front leg enabled the actuator to have three degrees of freedom: protraction/retraction, levation/depression, and extension/flexion. We observed that the threshold amplitude (voltage) required to elicit leg motions was approximately 1.0 V; thus, we fixed the stimulation amplitude at 1.5 V to ensure a muscle response. The leg motions were finely graded by alternation of the stimulation frequencies: higher stimulation frequencies elicited larger leg angular displacement. A closed-loop control system was then developed, where the stimulation frequency was the manipulated variable for leg-muscle stimulation (output from the final control element to the leg muscle) and the angular displacement of the leg motion was the system response. This closed-loop control system, with an optimized proportional gain and update time, regulated the leg to set at predetermined angular positions. The average electrical stimulation power consumption per muscle group was 148 µW. These findings related to and demonstrations of the leg motion control offer promise for the future development of a reliable, low-power, biological legged machine (i.e., an insect–machine hybrid legged robot).

Proton exchange membrane fuel cells (PEMFCs) suffer severe performance loss in the high current density (HCD) region as Pt‐loading decreases. A smaller electrocatalyst size inducing a higher electrochemically active surface area (ECSA) is critical for solving this issue. However, the poor electrocatalytic activity and stability of sub‐2 nm nanoclusters limit the potential to reduce their size. In this study, 1.69 nm Co‐doped Pt nanoclusters with a large ECSA (116.19 m2 gPt–1) are synthesized. The mass activity (MA) (0.579 A mgPt–1) and stability (9% MA loss after 30k potential cycling) refresh the record of sub‐2 nm nanoclusters. The structural characterization and theoretical calculations reveal that doping reduces the total energy required to stabilize the nanoclusters. Dopant tailoring of the d‐band center and vacancy formation energy account for the activity and stability enhancement, respectively. Due to the larger ECSA and MA induced by doping, HCD voltage loss due to lower Pt‐loading is significantly reduced compared with commercial Pt/C. The peak power density of low‐Pt‐loading PEMFCs (0.075 mgPt cmMEA–2) with a doped nanocluster cathode is 0.811 W cm–2 (H2–air condition), which far exceeds commercial Pt/C (0.5 W cm–2) and that of most reported electrocatalysts.

Some researchers have long been interested in reconstructing natural insects into steerable robots or vehicles. However, until recently, these so-called cyborg insects, biobots, or living machines existed only in science fiction. Owing to recent advances in nano/micro manufacturing, data processing, and anatomical and physiological biology, we can now stimulate living insects to induce user-desired motor actions and behaviors. To improve the practicality and applicability of airborne cyborg insects, a reliable and controllable flight initiation protocol is required. This study demonstrates an electrical stimulation protocol that initiates flight in a beetle (Mecynorrhina torquata, Coleoptera). A reliable stimulation protocol was determined by analyzing a pair of dorsal longitudinal muscles (DLMs), flight muscles that oscillate the wings. DLM stimulation has achieved with a high success rate (> 90%), rapid response time (< 1.0 s), and small variation (< 0.33 s; indicating little habituation). Notably, the stimulation of DLMs caused no crucial damage to the free flight ability. In contrast, stimulation of optic lobes, which was earlier demonstrated as a successful flight initiation protocol, destabilized the beetle in flight. Thus, DLM stimulation is a promising secure protocol for inducing flight in cyborg insects or biobots.

We have constructed an insect-computer hybrid legged robot using a living beetle (Mecynorrhina torquata; Coleoptera). The protraction/retraction and levation/depression motions in both forelegs of the beetle were elicited by electrically stimulating eight corresponding leg muscles via eight pairs of implanted electrodes. To perform a defined walking gait (e.g. gallop), different muscles were individually stimulated in a predefined sequence using a microcontroller. Different walking gaits were performed by reordering the applied stimulation signals (i.e. applying different sequences). By varying the duration of the stimulation sequences, we successfully controlled the step frequency and hence the beetle's walking speed. To the best of our knowledge, this paper presents the first demonstration of living insect locomotion control with a user-adjustable walking gait, step length and walking speed.