It is hard to believe: A tiny spiral - a micro robot - catches a single sperm, moves it directly to an egg cell and delivers it right there.

So far, this spermbot only functions in a petri dish and with bovine sperm. But maybe one day, it could help women who wish to get pregnant, Oliver Schmidt, Professor at the Leibniz Institute for Solid State and Materials Research (IFW) Dresden told DW.

"With some men, the sperm are not moving, but still healthy. We would like to propel them artificially to be able to reach their final destination," he said. But the physicist admitted there is still a long journey ahead before the technique becomes a medical application.

Right now, the main challenge for using such micro robots inside a human body is imaging: "In a petri dish we can do all our experiments with high resolution microscopy," Schmidt said. "But when we operate deeply inside the tissue, the resolution fades."

Even the most modern computer tomographs, which are used to display a cross-section of a human body, are not strong enough to help guide the micro robot to its target. One would need real time imaging to observe the robot, he added.

The researchers from Dresden control their spiral with a magnetic field that rotates outside around the experiment. "It can not just be a permanent magnetic field. But on the other hand, the field does not need to be very strong." Certainly, for the human body it would not cause any harm, Schmidt stresses.

Production with laserlight in a liquid

The micro robot spiral was produced with a 3D-printer of the Karlsruhe based company Nanoscribe. Its printers are able to print dots with a diameter of only 200 nanometers (nm). By comparison, a human hair has a diameter of 50.000 nm.

The printing is done with special laser light in a specific photoresist. "In the places, where the laser is strongly focused, the liquid material will harden," Andreas Frölich from Nanoscribe explains. "This way, one can draw in a three dimensional way - just like with a tip of a pen." The hardened structures are made of plastic - a polymer.

In principle, this is a technique stemming from a well known photochemical process. With normal photoresist, one light particle - a photon - will trigger polymerization.

But that would not be enough to do 3D printing effectively. To turn the liquid into a hard substance, one needs two photons hitting the molecules simultaneously. That's why the process is also called two-photon-polymerization. 

Extremely short light pulses generate hard plastic

Under normal circumstances, it is highly unlikely that two photons would hit anything at exactly the same time. To generate enough photons, the engineers use a femtosecond laser. It generates light pulses, which only last a hundred thousandth of a billionth of a second. The pulses are loaded with intense energy, but the laser beam does not get dangerously hot.

The structures are so tiny that instead of using a container filled with liquid, one uses a tiny chip. On one chip, it is possible to generate hundreds of thousands of micro robots.

The spirals on the chip are coated with a magnetic material and then dropped into a liquid. In that form, they can easily be applied for medical or other laboratory uses.

Fighting cancer with sperms

Long before any human egg cell is ever fertilized by such a micro robot, Schmidt hopes there will be another medical application. He and his team want to fight cancer using the spermbot. How would that work? He told DW that sperm have a special property; they can penetrate cell walls.

"It is possible to equip sperm with chemotherapy medication," Schmidt says. "Then they transport the substance directly to the cancer cell."

The problem with insufficient imaging may be easier to solve in this type of application. Instead of using just one micro robot, researchers would deploy a huge swarm of spermbots. And that could become visible much easier, using existing technologies.

If it works, doctors will be able to apply their cancer medication right there, where it is needed and chemotherapy, for example, would become much less of an ordeal for the patient.

Many more potential uses in medicine

There are several other possible medical applications for micro structures from the Nanoscribe 3D printers. But to date, only one of them has been tested successfully.

Italian researchers managed to make a micro CT scan of the tiny surface structures of a bone. They then copied those exact structures to a new surface. Finally, the researchers applied living bone cells to the printed fake bone microstructures and the results were clear: "The living cells accepted the new surface much better than they would have with a flat surface," Andreas Frölich of Nanoscribe told DW.

Researchers at the Karlsruhe Institute of Technology (KIT) used a similar approach. They generated cage-like structures which make cells feel comfortable and settle there.

"The purpose is to lead the cells to believe that they are in a natural environment," Frölich said.

The micro printers can also be used to produce tiny instruments for minimally-invasive surgery. "We have customers who used our printers to attach lenses to extremely thin endoscopes. Or they have printed micro pliars onto the tips of wires," the physicist told DW. "This way one can monitor surgery inside a blood vessel and possibly remove a clot there," he added. So far, the technology has not reached hospital surgery rooms, but some medics are already running tests.