February 13, 2006
Conducting Polymers Make On-Demand Drug-Releasing Nanotubes
Nanotubes made of a polymer that conducts electricity will release drug in response to an electrical signal. Depositing such nanotubes onto the surface of a microelectrode could yield implantable drug delivery devices capable of treating tumors repeatedly on a programmed time schedule.
Reporting its work in the journal Advanced Materials, a team of investigators led by David Martin, Ph.D., at the University of Michigan, describe how it prepared drug-loaded nanotubes from the conducting polymer known as poly(3.4-ethylenedioxythiophene), or PEDOT, on the surface of a microelectrode. The process starts by first coating a gold microelectrode with nanofibers of the biodegradable polymer PLGA mixed with drug molecules. Adding a solution of PEDOT and applying an electrical current to the PLGA-coated electrode causes the PEDOT to grow into nanotubes on the well-defined surface created by the PLGA nanofibers.
Normally, PLGA will slowly degrade, which would release any drug entrapped within the polymer nanofibers. But when these fibers are surrounded by the PEDOT nanotubes, very little drug can escape from the fibers. Applying a current as small as one volt for as little as 10 seconds triggers drug release. The investigators explain this observation by noting that the nanotubes contract when electrically stimulated and squeeze drug molecules out through the ends of the nanotubes. Indeed, the researchers were able to control the amount of drug released by varying the voltage applied to the electrode and the duration of electrical stimulation.
As an added benefit, the conducting polymer nanotubes had a marked effect on the impedance (related to electrical resistance) of the gold microelectrodes. The researchers note that reducing the impedance characteristics of an electrode has been shown to significantly enhance the performance of electrodes implanted into the body.
This work is detailed in a paper titled, “Conducting-polymer nanotubes for controlled drug release.” This work was published online in advance of print publication. An abstract is available at the journal’s website.