3D printing polymer - ceramic composites for orbital floor reconstruction

The delicate structure of the orbital floor makes it prone to fractures. Implants are often used to repair fractures, -which are tailored to the estimated defect size and shape by surgeons. Deficiencies in shaping or positioning may require additional surgeries to correct or remove the implant, as can infections and other postoperative complications. Additive Manufacturing (AM) processes can produce complex geometries, and therefore present an opportunity to address some of these deficiencies. However, this requires knowledge of suitable materials and of their behaviour in the chosen AM process; this is the focus of this thesis. The processability of polymer-ceramic composites with antimicrobial properties were investigated on laser sintering (LS) and high speed sintering (HSS) as they can produce parts with a high accuracy and a rough surface finish to encourage osseointegration. Polyamide 12 (PA12) was chosen as it is an ideal polymer for these processes, hydroxyapatite (HA), due to its osteoconductive properties and zinc (Zn), which is known to possess antimicrobial properties. The processability of varying compositions of HA:PA12 and 2:98 wt% Zn:PA12 composites were initially investigated separately. It was found that the upper limit for processing HA:PA12 differed (20:80 for LS and 40:60 for HSS) while the 2:98 wt% Zn:PA12 composition was successfully processed on both LS and HSS. Analysis proved the presence of well distributed additives after processing, indicating that samples are likely to exhibit osteoconductive and antimicrobial properties. The addition of the additives increased the porosity and the specific surface area, more so for HSS than LS samples. However, there was a decrease in the tensile and flexural properties of the samples with the addition of the additives. Overall, the LS samples had higher mechanical properties than HSS samples, nonetheless, both processes produced samples with similar flexibility to the natural orbital floor bone1, 2 with potentially enough strength for orbital reconstruction applications. Cell viability tests showed that all the HA:PA12 samples were biocompatible and the 2:98 wt% Zn:PA12 samples proved to be effective against Staphylococcus aureus. However, when the materials were combined (Zn:HA:PA12) both the LS and HSS samples that contained Zn, showed cytotoxic effects against MG 63 cells. In conclusion, both processes have shown a potential in the fabrication of polymer-ceramic composites with antimicrobials for orbital floor reconstruction application however further work is required to investigate whether there is an optimal Zn:HA:PA12 ratio that has a bacteriostatic effect and is biocompatible.