Dario Beruto

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.

Use of the Langmuir method for kinetic studies of decomposition reactions: calcite (CaCO3)

The Langmuir method for measurement of vapour pressures has been tested for use in studies of decomposition reactions. The isothermal weight loss in vacuum from cleavage (10text-decoration:overline11) planes of calcite (CaCO3) single crystals was measured continuously at temperatures from 934 to 1013 K. The rate was constant until approximately 80% of a 1 mm slice had decomposed. The apparent activation enthalpy was 205 kJ (49 kcal) mol–1. Micrographic examination showed an approximately 30 µm thick layer, probably a metastable form of calcium oxide, separating the calcite from the growing layer of oriented stable calcium oxide. The 30 µm layer yielded a single X-ray diffraction peak which was displaced slightly from the strongest (220) peak of the oriented normal calcium oxide. Lower apparent activation enthalpies measured in previous studies of calcite decomposition in inert atmospheres are suggested to result either from partial diffusion control of the process or from catalysis of the direct formation of normal calcium oxide by carbon dioxide or a component of the system atmosphere. The ratio of the measured decomposition rate in vacuum to the maximum rate, which can be calculated from the Hertz–Knudsen–Langmuir equation, is suggested to be a useful parameter in correlating and predicting decomposition reaction rates.

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.

Calcium oxides of high reactivity

A RECENT study of the kinetics of decomposition of calcite (CaCO3) single crystals in vacuo showed that if the reaction was interrupted before completion a 30-µm layer of a poorly crystalline material was present between the undecomposed CaCO3 and a layer of normal polycrystalline CaO1. It was hypothesised that the material of this 30-µm layer is a metastable form of CaO that transforms irreversibly to the stable polycrystalline oxide when the accumulated strain exceeds a critical level. If so, the free energy of formation of the metastable oxide from the stable oxide must lie in the range between zero and +31,500−21 TJ mol−1 and might well lie at the positive end of this range2. Such a metastable oxide should be chemically more reactive than the stable oxide. If the hypothesis is true, then the principal product of decomposition in vacuo of calcite particles of diameter < 30 µm should be the metastable oxide. We present here evidence that this inferrence is correct, and we demonstrate that not only this oxide, but also a highly crystalline oxide which is produced when large calcite crystals are decomposed in vacuo, reacts more vigourously with water than does the product of calcite decomposition in air or nitrogen.

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.

Calcite and aragonite formation from aqueous calcium hydrogencarbonate solutions: effect of induced electromagnetic field on the activity of CaCO3 nuclei precursors

Calcite and aragonite formation from aqueous solution compete in the temperature range 353–373 K at a pressure of 0.1 MPa. Despite the fact that the calcitic phase is more stable than the aragonitic phase, often the latter phase is formed. In this paper the kinetic features related to this reaction are investigated and it is shown that a fast precipitation rate enhances the formation of calcite, which is the phase with higher entropy content.Several routes are possible for increasing the precipitation rate. The experimental evidence illustrated in this paper shows that the precipitates obtained by thermal evaporation of aqueous calcium hydrogencarbonate solutions previously exposed to the action of an induced electromagnetic low-frequency (ELF) field, have an XRD pattern where calcite is the predominant phase. After the same thermal treatment, the untreated aqueous solutions yield a precipitate formed by aragonite. The effect of the induced ELF field on the calcite: aragonite ratio in the precipitate is non-linear with the average modulus of the electromagnetic force. Data analysis allows the experimental evidence to be correlated with a faster precipitation rate due to the effect of the induced ELF on the surface chemistry of the pre-existing calcium carbonate nuclei in the hydrogencarbonate solutions at room temperature. Both calcite and aragonite micrograins obtained through thermal evaporation of treated solutions are about three times larger than those obtained from untreated aqueous solutions. The mechanism of facilitated crystal growth is discussed in relation to the modification in surface activity induced by the ELF field on the pre-existing calcium carbonate nuclei.

INFLUENCE OF AGAR ON IN VITRO CULTURES: I. PHYSICOCHEMICAL PROPERTIES OF AGAR AND AGAR GELLED MEDIA

SummaryThe success of in vitro culture is related to several factors. Beside factors associated with the plant material or the medium composition, the physicochemical characteristics of gelled media can play an important role. In this paper, the latter aspect has been considered and the nature of agar powders has been investigated. Moreover, the process of gel formation for three different media and the availability of water and minerals for the corresponding gels have been studied. Analysis of agar powders showed that they can contain different amounts of impurities and the dialysis of these powders suggested that the impurities might be available to the tissues. Thermal analysis on the hygroscopic properties of the agar brands suggest the importance of these data to obtain comparable and reproducible gelled media. The study on the process of formation of gelled media indicates that there is a critical temperature Tss which can be used to control the gel processing. In fact, at this temperature, agar powders in water transform into a sol status through a rapid shift of electrical conductivity. Water potential of the medium, water loss from gels over the culture period, and the ease of releasing liquid from gels under pressure were shown to be different for different agar brands. A different availability of water and minerals in Murashige and Skoog medium was deduced from the gels prepared with three agar brands (Oxoid, Merck, and Roth).

Influence of microstructures on the functional properties of tin oxide-based gas sensors

Abstract Three types of SnO 2 sintered-pellet gas sensors with different relative densities ranging between 0.5 and 0.3 and with almost equal grain and neck sizes have been prepared and tested. The influence of such microstructures on the functional properties of SnO 2 gas sensors has been investigated using dry air and 1000 ppm ethanol in air, over the temperature range 600-700 K. Experimental data are discussed in the light of existing theories. Different equations for the sensitivity have been rewritten and discussed in order to separate the contribution of the microstructure from other contributions. The equations allow one to understand the sensitivity behaviour versus temperature and applied external electrical field. Furthermore, such equations predict the effects of the average coordination number on the electrical sensitivity of the three families of sensors, in significant agreement with the experimental data.

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.