Fully physical crosslinked BSA-based conductive hydrogels with high strength and fast self-recovery for human motion and wireless electrocardiogram sensing.

The emergence of protein hydrogel sensors has attracted intensive attention because of their biocompatibility and biodegradability, and potential application in wearable electronics. However, natural protein hydrogel sensors commonly exhibited low conductivity, weak mechanical strength, and unsatisfactory self-recovery performance. Herein, a fully physical crosslinked conductive BSA-MA-PPy/P(AM-co-AA)/Fe hydrogel based on methacrylic anhydride (MA)-modified and polypyrrole (PPy)-functionalized bovine serum albumin (BSA) introduced into poly(acrylamide-co-acrylic acid) (P(AM-co-AA)) matrix was constructed. Due to the presence of the hydrogen bond complexation and the metal-ligand coordination between ferric ion (Fe) and the polymer chain, the as-prepared hydrogel showed outstanding mechanical strength (5.36 MPa tensile stress, 17.66 MJ/m toughness, and 1.61 MPa elastic modulus) and fast self-recovery performance (99.89 %/96.18 %/93.57 % stress/elastic modulus/dissipated energy within 10 min at room temperature). Meanwhile, the hydrogel exhibited outstanding conductivity (1.13 S/m) due to the presence of PPy and Fe moieties, high strain sensitivity (GF = 4.98) and good biocompatibility without causing skin allergic reactions. Thus, the hydrogel can be fabricated into strain sensor to monitor the joint motion of the human body. Moreover, it can be used as soft electrode in electrocardiogram device to realize wireless heart-rate monitoring in the real-time conditions (relaxation and post-exercising), which exhibited excellent reusability, stability, and reliability simultaneously.