Embedded Files
Final CAD Model of Bioprinter made in Fusion 360
The Genmitsu 4040 Pro CNC machine frame has been repurposed for dual-head 3D bioprinting capabilities with a large working area, high running accuracy, stability, and high quality components. Some major modifications to the system include: a custom magnetic toolhead mount that allows for simple attachment and removal of the syringe holder and extruder, two 152 mm gantry risers for added working space, magnetic swappable bed feet for altering z-height, and a polished 600 x 480 mm Aluminum bed with holes for securing the English rabbit test patient. Also, a digital microscope is used for precise indexing of the toolheads in the x and y coordinates, while a custom-designed z-probing tool helps to locate the z-coordinate of the test subject. Finally, a pneumatic extrusion system is used for controlling pressure and printing bio-ink directly into the target site.
Fully Assembled "UC San Diego Bio-Mill" Ready for Operation
The UC San Diego Bio-Mill has been built with a significantly larger build volume than the previously used Inkredible, with a maximum operating area of 400 mm x 400 mm x 85 mm, compared to the Inkredible’s 130 mm x 80 mm x 50 mm capabilities. This equates to over 3 times the x-direction space, 5 times the y-space, and 1.7 times the z-direction toolhead motion. Weighing a total of 11 kilograms including the bed and attachments, the machine was able to be safely carried over two kilometers and transported by a single person without damage, ensuring two-person portability of the machine. The aluminum bed with tall feet was able to withstand a full 91 kg load without any deflection or instability, confirming that it will maintain rigidity when used on English rabbits, which weigh up to 5 kg and grow up to 300 mm in length.
Key Components
Key Components
Previously used, Sub-optimal Bioprinter that inspired the need for a larger, more stable and accurate bioprinter
Features
Features
The silver and blue CNC machine functions as the frame for the bioprinter, with linear rails on for movement of the gantry system in the x and y directions. A majority of these components are inexpensive and convenient to manufacture in large quantities as needed. The key features of the UC San Diego Bio-Mill include its large, modular, open-frame design, high stability, portability, and accuracy.
Genmitsu 4040 Pro CNC Machine used as the basis for our bioprinter design
Female Magnetic Toolhead
Male Magnetic Toolhead
Magnetic Toolhead Mount
Magnetic Toolhead Mount
The magnetic toolhead mount is a secure, convenient method to attach the syringe extruder and easily swap between different toolheads. Threaded ball bearings are fastened with standoffs and secured onto the the male piece of the toolhead, where rectangular neodymium magnets, attached to the female part with epoxy, hold the two pieces together.
Aluminum Bed and Swappable Bed Feet
Aluminum Bed and Swappable Bed Feet
The printing bed is made out of 6061 aluminum, and the dimensions are 600 mm x 480 mm. Three sets of bed feet have been designed with differing heights for simple swapping and adjustability of z-height. Standardized, fitted magnetic connections to the machine frame and 0.5 mm-tolerance square registration slots to the aluminum bed allow for constrained, stable positioning when locked into place. Finally, aluminum beams between the bed feet provide maximum rigidity to prevent deflection or motion during operation.
Shortest Bed Feet
Aluminum Bed
Pneumatic Extrusion System
Pneumatic Extrusion System
The pneumatic extrusion system incorporates an air pressure pump, solenoid valve, and syringe barrel to extrude bio-ink in a controlled manner during the operation. A pressure gauge and knob allow for simple tuning of the output pressure, which feeds directly into the solenoid valve. The solenoid valve opens and closes with M-codes, and allows the pressure to pass through the syringe to extrude the bio-ink onto the site of operation. The feed rate and pressure have been adjusted and measured to ensure optimal extrusion consistency is performed during the additive procedure.
Air Pressure Source
for Extrusion
Side View of Extrusion System with Solenoid Valve
Rat Model Fixtured Beneath Toolheads for Operation on Grape Lodged in Skull
Z Probing Tool
Z-Probing Tool
Z-Probing Tool
The Z-probing tool is a 3D printed component used to locate the precise z-coordinate of the test subject. Aluminum foil is an inexpensive, readily available, and extremely thin (.025 mm) conductive material that is flexible and can be suspended between the two posts of the design to make direct contact with the target site (the rabbit’s knee). When the milling tool is lowered into contact with this material, the connected z-probe sends a signal to the machine software to save this exact z-coordinate location with respect to the pre-defined origin.
X-Y Coordinate Finder
X-Y Coordinate Finder
The X-Y Coordinate Finder is a 3D printed part that connects with magnets to fit snugly over the tip of the milling tool. A laser pointer, attached from the bottom, serves as a guide for finding the X-Y location of the operation site. The laser can easily be removed from the coordinate finder, which then acts as a safety cap for the milling tool to prevent direct collision.
X-Y Coordinate Finder
Performance Results
Performance Results
The “jogging” and indexing of the toolheads is proven accurate to 0.001 mm, based on the minimum step size of the CNC machine and user-defined “center” crosshair position. Also, the magnetic toolhead mount has a dimensional repeatability within 0.05 mm and weight capacity of 950 g, confirmed by ten repetitions of attaching and detaching the head and running simple G-code commands, as well as loading an attached bag with weights until any deflection or slipping occurred. All components contacting the operating material are steam sterilization friendly. Successful testing and operation was performed nine times on sawbone and foam materials before authorization was achieved for testing on rabbits. Overall, smooth transitions between additive and subtractive G-code led to a total indexing, milling, and filling procedure time of 11 minutes from start to finish, nearly half the time of the Inkredible. Various toolpaths and G-codes were generated for testing the operation on differently sized defect holes. Diameters were specified to be 5 mm, 10 mm, and 25 mm with depths of 1.2 mm, 3 mm and 5 mm each. Ultimately, the drilled holes were measured on average to be 5.41 mm, 10.28 mm, and 25.39 mm in diameter respectively, which confirms that the milling procedure is accurate within 0.5 mm as desired. Furthermore, the extrusion procedure was performed with pluronic gel, similar to bio-ink, with the pressure tuned to about 102kPa as expected, and measured overflow of less than 0.1 mm. Thus, the bioprinter achieves all targeted deliverables and requirements, displaying successful proof of concept and performance.
media-monster-video410.2023-03-22_065028_0000.movSubtractive Process: Milling Cavity
output.MP4Additive Process: Extruding Bio-gel Into Cavity
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