Rodolfo Botter

A bone substitute composed of polymethylmethacrylate and α-tricalcium phosphate: results in terms of osteoblast function and bone tissue formation

The biological properties of a composite polymeric matrix (PMMA + alpha-TCP) made of polymethylmethacrylate (PMMA) and alfa-tricalciumphosphate (alpha-TCP) was tested by means of in vitro and in vivo investigations. PMMA was used as a comparative material. Osteoblast cultures (MG 63) demonstrated that PMMA + alpha-TCP significantly and positively affected osteoblast viability, synthetic activity and interleukin-6 level as compared to PMMA. At 12 weeks, the PMMA + alpha-TCP implants in rabbit bone successfully osteointegrated in trabecular and cortical tissue (affinity index: 57.14+/-8.84% and 68.31+/-6.18%, respectively). The newly formed bone after tetracycline labelling was histologically observed inside PMMA + alpha-TCP porosity. The microhardness test at the bone-PMMA + alpha-TCP interface showed a significantly higher rate of newly formed bone mineralization compared with PMMA (+83.5% and +58.5%, respectively), but differences still existed between newly formed and pre-existing normal bone. It is herein hypothesized that the present positive results may be ascribed to the porous macroarchitecture of PMMA + alpha-TCP and the presence of the bioactive ceramic material that could have a synergic effect and be responsible for the improvement of (a) the material colonization by bone cells, (b) osteoblast activity, (c) osteoinduction and osteoconduction processes, (d) bone remodelling.

Liquid-like H2O adsorption layers to catalyze the Ca(OH)2/CO2 solid-gas reaction and to form a non-protective solid product layer at 20°C

Abstract Porous calcium hydroxide particles have been equilibrated with water vapor in the relative pressure range 0.4–0.85 at the temperature of 20°C. Then the particles were used in the reaction with gaseous carbon dioxide at the same temperature and at pressure of 0.65 kPa. The system is converted up to 85% into a non-protective layer of calcium carbonate which is all distributed inside the initial porous particles. The same reaction with dry-calcium hydroxide powders converts up to 10% at a temperature of 100°C. The observed catalytic effect is dependent upon the initial amount of water adsorbed. A minimum number of four layers of water adsorbed onto the calcium hydroxide surfaces is required to promote the catalytic effect.

Use of α-tricalcium phosphate (TCP) as powders and as an aqueous dispersion to modify processing, microstructure, and mechanical properties of polymethylmethacrylate (PMMA) bone cements and to produce bone-substitute compounds

Addition of tricalcium phosphate (alpha-TCP) powders as an aqueous dispersion to a polymethylmethacrylate (PMMA) bone cement is shown to produce a class of composites that due to their microstructure and mechanical properties may be suitable for application as bone substitutes. The PMMA forms a solid cellular matrix with open cells about 100 micrometer in size and incorporating TCP clusters. The TCP aggregates inside the cells form a porous network, with average mesopore diameters of about 0.1 micrometer, that is accessible from the outer surface. If TCP is added to PMMA in the form of dried powders, the composites are not applicable as bone substitutes. The dynamic elastic modulus (DEM) and compressive and tensile strengths were measured and discussed for both classes of composites. The mechanical properties of the bone-substitute composites, although lower than the other class of composites, are still competitive with those properties of a porous ceramic matrix of hydroxyapatite and with those of natural bones.

α-Tricalcium phosphate hydrolysis to octacalcium phosphate: effect of sodium polyacrylate

Alpha-Tricalcium phosphate (alpha-TCP) hydrolysis into octacalcium phosphate (OCP) has been investigated in phosphoric acid solution at different concentrations of sodium polyacrylate (NaPA). The hydrolysis process has been followed by powder X-ray diffraction, infrared absorption and scanning electron microscopy analyses. In the absence of the polyelectrolyte, alpha-TCP undergoes a complete transformation into OCP in 24 h. The presence of polyacrylate in solution inhibits the hydrolysis so that a NaPA concentration of 0.5 microm is sufficient to lengthen the time required to complete the hydrolysis to 4 days. The variation of Ca2+ concentration in the soaking solution suggests that the transformation occurs through alpha-TCP dissolution followed by OCP precipitation. The delayed OCP nucleation and growth in the presence of polyacrylate implies a preferential adsorption of the polyelectrolyte on the growing OCP crystals, which induces an anisotropic reduction of the coherence lengths of the perfect crystalline domains.

The effect of water in inorganic microsponges of calcium phosphates on the porosity and permeability of composites made with polymethylmethacrylate

Bone-substitute compounds were obtained by mixing pre-polymerised powders of polymethylmethacrylate and liquid methylmethacrylate monomer with two aqueous dispersions of alpha-tricalcium phosphate (alpha-TCP) grains and calcium-deficient hydroxyapatite (CDHA) powders. The final composites appeared to be porous. The total open porosity was a function of the amount of water added. The water, which was the pore-forming agent, vapourised after the polymerisation process, leaving behind empty spaces in the polymeric matrix. The inorganic powders placed inside the polymeric matrix were shown to act as local microsponges. The water capacity of these microsponges can be determined by a centrifugation step carried out on aqueous dispersion of alpha-TCP and/or CDHA powders that occur before any reaction with the organic compound. The relationship between the total open porosity of the composites and the amount of water trapped inside the inorganic agglomerates proved to be almost linear. The effect of the chemical composition of the powder on the total open porosity is not too great, provided that the two kinds of pellets are prepared with the same amount of water. Both the permeability and shape of the pores proved to be a function of the total open porosity. An increase of the latter parameter produces an increase in permeability and a decrease in tortuosity. Osteoconductivity and osteoinductivity of the final composites were tested in vivo by implantation in rabbits. Formation of new trabecular bone was observed inside the pores where the inorganic powders had been placed.

