Fabrication of Eco‐Friendly Wearable Strain Sensor Arrays via Facile Contact Printing for Healthcare Applications

Abstract

Wearable flexible strain sensors with spatial resolution enable the acquisition and analysis of complex actions for noninvasive personalized healthcare applications. To provide secure contact with skin and to avoid environmental pollution after usage, sensors with biocompatibility and biodegradability are highly desirable. Herein, wearable flexible strain sensors composed of crosslinked gold nanoparticle (GNP) thin films as the active conductive layer and transparent biodegradable polyurethane (PU) films as the flexible substrate are developed. The patterned GNP films (micrometer‐ to millimeter‐scale square and rectangle geometry, alphabetic characters, and wave and array patterns) are transferred onto the biodegradable PU film via a facile, clean, rapid and high‐precision contact printing method, without the need of a sacrificial polymer carrier or organic solvents. The GNP‐PU strain sensor with low Young's modulus (≈17.8 MPa) and high stretchability showed good stability and durability (10 000 cycles) as well as degradability (42% weight loss after 17 days at 74 °C in water). The GNP‐PU strain sensor arrays with spatiotemporal strain resolution are applied as wearable eco‐friendly electronics for monitoring subtle physiological signals (e.g., mapping of arterial lines and sensing pulse waveforms) and large‐strain actions (e.g., finger bending).

Cross-Linked Gold Nanoparticle Assemblies: What Can We Learn from Single Flat Interfaces?

“…The sensing mechanism of GNP assemblies is based on the strong dependence of the charge transport through the films on external stimuli. ,,,− Experimental studies of the conductivity of GNP films capped with alkanethiol ligands of different chain lengths in combination with structural investigations of the film structure using NMR and small-angle X-ray scattering (SAXS) revealed that the charge transport in these films occurs via thermally activated tunneling, whereby neighboring GNP cores are charged or uncharged by the tunneling electrons. The conductivity σ depends on the interparticle distance δ, the tunneling decay constant β, a pre-exponential tunneling factor σ 0 , and the activation energy E A that is required for charging the gold cores , σ ( T , δ ) = σ 0 e − δ β e − E A / normalR T …”

“…External stimuli, such as applying strain or sorption of analyte molecules, can change the interparticle distances (“swelling”) and/or the permittivity of the GNP matrix. ,,,− Both changes can affect the conductivity, making GNP films suitable as strain sensors and chemiresistors.…”

Recent Study Advances in Flexible Sensors Based on Polyimides

“…Polymers with the combination of easy preparation process, good chemical stability, and high mechanical compliance are ideal materials for making flexible sensors. Commonly used polymers include polyimide (PI) [ 5 ], poly(dimethylsiloxane) (PDMS) [ 6 , 7 ], poly(ether-ether-ketone) (PEEK) [ 8 ], polycarbonate (PC) [ 9 ], polyethylene naphthalate (PEN) [ 10 ], poly (ethylene terephthalate) (PET) [ 11 ] and polyurethane (PU) [ 12 , 13 ], and polyvinylidene fluoride (PVDF) [ 14 , 15 , 16 , 17 ]. Among these polymers, PI is extensively used owing to its excellent thermal stability [ 18 ], high chemical resistance, good dielectric properties, outstanding mechanical strength, and other comprehensive properties.…”

Performance Optimization of Ionic Polymer Sensors through Characteristic Regulation of Chemically Prepared Interfacial Electrodes

“…With the rapid development of wearable electronic devices as well as materials science, flexible sensors with the characteristics of light weight, stretchability, and great compliance have generated widespread research interest, having broad application prospects in health monitoring, environmental perception, human–computer interaction, and other fields. − In terms of the sensing mechanism, the existing flexible sensors can be divided into resistive, capacitive, piezoelectric, triboelectric, and ionic sensors. − Compared with other sensing mechanisms, ionic sensors achieve signal transmission through the directional migration of ions, which is closer to the biological sensing mode. , Therefore, ionic sensors have great potential for application in the field of bionics.…”