Understanding of the role of the radical-generating ability of wear particles of the existing and new implant materials as well as application of efficient antioxidants is one of the necessary conditions for improvement of the results of joint replacements. Functioning of joint prostheses is accompanied by a continuous formation of wear particles and their accumulation in surrounding tissues. The impact of microroughnesses of joint prosthesis friction units may bring about chemical bond breakage and free-radical generation on a newly-formed wear surface. Wear particles of orthopedic alloys are capable to produce free radicals, and Co-Cr-Mo alloy particles are especially active. Free radicals generated by wear particles can cause oxidation and reduced wear resistance of polyethylene. Oxidised polyethylene particles stimulate the activity and release of bone-resorbing cytokines by human monocytes/macrophages. The ability of free radicals to cause damage to surrounding tissues and implant components makes it necessary to estimate comprehensively the radical-generating activity of wear particles of different orthopedic materials and develop the ways of its inhibition.Summary
Introduction
The intensification of free radical processes at total joint replacements is well known. Wear particle-induced inflammatory reaction and metal corrosion is associated with generation of the oxygen radicals. At the normal functioning of joint implants there is a natural deterioration and constant updating of their surfaces. In these conditions probably also formation of free radicals during tribochemical reactions. The radical-generating ability of the wear particles of orthopaedic alloys, alumina ceramics and antioxidant properties of various cured cements and UHMWPE were studied using the model reaction of cumene oxidation. Artificial wear particles of different alloys and ceramics were obtained using dry friction of a ball against a disk made of appropriate materials. Cement powders were obtained by grinding cement samples in a ceramic mortar. Wear particles of orthopaedic alloys were found to initiate cumene oxidation whereas ceramic particles were inert. It was revealed that cobalt-chromium-molybdenum particles were much more active than titanium-aluminum-vanadium and stainless steel particles. Different amounts of antioxidants (from 2.3 to 12 millimole/kg) were detected in cured cements which considerably exceeded their amounts in the initial liquid cement components. The content of antioxidants in cured ÑÌW-1 cement was 3-5 times more than that in Palacos P and Sulcem1 cements. The amount of anti-oxidants was considerably lower in UHMWPE than in the mentioned cements. The reactivity of combinations of different particles is determined by relative particles’ contributions, and such mixtures are able to demonstrate either antioxidative (alloy-cement mixture) or prooxidative (alloy-UHMWPE mixture) properties. In particular, cement particles suppressed cumene oxidation caused by cobalt alloy particles. Inhibition duration depends on the ratio between alloy and cement particles and on the content of antioxidants in cements. Polyeth-ylene particles were not able to inhibit cumene chain oxidation caused by cobalt alloy particles. Investigation of prooxidant and antioxidant behavior of the wear particles of orthopaedic materials provides better insight into their action on surrounding tissues and implant components. In particular, it is necessary to develop methods of preclinical testing that can simulate and estimate the action of radical intermediates generated in the course of tribochemical reactions on implant components.
