Extrusion of PEEK struts: predicting material behavior on the small scale for AM of stent grafts

Abstract Additive Manufacturing (AM) has become a crucial technology in many industries. Its inherent design flexibility makes it particularly interesting for medical applications, where implants are typically customized for each patient. Since AM processes tend to be fully automated, they also offer a significant time advantage over conventional manufacturing, which often requires manual labor. However, AM has a downside: due to the layer-by-layer approach, parts exhibit anisotropic behavior depending on their build orientation. While this can be partially avoided by carefully redesigning parts or the process itself, it won’t work for certain applications. As a rule of thumb, the smaller a part gets, the more prone it becomes to mechanical failure due to this anisotropy, as the failure of individual elements (i.e. lines and/or layers) cannot be absorbed by the relatively small number of remaining elements. This is especially critical for stents and stent grafts, which combine small cross-sections with high mechanical requirements and need to remain in the human body for several years. To be able to better predict small-scale mechanics this work intends to find a reliable way of testing struts manufactured by material extrusion (MEX) of polyether-ether-ketone (PEEK), a polymer regularly used for implants. To determine the relationship between process parameters and mechanical properties, tensile testing and nano-CT imaging were carried out. Additionally, simplified thermal simulation and differential scanning calorimetry (DSC) measurements provide insight into the thermal profile during the process. The results reveal the structure–property relationship and may be helpful for predicting part quality in the future.