Estabilización oxidativa del polietileno de ultra alto peso molecular en prótesis articulares

En la tesis "estabilización oxidativa del polietileno de ultra alto peso molecular en prótesis articulares" se ha desarrollado un trabajo de investigación original sobre la consecución y evaluación de la estabilidad oxidativa de este biopolimero con la incorporación de vitamina como antioxidante natural. Asimismo, se ha estudiado la validez de técnicas termo gravimétricas para discriminar el diferente comportamiento oxidativo de polietileno de ultra alto peso molecular irradiados y dopados con vitamina e, confirmando la utilidad de esta técnica en este objetivo. También se han estudiado los métodos de incorporación de vitamina e, mezclado y difusión, en el polímero, así como las técnicas apropiadas para la detección del antioxidante y medida de su concentración, destacando entre estas últimas las técnicas de colorimetría, de ángulo de contacto y dmta. Por último, la tesis aborda el efecto reforzante de nanotubos de carbono en el polietileno de ultra alto peso molecular, y por otra parte la actividad de los mismos como eliminadores de radicales libres.Peer reviewe

On the assessment of oxidative stability of post-irradiation stabilized highly crosslinked UHMWPEs by thermogravimetry

The characterization of the oxidative resistance of contemporary UHMWPE formulations currently relies upon time-consuming accelerated aging protocols and subsequent FTIR assessment. The potential of thermogravimetric analysis (TGA) for this purpose, however, remains mostly unknown. To study radiation and stabilization-induced changes in the decomposition process, TGA curves corresponding to virgin, e-beam irradiated, and post-irradiation stabilized UHMWPE materials were registered and analyzed. TGA traces of most materials exhibited similar features, with two weight increases before an initially non-linear decomposition and a portion of linear volatilization starting near 400 °C. After irradiation, the onset of the second weight increase shifted to lower temperatures and the linear volatilization stage began at higher temperatures. While post-irradiation annealing did not introduce significant changes in TGA curves, remelting delayed the onset of the second weight gain. Furthermore, this weight increase disappeared after vitamin E diffusion. Energies of activation of the initially predominant Thermoxidation and the subsequent thermodegradation processes were also calculated from fraction of conversion and reciprocal of temperature plots. As opposed to TGA, FTIR assessment of oxidation following accelerated aging at 120 °C for 36 h appeared to be less sensitive to discriminate between the different materials. This study confirms TGA as a promising technique to characterize the oxidative resistance of medical grade UHMWPEs.Research funded by Comisión Interministerial de Ciencia y Tecnología (CICYT), Spain. Project: MAT 2006-12603- C02-01.Peer Reviewe

Thermal and dynamic mechanical properties of vitamin E infused and blended ultra-high molecular weight polyethylenes

10 páginas, 10 figuras.Vitamin E (or α-tocopherol) is an alternative via to thermal treatments to achieve oxidative stability of gamma or electron beam irradiated ultra-high molecular weight polyethylenes (UHMWPE) used in total joint replacements. Our aim was to study the effects of vitamin E on the molecular dynamics and microstructural properties of UHMWPE. We hypothesized that the antioxidant would plasticize UHMWPE. Vitamin E was incorporated into UHMWPE at different concentrations by diffusion and blending and detected by ultraviolet and infrared spectroscopies from 500 ppm and 4000 ppm, respectively. Dynamic mechanical thermal analysis was used to characterize the influence of this antioxidant in the relaxations of the raw material. Differential scanning calorimetry and transmission electron microscopy served to characterize thermal and microstructure properties, respectively. Vitamin E concentrations above 3% by weight significantly reduced the degree of crystallinity and increased the melting transition temperature of raw UHMWPE. The presence of increasing concentrations of α-tocopherol introduced and/or strengthened the beta relaxation, which was also shifted toward gradually lower temperatures and had rising activation energies up to 188 kJ/mol. In addition, the gamma relaxation remained unaltered on vitamin E addition. Therefore, no plasticizing effects of vitamin E on the molecular dynamics of UHMWPE could be confirmed from mechanical spectroscopy data. However, the α relaxation was modified in intensity and location due to the changes in the degree of crystallinity introduced by the incorporation of vitamin E.Contract grant sponsor: Comisión Interministerial de Ciencia y Tecnología (CICYT), Spain. Contract grant sponsor: Ministerio de Ciencia e Innovación; contract grant number: MAT 2006-12603-C02- 01 and Consolider-Ingenio CDS2008-0023.Peer reviewe

Multi-walled carbon nanotubes acting as free radical scavengers in gamma-irradiated ultrahigh molecular weight polyethylene composites

