The John Charnley Award: An Accurate and Extremely Sensitive Method to Separate, Display, and Characterize Wear Debris Part 2: Metal and Ceramic Particles

Metal-on-metal and ceramic-on-ceramic bearings were introduced as alternatives to conventional polyethylene in hip arthroplasties to reduce wear. Characterization of wear particles has been particularly challenging due to the low amount and small size of wear particles. Current methods of analysis of such particles have shortcomings, including particle loss, clumping, and inaccurate morphologic and chemical characterization. We describe a method to recover and characterize metal and ceramic particles that (1) improves particle purification, separation, and display; (2) allows for precise particle shape characterization; (3) allows accurate chemical identification; and (4) minimizes particle loss. After enzymatic digestion, a single pass of ultracentrifugation cleaned and deposited particles onto silicon wafers or grids for imaging analysis. During centrifugation, particles were passed through multiple layers of denaturants and a metal-selective high-density layer that minimized protein and nucleic acid contamination. The protocol prevented aggregation, providing well-dispersed particles for chemical and morphologic analysis. We evaluated the efficacy and accuracy of this protocol by recovering gold nanobeads and metal and ceramic particles from joint simulator wear tests. The new protocol recovered particles ranging in size from nanometers to micrometers and enabled accurate morphologic and chemical characterization of individual particles. Both polyethylene and metal wear debris can be simultaneously analyzed from the same sample by combining a silicon wafer display protocol for polyethylene and the metal and ceramics silicon wafer display protocol. Accurate analysis of wear debris is essential in understanding the processes that produce debris and a key step in development of more durable and biocompatible implants.