Characterization of biomimetic calcium phosphate coatings on Ti6Al4V alloy

Los metales se emplean ampliamente para la fabricación de implantes óseos debido a su elevada resistencia mecánica. Sin embargo, los metales son solo materiales biotolerables incapaces de desarrollar un enlace directo con el tejido óseo vivo. Por otra parte, los materiales bioactivos sí forman enlace químico directo con el tejido óseo, pero por lo general, no poseen propiedades mecánicas adecuadas. La combinación de elevada resistencia mecánica y bioactividad se puede alcanzar mediante el recubrimiento de la superficie de un substrato metálico con hidroxiapatita (HA). Se pueden emplear varios métodos para la aplicación de recubrimientos de hidroxiapatita sobre metales, como son implantación iónica, plasma spray, sol-gel, electrodeposición y el método biomimético, siendo este último particularmente atractivo porque imita las condiciones fisiológicas existentes en el organismo durante la formación del recubrimiento. Otro aspecto definitorio de la calidad de un recubrimiento de HA es su adhesión al substrato, sin embargo la adhesión de los recubrimientos obtenidos por el método biomimético han sido escasamente estudiadas. El objetivo de este trabajo fue estudiar el efecto de la sustitución del vidrio G, empleado en la etapa de nucleación en el método biomimético convencional, por una disolución de silicato de sodio, sobre las características químicas, morfológicas y la adhesión de los recubrimientos obtenidos sobre una aleación de Ti6Al4V. Los recubrimientos obtenidos se analizaron mediante espectroscopia FTIR en modo de reflectancia difusa (DRIFT), microscopia electrónica de barrido (SEM) y ensayos de adhesión según la norma ASTM C 633 -79

Anticipated Overfiring in Porcelain Tiles: Effects of the firing cycle and green bulk density

In order to reduce production costs, the ceramic tiles have been produced in ever faster firing cycles. One of the undesirable consequences of the acceleration of the firing cycles is the anticipated overfiring, when the tiles stop shrinking and start to expand before the water absorption reaches the required values. The present study evaluated, through statistical analysis (DOE), the effects of the main characteristics of the firing cycle and the green bulk density of the compacts of porcelain tiles on this phenomenon. The results showed that the main factors responsible for porcelain tiles anticipated overfiring are very short holding periods on firing and relatively low green densities. The results also suggest that these factors contribute to the expressively heterogeneous development of the microstructure of the products, which may contribute to the development of the anticipated overfiring. Resumen: A fin de reducir los costos de producción, las baldosas cerámicas se han producido en ciclos de cocción cada vez más rápidos. Una de las consecuencias indeseables de la aceleración de los ciclos de cocción es la sobrecocción anticipada, cuando las baldosas dejan de retraerse y comienzan a expandirse antes de que la absorción de agua alcance los valores requeridos. El presente estudio evaluó, a través del análisis estadístico (DOE), los efectos de las principales características del ciclo de cocción y la densidad aparente en verde de los compactos de gres porcelánico en este fenómeno. Los resultados mostraron que los principales factores responsables por la sobrecocción anticipada del gres porcelánico son los tiempos muy cortos de permanencia en la temperatura máxima del ciclo de cocción y las densidades en verde relativamente bajas. Los resultados también sugieren que estos factores contribuyen al desarrollo expresivamente heterogéneo de la microestructura de los productos, lo que puede contribuir al desarrollo de la sobrecocción anticipada. Keywords: Overfiring, Firing cycle, Tiles, Sintering, Porosity, Palabras clave: Sobrecocción, Ciclo de cocción, Revestimientos, Sinterización, Porosida

Dual-setting Calcium Phosphate Cement Modified With Ammonium Polyacrylate.

alpha-Tricalcium phosphate bone cement, as formerly designed and developed by Driessens et al., consists of a powder composed by alpha-tricalcium phosphate (alpha-TCP) and hydroxyapatite (HA) seeds, and an aqueous solution of Na2HPO4 as mixing liquid. After mixing powder and liquid, alpha-TCP dissolves into the liquid and calcium deficient hydroxyapatite (CDHA), more insoluble than the former, precipitates as an entanglement of crystals, which causes the setting and hardening of the cement. alpha-TCP bone cement offers several advantages in comparison to calcium phosphate bioceramics and acrylic bone cements as bone graft and repairing material, like perfect adaptability to the defect size and shape, osteotransductibility, and absence of thermal effect during setting. The main handicap is its low mechanical strength. Therefore, approaching its mechanical strength to that of human bone could considerably extend its applications. In the present work, an in situ polymerization system based on acrylamide (AA) and ammonium polyacrylate (PA) as liquid reducer was added to alpha-TCP cement to increase its mechanical strength. The results showed that the addition of 20 wt% of acrylamide and 1 wt% AP to the liquid increased the compressive and tensile strength of alpha-TCP bone cement by 149 and 69% (55 and 21 MPa), respectively. The improvement in mechanical strength seems to be caused by a decrease of porosity and the reinforcing effect of a polyacrylamide network coexisting with the entanglement of CDHA crystals. The studied additives do not affect the nature of the final product of the setting reaction, CDHA, but promote the reduction of its crystal size.27412-

