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OMIS: the Open Millifluidic Inquiry System

by bobthechemist, published

OMIS: the Open Millifluidic Inquiry System by bobthechemist Jun 28, 2016

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Summary

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.

Print Settings

Printer Brand:

RepRap

Printer:

i3v Prusa

Rafts:

No

Supports:

Yes

Resolution:

0.2

Infill:

See notes


Notes:

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.

Post-Printing

Bill of Materials

syringe pump

  • 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.

fluidics system

  • 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

controller

  • Arduino Uno or similar
  • L293D or similar

Build Guide

A complete build guide, with pictures, is hosted on github.

Electronics (Arduino)

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

Overview

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.

Custom Section

Project

  • Project Name

    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.

  • Objectives

    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.

  • Audiences

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.

  • Subjects

    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
  • Skills Learned

    • 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.
  • Sample activities

    • 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.
  • References
    • 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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Comments deleted.

Can you please send us some more detailed pictures so we can figure out how to make it attach to the nut the plate on the plungers

Are you referring to carriage.stl? If so, I just press fit the nut. I print in PETG and I end up with a nut trap that results in a tight fit. You could glue the nut to the carriage if you want the nut to remain attached to the plastic. I don't prefer this option since it makes removing the syringe take longer (having to wait for the stepper motor to retract the carriage).

HTH. If not, tell me the filename of the object you're having problems with.

Thanks for the quick response, yes the carriage.stl is the part, sorry for not being specific. I have printed in PLA and ABS and have not had a tight enough fit but used some epoxy and this has done the job.

The only other parts that I can't get to work is the

  1. Regular nut and the jam nut stop on the lead screw- Can I do without this as long as I watch to make sure the lead screw doesn't completely screw out?

  2. The jam nut between the driven gear and the motor assembly plate-When I put this spacer in, the gears don't fit together, can I do without this?

Thanks again for your very thorough and helpful responses!!!

I think it will be very difficult to get the pump to work properly without the jam nuts. When engaged, the syringes will apply a force on the carriage plate which gets transmitted to the jam nuts. Without these in place, the motor assembly will be pushed off of the lead screw.

Looking at the build guide https://github.com/bobthechemist/omis/blob/master/documentation/BuildGuide.md step 6, you'll see a picture of the motor assembly plate with the two sets of jam nuts. The one on the left is on the carriage plate side of the lead screw and is the critical one. The jam nut on the right hand side ensures that the driven gear turns the lead screw. Unfortunately in this design, the teeth of the compound gear extend just beyond the nut trap of the driven gear, so it is critical that the nut is flush against the plastic of the driven gear (see step 7 of the build guide for a picture of what I'm trying to say). Again, a bit of epoxy might be helpful here to make sure the gear doesn't come off of the nut; I don't need to do this with my printer/filament, but it sounds like your tolerances differ from mine.

An addition one of my students has made to her syringe pump is a set of spacers around the M3x24 bolts. They serve to provide some much needed stability to the motor assembly and may address the problem of the gears not fitting together. She also found that taking a Dremmel to the M3 hole in the motor assembly support plate (see the middle bolt in the figure in step 6) introduced some "play" in the compound gear positioning which allowed the components to fit snugly together.

Lastly, a bit of silicone grease, on the gears and on any plastic/metal faces that turn against one another, helps make the pump run a bit more smoothly.

Thanks for the design and the links to curriculum and experiments! hi

Glad to see someone is trying it out. I'd love to hear more about how you are using the system.

Comments deleted.

I don't understand it, but it looks amazing!

Thanks - I'm working on some video demonstrations to show off how I think it can be used.

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