Initial Cadaver Implantation Strength and Polymer BioCompatibility of a Fused Filament Fabricated Osseointegration Screw for Transhumeral Amputation Prosthetics

Presented here are the initial biocompatibility and implant strength results of our previously developed thermoplastic Fused Filament Fabrication osseointegration screw for transhumeral amputations. Testing performed included three-point bending and torsion testing, 48-hour live-dead cytotoxicity assay with osteo cells, and a 36-day polymer incubation study in a phosphate buffer saline solution (PBS).

The mechanical testing was used to demonstrate the change in mechanical performance when going from a simulated to cadaver bone environment. The results show that there is minimal change in torsion values when going from a simulated steel to cadaver environment and a maximum bending force decrease of 12.29% and maximum displacement increase of 43.28% when going from the simulated steel to cadaver environment.

The 48-hour cytotoxicity assays showed that the average control medium and test medium samples had little difference in live and dead cell counts, with similar error bars. Imaging results showed no change in living cells when comparing the cells placed in either the control or test mediums.

The PBS incubation testing showed that, at up to 192 hours, there was no change in optical density, indicating that, for the cytotoxicity testing, there were no additional substances released from the polymer. The pH level also stayed the same after 864 hours of incubation, demonstrating that the polymer does not affect the solution's acidity level. However, at 864 hours of incubation, there are some changes in optical density. This change in optical density is caused by hydrolysis and resulted in a small mass loss of 6.67 mg, or 0.415% of overall mass.