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Teixeira M.,University of Lisbon | Teixeira M.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | Loable C.,University of Lisbon | Loable C.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | And 7 more authors.
ICALEO 2013 - 32nd International Congress on Applications of Lasers and Electro-Optics | Year: 2013

Ti and its alloys are commonly used for biomedical implants. These alloys, developed for aeronautical applications, are not optimized for medical use. Major limitations of current alloys are the presence of elements that are toxic or associated to neurological disorders, and excessive stiffness, that leads to stress shielding and may result in bone resorption and implant failure. A need remains to design new alloys for biomedical applications that fulfill requirements such as biocompatibility, wear and corrosion resistance, and adequate stiffness, strength, toughness and fatigue resistance. Alloying Ti with ?-phase stabilizers allows obtaining alloys with biomechanical behavior closer to that of bone than current ones. However, new materials development using conventional alloying techniques can be time- and resources-consuming, since it requires the production, characterization and testing of a significant number of discrete composition samples. In this study, the combinatorial method based on variable composition laser deposition is used to produce new Ti-based alloys with composition varying continuously along a single clad track. The alloys are then characterized and tested using microscale techniques, allowing a rapid screening of their structure and properties over a wide range of compositions. A summary of the results obtained for the Ti-Ta alloy system will be presented and discussed in terms of alloy constitution, microstructure and resulting properties, demonstrating the potential application of the laser-assisted combinatorial method to discover Ti alloys with most promising properties for biomedical load-bearing applications.


Cunha A.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | Cunha A.,University of Lisbon | Cunha A.,University of Bordeaux 1 | Oliveira V.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | And 9 more authors.
ICALEO 2013 - 32nd International Congress on Applications of Lasers and Electro-Optics | Year: 2013

By controlling processing parameters such as the average fluence, number of laser pulses and beam polarization direction, different types of multiscale surface textures were produced on Ti-6Al-4V surfaces by ultrafast laser processing. The samples were textured in ambient atmosphere using an Yb: KYW chirped-pulse-regenerative amplification laser with a wavelength of 1030 nm and pulse duration of 500 fs. The wetting of simulated biological fluids as well as the human mesenchymal stem cells (hMSCs) behavior were assessed. Three types of textured surfaces were tested, consisting of: (i) Laser-Induced Periodic Surface Structures-LIPSS; (ii) nanopillars-like structures; and (iii) LIPSS overlapped to microcolumns. The laser textured surfaces present hydrophilic behavior and high affinity for HBSS (Hank's balanced salt solution). Cell spreading and adhesion strength is reduced by the laser nanotextures as compared to a polished control surface. Cytoskeleton stretching and stress fibers were clearly observed on LIPSS while significant filopodia formation was verified on nanopillars. There was no cell proliferation on the laser nanotextured surfaces. Ultrafast laser texturing of Ti-6Al-4V surfaces is an efficient technique for increasing surface wettability, and is potentially useful as a technique to control the behavior of hMSCs by changing the cytoskeleton shape, FAPs distribution and area, and proliferation.


Oliveira V.,Polytechnic Institute of Lisbon | Oliveira V.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | Vilar R.,University of Lisbon | Vilar R.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | And 6 more authors.
Optics and Laser Technology | Year: 2013

We report the fabrication of planar sub-micron gratings in silicon with a period of 720 nm using a modified Michelson interferometer and femtosecond laser radiation. The gratings consist of alternated stripes of laser ablated and unmodified material. Ablated stripes are bordered by parallel ridges which protrude above the unmodified material. In the regions where ridges are formed, the laser radiation intensity is not sufficient to cause ablation. Nevertheless, melting and a significant temperature increase are expected, and ridges may be formed due to expansion of silicon during resolidification or silicon oxidation. These conclusions are consistent with the evolution of the stripes morphology as a function of the distance from the center of the grating. © 2013 Elsevier Ltd.


Cangueiro L.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | Cangueiro L.,University of Lisbon | Vilar R.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | Vilar R.,University of Lisbon
ICALEO 2013 - 32nd International Congress on Applications of Lasers and Electro-Optics | Year: 2013

Ultrafast lasers are extremely promising tools for minimally-invasive orthopedic surgery, but the influence of femtosecond laser ablation on the surface topography, structure and composition of bone was scarcely investigated up to now. The purpose of this work is to study this influence in vitro, using bovine cortical bone as a model. The ablation tests were performed in air and in dry conditions and under flowing water, with a 500 fs pulse duration laser (1030 nm wavelength) using fluences from 0.55 to 2.18 J/cm2 and pulse frequencies between 50 and 3000 Hz. The results show that when processing is carried out in dry conditions and with pulse repetition rates up to 50 Hz, the structure of the remaining tissue is preserved and the only compositional changes detected are a slight reduction of the organic material content and a partial recrystallization of hydroxyapatite in the most superficial region of the samples. When the laser pulse frequency is increased to 2 kHz, the organic matter content at the samples' surface decreases further and slight surface carbonization occurs. On the contrary, no compositional alterations were observed when ablation was performed under flowing water. The results suggest that ablation occurred by a combination of thermal and electrostatic mechanisms, the first explaining the thermal effects observed. This work confirms that femtosecond lasers are a viable alternative to mechanical tools for delicate orthopaedic surgeries, where small amounts of bone must be cut or removed with negligible damage. Water cooling allows high pulse frequencies to be employed and, consequently, higher tissue removal rates to be achieved.


