Micro- and nanorobotics in the body: Precision treatment with medical microrobots

VDE dialog: To understand exactly what we’re talking about, what are the main differences between micro- and nanorobotics?

Dr. Anna C. Bakenecker: As the name suggests, the size of the robots plays a major role. The term microrobotics is sometimes used for robots that are just a few millimeters to a few micrometers in size. The shape is also important; systems with a helical shape are often used in the case of microrobots. In the field of nanorobots, we tend to talk about controllable spherical particles – tiny spheres that are loaded with an active ingredient and then guided through the body. In practice, the boundary between micro- and nanorobotics is fluid.

Where are the areas of application?

First of all, everything is still in the development stage. Of course, nanobots are always useful when it comes to very small structures such as vascular capillaries. Microrobots simply don’t fit through them. However, there are also approaches where microrobots are loaded with nanobots. The microrobot then releases the nanobots when it enters the capillaries. Basically, the technologies are always used to treat localized diseases; that could be a tumor, a vascular constriction or other hard-to-reach areas of disease.

That sounds complicated. How are micro- and nanorobots precisely controlled through the body?

There are several ways to control micro- and nanorobots. They can be controlled by light, ultrasound or chemical reactions on the surface of the micro- and nanobots, which then cause locomotion. But I mainly focus on magnetic control.

Why is that?

Magnetic fields have the advantage that they are harmless to the human body at the field strengths and frequencies used. In contrast to light control, they have an effect deep inside the body. Looking at the current scientific research, magnetic propulsion seems to me to be the most widespread. However, chemical reactions are also very promising. In bladder cancer, for example, nanobots can be powered by urea. This works with enzymes that are attached to the shell of the nanoparticles. The enzymes then break down the urea, which causes the particle to be propelled forward.

You have explained that magnetic fields are harmless. What about the general use of micro- and nanobots in the body?

There are still some challenges to overcome. Regardless of whether magnetic fields or another type of control system are used, we always have to ensure reliable tracking of the microrobots. This is where imaging comes into play. We need reliable, three-dimensional imaging in real time that makes it possible to track and control the robot precisely. I currently regard that as the biggest challenge in development. The reliability of the control system is particularly important when it comes to actual clinical use.

What happens to the microrobots after the work is done?

There are two possibilities: either they are retracted, or they disintegrate in situ. A great deal of research is therefore being carried out into degradable materials or materials that release an active ingredient in response to a heat trigger and then dissolve. For magnetic control, we often use iron oxide – a substance that is magnetic enough, but also very well tolerated by the body.

Micro- and nanobots are tiny. How are they produced?

Developments in the field of additive manufacturing – also known as 3D printing – have led to a real surge in development in this field. The key word is two-photon lithography. This is a photopolymerization process that enables resolutions higher than 25 nanometers. This technology can be used to produce very small structures with an extremely high degree of freedom in terms of shapes. There are also other processes, including the deposition of materials, for example. The chemical synthesis of various nanoparticles is also used in nanorobotics.

Where do science and industry stand in terms of development?

The first tentative attempts are being made to actually mold the technologies into startups in order to bring them to market. However, safety, imaging and tracking in particular still require a great deal of research. In Germany, we are doing particularly well in magnetic microrobotics, because there are several research groups. Overall, however, the scientific micro- and nanorobotics community is very international, and good work is being done in this field.

Dr. Anna C. Bakenecker is Group Leader Magnetic Methods at the Fraunhofer Research Institution for Individualized and Cell-Based Medical Engineering IMTE, where her work includes the development of innovative magnetic methods for medical applications.