Estimation of shelf life of 3D-printed PLA scaffolds by accelerated weathering

Abstract

The widespread use of PLA, in many different applications, has raised the demand to understand the post-manufacturing structural changes due to degradation processes. In the context of medical devices, this type of investigation is particularly important to predict the period within which they can be used in surgical procedures without considerable risk of failure during implantation, i.e., their shelf life. This work aims to analyze the effects of accelerated weathering on the mechanical resistance of a poly(lactic acid) scaffold manufactured by Fused Filament Fabrication. Moreover, the shelf life of the scaffold was also estimated. Two accelerated weathering methodologies were applied. First, the samples were submitted to 25, 35, or 45 °C, according to ASTM F1980. Alternatively, the scaffolds were placed under controlled cycles of temperature, ultraviolet radiation, and humidity according to ASTM G154. The weathered samples were subjected to measurement of maximum torque strength, and the results were used to establish the functional failure of the PLA scaffold. Additionally, scanning electron microscopy analyses were performed to assess if the tests caused the formation of surface defects on the specimens. Considering the ASTM F1980 method, the failure occurred after 456 h exposure at 45 °C, and conversely, for ASTM G154, it occurred after 168 h; corresponding to 171 or 38 days in natural weathering, respectively. Therefore, a shelf life of 150 days was defined for the PLA scaffold, in addition to the preconditions of maintaining it away from sunlight radiation, at temperatures up to 25 °C and relative humidity up to 70%. Noticeable pores and cracks appeared only on the PLA scaffold subjected to the ASTM G154 test (336 h exposure). The methodology proposed in this study is regarded to be efficient to determine the scaffold’s shelf life.