Soft biosensors

The electrical activity of the nervous tissue or heart can be recorded directly from the organs using microelectrodes. But for this, devices that fix potentials must be made of soft materials. Existing methods do not allow attaching electrodes to such materials.

Researchers from the Technical University of Munich (Technical University of Munich) printed the electrodes with an inkjet printer directly on soft materials. Their technology will provide the basis for serious improvement of clinical diagnostics. For example, printed components consisting of a large number of microelectrodes can register electrical potentials resulting from the activity of neurons or muscle cells.

The soft base allows the use of microelectrodes to register the activity of living cells without the risk of inflammation or organ dysfunction, as happens when using solid silicon sensors.

The idea of creating a device for direct recording of electrical impulses from soft materials is not new. But for the first time, scientists printed electrodes using an inkjet printer. This saved effort and money, because other methods require access to expensive specialized laboratories and a lot of time. Inkjet printing solves these problems. In addition, they are easily recycled after use.

The electrodes are printed with carbon-based ink. In order to prevent scattering signals from hitting them, the electrodes are covered with a neutral protective layer on top.

The scheme of the device with microelectrodes and printing technology. a – outer lines are printed with ink with silver nanoparticles on a 12x12 mm plate; b – inner lines and microelectrode arrays are printed with ink with carbon nanoparticles; c – passivation layer 9x9 mm is printed with polyimide ink. d, e, f – sequential process of printing a microelectrode array on PDMS under a microscope: d – silver ink, e – carbon ink, f – polyimide ink. g is the principle of registration of action potentials. Source: article in Npj Flexible Electronics. To prove the versatility of the technology, the researchers tested it on various hydrogel substrates, including PDMS (polydimethylsiloxane), a soft form of silicon agarose commonly used in biological experiments, as well as various forms of gelatin and even marmalade candies.

Each of these materials has properties suitable for certain purposes. For example, gelatin-coated implants can reduce unwanted reactions in living tissue.

Microelectrode arrays on marmalade candies. Source: Technical University of Munich.

In experiments on cell cultures, scientists have proven the reliability of soft sensors. With an average width of 30 micrometers, they allow measurements to be carried out in one or more cells.

The difficulty lies in fine–tuning all the components - both the printer parameters and the ink composition. In the case of PDMS, for example, it was necessary to use pretreatment to make the ink stick to the surface.

Printed microelectrode arrays on soft materials can be used in various fields, both for research work and in medical practice. In the future, such soft structures can be used to monitor the functions of the heart or a certain nerve, and even serve as a pacemaker.

The authors are currently working on printing more complex three-dimensional microelectrode circuits. They are also developing sensors that would selectively respond to chemicals, not just electrical impulses.

Article by N. Adly et al. Printed microelectrode arrays on soft materials: from PDMS to hydrogels is published in the journal Npj Flexible Electronics.

Aminat Adzhieva, portal "Eternal Youth" http://vechnayamolodost.ru based on the materials of the Technical University of Munich: Producing sensors with an inkjet printer.