Biomedical subjects

L M Rodríguez-Lorenzo

Publications and source records attributed to L M Rodríguez-Lorenzo.

10 recordsLinked to original sources

PubMed2005

Influence of ferrous iron incorporation on the structure of hydroxyapatite.

Iron is a vital element of cellular function within the body. High concentrations of iron can be found in the kidneys and the circulatory system. In bones and teeth it is present as a trace element. The use of iron-based compounds in combination with hydroxyapatite offers a new alternative for prosthetic devices. This work investigates the synthesis and processing of iron containing apatites as a possible new type of ceramic for biomedical devices. Stoichiometric and calcium deficient iron containing apatites were synthesized by a wet chemical reaction with di-ammonium-hydrogen-phosphate, calcium nitrate and a ferrous iron nitrate solution. A secondary phase of tri-calcium-phosphate (TCP) was observed after heat treatment of iron containing, calcium deficient, hydroxyapatite. The apatite structure was maintained after heat treatment of stoichiometric apatite, synthesized in the presence of iron. Sintering in air produced oxidation of Fe2+ to Fe3+, resulting in the formation of hematite as a secondary phase. The introduction of iron into the synthesis of hydroxyapatite causes: (i) an increase of the a-lattice parameter after synthesis and heat treatment in air; (ii) an increase in the c-lattice parameter after sintering in air.

Bone Substitutes↗

PubMed2005

Studies on calcium deficient apatites structure by means of MAS-NMR spectroscopy.

The development of synthetic apatites that replicate the features and properties of the contained in natural tissues will help to diminish the misfit between artificial implants and natural hostesses but the structure of these compounds is still under discussion. The variability in Ca/P ratio of calcium deficient apatites has been explained through different models: surface adsorption, lattice substitution and intercrystalline mixtures of hydroxyapatite and octacalcium phosphate. This work investigates which of the models mentioned suits better in a range of samples. Hydroxyapatites obtained by precipitation, by hydrolysis of dicalcium phosphate and calcined samples with Ca/P ratio between 1.50 and 1.77 and specific surface area between 7 and 108 m2/g have been analysed. OCP and surface adsorption models suit better for great SSA particles and low Ca/P ratio while for smaller SSA particles the lattice substitution model is more accurate. SSA also plays the main role when the capacity to absorb substances is studied though their chemistry can not be explained solely in terms of surface reactivity.

Absorption↗

PubMed2003

Influence of fluorine in the synthesis of apatites. Synthesis of solid solutions of hydroxy-fluorapatite.

Hydroxy-fluorapatites (OH-FAps) occur biologically in teeth and form the basis for application as biomaterials. This work aims to synthesize a series of fluoride substituted calcium hydroxyapatites (OHAps) to determine how fluoride influences the synthesis and the resulting characteristics of solid solutions. OH-FAPs powders were synthesized with a chemical composition of Ca(10)(PO(4))(6)(OH)(2-x) F(x), with x=0.0, 0.4, 0.8, 1.2, 1.6 and 2.0. The synthesis of partially substituted OHAp yields materials with lower crystallinity and higher specific surface area than OHAp or fluorapatite (FAp). The smallest crystal size of 263A, occurs at less than 50% hydroxyl substitution with fluoride at x=0.4, and the highest surface area of 132m(2)/g occurs at x=0.8. Reaction kinetics occur faster at higher fluoride content, producing the expected Ca/P ratio of 1.67 only for x=2.0. X-ray and IR studies show that OH-FAPs are homogeneous solid solutions instead of mixtures of OHAp and FAp. The presence of a high fluoride concentration increases the driving force for crystal growth during the calcination process.

Apatites↗

PubMed2003

Encapsulation of apatite particles for improvement in bone regeneration.

The layering of fluorapatite on hydroxyapatite bodies provides a means of decreasing the solubility of hydroxyapatite, providing fluoride for possible stimulation of bone formation and delaying the release of calcium and phosphate from the more soluble hydroxyapatite. The purpose of this work was to encapsulate hydroxyapatite particles with fluorapatite spanning a thickness more than several crystallites deep. A three-step procedure was employed. Hydroxyapatite powder was immersed in an electrolyte solution until an equilibrium was established between the solid and the dissolved calcium at pH 4.67 and 37 degrees C. Equilibrium was determined by measurement of dissolved calcium with a calcium-specific ion-specific electrode. A 5x10(-2) M ammonium fluoride added to the suspension resulted in a rapid decrease of both calcium and fluoride in the solution. Analysis with X-ray diffraction indicated that a fluoride rich layer containing calcium fluoride deposited onto the particle surface. Scanning electron microscopy revealed submicron spherical precipitate clusters on the hydroxyapatite particles. These clusters transformed to fluorapatite by soaking in a 0.1 M K(2)HPO(4) solution at pH 8 and 70 degrees C. A total time of 10 h was necessary for complete transformation of CaF(2) into fluorapatite.

Journal Article↗

PubMed2002

Fabrication of porous hydroxyapatite bodies by a new direct consolidation method: starch consolidation.

