S. Martínez

Rheological properties of an apatitic bone cement during initial setting

One scientific and technological aspect of main importance to the medical profession is to develop injectable calcium phosphate cements (CPCs) to be used through minimally invasive surgery techniques with still suitable mechanical and biodegradable properties. The objective of this research was to study the influence of several technological factors on the injectability of CPCs. This was performed by studying the rheological behavior of the cement pastes during their initial setting. Cement rheology was approached by looking at the creep response of apatitic cements as a function of the shear stress, the liquid-to-solid (L/S) ratio, the temperature and the addition of organic admixtures. Results showed creep experiments to be a finer method to detect characteristic setting times than other established subjective procedures. However, of all transition times detected none but the dough time seems to be of relevant importance when injectability of cement is concerned. Creep experiments also showed that the addition of organic admixtures such as citric acid increased injectability by retarding the hydration time.© 2001 Kluwer Academic Publishers

Acoustic barriers obtained from industrial wastes

Acoustic pollution is an environmental problem that is becoming increasingly more important in our society. Likewise, the accumulation of generated waste and the need for waste management are also becoming more and more pressing. In this study we describe a new material--called PROUSO--obtained from industrial wastes. PROUSO has a variety of commercial and engineering, as well as building, applications. The main raw materials used for this environmentally friendly material come from slag from the aluminium recycling process, dust from the marble industry, foundry sands, and recycled expanded polystyrene from recycled packaging. Some natural materials, such as plastic clays, are also used. To obtain PROUSO we used a conventional ceramic process, forming new mineral phases and incorporating polluted elements into the structure. Its physical properties make PROUSO an excellent acoustic and thermal insulation material. It absorbs 95% of the sound in the frequency band of the 500 Hz. Its compressive strength makes it ideal for use in ceramic wall building.

Fabrication of Low Temperature Hydroxyapatite Foams

Bone tissue engineering requires appropriate scaffold materials with a highinterconnected macroporosity. In this work a novel two-step method, based in the foaming of a calcium phosphate cement paste by the addition of hydrogen peroxide, and its subsequent hy drolysis to a calcium deficient hydroxyapatite (CDHA) is presented. The s iz of the interconnected macropores ranged between 50 μm and 2 mm, reaching the total porosity a maximum value of 66 %. The foaming capacity of the H 2O2 solution was strongly influenced by the particle size of the αtricalcium phosphate ( α-TCP) powder. The size of the macropores increased with increasing L/P ratio. As expected, the compressive strength of the apatitic foams decreased with increasing porosity, ranging between 2 and 9 MPa. Introduction One of the most promising approaches to the problem of bone regeneration a nd rep ir is bone tissue engineering (BTE). To guide in vitro or in vivo tissue regeneration, it is necessary to obtain appropriate scaffold materials with a high-interconnected macroporosi ty. For this application, several porous ceramic manufacturing techniques have been proposed [1-3]. How ever, the majority of these methods are based on the production of high temperature apatites , which are known to be hardly resorbable in normal physiological conditions. In this work an alte rn tive route is proposed to develop macroporous calcium phosphate scaffolds at low temperature, fr om calcium phosphate cements. Consolidation is obtained not by sintering, but through a low temper ature setting reaction. This approach has several advantages: the cementing reaction takes place at low temperature and therefore the final product is a low temperature pr cipitated hydroxyapatite, chemically more similar to the biological apatites, and with a much higher specific surface than that of a sintered hydroxyapatite. All these factors contribute to bring this materia l a higher reactivity, as compared to a ceramic hydroxyapatite. In addition, the low temperature processing allows the introduction of drugs, proteins or signaling molecules into the material. Materials and Methods To prepare the foams, an α-TCP powder obtained by solid state reaction at 1400oC, which contained a 2 wt% PHA as a seed material [4], was mixed with a 10 vol% aqueous solutions of hydrogen peroxide (H2O2) as foaming agent. The parameters studied were: (i) The liquid to powder ratio of the mixture (L/P = 0.32 and 0.38 ml/g) and (ii) the particle size of the α-TCP powder: two powders were studied, a coarse powder (average size 5.6 μm) and a fine powder (average size 2.2 μm). In order to evaluate the efficiency of foaming process, materials w ith no hydrogen peroxide on the liquid phase were also prepared. The experimental design is shown in Table 1. Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 1001-1004 doi:10.4028/www.scientific.net/KEM.254-256.1001

