I assembled and assayed a novel composite 3D printer filement that is temperature-sensitive, variable density, biodegradable, and bioactive for use in patient- specific bone reconstructive implants. Showed successful control of physical properties with adjustment of printing temperature.
Current implants are restricted in the patient specificity they can achieve. Usually injection molded or CNC machined, these parts cannot be adjusted on a patient-by-patient scale and have monolithic designs. This is important in large bone defect correction and in patients with osteoporosis, who are at greater risk for bone stress shielding from implants that are too stiff.
My research set out to test a solution to these problems that combines three factors. The first, a structural polymer, in this case biodegradable, to act as a scaffold for bone growth. Second, a bioactive agent, hydroxyapatite, to encourage bony ingrowth. And most importantly, a Chemical Foaming Agent sensitive to changes in temperature. This foaming agent allows the filament's physical properties to be tuned during the 3D printing process. Furthering the patient-specificity achievable.
For my research, I used a solvent-based method for creating the composite filament. I first dissolved the PLA filament in dichloromethane, before mixing in the hydroxyapatite and foaming agent to produce a slurry. I dried this slurry thoroughly before shredding and extruding it into usable filament.
With limited filament extrusion devices within my price range, I decided to build a filament extruder from a kit. However, this kit did not include a method of maintaining filament diameter. I designed and built an arduino-based automatic spool winder which created consistent filament.
After filament extrusion, I printed the test filament at varying temperatures to assay the foaming response. I measured material properties such as desnsity and modulus of elasticity to determine the effectiveness of the foaming agent. Successful control of foaming was determined, as shown in the image to the right. This image shows the same blend of filament printed above (left) and below (right) the foaming temperature
This test piece showcases the effectiveness of the composite material. Both macro and micro structure control can be observed, due to the utility of the 3D printer in controling the macrostructure and the filament foaming controlling microstructure. Solid outer rings can be observed, with a foamed and patterned inner core. This closely imitates bone and provides excellent surfaces for bony ingrowth.