N. Campo

Wetting modifications of uhmwpe surfaces induced by ion implantation

Ultra-high-molecular-weight-polyethylene (UHMWPE) surfaces are characterized in terms of roughness and wetting. Changes in the surface morphology of the polymer were induced macroscopically by mechanical friction and microscopically by ion implantation. The ion irradiation was obtained by using 300 keV Xe+ beams with doses ranging between 1014 and 1015 ions/cm2. Roughness and wetting measurements were performed in order to investigate the UHMWPE surface properties before and after the surface treatments. The wetting angle of the polymeric surface increases with the decrease of the roughness and with the increase of the absorbed dose. Results are discussed from the point of view of the biological reactions that could degrade the UHMWPE biocompatible surfaces employed in different mobile prostheses.

Incorporation of Carbon Nanotubes into Ultra High Molecular Weight Polyethylene by High Energy Ball Milling

Multiwalled carbon nanotubes, CNTs (0.3–1.0 wt.%), were incorporated in the ultra high molecular weight polyethylene (UHMWPE) matrix by solid state dry mixing in order to avoid the use of high temperature, solvents, and materials pretreatments. Physical, morphological, and mechanical tests were performed on both the pristine materials and the nanocomposites. Experimental results showed that the CNTs are homogeneously dispersed into the polymeric matrix but no close interaction occurs between the two components. In fact, no appreciable mechanical or thermal improvement was observed. Instead, a bi-dimensional CNT conductive network was formed within the polymeric matrix, which increased its crystalline order.

Mechanical performance of electron-beam-irradiated UHMWPE in vacuum and in air

Ultrahigh molecular weight polyethylene (UHMWPE) was modified by a 5-MeV energy electron beam at different temperatures before, during, and after irradiation, both in air and in high vacuum. Wear resistance, hardness, and tensile strength of irradiated polyethylene were compared with those of untreated one. Physical analyses (like infrared spectroscopy and calorimetric analysis) were carried out to investigate about the changes in the material induced by irradiation. Experimental results suggested that structural changes (double bonds, crosslinks, and oxidized species formation) occur in the polymer depending on the environmental conditions of the irradiation. Mechanical behavior is related to the structural modifications. A temperature of 110 degrees C before, during, and after the in vacuum irradiation of UHMWPE produces a high amount of crosslinks and improves polymeric tensile and wear resistance, compared to that of the untreated material.

Radiation effects induced by MeV electron beams irradiating dense polyethylene (UHMWPE)

Ultra-high-molecular-weight-polyethylene (UHMWPE) is irradiated with 5 MeV electrons in vacuum at different doses. The radiation effects induced by the electron irradiation are investigated by using different physical analyses such as mechanical tensile stress measurement, hardness measurements, specific heat measurements, infrared molecular absorption, surface wetting, polymer darkness and morphological scanning electron microscopy. The results indicate that the effects induced by high electron dose absorption consist mainly of a dehydrogenation of the polymer with an increase of the C–C cross-linking bonds, of an increase of the macroscopic mechanical resistance of the polymer, and of a darkness increase of the polymer color. Obtained results are compared with those produced by ion irradiation of the polymer by using ion implants at different stopping powers. Some applications of electron-irradiated UHMWPE are presented and discussed.

Mechanical modifications in dense polyethylene induced by energetic electron beams

Effects of radiation damage in ultra high molecular weight polyethylene are investigated by using energetic electron beams. Special attention is devoted to the mechanical characterization of the polymer, before and after the modification induced by 5 MeV electrons, as a function of the absorbed dose. Elastic modules, ultimate tensile and compressive strengths and roughness and hardness, have been measured in pristine and electron irradiated polymers. Infrared spectroscopy, scanning electron microscopy and differential scanning calorimetry are employed in order to investigate the microscopic modifications induced by the electron energy release to the polymeric chains. Results indicate that the polymer loses hydrogen and becomes rich in carbon content. Cross-linking effects are responsible for the higher mechanical resistance, fragility and hardness of the polymer submitted to a high absorbed dose.

