Available online at www.sciencedirect.com Sensors and Actuators B 129 (2008) 834–840 Electrochemical actuation in chitosan/polyaniline microfibers for artificial muscles fabricated using an in situ polymerization Yahya A. Ismail, Su Ryon Shin, Kwang Min Shin, Seong Gil Yoon, Kiwon Shon, Sun I. Kim, Seon Jeong Kim ∗ Centre for Bio-Artificial Muscle and Department of Biomedical Engineering, Hanyang University, Seoul 133-791, Republic of Korea Received 2 June 2007; accepted 24 September 2007 Available online 3 October 2007 Abstract We have fabricated a new type of electroactuating biopolymer hydrogel/polyaniline microfiber by wet spinning a chitosan solution, followed by the in situ chemical polymerization of aniline. This novel biomaterial showed an enhanced chemical and electrochemical actuation in response to pH and an electrical stimulus. The fibers showed a reasonable electrical conductivity of 2.856 × 10 -2 S/cm at room temperature. The strain ratio and response time during electrochemical actuation were highly dependent on the pH of the electrolyte. An isotonic strain of 0.39% during electrochemical actuation in an aqueous HCl solution at pH = 0, along with a strain of 6.73% corresponding to pH actuation was realized in the microfibers. The higher strain ratio at lower pH values is probably due to a faster diffusion rate. Although the electrochemical actuation was due to the polyaniline, the actuation mechanism was different from that in pure polyaniline. EDX analysis showed the presence of polyaniline inside the fibers, which gradually decreased moving towards the center of the fiber. SEM images of the fibers showed an agglomerated granular morphology of polyaniline particles coated on the surface of the chitosan fibers. The electrochemical properties of the fibers were due to polyaniline, as evidenced by cyclic voltammogram. © 2007 Elsevier B.V. All rights reserved. Keywords: Electrochemical actuation; Chitosan; Polyaniline; Artificial muscle 1. Introduction One of the primary requirements for designing advanced artificial materials is a change in their properties in response to external stimuli. Materials that can be used as artificial muscles must respond to an electric field, pH, temperature, ionic strength, and/or light with a corresponding change in their shape and size [1]. Recent literature shows an emerging interest in hydrogel-based actuating systems because of their stimuli-responsive behavior [2–8]. Very recently, Sidorenko et al. have demonstrated the reversible and fast switching of poly- mer hydrogel-based actuating systems leading to a variety of applications, including the development of artificial muscles [2]. Kim et al. recently reported self-oscillatory actuation at a constant DC voltage for a polyaniline/hydrogel blend film [3]. ∗ Corresponding author at: Seongdong, P.O. Box 55, Seoul 133-605, Republic of Korea. Tel.: +82 2 2220 2321; fax: +82 2 2291 2320. E-mail address: sjk@hanyang.ac.kr (S.J. Kim). Chitosan is a nontoxic cellulose-like polyelectrolyte polymer hydrogel that is suitable for the fabrication of artificial muscles, as this material undergoes a large volume change in response to a change in pH, temperature, or solvent composition [9–11]. Apart from its nontoxic nature, chitosan is important because of its bioactivity, biocompatibility and its ability to sorb and bind water molecule [12]. However, the poor electrical conduc- tivity of hydrogels results in a poor response time and a high operational voltage limits their applicability in devices. Similarly, there has been a growing interest in conducting polymer-based actuators owing to the volume change produced from their exchange of ions with an electrolyte during an elec- trochemical oxidation/reduction process [4,13–21]. Moreover, conducting polymer actuators have received special attention due to their large active strain and stress, moderate and accept- able response times, and high power/weight ratios [13,15–17]. These materials offer muscle-like properties that could be used in the creation of biomimetic devices. Polyaniline (PANi) is unique among the conducting polymers due to: high conductivity; ease of synthesis; lightweight, high-stress, and low operational volt- 0925-4005/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2007.09.083