Interfacial fracture of 3D-printed bioresorbable polymers

A micro specimen for tensile testing was designed with two primary aims: (i) to characterise interface fracture behaviour between fused 3D-printed polymer filaments; and (ii) to minimise material use of high-cost medical-grade polymer since a high number of specimens are required for time-series studies (e.g. polymer degradation). Polylactide specimens were fabricated on an extrusion 3D-printer as a single-filament-wide wall. The widths of filaments were set individually, with a custom machine-control code, to achieve a higher width in the grip sections of specimens and a narrower width in their gauge section. On average, the interface between filaments was 114 µm narrower than the widest point of the filaments. Each specimen was tested in the build direction to determine the interfacial strength between 3D-printed layers. Optical microscopy was employed to characterise geometry of specimens and fracture surfaces. Samples fractured in the gauge section and the fracture surface demonstrated brittle characteristics. The specimens utilised an order of magnitude less material than ASTM D638 samples, whilst maintaining repeatability for tensile strength similar to that in other studies. The average strength was 49.4 MPa, which is comparable to data in the literature. Further optimisation of the specimen design and 3D printing strategy could realise greater reductions in material use.