Mechanistic Study of Electroosmotic Pumping through Atomically Smooth Carbon Nanotube Membranes with Application in Programmed Drug Delivery

Mechanistic study of electroosmotic pumping through atomically smooth carbon nanotube membranes with application in programmed drug delivery<br/>An important challenge for the membrane community is to mimic natural protein channels that outperform, by orders of magnitude, man-made systems based on pore size and coarse chemical selectivity. To mimic protein channel pumping on a robust engineering membrane platforms, applied bias can be used to actuate charged gatekeepers and induce ionic pumping. Carbon nanotubes have three key attributes that make them of great interest for novel membrane applications 1) atomically flat graphite surface allows for ideal fluid slip boundary conditions and extremely fast flow rates [1,2] 2) the cutting process to open CNTs inherently places functional chemistry at CNT core entrance for chemical selectivity and 3) CNT are electrically conductive allowing for electrochemical reactions and application of electric fields gradients at CNT tips. The CNT membrane, with tips functionalized with charged molecules, is a nearly ideal platform to induce electro-osmotic flow with high charge density at pore entrance and a nearly frictionless surface for the propagation of plug flow [3,4]. Use of the electro-osmotic phenomenon for responsive/programmed transdermal drug delivery devices for nicotine addiction [5]. Our recent work [6] shows highly energy efficient electroosmotic pumping of nicotine with optimal power consumption/flux efficiency of 111(µW/cm2)/µmoles/cm2/h. This allows watch-battery lifetimes of 7-62 days for conventional treatment dosing regimens. On/off nicotine flux ratios of 68 were achieved allowing programmed delivery between therapeutically relevant nicotine patch and nicotine gum levels. By varying degree of chemical functionalization at CNT tips and pH control of ionic/neutral species ratio, the relative contribution of electroosmosis and electrophoresis within atomically smooth CNT conduits was quantified. More recent work with the direct measurement electroosmotic flow in a capillary flow cell shows the enhancement is due to atomic smoothness of CNTs, as seen the reversable stopping of flow by benzyl alcohol adsorption but no effect by H-bond chain disrupter NaSCN. Increased cation size had minimal improvement in EO pumping through DWCNT conduits.<br/><br/>1 “Nanoscale hydrodynamics: Enhanced flow in carbon nanotubes” Majumder, M.; Chopra, N.; Andrews, R; Hinds, B.J Nature 2005, 438, 44.<br/>2 ‘Mass Transport through Carbon Nanotube Membranes in three different regimes: ionic diffusion, gas, and liquid flow’ Mainak Majumder, Nitin Chopra, B.J. Hinds ACS Nano 2011 5(5) 3867-3877<br/>3 ‘Highly Efficient Electro-osmotic Flow through Functionalized Carbon Nanotubes Membrane’ Ji Wu, Karen Gerstandt, Mainak Majunder, B.J. Hinds, RCS Nanoscale 2011 3(8) 3321-28<br/>4 “ Programmable transdermal drug delivery of nicotine using carbon nanotube membranes” J. Wu, K.S. Paudel, C.L. Strasinger, D. Hamell, Audra L. Stinchcomb, B. J. Hinds Proc. Nat. Acad. Sci. 2010 107(26) 11698-11702.<br/>5 “Electrophoretically Induced Aqueous Flow through sub-Nanometer Single Walled Carbon Nanotube Membranes” Ji Wu, Karen Gerstandt, Hongbo Zhang, Jie Liu, and B. J. Hinds Nature Nano 2012 7(2) 133-39<br/>6 ‘Electrically controlled nicotine delivery through Carbon nanotube membranes via electrochemical oxidation and nanofluidically enhanced electroosmotic flow’ Gulati G.K., Hinds B.J. Biomedical Microdevices 2021 DOI: 10.1007/s10544-021-00580-1