Microfluidic Devices for Cell Based High Throughput Screening

Abstract

Cell based High Throughput Screening (HTS) has become a very important method in pharmaceutical drug discovery and presently carried out using robots and well plates. A microfluidics based device for cell based HTS using traditional cell culture protocol would be a significant addition to the field. In this thesis novel microfluidic HTS devices targeted for cell based assays having traditional non-compartmentalized agar gel as cell culture medium and electric control over drug dose is being reported. The basic design of device consists of a gel layer supported by a nanoporous membrane that is bonded to microchannels underneath it. The pores of membrane are blocked everywhere except in selected regions that serve as fluidic interfaces between the microchannel below and the gel above. Upon application of electric field nanopores start to act as electrokinetic pumps. By selectively switching an array of such micropumps, a number of spots -containing drug molecules- are created simultaneously in the gel layer. By diffusion drugs reach to the top surface of gel where cells are to be grown. Based on this principle, a number of different devices are fabricated using microfabrication technology. The fabricated devices include, single drug spot forming device, multiple drug spot forming device and microarray of drug spots forming device. By controlling pumping potential and duration spots sizes ranging from 200μm to 6mm diameter and having inter-spot distances of 0.4mm-10mm have been created. Absence of diffusional transport through the nanoporous interfaces without electric field is demonstrated. A number of representative molecules, including surrogate drug molecules (trypan blue, and methylene blue) and biomolecules (DNA and protein) were selected for demonstration purpose. Dosing range of 50-3000 μg and spot density of 156 spots/cm² were achieved. The drug spot density was found to be limited by molecular diffusion in gel and hence numerical study was carried to find out ways for density increase. Based on this simulation, a method for diffusion reduction called diffusion barrier was proposed. Diffusion barrier used specially dimensioned (having shallow grooves) gel sheet to reduce the diffusion.