L. Morejón

Kinetic effect of hydroxyapatite types on the polymerization of acrylic bone cements

The effect of type and amount of hydroxyapatite on the setting kinetics of an experimental bone cement based on poly(methyl methacrylate-co-styrene) was studied. The average molecular weights of the polymeric beads synthesized were determined by SEC and the average particle size was determined by Optical Microscopy. Three types of hydroxyapatites were synthesized in the laboratory and then characterized by ICP, FTIR and X-ray diffraction. To obtain more compatible fillers, the hydroxyapatites were treated with 3-trimethoxysilylpropylmethacrylate. Bone cements formulations filled with 0, 10, 30, and 50 weight % of hydroxyapatite powders were prepared and the kinetics of setting was followed by Differential Scanning Calorimetry. The presence of hydroxyapatite decreased the reaction rate and increased the degree of conversion, which could be beneficial for the long time stability of the implant.

α-Tricalcium phosphate cements modified with β-dicalcium silicate and tricalcium aluminate: Physicochemical characterization, in vitro bioactivity and cytotoxicity

Biocompatibility, injectability and in situ self-setting are characteristics of calcium phosphate cements which make them promising materials for a wide range of clinical applications in traumatology and maxillo-facial surgery. One of the main disadvantages is their relatively low strength which restricts their use to nonload-bearing applications. α-Tricalcium phosphate (α-C3P) cement sets into calcium-deficient hydroxyapatite (CDHA), which is biocompatible and plays an essential role in the formation, growth and maintenance of tissue-biomaterial interface. β-Dicalcium silicate (β-C2S) and tricalcium aluminate (C3A) are Portland cement components, these compounds react with water to form hydrated phases that enhance mechanical strength of the end products. In this study, setting time, compressive strength (CS) and in vitro bioactivity and biocompatibility were evaluated to determine the influence of addition of β-C2S and C3A to α-C3P-based cement. X-ray diffraction and scanning electron microscopy were used to investigate phase composition and morphological changes in cement samples. Addition of C3A resulted in cements having suitable setting times, but low CS, only partial conversion into CDHA and cytotoxicity. However, addition of β-C2S delayed the setting times but promoted total conversion into CDHA by soaking in simulated body fluid and strengthened the set cement over the limit strength of cancellous bone. The best properties were obtained for cement added with 10 wt % of β-C2S, which showed in vitro bioactivity and cytocompatibility, making it a suitable candidate as bone substitute.

Propagation of fatigue cracks in acrylic bone cements containing different radiopaque agents.

Abstract In this work three iodine-containing monomers were proposed as new radiopaque agents for acrylic bone cements. In previous studies the addition of iodine-containing methacrylate monomers provided a statistically significant increase in tensile stress, fracture toughness and ductility, with respect to the barium sulphate(BaSO4)-containing cement. However, since fatigue resistance is one of the main properties required to ensure a good long-term performance of permanent prostheses, it is important to compare the fatigue properties of these new bone cement formulations with the radiolucent and BaSO4-containing bone cements. Because the acrylic cements have initial cracks, fatigue crack propagation studies were performed. It can be observed that these acrylic cements followed the Paris-Erdogan model. The results showed that the addition of some organic radiopacifiers (DISMA, TIBMA) increased the fatigue crack propagation resistance as compared to the radiolucent cement, being similar to the BaSO4-containing cement. The radiolucent cement showed a low crack propagation resistance.

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.