Conducting‐Polymer Nanotubes for Controlled Drug Release

The ability to create materials with well-controlled structures on the nanometer length scale is of intense interest for a variety of applications,[1,2] including controlled drug delivery[3] and biomedical devices.[4] Preparing nanoscale objects using self-assembly and templated growth techniques has been described in some recent reviews.[2,5] For example, porous membranes can be used to synthesize desired materials within the pores.[4,6] Conducting polymers are of considerable interest for a variety of biomedical applications.[7] Their response to electrochemical oxidation or reduction can produce a change in conductivity, color,[8,9] and volume.[10] A change in the electronic charge is accompanied by an equivalent change in the ionic charge, which requires mass transport between the polymer and electrolyte.[11] When counterions enter a polymer it expands and when they exit it contracts. The extent of expansion or contraction depends on the number and size of ions exchanged.[12] Electrochemical actuators using conducting polymers based on this principle have been developed by several investigators.[13–15] They can be doped with bioactive drugs, and can be used in actuators such as microfluidic pumps.[16,17] The precisely controlled local release of anti-inflammatory drugs at desired points in time is important for treating the inflammatory response of neural prosthetic devices in the central and peripheral nervous systems.[18] Here we report on a method to prepare conducting-polymer nanotubes that can be used for precisely controlled drug release. The fabrication process involves electrospinning of a biodegradable polymer, into which a drug has been incorporated, followed by electrochemical deposition of a conducting-polymer around the drug-loaded, electrospun biodegradable polymers. The conducting-polymer nanotubes significantly decrease the impedance and increase the charge capacity of the recording electrode sites on microfabricated neural prosthetic devices. The drugs can be released from the nanotubes in a desired fashion by electrical stimulation of the nanotubes; this process presumably proceeds by a local dilation of the tube that then promotes mass transport.