Microfluidic Concentration Gradient Generator Chips for Applications in Cellular and Organismal Biology

Abstract

In this article, we review the design and function of microfluidic chips purposed as fluidic concentration gradient generators for different experiments in chemistry and biology. The microfluidic chips are designed using CAD tools and fabricated using methods of soft lithography and etching using SU-8 as the master mold and polydimethylsiloxane as the microfluidic chip material. The most common design of concentration gradient chips are Christmas-tree design structures which have evolved to speed up the fabrication process and address any issues with fluid flow. A number of experiments in bioengineering have been conducted using these concentration gradient generators, including tests using model organisms such as C. elegans, nematodes, zebrafish, bacteria and different types of cells for cancer screening and toxicological screening. The toxic effects of chemicals on the model organisms have been studied with simultaneous imaging and video recording of cellular health outcomes or behavioral changes indicative of mortality. The concentration gradient chip designs have been improved over the past years to make them more user-friendly and low-cost with a wider range of applications in bioengineering. New technologies, such as 3D printing, has further incorporated automation and design flexibility in the fabrication of microchips for generating concentration gradients. Moving forward, the value of concentration gradient chips lies in its ability to conduct many tests in parallel that help to better predict the clinical outcomes. For this, the concentration gradient chips need to have design considerations that closely mimic the natural biological systems and hierarchical topologies seen in cells, tissues, and organs.