Mariano Pérez Amor

Influence of the Network Modifier Content on the Bioactivity of Silicate Glasses

The influence of the substitution of calcium oxide for sodium oxide in the composition of silica-based glasses on the in vitro bioactivity is presented. Valuable information on the active Si-O groups present in the glasses is obtained by Fourier Transform Ra man and Infrared spectroscopies. In vitro test analysis by Scanning Electron Microscopy and Energy Dis persive X-ray Analysis show a correlation between the network disruption induced by the modifier type and the bioactive process. It is demonstrated that glasses with high SiO 2 content can be bioactive depending on the alkali/alkali-earth modifiers ratio included into the vitreous silica network. Introduction Bioactive glasses are interesting materials for medical pur poses due to their ability to bond chemically to living bone and soft tissues when soaked in physiologica l fluids [1, 2]. The clinical applications of bioactive glasses are numerous, especially in maxi llofacial reconstruction, otorhinolaryngology, oral surgery and periodontal repair [1]. The bioactive silica-based glass network is basically the same of vitreous silica, where the structural units consist of slightly distorted SiO 4 tetrahedra. This structure enables the accommodation of alkali and alkali-earth cations which create non-bridging oxygen s it s (Si-O-NBO) throughout the glass network [3]. When the bioactive glasses are soaked in human plasma or an analogous solution, it is known that a partial dissolution of the glass surface oc urs leading to the formation of a silica-rich gel layer and, subsequently, the precipitation of a c alcium phosphate film on the bioactive material takes place. The formation rate of this lay er is a critical parameter, which is directly related to the type and content of the network modifiers [1]. Several spectroscopic techniques, such as Infrared and Raman spectrosc opies, are sensitive to changes in the composition and the bonding configuration of the glasses, and they provide valuable information on the local structure of the silicate glasses. Thus, the aim of this work is to evaluate, through spectroscopic tec hniques and in vitro tests, the role of content and type of network modifiers on the bioactivity of silica-based gla sses. Materials and methods Glasses of different compositions in the quaternary system Na 2O-C O-P2O5-SiO2, with a systematic substitution of CaO and Na 2O concentrations, have been investigated (Table 1). Glasses were obtained by melting the appropriate quantities of analytical grade CaCO3, Na2CO3, CaHPO4·2H2O and commercial Belgian quartz sand in a Pt-crucible at 1360 oC for 3 h. The glasses were cast, annealed, crushed, and remelted to improve homogeneity. In the final casting, a graphite mould of 20 mm diameter and 100 mm long was used. The test pieces were obtai ned by sawing discs of 2 mm thick. The discs were washed and stored in ethanol. The structure of the glasses was studied by X-ray Diffract ion (XRD). Information on the active SiO groups present in the glasses was obtained by Fourier Transfor m Infrared (FTIR) and Raman spectroscopies. Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 23-26 doi:10.4028/www.scientific.net/KEM.254-256.23

Evaluation of the Glass Bioactivity Grade by IR Analysis and the Stevels Parameter

The structure of silica-based glasses consists on a disrupted network of SiO4 tetrahedra where network modifiers generate non-bridging oxygen groups (NBO), that play an important role at the initial steps of the bioactive process. Infrared spectroscopy is a sensitive technique to the presence of NBO groups and glass local structure modifications. The infrared study has been complemented with a theoretical approach using the Y Stevels parameter. Moreover, the in vitro bioactivity of the glasses as a function of Y Stevels paremeter has been studied, which can be a finding of a predictive tool for bioactivity of glasses.

In Vitro Bioactivity Study of PLD-Coatings and Bulk Bioactive Glasses

Bioactive glass coatings have been obtained by Pulsed Laser Deposition (PLD) from bulk glasses of different compositions in the system SiO 2-Na2O-K2O-CaO-MgO-P2O5-B2O3. A comparative study of the in vitro bioactive behaviour of the PLD-coatings and bulk glasses was carried out. Fourier Transform Infrared and X-ray Induced Photoele ctron Spectroscopies show that the bonding configuration of the bulk glasses is not congruently trans fe red to the coatings during the ablation process. These results are in agreement with the in vitro tests that show a similar bioactive process but a different bioactivity grade between the bulk glasses and the corresponding PLD coatings. The composition and bonding configuration of the bioactive coa tings grown by PLD should be carefully tuned in order to obtain an adequate biological response.

Mechanical Evaluation of the Use of a Buffer Layer in Hydroxylapatite Coatings Produced by Pulsed Laser Deposition at High Temperature

Abstract. Hydroxylapatite is used as coating on metallic implants because its composition and structure is similar to those of bone. As an alternative to plasma spraying, pulsed laser deposition has been successfully applied. Nevertheless, to obtain a high crystal line coating at temperatures higher than 550 oC are needed, leading to a deterioration of the coating-to-substrate adhesion. Some coatings were produced by pulsed laser deposition at 650 oC with a previous buffer layer deposited al lower temperature (460 oC). The combination of this buffer layer with a hi gh water vapour flow (60 Pa l/s) clearly improved the mechanical behaviour of the system coating-metal.

Influence of Substrate Temperature in Plasma Assisted Pulsed Laser Deposition of Hydroxyapatite Thin Films

The bioactive properties of hydroxyapatite (HA) are well known in the implant industry and coatings of HA have been used to enhance the adhesion of living tissue to metal prostheses. Pulsed laser deposition (PLD) in a water vapour atmosphere is an appropriate method for the production of crystalline HA coatings. In this work the effect of RF plasma on thin films of HA grown by PLD at different substrate temperatures has been studied. The physicochemical properties of the films were studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS), showing that the incorporation of RF discharge in the deposition chamber can lead to changes in the crystallinity and deposition rate of the films but substrate temperature still plays the most important role.

Laser Drilling of Natural Stones

Following previous work focused on the laser processing of natural stones, we present in this paper the results of the study carried out to verify the feasibility of the lasers to drill slate tiles and granite slabs. The two types of laser equipments most used in the industry (CO2 and Nd:YAG) have been used to fulfil a comparative study. The influence of different parameters involved in the process, such as, average power, stand-off distance, and assist gas pressure, have been studied to characterise the drilled holes size and geometry. Results from the different tests show that it is possible to obtain holes according to the required dimensions at reasonable powers ( i.e. no more than 400 W for the Nd:YAG and 1 kW for the CO2 laser). Holes up to 2 mm can be achieved in a very reduced time without breaking of the stone plates. The overall results show that the laser drilling technique could be an alternative to mechanical drilling of plates of natural stones to be used in ventilated façades or for roof fixation.