Ramírez Julian, Rodriquez Daniel, Urbina Armando, Cardenas Anne, Lipomi Darren J
Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, CA 92093-0448.
ACS Appl Nano Mater. 2019 Apr 26;2(4):2222-2229. doi: 10.1021/acsanm.9b00174. Epub 2019 Mar 25.
Wearable mechanical sensors have the potential to transform healthcare by enabling patient monitoring outside of the clinic. A critical challenge in the development of mechanical-e.g., strain-sensors is the combination of sensitivity, dynamic range, and robustness. This work describes a highly sensitive and robust wearable strain sensor composed of three layered materials: graphene, an ultrathin film of palladium, and highly plasticized PEDOT:PSS. The role of the graphene is to provide a conductive, manipulable substrate for the deposition of palladium. When deposited at low nominal thicknesses (~8 nm) palladium forms a rough, granular film which is highly piezoresistive (i.e., the resistance increases with strain with high sensitivity). The dynamic range of these graphene/palladium films, however, is poor, and can only be extended to ~10% before failure. This fragility renders the films incompatible with wearable applications on stretchable substrates. To improve the working range of graphene/palladium strain sensors, a layer of highly plasticized PEDOT:PSS is used as a stretchable conductive binder. That is, the conductive polymer provides an alternative pathway for electrical conduction upon cracking of the palladium film and the graphene. The result was a strain sensor that possessed good sensitivity at low strains (0.001% engineering strain) but with a working range up to 86%. The piezoresistive performance can be optimized in a wearable device by sandwiching the conductive composite between a soft PDMS layer in contact with the skin and a harder layer at the air interface. When attached to the skin of the torso, the patch-like strain sensors were capable of detecting heartbeat (small strain) and respiration (large strain) simultaneously. This demonstration highlights the ability of the sensor to measure low and high strains in a single interpolated signal, which could be useful in monitoring, for example, obstructive sleep apnea with an unobtrusive device.
可穿戴式机械传感器有潜力通过实现诊所外的患者监测来变革医疗保健。机械（如应变）传感器开发中的一个关键挑战是灵敏度、动态范围和鲁棒性的结合。这项工作描述了一种由三层材料组成的高灵敏度且鲁棒的可穿戴应变传感器：石墨烯、钯超薄膜和高度增塑的聚（3,4-乙撑二氧噻吩）：聚苯乙烯磺酸盐（PEDOT:PSS）。石墨烯的作用是为钯的沉积提供一个导电、可操控的基底。当以低标称厚度（约8纳米）沉积时，钯形成粗糙的颗粒状薄膜，具有高压阻性（即电阻随应变增加且灵敏度高）。然而，这些石墨烯/钯薄膜的动态范围较差，在失效前只能扩展到约10%。这种脆弱性使得这些薄膜与可拉伸基底上的可穿戴应用不兼容。为了提高石墨烯/钯应变传感器的工作范围，使用一层高度增塑的PEDOT:PSS作为可拉伸导电粘合剂。也就是说，当钯膜和石墨烯开裂时，导电聚合物为导电提供了一条替代路径。结果得到了一种应变传感器，它在低应变（0.001%工程应变）时具有良好的灵敏度，但工作范围高达86%。通过将导电复合材料夹在与皮肤接触的柔软聚二甲基硅氧烷（PDMS）层和空气界面处的较硬层之间，可以在可穿戴设备中优化压阻性能。当附着在躯干皮肤上时，贴片式应变传感器能够同时检测心跳（小应变）和呼吸（大应变）。这一演示突出了该传感器在单个内插信号中测量低应变和高应变的能力，这在例如使用不显眼的设备监测阻塞性睡眠呼吸暂停方面可能会很有用。
