A scientist who has sensitive information falls into a coma and must be saved. A submarine and its crew are miniaturised to the size of a microbe and introduced into the scientist’s blood stream to repair the problem-causing clot. This was the plot of a 1966 science-fiction movie, Fantastic Voyage.

What was ‘fantastic’ half a century ago, is cruising towards reality today. Physics and biology are joining hands to produce very tiny robots that could enter a person’s bloodstream and perform important tasks, such as delivering drug to specific sites—for applications like treating cancer and reproductive medicine.

Bradley J Nelson of the Institute of Robotics and Intelligent Systems, Zurich, Switzerland, is a known name in this field. In a co-authored article published in Annual Reviews last year, he writes that “over the past decade, significant progress has been made in the construction of intelligent micromachines, evolving from simple micromachines to soft, compound, reconfigurable, encodable, multifunctional and integrated micromachines, as well as from individual to multiagent, multiscale, hierarchical, self-organising and swarm micromachines.” That is quite a lot for a machine that may only be a few hundred nanometres in size.

A word of caution: medical microrobotics is not yet a market-ready technology—but is getting there.

Last year, a group of scientists from the Colorado University, Boulder, USA, put a fleet of microrobots carrying dexamethasone—a steroid—to the bladders of lab mice. Their bubble-based, polymeric microrobots were able to “swim with non-linear trajectories”, mechanically pin themselves to the epithelium (inner lining of hollow organs) and “slowly release therapeutic drugs”, the scientists say in a paper published in Small. “The sustained release of the drug is shown to temper inflammation in a manner that surpasses the performance of free drug controls,” the paper says, adding that the system “provides a potential strategy to use microrobots to efficiently navigate large volumes, pin at soft tissue boundaries, and release drugs over several days for a range of diseases.

Swallow a surgeon

Medical microrobotics is an excellent illustration of how a wild dream could become a reality. The origins of this field traces back to an epoch-making speech delivered by the American theoretical physicist, Richard Feynman, on December 29, 1959, on the topic ‘There’s Plenty of Room at the Bottom’, in which he said that “small machines might be permanently incorporated in the body to assist some inadequately functioning organ.” Feynman is said to have credited the “very wild idea of swallowing the surgeon” as originally proposed by mathematician Albert Hibbs.

But, manufacturing these microrobots presents a huge challenge. All the components need to be packaged in an ultra-tiny space. Even within that space, some onboard computing capabilities must be given to impart some intelligence to the microrobot. The design also varies with the degree of autonomy the microrobot will have, be it internally (they pick up energy from their interactions from other bodies) or externally (ultrasound) powered.

“Medical microbots for surgery use two methods to guide its motion inside the human body. One is optical-based guidance and the other is magnetic field-based guidance. In India, researchers have worked intensely in both ways of navigation in the last decade. The microbots are fabricated in-house using nanotechnology techniques and tested specifically for the purpose of cell specimen reshaping, drug delivery and cell removal from target area,” Dr Jayant Kumar Mohanta, Assistant Professor, Department of Mechanical Engineering, IIT Jodhpur, told quantum.

In Fantastic Voyage, the scientist’s immune system thinks of the rescue submarine as an enemy and starts attacking it. Today’s microrobots will face the same problem, so they must either become invisible to the body’s immune system or advertise themselves as friends. Therefore, scientists are developing microrobots with materials that are compatible with the body’s immune reactions. They may design surface coatings or camouflage techniques that help microrobots avoid detection. Some strategies involve bio-mimetic coatings that resemble cells or tissues in the body, which can deceive the immune system into recognising the microrobots as ‘self’ rather than ‘foreign’.

In a paper published in Surgery, scientists at the University of Sheffield, UK, note that medical microrobots can be classified into three categories, depending upon their task difficulty level (TDL). TDL-1 microrobots are devices like sensing devices including remotely activated stents and scaffolds and capsule endoscopes “that can carry out telemetry and send information about the internal environment.” TDL-2 robots show basic levels of local environment sensing, motion and simple decision-making capabilities which enable them to assist medical professionals with a series of one-time treatments including drug delivery and biopsies. This is where much of the current research is on. These are not yet robots with onboard intelligence and hence require human control. TDL-3 microrobots, are “still in the exploration stage and are far from realisation.” They are fully autonomous and can carry out various diagnostic and treatment processes.

Microrobotics can—will—revolutionise medicine. Microrobots for drug delivery at site seems to be the nearest hanging fruit. Take cancer treatment (chemotherapy) for example. A microrobot can be enabled to detect acidity or temperature gradients of a tumor and move towards the tumor, carrying a drug.

The submarine crew of Fantastic Voyage did come out successfully through a tear drop out of the scientist’s eye (even if one of them—a baddie—was killed by the scientist’s antibodies.) In real life too, by the looks of it microrobotics will be similarly successful. When it happens, it will be a huge breakthrough in medicine.

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