Investigation of polypyrrole coated hyaluronic acid filaments for biomimetic Smooth muscle actuators

Conducting polymer coatings on hydrogels offer promising applications in bioelectronics and tissue engineering to mimic the actuation of smooth muscle through electrochemically controlled swelling and contraction. This study investigated the formation of polypyrrole coating on hyaluronic acid hydrogel filaments through chemical and electrochemical synthesis, comparing the effect of different oxidants, soaking time, polymerization time, dopant concentrations and electrosynthesis times on electrochemical induced swelling and contraction. Additionally, the biocompatibility with human dermal fibroblasts was also investigated. Chemical polymerization with ammonium peroxydisulfate (APS) and ferric chloride (FeCl3) revealed differences in reaction rate and its effect on controlling diffusion. APS yielded controlled pyrrole diffusion and polymerization depth due to rapid polymerization whereas FeCl3 due to slower polymerization made controlling polymerization depth difficult. Incorporation of sodium dodecyl benzenesulfonate (NaDBS) during chemical synthesis led to increased coating uniformity and swelling during redox cycling. Electrochemical polymerization following chemical polymerization showed promise in controlling thickness of the coating using time as control. Electrochemical synthesis led to further increased in swelling during redox cycling but highlighted difficulties in controlling the swelling behaviour due to different ion motions during longer redox intervals. Cell viability tests of fibroblasts showed that polymerization in the presence of cells lead to significant cell death while post polymerization cell seeding showed promising results in cell attachment but with limited viability, likely due to residual oxidants. NaDBS doped coatings supported greater cell attachment than non-doped coatings suggesting improved biocompatibility and promise in making biomimetic smooth muscle actuators.