There have been plenty of movies about humans going on impossible expeditions, travelling through space and time, but the 1966 Sci-Fi Fantastic Voyage achieved something no other movie had achieved before, a journey through the inner space – the human body. Scientists shrink a submarine
full of people, enabling them to travel into the brain of a scientist to treat a life-threatening blood clot. The movie follows their journey through the human body, as they come across the obstacles every antigen must face. While the special effects were limited by the technology of the 60s, Fantastic Voyage was clearly a landmark film as the concept of micro-surgeons being able to reach the inaccessible parts of the body would be every scientist’s fantasy. With the help of modern technology this fantasy could soon become reality. Well of course, no one can possibly shrink and send neurosurgeons to perform micro-surgeries in the brain, as we don’t expect to see a real-life Ant-man any time soon. Instead, researchers have attempted to create minuscule robots that would be able to enter the human body and behave as micro-doctors. These ‘Microbots’ could deliver drugs to targeted sites, perform a tissue biopsy, clear a blood clot and even build a scaffold on which new
cells could grow.
Over the past decade a number of Biohybrid Microbot designs have emerged that make it possible for the bot to navigate through the body. The basic idea is to combine a structure for carrying the drugs or performing the required function with a microbe for locomotion. A number of techniques can be used to attach the two components together without killing the microbe. In some cases, electric charges can bind a bacterium carrying positive charges, to negatively charged polystyrene plastic particles.
Sometimes multiple microbes can be used to carry a single structure, and other times one or two microbes can manage the same as there is no single design that will be suitable for all the situations. All these designs rely on the ability of the microbes to self-propel by drawing chemical energy from the surrounding.
Using microbes for propulsion is fitting as they are small enough to move rapidly through the body and have the ability to interact with the body’s cells. Some of the drawbacks of using microbes are the speed and accuracy of steering. Researchers in recent years have been developing efficient steering strategies. One design involves the use of bovine sperm cells trapped inside magnetic microtubules which can also be remotely controlled by a magnetic field along with the ability of the sperm cell to propel using its flagellum like
tail. Another model, involving an artificial bacterial flagellum as helical micro swimmers used for targeted gene delivery under low-strength rotating magnetic fields. A 2017 study showed success in coating a cyanobacteria with magnetic nanoparticles and guiding it through a rat’s stomach by applying an external magnetic field. White Blood Cells loaded with magnetic nanoparticles have also been steered toward a tumor to deliver drugs. Another study showed that algae-based Microbots can be guided by LED light pulses.
In some designs, steering relies on the Microbot’s own ability to sense the chemistry of its environment. At Johns Hopkins University, researchers have developed star shaped devices called microgrippers that respond to environmental factors like temperature, pH, and enzymes. For example, a temperature sensitive gripper’s arms will close when exposed to body heat thus enabling it to perform a biopsy. Another design by Caltech professor Lihong Wang involves the use of micromotors that are powered by gastric acid. These microbots consist of microscopic spheres of magnesium metal coated thin layers of gold and a polymer that resists digestion. This layer leaves a small portion of the magnesium uncovered which reacts with the fluids in the digestive tract generating small bubbles and this acts like a jet thus propelling the sphere forward. They used a technique called photoacoustic computed tomography (PACT) which involves the use of pulses of infrared laser light, then absorbed by oxygen carrying hemoglobin molecules causing them to vibrate ultrasonically. These vibrations are picked up by ultrasonic detectors and can be used for detecting the location of tumors as well as the Microbots.
While Microbots prove to be a promising development, a number of problems need to be solved before this technology can enter mainstream medicine. Just like one of the characters in the movie is almost killed by antibodies, the Microbots too, could be attacked by our immune system. Thus, the materials used to make these bots need to be inert to the body’s immune system as well as the microbes carrying them. They should be safe and easy to dispose of once the task is achieved, as unlike the movie, these bots cannot escape
through the patients tear ducts. One of the methods of disposal is loading the Microbot with sensors that can be achieved by infrared light to generate enough heat to degrade the bot on command. More than one Microbot would be required to successfully carry out a medical procedure, which in turn raises the need of devising techniques that allows one to control and coordinate movements of an entire swarm of bots. With scientists working hard to overcome these hurdles, we could soon witness Microbots going on a Fantastic Voyage!