Marcelo Henrique Prado da Silva

Porous Triphasic Calcium Phosphate Bioceramics

In the present study, calcium phosphate powders were produced by precipita tion in aqueous solution. Porous discs were produced by organic additives incorporation. The final microstructure consisted of a triphasic bioceramic after sinter ing. The produced material is a good candidate to be used as bone-filler. In the present study a detailed s udy of the sintering temperature to produce triphasic calcium phosphate ceramics is presented. Introduction Calcium phosphate bioceramics can be used in applications where bone ingr owth is intended. In this application, the ideal material is the one with a degradation ratio similar to that of new bone formation. It is well established that pure and crystalline hydrox yapatite, Ca 10(PO4)6(OH)2 has a low degradation ratio in vivo. For this reason, recent studies have pointed to the design of multiphasic calcium phosphate bioceramics as bone fillers [1-3]. The se materials contain other calcium phosphates with higher solubility when compared to pure hydroxyapat ite. Tricalcium phosphates are bioactive ceramics that can be associated to hydroxya patite. These bioceramics exhibit polimorphism: α-Ca3(PO4)2 (alpha-TCP) and βCa3(PO4)2 (beta-TCP). In temperatures above 1300°C, beta-TCP is likely to decompose in alpha-TCP [4,5]. Porous bioceramics are suitable for being used as bone-fillers. In this application, pores are requested to have diameters above 100 μm to allow proper vascularisation of the newly formed bone [6-7]. In recent studies, porous triphasic bioceramics were produced by dry pressing and sintering a patented glass-reinforced hydroxyapatite [8]. In the present study, similar results were obtained by a simple method. Materials and Methods In this study, apatite nanoparticles were produced by aqueous precipitati on. The starting solution was 0.3M H3PO4, 0.5M Ca(OH) 2, 1M CH3CHCO2HOH. The pH value of the solution was adjusted to pH=10 by NH4OH addition. The suspensions were left overnight for ageing. The suspe n ion was then vacuum filtered and washed in deionised water to remove NH 4OH. The powders were dried in an oven at 100oC overnight. Porous specimens were produced using a dry method developed in previous studies [1,2]. In this study, wax spheres (Licowax , Clariant) with two different particle sizes were used to produce porous structures: 0.8mm (90%>800μm) and 0.3mm (90%>300μm). Porous discs with 65 vol% of Licowax  were produced by dry mixing spheres to the powders and green bodies were produced by uniaxially pressing the mi xture at 40 MPa. The discs were heated at 550oC in a muffle furnace at a heating rate of 0.5oC/min to burn the organic additives. Final sintering was performed at a heating rate of 4oC /min to consolidate the porous structures. Five different temperatures were used to assess t he microstructural evolution: 900oC, Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 1021-1024 doi:10.4028/www.scientific.net/KEM.254-256.1021

High-Resolution Transmission Electron Microscopy Study of Nanostructured Hydroxyapatite

Crystalline properties of synthetic nanostructured hydroxyapatite (n-HA) were studied using high-resolution transmission electron microscopy. The focal-series-restoration technique, obtaining exit-plane wavefunction and spherical aberration-corrected images, was successfully applied for the first time in this electron-beam-susceptible material. Multislice simulations and energy dispersive X-ray spectroscopy were also employed to determine unequivocally that n-HA particles of different size preserve stoichiometric HA-like crystal structure. n-HA particles with sizes of twice the HA lattice parameter were found. These results can be used to optimize n-HA sinterization parameters to improve bioactivity.