Mineralogical characterization of the Garumnian subbituminous lignite from the central Pyrenees by SEM-EDX, X-ray diffraction and Mössbauer spectroscopy

Abstract A full mineralogical characterization of a Garumnian subbituminous lignite found in the Pyrenees is performed and a good correlation between the mineral diagenesis and the coal rank is obtained. The mineral matter is characterized in the different sequences and analysed by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and transmission Mossbauer spectroscopy. Carbonates, quartz, clay minerals, sulfides and sulfates are identified and their presence is related to the diagenesis suffered by the mineral matter. Full transformation of smectite indicates temperatures > 360 °C, but the small formation of ankerite is related to low-grade metamorphism, in good agreement with the coal rank determination (Rock-Eval maximum temperature 430 °C).

Development of a New Calcium Phosphate Glass Ceramic Porous Scaffold for Guided Bone Regeneration

In this work, different porous scaffolds were developed using calcium phos phate glass particles in the system (P 2O5-CaO-Na2O-TiO2) and H2O2 as foaming agent. The different 3D structures were obtained by varying the foaming agent content and the thermal treatment. The microstructure and morphology of the specimens were observed by SEM (S canning Electron Microscopy) and the percentage of porosity was quantified by image a nalysis. XRD (X Ray Diffraction) was used to study the formation of new crystalline pha ses. The results showed that a increase in the amount of H 2O2 solution mixed with the glass particles increased both, the number of pores and their size. Indeed, the percentage of porosity ranged betw een 35% and 55% and the pore size varied from 100 to 500 μm for the samples with 40 and 60% w/w of H 2O2 respectively. The thermal treatments induced the formation of crystalline phases in the material. After sintering at 540oC a vitreous phase was the predominant, while at 570oC, the percentag of crystalline phases was higher The crystalline phases detected were meta and pyrophos phates. The pores sizes and interconnectivity obtained were in good agreement with those demanded for bone engineering scaffolds. Introduction Nowadays, the study of new resorbable porous scaffolds for guided bone rege ration is acquiring great importance, given the limitations that bone grafts present s uch as the material availability, and the risk of inducing transmissible diseases among others. It is well known that one of the main features this kind of materia ls must accomplish is the reabsorbability at controlled rates, to match that of tissue repai r. C lcium phosphate glasses are particularly suitable for this application, since they have a composi tion similar to the mineral phase of bone, and their dissolution rate can be precisely modulated by modifying their chemical composition as it has been demostrated in previous studies [1]. Another characteristic of paramount importance in the development of Ti ssue Engineering scaffolds is a high interconnected macroporosity, to ensure cell colonization and f low transport of nutrients and metabolic waste. Several methods for obtaining these porous scaffolds have been proposed. Some of the are based in the introduction of porogenic agents, foaming agents or emulsifiers. Other approaches use the casting or moulding technique, through the impregnation of a porous polymer foa m with ceramic emulsions [2-8]. The scope of this work is to develop glass ceramic porous scaffolds fr m a calcium phosphate glass in the system P 2O5-CaO-Na2O-TiO2, whose in vitro biocompatibility was assessed in a former study [9]. In these scaffolds, the kinetics of resorption is expected to be controlled by the chemical composition, percentage of crystalline phases and porosity. Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 945-948 doi:10.4028/www.scientific.net/KEM.254-256.945

Aplicaciones de los Vidrios de Fosfato de Calcio en el Desarrollo de Composites Bioactivos para la Sustitución del Tejido Óseo

Nowadays bioactive glasses are frequently used for bone tissue replacement. In this work two new different calcium phosphate glasses were prepared and characterized. The chemical compositions were (in mol%): 11Na2O-44.5P2O5-44.5CaO (Bv11) and 6Na2O-44.5P2O5-44.5CaO-5TiO2 (G5). Both materials were silanyzed and characterized by Differential Thermal Analysis (DTA), Transformed Fourier-Infrared Spectroscopy (FTIR) and Dilatometry. The bioglasses prepared were also used as filler of conventional polymethylmetacrylate (PMMA) bone cement and it’s bioactive behavior explored by soaking composites in Simulated Body Fluid (SBF). The samples of modified cements exhibited significant morphological surface changes. Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) and Field Emission-SEM (FE-SEM) analysis confirmed the formation of calcium phosphate precipitates on the surface of the cement. The amount of precipitates was higher for cements which contained Bv11 as filler than those loaded with G5 glass particles. These results revealed that the higher bioactivity of the cement load with Bv11 could be related with the higher solubility of this glass.

