Mechanical performance of 3D printed polylactide during degradation

Although widely-used biodegradable polymers have been extensively studied for conventional manufacturing processes, this is the first study considering the effect of interfacial bonds between extruded filaments – the most important aspect related to additive manufacturing – on degradation at 37 °C. Its results improve the confidence in the material extrusion additive manufacturing process and negate one of the crucial unknown factors for bioresorbable products, by demonstrating that the interface degrades in a similar manner to the bulk polymer material. To do this, specially designed micro-tensile specimens were developed to analyse the degradation of 3D-printed parts for the first time at 37 °C and accelerated temperatures. The mechanical properties of the interface between extruded filaments (Z specimen) were compared against the control, i.e. along filaments (F specimen), under medically relevant testing conditions (submerged at 37 °C). Monitoring the degradation of tensile strength showed that both specimen types behaved similarly, exhibiting an initial delay followed by a reduction in properties. Comparison of thermal and chemical properties revealed that during the early stage of degradation, crystallinity was the dominating factor, whilst at later stages, mechanical properties were mainly defined by the molecular weight and autocatalytic degradation. The findings suggest that understanding developed in the long-standing field of polymer degradation can be applied to additive-manufactured medical devices, which unavoidably contain interlayer interfaces.