Poly(acrylic acid)/polypyrrole interpenetrated network as electro‐responsive hydrogel for biomedical applications

The combination of conducting polymers and hydrogels in a conductive interpenetrated polymer network (CIPN) is an interesting strategy to mimic muscles and to create bending actuators. Whereas the conducting polymer ensures the electro pulse flux, the hydrogel provides structural support similar to human tissues. In this work, poly(acrylic acid) (PAA) and polypyrrole (PPy) CIPNs were synthesized in aqueous solution in three different compositions and characterized in terms of their morphology, composition, mechanical, and electrochemical properties, as well as cytotoxic and the bending behavior when submitted to an electric field. Fourier transform infrared spectroscopy indicated hydrogen interaction between PAA and PPy, and PPy doping level was not modified when polymerized inside the PAA structure. Mechanical properties and density were shown to increase with an increase in PPy content, whereas water content decreased. Surprisingly, PAA/PPy CINPs presented some toxicity that may be due to the sterilization technique. Finally, PAA/PPy CIPNs responded mechanically to electrical stimuli and good curve symmetry and reversibility were observed in the cyclic voltammogram tests. These results indicate that the CIPN containing a PAA/PPy ratio of 1:0.3 is promising to prepare biocompatible soft bending actuators such as artificial muscles.