Betty León

Effect of heat treatment on pulsed laser deposited amorphous calcium phosphate coatings

Amorphous calcium phosphate coatings were produced by pulsed laser deposition from targets of nonstoichiometric hydroxyapatite (Ca/P = 1.70) at a low substrate temperature of 300 degrees C. They were heated in air at different temperatures: 300, 450, 525 and 650 degrees C. Chemical and structural analyses of these coatings were performed using X-ray diffraction (XRD), FTIR, and SEM, XRD analysis of the as-deposited and heated coatings revealed that their crystallinity improved as heat treatment temperature increased. The main phase was apatitic, with some beta-tricalcium phosphate in the coatings heated at 525 and 600 degrees C. In the apatitic phase there was some carbonate substitution for phosphate and hydroxyl ions at 450 degrees C and almost solely for phosphate at 525 and 600 degrees C as identified by FTIR. This was accompanied by a higher hydroxyl content at 525 and 600 degrees C. At 450 degrees C a texture on the coating surface was observable by SEM that was attributable to a calcium hydroxide and calcite formation by XRD. These phases almost disappeared at 600 degrees C, probably due to a transformation into calcium oxide.

A new generation of bio-derived ceramic materials for medical applications

A new generation of bio-derived ceramics can be developed as a base material for medical implants. Specific plant species are used as templates on which innovative transformation processes can modify the chemical composition maintaining the original biostructure. Building on the outstanding mechanical properties of the starting lignocellulosic templates, it is possible to develop lightweight and high-strength scaffolds for bone substitution. In vitro and in vivo experiments demonstrate the excellent biocompatibility of this new silicon carbide material (bioSiC) and how it gets colonized by the hosting bone tissue because of its unique interconnected hierarchic porosity, which opens the door to new biomedical applications.

Photo-induced chemical vapour deposition of silicon oxide thin films

A review of the photo-induced chemical vapour deposition (photo-CVD) processes yielding silicon oxide thin films that have emerged in the last decade is presented. Both lasers and UV lamps as photon sources are included. The basic principles, processing conditions, precursors, geometries, advantages and limitations of the various types of photo-CVD processes are described and compared. Their technological applicability and potential for industrial large-scale installation are discussed.

Cytocompatibility of bio‐inspired silicon carbide ceramics

Due to its good mechanical and biochemical properties and, also, because of its unique interconnected porosity, bio-inspired silicon carbide (bioSiC) can be considered as a promising material for biomedical applications, including controlled drug delivery devices and tissue engineering scaffolds. This innovative material is produced by molten-Si infiltration of carbon templates, obtained by controlled pyrolysis of vegetable precursors. The final SiC ceramic presents a porous-interconnected microstructure that mimics the natural hierarchical structure of bone tissue and allows the internal growth of tissue, as well as favors angiogenesis. In the present work, the in vitro cytocompatibility of the bio-inspired SiC ceramics obtained, in this case, from the tree sapelli (Entandrophragma cylindricum) was evaluated. The attachment, spreading, cytoskeleton organization, proliferation, and mineralization of the preosteoblastic cell line MC3T3-E1 were analyzed for up to 28 days of incubation by scanning electron microscopy, interferometric profilometry, confocal laser scanning microscopy, MTT assay, as well as red alizarin staining and quantification. Cells seeded onto these ceramics were able to attach, spread, and proliferate properly with the maintenance of the typical preosteoblastic morphology throughout the time of culture. A certain level of mineralization on the surface of the sapelli-based SiC ceramics is observed. These results demonstrated the cytocompatibility of this porous and hierarchical material.

Gas mixture dependence of the LCVD of SiO2 films using an ArF laser

Abstract Large-area silica films have been deposited on silicon wafers using silane, nitrous oxide and argon gas mixtures and an ArF excimer laser in parallel configuration. An exhaustive study has been carried out on the role of the total and partial pressure of the various components of the gas mixture on the growth and the properties of silica films. Films are characterized by FT-IR spectroscopy and ellipsometry.

