Highly crosslinked vs conventional polyethylene particles: relative in vivo inflammatory response.

Crosslinked polyethylenes have been introduced to reduce wear and osteolysis. The osteolysis rate depends on many factors including the biologic activity of the wear particles. This study examines the relative inflammatory potential of highly crosslinked and non-crosslinked polyethylene particles. Polyethylene particles were crosslinked and characterized. Dose-response curves were generated for endotoxin-positive and endotoxin-negative particles at each degree of cross-linking using an in vivo model. The 10-MRad crosslinked polyethylene was more inflammatory than an identical dose (25 mg/mL) of non-crosslinked polyethylene (P = .05). Endotoxin increased the inflammatory response to crosslinked and non-crosslinked polyethylene in a similar fashion. These data suggest that the improved wear characteristics of highly crosslinked polyethylenes may be offset somewhat by the modestly increased inflammatory profile of the highly crosslinked compared with non-crosslinked particles.

Highly crosslinked vs conventional polyethylene particles--an in vitro comparison of biologic activities.

Highly cross-linked polyethylenes (HXPEs) have been introduced to reduce wear after hip arthroplasty. The improved wear characteristics of HXPEs are well documented, but the relative biologic activity of HXPE and conventional polyethylene (CPE) particles remains unclear. Longevity (Zimmer, Warsaw, Ind; HXPE) and GUR 1050 (Zimmer; CPE) particles were isolated and characterized from a hip simulator and their in vitro inflammatory responses (tissue necrosis factor *, interleukin 1*, and vascular endothelial growth factor levels) were compared using macrophages. The average diameter of Longevity particles (0.111 microm) was smaller than CPE particles (0.196 microm), and both were predominantly round (granular appearance). The inflammatory response to HXPE and CPE was concentration-dependent. No statistically significant differences were noted at low (0.1 surface area ratio [SAR]) and intermediate (0.75 SAR) doses. At the highest dose tested (2.5 SAR), HXPE was significantly more inflammatory than CPE based on relative tissue necrosis factor alpha and vascular endothelial growth factor secretion levels. Further study is needed to determine if similar findings would be noted in vivo over a broad concentration range.

Production of cloned cattle from in vitro systems.

The pregnancy initiation and maintenance rates of nuclear transfer embryos produced from several bovine cell types were measured to determine which cell types produced healthy calves and had growth characteristics that would allow for genetic manipulation. Considerable variability between cell types from one animal and the same cell type from different animals was observed. In general, cultured fetal cells performed better with respect to pregnancy initiation and calving than adult cells with the exception of cumulous cells, which produced the highest overall pregnancy and calving rates. The cell type that combined relatively high pregnancy initiation and calving rates with growth characteristics that allowed for extended proliferation in culture were fetal genital ridge (GR) cells. Cultured GR cells used in nuclear transfer and embryo transfer initiated pregnancies in 40% of recipient heifers (197), and of all recipients that received nuclear transfer embryos, 9% produced live calves. Cultured GR cells doubled as many as 85 times overall and up to 75 times after dilution to single-cell culture. A comparison between transfected and nontransfected cells showed that transfected cells had lower pregnancy initiation (22% versus 32%) and calving (3.4% versus 8.9%) rates.