Cactus‐Spine‐Inspired Sweat‐Collecting Patch for Fast and Continuous Monitoring of Sweat

Abstract

Recently, some researchers have incorporated a sweat-collecting system into sweat sensors for sweat collection and transportation. [6] The sweat-absorbing layers that have been tested include paper [7] and rayon; [2a] however, these collection layers have no directionality in sweat transportation and are therefore not appropriate for continuous monitoring of freshly generated sweat in the sensing area. An alternative is a microfluidics channel system; [8] however, such a system can cause contamination of the sample by allowing old and new sweat to mix by diffusion within the channel. Such devices also have low sweatcollection efficiency because the channel must be filled to fill the sensing area. [9] In all cases, the directionality and the sweatcollecting efficiency are insufficient.In the present study, we demonstrate a sweat-collecting patch with directional sweat transportation and high sweat-collection efficiency, enabling fast and continuous monitoring of sweat by a sensor. The collecting component of the patch consists of channels with a narrow superhydrophilic wedge-shaped pattern within superhydrophobic bounds on a hierarchical microstructured/ nanostructured surface and a sweat reservoir that can be combined with a sweat sensor. The wedge-shaped wettability patterns were inspired by spines of cacti; they are narrow at the perimeter of the patch and gradually widen toward the junction with the sensing area at the center. The Laplace pressure is centripetal because of a combination of geometric structure and the difference between the surface energies of the superhydrophobic and superhydrophilic components. As a result, the sweat is transported spontaneously irrespective of gravity even when the substrate is aligned vertically. The patch transports the sweat almost without leaving it inside the channel and thereby concentrates the sweat from a large area of the skin onto the sensing area. The wedge-shaped wettability-patterned channel has greater sweat-collection efficiency than a conventional microfluidics channel and enables doubling of the speed of sweat collection. In an on-body test, the patch with a sensor responded to biochemicals within 5 min of its wearer beginning to exercise. By accelerating the circulation rate of sweat, the patch reduces the time that sweat remains in the sensing area and, by providing freshly generated sweat to it, enables the continuous sensor-based monitoring of changes in sweat biochemicals as blood changes.A sweat sensor is expected to be the most appropriate wearable device for noninvasive healthcare monitoring. However, the practical use of sweat sensors is impeded by irregular and low sweat secretion rates. Here, a sweatcollecting patch that can collect sweat efficiently for fast and continuous healthcare monitoring is demonstrated. The patch uses cactus-spine-inspired wedge-shaped wettability-patterned channels on a hierarchical microstructured/nanostructured surface. The channel shape, in combination with the superhydrophobic/superhydrophilic surface materials, ...

Electrochemical On‐Site Switching of the Directional Liquid Transport on a Conical Fiber

“…When the cone was homogeneously superoleophilic, the droplet moved from the tip to the bottom spontaneously (Figure 4e; Figure S8a and Movie S2, Supporting Information), which explains the traditional uncontrollable DLT-CF. [9][10][11][12][13] When the base side of the cone was set as superoleophobic, corresponding to the experimental switching off the electric potential. The DLT-CF stopped and the droplet was pinned stably at the superoleophilic/superoleophobic boundary (Figure 4f; Figure S8b and Movie S3, Supporting Information).…”

“…For example, the spider silk, cactus spine and Sarracenia trichome are capable of collecting water efficiently due to the DLTs on their conical fibrous organisms. [1a,3a,8] Drawing inspirations, various artificial conical fibrous systems capable of DLT have been developed, which have demonstrated outstanding performances in liquid pumping and collection, [9] sensor, [10] separation, [11] and electrocatalysis. [12] In general, for a droplet on the liquid-philic fiber, the conical structure enables the asymmetric triphase contact line, and the as-generated Laplace pressure difference (F L ) thus drives the droplet move directionally without any external energy input.…”

“…[1a,3a] However, these DLTs-CF hardly proceed in a controllable manner, due to the difficulty in on-site tuning the driving force imparted by the structural gradient for certain system. [9][10][11][12][13] So far, on-site switching of the DLT-CF remains a challenge, which greatly limits its applications.…”

Wearable Near-Field Communication Sensors for Healthcare: Materials, Fabrication and Application

“…It seems that this classification is better for us to design wearable NFC sensors for healthcare. Biophysical signal sensors are the most standardized of the applications for wearable sensors [ 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 ]. Body temperature, blood pressure, pulse, and muscle stretching, etc., are examples of physical signals directly related to people health.…”

Super‐Hydrophilic Zwitterionic Polymer Surface Modification Facilitates Liquid Transportation of Microfluidic Sweat Sensors

“…[46,47] Engineering microfluidic devices with wetting channels, suitable mechanical properties, and long-term stability remains to be a challenge for developing epidermal sweat sensors. [48,49] Zwitterionic polymers such as poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly (sulfobetaine methacrylate) are a class of polyelectrolytes that contain both a positive and a negative charge in the same functional monomer. [50][51][52][53] Due to the zwitterionic nature, such polymers are overall charge neutral but with high charge density.…”