Team:Penn/Design
Breaking Down the Design
Key Components
Custom Metal Syringe Holder
Pressure Driven Extrusion
Adapted Open Source 3D Printer
Custom Metal Syringe Holder
Pressure Driven Extrusion
Adapted Open Source 3D Printer
Heating
The first step in printing wax is heating the wax.
For wax to print, it must be heated above its melting temperature. Temperature control is a critical component of wax printing to ensure that the wax melts and prints uniformly without clogging. To heat the wax evenly, we explored wrapping plastic syringes in nichrome wire to melt the wax inside. Though the nichrome wire melted the wax, it did not heat evenly and made it difficult to accurately read the wax temperature. Our next design included a thermally conductive aluminum syringe holder wrapped in heating pads to evenly heat the wax and provide consistent temperature readings.
Extrusion
The next step is extruding the wax.
Once the wax is melted, an extrusion mechanism is necessary to push the wax onto the substrate. After researching the extrusion methods of devices ranging from pancake printers to glue pumps, we found two main extrusion mechanisms: mechanical and pressure-driven. Mechanical extrusion consists of stepper motors and threaded rods moving a syringe plunger downwards and push out the melted wax. Pressure-driven extrusion uses pressurized air to generate back pressure behind the melted wax, forcing it out the syringe tip. After testing both possible methods, we chose to pursue a pressure-drive extrusion system due to its rapid response to commands and low cost. Our design includes a pressure regulator to set the air pressure to an optimal value between 5-10 psi, a micro solenoid valve to switch between pressurized air and atmospheric pressure, and a custom syringe adapter to create an airtight seal on the syringe.
XY motion
The final step is spatially-paterning the wax to form channels.
Once wax is extruding, the syringe tip must be moved in the desired direction to produce the designed microfluidic device. XY motion controls the speed and position of the extruder head during the print and has a direct impact on the final resolution of the microfluidic device. At the start of the design process, we experimented with making our own XY table specific for our device requirements. After understanding the approximate cost and resolution of the XY table we would be able to produce, we decided to utilize an existing open source 3D printer to achieve high quality XY motion for our printer. In recent years the cost of 3D printers has steadily decreased while the precision of XY motion has increased. Our design takes a popular open source 3D printer, the Prusa I3 MK3S, and adapts its XY motion to work for our purposes.
Why Prusa?
We chose to convert a Prusa because it is low cost and open source.
We converted the Prusa I3 MK3S printer from a 3D printer to a 2D wax printer for microfluidic devices. Prusa is one of the leaders of the 3D printing industry, offering low cost, high resolution printers with detailed documentation. We chose the Prusa printer for our project because it is an open-source device, allowing us to modify the existing software and firmware for our own project. Prusa printers are commonly used in research laboratories across the world and are popular among hobbyists. If a lab already owns a Prusa device, they would only need to purchase the additional wax printer parts for less than half the cost of traditional wax printers. For labs without a Prusa device, the combined cost of a Prusa 3D printer and additional parts is still less than traditional wax printers. By adapting a commonly used, low cost 3D printer, our project represents an opportunity for microfluidic devices to be developed at a significantly lower price.
