Microelectrodes can be used to measure electrical signals directly at the brain or heart. For such applications, however, soft materials are required on which the electrodes could previously only be applied with great effort. A team from the Technical University of Munich (TUM) has now succeeded in printing them directly onto various soft surfaces.
A team from TU Munich and Forschungszentrum Jülich have joined forces to print a . What sounds at best like a gimmick at first could change medical diagnostics. On the one hand, the scientists around Prof. Bernhard Wolfrum did not print an image or lettering, but a microelectrode array. These components consist of a large number of electrodes and can measure changes in the electrical voltage in cells. These occur, for example, during the activity of nerve or muscle cells.
On the other hand, gummy bears have a property that is particularly important for the use of microelectrode arrays on living cells: They're soft. Microelectrode arrays have been around for a long time. In their original form, they are made of hard materials such as silicon. In contact with living cells, this results in various disadvantages. This is why the shape and fusion of cells change in the laboratory. These can cause inflammation in the body and impair the functioning of organs.
These problems can be avoided with electrode arrays on soft materials. Accordingly, intensive research is being conducted on them. So far, mainly traditional methods have been used, which are relatively time consuming and depend on costly special laboratories. "If you print the electrodes instead, you can produce a prototype comparatively quickly and inexpensively and rework it just as easily," says Bernhard Wolfrum, Professor of Neuroelectronics at TUM. "Such rapid prototyping allows for completely new ways of working."
Wolfrum and his team use a high-tech version of the inkjet printer. The electrodes themselves are printed with carbonaceous liquid. To prevent the sensors from recording unwanted signals, a neutral protective layer is applied over the carbon tracks.
The researchers tested the method on various materials, including soft silicone PDMS (short for polydimethylsiloxane), the substance agar, which is frequently used in biological experiments, and finally gelatine, including a molten and resolidified gummy bear. Each of these substances has properties that are particularly suitable for certain applications. For example, gelatin-coated implants can reduce undesirable reactions in tissue.
The team was able to prove that the sensors deliver reliable data values through experiments with cell cultures. With an average width of 30 micrometers, they also enable measurements on individual or few cells, which is difficult to achieve with established printing methods.
Printed soft microelectrode arrays could be used in various areas. They are not only suitable for a rapid prototyping approach in research, but could also change the treatment of patients. "In the future, similar soft structures could, for example, monitor nerve or heart function in the body or even serve as pacemakers," says Prof. Wolfrum. He and his team are currently working on printing more complex, three-dimensional microelectrode arrays. Secondly, they are investigating printable sensors that do not react to voltage fluctuations but selectively to chemical substances.