Manufacturing of microcavities by milling for X-ray identification of orthopedic implants

Due to its low X-ray attenuation, Ultra-high molecular weight polyethylene (UHMWPE) has limited visibility in radiographic images, making it difficult to monitor in-vivo. In this paper, a method is represented to address this limitation by integrating radiopaque markers into UHMWPE implant components, facilitating their identification in radiographs. For this purpose, micro-cavities are inserted into UHMWPE blocks by micro-milling. Due to the increasing individualisation of implants, a manufacturing process that is adaptable was selected for this purpose. If the idea of a patientspecific implant that is manufactured in the shortest possible time is taken as a starting point, the milling process provides promising opportunities. The entire production of the implant and the insertion of the microstructures is possible in a cost- and time-efficient form on a single machine. The primary challenge encountered was the formation burrs during the machining process. Milling tools with a diameter between 0.4 mm and 0.8 mm were investigated under variation of the process parameters spindle speed, feed rate and depth of cut. Based on the appearance and height of the burr, suitable parameters were found and links between burr-free cavities and process parameters were identified. The machined cavities were subsequently filled with a radiopaque composite material comprising of high density polyethylene (HDPE) and (10, 20, 30 wt. %) BaSO4 using a pellet extruder. By employing various analogue components, this method demonstrated improved visibility of individual structures and patterns in X-ray images.