Carbonized Silk Nanofiber Membrane for Transparent and Sensitive Electronic Skin

Abstract

Recent years have witnessed the explosive development of electronic skin. Highly sensitive pressure sensing is one of the primary abilities of electronic skin. To date, most of the reported skin‐like pressure sensors are based on nanomaterials and microstructured polydimethylsiloxane (PDMS) films, limiting their wide practical applications due to the unknown biotoxicity and the redundant fabrication procedure. A cost‐effective, large‐area‐capable, and biocompatible approach for fabrication of high‐performance skin‐like pressure sensors is highly desired. Silk fibroin (SF) is a natural protein that has recently drawn great attention due to its application as the substrate for flexible electronics. Here, the fabrication of skin‐like pressure sensors is demonstrated using SF‐derived active materials. Flexible and conformal pressure sensors can be fabricated using transparent carbonized silk nanofiber membranes (CSilkNM) and unstructured PDMS films through a cost‐effective and large‐scale capable approach. Due to the unique N‐doped carbon nanofiber network structure of CSilkNM, the obtained pressure sensor shows superior performance, including ultrahigh sensitivity (34.47 kPa−1) for a broad pressure range, an ultralow detection limit (0.8 Pa), rapid response time (<16.7 ms), and high durability (>10 000 cycles). Based on its superior performance, its applications in monitoring human physiological signals, sensing subtle touch, and detecting spatial distribution of pressure are demonstrated.

Nanomaterial‐Enabled Wearable Sensors for Healthcare

“…Pressure sensors made of electrospun silk nanofiber membranes achieved excellent piezoresistive response. [57] Low detection limit of 0.8 Pa, fast response time of less than 16.7 ms and superior sensitivity of 34.47 kPa −1 for low pressure range (0.8-400 Pa) and 1.16 kPa −1 for high pressure range (400-5000 Pa) were demonstrated. A cyclic test of 10 000 cycles confirmed the good stability.…”

“…[170] Copyright 2016, Nature Publishing Group. the strain or pressure induced by radial artery waves at the wrist or finger tip, [44,57,59,103,120,123,126,139,203] jugular venous pulses at the neck [57,59,151] or ankle brachial artery pulses near the foot. [21] Monitoring of respiration rate is critical in diagnosis of many disorders or diseases such as sleep disorders, asthma and anemia.…”

“…[21] Monitoring of respiration rate is critical in diagnosis of many disorders or diseases such as sleep disorders, asthma and anemia. [70] It can be accessed by measuring the deformation associated with respiration using wearable strain [103,120,121] or pressure sensors [57] placed on the chest, or by measuring the pressure caused by the air flow using a pressure sensor placed under the nose. [141] As an example, Figure 9b gives the output signals of a graphene based resistive strain sensor (attached on the chest) corresponding to the respiration under normal state and after exercise.…”

“…[6,138] Numerous materials and configurations have been reported for resistive pressure sensing. Pressure sensitive pathways can be formed using interlocked structures, [139][140][141][142][143][144] percolative networks of nanomaterials, [57,145,146] microfabricated structures (e.g., micropyramids, micropillars), [147][148][149] porous structures (e.g., sponges, foams, porous rubbers) [26,150,151] and so forth. For example, Figure 5a presents the working principle of a pressure sensor using interlocked microdome array.…”

“…Direct spinning of CNTs onto a substrate or into yarns [53][54][55] and electrospinning of nanofibers or NWs were reported to produce fiber-like nanomaterials. [56][57][58][59] In addition, novel direct printing or writing techniques [60,61] such as inkjet printing, [62] gravure printing, [63,64] screen printing, [65][66][67] nozzle jet printing, [26] and direct writing [68,69] enabled the fabrication of wearable sensors that possess complex patterns with high resolution.…”