Introduction: UHMWPE wear particles induce osteolysis and loosening of total joint replacements. Much effort has been directed at reducing the wear volume of UHMWPE, such as crosslinking treatments [1]. Recently, interest in UHMWPE with vitamin E (VE) has increased due to its improved wear resistance in knee prostheses [2], as well as improved mechanical properties. The aim of this study was to culture human peripheral blood mononuclear cells (PBMNCs) with known volumes of clinically relevant wear debris from UHMWPE with and without VE in order to quantify and compare their respective biological activities.

Methods: For UHMWPE with VE, GUR1050 UHMWPE powder was mixed with VE at 0.3% (w/w) and 3% (w/w) using a screw cone mixer. The wear rates were evaluated using a six-station multidirectional pin on plate wear simulator against a smooth CoCr plate (Ra 0.01–0.03 micrometres), in 25% bovine serum, under a load of 160N and a frequency of 1 Hz. Endotoxin-free clinically relevant wear debris was generated aseptically for cell culture studies, using a single-station multidirectional pin on plate wear rig housed in a class II safety cabinet. PBMNCs were isolated from blood collected from three healthy donors then cultured with debris at particle volume (μm3) to cell number ratios of 100:1 using the agarose gel technique [3]. Cells without particles were used as the negative control, and LPS at 200 ng/ml was the positive control. Cell viability was assessed by ATP-Lite assay, and TNF-alpha, interleukin (IL)-1beta, IL-6 and IL-8 were measured by ELISA at 12 and 24 h.

Results: The 3% VE UHMWPE was found to have a higher wear rate than both the Virgin and the 0.3% VE UHMWPE, although there were no significant differences. Particle size and volume distributions were similar for all materials, with the mode of the frequency distributions being in the 0.1–1 micron size range. Cell viability was not adversely affected by any of the treatments. Cells cultured with virgin UHMWPE debris secreted significantly higher quantities (P< 0.05) of TNF-alpha compared to debris from both the 0.3% and the 3% VE UHMWPE, which released comparable levels of TNF-alpha to the cell only control group. The results for the other cytokines, IL-1beta, IL-6 and IL-8, and for the two additional donors showed similar trends as the results for TNF-alpha.

Discussion: The biological response to wear particles is strongly influenced by particle size and volume [3]. Cells cultured with wear debris of UHMWPE containing VE released very low levels of cytokines in comparison with virgin UHMWPE, even there were no significant differences in particle size. Differences in the chemical composition of the particles or different rates of protein adsorption may explain these differences. VE has anti-inflammatory properties, which may act by free radical scavenging. VE has been shown to reduce production of reactive oxygen species and pro-inflammatory cytokines such as TNF-alpha and IL-1beta from monocytes [4]. The anti-inflammatory effects of UHMWPE particles containing VE are currently being investigated.

Introduction: Nanometre sized UHMWPE particles have recently been isolated from periprosthetic tissues and hip simulator lubricants [1,2]. The biological response to UHMWPE particles of 0.1 μm and above has been well characterised, with particles in the 0.1–1.0 μm size range having the highest biological activity [3]. The purpose of the study was to determine the biological activity of nanometre-sized particles in terms of osteolytic cytokine release from primary human monocytes.

Methods: Monocytes were isolated from peripheral blood from 5 healthy donors by density gradient centrifugation over Lymphoprep. Cells were cultured using the agarose gel technique [3] at particle volume (μm3):cell number ratios of 10:1 and 100:1. The particles used were:

1 Polystyrene FITC-conjugated FluoSpheres (FS; Invitrogen) in 20 nm, 40 nm, 0.2 μm and 1.0 μm sizes.

All particles were tested for the presence of endotoxin prior to culture with cells. Cells without particles were used as a negative control and 200 ng/ml LPS was used as a positive control. Cell viability was assessed using the ATP Lite assay (Perkin Elmer) and ELISA was used to determine TNF-alpha, IL-1beta, IL-6 and IL-8 release at 3, 6, 12 and 24 h.

Results: FluoSpheres and CD had no effect on cell viability at 10 or 100:1. Clinically relevant UHMWPE particles had no effect on cell viability at 10:1, however, at 100:1 significant differences (P< 0.05) were seen at 3, 12 and 24 h for Donors 1 and 3. The 40 nm, 0.2μm and 1.0 μm FS caused significant elevation of TNF-α release at the 12 and 24 h time points at 100:1. There was no significant increase in TNF-α release for the 20 nm FS (3/5 donors). Particle volume and particle size showed correlation with cellular response, with the 20 nm FS showing the lowest biological activity. Clinically relevant UHMWPE particles and nanometre sized CD produced significantly higher quantities of TNF-alpha at 100:1. Release of interleukins IL-1beta, IL-6 and IL-8 followed a similar trend to TNF-alpha release.

Discussion: This study found that all nanometre-sized particles had the potential to provoke inflammatory cytokine release from macrophages. Particle volume and particle size played critical roles in initiating cellular responses. There was a lower particle size limit, with the 20 nm FS showing the lowest activity. Nanometre-sized polyethylene particles (CD) caused elevated TNF-α release, and since it has been shown that nanometre-sized UHMWPE particles are produced in large numbers in vivo [2], the relative contribution of these particles to osteolysis should be considered. The biological response to nanometre-sized clinically relevant UHMWPE particles is currently under investigation.