Magnetic tweezers construct miniature medical equipment

Patients can recover faster from surgery if the instruments used by doctors during an operation are small. Millimeter-sized, fiber-based electronic tools—made by stamping two-dimensional circuits to the surface of optical fibers—are versatile and less invasive than standard surgical instruments. They can image, sense, and manipulate medical structures in vivo and potentially deliver drugs to hard-to-reach places. Making such tools requires deft hand motions to precisely transfer the 2D circuits to a fiber’s curved surface, and researchers have struggled to accomplish the task in the lab. Antoine Barbot , Haijie Tan , Guang-Zhong Yang, and their colleagues at Imperial College London solved that problem by deploying two robots and controlling them with a single permanent magnet.

The experimental apparatus is shown in the schematic. The robots, which measure 2 mm by 3 mm, are made from an elastic material (polydimethylsiloxane) mixed with iron powder and then cured to set their magnetic orientation. The design gives a preferred magnetization direction to each robot. Together the robot pair form a set of tweezers that can be manipulated with a permanent magnet.

The researchers used the robots to push the 2D circuitry across the air–water interface, rotate it into a desired position, and release it so that it can precisely adhere to the cylindrical fiber surface. Repeated experiments showed that the magnetic robot tweezers placed the 2D structure with a precision a bit better than 5 µm and an angle error of about 4°. That’s a big improvement over traditional transfers of 2D structures. Even slight hand vibrations can easily cause a placement error of 1 mm. The magnetic tweezer design could be useful in various applications, including microactuators for laser ablation and the placing of electronic circuits for in situ detection of biomarkers. (A. Barbot et al., Sci. Robot. 4, eaax8336, 2019 .)