Mini robo-snakes in our brains?

Perching exactly at the intersection of amazing and deeply creepy, tiny snake-like robots may soon be used to perform complex brain surgery.

In a paper published in the journal Science Robotics, researchers led by mechanical engineer Yoonho Kim from the Massachusetts Institute of Technology, US, present a proof-of-concept for a miniaturised, soft, and highly flexible robot that can navigate through the tortuous and narrow capillaries of the human brain.

The broad design of the machine is not in itself unusual. It falls within a class known in the jargon as soft continuum robots – and, more colloquially, as robo-snakes. Variants are already being tested for use in heart surgery.

Until now, however, physical and mechanical considerations have placed constraints on miniaturisation. Propulsion, steering and power systems – including rigid magnets and hydraulic networks – have restricted the robots to centimetre or, sometimes, millimetres scales. As impressive those feats of engineering are, they still result in vehicles far too large to navigate through the delicate vasculature of the brain.

A second problem with soft continuum designs has been friction. Much like a worm moving through soil, the robots scrape against their surroundings, generating heat and risking tissue damage.

The version designed by Kim and colleagues, however, goes a long way to solving most of the problems. The body is made from a soft polymer matrix – which can be 3D-printed or injection moulded – into which are implanted a network of magnetic microparticles. The mini-magnets, activated in concert or individually by a roboticist-surgeon, can be used to determine direction. 

A hydrogel skin, just a few nanometres deep and made from cross-linked polymers, coats the outside of the robot. The researchers say that in tests the coating reduced friction by an order of magnitude compared to existing products.

The absence of hard components, wires or fluid-filled sacs means that the robo-snake can be produced at submillimetre scales – just a few micrometres in length.

To demonstrate its potential, the researchers constructed a virtual scale model to represent brain vasculature, full of tight corners, twisting routes and obstacles in the form of simulated aneurisms. A digital analogue of robo-snake made it through with ease – and was also able to demonstrate a tiny inbuilt laser, used to perform surgery on the blockages.

Kim and colleagues see refinements of the design resulting in remote, steerable machines capable of meeting the clinical challenges of treating brain injury in a manner that is less invasive than current surgical approaches. In addition, it will enable treatment of lesions in currently inaccessible positions.

The research to date has been done either in computer models, or tissue samples. The researchers concede that more testing is necessary – particularly in the areas of biocompatibility and mechanical lifespan – before human trials can begin.

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