Monolithic Dual‐Material 3D Printing of Ionic Skins with Long‐Term Performance Stability

Abstract

Artificial "ionic skin" is of great interest for mimicking the functionality of human skin, such as subtle pressure sensing. However, the development of ionic skin is hindered by the strict requirements of device integration and the need for devices with satisfactory performance. Here, a dual-material printing strategy for ionic skin fabrication to eliminate signal drift and performance degradation during long-term use is proposed, while endowing the ionic skins with high sensitivity by 3D printing of ionic hydrogel electrodes with microstructures. The ionic skins are fabricated by alternative digital light processing 3D printing of two photocurable precursors: hydrogel and water-dilutable polyurethane acrylate (WPUA), in which the ionically conductive hydrogel layers serve as soft, transparent electrodes and the electrically insulated WPUA as flexible, transparent dielectric layers. This novel dualmaterial printing strategy enables strong chemical bonding between the hydrogel and the WPUA, endowing the device with designed characteristics. The resulting device has high sensitivity, minimal hysteresis, a response time in the millisecond range, and excellent repetition durability for pressure sensing. The results demonstrate the potential of the dual-material 3D printing strategy as a pathway to realize highly stable and high-performance ionic skin fabrication to monitor human physiological signals and humanmachine interactions.

3D Printing of Flexible Strain Sensor Array Based on UV‐Curable Multiwalled Carbon Nanotube/Elastomer Composite

“…[ 38 ] Yin's group reported a capacitive pressure sensor using an ionic conductive hydrogel by DLP dual‐material printing. [ 8 ] Despite the impressive success in DLP printing of various flexible sensors, to the best of our knowledge, seldom researchers have utilized DLP 3D printing technology to fabricate flexible strain sensor using nanomaterial percolated composites. Wang's group has successfully developed a flexible strain sensor using multiwalled carbon nanotubes (MWCNT) infiltrated resin fabricated by DLP‐based 3D printer, nevertheless, the strain detection window of the sensor is limited, which is not applicable for the biomedicine, soft robotics, and structural health monitoring where larger detection window and higher linearity are desired.…”

“…Internet of Things (IoT), interconnecting people, machine, and things at anywhere and anytime via a variety of sensor network and a set of communication technologies, [1][2][3][4] is anticipated to significantly improve the effectiveness and functionality of industry and our daily life, especially in areas of biomedicine, [5] soft robots, [6,7] and structural health monitoring. [8][9][10] For example, an integrated strain sensor network with the multihop wireless communication module was developed by Hu et al for the real-time bridge structural health monitoring, which first one is to print substrates or encapsulations using DLP, followed which the active components are prepared by additional techniques. For example, Liu et al utilized DLP technology to print flexible substrate and fabricate strain sensor on the substrate by inkjet printing.…”

3D Printed Flexible Strain Sensors: From Printing to Devices and Signals

“…Based on the PAAm–PEGDA system discussed above, water‐dilutable PUA (WPUA) precursor was introduced as dielectrics. [ 45 ] As shown in Figure a, the WPUA ink was cured first to obtain the cover layers of strain sensor. After a designed number of sections were cured, the ink tank was replaced with PAAm–PEGDA precursor.…”

Reprintable Polymers for Digital Light Processing 3D Printing

“…[ 8–15 ] During DLP printing process, the rapid liquid–solid transition under light irradiation always requires dual‐functional or multifunctional monomers, which cause 3D items to be constructed by thermosets crosslinked by covalent bonds. [ 13,16–19 ] Although thermosets show better durability and mechanical properties than uncrosslinked thermoplastics, their infusible and insoluble features make them hard to be reprocessed or recycled, and will be inevitably discarded as waste at the end of their life cycle. [ 20–24 ] The gradually expanded DLP application and the complex 3D geometries of the products will result in more serious resources waste and environmental problems.…”