A new direct consolidation method known as "starch consolidation" was developed especially for the fabrication of porous ceramics, as adopted to prepare hydroxyapatite (OHAp) bodies with different pore sizes and pore volume fractions. The method is based on the swelling ability of starch when it is heated to 80 degrees C in the presence of water. An OHAp powder prepared by a precipitation method and heat treated at 900 degrees C to obtain an appropriate specific surface area for colloidal processing was used in the present work. Wet ball milling was required to deagglomerate the powder and improve its processing ability. Different starch volume fractions and starch particle sizes were added to the OHAp slurries, which were then heat treated to promote consolidation by starch gelification. A linear relationship between the planned and measured porosity values was observed. SEM pictures reveal the presence of interconnected pores with shape and sizes corresponding to starch granules used. Flexural strength varied from about 2 to 15 MPa, for pore volume fractions of approximately 70 and 45%, respectively. A degradation study in an acellular synthetic body fluid (SBF) has shown that the prepared bodies keep their integrity under physiological conditions during the studied time. The method offers possibilities of manufacturing materials that can be used as scaffolds engineering and/or systems for controlled delivery of drugs.

Adsorption↗

PubMed2002

Hydroxyapatite ceramic bodies with tailored mechanical properties for different applications.

A perfect control on the final ceramic features will enable the research/clinical community to spread the use of calcium phosphate ceramic bodies to a large number of applications and/or requirements. The mechanical properties of hydroxyapatite ceramic bodies manufactured by different techniques and with different porosities is presented. The flexural strength, hardness, fracture toughness, surface roughness, and their evolution after immersion in SBF are studied. An increase of the mechanical properties with density is observed. The factors governing these results are analyzed. The increase of the porosity percentage of the bodies results in an increase on the surface roughness. The degradation studies show that the HA ceramics keep their integrity and mechanical properties under physiological conditions during the soaking time studied. The OHAp ceramic bodies with controlled porosity could be appropriated for hard tissue substitution or as a carriers for controlled delivery of drugs or as scaffolds for tissue engineering.

Algorithms↗

PubMed2002

Preparation and in vitro bioactivity of hydroxyapatite/solgel glass biphasic material.

Hydroxyapatite/solgel glass biphasic material has been obtained in order to improve the bioactivity of the hydroxyapatite (OHAp). A mixture of stoichiometric OHAp and the precursor gel of a solgel glass, with nominal composition in mol% CaO-26, SiO2-70, P205-4, has been prepared. The amounts of components used have been selected to obtain a final relationship for OHAp/solgel glass of 60/40 on heating. Two different thermal treatments have been used: (i) 700 degrees C, temperature of solgel glass stabilisation and (ii) 1000 degrees C, lower temperature of hydroxyapatite sintering. The bioactivity of the resulting materials has been examined in vitro by immersion in simulated body fluid at 37 degrees C. The results obtained show that both materials are bioactive. The apatite-like layer grown is greater for the new materials than for the OHAp and the solgel glass themselves.

Calcium Compounds↗

PubMed2001

Fabrication of hydroxyapatite bodies by uniaxial pressing from a precipitated powder.

Hydroxyapatite (OHAp) has been obtained by using a precipitation method. Thermal stability of the precipitated powder has been checked to define an appropriate working range to process ceramic bodies without the appearance of odd phases. Pellets of hydroxyapatite have been manufactured by means of uniaxial pressing and convenient thermal treatments have been investigated to achieve high density OHAp bodies. Finally, factors that could affect the ultimate mechanical properties of the sintered bodies prepared by uniaxial pressing have been discussed.

Hydroxyapatites↗

PubMed2001

Colloidal processing of hydroxyapatite.

Reliable bioceramics are needed to implement the high requirements that living tissues demand. This work focuses on the processing steps necessary to manufacture advanced ceramics that can be used as implant devices. The influence of the heat treatment temperature on the characteristics of a precipitated hydroxyapatite (OHAp) powder was evaluated in order to obtain an appropriate specific surface area for colloidal processing. Ball milling of the calcined powders for 20 h was required to improve the rheological properties of the suspensions and the packing ability during consolidation. Different dispersing agents were tested and the first trial was made based on their effect on the zeta potential. The most promising ones were then selected and their efficiency was evaluated from rheological measurements and slip-casting performance of suspensions prepared at different solids loading. Targon 1128 was revealed to be the most efficient dispersant, enabling to prepare fluid suspensions containing 50 vol% solids and the highest green and sintered density values to be obtained.

Colloids↗

PubMed1996

Composite biomaterials based on ceramic polymers. I. Reinforced systems based on Al2O3/PMMA/PLLA.

Composite biomaterials with good mechanical response and a partially biodegradable character were prepared by the free radical polymerization of mixtures of alpha-Al2O3, low-molecular-weight but crystalline poly(L-lactic acid) (PLLA), and methyl methacrylate (MMA). Cylindrical specimens prepared with different composition were characterized by thermogravimetry, calorimetry, 1H-NMR spectroscopy, and x-ray diffraction (XRD). The in vitro biodegradative process was studied in different media, following variations of the pH, gravimetric weight loss of the specimens, and crystalline domain change by XRD after immersion in pure water and buffered solutions at pH 4.0 and pH 8.0 for 90 days. Formation of a relatively porous structure with good cohesion after the biodegradative treatment (confirmed by SEM) was observed. These systems can be considered for applications in orthopedic surgery as filling biomaterials and even as control drug-delivery systems.

Aluminum Oxide↗