By combining tissues from a slug with flexible 3D-printed parts, researchers have created a 'biohybrid' that crawls like a sea turtle on the beach – albeit extremely slowly.
A muscle from the slug's mouth helps the robot move, which is currently controlled by an external electrical field. Future iterations of the device will include ganglia – bundles of neurons and nerves that normally conduct signals to the muscle as the slug feeds – as an organic controller.
The researchers also manipulated collagen from the slug's skin to build an organic 'scaffold' that will be tested in future versions of the robot.
The team at Case Western Reserve University chose the sea slug because the animal can cope with substantial changes in temperature and salinity as Pacific Ocean tides shift its environment between deep water and shallow pools. Compared to mammal and bird muscles, which require strictly controlled environments to operate, the slug's are much more adaptable.
In the future, swarms of biohybrid robots could search for the source of a toxic leak in a pond, the scientists said. Or they could search the ocean floor for a black box flight data recorder, a potentially long process that may leave current robots stilled with dead batteries.
"We're building a living machine – a biohybrid robot that's not completely organic – yet," said Victoria Webster, a PhD student who is leading the research.
Webster worked with Roger Quinn, the Arthur Armington, professor of engineering and director of Case Western Reserve's Biologically Inspired Robotics Laboratory.
By combining materials from the California sea slug, Aplysia californica, with three-dimensional printed parts, "we're creating a robot that can manage different tasks than an animal or a purely manmade robot could," Quinn said.
For the searching tasks, "we want the robots to be compliant, to interact with the environment," Webster added. "One of the problems with traditional robotics, especially on the small scale, is that actuators – the units that provide movement – tend to be rigid."
Muscle cells additionally carry their own fuel source; nutrients in the medium around them. Because they're soft, they're safer for operations than nuts-and-bolts actuators and have a much higher power-to-weight ratio.
The researchers originally tried using muscle cells but changed to using the entire 12 muscle from the mouth area, or buccal mass. By integrating the muscle with its natural structure, it becomes "hundreds to 1,000 times better."
In the team's first robots, the buccal muscle, which naturally has two 'arms,' is connected to the robots printed polymer arms and body. The robot moves when the buccal muscle contracts and releases, swinging the arms back and forth. In early testing, the bot pulled itself about 0.4 centimetres per minute.
To control movement, the scientists are turning to the animal's own ganglia. They can use either chemical or electrical stimuli to induce the nerves to contract the muscle.
"With the ganglia, the muscle is capable of much more complex movement, compared to using a manmade control, and it's capable of learning," Webster said.
The team hopes to train ganglia to move the robot forward in response to one signal and backward in response to a second. It is also preparing to test organic versions as well as new geometries for the body, designed to produce more efficient movement.
If completely organic robots prove workable, the researchers said, a swarm released at sea or in a pond or a remote piece of land, won't be much of a worry if they can't be recovered. They're likely to be inexpensive and won't pollute the locations with metals and battery chemicals but be eaten or degrade into compost.
Webster will discuss mining the sea slug for materials and constructing the hybrid, which is a little under two-inches long, at the Living Machines conference in Edinburgh this week. The research team also included Hillel Chiel, a biology professor, Ozan Akkus, professor of mechanical and aerospace engineering and director of the CWRU Tissue Fabrication and Mechanobiology Lab, Umut Gurkan, head of the CWRU Biomanufacturing and Microfabrication Laboratory as well as undergraduate researchers Emma Hawley and Jill Patel and master's graduate Katherine Chapin.
However, these are not the first researchers to develop and test the potential of biohybrid machines. Sung-Jin Park from Harvard University recently built a miniature, soft tissue robot with similar qualities and efficiency as a stingray.
His team created 'charged' gold skeletons that mimic the stingray's shape. These were then overlaid with a thin layer of stretchy polymer. Along the top of the robotic ray, the researchers placed muscle cells from rats, known as cardiomyocytes. The cardiomyocytes, when stimulated, contract the fins downward.
Each of these cells were genetically engineered to respond to light, and this meant the researchers could control the robot's movement using flashes and light cues. Asymmetrical pulses of light can be used to turn the robot to the left or right, the researchers showed, and different frequencies of light can be used to control its speed, as demonstrated in a series of videos.
The method works well enough to guide the robot through a basic obstacle course. The robotic stingray, containing roughly 200,000 cardiomyocytes, is 16 millimeters long and weighs just 10 grams.
Batoid fish, which include stingrays, are instantly recognisable by their flat bodies and long, wing-like fins extending from their heads.
These fins move in such a way to generate the most movement while using the least amount of energy possible. These energy-efficient waves emulate from the front of the fin to the back, allowing batoids to glide gracefully through water.
This article was originally published by WIRED UK
