Untethered Microgrippers Sample Biologic Tissue

A new study describes thermally activated microgrippers that can reach narrow conduits in the body and be used to excise tissue for diagnostic analyses and biopsies.

Researchers at Johns Hopkins University (JHU; Baltimore, MD, USA) designed the submillimeter endoscopic microgrippers (μ-grippers) to resemble biological appendages, such as hands, with rigid phalanges and flexible joints. The residual stress powered actuators allow them to close and grasp without the need for tethers, while the rigid phalanges of the μ-grippers are composed of nickel, and hence, respond to an applied magnetic field. A thermo-sensitive polymer trigger layer on the joints keeps the μ-grippers flat at 4 °C, but softens at 37 °C, causing the μ-grippers to close.

The μ-grippers are small enough that hundreds can be deployed at a time and actuated en masse, and could therefore form the basis for a more statistically efficient means to screen large surface area organs such as the colon. To test the feasibility of biologic tissue sampling with μ-grippers, the researchers used a swine colon in ex vivo studies. They uniformly spread hundreds of μ-grippers by rotating the endoscope during the deployment. The arms of each millimeter-long μ-gripper is composed of chromium and gold actuators that naturally want to bend inwards, but are held back by the thin layer of polymer coating.

To simulate the normal human temperature, the colon was submerged in a water bath kept at 37 °C, whereupon the coating dissolved and the talons snatched up cells at close proximity; the researchers then visually verified the closure of the μ-grippers using endoscopic imaging. After closure, the vast majority of μ-grippers were retrieved using a magnetic catheter inserted through the endoscope. The researchers found that the μ-grippers identified the lesion 45% of the time; when the swarm was boosted up to 1,500 μ-grippers, the efficiency rose to 95%. The study was published in the April 2013 issue of Gastroenterology.

“Our results suggest a new paradigm in medicine whereby large numbers of small, tether-free microsurgical tools could complement individual, large, tethered biopsying devices,” concluded lead author Evin Gultepe, PhD, and colleagues of the department of chemical and biomolecular engineering. “The tissue retrieved by the μ-grippers is of sufficient quality and quantity to allow DNA and RNA extraction, as well as polymerase chain reaction (PCR) amplification in an effort to look for previously identified disease-diagnostic markers.”

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