The market for wearable electronic devices has exploded in recent years, with a concomitant increase in their sophistication due to the integration of complex electronic circuits. However, devices that are worn on the body are rigid and do not respond well to the body’s movement. A team of biomedical engineers based in Japan has devised a biocompatible, flexible, adhesive gel patch that senses internal or external electrophysiological biological signals. The adhesive gel fixes a delicate grid of detectors in place, even while in contact with a surface that is not static, such as a joint or an internal organ. The precision with which the detector acquires readings depends on an array of sensors printed 4 mm apart on a thin sheet of plastic. The result is a flexible patch that fits in the palm of your hand and can house as many as 144 sensors.
While still in its preclinical testing phase, this technology shows promise as a sophisticated, comfortable, long-term biometric measurement device that can be applied internally or externally. The researchers have shown proof of principle with the device attached to the surface of a rat’s heart. They demonstrated that the device adheres to the wet, dynamic surface of heart muscle for more than 3 hours, facilitating the reliable measurement of biological signals. The multielectrode array was shown to be sensitive and flexible, conforming to the dynamic characteristics of complex tissue.
More details about the technology according to the Japan Science and Technology Agency:
The research group first fabricated high-performance organic transistor integrated circuits on 1.4 micrometer extremely thin polyethylene terephthalate (PET) polymeric film, then coated only the electrodes that come into direct contact with the living body with adhesive gel pattern. On their prototype integrated circuits, 144 (12 × 12) sensors are distributed 4mm apart from each other on a surface area of 4.8 × 4.8cm2. Gel-coated Electrodes function as sensors that measure electronic signals directly from a living body. The integrated circuits stay functional even when the subject moves dynamically. It was proved in the following experiment where integrated circuits were placed on the surface of an inflated balloon. 100% compressive strain was applied, but their electrical performance did not fail.
The decisive factor in the research was the success in making adhesive gel that can fabricate patterns with light using only materials with superior biocompatibility. This new type of gel material is created by evenly distributing polyvinyl alcohol (PVA) in a rotating gel called. Since the pattern can be fabricated by light, this new type of gel can be coated only on the electrodes of sensors arranged in a grid pattern. Good adhesiveness is maintained even with wet living tissue since the new gel itself is adhesive. The adhesiveness of the gel resolves the problem found in the conventional methods where the electrode in contact with the living surface slips or peels off as the living tissue moves.
Their prototype device maintained a good contact for over 3 hours when affixed to the surface of a rat heart due to the astounding flexibility of the organic device and the adhesive gel. This resulted in an electrocardiograph with good quality signals. Since PVA loses flexibility by melting, the device can be easily removed without imposing a burden on the heart after measurement. Furthermore, the team built a supersensitive, flexible strain sensor with the same design method. They were able to measure dynamic body movements such as the moving of fingers by directly applying the
Study in Nature Communications: A strain-absorbing design for tissue–machine interfaces using a tunable adhesive gel
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