Evaluation of different methods to eliminate adherent endotoxin of polyethylene wear particles

Abstract

Wear particles have to be cleaned from any substances, which could eventually lead to confounding effects in studies concerning the in vitro or in vivo biological activity of wear debris. Several observations have demonstrated that lipopolysaccharide (LPS) as a component of the outer membrane of gramnegative bacteria can modulate the cell response to wear debris.There are numerous methods described in the literature for the removal of LPS. But there is an exception for polyethylene particles, they cannot be treated with radiation and heating processes.There remain four possible methods: Cleaning the particles with sodium hydroxide or with acetic acid, washing them with ethanol or via using a demanding ultracentrifugation procedure. Thus we decided to compare the different methods in consideration of the remaining LPS level and their effects on the particle numbers and morphology.During the study several problems regarding these methods appeared: Either they could not remove the LPS below the demanded detection level, or the methods had influence on amount and morphology of the particles.Due to these findings the authors developed a new method based on ultracentrifugation. With this method the LPS could be removed as required, amount and morphology of the particles were not affected.