Damage in extrusion additive manufactured biomedical polymer: Effects of testing direction and environment during cyclic loading. (June 2021)

• Record Type: Journal Article
• Authors: Moetazedian, Amirpasha; Gleadall, Andrew; Mele, Elisa; Silberschmidt, Vadim V.
• Is Part Of: Journal of the mechanical behavior of biomedical materials. Volume 118(2021)
• Publication Date: 2021-06
• Subjects: Additive manufacturing -- Polylactide -- Damage -- Interface -- Submerged; Biomedical materials -- Periodicals; Biomedical materials -- Mechanical properties -- Periodicals; Biomedical materials; Biomedical materials -- Mechanical properties; Periodicals; Electronic journals; 610.28
• DOI: 10.1016/j.jmbbm.2021.104397
• Languages: English
• ISSNs: 1751-6161

Abstract

Abstract: Although biodegradable polymers were widely researched, this is the first study considering the effect of combined testing environments and cyclic loading on the most important aspect related to additive manufacturing: the interfacial bond between deposited layers. Its results give confidence in applicability of the material extrusion additive manufacturing technology for biomedical fields, by demonstrating that the interface behaves in a manner similar to that of the bulk-polymer material. To do this, especially designed tensile specimens were used to analyse the degradation of 3D-printed polymers subjected to constant-amplitude and incremental cyclic loads when tested in air at room temperature (control) and submerged at 37 °C (close to in-vivo conditions). The mechanical properties of the interface between extruded filaments were compared against the bulk material, i.e. along filaments. In both cases, cyclic loading caused only a negligible detrimental effect compared to non-cyclic loading (less than 10 % difference in ultimate tensile strength), demonstrating the suitability of using 3D-printed components in biomedical applications, usually exposed to cyclic loading. For cyclic tests with a constant loading amplitude, larger residual deformation (>100 % greater) and energy dissipation (>15 % greater) were found when testing submerged in solution at 37 °C as opposed to in laboratory conditions (air at room temperature), as used by many studies. This difference may be due to plasticisation effects of water and temperature. For cyclic tests with incrementally increasing loading amplitudes, the vast majority of energy dissipation happened in the last two cycles prior to failure, when the polymer approached the yield point. The results demonstrate the importance of using an appropriate methodology for biomedical applications; otherwise, mechanical properties may be overestimated. Graphical abstract: Image 1 Highlights: Combined environmental and cyclic loading factor studied for polylactide. Less than 10 % difference was found between cyclic and non-cyclic loading. Submerged tests at 37 °C plasticised PLA with 50 % reduction in strength. Submerged tests allowed higher energy-loss for constant-amplitude loading.