Team:Penn/Notebook
MIYAGI:Notebook
Open Source Wax Printing Conversion Kit
Research
We spent the week researching different methods of fabricating microfluidic paper analytical devices (uPADs). We weighed the pros and cons of different fabrication methods such as photolithography and wax screen printing. We looked into the differences between piezoelectric and thermal printheads. We also considered various possible substrates and hydrophobic substances for making low cost uPADs.
Hardware
We took apart a Xerox ColorQube 8580 wax printer to understand how the printer deposits the wax. This printer has been used to design uPADs and is used in the bioengineering lab course at the University of Pennsylvania. While it allows rapid prototyping and is easy to use, the printer and its cartridges are expensive and is no longer manufactured. This type of uPAD fabrication also allows limited resolution because once the wax is printed onto the paper, the paper must be heated to allow the wax to fully permeate through the paper. This heating process causes the wax to spread into the channels limiting the resolution.
Research
We reached out to a Philadelphia local startup, Chip Diagnostics, to get insights and feedback on our design for our wax printer.
Hardware
Replicating open source projects
We began experimenting with different XY table designs. One design incorporated a pulley system and stepper motors to create a vertical plotter for drawing on a whiteboard. Another design was taken from an open source XY table used for depositing liquid into a microwell plate. We adapted it to fit our needs to create a general XY table.
Taking apart existing projects
We took apart a crayola crayon melter and a wax jewelry gun to analyze the heating elements and extrusion mechanisms. The crayon melter uses a heating element and a temperature feedback system that rises to ~160 F to heat regular crayola crayons that are made of paraffin wax. The extrusion mechanism was a large ball point that had to be pressed down to the paper to extrude the molten wax in thick streams.
Research
We met with Evan Weinstein, CEO and founder of local 3D chocolate printing startup Cocoa Press, to discuss the difficulties associated with building a CNC machine from scratch and to gain insight into the design process. Evan gave us recommendations on which hardware components are most commonly used and which firmware programs have the best documentation.
Hardware
Replicating open source projects
The XY table project was completed. We were successfully able to control the movement of a marker in 2 dimensions by using G-code to control stepper motors. Through this project we learned the hardware and software fundamentals of CNC machining. Heating pads were used to heat a syringe to the point of melting the wax inside. As recommended by the representative from Chip Diagnostics, we used adhesive motorcycle hand warmers to achieve even contact around the cylindrical syringe body. We assembled a Prusa i3 MK3S to be used in the University of Pennsylvania George H. Stephenson Foundation Undergraduate Laboratory and Bio-Makerspace. This open source 3D printer is considered the industry standard for desktop 3D printing and costs $750 in parts.
PIVOT
After considering the cost of building an XY table compared to the position accuracy we would likely be able to achieve, we decided to modify an existing open source 3D printer into a wax printer instead of designing a custom XY stage. In recent years, 3D printer costs have steadily decreased while printer quality has increased. Many research facilities and universities now have access to 3D printers. Our new plan was to make a kit to convert the Prusa i3 MK3S into a wax printer capable of making paper based microfluidic devices. Research groups with access to a Prusa printer would then only need to source parts for the conversion kit, saving time and money compared to building or buying a new wax printer. Research groups without access to a similar 3D printer would need to purchase more parts, but at a price similar to the expected cost for our original design.
Research
Most extrusion based printers are either powered by a mechanical pump or a pneumatic system. After weighing the pros and cons of each mechanism, we decided that the pneumatic system was better for our purpose. We anticipate that using a pneumatic powered syringe pump will allow more precise control of the wax extrusion.
Hardware
Heating
We started experimenting with motorcycle heating pads and nichrome wire as our heating elements. We have wrapped the motorcycle heating pads around 50 ml syringes and used thermistors and feedback control to regulate the syringe temperature. We have also tried wrapping nichrome wire around the syringes, however the nichrome wire becomes too hot and melts the plastic. Without any insulation or covering over the syringe, it takes a long time for the syringe to get hot and actually melt wax. The wax we are using is Sigma-Aldrich Paraffin wax with a melting temperature of 53-58 C.
Research
We met with Jordan Miller, a previous University of Pennsylvania professor and iGEM advisor, to speak about his work with the BariCUDA Extruder, an open source air pressure driven extruder. Dr. Miller uses his design for precise pneumatic extrusion of sugar filaments for plating living vascular tissues. We spoke with him about our design considerations and received input about in regards to heating our device and using a pressure system to drive the extrusion mechanism.
