Shape and size of virgin ultrahigh molecular weight GUR 4150 HP polyethylene powder.

Sizes and shapes of micron- and submicron-sized structures in four lots of virgin GUR 4150 HP ultrahigh molecular weight polyethylene powder were determined by using low-voltage scanning electron microscopy and image analysis. One thousand two hundred micron-sized virgin powder particles and 1200 of their constituent submicron-sized structures were analyzed. The mean maximum diameter of the micron-sized particles was 81.3 microns, and that of the submicron-sized particles was 0.82 micron. Particle shapes, as determined by the aspect ratio (maximum diameter divided by minimum diameter), were remarkably consistent from lot to lot and between micron- and submicron-sized particles (1.55 versus 1.53, respectively). Significant lot to lot variability was observed in the sizes of the micron-sized particles, and the size distribution of the submicron-sized particles closely follows the size distribution of the submicron-sized particles observed in tissue retrievals. This variability leads to questions about variability in polyethylene quality and in vivo wear performance. Size similarity between the submicron-sized particles retrieved from tissues and that observed in virgin powder supports the hypothesis that polyethylene debris has two origins: particles released from structures retained from the virgin powder, and particles generated de novo by friction and wear.