High throughput nano-electrokinetic purifier for an artificial kidney

Abstract

After the recent development of perm selective membrane and nano-scale fabrication process, various electrokinetic methods for water treatment have been emerged. In case of these methods, ion concentration polarization (ICP) phenomenon has been extensively researched concerning new fundamentals in nanoscale electrokinetics and novel engineering applications. However, effective platform for ICP device has not been sufficiently accomplished and the technique has suffered from the critical limitation of low processing capacity. In this thesis, microfluidic apparatuses were adapted to develop highly utilized ICP platform and micro-scale structure was installed the layer near the membrane to enhance throughput of ICP devices, respectively. And we finally invented the electrokinetic purification system for an artificial kidney system. Firstly, we devised a new micro/nanofluidic preconcentrator using ICP phenomenon by integrating a two-phase droplet generator and pneumatic valve. One of the most interesting features of ICP is collecting any charged species at the interface between ICP layer and bulk electrolyte so that its concentration would be amplified more than 10,000 times within a minute. In order to prevent the unwanted diffusion of highly concentrated sample plug, a droplet generator was employed to capture the preconcentrated plug and finally we can keep the high amplification ratio in high throughput manner by tweaking electrical input, flow rate, and concentration/release time. In addition, we adapted pneumatic valve to continuous type ICP preconcentrator. Highly concentrated plug is released to opened branch by controlling pneumatic valve within 100 ms so that we can continuously gather only concentrated sample. Manipulation of amplification ratio is similar with ICP droplet preconcentrator which could be amplified more than 100 times. Secondly, we devised micro fin structures inside a macroscale (>O(2) um) highthroughput ICP device and successfully demonstrated a stable formation of ICP layer and its performance. Since the fin structures created electroosmotic fluidic circumstances and assisted in physically suppressing undesirable electrokinetic vortices generated in this fluidic regime, ICP was stably generated even in this macroscale system. The micro fin structure was designed after proceeding analytical solution and numerical simulation. Finally, batch-type droplet ICP preconcentrator and continuous-type ICP separator were introduced as examples for high-throughput millimeter-scale ICP devices using the implanted fin structures. Finally, we proposed high-throughput electrokinetic purification device for an artificial kidney system. Peritoneal dialysis (PD)-based wearable artificial kidney (WAK) device with portable and automate purification capability will provide dialysis treatment that has maximum freedom of time and space constraints for end stage renal disease (ESRD) patients compared to conventional PD or hemodialysis (HD) treatment. ICP phenomenon has been intensively attracted attention for portable purification applications because of extensive separation capabilities from ion to micro-scale substances by nanoelectrokinetic fundamental. In this work, nanoelectrokinetic purifier, for the first time, was applied for a portable PD device which can overcome several limitations of a conventional PD treatment. First of all, dialysate purification mechanism was verified using a micro-nanofluidic platform. Uncharged toxin (urea) was completely decomposed to non-toxic gases (~99 % purified) by electrochemical reactions and positive toxin (creatinine) was sufficiently removed (~40 % purified) by nanoelectrokinetic transportation which is similar to the cation transport mechanism due to ICP phenomenon. And a macro-scale nanoelectrokinetic purifier (10 mL/min throughput) with a creation of micro-nanofluidic environment inside the device was successfully demonstrated as a dialysate purification device for continuous flow PD. As a result of extensive in-vitro and in-vivo experiments, the toxin level in a body fluid of the dog was verified to be reduced around 10 % during 3 hours of nanoelectrokinetic-PD treatment. One would expect the WAK for significantly advancing a quality of life for ESRD patients by this portable nanoelectrokinetic purifier.