Microstructural development during the oxidation process in SnO2 thin films for gas sensors

Abstract Polycrystalline SnO2 thin films with different thicknesses and microstructures have been produced by using the rheotaxial growth and thermal oxidation technique (RGTO), which allows one to obtain connected granular films. In this paper, we describe the basic mechanism of formation of a granular metallic film and the development of its microstructure during the oxidation process. Samples with different degrees of connection have been produced, starting from the same initial tin films, but changing the thermal treatment and the partial O2 pressure. SEM and XRD analysis are used to characterize the microstructures of the produced films. The functional properties of such sensors are tested by performing I–V and I-time measurements in dry air and in 1000 ppm of ethanol in air. A relation between the functional properties and the microstructure of the sensors has been established.

Aluminum hydroxide microstructural units in gelled media aged, or nonaged, with alcohol and water.

Aluminum hydroxide gelled media dispersed and then aged in alcohol (ES) or in water (WS) were prepared with a solid phase concentration equal to 0.45% v/v. The media were characterized through rheological measurements and detailed analysis. Xerogels were obtained through a designed drying process at 8 degrees C under vacuum for 24 h, followed by a heating treatment at 105 degrees C and a pressure of 10(-3) Pa for 2 h. The xerogel microstructure was carefully investigated using N2 adsorption-desorption methods at 78 K. Rheology data on ES and WS colloidal dispersions were compared with data computed from adsorption isotherms of corresponding xerogels, in order to infer information about particles organization in the dispersions. On this ground, a model for microstructural units dispersed in the liquid phase has been derived. The beneficial action of alcohol in giving xerogel powders with higher specific surface area and higher porosity has been explained on the basis that alcohol produces changes in the corresponding dispersed microstructural units. The effect of the aging time in alcohol and in water was evaluated, and the evolution of all microstructural parameters was described.

Double-layer granular SnO2 sensors

Abstract Double-layer SnO2 films made up of quasi-spherical grains have been prepared using a thermal evaporation and oxidation technique. The tin is evaporated on a hot substrate, producing a film of metallic drops. The films are oxidized under low partial oxygen pressure in order to obtain SnO2 grains with smooth surfaces. This granular film is electrically non-connected; the interconnection between grains is obtained by the deposition (using the same process) of a second layer. Samples with different particle sizes in the first and second layers can be produced by varying the amount of tin deposited per unit area. Alcohol and hydrogen sensitivity measurements have been performed on samples with different microstructures in order to investigate the relationship between the microstructure and the functional properties and to optimize the grain sizes of the two layers.

Effect of weak uniaxial loads on creep strain rate in high-porosity MgO compacts during early sintering stages

Creep phenomena accompanying the early stage of sintering of high-porosity MgO powder compacts were investigated with regard to the dependence of creep rate on the applied stress. This dependence was found to be non-linear, obeying a power law with an exponentn <1, in contrast with the behaviour of dense compacts which exhibit linear Nabarro-Herring creep under the same type of loading. The nature of the creep exponent, expected to be in relation to mechanisms of particle disconnection and rearrangement, frequently observed in a high-porosity compact during the early stage of neck formation, has been explored using an appropriate physico-mathematical model. The relevant point concerning high-porosity compacts is that, owing to the loosely packed microstructure, the necks must resist not only normal forces, but also bending moments. It is the action of such bending moments which is supposed to drive the particles rearrangement. In this framework, the nature of the creep exponent appears to be related mainly to the green density, but it is substantially constant with densification. The predictions of the model explain the experimental results forn <1 (high-porosity green compacts), with a smooth transition to the case ofn=1 (low-porosity green compacts).

Effect of vacuum and of strong adsorbed water films on micropore formation in aluminum hydroxide xerogel powders.

Aluminum hydroxide gels were washed with water, ethanol, methanol and isopropanol to obtain new gels with different liquid phases that were dried either in air at 120 degrees C or under vacuum at 80 degrees C. Drying in air leads to alcoholic xerogels with BET surface areas larger than the aqueous ones. The effect of the alcoholic groups as substitutes of the hydroxyl ones has been discussed to account for the final size of xerogel crystallites. Drying under vacuum decreases the BET surface of the methanol xerogels, but no micropores are formed in all the alcoholic xerogel matrixes. On the contrary, the vacuum drying process changes significantly the microstructure of the aqueous xerogels. Their BET surface increases by 34 m(2)/g, and micropores are formed within their crystallite aggregates. It has been experimentally shown that these changes are due to a shear transformation that occurs in the boehmite xerogels obtained under vacuum. To discuss these data, the existence of chemical compounds such as AlOOHnH(2)O was postulated. On this ground, a neat analogy between vacuum drying process and vacuum interfacial decomposition reactions of inorganic salts can be drawn. This analogy explains how a state of stresses forms in aqueous xerogel matrix during vacuum drying process.