Polyaniline as potential radical scavenger for ultra-high molecular weight polyethylene Frédéric Addiego *, Iulia Mihai, David Marti, Kui Wang, Valérie Toniazzo, David Ruch Public Research Centre Henri Tudor, Advanced Materials and Structures Department, 5 Rue Bommel, ZAE Robert Steichen, L-4940 Hautcharage, Luxembourg A R T I C L E I N F O Article history: Received 17 June 2014 Received in revised form 27 August 2014 Accepted 15 October 2014 Available online xxx Keywords: Biomaterials Composites Polyaniline Reinforcement UV–vis spectroscopy A B S T R A C T Novel ultra-high molecular weight polyethylene (UHMWPE) composites were processed by micro- extrusion with polyaniline (PANI) as potential reinforcing and radical scavenging agent and with lauryl gallate (LG) as coupling agent. By means of UV–vis spectroscopy, it was found that the presence of PANI reduced at maximum by 27.3% the concentration in free radicals of a 2,2-dimethyl-1-picrylhydrazyl (DPPH) solution in which was immersed the composite. This result was obtained with the UHMWPE/LG/ PANI weight composition 89/1/10, which also demonstrated to retain the viscoelastic and tensile properties of neat UHMWPE. The dispersion of PANI micro-particles within the UHMWPE matrix may be an alternative to the stabilization step of crosslinked UHMWPE used in joint prosthesis. ã 2014 Elsevier B.V. All rights reserved. 1. Introduction Crosslinked ultra-high molecular weight polyethylene (UHMWPE) has replaced conventional UHMWPE in total hip and knee arthroplasty due to a higher wear resistance [1]. In particular, during the joint motion the surface deformation of the crosslinked UHMWPE network was significantly reduced compared to the reference non-crosslinked network, resulting in a less fibrils induced by large plastic deformation, and hence, less release of debris [1,2]. However, crosslinking that is generally conducted by gamma-irradiation has two major issues: (i) a reduced molecular mobility resulting in a lower toughness and fatigue resistance compared to conventional UHMWPE and (ii) a low chemical stability due to the presence of excess free-radicals and trapped free-radicals in the crystalline domains that react with oxygen and induce oxidation [1,3]. Gamma-sterilization of UHMWPE also led to the presence of excess free-radicals [4]. To quench free-radicals, different treatments have been developed: (i) annealing below the melting temperature after crosslinking [1], (ii) melting after crosslinking [1,5], (iii) sequential crosslinking/annealing proce- dures [6], and (iv) diffusion of vitamin E to the polymer matrix [1,7,8]. The two last treatments appear to be the most effective ones concerning UHMWPE implant longevity [1]. In particular, vitamin E-blended UHMWPE resins are commercially available since 2009 with proven post-irradiation chemical stability [1]. We propose in this paper an alternative treatment to the diffusion of vitamin E to UHMWPE. A radical scavenger agent could be distributed and dispersed within the UHMWPE matrix from the processing step of the polymer. An agent of interest could be polyaniline (PANI) that was proved to have a radical scavenging activity [9–12]. In particular, it was shown that solid sample of PANI immersed in a stable 2,2-dimethyl-1-picrylhydrazyl (DPPH) radical solution enabled to reduce by a factor of 5.8 the content in DPPH radicals [9]. It was also demonstrated that the scavenging activity increased when considering the more reduced PANI type [12]. Although some authors prepared some UHMWPE/PANI composites from solution [13,14] or from in-situ polymerization of PANI in the presence of UHMWPE [15], the potential radical scavenging activity of the obtained composite has never been investigated. At the same time, it is of high importance to verify that the presence of PANI inclusions is not detrimental to the mechanical properties of UHMWPE. However, the use of compo- sites for joint replacement may present issues concerning the biocompatibility of the composite itself and of its wear debris. Some proof of concepts proved the possible biocompatibility of PANI [16,17], which is obviously suitable for joint replacement application. Biocompatibility is crucial in the case of hip or knee arthroplasty and would require further investigation in the case of these composites. The objective of the paper is to elaborate composites of UHMWPE with PANI inclusions and to study the potential scavenging activity of the composites by means of the DPPH assay, as a pilot study. The distribution and dispersion of rigid inclusions within the UHMWPE matrix represents a challenge due * Corresponding author. Tel.: +352 42 59 91 4639. E-mail address: frederic.addiego@tudor.lu (F. Addiego). http://dx.doi.org/10.1016/j.synthmet.2014.10.020 0379-6779/ ã 2014 Elsevier B.V. All rights reserved. Synthetic Metals 198 (2014) 196–202 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.else vie r.com/locat e/synme t