Is Fused Filament Fabrication a Viable Fabrication Method for Bioabsorbable Devices?
Authors:   , Schachtner Jackie Theresia , Kurtz Steven M. 
Published: July 2021

Lower back pain impacts a majority of the world population at least once in their lifetime. The source of this pain is often due to degenerative changes in the lower spine, sometimes requiring surgical intervention in the form of lumbar spinal fusion. Surgical site infection (SSI) is a serious complication of spinal surgery, affecting as high as 8.5% of the patient population. If the SSI cannot be eradicated with intravenous antibiotic therapy, the next step is a second surgery, involving debridement of the wound and replacing the infected device. Additional surgery not only increases the cost imposed on the patient but also extends recovery time. In this study, an ultrasound triggered device for the dispersal of antibiotics, was developed as a potential solution. The device is constructed of a bioabsorbable polymer via fused filament fabrication (FFF). This device attaches to a standard 5.5 mm fusion rod and will degrade in vivo. Initially, a literature review was performed to determine the most appropriate polymer for this device. Poly-L-co-D,L-lactic acid (PLDLLA) 70/30 was chosen and a filament was fabricated. Gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) analysis were performed to determine the molecular weight and thermal properties of the filament. The filaments were found to be consistent in molecular weight and thermal properties (p = 0.348 and p = 0.487, respectively). Once analyzed, the filament was then used for FFF printing. Initially, 1cm3 cubes were printed for optimization of printing parameters such as print speed and layer height. Then, printing of the spinal clip was attempted. Slight modifications were made to the clip design and printing parameters to reach the final product. Dimensional accuracy was assessed using [mu]CT analysis. There was a difference between the thickness of the printed clip and the intended design (p = 0.029). All other dimensions were found to be similar. To assess the degradation, the clips were incubated at 37°C in PBS for a month and mass loss was measured at one-week time points. Additionally, raw pellets of PLDLLA 70/30 and the filament were degraded, and mass loss was assessed to evaluate how melting the material multiple times impacted the degradation properties. Degradation rate was found to be similar among the samples throughout the first three weeks of degradation however, the raw pellets were found to degrade at a slower rate by the final week (p = 0.039). Further research should focus on additional print optimization as well as determination of the device coating method. Currently, the procedure for device coating involves dipping the device in PLA to create a thin film, but this has proven to result in a coating that is too thick to rupture with ultrasound. The next step would be to formulate a 3D printed coating option to optimize the coating thickness. This study demonstrated a promising future for this device and the viability of not only FFF with PLDLLA but other bioabsorbable polymers, increasing the reach of personalized medicine.