One of the goals of low cost 3D printing is to be able to create medical and scientific devices from it. Diagnostically capable microfluidic models represent the first step into this exciting new world of 3D printing and biosensing capabilities.
A microfluidic device is a small chip that allows liquid to flow through it, which is useful in many applications, including medical diagnostics. They are typically made from glass, plastic, or paper to facilitate the flow of fluids to the desired location.
What makes a device “microfluidic” is that fluid flow physics works differently on this small scale. This allows for things like fluid separation, counting, and other cool effects. Low contamination and water tightness are additional considerations for these types of devices.
Typically, microfluidic devices have structures less than 100 micrometers in size. However, many of the following projects have structures that exceed this limit by 200 micrometers or more. Nevertheless, the fluidic functionality is similar in most cases, despite the flow being in the milli–micro regime.
Traditionally manufactured polymer microfluidic chips cost around $40 or more per device, and that without any customization. On the other hand, 3D printing a microfluidic chip reduces cost and improves customizability.
In the following, we’ll look at a few different types of microfluidic chip structures using a variety of 3D printing techniques. Let’s dive in!
Our first 3D printed microfluidic device is the Tesla valve. The Tesla valve is a type of one-way valve invented by Nikola Tesla in 1920.
The Tesla valve has no moving parts and only allows fluid to travel forward. This can be particularly helpful when paired with a pump to create a high-efficiency water pump. In microfluidics, this can be used to ensure that fluid only moves down the channel without substantial losses.
In their work on a lithographic Tesla pump, Mohammed-Baker Habhab and his team used a valve as part of a pump system integrated onto a microfluidic chip.
From Thingiverse comes a large version of the Tesla valve.
A microfluidic mixer is a device that causes fluids flowing within to mix more than they otherwise would. Given the flow properties of very small liquid flows, this is usually a challenge.
Having a specific device dedicated to mixing allows for small quantities of expensive medications to be manufactured. In a review by Anton Enders and his team, several different types of microfluidic geometries are compared using the MultiJet 3D printing method.
One of the advantages of microfluidics is its ability to separate and create small countable units of fluid. Researchers from Cardiff University used Ultimaker 3D printers to do just that.
But why would we need to make spheres using microfluidics? As they mention in the video, spheres are made for biomedical applications as well as nuclear energy applications. Furthermore, the simple ability to “count” small volumes of fluid can be helpful. Exact volumes of fluid can be deposited in a digital manner based upon the number of counted spheres, for example.
Multilayer or complex microfluidic geometries, including components like mixers and valves, are oftentimes difficult to create. Thankfully, researchers at Wageningen University and the University of Castilla-La Mancha developed the ESCARGOT method, which allows for complex three-dimensional microfluidic forms to be created along with embedded non-3D-printed materials, if desired.
This method involves printing an ABS template that is encapsulated in PDMS. After curing, the template is removed using solvent extraction. The process has many uses, including an embedded heating element for selective heating of fluid across a particular area of the microfluidic device.
This method, developed by researchers at North Carolina State University, uses fugitive metal ink to draw microfluidic structures.
Essentially, a thin layer of gallium metal is printed onto a surface. After solidifying, the surface is encapsulated in another polymer layer poured over it. After the polymer solidifies, the fugitive metal ink can be removed using solvent methods (HCl). Alternatively, it can be removed by using an electrical field to drive the metal out over time.
Future applications of 3D printed microfluidic technology aim to improve the resolution of the 3D printed materials. This should, in turn, improve the flow characteristics and fall well within the ideal microfluidic range. Current research is ongoing in this realm.
Additional applications include expanding the use to other 3D printable materials, such as biological materials. Overall, the future for microfluidics looks minimal, but good things come in small packages!
Feature image source: Eran Gal-Or / YouTube
License: The text of "3D Printing Microfluidic Models – 5 Most Interesting Projects" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.
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