1. 3D Staggered Herringbone Micromixer for Biomedical Applications
Mentee: Andrea Daniel
Mentor: Shaneen Braswell
Advisor: Professor Lynford Goddard
Motivation
Preliminary Results
Microfluidics is the study of controlling the flow of fluids at micro-, nano- and picoliter scale. It is commonly employed in
Microanaylsis of biological and chemical samples
Drug Delivery
Tissue Engineering
Micromixing is a way to mix miniscule amount of liquids by running them through a small, usually complex chamber.
Most micromixers are planar in geometry limitations of conventional lithography.
3D micromixers tend to have better mixing performance, but are difficult to fabricate and costly.
Optical Inspection of 3D Staggered Herringbone Structures
Blue
Green
White
All samples could be viewed. The structures that etch for a long time appear brighter relative to the other etched structures.
Background
Scanning Electron Microscopy of 3D Staggered Herringbone Structures
Staggered herringbone mixer (SHM) is a microfluidic device that consists of a microchannel with “herringbone grooves” along the upper or bottom side of the channel.
In order to increase the mixing efficiency, we will utilize a novel digital projector-based photochemical method to create a SHM with varying groove heights.
Our goal is to develop a micromixer to increase the labelling efficiency of cells using nanoparticles for enumerate surface proteins.
The SEM only produced visuals for the 30 minute and 1 hour samples.
Profilometry of 3D Staggered Herringbone Structures A B C D
Digital Photochemical Etching Method
A newly developed process known as photochemical etching (PC etching) combines optical imaging and wet chemical etching to structures on a substrate. This process can be utilized as an alternative to fabricate the master mold of a microfluidic device in a single processing step.
Process: (1) Submerse a semiconductor substrate into an etchant solution. (2) Project digital mask using a commercial projector to etch structures onto its surface. The etching time dictates the feature thickness.
Benefits: Low-cost and User Friendly Operation
Profilometry data was collected using the Alpha-Step IQ tool shows a correlation between length of light exposure and etch depth.
A and C was etched using white light and B and D was etched using green light.
White light etched much deeper than using green light.
Low intensity values (0, 32) did not produce measurable etch depth.
Future Work
Experimental Plan
Short-term Goals
Repeat experiments using a fresh etchant to alleviate contamination.
Etch for longer times and calculate the etch rates for each color.
Use COMSOL to simulate the optimal groove heights in microchannel.
First, a digital mask was created using Microsoft PowerPoint to create an array of herringbone structures. Gallium arsenide was used as a substrate.
Intensity was varied to produce different groove heights: 0, 32, 64, 128, 255
Colors were varied to verify which hue will give the optimal etch quality.
Below is the template that was used for the etching the samples.
Use master mold to create the 3D Staggered Herringbone Micromixer
Acknowledgements
I would like to thank the PURE committee for this opportunity and especially my mentor Shaneen Braswell who guided and mentored me through this project 
Each color was tested at 10 minutes, 30 minutes, and 1 hour on the film in the layout as shown bellow.
References