Adsorption of recombinant human bone morphogenetic protein rhBMP-2m onto hydroxyapatite.

Recombinant human mature bone morphogenetic protein 2 (rhBMP-2m) has been expressed to study its adsorption onto precipitated hydroxyapatite (HA). The influence on the adsorption process of different parameters such as pH and concentrations of calcium, phosphate or NaCl has been investigated. Although the adsorption proceeds rapidly at the initial stages, the maximum adsorbed amount is reached after four hours. The process is notably influenced by adding calcium or phosphate to the system but, while calcium ions increase the adsorption of rhBMP-2m onto HA, phosphate ions inhibit it. The influence of pH and NaCl concentration are notable but less important than those of calcium and phosphate. The adsorption data fit well to a Langmuir adsorption isotherm. The values of the isotherm parameters have been calculated and discussed, and an adsorption mechanism has been proposed.

Controlled nucleation and growth of thin hydroxyapatite layers on titanium implants by using induction heating technique.

This paper reports the results obtained by the development of a new wet method of hydroxyapatite (HA) thin layer deposition. The method is based on the localized precipitation of HA on metallic substrates activated by induction heating. The technique developed has been shown to allow for the complete coating of substrates with micrometric thin films of HA within a low processing time. The method has been successfully applied to coat Ti plaques and Ti-6A1-4V cylinders.

Hydrolytic stability of experimental hydroxyapatite-filled dental composite materials.

OBJECTIVES: The purpose of this study was to analyze the behavior in water, related to mechanical properties, of experimental composites for dental restoration. METHODS: The studied materials were composed of a visible-light-curing monomer mixture (Bis-GMA and TEGDMA or HEMA) and micrometric, nanometric or a mixture of both sizes hydroxyapatite particles as a reinforcing filler. Filler particles were modified with a coupling agent (citric, hydrosuccinic, acrylic or methacrylic acid or silane). The hydrolytic stability of the evaluated materials was studied through total elution and water-uptake tests. Percent net-mass variation was daily monitored and analyzed as a function of time. Mechanical performance was examined through flexural properties and Vickers hardness. Morphological surface changes were observed with scanning electron microscopy. ANOVA statistical analysis was performed (P<0.05). RESULTS: In general, the use of HEMA instead of TEGDMA did not substantially worsen the composite quality. Dental composites containing only nanometric particles of hydroxyapatite as a filler are unsuitable for clinical performance. Midway-filled composite resins loaded with micro-HAP particles, coated with citric, acrylic or methacrylic acid displayed low percent elution and water-uptake values. Mechanical properties were similar or even superior to those measured for silane treated particles. SIGNIFICANCE: More research is needed to further improve the interaction of nano-HAP particles with the polymeric matrix, either as a single filler or, preferentially, mixed with micro-HAP, that will allow to increase the total loading of reinforcing filler and, hence, to improve the mechanical properties.

Estudio de la cinética de fotopolimerización de nuevos materiales compuestos con carga híbrida de hidroxiapatita / No disponible

En el presente trabajo se describe el estudio cinético de la fotopolimerización de nuevos composites experimentales, utilizando cargas híbridas de hidroxiapatita. Los composites se prepararon a partir de una mezcla monomérica (matriz) compuestapor el 2,2 bis [p-(2-hidroxi-3-metacriloxipropoxi) fenil] propano(Bis-GMA) y dimetacrilato de trietilenglicol (DMTEG). Se utilizó como carga o relleno inorgánico mezclas de hidroxiapatita sinterizada (HAS) e hidroxiapatita nanométrica (HAN). Se analiza también la influencia, sobre las medidas cinéticas, del contenido en relleno y del tratamiento superficial de estas cargas empleando como agentes funcionalizantes: ácido málico (Mal.) y citratotrisódico (Cit.).La medidas fotocalorimétricas han permitido obtener una valiosa información con respecto al comportamiento cinético de estos materiales. Se ha evaluado la dependencia de la velocidad depolimerización (Rp) con el contenido y la naturaleza del relleno empleado, habiéndose observado un aumento de la misma y de los porcentajes de conversión del monómero (polimerización) en los composites preparados con relleno hidroxiapatita sinterizada y tratada superficialmente con compuestos carboxílicos. Los mejores resultados cinéticos se obtienen con el empleo de HAS modificada con ácido málico (AU)

This work described the photopolymerisation kinetic study of new experimental composites, using hybrid loads of hydroxyapatite. The composites got ready starting from a monomeric mixture (matrix)composed by bis 2,2 [p-(2-hydroxy-3-methacryloxypropoxy) phenil]propane (Bis-GMA) and triethylenglycoldimethacrylate (DMTEG). It was used like load or filling inorganic mixtures of syntherized hydroxyapatite (HAS) and nanometric hydroxyapatite (HAN). It is also analysed the influence, on the kinetic measures, of the content in filling and of the superficial treatment of these loads using coupling agent: malic acid (Mal.) and tri-sodium citrate (Cit.).The photocalorimetric measured has allowed obtaining valuable information with regard to the kinetic behaviour of these materials. The dependence of the polymerisation speed has been evaluated (Rp) with the content and the nature of the used filling, were observed an increase of the same one and of the percentages of the monomer conversion (polymerisation) in the prepared composites with padded HAS and treated superficially with carboxylic compounds. The bestkinetic results are obtained with the employment of you have modified with malic acid (AU)

Dental composites reinforced with hydroxyapatite: mechanical behavior and absorption/elution characteristics.

The purpose of this study was to analyze the behavior in water as well as the mechanical and surface properties of experimental composites designed for dental restoration. Studied materials were composed of a visible-light-cured monomer mixture as a matrix (bisphenol-alpha-glycidyl methacrylate with triethyleneglycol dimethacrylate or hydroxyethyl methacrylate) and either micrometric or nanometric hydroxyapatite (HA) particles as a reinforcing filler. The surface of the filler particles was modified by using different coupling agents (citric, hydroxysuccinic, acrylic, or methacrylic acid). The hydrolytic stability of the evaluated materials was studied through elution-in-water and water-uptake tests. Mechanical and surface properties were examined through the results of flexural, hardness, and surface roughness tests. Means and standard deviations were calculated for each variable. Analysis of variance and multiple comparison tests were performed. Materials containing bisphenol-alpha-glycidyl methacrylate:triethyleneglycol dimethacrylate and micrometric-HA coated with citrate, acrylate, or methacrylate displayed the most favorable results. Improvements should be obtained by increasing the total filler amount, and by the introduction of nanometric-HA filler into a micrometric-HA reinforced composite resin system.