Robust Hydrogel Sensors Induced by Intermolecular Mechanical Interlocking of Covalent Organic Frameworks for Non-Invasive Health Monitoring.

Abstract

The compromise of tensile strength and toughness is essential for conductive hydrogels to enhance their cycling stability and mechanical durability in wearable strain sensors. It is effective but challenging to balance energy dissipation. Herein, a new strategy based on the intermolecular mechanical interlocking of the hydrogels has been proposed for improving their tensile strength and toughness. The hydrogels are readily fabricated through non-covalently threading linear polymer chains into covalent organic frameworks (COFs). The mechanical interlocking between polyacrylamide and COFs significantly promotes the energy dissipation with synchronous increment of ion transport, which endows hydrogels with superior mechanical performance and high conductivity. The tensile strength, toughness, and ionic conductivity are as high as 0.19 ± 0.03 MPa, 2.11 ± 0.33 MJ m^-3 and 2.30 ± 0.55 S m^-1, respectively, which greatly surpass those in the polyacrylamide counterpart and rank the top in the reported hydrogels. The resultant hydrogel sensor achieves a fast strain response of 4.8 ms and high cyclic stability over 100 cycles, and could non-invasively monitor human health. This work provides one promising approach to the construction of robust hydrogels based on COFs for the development of advanced wearable sensors.