Amino acid-derived Cu(ii)-coordinated supramolecular hydrogel with tunable mechanics, self-healing, and underwater adhesion

Abstract

For the first time, an amino acid-derived polymeric supramolecular hydrogel, poly(Cu(lysine methacrylamide)₂-random-acrylamide) [poly(Cu(LysMAM)₂-r-AM)], is synthesized via radical polymerization of Cu(lysine methacrylamide)₂ (Cu(LysMAM)₂) and acrylamide (AM) at room temperature. The hydrogel exhibits remarkable multifunctionality by demonstrating rapid self-healing within 5 seconds at 25 °C for a 3 mm cut, along with excellent load-bearing capability with a tensile strength of 0.14 MPa and an ultimate strain exceeding 35%. It further shows responsiveness to Cu²⁺ ions, possesses inherent electrical conductivity, and displays strong underwater adhesion driven by hydrophobic aggregation, highlighting its advanced and versatile performance characteristics. Upon treatment with 8-hydroxyquinoline, the hydrogel disassembles into poly(LysMAM-r-AM), which further forms a nanogel in the presence of Cu²⁺ at pH 9.5. The polymer selectively senses different heavy metals such as cadmium, lead, zinc, mercury, and nickel, but forms a nanogel exclusively with copper. Notably, the incorporation of Cu²⁺ imparts conductivity to the hydrogel, allowing it to function as a pressure-sensitive material. The conductivity variation with applied pressure makes this hydrogel a promising candidate for flat-foot detection via shoe sensors. This innovative hydrogel platform, combining metal selectivity, self-healing, underwater adhesion, and conductivity, opens avenues for applications in healthcare, wearable sensors, and adhesives.