Successful development of flexible amplifier circuit sheets with biocompatible gel electrodes

In vivo measurement of small action potential achieved

Apr 29, 2016

A group of researchers led by Professor SOMEYA Takao at The University of Tokyo and Professor SEKITANI Tsuyoshi at Osaka University succeeded in developing a flexible organic amplifier circuit sheet with biocompatible gel electrodes.

This group developed an electrically conductive gel material with a small inflammation reaction and used it in sensor electrodes. By integrating these electrodes to amplifier circuits of organic transistors produced on ultra-thin high molecular films, the implantation of a long-term in-vivo sensor system has become possible. As a result, it has also become possible to measure even weak heart signals, leading to the identification of the site of heart disease.

The new gel material developed by this group has excellent biocompatibility, flexibility, and conductivity. Using this gel for electrodes and integrating them to 1 - μm-thick ultra-thin organic film transistors, a sheet-type biopotential sensor with amplifier circuits was produced.

This new type of gel is produced by evenly mixing single-walled layer carbon nanotube into a hydrogel named polyrotaxane. Usually, as the surface area of carbon nanotubes was so big that they often aggregated into bundles , it was difficult to evenly disperse them in gel. So, this group evenly dispersed nanotubes using technology for untangling carbon nanotubes by ion liquid, succeeding in making the gel conductive.

In order to evaluate biological compatibility of this new gel material, 4-week in vivo implantation tests of the material were conducted, showing that this material caused less inflammation reaction than metal implantable electrodes used in conventional electronic devices.

This group realized a sheet-type biopotential sensor capable of performing long-term in vivo measurement of biopotential. Even if this sensor is attached to the organ directly, the inflammation reaction is so small that it will become possible to examine organs weakened by disease with a minimum load. For example, it will help doctors decide how to conduct surgery by putting this sheet-type biopotential sensor to the heart of the patient in order to identify the place of cardiac infarction during an operation with a high degree of accuracy.

The long-term implantation of this sheet-type biopotential sensor into the body will be helpful in early detection and treatment of disease. In this way, various applications of this next-generation medical device are anticipated.


In vivo electronic monitoring systems are promising technology to obtain biosignals with high spatiotemporal resolution and sensitivity. Here we demonstrate the fabrication of a biocompatible highly conductive gel composite comprising multi-walled carbon nanotube-dispersed sheet with an aqueous hydrogel. This gel composite exhibits admittance of 100 mS cm −2 and maintains high admittance even in a low-frequency range. On implantation into a living hypodermal tissue for 4 weeks, it showed a small foreign-body reaction compared with widely used metal electrodes. Capitalizing on the multi-functional gel composite, we fabricated an ultrathin and mechanically flexible organic active matrix amplifier on a 1.2-μm-thick polyethylene-naphthalate film to amplify (amplification factor: ~200) weak biosignals. The composite was integrated to the amplifier to realize a direct lead epicardial electrocardiography that is easily spread over an uneven heart tissue.

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To learn more about this research, please view the full research report entitled “ Ultraflexible organic amplifier with biocompatible gel electrodes ” at this page of the Nature Communications website.

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