In a breakthrough, scientists have successfully made a completely recyclable electronic skin that has self-healing properties and can automatically heal itself when torn apart. The new find can redefine the robotics and can have remarkable use in the biomedical devices and smart textiles.
Named as e-skin, the electronic device has properties of human skin — it is thin, flexible and can mimic functional and mechanical aspects of human skin. Scientists have equipped the device with several sensors to measure pressure, temperature, humidity, and air flow.
Researchers used three compounds to make the e-skin. They mixed the compounds in a specific way in a matrix and added silver nanoparticles that gave the film self healing properties. While explaining, study authors said that when the skin is cut into two, the thin film recreates bond between the two sides on its own that way the matrix structure of skin gets restored and the skin looks like as if nothing had happened.
However, the skin can heal a certain amount of damage. If the damage is much larger than the self-healing capacity of the compound then one can recycle it with the help of recycling solution. The solution dissolves the matrix structure of the skin and separates the nanoparticles sinking it to the bottom. Later on, the materials can be reused to make the new skin within few hours. According to scientists, the entire recycling process takes about 10 hours at room temperature. Apparently, the process can be fastened by heating the solution at 140 degrees Fahrenheit (60 degrees Celsius) where it takes just 30 minutes to recycle the skin.
Although, the study is still in its nascent stage, the remarkable breakthrough has given a direction to scientists to experiment and change the world for good.
Abstract
Electronic skin (e-skin) mimicking functionalities and mechanical properties of natural skin can find broad applications. We report the first dynamic covalent thermoset-based e-skin, which is connected through robust covalent bonds, rendering the resulting devices good chemical and thermal stability at service condition. By doping the dynamic covalent thermoset with conductive silver nanoparticles, we demonstrate a robust yet rehealable, fully recyclable, and malleable e-skin. Tactile, temperature, flow, and humidity sensing capabilities are realized. The e-skin can be rehealed when it is damaged and can be fully recycled at room temperature, which has rarely, if at all, been demonstrated for e-skin. After rehealing or recycling, the e-skin regains mechanical and electrical properties comparable to the original e-skin. In addition, malleability enables the e-skin to permanently conform to complex, curved surfaces without introducing excessive interfacial stresses. These properties of the e-skin yield an economical and eco-friendly technology that can find broad applications in robotics, prosthetics, health care, and human-computer interface.
Introduction
As the largest organ in the human body, skin plays an important role in our daily interaction with the environment. Skin not only protects the internal tissues and organs but also provides sensation of temperature, pressure, vibration, and haptics . It has been of great interest to the research community to design and fabricate electronic skins (e-skins) with functionalities and mechanical properties comparable to natural skin because of their great potential in robotics, prosthetics, health care, and human-computer interface. Different sensing capabilities of e-skins have been realized by integrating tactile/pressure sensors , temperature sensors , strain sensors, humidity sensors, and chemical sensors. To obtain good compliance and conformability, design principles developed in flexible and stretchable electronics were introduced to create flexible and stretchable e-skins. Serpentine and mesh structures were adopted to achieve very high stretchability and softness comparable to natural skin. Off-the-shelf chips were successfully integrated with stretchable networks to realize high-performance, multifunctional e-skins with acquisition, filtering, amplification, and communication capabilities. Advanced materials—including single-crystal silicon, organic semiconductors, nanoparticles, nanowires, nanotubes, and graphene—were used to realize superior sensing performances of e-skins. Inspired by the wound healing capability of natural skin, rehealable e-skins have also been developed.
Here, we demonstrate a not only rehealable but also fully recyclable and malleable e-skin that can sense pressure, flow, temperature, and humidity. This e-skin is based on a newly developed dynamic covalent thermoset (polyimine) doped with silver nanoparticles (AgNPs). Compared with the other rehealable devices and electronics, our e-skin can be not only rehealed but also fully recycled and reprocessed because of the reversible bond exchange through simultaneous bond forming and breaking reactions under certain external stimuli. The recyclability of our e-skin can greatly reduce electronic waste and environmental impact and can also potentially decrease manufacturing cost. The malleability renders our e-skin the capability of changing into different configurations while keeping a stress-free state in the polymer network. This capability could avoid introducing excessive interfacial stresses when the e-skin is integrated with complex, irregular surfaces. Furthermore, the covalently bonded thermoset matrix used in this work ensures better mechanical strength and chemical stability of the e-skin at service condition than that of other approaches.These properties are distinct from conventional thermoset materials that cannot be reprocessed, reshaped, and recycled because of their highly cross-linked polymeric networks connected with irreversible covalent bonds. The prominent characteristics of the e-skin represent an economical and eco-friendly technology that can find wide applications in robotics, prosthetics, health monitoring, and biomedical devices.
RESULTS AND DISCUSSION
The rehealable and recyclable e-skin integrates tactile, flow, temperature, and humidity sensors, as conceptually shown in. These sensors are fabricated using conductive polymers, obtained by doping a dynamic covalent thermoset, polyimine, with AgNPs. They are then integrated onto a polyimine substrate by heat pressing to ensure malleability, rehealability, and full recyclability of the entire e-skin. Covalent bonds are formed between the sensors and the substrate because of dynamic covalent bond exchange reactions at the interfaces. Serpentine interconnects are adopted to minimize the effects of strain on sensor performance when deformed. The e-skin can be easily confirmed onto curved surfaces (for example, human arms and robotic hands) by applying moderate heat and pressure. The geometrical conformity of the e-skin is permanent because of its malleability, even after the pressure or force is removed. When moderately damaged. The rehealed e-skin can restore mechanical and electrical properties comparable to the original device. When severe damage occurs or the device is never needed, the whole e-skin can be fully recycled, leaving no waste at all. Once recycled, short-oligomer/precursor solution and AgNPs are obtained. Optical images illustrate the rehealing process of an e-skin. Because of the malleability provided by the polyimine substrate, the e-skin can be conformally mounted onto a human arm. When a sensor is broken because of mechanical cutting, it completely loses its functionality. By applying a small amount of rehealing agent and heat pressing (8.5 kPa at 80°C), the broken sensor is rehealed, regaining its full sensing capability and mechanical integrity. To recycle the e-skin, simply soaking the whole device into the recycling solution makes the polymer matrix degrade into oligomers and monomers that are soluble in ethanol, and the AgNPs sink to the bottom of the solution (bottom dark part). The recycled solution and nanoparticles are then used to make a new, functional e-skin.
You can read the complete study here.