Biocompatible silk-conducting polymer composite trilayer actuators

Abstract

Biocompatible materials capable of controlled actuation are in high demand for use in biomedical applications such as dynamic tissue scaffolding, valves, and steerable surgical tools. Conducting polymer actuators are of interest because they operate in aqueous electrolytes at low voltages and can generate stresses similar to natural muscle. Recently, our group has demonstrated a composite material of silk and poly(pyrrole) (PPy) that is mechanically robust, made from biocompatible materials, and bends under an applied voltage when incorporated into a simple bilayer device architecture and actuated using a biologically relevant electrolyte. Here we present trilayer devices composed of two silk-PPy composite layers separated by an insulating silk layer. The trilayer architecture allows one side to expand while the other contracts, resulting in improved performance over bilayer devices. Specifically, this configuration shows a larger angle of deflection per volt applied than the analogous bilayer system, while maintaining a consistent current response throughout cycling. In addition, the overall motion of the trilayer devices is more symmetric than that of the bilayer analogs, allowing for fully reversible operation.

Performance of silk‐polypyrrole bilayer actuators under biologically relevant conditions

“…Mechanical stress was calculated by dividing the force output during actuation by the cross‐sectional area of the device. A stress of about 3.0 MPa was applied to samples and maintained for 30 min prior to actuation in order to help align the polymer networks and allow samples to relax …”

“…Towards the end of the 20 cycles measured, the linear stress generated for devices tested at room temperature (22 °C) remained within error of the original value at 0.77 MPa, while the values for devices tested at 37 and 43 °C decreased slightly to 0.53 and 0.49 MPa, respectively. However, it is worth noting that the devices continued to generate significant stresses as compared to state‐of‐the‐art silk‐CP actuators at all temperatures over the full 20 cycles shown.…”

“…The linear stress generated by the devices during actuation was measured using an Aurora Dual‐Mode Muscle Lever System . Electrical contact was made to the films by using a wire covered with copper tape and encapsulating the connection with Kapton tape.…”

Actuator Materials: Review on Recent Advances and Future Outlook for Smart Textiles

“…Linear actuators are fabricated by lamination of anionic and cationic driven actuators on a stretchable film. The fabrication of bi-layer and tri-layer conducting polymer actuators have also been reported in the literature [65][66][67][68][69]. The solvent and salts used in deposition and the electrolyte employed during actuation are the three major factors that play a significant role in determining the properties of these actuators.…”

Electroactive macromolecular motors as model materials of ectotherm muscles

“…CP/tape or CP/metal foil, or triple layers as CP/tape/CP, getting bending articial muscles. 53,81,81,85,86,[86][87][88][89][90][91][92][93] The resulting linear or bending articial muscles are electro-chemomechanical transducers: they transform electrical energy into macroscopic mechanical (linear or bending) movements driven by electrochemical reactions through the cooperative actuation of their multi-step macromolecular or polymeric motors. Being electrochemical (faradaic) motors, when the reaction drives the exchange for charge balance of only one ionic specie from the electrolyte, the consumed specic (per unit of dry polymer mass) anodic charge, q a , controls, in absence of parallel reactions (e.g.…”