Enhancing polymeric implant component visibility with integrated radiopaque markers

Abstract text (incl. figure legends and references)

Introduction

Due to its low X-Ray attenuation, UHMWPE (Ultra-High Molecular Weight Polyethylene) has limited visibility in radiographs, making it difficult to monitor in-vivo. To tackle this limitation, this project aims to incorporate radiopaque markers into the polymeric components of implants to enable clinical monitoring during routine radiographs.

Methods

UHMWPE was chosen as the test material and was processed in blocks measuring 100 x 75 x 13 mm. A 5-axis milling machine (Ultrasonic10) and three solid carbide end mills with nominal diameters of 0.4, 0.6, 0.8 mm were used to model the process. Burr formation was detected using a reflecting light microscope (Keyence VHX-5000). Radiopaque composites based on high-density polyethylene (HDPE 76303) and 10, 20 and 30 wt% BaSO₄ were chosen for the markers and mixed using a twin-screw extruder. The markers were filled into the microstructures using a pellet extruder. Digital X-Ray radiographs were taken to evaluate the radiopacity.

Results

20 wt% BaSO₄ was sufficient to create visible contrast. Microstructures with d > 0.4 mm had superior visibility and fill quality. With increasing cutter diameter the proportion of burr-free or acceptable samples increased. A spindle speed between 5,000 rpm and 10,000 rpm was suitable for microstructuring UHMWPE.

Conclusion

Radiographically detectable markers were successfully integrated into the UHMWPE blocks. Some unfilled voids were detectable which were likely a result of burr occlusion. Burr formation was found to be strongly dependent on the workpiece/tool pairing thus further optimisation of parameters is necessary.

References

Pegg EC, Gill HS, Zaribaf FP. Characterisation of the physical, chemical and mechanical properties of a radiopaque polyethylene. J Biomater Appl. 2020 Aug;35(2):215-223. doi: 10.1177/0885328220922809. Epub 2020 May 16. PMID: 32419587.