Scientists create microrobots capable of handling single cells

Nanoscale robots can grasp, move, and rotate individual cells that are 30 to 40 micrometers in size. The precision these microrobots offer for imaging individual cells and their ability to manipulate the interactions between them expands researchers' ability to answer fundamental questions. Biophysicist Lornd Kelemen of the Institute of Biophysics in Szeged, Hungary, worked with colleagues in Hungary and Slovakia to develop a series of micro-robotic instruments for use with optical tweezers, a decades-old technology used to focus microscopic objects.

"If a small object comes into the beam's focus, the beam is refracted by the object and changes direction," Kelemen explains. According to the light body, the changes in the direction mean that the amount of light will change. "But changes in the amount of pulse means that the ray that causes these changes is used, and because the small object reflects the beam, the small object will be suitable for the beam," Kelens continued. Each action has an equal and opposite reaction, meaning that the beam acts on the small object to hold it in place.

Make optical tweezers softer

Using optical tweezers alone to study single cells is imperfect because trapping the cell itself in the beam can heat up and damage some cellular machinery. The stability and force generated by the tweezers is also weak due to the size and shape of the cells relative to the beam itself and the water in which it is suspended.

To solve this problem, scientists have previously attached tiny beads or structures like handles to cells that can be grasped with optical tweezers. Unfortunately, they also damage the cell and cannot be removed once added.

"It's like using duct tape to mount a cotton swab on a scapula," Kelemans explained. "You can grab the paddle to move the ball without crushing it, but when you want to remove it, you tear the ball."

Often these attachments also require changes in the cellular environment, such as the addition of pH or other chemicals, to complete attachment. The new microtools developed in the current study avoid this and are small and flexible enough to gently grasp cells while they themselves are captured by the optical tweezers beam. Another set of lasers is required to create microbots. The process, called two-photon polymerization, uses light to polymerize or harden the polymer only when it comes into contact with the material. "We focus the light on a tiny fraction of a micron, and the polymer hardens just in that tiny spot," Keleman said. This allows them to make tools precisely to nanometer-sized specifications. Microrobot performs well in tests

The challenge is to make the tool thin enough and flexible enough to grip the cells while being gripped by the beam itself. "We have to be very precise, because if the elastic element in our microstructure is 400 nm thick, it can be bent with optical tweezers, but not if it is 600 nm thick," he explains. During the test, the team showed that they can use the optical tweezers beam to bind part of the micro robot, for example, to open them to grab the cells. When the micro -robot elasticity is kept, the cells can be kept in a proper position, release the stiff part of the capture tool and manipulate, just like cotton balls and scraping the example above. The team developed three tools that allowed the researchers to move individual cells from one place to another, rotate the cell precisely for microscopy imaging, or grab two cells and squeeze them together to study their reactions.

"It was a long development process with a lot of surprises," Keleman said. However, these tools work as intended and provide a non-destructive way to manipulate and image single cells in their natural environment.

Because optical tweezers are still specialized, Kelemans doesn't expect all labs to be able to use their new micro-instruments, but those with the equipment can modify and optimize it for new tasks. "Sometimes the flex rods need to be longer, or a part of the structure needs to be a little shorter, or at a different angle," Keleman said. Now, given their plan and the increasing availability of two-photon polymerization systems, "laboratories that can afford them can in principle produce such structures."