Microfluidic Mixing Chip

A simple to use, low-cost microfluidic mixing device

Group Members: Nicholas Whyte, Maria Tejada, Emily Mckee

The Problem

Microfluidics is a growing field of interest in chemistry, physics, drug discovery, biomedical research, and tissue engineering. Due to the laminar nature of fluid flow in microfluidic devices, a central issue is the lack of available technology and designs that can sufficiently mix fluids at the micro scale. This project was assigned a grade of A.

The Design

Based off existing devices and their needs, the following design constraints and objectives had to be met:

Objectives

Low cost
Fluids are thoroughly mixed when reading takes place
Device is portable
Time for fluid flow and sensor reading is efficient
Device is durable
Design allows for efficient manufacturing time

Constraints

Two separate ports for fluid entry
Individual samples must travel a minimum of 100 mm in separate channels
Mixing area required
After mixing, the fluids must travel in a third channel for at least 50 mm
Colour sensing required in an analysis area
Constant flow throughout operation
Cross-sectional area of channels is a maximum of 300 µm by 100 µm
Maximum chip size of 50 mm by 75 mm

Three mixing patterns were identified and compared. Taking into account the manufacturing processes availability, cost and time as well as the pattern's ability to create turbulence, a "tesla valve" pattern was chosen.

Using a weighted objectives chart, three material designs were compared based off existing device results. A device involving a laser cutter to etch our pattern into acrylic achieved the highest score by meeting our design objectives most effectively.

Our chip was then modelled using solidworks and drawings were produced. The UVic Machine Shop laser cutter was used to etch one side of an acrylic rectangle. A matching, un-etched, acrylic rectangle was then secured to the etched side and screwed in place.

O-rings surrounded the entire mixing area as well as each of the individual screws. Initially, to minimize cost and weight, fewer screws were used to hold the two acrylic sides together. This resulted in a small amount of leakage when two fluids were pumped through at high pressures. To fix this problem the area of leakage was identified and two more screws were added.

Following tests, the device was able to mix two fluids in less than one second. The manufacturing time was less than one hour and the cost less than $30.