制造更便宜、生物相容的电子皮肤电极

诸平

据韩国大邱庆北科技大学（Daegu Gyeongbuk Institute of Science and Technology，DGIST）2020年12月10日提供的消息，该大学的材料科学家改善了用于电子皮肤（E-skin）应用的聚合物电极中的电导率。他们的方法既简单又便宜，但是还需要进一步增强聚合物，使其成为更昂贵的金电极的可行替代品。

世界各地的科学家正在努力开发可附着在人体上并监测生命体征的电子皮肤。这些电子皮肤在日常使用中需要舒适、透气和灵活。在这些应用中，金通常用于制造传导电信号的电极。但是，黄金价格昂贵，涉及复杂的制造过程，必须经过消毒才能在人体上使用。

极有希望的电极替代材料是聚合物PEDOT:PSS。它与人体皮肤具有生物相容性和柔韧性，相对便宜，并且易于制造并制成电极。不幸的是，其导电性远不如黄金。科学家们已经找到了改善其导电性的方法，但是这些方法涉及有毒的产品，例如采用酸类物质进行处理，也可以改变其导电性，但是会留下酸类物质的残留物，因此对于应用到电子皮肤方面来讲，酸处理并不是理想的选择。

大邱庆北科技大学（DGIST）的研究人员发现了一种无毒的方法，可以显著提高导电性能。DGIST材料科学家李成元(Sungwon Lee)说：“我们开发了一种涉及湿度和加热的水热处理，将PEDOT：PSS薄膜的电导率提高了250倍。”

特别是，研究人员发现，对PEDOT:PSS薄膜施加80％的湿度和加热到60℃以上，会导致材料内部的结构变化，从而增强其导电能力。

PEDOT:PSS由水不溶性导电PEDOT分子和水溶性绝缘PSS分子组成。在PEDOT:PSS薄膜上加湿气可以通过水幕将两种类型的分子分开，同时通过加热使PEDOT链膨胀，从而提高了材料的整体结晶度。这些结构上的变化将材料的电导率从0.495 S/cm提高到了125.367 S/cm。

然后，科学家们用增强的PEDOT:PSS材料制成了电极，发现它在暴露于空气、加热、弯曲和拉伸时能稳定地导电。他们还发现，将电极喷到用于监测关节运动、皮肤温度和心脏电活动的电子皮肤设备（E-skin devices）上时，它们可以很好地工作。

但是，仍需要进一步的改进，因为用酸处理PEDOT:PSS可以将其电导率一直提高到2,244 S/cm。李成元说：“尽管如此，我们的结果还是值得关注的，我们的新型水热处理技术显示出在生物医学领域的巨大潜力。”相关研究结果已经在Biosensors and Bioelectronics杂志网站发表——Wooseong Jeong, Gihyeok Gwon, Jae-Hyun Ha, Dongha Kim, Ki-Joo Eom, Ju Hyang Park, Seok Ju Kang, Bongseop Kwak, Jung-Il Hong, Shinbuhm Lee, Dong Choon Hyun, Sungwon Lee. Enhancing the conductivity of PEDOT:PSS films for biomedical applications via hydrothermal treatment. Biosensors and Bioelectronics, 2021; 171: 112717 DOI: 10.1016/j.bios.2020.112717.更多信息请注意浏览原文或者相关报道。

Highlights

•Novel, biocompatible method for enhancing the conductivity of PEDOT:PSS films.

•Treatment shown in the study has great potential as a health monitoring system.

•Simple conditions for treatment (relative humidity > 80% and temperature <100 ℃).

•Conductivity enhancement from 0.495 to 125.367 S cm⁻¹ achieved for the films.

•Conductivity enhanced due to continuous conductive pathways along PEDOT chains.

Abstract

This paper reports a new biocompatible conductivity enhancement of poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) films for biomedical applications. Conductivity of PEDOT:PSS layer was reproducibly from 0.495 to 125.367 S cm⁻¹ by hydrothermal (HT) treatment. The HT treatment employs water (relative humidity > 80%) and heat (temperature > 61 ℃) instead of organic solvent doping and post-treatments, which can leave undesirable residue. The treatment can be performed using the sterilizing conditions of an autoclave. Additionally, it is possible to simultaneously reduce the electrical resistance, and sterilize the electrode for practical use. The key to conductivity enhancement was the structural rearrangement of PEDOT:PSS, which was determined using atomic force microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible spectroscopy. It was found that PEDOT inter-bridging occurred as a result of the structural rearrangement. Therefore, the conductivity increased on account of the continuous conductive pathways of the PEDOT chains. To test the biocompatible enhancement technique for biomedical applications, certain demonstrations, such as the monitoring of joint movements and skin temperature, and measuring electrocardiogram signals were conducted with the hydrothermal-treated PEDOT:PSS electrode. This simple, biocompatible treatment exhibited significant potential for use in other biomedical applications as well.