Isolation and characterization of UHMWPE wear particles down to ten nanometers in size from in vitro hip and knee joint simulators

Abstract

There is currently considerable interest in the wear debris and osteolytic potential of different types of bearings used in total joint replacements. The biological activity of the wear debris is dependent on the size and volume of the particles produced. Wear volume also plays an important role in the functional biological activity of a joint replacement. In vitro studies have shown that crosslinking of ultra high molecular weight polyethylene (UHMWPE) acetabular cups and tibial trays produces a reduction in wear volume, and crosslinking has now been introduced clinically for both types of prostheses. Previous studies have identified both micron and submicron-sized polyethylene wear particles. The aim of this study was to characterize the wear and wear particles generated from moderately crosslinked GUR 1,020 GVF UHMWPE acetabular cups and tibial trays in hip and knee joint wear simulators down to 10 nanometers in size. The wear rates of the two prosthesis types were very similar at 25.6 +/- 5.3 mm(3) per million cycles for the hip prostheses and 22.75 +/- 5.95 mm(3) per million cycles for the knee prostheses. Nanometer-sized wear particles were isolated and characterized from both hip and knee simulator lubricants for the first time. Significantly higher numbers (p < 0.05) of particles in the nanometer (<0.1 microm) size range were produced by the hip prostheses compared to the knee prostheses. The knee prostheses produced larger particles, with the mode of particle size in the 0.1-1.0 microm size range, compared to <0.1 microm size range for the hip prostheses. In addition, the knee prostheses produced a greater volumetric concentration of wear particles in the 1.0-10 microm size range, and consequently lower specific biological activity and functional biological activity indices. These results indicated that the knee prostheses had a lower osteolytic potential compared to the hip prostheses.

Phagocytosis of Simulated Nano-wear Debris by Osteoblasts

“…With the introduction of improved wear resistant materials (like highly cross-linked UHMWPE) to fabricate total joint components, there has been a decrease in wear debris volume, but has led to increased generation of nano-debris 32 . Although a well corroborated mechanism as to how cells respond to nano-wear-debris is presently elusive, even these smaller nano-size particles (like their larger counterparts) are phagocytosed by cells prior to eliciting a biological response.…”

Cross-linked Compared with Historical Polyethylene in THA: An 8-year Clinical Study

“…Although strong correlations between wear rates and osteolysis were reported in a literature review [11], such findings could be expected, as smaller particle volumes are released into the periprosthetic tissue triggering less cytotoxic response. However, a cell culture study [38] suggested wear particles of cross-linked PE can be smaller and shaped differently from those of alternative PE and thus may have a higher cytotoxicity (functional osteolytic potential). As a result, cross-linked PE may produce equal or higher levels of osteolysis despite reduced wear volumes.…”

The John Charnley Award: An Accurate and Sensitive Method to Separate, Display, and Characterize Wear Debris: Part 1: Polyethylene Particles

“…The average size of crosslinked PE is reported to be smaller than conventional PE [40,47]. Combined with the reduced volume, this poses new challenges in purification, isolation, and characterization of nanometer-sized particles because even a small loss of particles through the digestion process or overestimation of size due to artifactual clumping can greatly skew the size distribution and morphologic analysis.…”