title: Does cyclic stress and accelerated ageing influence the wear behavior of highly crosslinked polyethylene?
abstract: First-generation (irradiated and remelted or annealed) and second-generation (irradiated and vitamin E blended or doped) highly crosslinked polyethylenes were introduced in the last decade to solve the problems of wear and osteolysis. In this study, the influence of the Vitamin-E addition on crosslinked polyethylene (XLPE_VE) was evaluated by comparing the in vitro wear behavior of crosslinked polyethylene (XLPE) versus Vitamin-E blended polyethylene XLPE and conventional ultra-high molecular weight polyethylene (STD_PE) acetabular cups, after accelerated ageing according to ASTM F2003-02 (70.0±0.1°C, pure oxygen at 5bar for 14 days). The test was performed using a hip joint simulator run for two millions cycles, under bovine calf serum as lubricant. Mass loss was found to decrease along the series XLPE_VE>STD_PE>XLPE, although no statistically significant differences were found between the mass losses of the three sets of cups. Micro-Raman spectroscopy was used to investigate at a molecular level the morphology changes induced by wear. The spectroscopic analyses showed that the accelerated ageing determined different wear mechanisms and molecular rearrangements during testing with regards to the changes in both the chain orientation and the distribution of the all-trans sequences within the orthorhombic, amorphous and third phases. The results of the present study showed that the addition of vitamin E was not effective to improve the gravimetric wear of PE after accelerated ageing. However, from a molecular point of view, the XLPE_VE acetabular cups tested after accelerated ageing appeared definitely less damaged than the STD_PE ones and comparable to XLPE samples.
authors.affiliation: Laboratorio di Tecnologia Medica, Istituto Ortopedico Rizzoli, Bologna, Italy. Electronic address: affatato@tecno.ior.it.
authors.forename: Saverio
authors.initials: S
authors.lastname: Affatato
authors.affiliation: Laboratorio di Tecnologia Medica, Istituto Ortopedico Rizzoli, Bologna, Italy.
authors.forename: Jonathan Salvatore
authors.initials: JS
authors.lastname: De Mattia
authors.affiliation: Chemistry Department and Nanostructured Interfaces and Surfaces (NIS) Centre, University of Turin, Via Giuria 7, 10125 Turin, Italy.
authors.forename: Pierangiola
authors.initials: P
authors.lastname: Bracco
authors.affiliation: Dipartimento di Scienze Biomediche e Neuromotorie, Università di Bologna, Via Belmeloro 8/2, 40126 Bologna, Italy.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Pavoni
authors.affiliation: Dipartimento di Scienze Biomediche e Neuromotorie, Università di Bologna, Via Belmeloro 8/2, 40126 Bologna, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Taddei
mesh_terms: D000077:Acetabulum; D000818:Animals; D002417:Cattle; D006622:Hip Prosthesis; D008422:Materials Testing; D011095:Polyethylenes / Q000737:chemistry*; D011475:Prosthesis Failure
chemical_list: D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene
keywords: Accelerated ageing; Crosslinked PE; Hip simulator; Raman spectroscopy; Vitamin E