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)/Fe3+ 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 (Fe3+) and the polymer chain, the as-prepared hydrogel
showed outstanding mechanical strength (5.36 MPa tensile stress, 17.66 MJ/m3 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 Fe3+ 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.