Designable polypyrrole pattern in hydrogel achieved by photo-controllable concentration of Fe³⁺ initiator

Conductive polymer hydrogels (CPHs) are promising in cutting-edge applications including bioelectronics and tissue engineering. However, the precise regulation of the spatial distribution of the conductive polymer (CP) in the hydrogel network is still an issue for designing a smart material. Herein, we propose a facile method for preparing CPH-based smart materials by controlling the distribution of Fe³⁺ initiator with UV light irradiation. Thus, designable polypyrrole (PPy) conductive patterns in the polyvinyl alcohol/sodium alginate (PVA/SA) semi-interpenetrating hydrogel network are demonstrated by controlling the concentration of Fe³⁺ ions coordinated with carboxylate groups. Depending on the irradiation time, the reduction of Fe³⁺ to Fe²⁺ occurs in different extents. As a result, the controllable polymerization of pyrrole only initiated by Fe³⁺ is achieved to form desirable CPH patterns, which are confirmed by the characterization results of Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy. Moreover, the developed hydrogel with PPy patterns is illustrated for the application in smart conductive circuit and information encryption. The simple procedure and the controllable conductive patterning of the proposed method make it a promising route in developing smart hydrogel materials, which can be extended to other Fe³⁺ initiated CP patterns.