Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough, LE11 3TU, UK.
Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough, LE11 3TU, UK.
J Mech Behav Biomed Mater. 2021 Jun;118:104397. doi: 10.1016/j.jmbbm.2021.104397. Epub 2021 Feb 20.
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.
尽管可生物降解聚合物已得到广泛研究，但这是首次研究综合测试环境和循环载荷对增材制造中最重要的方面——沉积层之间的界面结合的影响。其结果使人们对材料挤出增材制造技术在生物医学领域的适用性充满信心，证明了界面的行为与本体聚合物材料相似。为此，专门设计了拉伸试样，以分析在室温下的空气（对照）和 37°C 下的浸没（接近体内条件）中进行恒幅和递增循环载荷测试时，3D 打印聚合物的降解情况。挤出丝之间的界面机械性能与本体材料（即丝材）进行了比较。在这两种情况下，与非循环载荷相比，循环载荷仅产生可忽略的有害影响（极限拉伸强度差异小于 10％），这表明在生物医学应用中使用 3D 打印组件是合适的，这些组件通常会受到循环载荷的影响。对于恒幅循环测试，与在许多研究中使用的实验室条件（室温下的空气）相比，在 37°C 的溶液中进行测试时，残余变形（大 100％以上）和能量耗散（大 15％以上）更大。这种差异可能是由于水和温度的塑化作用所致。对于递增加载幅值的循环测试，在聚合物接近屈服点之前的最后两个循环中，绝大多数能量耗散发生。结果表明，对于生物医学应用，使用适当的方法非常重要；否则，机械性能可能会被高估。
