Tiny robot with ‘caterpillar’ legs could deliver drugs inside human body

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A tiny robot with ‘caterpillar’ legs could be used to carry drugs inside the human body.

Researchers behind the technology say it has the equivalent strength of a human able to lift a 26-seat minibus.

It can adapt to adverse environments and move efficiently along surfaces within the body lined with, or entirely immersed in, body fluids such as blood or mucus.

But what makes the ‘milli-robot’ stand out is its hundreds of less than one millimetre long pointed legs that look like tiny hairs. 

Study leader Shen Yajing said the robot’s pointed legs ‘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. 

Lab tests showed that it was capable of carrying a load 100 times heavier than itself, a strength comparable to an ant, one of the strongest creatures in nature.

Previous research on the caterpillar-inspired robots has proposed that patients would swallow the device or receive it through a cavity in the skin. 

Scientists have developed the technology to pinpoint parts of the body which are difficult to access without surgery, Futurism reported earlier this year. 

The research team at City University of Hong Kong (CityU) studied the leg structures of hundreds of ground animals including those with two, four, eight or more legs, in particular the ratio between leg-length and the gap between the legs. 

The robot’s body thickness is around 0.15mm, with each conical leg measuring 0.65mm long and the gap between the legs measuring about 0.6mm, making the leg-length-to-gap ratio around 1:1.  

Dr Shen said: ‘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.’ 

Apart from the multi-leg design, Dr Shen said the materials also matter.

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.

Professor Wang Zuankai, who conceived the research idea, said: ‘Both the materials and the multi-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.’

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.

Prof Wang said: ‘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.’

The research team further proved that when facing an obstacle ten times higher than its leg length, the robot, with its deformable soft legs, is able to lift up one end of its body to form an angle of up to 90 degrees and cross the obstacle easily.

And it can increase its speed by increasing the electromagnetic frequency applied.

The researchers said the robot also shows a ‘remarkable’ loading ability. 

Dr Shen said: ‘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.’

Before conducting further tests in animals and eventually in humans, the research teams are further developing and refining their research in three aspects, namely finding a biodegradable material, studying new shapes, and adding extra features.

Dr Shen added: ‘We are hoping to create a biodegradable robot in the next two to three years so it will decompose naturally after its meds delivery mission.’

The robot was described in the journal Nature Communications.

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