Multi-walled carbon nanotubes (MWCNTs) were incorporated in ultrahigh molecular weight polyethylene (UHMWPE), which is a polymer used in industrial and orthopedic applications. The composites were prepared by ball milling and thermo-compression processes at concentrations up to 3 wt.% and subsequently gamma irradiated at 90 kGy. Electrical conductivity measurements showed a low percolation threshold of 0.5 wt.%. Electron spin resonance detection of the radiation-induced radicals proved the radical scavenger behavior of MWCNTs: when the nanotube concentration increased, the number of radicals generated by the gamma irradiation process decreased. Allyl radicals seem to be the radicals most affected by the presence of nanotubes in this polymeric matrix. Fourier transformed infrared spectroscopy measurements and an accelerated ageing protocol were performed to ascertain the influence of the irradiation on the oxidation index. The results pointed to the positive contribution of the MWCNTs in increasing the oxidative stability of the composite compared to pure UHMWPE. Crosslinking density induced by gamma irradiation was obtained by swelling measurements. The findings showed that, despite the radical scavenger performance, MWCNTs are capable of maintaining the efficiency of the crosslinking density, unlike the other antioxidants, which inhibit radiation crosslinking. © 2012 Elsevier Ltd. All rights reserved.Research funded by the Comisión Interministerial de Ciencia y Tecnología (CICYT), Spain. Project: MAT 2010-16175.Peer Reviewe

A novel approach to the chemical stabilization of gamma-irradiated ultrahigh molecular weight polyethylene using arc-discharge multi-walled carbon nanotubes

A complete study was made of the stabilization of gamma-irradiated ultrahigh molecular weight polyethylene (UHMWPE) using arc-discharge multi-walled carbon nanotubes (MWCNTs) as inhibitors of the oxidative process. MWCNTs were efficiently incorporated into the polymer matrix by ball milling and thermo-compression processes at concentrations up to 5 wt% and subsequently gamma irradiated at 90 kGy. Raman spectroscopy demonstrated the generation of radicals on the walls of the MWCNTs and that the G/D ratio was altered by their generation. The same spectra showed interactions between the polymer chains as a series of shifts are observed in the UHMWPE bands. The effect of the MWCNTs as inhibitors for the oxidative process of the UHMWPE was evaluated by means of Electron Spin Resonance (ESR) and Fourier Transformed Infrared Spectroscopy (FTIR). ESR detection of the radiation-induced radicals proved the radical scavenger behaviour of MWCNTs. FTIR measurements were performed to ascertain the influence of the irradiation and of the accelerated ageing protocol in the oxidation index of the polymer and the composites. The results pointed to the positive contribution of the MWCNTs in increasing the oxidative stability of the composite when compared to pure UHMWPE. A comparison is made between composites obtained using MWCNTs produced by the carbon vapour deposition and arc-discharge methods. © 2013 Springer Science+Business Media New York.The research was funded by the Comisión Interministerial de Ciencia y Tecnología (CICYT), Spain, Project: MAT 2010-16175.Peer Reviewe

Effects of gamma-irradiation on UHMWPE/MWNT nanocomposites

Ultra high molecular weight polyethylene (UHMWPE) is a polymer that is widely used in industrial and orthopaedic applications. In this work, pristine multiwalled carbon nanotubes (MWCNTs) were incorporated into UHMWPE in different concentrations (1, 3 and 5. wt.%) using a ball milling process. UHMWPE/MWCNT nanocomposites were gamma irradiated at 90. kGy to improve the interaction between MWCNTs and the polymer matrix. Structural, thermal and mechanical characterizations were conducted by means of transmission electron microscopy (TEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and uniaxial tensile techniques. Gamma irradiation produced an increase in the melting temperature, crystallinity and temperature of maximum decomposition rate. The irradiation produced a 38% decrease in the toughness of neat UHMWPE. The incorporation of MWCNTs did not significantly affect the melting point of the neat UHMWPE but decreased the degree of crystallinity of the raw UHMWPE, which was related to a reduction in the UHMWPE lamellar density. An increase in thermal stability was also observed for the nanocomposites compared to neat UHMWPE. The tensile tests showed a 38% increase in the Young's modulus in the reinforced nanocomposites and a small decrease in toughness (5%). Gamma irradiation of the nanocomposites increased crystallinity, which was related to an increased lamellar thickness, and also improved their thermal stability. The Young's modulus increased by up to 71% for irradiated nanocomposites and their toughness showed no significant changes in comparison with the non-irradiated nanocomposites. The incorporation of MWCNTs reduced the negative effects of irradiation and compensated for the reduction in toughness. This fact might be attributed to the radical scavenger behaviour of the MWNT as was proved by Electron Spin Resonance (ESR) detection of the radiation-induced radicals. © 2010 Elsevier Ltd.Research funded by the Comisión Interministerial de Ciencia y Tecnología (CICYT), Spain. Project: MAT 2010-16175.Peer Reviewe