Microtweezers for Building MEMS Structures like Microsopic LEGO Blocks
Researchers at Purdue have produced a new type of microtweezers able to manipulate objects for building miniature structures, printing coatings to make advanced sensors, and grabbing and positioning live stem cell spheres for research projects.
Moreover, these microtweezers could be used to assemble structures in microelectromechanical systems, or MEMS, which include tiny moving parts. MEMS accelerometers and gyroscopes are already being used in commercial products. A wider variety of MEMS devices, however, could be produced through a manufacturing technology that assembles components like microscopic Lego pieces moved individually into place with microtweezers, said Cagri Savran, associate professor of mechanical engineering at Purdue University.
“We’ve shown how this might be accomplished easily, using new compact and user-friendly microtweezers to assemble polystyrene spheres into three-dimensional shapes,” he explains. The two-pronged tweezer is micromachined in a laboratory called a “clean room” using the same methodology as in microcircuit and computer chip fabrication. The research was based at the Birck Nanotechnology Center in Purdue’s Discovery Park. Research results are detailed in a paper that appeared in the Journal of Microelectromechanical Systems, or JMEMS, written by Savran and associates.
The new tool consists of three major parts:
1. a thimble knob from a standard micrometer 2. a two-pronged tweezer made from silicon 3. a “graphite interface,” which converts the turning motion of the thimble knob into a pulling-and-pushing action to open and close the tweezer prongs.
No electrical power source is required, increasing the potential for practical applications. Other types of microtweezers have been developed and are being used in research. However, the new design is simpler both to manufacture and operate, Savran said.
The design contains a one-piece “compliant structure,” which is springy like a bobby pin or a paperclip. Most other microtweezers require features such as hinges or components that move through heat, magnetism or electricity, complex designs that are expensive to manufacture and relatively difficult to operate in various media, he said.
The tweezers make it practical to accurately isolate individual stem cell spheres from culture media and to position them elsewhere. At this time, such spheres are analyzed in large groups, but microtweezers could offer an easy way to study them by individually selecting and placing them onto analytical devices and sensors.
“We currently are working to weigh single micro particles, individually selected among many others, which is important because precise measurements of an object’s mass reveal key traits, making it possible to identify composition and other characteristics,” Savran said. “This will now be as easy as selecting and weighing a single melon out of many melons in a supermarket.”
Microcantilver Dot Printing
The microtweezers also could facilitate the precision printing of chemical or protein dots onto “microcantilevers,” strips of silicon that look like tiny diving boards. The microcantilevers can be “functionalized,” or coated with certain chemicals or proteins that attract specific molecules and materials. Since they vibrate at different frequencies depending on what sticks to the surface, they are used to detect chemicals in the air and water.
By and large, microcantilevers are functionalized to distinguish one type of substance by exposing them to fluids, Savran said. But being able to microprint a sequence of precisely placed dots of different chemicals on each cantilever could make it possible to functionalize a device to detect several substances at once. Such a sensing technology also would require a smaller sample size than conventional diagnostic technologies, making it especially practical.
The new microtweezers are designed to be attached easily to “translation stages” currently used in research. These stages are essentially platforms on which to mount specimens for viewing and manipulating. Unlike most other microtweezers, the new device is highly compact and portable and can be easily detached from a platform and brought to another lab while still holding a micro-size object for study, Savran said.