A research team led by Kit Parker, from Harvard, has developed a scaled version of a ray fish with a rubber body and a gold skeleton, along with rat heart muscle cells that were specifically designed to respond to light sources. Parker’s team had already developed an artificial jellyfish, so he approached one of his head scientists Sung-Jin Park to try and create an artificial stingray.
The project was featured in the latest issue of Science. The morphology of the ray fish was replicated at a 1/10 of its scale. The robot can steer and turn depending on the source of light it perceives. The research team can modify the ray’s speed and direction by changing the frequency of the light flash. They even managed to guide the robot ray successfully through an obstacle course.
Why a robotic ray fish?
The robotic stingray is necessary because it has been developed by using mainly soft materials and allowing it to be guided by light, very much like most living organisms. The idea behind the study is to get even closer to successfully replicating biological muscles, as they are complex structures that are yet to be developed in an artificial environment. Soft robotics have used polymers and pressurized fluids to try and replicate muscles and biological tissue, but these materials are yet a long way to go for such purpose.
Existing technology able to replicate tissue and muscles have been able to be paired up with artificial sensors of movement and light, just like those that appear in the robotic ray. The team chose a ray as their ideal model because they are flat as a disk and possess pectoral fins. This allows for a reduced spectrum of movement, as ray fish and batoid fish are not able to turn over by themselves. Ray fish also swim with high efficiency, bending their bodies so that they can perform a sort of movement classified as “flagellar,” similar to jellyfish.
The robot’s composition
The ray fish robot is comprised of a body made out of PDMS, a material frequently used to manufacture medical devices, kinetic sand, and lubricants. It also has a skeleton made out of evaporated gold and, last but not least, a layer of rat cardiac muscle cells.
The robot has two parallel layers of muscle designed to pull each other as they contract and relax, allowing for a wave-like movement.
The rat cardiac muscle cells, or myocytes, were modified to respond to light sources. This is so the muscles could act by themselves without having to send or receive information from a central nervous system. When a beam of light is pointed at the front of the ray, the nearest myocytes would respond accordingly. If the stingray were exposed to a global electrical field, the ray would move forward very fast. When it was exposed to a pulse of light, it would also move forward, but in a segmented way, similar to a jellyfish.
What does the project yield?
The same technology used for creating the robot’s motor system may be able to serve as a mean of developing an artificial heart. According to the research team, the ray experiment has many similarities with the possible creation of a human heart. Both have to deal with liquids and with synchronized motion, as the ray has to propel itself to swim and the human heart must pump blood through the circulatory system.
Since the ray reacts in fractions of a second to optical stimuli, it was also highlighted as a means of comparison with the human heart, as the heart must perform changes in its performance depending on blood pressure and cardiac frequency.
The robot was tested in a controlled environment, only moving in two dimensions, where real ray fish can also move up and down.
When the robot’s engineering was deemed satisfactory, it was subjected to an obstacle course. The research team managed to guide the robot at a speed of 1.5 millimeters per second, along the 250 millimeters that the obstacle course spanned.
Although it is a scaled-down version of a ray fish, it was able to maintain its initial speed as it went through the obstacle course.
An exciting future in robotics
This study has accomplished to serve as a statement to the potential of combining engineering and materials science, along with neurodynamics, which allows scientists to design robots that react to environmental stimuli.
The ray robot is only able to perceive light, but it is a matter of time until new versions can sense temperature, touch, sound and any perceivable sensory input. Robots are limited by their cognitive capacity since they are only able to receive and execute commands dictated by humans.
By allowing them to perceive natural sources of information, such as light in the case of the ray robot, an artificial cognitive system may be created from the ground up. The technology could be implemented in future robots so that they can sense their surroundings and act accordingly, without the need of being programmed to do so.