Medical technology: Robots in the blood

Retinal diseases bring great suffering to those affected. In age-related macular degeneration, the ability to see in the yellow spot area of the eye decreases, which can lead to visual impairment. The problem is that retinal diseases are difficult to treat due to their poor accessibility, and those affected regularly receive costly injections in the eye.

Prof. Dr. Peer Fischer, Professor of Experimental Physics at the Institute for Molecular Systems Engineering at Heidelberg University, aims to change this. He has been working on the use of robotics in the human eye for many years. His goal: to guide tiny robots loaded with active substances through the eye to make them act on the retina. “We want to enable direct transport, which is minimally invasive and takes place directly through the vitreous humor,” says Fischer. Minimally invasive also means the smaller, the better. Therefore, scientists like Fischer use either microrobots, which are less than one millimeter in size, or nanorobots that are only 500 nanometers wide. This is around 200 times smaller than the diameter of a human hair. One of the things scientists are using is specially coated propellers of this size, which can be navigated through dense tissue such as the vitreous humor. These robots have a helical structure – “like a corkscrew”, explains Fischer.

However, as such small dimensions leave no room for a conventional motor, special types of drive are required. Several options are available if robots are to be moved through the body. In addition to ultrasound and acoustic solutions, light control, for example using infrared, is also a possibility. Or, depending on the design of the robot, a chemical or biological drive could even be considered. “Magnetic propulsion is the most advanced,” says Dr. Erdost Yildiz, postdoctoral researcher at the Max Planck Institute for Intelligent Systems in Stuttgart. His work in neurostimulation includes the treatment of Alzheimer's and Parkinson's disease with microscopic robots.

The applications are very diverse and range from neurodegenerative diseases to cancer, from thromboses to infections. “Treating cancer is of course one of the most important research interests,” explains Yildiz. This relates specifically to the types that are difficult to reach in the body, such as tumors in the brain, liver or pancreas. However, micro- and nanorobots could also be used to dissolve thromboses using ultrasound or to treat other vascular diseases such as stenoses or aneurysms.

“There are aneurysms that you can't reach with a catheter,” says Dr. Anna C. Bakenecker, Group Leader of Magnetic Methods at the Fraunhofer Research Institution for Individualized and Cell-Based Medical Engineering, IMTE in Lübeck. Different methods are used to magnetically control the small robots. One option is to apply a magnetic gradient field that increases and decreases in strength. Such electromagnetic coil assemblies are used to pull the microrobots into the right place, but the forces achieved are often very small. Rotating, homogeneous fields that generate torque are somewhat easier to control. This is particularly useful for helical robots – such as the aforementioned nanopropeller that goes through the eye. “The robot then rotates at the same frequency as the magnetic field,” explains Bakenecker. Another method that is being used in research is oscillating magnetic fields. These cause a swimming movement in the microrobots.

However, it will probably be some time before micro- and nanorobots are used clinically. “We are currently in the preclinical phase,” says Erdost Yildiz. The first research applications on the human body are being carried out in China and Japan. Yildiz estimates that the first tests could begin in Germany in five to ten years. “The biggest challenge is the safety of these applications,” says Bakenecker. In Germany and Europe in particular, people are very concerned about safety. “In terms of companies and spin-offs, other countries are further ahead, but we are doing well in research,” says Peer Fischer.

The three researchers are certain that the further development of micro- and nanorobotics in medicine should be driven forward: “There is quite a lot of potential for the use of these technologies,” says Peer Fischer. And there are also plenty of medical problems that need to be solved.