A comprehensive study on the biodegradability, biocompatibility, and antibacterial properties of additively manufactured PLA-ZnO nanocomposites

The addition of zinc oxide (ZnO) nanofillers to 3D printable poly(lactic acid) (PLA) filaments for material extrusion (MEX) additive manufacturing (fused filament fabrication, FFF, a.k.a. fused deposition modelling, FDM) has the potential to enable the fabrication of biomedical devices with embedded antibacterial functionality. This work investigates the biological properties, mainly the biodegradability, antibacterial activity, and cytotoxicity of 3D printed PLA-ZnO nanocomposites containing between 1 wt% to 5 wt% of either untreated or silane-treated filler. This study demonstrated that the concentration and surface properties of the filler control the matrix degradation rate, which directly influences the release rate of ZnO and Zn2+, which in turn governs the antibacterial properties of the nanocomposites. All nanocomposites showed excellent antibacterial properties (> 99% reduction in bacteria) against both gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) strains. Potential cytotoxic effects against human immune THP-1 cells were only evident at the highest filler loading (5 wt%), whereas nanocomposites with < 5 wt% filler loading were non-cytotoxic after 7 days of exposure. The 3D printed PLA-ZnO nanocomposites produced in this study show potential for use in clinical settings, with nanocomposites having filler loadings of < 2 wt% being the most appropriate candidates due to their excellent antibacterial properties while showing comparable biocompatibility to pristine PLA.