Skin‐Adhesive Flexible Force Sensors Based on Piezoelectric Poly(l‐lactic acid) for Human Behavior Recognition (Adv. Mater. Technol. 14/2023)

Abstract

Flexible Force Sensors In article 2202142, Terry Tao Ye, Zhaoli Gao, Jian Yang, and co‐workers present the layout of the skin‐adhesive force sensor based on piezoelectric poly(l‐Lactic acid) and its potential applications in human behavior recognition, such as finger, wrist, and laryngeal knot movement. The sensor is composed of photocurable acrylate films, gold electrodes and poly(l‐Lactic acid) film with a sandwiched structure, the acrylate film is skin‐adhesive and transparent as a substrate. The piezoelectric signal of the sensor during swallowing is presented alongside with a human larynx. Finger pressing and wrist bending are listed in the bottom of cover.

Improving the Strain Control Performance of MoS2 Monolayer to Develop Flexible Electronics

“…The third substrate was made using two monomers of 4‐HBA marked as H and tetrahydrofuran acrylate (THFA) marked as T was mixed in H:T = 5:5 ratio (name marked as H5T5) and add 2.0% of its total volume of 2‐hydroxy‐2‐methyl‐1‐phenylacetone (photoinitiator 1173, Irgacure, BASF, Germany) to prepare UV curing solution ( Figure a). [ 41 ] The quadrat silica gel mold with a side of 2 cm and a thickness of 300 μm was used for making UV‐curable film. UV source (UV Diode 365 nm, Shenzhen, China) with wavelength 365 nm and power intensity 11 mW cm −2 during 30 s was used for the formation of this film.…”

“…[ 96 ] A NOVA2S spectrometer and Gora‐light system (ideaoptics, Shanghai, China /ideaoptics.com/) were employed for Raman spectroscopy and mapping in the backscattering configuration with 532 nm excitation by Nd:YAG diode‐pumped solid‐state (DPSS) laser. [ 41,97 ] There was one grating with 1200 L mm −1 (lines per millimeter). The power density of laser irradiation did not exceed ≈10 6 W cm −2 to avoid changes in the film structure during the measurements.…”

“…[ 36,37 ] Considering that most polymers have a positive TEC (for PMMA (polymethyl methacrylate) this value of 180 × 10 −6 K −1 and for PDMS (polydimethylsiloxane) value of 906 × 10 −6 K −1 ), [ 36 ] this discrepancy significantly impacts the strain growth during heating steps, resulting in wrinkling, and cracking when polymers are used to transfer graphene. Also, Young's modulus of PMMA is around E Young = 8 MPa [ 40 ] (PDMS – E Young = 1 MPa, and for H5T5 (4‐hydroxybutyl acrylate (4‐HBA) and tetrahydrofuran acrylate) is equal to E Young = 0.032 MPa), [ 41 ] much lower than that of MoS 2 and graphene. Due to this, graphene on a flexible substrate can also have wrinkles that reduce the contact between the 2D materials and the surface.…”

Flexible strain sensors based on silver nanowires and UV-curable acrylate elastomers for wrist movement monitoring

“…Flexible strain sensors have great potential for applications in personalized health monitoring, 1 robotics, 2 and pressure sensing. 3 Sensitive, highly stretchable strain sensors can be attached to human skin to monitor pulse, heartbeat, blood pressure, muscle movement, vocalization, and facial expression. 4 Flexible or stretchable sensors can be directly applied to the skin surface and combined with clothes, 5 of which are highly adaptive.…”

“…18 and 19 have focused on crack-assisted resistive strain sensors, along with the geometric modulation of the elastomer substrate. 8 Elastic polymer is one of the effective materials utilized as a substrate 20 or capsulation layer 3,21 of flexible sensors. Compared to traditional polymers, including polyethylene terephthalate, polyethylene naphthalate, polyimide, polymethyl methacrylate, etc., 22 to improve the mechanical properties of wearable sensors, it is essential to use a flexible substrate that is also flexible and biocompatible.…”