por Lynn Shapiro
, Writer | January 21, 2009
The microgrippers' grasping ability is rooted in the chemical composition of the joints embedded in the finger-like digits. These joints contain thin layers of chromium and copper with stress characteristics that would normally cause the digits to curl themselves closed like fingers clasping a baseball. But the researchers added a polymer resin, giving the joints rigidity to keep the fingers from closing.
When the microgrippers arrive at their destination, however, the researchers raise the temperature to 40 degrees C (or 104 degrees F, equivalent to a moderate fever in humans). This heat softens the polymer in the joints, causing the fingers to flex shut. The researchers also found an alternative method: Some nontoxic biological solutions can also weaken the polymer and cause the grippers to clamp down on their target.
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In their lab experiments, the Johns Hopkins researchers used a microgripper, guided by a magnet, to grab and transport a dyed bead from among a group of colorless beads in a water solution. Team members also captured dozens of live animal cells from a cell mass at the end of a capillary tube. The cells were still alive 72 hours later, indicating the capture process did not injure them. Also, the microgrippers captured samples from relatively tough bovine bladder tissue.
The experiments showed that the tetherless microgripper concept is viable and has great potential for medical applications, the researchers said. Gracias' team is now working to overcome some remaining hurdles. As currently designed, each biologically compatible gripper can close on a target only once and cannot be reactivated to reopen and release its contents. (A similar device from the Gracias team, aimed at industrial micro-assembly applications, can be directed to both capture and release its load, but this requires chemicals that are not safe for patients. This pick-and-place microgripper was described in a recent article in the Journal of the American Chemical Society.)
Gracias, who also is affiliated with the Institute for NanoBioTechnology at Johns Hopkins, hopes to collaborate with medical researchers who can help to move the microgrippers closer to use as practical biopsy and drug delivery tools in human beings. In September, he received a $1.5 million New Innovators Award from the National Institutes of Health.
He plans to use the five-year grant to develop an entire mobile, biochemically responsive micro- and nanoscale surgical tool kit.