A multi-legged mini-robot made for drug delivery

Soft robots come in many shapes and sizes. Here is one of the latest, developed at the City University of Hong Kong.

Its standout feature is a set of tiny caterpillar-like legs that can carry heavy loads while also reducing friction, allowing it, the designers say, to move efficiently inside the human body, even where fluids such as blood or mucous are present.

This, they hope, could pave way for new approaches to drug delivery.

The robot is equipped with hundreds of pointed legs, each less than one millimetre long. This is because of design decision taken after studying the leg structures of hundreds of ground animals with two, four or eight 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,” says research leader Shen Yajing, from the university’s Department of Biomedical Engineering.

The robot is fabricated with a silicon material called polydimethylsiloxane (PDMS) embedded with magnetic particles, which allows it to be remotely controlled by applying electromagnetic force. Increasing the frequency increases the speed.

“Both the materials and the mutli-leg design greatly improve the robot’s hydrophobic property,” says Yajing’s colleague Wang Zuankai. “Besides, the rubbery piece is soft and can be cut easily to form robots of various shapes and sizes for different applications.”

The researchers say that in laboratory tests the robot was able to carry a load 100 times heavier than itself, giving it strength comparable with one of nature’s great performers, the ant.

In the next two to three years they hope to create a biodegradable version that will decompose naturally after it has completed its drug delivery.

The paper was published in the journal Nature Communications.