An inchworm crawling along a leaf

An inchworm lurches along a leaf. Similar movements could allow an enzyme-coated sheet to advance along a surface. Credit: Freiheit/Alamy

Materials science

Micro-robots powered by chemistry grasp and creep

Gel sheets immersed in liquid could crawl forward like inchworms.

An enzyme-coated flexible robot could ‘swim’ through fluids by triggering chemical reactions in its surroundings.

Current catalyst-covered robots ‘swim’ by expelling reaction products backward, which allows the robots to spurt forward. Anna Balazs and her colleagues at the University of Pittsburgh in Pennsylvania propose a model for a swimmer made from a flexible, enzyme-covered gel sheet, which would billow in the currents it creates.

Using computer simulations, the team modelled a flower-like sheet composed of flexible ‘petals’ coated with the enzyme catalase. If immersed in hydrogen peroxide, the petals’ catalase would decompose the fluid into water and oxygen. These compounds — which are less dense than hydrogen peroxide — would rise, creating a convective current above the flower that would enable the petals to spring upward and ‘grab’ an object.

The team also modelled a free-floating catalase-covered sheet. This sheet would trigger convective flows that pull the middle of the sheet upward, creating an inchworm-like effect. The sheet could then creep along a surface.

Researchers employing these techniques could develop soft, small, cargo-delivery robots to ferry drugs through the body, the authors write.