2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Voltage Gated Carbon Nanotube Membranes for Transdermal Drug Delivery

M. Majumder, X. Zhan, H.K. Vaddi, A.L. Stinchcomb and B.J. Hinds
Univ. KY, US

transdermal programmed release

Membranes composed of an array of aligned carbon nanotubes, functionalized with charged molecular tethers, show voltage gated control of ionic transport through the cores of carbon nanotubes. The functional density of tethered charge molecules is substantially increased by the use of electrochemical grafting of diazonium salts. Functionality can be forced to occur at the CNT tip entrances by fast fluid flow of an inert solvent through the core during electrochemical functionalization. The selectivity between Ru(bi-pyridine)32+ and methyl viologen 2+ flux is found to be as high as 23 with -130mV bias applied to the membrane as the working electrode. Changes in the flux and selectivity support a model where charged tethered molecules at the tips are drawn into the CNT core at positive bias. For molecules grafted along the CNT core, negative bias extends the ligand into the core. Electrostatically actuated tethers induce strong steric hindrance in the CNT core to mimic voltage gated ion channels in a robust large area platform. CNT membranes are incorporated into a conventional skin patch geometry allowing for programmed drug delivery regrement. A drug permeation from a nicotine solution (10 mg/ml) in isotonic phosphate buffer pH 7.4 across CNT membrane with or without octadecyl amine groups was studied in a diffusion cell. The isotonic phosphate buffer pH 7.4 receiver solution samples were collected at various time intervals and stored at 4ºC until analysis for nicotine content by high pressure liquid chromatography (HPLC). The fluxes of nicotine through CNT membrane and octadecyl amine functionalized CNT membrane were 17 µmol/cm2/h and 2.7 µmol/cm2/h, respectively. The flux reduction through octadecyl amine CNT membrane by a factor of 6.2 corresponded with the reduced cross-section porous surface area by a factor of 7.5, due to the addition of long chain alkane groups to the CNT tips. The nicotine flux through octadecyl amine CNT membrane was in the preferred transdermal nicotine delivery range of 0.08-4 µmol/cm2/h. This aligned membrane structure has been incorporated into a working skin patch geometry with conventional materials. Overall nicotine flux through the skin patch was in the therapeutically useful flux of 0.90 mol/cm2-h.

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