Video: Microgripper captures single cells for tissue biopsy

Sampling diseased tissue, which can contain many different types of cells, calls for precise biomedical tools. Current methods for manipulating single cells, like laser microdissection, require complicated setups and can damage cells. Now, researchers led by David H. Gracias at Johns Hopkins University have developed devices that could offer a simpler and less-harmful way to isolate single cells (Nano Lett. 2020, DOI: 10.1021/acs.nanolett.0c01729). Remotely guided by a magnetic field, these so-called microgrippers can wrest single cells from a tissue sample and carry them on demand. Though the tiny grippers require more optimization and testing, the researchers hope one day to use them to perform single-cell biopsies inside a human body.

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The following is the script for the video.

Tien Nguyen: Watch as this device descends on a single cell. Remotely controlled by a magnetic field, the device fumbles for a moment, flitting around the cell’s edges, before finally settling and closing its grip to trap the cell.

Just 70 μm from tip-to-tip, these so-called microgrippers could come in handy as precision biomedical tools. For example, they could help doctors analyze diseased tissue under a microscope at the cellular level.

Currently, researchers isolate single cells with techniques like microfluidics, which capture cells using droplets, or laser microdissection, which uses laser beams to cut out individual cells. But these methods require complicated sample prep and can damage cells.

Designed by a team of researchers at Johns Hopkins University, the novel microgripper offers a simpler and less harmful way to manipulate the single cells.

The device is made of three biocompatible layers. At the bottom is a layer of silicon oxide and silicon dioxide. The team calls this the stress layer, because it holds tension in its chemical bonds and gives the device its ability to grab a cell when the time is right.

Next comes a magnetic layer made of silicon dioxide and magnetic iron, which lets the researchers control the device’s movements with an external magnetic field.

Finally, a top layer of food-grade paraffin wax seals the other two layers into place and serves as a heat-controlled trigger. At 26 °C, the device lays mostly flat. But as the researchers raise the temperature to 37 °C—or body temperature—the wax will soften enough to release the bottom stress layer, which then folds in to form the device’s grip.

Using a weak magnetic field, the researchers remotely guided the device through the channels of human fallopian tube tissue. In another experiment, the team showed that the microgrippers could safely carry live cells that they had tagged with green fluorescent dye.

The microgrippers could also wrest cells away from a cell cluster by rapidly switching the direction of the magnetic field. Next, the researchers want to add features to the device like a tiny camera. The team says this device brings them one step closer to their ultimate goal of performing single cell biopsies inside real patients.