Bio-inspired Acousto-Magnetic Micro-swarm Robots with Upstream Motility.
We are living in 21st century
where our medical science is so advance but even there are some fields that are
beyond human comprehension. This technology based on acoustic and magnetic field is a try in the medical industries against incurable disease.
Currently there is no bio compatible technology exists that can be used to navigate micro-particles upstream against background fluid flow. Professors and students at IRIS are inspired by micro-swimmers like bacteria, spermatozoa and plankton for this research. These micro-swimmers are natural and use non-slip boundary conditions of wall to exhibit upstream propulsion. Scientists are working on micro-bots called as self assembled micro-swarms that can execute upstream motility in a combination of external acoustic and magnetic field. The specialization of acoustic and magnetic field is that both are safe for humans and can penetrate deeply into the human body. Researchers are working on development of a system that can be powerful tool which can allow special tasks to be performed and this includes non invasive surgical procedure and delivery of drug molecules that are hard to reach site.
Micro-particles can be manipulated in liquid medium via two approaches i.e. use of external field or their gradient and adoption of Purcell’s scallop formulation. Existing micro-bots and nano-bots shows compatibility in biomedical context however they are limited but idea to manipulate micro or nano particles capable of executing synthetic Rheotaxis have been a fundamental challenge. This achievement can change the entire medical sciences. Researchers faced challenges with use of strong magnetic field to move nano or micro particles. Theoretically transportation is limited as gradient of magnetic field scales with its volume and is too low to prompt useful motion. Moreover propulsion generated by existing nano/micro bots is insufficient to move under physiological conditions. But nature provides the solution. Recent studies in the field show that naturally occurring micro-swimmers developed rheotaxis strategies that exploits non slip boundary conditions. Study was done on bacteria, spermatozoa and planktons and as result it was observed that trio used different techniques while approaching boundary. The velocity gradient at the wall generates torque on cells which is responsible for their interesting motion and essential for their survival. Phytoplankton undergoes Gyro-tactic trapping and periodic rotation relative to direction of flow to collect nutrition from ocean bed. On the other hand bacteria and spermatozoa switch their orientation within gradient of shear flow and exhibit rheotaxis. But in the artificially developed system micro particles can’t exploit boundary conditions of wall when exposed on an external fluid flow. Particles will experience wall induced lift force that acts opposite to wall. Particles have to be energized chemically or by external acoustic or magnetic field to migrate toward wall to exploit non slip boundary conditions. Presently we have the systems that use chemical activation. To date no micro or nano system has been developed that can perform rheotaxis in external field.
Concept
Each micro-swarm is formed by the self assembly of individual super paramagnetic particles resulting from dipole-dipole interactions in a rotating magnetic field. The spinning micro-swarm is then acoustically directed toward the wall where it executes rolling and subsequent rheotaxis. As the forces that are generated by most micro and nano-bots are not sufficient to propel against background fluid flows. The hydrodynamic interactions of moving micro-robots within the channel wall give rise to wall-induced lift forces, which prevent particles from reaching the wall to exploit the boundary conditions of a wall. Here, we investigate the upstream propulsion of micro-swarms in the presence of a background flow. The onset of motion in a fluid flow requires a reaction force from the wall that is compensated for by an acoustic radiation force exerted on the micro-swarm. The acoustic-induced reaction force further assists in overcoming the oppositely directed wall-induced lift force, enabling the micro-swarm to reach the wall and to execute rolling. An essential aspect of our system is that it exploits the flow characteristics near a wall.
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