Importancia do Controle da velocidade de resfriamento na Obtencao de Vidrados Vitro-Cristalinos

Industrial compositons of glass-ceramics used for tile glazes have been investigated with reference to the cooling rate

Synthesis of chitosan/hydroxyapatite membranes coated with hydroxycarbonate apatite for guided tissue regeneration purposes

Chitosan, which is a non-toxic, biodegradable and biocompatible biopolymer, has been widely researched for several applications in the field of biomaterials. Calcium phosphate ceramics stand out among the so-called bioceramics for their absence of local or systemic toxicity, their non-response to foreign bodies or inflammations, and their apparent ability to bond to the host tissue. Hydroxyapatite (HA) is one of the most important bioceramics because it is the main component of the mineral phase of bone. The aim of this work was to produce chitosan membranes coated with hydroxyapatite using the modified biomimetic method. Membranes were synthesized from a solution containing 2% of chitosan in acetic acid (weight/volume) via the solvent evaporation method. Specimens were immersed in a sodium silicate solution and then in a 1.5 SBF (simulated body fluid) solution. The crystallinity of the HA formed over the membranes was correlated to the use of the nucleation agent (the sodium silicate solution itself). Coated membranes were characterized by means of scanning electron microscopy - SEM, X-ray diffraction - XRD, and Fourier transform infrared spectroscopy - FTIR. The results indicate a homogeneous coating covering the entire surface of the membrane and the production of a semi-crystalline hydroxyapatite layer similar to the mineral phase of human bone. (C) 2010 Elsevier B.V. All rights reserved.CNPqFAPESP (Brazil

Influence of beta-to-alpha quartz transition on residual stresses of a feldspar glass matrix composite : a relationship with catastrophic fracture due to thermal shock

A wide range of porcelain-based materials is composed of quartz crystalline particles dispersed in a homogeneous glassy phase. During the cooling stage these composites are subjected to stresses related to the transition from β to α quartz at 573 °C. This work studies, numerically and experimentally, the influence of the cooling rate, the quantity, and the size of the quartz crystalline particles on the stresses suffered by the material throughout the cooling process. This procedure allows calculating the instantaneous profile of stresses through the cross-section specimen during the whole cooling stage. For this, a dense glass matrix from sodium feldspar was prepared. The results reveal that the evolution of the stress profile is strongly affected by the cooling rate. The evolution of the tension state in the sample during the cooling can help to understand the catastrophic fracture suffered during the β to α quartz transition related to thermal shock

Quartz particle size and cooling rate effects on microstructural defects and mechanical properties of feldspar-based ceramic materials

Reinforcement or microstructural damage? What effect do quartz particles have on a feldspar-based ceramic material? To answer this question, this study investigates the impact of different cooling conditions on the generation of microstructural defects in a sodium feldspar matrix caused by quartz particles. Moreover, the study aims to analyze how these defects influence the mechanical properties of the final product. Therefore, high-purity sodium feldspar and varying-sized quartz particles were used. The materials was sintered and subjected to different cooling rates during the quartz allotropic transition (). The results showed that the addiction of coarse quartz particles significantly reduced the mechanical properties of the ceramic composition. Cooling types only had a noticeable impact when a material with a high percentage of coarse quartz was rapidly cooled during the quartz allotropic transition. In summary, no evidence of microstructural reinforcement was found when adding quartz particles to a sodium feldspar matrix

Quartz particle size and cooling rate effects on microstructural defects and mechanical properties of feldspar-based ceramic materials

Reinforcement or microstructural damage? What effect do quartz particles have on a feldspar-based ceramic material? To answer this question, this study investigates the impact of different cooling conditions on the generation of microstructural defects in a sodium feldspar matrix caused by quartz particles. Moreover, the study aims to analyze how these defects influence the mechanical properties of the final product. Therefore, high-purity sodium feldspar and varying-sized quartz particles were used. The materials was sintered and subjected to different cooling rates during the quartz allotropic transition (). The results showed that the addiction of coarse quartz particles significantly reduced the mechanical properties of the ceramic composition. Cooling types only had a noticeable impact when a material with a high percentage of coarse quartz was rapidly cooled during the quartz allotropic transition. In summary, no evidence of microstructural reinforcement was found when adding quartz particles to a sodium feldspar matrix