Enhancing the interfacial binding strength between modular stretchable electronic components

Abstract

Stretchable electronics are emerging for personalized and decentralized clinics, wearable devices, and human-machine interactions. Nowadays, separated stretchable functional parts have been well developed and approaching practical usage. However, the production of whole stretchable devices with full functions still faces a huge challenge: the integration of different components, which was hindered by the mechanical mismatch and stress/strain concentration at the connection interfaces. To avoid connection failure in stretchable devices, a new research focus is to improve the interfacial binding strength between different components. In this review, recent developments to enhance interfacial strength in wearable/implantable electronics were introduced and catalogued into three major strategies: 1) covalent bonding between different device parts, 2) molecular interpenetration or mechanical interlocking at the interfaces, and 3) covalent connection between the human body and devices. Besides reviewing current methods, we also discussed the existing challenges and possible improvements for stretchable devices from the aspect of interfacial connections.

Skin-Interfaced Superhydrophobic Insensible Sweat Sensors for Evaluating Body Thermoregulation and Skin Barrier Functions

“…Representative examples include a series of works that combine a closed chamber with a commercial humidity sensor to detect the moisture collected from the skin during a given period of time. ,− However, the need to separate the device from the skin for ventilating the chamber after each test makes it challenging for continuous monitoring. The bulky and stiff equipment is also not suitable for long-term wearable use. − To address these challenges, efforts have been devoted to developing a flexible humidity sensor with open chambers. − Representative examples include a honeycomb-like MoS 2 nanotube array on perforated Ecoflex, sputtered Au on PVA nanomesh, and MXene/silver nanowires on a silk textile . However, these humidity sensors only measure skin humidity (not accurate for insensible sweat assessment), and they are also susceptible to sensible sweat and external water (droplets or moisture) to cause irreversible changes in conductive materials .…”

Stretch-Induced Robust Intrinsic Antibacterial Thermoplastic Gelatin Organohydrogel for a Thermoenhanced Supercapacitor and Mono-gauge-factor Sensor

“…Conductive organohydrogels have attracted tremendous attention in flexible electronics and energy storage due to their virtues of stretchability, high environmental stability, and fair conductivity. − Actually, stretchable and conductive hydrogels are the essential substrates for flexible electronics. − However, flexible electronics based on organohydrogels, such as supercapacitors and hydrogel-based strain sensors, suffer defects: the multistage gauge factor cause complex signal processing, and the combination of different electronic units will result in mechanical mismatches and/or low binding strengths at the connection interfaces . The low interfacial reaction would evoke the high interface resistance, which would deteriorate the electromechanical performances and enlarge the energy loss. , Most previously reported organohydrogel flexible electronics to date, such as supercapacitors, can be divided into two types: the organohydrogel-electrode separation binary system and the “all-in-one” system. , The first model is more popular because of its diversification and high electrochemical performance. − Meanwhile, the strain sensors based on the detection of resistance changes caused by shape variations upon stimulation of external forces also require a monolinear gauge factor and high interfacial reaction between the organohydrogel and the signal transmission device. − Another challenging issue for flexible electronics from petroleum-based polymers is their inability to be recycled after failure due to the chemical cross-linking bonds. , These nonbiodegradable and nonreusable components of devices produce massive amounts of electronic waste and cause environment issues. , Consequently, there is an urgent necessity for flexible electronics fabricated by organohydrogels with high interfacial compatibility and recycling for their further utilization by a new strategy.…”

“…6−9 However, flexible electronics based on organohydrogels, such as supercapacitors and hydrogel-based strain sensors, suffer defects: the multistage gauge factor cause complex signal processing, and the combination of different electronic units will result in mechanical mismatches and/or low binding strengths at the connection interfaces. 10 The low interfacial reaction would evoke the high interface resistance, which would deteriorate the electromechanical performances and enlarge the energy loss. 11,12 Most previously reported organohydrogel flexible electronics to date, such as supercapacitors, can be divided into two types: the organohydrogel-electrode separation binary system and the "all-in-one" system.…”

Flexible-to-Stretchable Mechanical and Electrical Interconnects

“…27−29 Recently, covalent connections between two different types of substrates have become important to improve the stability and performance of stretchable electronics. 30 UVactivated carbene crosslinking is one example. 31,32 This chemistry has been used to bond polymer semiconductors and flexible substrates.…”

“…It is possible to bond PDMS to a variety of plastics including PET using chemically robust amine–epoxy or thiol–epoxy bonds. , This concept was recently utilized to create microchannels and soft robotic actuators by bonding silicone to PET . Similarly, there have been several reports of stretchable anisotropic conductive films, in which chemical bonding two substrates is one of the key concepts. − Recently, covalent connections between two different types of substrates have become important to improve the stability and performance of stretchable electronics . UV-activated carbene crosslinking is one example. , This chemistry has been used to bond polymer semiconductors and flexible substrates .…”