Analysis on micro-milling of UHMWPE for the integration of radiopaque markers on the surface of TKA inlays

Aseptic loosening and abrasion of implants are significant challenges in knee arthroplasty. In particular, the wear of ultra-high molecular weight polyethylene (UHMWPE) inlays can lead to prosthesis failure. The early detection of wear is complicated by the low radiopacity of the material. A promising method for detecting wear is the integration of radiopaque markers into the implant surface. This work focuses on the micro-structuring of UHMWPE to incorporate such markers using micro-milling processes. Experimental milling experiments were carried out with different tool diameters, whereby various milling strategies, cutting parameters, and approach strategies were analyzed. A central challenge was the formation of burrs, which makes subsequent marker insertion difficult. The influence of the process parameters on burr formation was investigated by systematically varying the process control variables. The results show that a tool diameter of 0.6 mm, a number of cutting edges of 2, a cutting speed of 25–30 m/min and a feed per tooth of 0.0125–0.02 mm led to a significant reduction in burr formation. In addition, the transferability of the determined process control variables to free-form surfaces was investigated. For this purpose, kinematic process parameters were determined by dexel-based material removal simulation. The results show a low reproducibility of burr formation due to inconstant cutting conditions (depth of cut and width of cut).