Behind the Build: Crafting MetalFlow's 3D-Printed Microfluidic Demo

In my previous post, I introduced my 3D-printed microfluidic demo for MetalFlow, which provides a visual presentation of how our metal extraction process works within a microfluidic chip. Here is how this demo came to life from an idea.

Initial Concept

The idea to build this demo came when the team was preparing the final demo presentation. We all felt that explaining MetalFlow's mechanism to the audience was quite dry. So, I set out to design a demo to make this complex process tangible and interactive.

My initial concept is creating a simplified, visible-scale flow cell featuring distinct channels to guide droplets of leachate and extractant solutions towards a common reaction zone. These droplets would be represented by small round pieces precisely designed to fit within the channels. I incorporated a lever at the end of the reaction zone, which visually demonstrates the precise control mechanism for phase separation that separates the enriched metal-containing extractant from the washed leachate solution.

Version 1: The First Attempt and Challenges

The design began in CAD with a 2D sketch of two curved channels that are initiated from one end of the chip, meet at a central reaction zone, and then separate again and exit the chip from the other end. This setup mimics how aqueous leachate and organic extractant fluids flow side-by-side in real microfluidic chips.

With the 2D sketch finalized, I extruded it into a 3D flowcell, creating the first iteration of the demo. Fresh off the 3D printer, it looked promising and functioned as intended when lying flat on a table. However, the biggest drawback quickly became apparent when I tried to hold this demo vertically to present it to the audience. The droplet pieces fall out easily from the flow cell board, and they and the lever are not held in place due to gravity.

Version 2: Refining for Vertical Stability & Control

To overcome the vertical stability issue and improve overall presentation, I implemented several key design modifications. First, to prevent the droplets from falling out, I made three specific changes to the flow cell itself:

1. Added a raised rim: The raised rim along the top edges of the channels allows the droplet pieces to move freely along the channels and holds the droplet pieces from easily sliding out.

2. Closed off one side of each inlet: I created a small lip for each inlet of the channel, which effectively prevents the droplets from the side of the flow cell.

3. Added square loading ports: To make inserting the droplet pieces easier and more intuitive, I cut a square loading port at each channel entrance.

   
   
   
   

   

   The refined 3D model showcases the added raised rims along the channel edges and the new square loading ports for droplet insertion

   
   

Beyond using a rim to hold the droplets, I also designed a simple lever arm to mimic flow control and phase separation within a microfluidic system. This lever arm includes a hole for a magnet, allowing it to be easily attached to the flow cell using a magnet at the back. It can be rotated to block or unblock channels, visually representing valve switching to direct flow within the system.

Version 3: Droplet Pieces To Showcase Metal Ion Extraction

With the flowcell structure and control mechanism in place, the next crucial step was to design the interactive "droplets" themselves.

The leachate droplet piece, representing the incoming e-waste stream, was designed as a rounded shape to fit snugly within the flow channels. The piece includes the following key features:

• A shallow magnet pocket: A precisely sized indentation on one side holds a small 6mm x 3mm neodymium magnet.

• A small handle: This allows for easy manual manipulation of the droplet or magnetic control using an external magnet.

The extractant droplet, representing the solvent that selectively binds to metal ions, shares a similar rounded shape but incorporates a few differences:

• A deeper internal magnet pocket: This pocket fully encases a magnet within the droplet.

• A cutout: This cutout can hold the magnet in the pocket of the leachate droplet piece perfectly.

  
  

When the extractant droplet gets close to the leachate droplet in the reaction zone, its internal magnet can attract and "pull" the magnet out of the leachate droplet. This magnetic interaction visually simulates the transfer of metal ions from the leachate to the extractant phase in Metalflow's real microfluidic system.

Final Touch: Printing and Presentation – Making it Real

Using a Bambu P1S 3D printer, I printed all the components. To enhance the visual clarity and user experience, I incorporated text directly into the print and color-coded all the inlets and outlets:

• Green: Clearly marks the “Leachate In” and “Raffinate Out” ports, representing the incoming and outgoing e-waste stream.

• Yellow: Identifies the “Solvent In” and “Extract Out” ports, indicating the flow of the extracting solvent.

• A bold, central “MetalFlow” label: Highlights the brand of the team

The final 3D print model is available at https://makerworld.com/en/models/1400620-metalflow-flowcell-demo#profileId-1452466

This 3D-printed demo has proven to be a useful tool for explaining the principles behind MetalFlow’s microfluidic extraction technology. We used it in our final demo presentation, and it truly helped simplify the complex microfluidic extraction mechanism for our audience.