The effect of geometry on mechanical properties of biodegradable polylactic-acid tensile-test specimens by material extrusion

Additive manufactured biomedical devices have been widely used in the biomedical fields due to the development of biomaterials and manufacturing techniques. Biodegradable Polylactic Acid-based polymers are the most common material that can be manufactured using material extrusion, one of the most widely known additive manufacturing methods. However, medical grade polymers are too expensive for degradation studies with common tensile specimens. Therefore, this paper aims to reduce the volume of the material used for manufacturing tensile specimen by introducing a new tensile specimen, Micro-X tensile specimen, developed for steel. Young’s Modulus and Ultimate Tensile Strength of micro-X tensile specimens were compared with the ASTM D1708 standard specimens. The experimental results showed that there is no significant difference in terms of mechanical properties. Furthermore, the micro-X tensile specimen was reduced the volume and as well as the cost by approximately 91% in comparison to ASTM D1708 standard tensile specimen

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