Saturday, 12 May 2012

Simple laser cut milli/microfluidics using Ponoko

In my last project the service Ponoko was used to laser cut and engrave the enclosure. As I had some room left on the template, I decided to make some milli/microfluidics using the free space on the template and look at the possibility of using laser engraving and cutting for homemade microfluidics for simple lab-on-a-chip applications.

In the Photon Factory (a laser lab at the University of Auckland where I work) we build microfluidic devices using femtosecond laser machining as well as laser spectroscopy. We machine many different materials, some of which are not able to be machined by normal nanosecond lasers.

Figure 1 | Single cell traps machined in the Photon Factory for use in medical research.

The material used was clear acrylic 3mm. Two different types of chips were made, one engraved and one cut. This was very easy to set up using Inkscape where the lines were cut and the shapes with transparency were engraved. All that was needed was to install Inkscape an open source vector art drawing program and to download the template from the website. After waiting for a week the parts arrived and the chips were analysed using equipment at the University of Auckland.


Figure 2 | Engraved milli/microfluidic devices.

Two different etched designs were created - a spiral and a shrinking channel. The engraving was found to be effective with the maximum engraving setting. Other engraving settings on acrylic did not provide a channel that was engraved all along the area and in some places a channel was not cut but produced a dotted line.

Figure 3 | Images of the shrinking channel design with the machined beam profile of 100 microns clearly seen.

Figure 4 | Edge of the chip showing  ~100 microns of melting.

Figure 5 | Close up of the spiral design showing the overlap of the channels.

The images would suggest that the design is rastered. To design a chip it would therefore be preferable to use straight channels. The recommended distance between the features can be no smaller than 50 microns and 100 microns. The minimum channel size is around 100 microns.

Surface Profiling

The Dektak II from the Microfabrication Facility at the University of Auckland was kindly lent in order to profile the surface of the chip with the shrinking channel. The Dektak uses a small needle that is run along a surface to detect the roughness. The needle was run perpendicular to the direction of the laser to measure the undulations made by the laser.

Figure 6 | Dektak II used to analyse the surface of the engraved chips.

The uneven surface is visible (figure 7). This could be particularly good for mixing of fluids in the channel.

Figure 7 | Plot of the surface of the engraved chip (the height of the channel is around 400±10 microns).

The average height of the undulations was found to be 30.4 microns (stdev 8.3). The width between the peaks was 100 microns (stdev 5.7). The depth of the channel (found using Vernier calipers) was 400±10 microns. Around the edges the channel was quite curved with around 50 micron before the maximum depth was attained.

Laser cut

A laser cut flow cell and reaction chamber was cut. These chips need sandwiched plastic around them to hold the fluid in the channels.

Figure 8 | Flow cell to right and reaction chamber bottom left.

A single line (100±5 microns wide) was cut in one of the chips. It has to also be remembered that heat effects at the edge do create a slight beveled edge.

Figure 9 | Microscope image of 100 micron channel.

Possible Applications

These chips could be used to make some simple reaction chips which could be probed using a similar spectrometer to that in my previous post. We are also looking into using the flow cell to run spectra in the femtosecond laser system. The engraved chips could be used for making chips that mixed liquid. The chips could be used before chemicals go into smaller microfluidic channels as a premixer. As the channels are small enough they could be used for Flow Injection Analysis in which chemicals are mixed and allowed to react in a chamber and then the resulting products or reactants are detected, usually spectroscopically.

You could have a plant on a chip, in effect a micro-hydroponics system to study biological responses to different herbicides.

The ability to 3D print is not discussed but could be used to create some great experiments and may be reviewed in the future.

At the lab we will be sticking to our femtosecond system for microfluidic devices, however hopefully this discussion will give others outside the lab the means to invent their own milli/microfludic devices.

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