OMIS: the Open Millifluidic Inquiry System
by bobthechemist, published
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OMIS is a platform for exploring lab-on-a-chip technologies and miniaturized analysis systems. It is a 3D printed, Arduino-based science and engineering project that allows the end-user (student/teacher/hobbyist) to explore the science of fluids. OMIS currently has two parts. The first is a syringe pump constructed from 3D printed parts, an inexpensive stepper motor and some items from the local hardware store. The second part is a “millifluidic device” which is also 3D printed. OMIS is designed with learning and inquiry in mind, and all elements of the design have been created to encourage exploration.
Infill was set at 20% for the syringe pump and between 20 and 100% for the millifluidic device. Qualitatively, the higher the infill, the greater the pressure tolerances of the device.
Bill of Materials
- 1/4" steel rod, 140 mm length, (2)
- 1/4"-20 TPI threaded steel rod, 155 mm length (1)
- 5V DC small reduction stepper motor from Adafruit.
- M3x10 hex-bolts (4)
- M3x24 hex bolts (4)
- M3x16 hex bolts (2)
- M3 hex nuts (12)
- 1/4" 20 TPI nuts (3)
- 1/4" 20 TPI jamnuts (2)
Syringes and needles
The default configuration uses a 3-mL HSW luer slip eccentric syringe which can be found at Restek although I purchased my batch from Fisher Scientific (and they apprently no longer sell them). A different syringe can be used by adjusting the parameters in the global file. I used 26 gauge needles from Sigma-Aldrich, but any that fit the inner diameter of the hosing used will be sufficient.
- flexible tubing. I used some that was lying around my lab. Cole Parmer sells small tubing. To use this build as is, the outer diameter of the tubing should be about 1.8 mm.
- quick-setting epoxy
- Arduino Uno or similar
- L293D or similar
A complete build guide, with pictures, is hosted on github.
The syringe pump uses a 5 V DC stepper motor which can be operated from a variety of controllers such as a Raspberry Pi or an Arduino. I have used the latter in this build, and have posted the Arduino sketch on github. The code is little more than a customized version of the stepper motor tutorial on Adafruit and the Arduino serial communications examples. I'll post a circuit diagram shortly, but if you are really anxious, though, the circuit is not different from the one found at Adafruit.
How I Designed This
All 3D parts were constructed using a home-built reprap 3D printer, and I assume that print quality would be improved on a commercial printer. PLA and PETG filaments can be used; however, PETG was found to have superior physical and chemical properties for this project (it's just not as pretty since it comes in clear or white). Printing of the syringe pump was done with support material, which increases the integrity of the support-rod clamps. Printing the millifluidic device requires special attention to the layers printed above the channels to ensure they are free from leaks. Typically, slower speeds and higher temperatures facilitated this process.
OMIS: the open millifluidic inquiry system
Overview & Background
My interest in this project is twofold. First, automatic syringe pumps are expensive, with some models costing in excess of $1000. These instruments are cost prohibitive for learning environments, especially under ideal circumstances where student groups of 2-3 work together with their own instrumentation. Second, there are several examples in the scientific literature of 3D printed millifluidic devices. (some claim to be microfluidic, but I am defining microfluidic as a device with channels in the tens of micrometers instead of merely sub-millimeter.) None of these sources have identified pathways to introduce fluid dynamics in a learning envionrment. 3D printing allows for what is otherwise considered an advanced topic to be explored, at least qualitatively, at an early age.
Students building OMIS will get a better understanding of how gears work and why they are needed; an introduction to building an "instrument" consisting of mechanical, electrical and fluidic components, and an introduction to physicochemical properties relevant to millifluidics such as diffusion and laminar flow.
The difficulty level of the project is aimed at college level introductory Chemistry, Physics and Engineering classes, but is in my opinion suitable for motivated high-school students interested in STEM fields. Materials can be adapted to honors and AP science classes or as science fair projects.
OMIS is intended to be a systems-based approach to science learning and incorporates aspects of engineering, physics and chemistry. I find it useful to break the project down into these categories:
- Building OMIS: Engineering design
- Controlling OMIS: Computer science and physical computing
- Using OMIS: Physics and Chemistry
- HS-PS2 Motion and Stability
- Using an inexpensive, low-torque motor in this project necessitates a consideration of gears and forces. Students building OMIS will learn the algebraic manipulations involved in gear ratios, relationships between torque and speed, and how materials used in a design influence frictional forces.
- HS-PS3 Energy
- Closely related to HS-PS2, students will learn how electrical energy can be converted into kinetic energy in order to perform work on a sysem (moving fluid through a channel).
- HS-PS1 Matter and its interactions
- Milli/microfluidic devices are used extensively in lab-on-a-chip systems that are designed to perform chemical reactions, detect the presence of specific materials, and analyze the properties of mixtures. While the material presented here focuses on engineering (instrument build) and physics (fluid flow) aspects, incorporating chemical concepts into explorations with OMIS is a logical next step.
- HS-PS2 Motion and Stability
- How does flow rate affect fluid mixing? Fill the syringes with two differently colored solutions (food coloring works well here). Observe the flow of the two liquids as the flow rate is increased from 10 uL/min to 100 uL/min. (Bonus: How can you explore the influence of temperature on fluid mixing?)
- How does fluid viscosity influence mixing? Repeat the above experiment with oil (you can add color to vegetable oil with tumeric or paprika). You can use solutions of sucrose to change the density as well, and this system is useful to explore how solutions with difference viscosities mix.
- What happens when you charge a millifluidic device with two immiscible liquids? Fill one syringe with water and the other with vegetable oil. Observe what happens in the mixing channel. Investigate how flow rate affects the observations.
- I'm not the first person to come up with an open hardware syringe pump design, and this more professional version is worth a look if you have more demanding specifications.
- Much of the inspiration for this project stems from the work of Lee Cronin at the University of Glasgow. A good place to continue your journey with 3D printed millifluidics is this article.
Rubric & Assessment
As mentioned above, there are many components of this project. Focusing solely on Building OMIS, here are some suggested learning outcomes. I assume that students would work in teams and have the ability to implement design changes. Learning outcomes are organized by cognitive behaviors following Bloom's Taxonomy
Remembering and Understanding
- common names use for components of a pumping device, hardware, fasteners and tools
- convert between metric and imperial units (mm/cm to inches)
Applying and Analyzing
- Calculate the mechanical advantage of a gear train
- determine the relative speeds of gears in a gear train based upon the mechanical advantage
- apply a chain of mathematical operations to convert motor rotations into linear distance traveled by an object on a lead screw
Evaluating and Creating
- follow directions to complete a moderately complex project
- leverage a team environment to overcome project obstacles
- Propose solutions to weak points in a design presented to them
- implement a proposed design change and evaluate the outcome
- Handouts and assets
- All CAD, software, instructions and educational documents will be stored on github.
- A PDF of the build guide is included as one of the items that can be download from this page.
- Seriously, if you've made it this far, you are a glutton for punishment. I will keep an extended commentary (!) of the OMIS project at my website.
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OMIS: the Open Millifluidic Inquiry System by bobthechemist is licensed under the Creative Commons - Attribution - Non-Commercial license.
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