Electric Current Responsive Drug Release

Other stimuli have been examined as mediators of drug release including magnetic field and light, however space restrictions in this review prevent further discussion of these aspects. For further information the reader should consult the review by Serchen and West (a. 196). 

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Muscles contract and expand in response to electrical, thermal, and chemical stimuli. Certain polymers, such as synthetic polypeptides, are known to change shape on application of electric current, temperature, and chemical environment. For instance, selected bioelastic smart materials expand in salt solutions and may be used in desalination efforts and as salt concentration sensors. Polypeptides and other polymeric materials are being studied in tissue reconstruction, as adhesive barriers to prevent adhesion growth between surgically operated tissues, and in controlled drug release, where the material is designed to behave in a predetermined matter according to a specific chemical environment. 

Hydrogels able to release drugs or biomolecules in response to variations in electric field. Thus, Y. Osada and co-workers studied the electro-activated release of pilocarpin from microparticles of sodium salt of poy(acrylic acid) gel, Na-PAA [141]. It was found that insulin diffuses out of a gel made of weakly crosslinked polyelectrolyte gels when electric current is turned on, but the flow ceases immediately when it is turned off. This kind of gel could be the basis on an implantable insulin pump with no moving parts [142 ]. 

The redox properties of conducting heterocyclic polymers like polypyrrole are central to many applications of these materials. For this reason the electrochemistry of thin films of these polymers have received a lot of attention. For use in electrically controlled ion binding and delivery, the general idea is that the heterocyclic conducting polymers have cationic backbones and will incorporate counter anions. Upon reduction of the backbone, the anions will be flushed out. Thus, in principle one can develop devices to absorb anions of interest or to release them in response to an electric current. Our work has been spurred by the possibility of delivering drugs with a rate controlled by the current. 

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