Home Projects Bot-vinnik Twitch III CTC Filter CTC Intro Microfluidics The Mechanism Device and Operation Teaching Pendulum Outdoors Leatherworking About Me

Circulating Tumor Cell Filter

Intro to microfluidics

This project is a microfluidic device, so it might be worthwhile to give a brief introduction to the field at large. Microfluidics refers to the study of fluid systems with sub-millimeter length scales and the field of engineering that employs these systems. The small length scales of microfluidic devices make them ideal for biological applications, where manipulating individual cells or even strands of DNA can be next to impossible with conventional lab techniques. While the field is over 40 years old, interest only peaked when new fabrication techniques from the Stephen Quake lab dramatically drove down cost and drove up possible complexity.

Soft lithography lets you make microfluidic channels from a master mold

By pouring a liquid polymer called PDMS over top of a mold and curing it, you can peel away the negative copy and then bond it to a substrate to make microfluidic channels. This process is cheap, easy, and can be done anywhere. To make the master mold, conventional lithography techniques are typically used. This costs a fair amount, but lithography is a fast and high-fidelity approach that lets you achieve feature sizes down to about the 1um range, limited primarily by the wavelength of light.

Tiny fluid channels are great, but things get really exciting once you start making valves. PDMS is an elastomer, so if you stack two channels on top of each other and separate them with a thin diaphragm, you can open or close the top channel by bending the diaphragm up or down with a differential pressure.

If the top channel is rounded, you can achieve a perfect seal. If the top channel is rectangular, your valve will leak around the corners, sometimes called a sieve valve.

Since the features are all patterned onto the master mold simultaneously in lithography, you can make your channels as complicated as you like without suffering a corresponding increase in fabrication complexity.

The full process for making a two-layer microfluidic device (with valves!) from scratch

The end result is that it is not so difficult or expensive to make extraordinarily complex devices like this.

A Quake lab bioreactor. Image from Balagadde et al,. Science, 2005