Microrobots armed with new force-sensing system to probe cells

October 14, 2014

This image shows a “microforce-sensing mobile microrobot” juxtaposed against a U.S. penny. The device is being developed at Purdue University (Credit: Purdue University)

Purdue University researchers have designed and built a “vision-based micro force sensor end-effector” to measure forces on cells by being attached to microrobots, like a tiny nose.

A camera is used to measure the probe’s displacement while it pushes against cells, allowing for a simple calculation that reveals the force applied. Researchers already know the stiffness of the probe. When combined with displacement, a simple calculation reveals the force applied.

Microrobots small enough to interact with cells already exist. However, there has been no easy, inexpensive way to measure the small forces applied to cells by the robots. Measuring these microforces is essential to precisely control the bots and to use them to study cells.

A new tool for studying cells

The new approach could make it possible to easily measure the “micronewtons” of force applied at the cellular level. Such a tool is needed to better study cells and to understand how they interact with microforces.

The forces can be used to transform cells into specific cell lines, including stem cells for research and medical applications. The measurement of microforces also can be used to study how cells respond to certain medications and to diagnose disease.

Microrobots used in research are controlled with magnetic fields to guide them into position. “But this is the first one with a truly functional end effector to measure microforces,” said said David Cappelleri, an assistant professor of mechanical engineering at Purdue University.

Current methods for measuring the forces applied by microrobots are impractical and expensive, requiring an atomic force microscope or cumbersome sensors with complex designs that are difficult to manufacture.

The findings were detailed in a research paper presented during the International Conference on Intelligent Robots and Systems in September, authored by postdoctoral research associate Wuming Jing and Cappelleri.

The new system combined with the microrobot is about 700 microns (millionths of a meter) square; the researchers are working to create versions about 500 microns square. To put this scale into perspective, the mini-machine is about one-half the size of the “E” in “One Cent” on a U.S. penny. Future research may also focus on automating the microrobots.

The system was fabricated at the Birck Nanotechnology Center in Purdue’s Discovery Park. The research has been supported by the National Science Foundation.

Abstract of Incorporating In-situ Force Sensing Capabilities in a Magnetic Microrobot

This paper presents the preliminary design of a microforce sensing mobile microrobot. The design consists of a planar, vision-based micro force sensor end-effector, while the microrobot body is made from a nickel magnetic layer driven by an exterior magnetic field. With a known stiffness, the manipulation forces can be determined from observing the deformation of the end-effector through a CCD camera attached to an optical microscope. After analyzing and calibrating the stiffness of a micromachined prototype, manipulation tests are conducted to verify this microrobot prototype is indeed capable of in situ force sensing while performing a manipulation task. This concept can be scaled down further for next generation designs targeting real biomedical applications on microscale.