Sharma S.P.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | Sharma S.P.,University of Lisbon | Oliveira V.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | Oliveira V.,Polytechnic Institute of Lisbon | And 3 more authors.
Journal of Applied Physics | Year: 2014

The aim of the present work was to characterize the internal structure of nanogratings generated inside bulk fused silica by ultrafast laser processing and to study the influence of diluted hydrofluoric acid etching on their structure. The nanogratings were inscribed at a depth of 100μm within fused silica wafers by a direct writing method, using 1030nm radiation wavelength and the following processing parameters: E=5μJ, τ=560 fs, f=10kHz, and v=100μm/s. The results achieved show that the laser-affected regions are elongated ellipsoids with a typical major diameter of about 30μm and a minor diameter of about 6μm. The nanogratings within these regions are composed of alternating nanoplanes of damaged and undamaged material, with an average periodicity of 351±21nm. The damaged nanoplanes contain nanopores randomly dispersed in a material containing a large density of defects. These nanopores present a roughly bimodal size distribution with average dimensions for each class of pores 65±20×16±8×69±16nm 3 and 367±239×16±8×360±194nm 3, respectively. The number and size of the nanopores increases drastically when an hydrofluoric acid treatment is performed, leading to the coalescence of these voids into large planar discontinuities parallel to the nanoplanes. The preferential etching of the damaged material by the hydrofluoric acid solution, which is responsible for the pores growth and coalescence, confirms its high defect density. © 2014 AIP Publishing LLC.


Serra R.,University of Coimbra | Oliveira V.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | Oliveira V.,Polytechnic Institute of Lisbon | Oliveira J.C.,University of Coimbra | And 4 more authors.
Applied Surface Science | Year: 2015

Abstract Amorphous and crystalline sputtered boron carbide thin films have a very high hardness even surpassing that of bulk crystalline boron carbide (≈41 GPa). However, magnetron sputtered B-C films have high friction coefficients (C.o.F) which limit their industrial application. Nanopatterning of materials surfaces has been proposed as a solution to decrease the C.o.F. The contact area of the nanopatterned surfaces is decreased due to the nanometre size of the asperities which results in a significant reduction of adhesion and friction. In the present work, the surface of amorphous and polycrystalline B-C thin films deposited by magnetron sputtering was nanopatterned using infrared femtosecond laser radiation. Successive parallel laser tracks 10 μm apart were overlapped in order to obtain a processed area of about 3 mm2. Sinusoidal-like undulations with the same spatial period as the laser tracks were formed on the surface of the amorphous boron carbide films after laser processing. The undulations amplitude increases with increasing laser fluence. The formation of undulations with a 10 μm period was also observed on the surface of the crystalline boron carbide film processed with a pulse energy of 72 μJ. The amplitude of the undulations is about 10 times higher than in the amorphous films processed at the same pulse energy due to the higher roughness of the films and consequent increase in laser radiation absorption. LIPSS formation on the surface of the films was achieved for the three B-C films under study. However, LIPSS are formed under different circumstances. Processing of the amorphous films at low fluence (72 μJ) results in LIPSS formation only on localized spots on the film surface. LIPSS formation was also observed on the top of the undulations formed after laser processing with 78 μJ of the amorphous film deposited at 800 C. Finally, large-area homogeneous LIPSS coverage of the boron carbide crystalline films surface was achieved within a large range of laser fluences although holes are also formed at higher laser fluences. © 2015 Elsevier B.V. All rights reserved.


Oliveira V.,Polytechnic Institute of Lisbon | Oliveira V.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | Sharma S.P.,Icems Institute Ciencia E Engineering Of Materiais E Superficies | Sharma S.P.,University of Lisbon | And 3 more authors.
Optics Letters | Year: 2013

A transmission electron microscopy study of nanogratings formed in bulk amorphous silica by direct writing with an ultrafast pulsed laser with a radiation wavelength of 1030 nm and pulse duration of 560 fs is presented. The results achieved show that the nanogratings are composed of planar nanostructures with an average periodicity of 250 nm and typical thickness of about 30 nm, consisting of alternating layers of heavily damaged material and layers of material where a dense precipitation of nanocrystals occurred. The crystallization of silica to form these nanocrystals can be explained by the large pressures and temperatures reached in these regions as a result of nanoplasma formation and recombination. © 2013 Optical Society of America.

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