Wollastonite Coatings on Zirconia Ceramics

A wollastonite coating on two different zirconia substrates was studied. The results obtained in the preparation and micro-structural characterization are discussed. The observations by scanning electron microscope (SEM) showed a good deposition of the coating n both zirconia substrates. The presence of peaks attributable to wollastonite and cubi c, tetragonal and monoclinic phases of the zirconia at the X-ray diffraction (XRD) patterns were identified. After two weeks in SBF, the observations by environment scanning electron microscopy (ESEM) and SE M revealed the formation of apatite layer which covered fully the samples. The che mical composition of the layer was confirmed by energy-dispersive-spectrometry (EDS). Introduction The use of bioactive coatings on zirconia ceramics is an attract ive al ernative to prepare implant materials which combines the good mechanical properties of the zirc onia with the ability to bond with the surrounding tissue owing to the coatings [1]. Wollastonite (CaSiO3) ceramics was studied as material to substitute bone because of its good bioactivity and bioc ompatibility [2-3]. Some authors reported that the rate of apatite layer formation on the sur face of wollastonite ceramics is faster than those of the other biocompatible materials in simulated body flui d so tion (SBF) [4]. On the other hand, the zirconia ceramics are already tested in anima l models and used in clinical applications and no local or systemic adverse reactions related to the materials were detected [5]. In this work, wollastonite coatings on zirconia were prepared, the minera logic l and chemical compositions, the microstruture and the changes occurring after aging in SBF were s tudied. Materials and Methods The wollastonite powder was obtained from a natural source. Two commer cial zi conia ceramics were used as substrates (magnesia-partially-stabilized zirc onia (Mg-PSZ) and ytria-partiallystabilized zirconia (Y-PSZ)). The ceramics were cut into sma ll bars and covered with a alcoholic suspension of powdered wollastonite, the suspension also contained some amount of polyvinylalcohol as binder. The thermal treatments were carried out at 1350°C for 2 hours in air. The cross-sections of the covered samples were polished and analysed at th interface by EDS and SEM. SBF solution was prepared by dissolving reagent-grade chemical and buffered to pH 7.4 at Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 379-382 doi:10.4028/www.scientific.net/KEM.254-256.379

Phosphorus solubility in basaltic glass: Limitations for phosphorus immobilization in glass and glass-ceramics

The composition of sewage sludge from urban wastewater treatment plants is simulated using P-doped basalts. Electron microscopy analyses show that the solubility of P in the basaltic melt is limited by the formation of a liquid-liquid immiscibility in the form of an aluminosilicate phase and a Ca-Mg-Fe-rich phosphate phase. The rheological behavior of these compositions is influenced by both phase separation and nanocrystallization. Upon a thermal treatment, the glasses will crystallize into a mixture of inosilicates and spinel-like phases at low P contents and into Ca-Mg-Fe phosphate at high P contents. Hardness measurements yield values between 5.41 and 7.66 GPa, inside the range of commercial glasses and glass-ceramics. Leaching affects mainly unstable Mg2+-PO43- complexes.

Sintering Behavior of Nanostructured Hydroxyapatite Ceramics

The synthesis of nanoparticles appropriate for the preparation of nanostructured hydroxyapatite ceramics intended for bone repairs and regeneration is an interesting field of biomaterials research today. In this work nanoparticles of hydroxyapatite were obtained by the precipitation method using conventional magnetic stirring (A) and ultra turrex homogenizer (T1) accompanied with surfactant (T2) and dispersant agents (T3). In all cases, powders with nanometric dimensions were obtained and the unique calcium phosphate phase detected was hydroxyapatite (HAp). The powders sintering behaviour was studied. The ceramics obtained from powders prepared by magnetic stirring (A) showed the best values of final density (96.7 %) which it was in agreement with the lowest temperature of the beginning of shrinking (648.6 °C) during sintering determined by dilatometry. Nanostructured nature of these ceramics was confirmed by Scanning Electron Microscopy (SEM).