Porous Bioceramics Produced with Calcium Phosphate Nanoparticles

In the present study, apatite powders were obtained from aqueous precipi tation under different pH values. The produced powders were used as a base materia l for the production of porous bioceramics. Porous samples were produced by a dry method using org anic additives and sintering at 1100oC. The powders were sintered and characterised by X -ray diffraction. The final microstructure consists of hydroxyapatite and tricalcium phosphate. S canning electron microscopy analysis showed an interconnected porous structure with pores larger t han 100μm. This method of production of porous bioceramics is simple and does not involve the use of comm ercial hydroxyapatite. These findings represent an alternative method for t he production of triphasic porous ceramics. Introduction Porous bioceramics are used in biomedical applications where bone ingrow th is needed [1-3]. In these applications pore sizes must be larger than 100 μm in diameter for allowing proper vascularisation of the newly formed bone tissue [4-5]. Hydroxyapatite, Ca 10(PO4)6(OH)2 is the most used bioceramic and its combination with other more resorbable calcium phosphates create conditions for dissolving in vivo while bone healing is taking place. Biodegradable calcium phosphate ceramics like alpha tricalcium phosphate, Ca 3(PO4)2 (α-TCP) and beta tricalcium phosphate, Ca 3(PO4)2 (β-TCP) are frequently used as bone grafts for allowing bone ingrowth. In previous studies, glass reinforced hydroxyapatite was used as a ba se material for the production of triphasic porous calcium phosphate ceramics [6-8]. However, this rout e has several steps: production of the calcium phosphate based glass; sieving and homogeneously mi xing the glass particles with commercial hydroxyapatite; sintering of the fina l body. Triphasic calcium phosphate ceramics can be produced in a simpler way, by aqueous precipitating a patite nanoparticles and further sintering [9]. Materials and Methods In this study, apatite nanoparticles were produced by aqueous precipitati on. The starting solution was 0.3M H3PO4, 0.5M Ca(OH) 2, 1M CH3CHCO2HOH. The pH value of the solution was adjusted to pH=8, pH=10 and pH=12 by NH 4OH additon. The suspensions were left overnight for ageing. The suspension was then vacuum filtered and and washed in deionised water to remove NH4OH. The powders were dried in an oven at 100oC overnight. The powders were anal ysed by X-ray diffraction (XRD) and then sintered. Sintered powders were again a n lysed by XRD to assess the final phase composition. Porous specimens were produced using a dry method developed in previous studies [6-8]. In this method, wax spheres are added to the ceramic powders to produce porous str uct re . 65 vol% of wax spheres was added to the powder and mixed to produce the porous specime ns. Th mixture was then heat treated at 550oC in a muffle furnace at a heating r te of 0.5oC/min to burn the organic additives and sintered at 1100oC at a heating rate of 4oC/min to consolidate the porous structur es. Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 23-26 doi:10.4028/www.scientific.net/KEM.240-242.23

Hydroxyapatite Scaffolds Produced by Hydrothermal Deposition of Monetite on Polyurethane Sponges Substrates

Hydroxyapatite scaffolds have been being produced by a wide range of processes. The optimun material to be used as bone graft has to be partially resorbable, with resorption rates similar to new bone formation ones. The samples must have porosity compatible with tissue ingrowth. Hydroxyapatite and tricalcium phosphate ceramics are good choices for designing such materials. In the present study, polymeric sponges were coated with hydroxyapatite and sintered. The method consists of coating polyurethane sponges substrates in an aqueous solution rich in phosphate (PO4)3- and calcium (Ca)2+ ions. The solution is composed by 0.5M Ca(OH)2, 0.3M H3PO4 and 1M CH3CHCO2HOH (lactic acid) at pH of 3.7. The sponges were immersed in a beaker with the solution and heated up to 80°C to precipitate monetite on the sponge. Continuous and adherent coatings were formed on the surface of sponges interconections. These coatings were characterised by X-ray diffractometry and the only identified phase was monetite. The substrates were converted to hydroxyapatite in an alkali solution.The total conversion from monetite to hydroxyapatite was confirmed by XRD analyses. The struts were heat treated in order to eliminate the organic sponge and sinter the scaffolds. After sintering, hydroxyapatite and tricalcium phosphate were identified on the struts. Optical microscopy revealed the morphology of the struts, while scanning electron microscopy (SEM) showed the precipitates morphology. The method showed to be efficient in the production of porous scaffolds.

In Vitro Assessment of New Niobium Phosphate Glasses and Glass Ceramics

Niobo-phosphate glasses were produced in order to assess the citotoxicity of samples with different compositions. Different P2O5/Ca ratios were studied in an attempt to correlate the biological behavior of new niobo-phosphate bioactive glasses with conventional bioactive calcium phosphate glasses. The most biocompatible glass composition was chosen to produce glassreinforced hydroxyapatite composites.

Structural Properties of Nanostructured Carbonate Apatites

B-type carbonate apatite samples were synthesized by wet chemical method and characterized by X-ray Fluorescence Spectrometry, X-ray Diffraction, Fourier Transformed Infrared Spectroscopy and High Resolution Transmission Electron Microscopy. The XRD and FTIR analysis confirmed the presence of one B-type carbonate apatite phase and the HRTEM images revealed the coexistence of amorphous and polycrystalline regions in the order of 2nm with the carbonate apatite structure. Second phases or precursors were not discovered.

