Electronic skin, or e-skin, represents a revolutionary advancement in biosensor technology, enabling the measurement of temperature, pressure, and biochemical markers with high precision. These flexible, stretchable, and often self-healing materials mimic the properties of human skin, making them ideal for applications in prosthetics, wearable health monitors, and human-machine interfaces. Recent developments have introduced wireless capabilities, further expanding their potential uses. However, challenges such as durability and signal cross-talk remain critical hurdles to widespread adoption.
The foundation of e-skin lies in its stretchable materials, which must maintain functionality under mechanical deformation. Polymers such as polydimethylsiloxane (PDMS) and polyurethane are commonly used due to their elasticity and biocompatibility. Conductive fillers like silver nanowires, carbon nanotubes, or graphene are embedded to ensure electrical conductivity. These composites enable the e-skin to stretch by over 50% without losing sensing capabilities. Some advanced formulations incorporate liquid metal alloys such as eutectic gallium-indium (EGaIn), which remain conductive even under extreme deformation.
Self-healing properties are another critical feature of modern e-skin designs. Materials capable of autonomously repairing mechanical damage enhance longevity and reliability. Hydrogen-bonded networks, dynamic covalent bonds, or supramolecular interactions enable self-repair at room temperature. For example, polymers with reversible disulfide bonds can recover over 90% of their original conductivity after being severed. This property is particularly valuable in prosthetics, where repeated mechanical stress can lead to wear and tear.
Temperature sensing in e-skin relies on thermistors or thermoelectric materials. Thin-film platinum resistors or conductive polymers with high thermal coefficients provide resolutions as fine as 0.1°C. Some designs utilize pyroelectric materials like polyvinylidene fluoride (PVDF), which generate electrical signals in response to temperature changes. These sensors are integrated into arrays to map spatial temperature variations, useful for detecting inflammation or poor circulation in prosthetic limbs.
Pressure sensing is achieved through piezoresistive, capacitive, or piezoelectric mechanisms. Microstructured elastomers with embedded conductive layers exhibit changes in resistance when compressed, enabling sensitivity as low as 1 Pa. Capacitive sensors measure changes in the distance between electrodes under pressure, while piezoelectric materials like zinc oxide nanowires generate voltage in response to mechanical stress. Multimodal sensors combine these approaches to distinguish between static and dynamic pressures, improving accuracy in real-world applications.
Biochemical sensing in e-skin involves detecting biomarkers in sweat, interstitial fluid, or wound exudate. Electrochemical sensors measure glucose, lactate, pH, or electrolytes through enzyme-based or ion-selective membranes. Recent prototypes incorporate microneedle arrays for minimally invasive sampling. Wireless transmission of data allows continuous monitoring without bulky external devices. For example, some e-skin patches use near-field communication (NFC) or Bluetooth Low Energy (BLE) to relay readings to smartphones or medical databases.
Applications in prosthetics are among the most promising for e-skin technology. By integrating temperature, pressure, and biochemical sensors, prosthetic limbs can provide sensory feedback to users, improving grip control and reducing phantom limb pain. Pressure mapping helps prevent tissue damage by adjusting force distribution. Some advanced systems even stimulate peripheral nerves to restore tactile sensations. Wireless e-skin patches also monitor residual limb health, detecting infections or pressure sores before they become severe.
Despite these advancements, several challenges persist. Durability remains a concern, as repeated stretching and environmental exposure can degrade sensor performance. Encapsulation layers of silicone or polyimide help protect sensitive components but may limit flexibility. Signal cross-talk between different sensors is another issue, particularly in high-density arrays. Advanced signal processing algorithms and shielding techniques are being developed to minimize interference.
Recent prototypes demonstrate significant progress in wireless e-skin systems. One example is a fully integrated patch capable of measuring temperature, pressure, and hydration levels while transmitting data via NFC. Another design uses stretchable organic electrochemical transistors (OECTs) for biochemical sensing with Bluetooth connectivity. These systems are powered by flexible batteries or energy-harvesting mechanisms such as triboelectric nanogenerators, which generate electricity from motion.
The future of e-skin biosensors lies in improving multifunctionality, durability, and seamless integration with the human body. Advances in materials science, nanotechnology, and wireless communication will drive further innovation. As these technologies mature, e-skin could transform healthcare, robotics, and human-computer interaction, bridging the gap between biological and electronic systems.
In summary, electronic skin biosensors represent a convergence of flexible electronics, materials science, and biomedical engineering. Their ability to measure temperature, pressure, and biochemical markers with self-healing and wireless capabilities opens new possibilities in prosthetics and beyond. Overcoming challenges in durability and signal interference will be key to unlocking their full potential.