Superhydrophobic asymmetric pH-responsive soft actuators: Implications for the development of anti-fouling medical devices

Biomedical engineering strives for innovation to enhance the safety and effectiveness of medical tools, such as catheters and stents that need to be operated in confined spaces, with precise drug delivery control and should possess anti-fouling properties. Soft actuators with superhydrophobic surfaces can provide adaptable shape change together with non-fouling attributes required for medical devices. In this study, we have developed a Janus film with a hydrophilic solvent-responsive bottom and superhydrophobic top surface using a self-assembly strategy. The devised new strategy involves the dispersal of modified silica nanoparticles into a homogeneous solution, where they were segregated from the polymer matrix and self-assembled to form a superhydrophobic layer on the surface with a water contact angle of >150°. The resulting asymmetric actuator demonstrated bidirectional actuation in solvents with extreme pH values i.e., pH 1 and 13. It could be tailored for specific hydrophilicity by adjusting the ratio of dispersed superhydrophobic and hydrophilic silica nanoparticles in the polymer solution. These films exhibited exceptional chemical stability against strong acids, alkaline solutions, ethanol, and salt, as well as mechanical stability against abrasion from sandpaper. In vitro studies confirmed their superior anti-fouling and anti-bacterial properties. Furthermore, actuation of printed 3D structures with different patterns was demonstrated, showcasing the possibility of developing these superhydrophobic asymmetric surfaces via 3D printing and their potential as cardiovascular stents.