Wear studies on prosthetic materials using the pin-on-disc machine

Area of Science:

• Biomaterials Science
• Tribology
• Orthopedic Engineering

Background:

• Ultra-high molecular weight polyethylene (UHMWPE) and cobalt-chromium-molybdenum (CoCrMo) alloys are common in joint replacements.
• Understanding their tribological behavior, specifically wear, is crucial for implant longevity.

Purpose of the Study:

• To investigate the wear characteristics of UHMWPE articulating against CoCrMo alloy.
• To evaluate the influence of various factors, including lubricant type, pin rotation, load, and velocity, on wear performance.

Main Methods:

• Pin-on-disc experiments were conducted for 1000 hours.
• Wear was assessed using volumetric and gravimetric methods at 100-hour intervals.
• Tested lubricants included bovine serum; pin rotation (stationary vs. rotating) was varied.

Main Results:

• Bovine serum demonstrated superior performance as a lubricant.
• Rotating the pin resulted in more favorable polyethylene surface characteristics compared to a stationary pin.
• Wear rate showed a slight increase with higher loads, potentially due to creep, but was insensitive to relative surface velocity.
• Disc storage environment did not impact wear.
• Dynamic coefficient of friction increased over time.

Conclusions:

• Bovine serum is recommended as a suitable lubricant for UHMWPE/CoCrMo articulation.
• Pin rotation is beneficial for improving UHMWPE surface integrity during articulation.
• Wear is primarily influenced by load and lubricant choice, with minimal impact from speed or storage conditions.