Conducting Polymers As Model-Membranes For Electrochemical Drug Release Systems

The development of pharmacological drugs had eveolved from the botanic period, in the beginning of human civilization, to the synthetic chemistry era, in the middle of the XX^th century. In the same way, new drugs appaered with very specific actions and being able to control and to prevent a variety of deceases. The administration and dosage of these phamacological drugs had also evolved inthe last 100 years from conventional pills to controlled/sustained relase systems with programable rate.

Two very important factors justify the search of new drug relase systems: (i) The oscillation of the “in vivo”drug concentrations higher and lowr to the minimum level and (ii) the necessity of systems (i.e adhesives or implants) that make possible and efficient the administration of “drug cocktails” that, in the present form, they demant patients to take up to 40 pills a day.

he term “controlled release”implies in the prediction and reproductibility of the drug release kinetics and the wide variety of controlled relase systems can be classified depending on the release technique used. The following table shows some examples some examples where polymers are used in these systems, calling attention to the technique under study in our laboratory.

Table 1: Some mechanisms producing drug release in the human organism.

Release agent	Polymer	Mechanism
pH	Acid or basic hydrogel	pH changes- swelling-drug release
Ionic Force	Ionic hydrogel	Changes in the ionic force— changes in the hydrogel effective charge— conformational changes – drug release.
Chemical species	Hydrogel containing electron acceptor groups	Charge transfer complex formation- conformation change- drug release
Enzyme -substrate	Hydrogel containing immo-bilized enzymes	Substrate – enzymatic convertion – product produces the conformational change of the hydrogel – drug release
Magnetic	Magnetic particles dispersed in microespheres	Magnetic field applied- changes in the microsphere pores – drug release
Sonication	poly(etilene-vinil alcool)	Sonication- temperature rise –drug release.
Electric	Polyelectrolite	Electric field – charging of the polyemric membrane – change of the electric charge of the polymer – drug release

Fig.1. Characteristic salicilic acid UV-Vis spectra, obtained in a solution where the electrorelease is performed

Polyaniline membranes capables to store both anionic or cationic drugs and being also able to release them by the application of potential pulses, are being developed in our laboratory. We have already verified the capability and good performace of this system in relaseing a model drug as salycilic acid by the electrochemical reduction of a doped polyaniline membrane (Fig. 1). By modifying the polyaniline membrane with Nafion^â, the libearation of a model cationic drug as dopamine is possible by oxidating the system.

Drug release from the polymeric system to an aqueous enviroment is followed by UV-Vis spectroscopy and form these data it is possible to plot drug release curves (Fig 2).

Fig.2. Drug release curves. A: Salycilic acid from a polyaniline membrane. B: Dopamine from the polyaniline/Náfion^Ò system.