Hardware
Syringe Holder
Uniform heating is a crucial element for extruding molten wax and preventing clogging of the syringe. To ensure the syringe is heated we made a CAD design of a metal syringe holder that our syringe will be placed inside of. The metal syringe holder will be wrapped in cylindrical heating pads so as to conduct heat more efficiently to the syringe full of wax. We met with the director of Penn’s machine shop to discuss design considerations and decided on aluminum for our design as it was a low cost metal that provided the heat conductance we wanted.
Pneumatic System
We started experimenting with a 3 way 2 position solenoid valve that we plan to use for the pneumatic system. The solenoid valve switches between pressurized air and atmospheric air. We are using a nitrogen tank to provide the pressurized air. Tubing will connect the nitrogen tank to the solenoid valve. We 3D printed a syringe adapter that will allow the tubing to connect the solenoid valve to the syringe.When the solenoid is powered on, it connects the pressurized air to the syringe resulting in extrusion. When the solenoid valve is powered off, it connects atmospheric air to the syringe resulting in no extrusion. To extrude molten wax, only 5-10 psi is needed. To incorporate the solenoid valve into our device, we have experimented using the fan port of the Prusa. Since our design does not necessitate a fan, we will use the fan port to turn the solenoid valve on and off.
Research
We looked into how the Prusa regulates the temperature of the plastic it is extruding. The Prusa relies on PID (proportional integral derivative) control which can be easily edited using the Prusa firmware. We plan on using the Prusa’s internal PID tuning and setting our own desired temperature.
Software
Before you can print an object on a 3D printer you first need an stl file that is then converted into G-code. G-code serves as a set of instructions for the machine and tells the printhead where to move, how fast to move, what path to follow, etc. A slicer program is used to convert stl files to G-code, the Prusa printers use the PrusaSlicer program. We have edited a python script from the Jordan Miller lab that converts the G-code from the PrusaSlicer into G-code that is needed to print our wax uPADs. The program edits the G-code so that all extrusion commands are replaced with commands to turn on the solenoid valve. We tested the conversion script and upload the edited G-code to the Prusa. We replaced the solenoid valve with an LED so that every time the solenoid was turned on, the LED would turn on as a visual indicator that the script was working.
Hardware
Syringe Holder
We updated the syringe holder design to include a full cylinder design instead of a tapered head at the syringe tip. Having a full cylinder will lower costs of the machined part as well as make it easier to adhere the heating pads to the outside of the syringe holder.
Pneumatic System
We experimented with extruding molten wax with the pressure system. However, melted paraffin wax has such a low viscosity, the wax just drips out of the tip when no pressure is being applied. We plan on trying smaller gauge syringe needles and potentially may implement a negative pressure system to prevent dripping.
Hardware
Pneumatic System
We tested smaller gauge syringe tips with the pneumatic extrusion system. We tried 20, 22, and 25 gauge syringe tips. The 25 gauge syringe tip worked the best and had the least amount of wax dripping out however became clogged the most frequently. Only about 1 drop of wax leaked out every ~ 10 seconds. We ordered smaller gauge needles and are also thinking of transitioning to shorter needles to reduce the amount of time the wax spends in the needle and prevent clogging.
Hardware
Heating
We experimented with new heating pads. Instead of using the motorcycle heating pads we started using heating pads from adafruit that are smaller and easier to wire to the Prusa. The replaced the 24V extruder heating prt on the Prusa Arduino mega with two 12V heating pads in series. We edited the firmware of the Prusa to override the usual heating settings and input our own. We successfully PID tuned the Prusa to heat to 65 C.
Hardware
Heating
We printed our first uPADs. Our main issues are that too much wax is extruded onto the paper, the syringe tip gets clogged, and the extruder head is too far from the print bed. To decreases the amount of wax being extruded we plan on trying smaller syringe tips, reducing the pressure, changing the syringe volume, increasing the feed rate, and experimenting with more viscous waxes.
Syringe Holder
We sent updated syringe holder designs to the machine shop for smaller volume syringes and smaller gauge syringe tips.
Research
We tested the effects of the melting point of wax on its extrusion to determine the best type of wax for our device. We found that the melting point of wax does not have any large effects on the extrusion of the wax from the syringe.
Hardware
Hardware
We designed and printed a final syringe mount that fully supports the extruder. We installed this mount onto the Prusa printer with screws and fit the syringe and holder onto it.
Pneumatic System
We ordered and received a smaller pressure gauge to regulate our input pressure to smaller values. We then tested the extrusion at smaller pressures.
Research
With all of the finalized parts, we performed experiments to determine the specifications of the printer. We printed many variations with wax onto cellulose filter papers and performed post-hoc measurements to calculate the resolution and reliability of the printer.
Research
We optimized the G-code to produce successful prints taking into consideration the dripping and pooling of wax. We then printed paper microfluidic devices of different designs onto the cellulose filter papers.