Optimisation and characterisation of nano-hydroxyapatite/polylactide composites using Fused Deposition Modelling technology

Abstract

In this study, polylactide/nanohydroxyapatite (PLA/nHA) composites were produced for fused deposition modelling (FDM), which is an additive manufacturing technology commonly used for prototyping and production applications. First, PLA/nHA composites (0.5%, 1%, 3%, 5 wt.%) were compounded using a twin-screw extruder, subsequently, these were shaped into filaments with a single-screw extruder. Thirdly, specimens for dynamic mechanical analysis (DMA) and tensile testing were FDM printed. Doehlert response surface methodology was applied to optimise the tensile properties of each formulation. A comparison of the mechanical properties of the printed tensile test specimens with injection moulded specimens showed a lower Young's modulus and ultimate strength and a higher storage modulus for the printed samples. Additionally, the same ultimate strength decreased with higher HA content. HA induced nucleation of PLA, but also a reduction of the degradation temperature, as shown by differential scanning calorimetry and thermogravimetric analysis respectively. Oscillatory rheological analysis showed the presence of a Newtonian plateau, followed by a shear thinning behaviour. The first HA addition resulted in a thickening effect, decreasing upon addition of HA, up to a thinning effect at 5 wt.%. In conclusion, this study proves successful printing of PLA/nHA nanocomposites using FDM, which might be promising e.g. for bone tissue engineering.