These painted e-tattoos could be the future of wearable biosensors
These painted e-tattoos could be the future of wearable biosensors
这些手绘电子纹身可能是可穿戴生物传感器的未来
Scientists at Pennsylvania State University have developed a novel conductive ink that can be painted directly onto the skin in colorful custom designs, turning into a functional electrode for biomonitoring after drying. They described their work in a new paper published in the Proceedings of the National Academy of Sciences (PNAS).
宾夕法尼亚州立大学的科学家们开发出一种新型导电油墨，可以直接在皮肤上绘制出色彩鲜艳的定制图案，干燥后即可转化为用于生物监测的功能性电极。他们在发表于《美国国家科学院院刊》（PNAS）的一篇新论文中描述了这项研究。
As previously reported, epidermal electronics attached to the skin via temporary tattoos (e-tattoos) have been around for more than a decade. So-called e-tattoos connect to skin without adhesives, are practically unnoticeable, and are typically attached via temporary tattoo, allowing electrical measurements (and other measurements, such as temperature and strain) using ultra-thin polymers with embedded circuit elements.
正如之前报道的那样，通过临时纹身（电子纹身）贴在皮肤上的表皮电子设备已经存在十多年了。所谓的电子纹身无需粘合剂即可与皮肤连接，几乎无法察觉，通常通过临时纹身的方式贴附，利用嵌入电路元件的超薄聚合物进行电学测量（以及温度和应变等其他测量）。
However, these e-tattoos have their limitations, most notably that they don’t function well on curved and/or hairy surfaces, as well as requiring personalized electrode placement design to cover larger areas, since biosignals are spatially distributed. So scientists have been getting creative. For instance, in 2024, researchers developed special polymer-based conductive inks that can be printed onto a person’s scalp to measure brain waves, even if they have hair. This could one day enable mobile EEG monitoring outside a clinical setting, among other potential applications.
然而，这些电子纹身存在局限性，最显著的是它们在弯曲或多毛的表面上效果不佳，而且由于生物信号在空间上是分布的，覆盖较大区域需要个性化的电极布局设计。因此，科学家们一直在发挥创造力。例如，2024年，研究人员开发出一种特殊的聚合物导电油墨，可以打印在人的头皮上以测量脑电波，即使有头发也不受影响。这未来有望实现临床环境之外的移动脑电图（EEG）监测，以及其他潜在应用。
Penn State mechanical engineer Larry Cheng, a co-author of the new PNAS paper, has been working on electrode designs for biomonitoring applications for more than 10 years, including EEGs, ECGs (for heart activity), and EMGs (for muscle contractions). Using rigid materials, like metals, makes for a stable biomonitor, but it is easily dislodged when the wearer moves too much, such as during exercise. Hydrogels have emerged in recent years as alternative materials, since they can absorb water, swell, and stretch with the body’s skin during movement. But hydrogels degrade rather quickly and lose those benefits with prolonged use.
宾夕法尼亚州立大学机械工程师、该PNAS论文的合著者Larry Cheng从事生物监测电极设计已超过10年，涵盖脑电图（EEG）、心电图（ECG）和肌电图（EMG）。使用金属等刚性材料可以制造出稳定的生物监测器，但当佩戴者剧烈运动（如锻炼）时，它们很容易脱落。近年来，水凝胶作为替代材料出现，因为它们可以吸收水分、膨胀，并随着身体皮肤的运动而拉伸。但水凝胶降解较快，长期使用会失去这些优势。
The team mercifully shortened the abbreviated moniker of their new conductive ink to WE-PPD. “The ink itself almost behaves like face paint,” said Cheng. “It starts out almost transparent, but you can use food dye to pigment the ink into whatever colors you need to paint whatever design you have in mind—like a cartoon or Superman. This allows us to completely personalize the wearable to a person’s preference.”
研究团队将他们这种新型导电油墨的缩写名称简化为WE-PPD。“这种油墨本身就像面部彩绘一样，”Cheng说。“它最初几乎是透明的，但你可以使用食用色素将其调配成任何你需要的颜色，画出你想要的任何图案——比如卡通人物或超人。这使我们能够根据个人的喜好完全定制可穿戴设备。”
Because the ink fills the contours of the skin, the resulting electrode has very high skin connectivity, and hence better signal recording. It can also be incorporated into a porous silver texture and integrated with rigid devices. The painted sensors were tested in the lab on human subjects to monitor heart activity while running on a treadmill and lifting weights; gesture recognition to control a prosthetic robotic hand; and brain activity (EEG), monitored through hair, as a co-author went about their daily activities.
由于油墨能填充皮肤的轮廓，由此产生的电极具有极高的皮肤贴合度，从而能获得更好的信号记录。它还可以结合多孔银纹理，并与刚性设备集成。实验室对人类受试者进行了测试，监测了跑步机跑步和举重时的心脏活动；控制假肢手的手势识别；以及在合著者进行日常活动时，通过头发监测脑电活动（EEG）。
The painted electrodes were able to stretch up to 170 percent before failing, per the authors, had much higher water vapor permeability than standard medical-grade films, and caused no skin irritation over prolonged use. “Although we tested the daily use application over a 12-hour period, this is not the limit for these electrodes,” Cheng said. “The electrodes themselves can be washed away and easily reapplied. The big idea behind this is that in the future, you could potentially have a more expensive sensing module that remains separate from the system, but the electrodes themselves can be disposable. A single bottle of ink could provide enough material to paint multiple electrodes over the course of several days or a week.”
据作者称，这种手绘电极在失效前可拉伸至170%，其水蒸气渗透性远高于标准的医用级薄膜，且长期使用不会引起皮肤刺激。“虽然我们测试了12小时的日常使用情况，但这并不是这些电极的极限，”Cheng说。“电极本身可以洗掉并轻松重新涂抹。其背后的核心理念是，未来你可能拥有一个与系统分离的、更昂贵的传感模块，而电极本身则是可抛弃的。一瓶油墨提供的材料足以在几天或一周内绘制多个电极。”
The team has filed a provisional patent for their conductive ink, but there are still a few limitations. While the absence of imaging artifacts holds promise for MRI imaging, the authors note that there still needs to be a comprehensive safety evaluation before deploying the painted sensors in a clinical setting. RF-induced heating is a particular concern, given the super-adhesive properties of the sensors. That’s a focus of future research, along with exploring the possibility of adapting the technology for plant health monitoring, since the painted sensors can conform so well to complex shapes.
研究团队已为他们的导电油墨申请了临时专利，但仍存在一些局限性。虽然没有成像伪影为核磁共振（MRI）成像带来了希望，但作者指出，在临床环境中使用这些手绘传感器之前，仍需进行全面的安全性评估。考虑到传感器超强的粘附特性，射频（RF）引起的加热是一个特别值得关注的问题。这是未来研究的重点，同时他们也在探索将该技术应用于植物健康监测的可能性，因为这种手绘传感器能够很好地贴合复杂的形状。