Scientists have developed a tiny, soft robot with caterpillar-like legs that can carry heavy loads and could be used to deliver drugs in the human body.
The robot developed by researchers from the City University of Hong Kong (CityU) can move efficiently inside surfaces within the body lined with, or entirely immersed in, body fluids such as blood or mucus.
The robot has hundreds of pointed legs, measuring less than a millimetre. Researchers studied the leg structures of hundreds of ground animals, including those with 2, 4, 8 or more legs, in particular the ratio between leg-length and the gap between the legs.
"Most animals have a leg-length to leg-gap ratio of 2:1 to 1:1. So we decided to create our robot using 1:1 proportion," said Shen Yajing, an assistant professor at CityU, who led the research.
The robot's body thickness measures approximately 0.15 mm, with each conical leg measuring 0.65 mm long and the gap between the legs measuring approximately 0.6 mm, making the leg-length-to-gap ratio around 1:1.
Moreover, the robot's pointed legs have greatly reduced their contact area and hence the friction with the surface. Laboratory tests showed that the multi-legged robot has 40 times less friction than a limbless robot in both wet and dry environment.
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The robot is fabricated with a silicon material called polydimethylsiloxane (PDMS) embedded with magnetic particles which enables it to be remotely controlled by applying electromagnetic force.
"Both the materials and the mutli-leg design greatly improve the robot's hydrophobic property. Besides, the rubbery piece is soft and can be cut easily to form robots of various shapes and sizes for different applications," said Wang Zuankai from CityU.
Controlled by a magnetic manipulator used in experiments, the robot can move in both a flap propulsion pattern and an inverted pendulum pattern, meaning that it can use its front feet to flap forward as well as swinging the body by standing on the left and right feet alternately to advance respectively.
"The rugged surface and changing texture of different tissues inside the human body make transportation challenging. Our multi-legged robot shows an impressive performance in various terrains and hence open wide applications for drug delivery inside the body," said Wang.
When facing an obstacle ten times higher than its leg length, the robot, with its deformable soft legs, is capable to lift up one end of its body to form an angle of up to 90-degree and cross the obstacle easily. The robot can increase its speed by increasing the electromagnetic frequency applied.
Laboratory tests showed that the robot was capable of carrying a load 100 times heavier than itself, a strength comparable to an ant, or to a human being able to easily lift a 26-seated mini-bus.
The amazingly strong carrying capability, efficient locomotion and good obstacle-crossing ability make this milli-robot extremely suitable for applications in a harsh environment, for example delivering a drug to a designated spot through the digestive system, or carrying out medical inspection," said Shen.
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