Science

Remote controlled cyborg cockroaches with self-charging batteries

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A team of scientists have managed to link electronic components to the nervous system of Madagascar cockroaches in order to control their movements. This remote control is carried out by stimulating insect cerci (appendages located at the end of their abdomen). This technology could one day be used for urban search and rescue, environmental monitoring or hazardous area surveys.

This is not the first time the team has developed such insect robots. However, the devices proposed so far have been limited in functionality and field of action by the energy available. Indeed, remote control involves the use of batteries, which necessarily have a limited volume and weight due to the size of insects. One strategy is to bring the cyborg insect back into the recharge zone before its battery runs out, but this approach remains impractical (especially in an emergency).

An alternative is to add an energy harvesting device directly to the insect in the form of an enzymatic biofuel cell. But the highest output power obtained in this way is 333 microwatts (microwatts). However, controlling wireless locomotion (as well as other advanced features) requires several milliwatts. Therefore, the Japanese team from RIKEN came up with the idea of ​​using a solar array that can generate 10mW/cm2 or even more in sunny weather. The ultrathin organic solar module they developed achieved an output power of 17.2 mW.

A device that perfectly adapts to insect morphology

So the researchers created remote-controlled cyborg cockroaches equipped with a wireless control module powered by a rechargeable battery attached to a solar panel. The insects used, Madagascar cockroaches (Gromphadorhina portentosa), can be up to 6 or 7 centimeters long; so the team had to develop a tiny, portable device containing all the necessary components that would remain securely attached to the insect’s back without interfering with its natural movements.

To do this, they used a model of a cockroach, printed on a 3D printer from an elastic polymer. Their end product resembles a small backpack that fits the insect’s curved surface perfectly and can remain stable on the thorax for over a month; it is equipped with a wireless control module and a lithium polymer battery. An ultra-thin (4 µm thick) organic solar cell was mounted on the back of the abdomen; its weight per effective area is approximately 5 g/m2.

a) Photograph of a cyborg cockroach (scale bar, 10 mm). b) Scheme of the remote control device. c) Scheme of attaching rigid components to the chest using a 3D printed backpack. © Y. Kakei et al.

The flexible materials used and ultra-thin electronics do not hinder the movement of cockroaches at all. To make sure, scientists closely studied the natural movements of these insects: it turns out that their abdomens change shape, and parts of the exoskeleton overlap during movement. To account for this, they alternated between adhesive and non-adhesive sections of solar cell films to make them both fixed and flexible.

diagram of a flexible film on the back of a cockroach

Schematic cross section of abdominal segments with thin films attached by an adhesive-non-adhesive weave structure. This allows thin films to be bent outwards during abdominal deformation. © Y. Kakei et al.

They pre-tested thicker or evenly attached films, but the cockroaches took twice as long to travel the same distance and found it difficult to straighten up when they were lying on their backs. “The combination of ultra-thin film electronics and the adhesive-non-adhesive weave structure on the abdomen of an insect has been shown to be over 80% successful in self-healing attempts,” researchers at npj flexible electronics report.

Adding sensors and cameras is already planned

Cyborg insects equipped in this way were tested: the battery was charged with artificial sunlight for 30 minutes, and the cockroaches were made to turn left and right using a wireless remote control. Electrical impulses applied to the insect’s cerci – two appendages located at the end of its abdomen, which are sensory nerves – induce the cockroach to move in one direction or another.

The device appeared to be fully functional. “The body-mounted, ultra-slim organic solar cell module provides an output power of 17.2 mW, which is more than 50 times the power output of modern live insect energy harvesting devices,” said Kenjiro Fukuda, who led the team.

The measured power consumption of the wireless motion control system was 73.3 mW. The battery (40 mAh) lasted about two hours after a full charge. “In the current system, most of the power consumed was used for wireless communication. By adjusting the communication intervals, the battery can last longer,” the researchers note in their paper.

More updates are planned before this army of cyborg cockroaches goes on a mission. Indeed, the current system only has a wireless traffic control system, which is not enough to prepare an application such as urban rescue. “By integrating other necessary devices such as sensors and cameras, we can use our cyborg insects for such purposes,” Fukuda told CNET. However, these components will require higher energy costs.

Fukuda also pointed out in his statement that the deformed belly is not unique to cockroaches, so this strategy could be adapted to other insects such as beetles in the future, or perhaps even flying insects such as cicadas.

Y. Kakei et al., npj flexible electronics.

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