3D‐Structured Stretchable Strain Sensors for Out‐of‐Plane Force Detection

Abstract

Stretchable strain sensors, as the soft mechanical interface, provide the key mechanical information of the systems for healthcare monitoring, rehabilitation assistance, soft exoskeletal devices, and soft robotics. Stretchable strain sensors based on 2D flat film have been widely developed to monitor the in-plane force applied within the plane where the sensor is placed. However, to comprehensively obtain the mechanical feedback, the capability to detect the out-of-plane force, caused by the interaction outside of the plane where the senor is located, is needed. Herein, a 3D-structured stretchable strain sensor is reported to monitor the out-of-plane force by employing 3D printing in conjunction with out-of-plane capillary force-assisted self-pinning of carbon nanotubes. The 3D-structured sensor possesses large stretchability, multistrain detection, and strain-direction recognition by one single sensor. It is demonstrated that out-of-plane forces induced by the air/fluid flow are reliably monitored and intricate flow details are clearly recorded. The development opens up for the exploration of next-generation 3D stretchable sensors for electronic skin and soft robotics.

Highly Stable and Stretchable Conductive Films through Thermal‐Radiation‐Assisted Metal Encapsulation

“…Stretchable conductors are the basic building blocks of advanced flexible electronic devices, such as flexible display, skin‐like sensors, stretchable batteries, soft actuators and so forth . They are used in a vast number of soft and stretchable devices developed in recent years, including biointerfacing electrodes, transistors, mechanical sensors, energy devices and many more . To meet most application requirements, stretchable conductors need to remain conductive under tensile strain of more than 100%, and even more importantly, to show stable performance in terms of interfacial adhesion between conductive metal film and the supporting polymer substrate .…”

Cyber–Physiochemical Interfaces

“…These stretchable strain sensors can be attached on neck muscles, which is useful for the diagnosis of damaged vocal cords, respiratory disorders, and throat cancers. These sensors laminated on wrists can assist in diagnosis of Parkinson's disease, hyperactivity, and tremor in epilepsy (Figure d) …”

“…Based on the bioresorbability of silk fibroin, when used as substrate for ultrathin electronics, silk will dissolve and resorb, which initiates a spontaneous, conformal wrapping to tissue surface driven by capillary forces (Figure c) . By controlling the plasticization by ambient hydration and calcium chloride (CaCl 2 ) amount, Young's modulus of silk protein is tunable from tens of GPa to 0.1–2 MPa and stretchability is from < 20% to > 400% . As revealed by molecular dynamics simulations, doped ions and H 2 O weaken the strength of crystallite and enhance the extension ability of secondary structures of amorphous domain.…”

“…As revealed by molecular dynamics simulations, doped ions and H 2 O weaken the strength of crystallite and enhance the extension ability of secondary structures of amorphous domain. By further evaporating Au on soft silk substrate, the achieved devices with good conform contact to epidermis enable the dynamic on‐skin EMG signal recording with high quality …”

A Stretchable Capacitive Strain Sensor Having Adjustable Elastic Modulus Capability for Wide‐Range Force Detection

“…Generally, these sensors are used to measure large strains (>2%) of objects . During stretching, force applied on sensor interacts with produced strain, and it is necessary to measure the exact value of the interacting force like in the case of joint bending . Wide‐range force detection sensors are crucial for soft robots lifting variable loads and rehabilitation training of patients having broken joints .…”