Bioprinter

Problem: Few existing commercial devices to fabricate and manipulate liquid based inks with a high-degree of precision → researchers often forced to make their own devices for printing.

Goal: Design a facile platform for Direct Ink Writing
(DIW) a range of polymer solutions.

Solution: The device designed is a bioprinter with a
traditional Core-XY design capable of multi-material
printing of polymers and inks. Utilizing a positive displacement
system, it depresses a 10mL syringe to create 3D structures designed in software. A 2" luer-lock needle allows inks to be printed within a
carbomer gel which enables the creation of complex free-standing structures.

Initial Design

The initial design for the bioprinter utilized a preexisting Lulzbot 3D printer frame that I had been able to borrow from my school. By adapting the gantry system to accommodate an extrusion attachment, I could then program the printer to follow custom Gcode commands to extrude the material as I wanted.

The extruder relied on a stepper motor which drove a lead screw to depress the plunger of a 10mL syringe. Additional capabilities included a UV array on the bottom of the extruder as well as a heating block manufactured on a lathe that I had acquired for cheap on Ebay. The assembly
was then wired into the 3D printer’s mainboard, utilizing the PWM signal for the printer’s fans to control the intensity of the UV light and the integrated heating capabilities intended for the hotend to the extruder’s heating block.

Printing and Testing

The design was tested using Molasses with an approximate viscosity of 5,000-10,000. The ingredient was used as an analogue of the material intended to be extruded from the printer.

The printer successfully extruded the material along a pre-programmed path utilizing a 20 Ga needle with a 0.64mm inner diameter.

Limitations:

Back-pressure was found to inhibit the system’s ability tochange directions quickly and rapidly change extrusionrates
The elastic behavior of the 3D printed parts as well as thesyringe itself delayed response of extrusion to G-Codecommands
System was bulky and lacked rigidity due to limitations of 3D printer gantry and heavy weight ofassembly (stepper motor, linear rails, etc.

Performance

Despite the limitations, the implementation of the extruder onto the machine was smooth and quite successful.

The machine was able to print the polymer within a laponite (clay-based) gel shown to the left, overcoming the high viscosity of the solution.

Though wobble was present in the system, the machine was still capable of accurately printing designs, with precision of ±0.25 mm approximately.

Changes and Improvements

To address some of the limitations with the design, improving both accuracy, speed, and functionality, a new extruder was implemented. The updated extruder assembly focused on compactness, relying on a single linear rail and bearing, and condensing the height of the device. Additional improvements included:

6W UV array output compared to previous 0.72 W output from 5mm UV LEDs
Changed to pinion vs. belt-driven gears w/ approx. same ratio to prevent slippage, bulky belt-tensioning system
Exchangeable syringe carrier-heating block

Exchangeable Syringes

The exchangeable capabilities of the new extruder allowed additional multi-material functionality, making composite structures between multiple different polymers mid-print possible. The system used pogo pins to transfer power and signal to different syringe assemblies without the need for wiring to each individual syringe carrier like most multi-material printers do nowadays. This additional functionality made it possible to create composite structures composed of multiple different types of polymers mid-print.

Challenges

In the midst of testing and prototyping, a wire was shorted, bypassing fuses on the motherboard to damage critical components. As replacement was not an option, I turned toward alternative framework, utilizing an Ender 3 gantry that I had in my possession instead. There were, however, limitations with the design:

Single z-screw on the Ender 3 created sag with the heavy extruder attachment
Smaller build areaFigure

Updated Bioprinter

A new custom-designed bioprinter was designed to accommodate these changes and increase the functionality of the printer.

Changes:

Core-XY design allows for faster travel andmore rigid linear rail-based design
Custom magnetic holders on perimeter of theprinting area allow transfer of syringes andthus materials during printing
CNC-ed aluminum bed has custom mountingholes for adaptable work-holding
Custom Marlin-based configurations allow increased control over printing speeds, heating, power, bed-leveling, and other inputs and outputs not easily accessible on commercial printers
Updated gel vat has greater visibility and rigidity for printing

Final Design and Performance

The final design for the bioprinter utilizes a CoreXY gantry system supported by linear rails on the XY axis and linear rods on the Z. The system is powered by NEMA 17 steppers and GT2 belts, allowing rapid and controlled movement of the custom DIW extruder assembly.

The device is capable of printing complex 3Dstructures within a gel support bath, utilizing everything from PDMS, hydrogel, or even liquid crystal elastomer inks. The extruder is capable of in-situ curing with a 6W LED array as well as an active-heating system, allowing precise control over rheological properties of the target ink.

Additionally a multi-material syringe exchange system allows the changing of materials mid-print, endowing the machine with the ability to manufacture composite structures designed in software.

The device has a maximum working area of 250mm x 200mm x 150mm

Reflection and Moving Forward

The design was quite successful overall, utilizing a fairly small amount of off-the-shelf components combined with 3D printed parts to create a machine that successfully prints a wide range of materials with a high degree of accuracy.

For further improvements, I would like to focus on:

Increasing rigidity: Both in the extruder and the gantry system, I would like to decrease flex in the system to improve print quality
Additional Pressure-Based Extrusion: Pressure-based extrusion would allow the device to have more rapid control over when the device is printing and when it is not, decreasing stringing
More Powerful Extrusion System: Steel-enclosed syringes and a more rigid extruder would allow even more viscous inks to be used and make faster printing possible

Ultimately, the bioprinter provides a platform for highly customizable fabrication of polymer composites, enabling a new class of smart materials that can be manufactured on-site and tailored to the needs of the patient, device, or anything that might require custom polymer structures.