Pulsed Laser Deposition of Thin Calcium Phosphate Coatings

This chapter reviews the work performed by the international research community on the production of thin calcium phosphate (CaP) coatings by p`ulsed laser deposition (PLD). Studies on the mechanisms of the technique shed light on the scientific bases for optimization of the coatings beyond empirical work. The relations between the physicochemical coating properties and the various processing parameters are presented. PLD can produce extremely thin, dense, well adhering CaP coatings with extraordinary controlled chemistry and crystallinity. No postdeposition thermal annealing is needed. Different CaP phases and morphologies can be deposited, so the degree of resorption may be adapted to a specific medical application. Coatings with graded composition or graded crystallinity can readily be produced, not only on metal substrates but also on polymers. In vitro and in vivo testing with various cells and animal models have verified similar or better osseointegration of the PLD coatings compared to the commercially available plasma-sprayed coatings, with improved adhesion properties and without risk of delamination or detachment of the coating. The technique is mature enough for an industrial scale-up and the start of clinical tests with real dental or orthopedic implants.

Excimer laser deposition of silica films: a comparison between two methods

Abstract Two different LCVD methods are compared, both using an ArF excimer laser in perpendicular configuration, but with different precursors: TEOS + O 2 and SiH 4 + N 2 O. The dependencies of the deposition rate on the substrate temperature, the total pressure and the laser energy density show that the process kinetics is completely different for both systems. In fact, the activation energy is much lower for the silane+nitrous oxide system than for TEOS + oxygen. Moreover, the TEOS + oxygen system leads to silica films with a higher water content and less spatial confinement.

Study of the gas-phase parameters affecting the silicon-oxide film deposition induced by an ArF laser

A study of the gas-phase parameters involved in ArF laser induced chemical vapour deposition of silicon-oxide thin films is presented. A complete set of experiments has been performed showing the influence of the concentration of the precursor gases, N2O and SiH4, and their influence on total and partial pressures on film growth and properties. In this paper we demonstrate the ability of this LCVD method to deposit silicon oxide films of different compositions and densities by appropriate control of gas composition and total pressure. Moreover, a material specific calibration plot comprising data obtained using different preparation techniques is presented, allowing determination of the stoichiometry of SiOxfilms by using FTIR spectroscopy independently of the deposition method. For the range of processing conditions examined, the experimental results suggest that chemical processes governing deposition take place mainly in the gas phase.

Silicon oxide films deposited by excimer laser chemical vapour deposition

Abstract To meet the needs of both metallurgy and microelectronics for an efficient non-destructive low temperature technique, we have examined the ArF laser-induced chemical vapour deposition (CVD) of silicon oxide films onto stainless steel and silicon substrates from SiH 4 and N 2 O presursors using argon as buffer gas. Our systematic study of the dependences of deposition rate and film properties on process parameters revealed that the deposition of good quality silica films is possible for N 2 O:SiH 4 flow ratios starting from as low as 3, but different growth behaviour is found when either the N 2 O or the SiH 4 partial pressure is kept constant. A comparison between conventional plasma and laser CVD reveals that the use of lasers greatly enhances ones freedom in tailoring film properties. By tuning the partial pressures, geometry and energy of the beam, fine control of the film properties can easily be achieved in a wide range not available with any other method.

Surface modification of a biodegradable composite by UV laser ablation: in vitro biological performance

Melt blends of chitosan and biodegradable aliphatic polyester have been physically and biologically studied, presenting great potential for biomedical applications. Structurally, poly(butylene succinate)–chitosan (PBS/Cht) composite scaffolds are covered by a thin PBS layer, preventing the desired interaction of cells/tissues with the chitosan particules. In the present work, a selective and controlled ablation of this skin layer was induced by UV laser processing. X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF–SIMS) data demonstrated an increment of chitosan components and others resulting from the laser ablation process. The biological activity (i.e. cell viability and proliferation) on the inner regions of the composite scaffolds is not significantly different from those of the external layer, despite the observed differences in surface roughness (determined by interferometric optical profilometry) and wettability (water contact angle). However, the morphology of human osteoblastic cells was found to be considerably different in the case of laser‐processed samples, since the cells tend to aggregate in multilayer columnar structures, preferring the PBS surface and avoiding the chitosan‐rich areas. Thus, UV laser ablation can be considered a model technique for the physical surface modification of biomaterials without detrimental effects on cellular activity. Copyright