You probably haven’t seen Fantastic Voyage, the 1966 sci-fi film in which a submarine crew is shrunk to microscopic size and sent into the body of an injured scientist to repair his damaged brain.

But if you have, it might provide a glimpse into a not-too-distant future where tiny “robots” are deployed to deliver treatments before being absorbed into the body.

A US team has developed microscopic bubble-like bots the diameter of a human hair that can carry a drug and magnetic nanoparticles, allowing scientists to guide them to a desired location using an external magnetic field.

When the bots reach their target, they remain there while the drug diffuses out.

Study author Professor Wei Gao, an expert in medical engineering at the California Institute of Technology (Caltech), said: “Rather than putting a drug into the body and letting it diffuse everywhere, now we can guide our microrobots directly to a tumour site and release the drug in a controlled and efficient way.”

Scientists have been trying to develop micro or nano-bots for the past couple of decades but have faced challenges when it comes to navigating with prevision through bodily fluids such as blood, urine or saliva.

The bots - which are tiny bubble-like spheres rather than metal humanoids - must also leave behind no toxic traces in the body.

Those developed at Caltech measure roughly 30 microns in diameter - the diameter of a human hair.

Study co-author Professor Julia Greer said: "This particular shape, this sphere, is very complicated to write. You have to know certain tricks of the trade to keep the spheres from collapsing on themselves.

“We were able to not only synthesise the resin that contains all the biofunctionalisation and all the medically necessary elements, but we were able to write them in a precise spherical shape with the necessary cavity."

The bubbles were designed with a hydrophilic external surface, which means they are attracted to water and prevents them clumping together as they travel through the body.

Meanwhile, their interior is hydrophobic - or water-repellant. Tests showed they could last for several days.

The Caltech team successfully used the bots to deliver a drug in mice with bladder tumours. Four doses of drugs delivered by the bots over 21 days was found to be more effective at shrinking the cancers than another therapy not delivered by the bots.

Prof Gao added: "We think this is a very promising platform for drug delivery and precision surgery.

“Looking to the future, we could evaluate using this robot as a platform to deliver different types of therapeutic payloads or agents for different conditions. And in the long term, we hope to test this in humans."

The findings were published in the journal Science Robotics.