Porous Biphasic and Triphasic Bioceramics Scaffolds Produced by Gelcasting

The present work suggests a modified gel casting process, including polyethylene wax spheres addition to the suspension with the objective of creating uniform and interconnected pores in the body of samples. In the present study, apatite powders were synthesized at pH 10 and pH 12 in order to give rise to biphasic and triphasic bioceramics after sintering.

Structural Properties of Hydroxyapatite with Particle Size Less Than 10 Nanometers.

Hydroxyapatite, HA, with crystal size smaller than 10 nm was synthesized by dropwise addition of calcium nitrate and ammonium phosphate under controlled conditions. Powder was composed by agglomerates of nano-particles with specific surface area higher than 200 m2/g. HA samples had a main pore size distribution centered at 13-15 nm with a secondary mode centered at 3-5 nm. High resolution TEM revealed that individual particles had nearly spherical shapes and were mainly composed of a crystalline core and an amorphous external component. EXAFS measurements confirmed that the short range order of those HA nanocrystals was similar to that of HA sintered at high temperature. HA powder with small particle size incorporates in its structure more water and carbonate ions than HA prepared in normal conditions.

Hydroxyapatite-alginate composite for lead removal in artificial gastric fluid

Millimetric spherical beads of a biocompatible composite were produced from sodium alginate, a natural polysaccharide, and nanostructured hydroxyapatite (HA). It was shown that the composite was effective in the removal of lead ions and lead phosphate nanoparticles from high-contaminated simulated gastric fluid. X-ray diffraction spectroscopy and scanning electron microscopy analyses performed on HA–alginate beads after the Pb 2+ uptake showed that nanocrystals of a lead phosphate, [Pb 10– x Ca x (PO 4 ) 6 Cl 2 ], were precipitated on the bead surface. The cross-linked polymer chain had a double role: (i) keep Pb 2+ ions and lead phosphate nanoparticles bounded to the bead surface, preventing their bioavailability in stomach fluid; and (ii) delay HA dissolution in the acidic conditions of the stomach, assuring that an excess of Ca 2+ will not be released to simulated gastric fluid. Desorption experiments in simulated enteric fluid revealed that lead remained immobilized in the calcium phosphate phase in the intestinal tract. These results indicate HA–alginate composite as a potential system for heavy metals removal from contaminated gastric and enteric human fluids, minimizing its adsorption by the human body.

Resposta do tecido subcutâneo de camundongos à implantação de um novo biovidro à base de óxido de nióbio

The aim of this study was to evaluate the biological response to the implantation of a new biocompatible glass based on niobium oxide and phosphorus oxide. Scanning electron microscopy with energy dispersive spectroscopy evaluated the morphology of the material (SEM/EDS) and the tissue response was evaluated by implantation of 30mg of biocompatible glass on subcutaneous tissue of Balb/c mice (n=15) as ISO 10993-6. After the period of 1, 3 and 9 weeks, the animals were killed and the necropsies were fixed in buffered formalin pH 7.2 and processed for inclusion in paraffin after demineralization step in Allkymia solution; however, no demineralization conventional procedure for bone and ceramics biomaterials was sufficient to decompose the material. Alternatively, the material was processed for inclusion in resin for being cut by high impact microtome. The histopathological study considered inflammatory reaction (intensity of polymorphonuclear, mononuclear and giant multinuclear foreign body cells) and repair process (granulation tissue and fibrosis) for evaluation. SEM/EDS analysis showed irregular particles with wide size variation and presence of niobium, phosphorus, calcium and oxygen. Despite of the presence artifacts included during the histolopatological processing, microscopic analysis showed moderate inflammatory infiltrate with the presence of mononuclear cells in week 1, that disapeared in the next implantation periods. After 3 and 9 weeks, blood vessels were observed, with discrete presence of foreign body giant multinuclear cells containing particles of niobium biocompatible glass. Even after 9 weeks, no fibrous capsules were observed around the granules of material. Necrosis foci and particles degradation signs were not detected in no one experimental period. Based in these preliminary results, it was possible to conclude that the tested material is biocompatible and not bioabsorbable. The comparison of this biocompatible glass containing niobium, specially grafted into intraosseous sites, will allow the evaluation of its real potential use as bone graft.