Comparison of Surface Modifications Induced by Ion Implantation in UHMWPE

This research is a study on ultrahigh molecular weight polyethylene (UHMWPE-GUR 1020) implanted with 100–300 keV ions in order to modify its surface chemical, physical, and mechanical properties. Boron, nitrogen, argon, and xenon ions, at doses between 1012 and 1016/cm2, have been employed to irradiate polyethylene in high vacuum. Roughness, hardness, wear resistance, and wettability represent some of the superficial properties that are modified by the ion irradiation versus dose. Results highlight the modification depth and surface property dependence on the ion specie and dose. The material wear resistance after the ion implantation has been improved up to about 70%.

Influence of α-Tocopherol Load and Annealing Treatment on the Wear Resistance of Biomedical UHMWPE Irradiated with Electron Beam

A biomedical UHMWPE electron beam irradiated in air with doses raging between 25 and 100 KGy was doped with different amounts of α-tocopherol (0.1–0.7 wt.%) to prevent oxidative degradation. The polymer was annealed just after the irradiation at 110° for 24 h. Physical and mechanical tests were performed on the UHMWPE before and after the irradiation and on neat or doped material. Results showed that heat treatment after irradiation improves cross-links in the UHMWPE and α-tocopherol has good antioxidant action. The UHMWPE blended with 0.7% of antioxidant became harder and more wear resistant (+52%) after the irradiation with 100 KGy.

Polyethylene film welding induced by a 532 nm pulsed laser

A Nd:YAG laser operating at 532 nm wavelength, 3 ns pulse duration, 150 mJ pulse energy and 10 Hz repetition rate is employed to irradiate in air polyethylene-based polymers and to induce thin film welding. Polyethylene thin films of different densities, with and without enclosed carbon nanotubes, have been irradiated at different exposition times. Measurements of static tensile, shear stress and morphology permitted us to investigate the polymer modifications and welding induced by the laser irradiation. The results demonstrated that the absorption of the laser light increases in the carbon nanotubes containing polyethylene sheets, that a strong emission of nanoparticles occurs from the nanostructured polymer surfaces and that the irradiated polymer becomes less resistant to mechanical stresses after laser irradiation. Besides the coupling of different polyethylene films, it is possible to induce film welding if the laser parameters are chosen opportunely. Different typologies of welding have been investigated by varying the material and the laser irradiation time. The film welding shows a mechanical resistance depending on the features of the material.

Study of the Radical Species Induced by Electron-Beam Irradiation in Vacuum on Biomedical UHMWPE

Ultra high molecular weight polyethylene (UHMWPE) is a component of mobile prostheses. The irradiation performed to sterilize and cross-link the polymer limits its life because of the free radicals originated during this process. In this work, a UHMWPE was electron-beam irradiated under high vacuum and annealed. Mechanical tests were performed on the UHMWPE samples before and after the annealing treatment. The results were compared with a study of radical species type and amount and the crystalline degree changes. Experimental results show that the annealing treatment prevents degrading reactions, favors intermolecular and/or intramolecular chemical rearrangements, and improves wear resistance without compromising the typical elasto-plastic mechanical behavior.

Comparison of the laser effects induced on ultra-high-molecular-weight polyethylene

Ultra-high-molecular-weight polyethylene (UHMWPE) is a versatile polymer employed in many fields for its good chemical–physics characteristics. In particular, it is widely utilized in biomedical fields due to its high degree of biocompatibility and its easy control on wettability of the surface. In this work, the laser radiation has been utilized to effect different degrees of change to the wettability characteristics of the UHMWPE depending on the laser used. The wettability modification was investigated by measuring the contact angles using the sessile drop method. It was observed that the interaction with laser wavelengths at 1064 and 532 nm effected very little change in the wettability characteristics of UHMWPE. On the contrary, the interaction of UHMWPE with 248 and 308 nm laser wavelengths resulted in a marked improvement in the wettability characteristics of the polymer; in particular, the UHMWPE irradiated by 308 nm, after 10 laser shots, reported a linearly increasing of the polymer wettability.