A Theoretical Investigation of the Ability of Magnetic Miniature Robots to Exert Forces and Torques for Biomedical Functionalities

Abstract

Magnetic miniature robots exert forces and torques onto the environment to conduct minimally invasive diagnostic and therapeutic tasks. The orders of magnitude of forces and torques determine what functionalities these robots can achieve. Although some studies have been dispersedly reported, the forces and torques have yet to be systematically investigated within biomedical context from underlying physical principles, leaving their theoretical limits elusive. This work constructs a theoretical framework from governing equations to calculate the forces and torques exerted by magnetic miniature robots in their respective targeted workspace to achieve functionalities. It reports that the existing miniature robots with a maximum characteristic length of 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-2}$</tex-math></inline-formula> m can exert a force and a torque up to the order of 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> N and 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-2}$</tex-math></inline-formula> Nm, respectively, considering realistic actuation paradigms and constraints. The attainable force and torque magnitudes are on par with the requirements of surgeries at human head (e.g., brain, eyes, and ears surgeries) or within adjacent regions of human skin (e.g., surgeries in the bladder and some blood vessels), as well as the surgeries on small animals. But they are insufficient for operations in deep-buried regions of large animals and human (e.g., implant therapy, biopsy, and tissue removal). Hence, potential strategies to further raise the ceiling of the ranges are examined to extend the functionality catalog and expand the operating scope of these robots.