Uncrewed Systems Technology 046

114 PS | Nanorobots N anobots are a staple of science fiction, usually depicted as bacteria-sized self-replicating machines created for benign purposes but which swarm in their trillions and transform everything with which they come into contact into either copies of themselves or some sort of grey goo (writes Peter Donaldson). However, scientists are experimenting with machines on this scale and are working out ways of building, powering and steering them. They are suggesting uses for them too, initially in medicine and environmental remediation. Leaving aside their potential as destroyers of worlds, it is worth looking at what they are as concepts and, tentatively, as real machines. They are usually described as devices whose largest dimension is between 1 and 100 nm. At this scale, creating devices is an exercise in chemical engineering, and the set of basic devices produced so far includes nanoswitches, motors, and ‘elevators’ and ‘cars’. Switches respond to chemical stimuli, ultraviolet light or heat by changing shape into binary on or off states. Motors also change shape, but use the energy released by the change to move. Elevators/cars can carry drugs, for example, into target areas of the body, and can be fitted with propulsion motors. Nanobots as cars are powered by steerable motors and are capable of more independent movement in response to stimuli. One example of a nanocar uses three carbon nanotubes as the chassis and four carbon 60 (C 60 ) spheres as wheels. While the C 60 wheels are one means of locomotion, biologically inspired alternatives include tail-like spinning flagella and hair-like cilia that behave rather like oars. As with any uncrewed vehicle, it must be possible to power, track and steer nanobots if they are to be useful, but at this scale these functions can overlap. For power and control, internal as well as external sources are being explored. Internal power sources being considered include chemical fuels catalysed by blood in medical applications, nanocapacitors and even radioactive materials, while a built-in chemical sensor could enable a nanobot to follow a chemical trail or gradient. External power sources include magnetic fields, X-rays, radio waves and ultrasound. Magnetic resonance imaging machines, for example, have both tracked and manoeuvred nanoscale devices onto cancer cells in experiments, while magnetic fields can also induce electric currents in circuits inside nanobots. Similarly, piezoelectric membranes can convert ultrasound into electric current, and sound pressure can be used to propel a nanobot in a selected direction. Also, in an analogue of how many macro-scale tethered ROVs are powered, they could be connected by tiny wires to an external energy and/or control signal source. Although nanobots have moved beyond science fiction and into the realm of science, the biggest challenges in making such tiny machines truly useful tools are most likely to be found in the realm of engineering. Fortunately, the deadly combination of self-replicating capability and poorly thought-through programming that might lead to a grey goo catastrophe is not an essential feature. Now, here’s a thing “ ” October/November 2022 | Uncrewed Systems Technology Creating nanobots is a chemical engineering exercise, and the basic devices produced so far include nanoswitches, motors and ‘cars’