A Self-Healing and Ionic Liquid Affiliative Polyurethane toward a Piezo 2 Protein Inspired Ionic Skin

Ionic skin (I-Skin) has the advantage of feasible compatibility with biological systems. Nevertheless, developing a stable and durable ionic skin is challenging. Here, an ionic polyurethane (i-PU) is synthesized, which is capable of self-healing and able to lock the ionic liquids (ILs). In detail, an ionic chain extender containing an ammonium cationic group is synthesized, followed by the polymerization to obtain the target i-PU. Through electrostatic interaction and chain diffusion, the i-PU can be fully self-healed at room temperature within 400 min. Afterward, low contact angle (37 degrees) of the i-PU against IL and the density functional theory (DFT) calculation prove their good compatibility and strong interaction, originating from the electrostatic interaction. The Raman intensity map shows the reversible process of the enrichment and restoration of ionic concentration on the i-PU/IL surface when external pressure is applied or released, proving stable binding of ions by ionic polymer chains. Lastly, the self-healing I-Skin based on the i-PU/IL is fabricated with a wide range of pressures (0-120 kPa), fast response time (32 ms), excellent antifatigue property (2% attenuation after 1000 cycles), and remarkable sensitivity (52.4 kPa(-1)).