Surface characterization, in vitro and in vivo biocompatibility of Mg-0.3Sr-0.3Ca for temporary cardiovascular implant.

Magnesium-based alloys are attractive candidate materials for medical applications. Our earlier work showed that the ternary Mg-0.3Sr-0.3Ca alloy exhibits slower degradation rates than both binary Mg-Sr and Mg-Ca alloys. The ternary alloy immersed in simulated body fluid (SBF) forms a compact surface layer of corrosion products that we hypothesized to be a Sr-substituted hydroxyapatite (HA). The main objectives of the current work are to understand the bio-degradation mechanism of Mg-0.3Sr-0.3Ca, to identify the exact nature of its protective layer and to evaluate the in vitro and in vivo biocompatibility of the alloy for cardiovascular applications. To better simulate the physiological environment, the alloy was immersed in SBF which was daily refreshed. Raman spectroscopy and X-Ray photoelectron spectroscopy (XPS) confirmed the formation of a thin, Sr-substituted HA layer at the interface between the alloy and the corrosion products. In vitro biocompatibility evaluated via indirect cytotoxicity assays using HUVECs showed no toxicity effect and ions extracted from Mg-0.3Sr-0.3Ca in fact increased the viability of HUVECs after one week. In vivo tests were performed by implanting a tubular Mg-0.3Sr-0.3Ca stent along with a WE43 control stent into the right and left femoral artery of a dog. Post implantation and histological analyses showed no thrombosis in the artery with Mg-0.3Sr-0.3Ca stent after 5weeks of implantation while the artery implanted with WE43 stent was extensively occluded and thrombosed. Microscopic observation of the Mg-0.3Sr-0.3Ca implant-tissue interface confirmed the in situ formation of Sr-substituted HA on the surface during in vivo test. These results show that the interfacial layer protects the surface of the Mg-0.3Sr-0.3Ca alloy both in vitro and in vivo, and is the key factor in the bio-corrosion resistance of the alloy.

[In vivo dosimetry study of semi-conductors EPD-20 in total body irradiation technique]. / Etude de la dosimétrie in vivo par semi-conducteurs EPD-20 dans les conditions de l'irradiation corporelle totale.

PURPOSE: The objective of this work was the study of in vivo dosimetry performed in a series of 54 patients receiving total body irradiation (TBI) at the Salah-Azaiz Institute of Tunis since 2004. In vivo dosimetry measurements were compared to analytically calculated doses from monitor units delivered. PATIENTS AND METHOD: The irradiation was conducted by a linear accelerator (Clinac 1800, Varian, Palo Alto, USA) using nominal X-rays energies of 6 MV and 18 MV, depending on the thickness of the patient at the abdomen. The dose was measured by semi-conductors p-type EPD-20. These diodes were calibrated in advance with an ionization chamber "PTW Farmer" type of 0.6cm(3) and were placed on the surface of plexiglas phantom in the same TBI conditions. A study of dosimetric characteristics of semi-conductors EPD-20 was carried out as a function of beam direction and temperature. Afterwards, we conducted a comparative analysis of doses measured using these detectors during irradiation to those calculated retrospectively from monitor units delivered to each patient conditioned by TBI. RESULTS: Experience showed that semi-conductors are sensitive to the angle of beam radiation (0-90 degrees ) and the temperature (22-40 degrees C). The maximum variation is respectively 5 and 7%, but in our irradiation conditions these correction factors are less than 1%. The analysis of the results of the in vivo dosimetry had shown that the ratio of the average measured doses and analytically calculated doses at the abdomen, mediastina, right lung and head are 1.005, 1.007, 1.0135 and 1.008 with a standard deviation "type A" respectively of 3.04, 2.37, 7.09 et 4.15%. CONCLUSION: In vivo dosimetry by semi-conductors is in perfect agreement with dosimetry by calculation. However, in vivo dosimetry using semiconductors is the only technique that can reflect the dose actually received instantly by the patient during TBI given the many factors that calculation can not take into account: patient and organs motions and the heterogeneity of the targets.

Estimation of the radiological risk related to the presence of radon 222 in a hydrotherapy centre in Tunisia.

The (222)Rn concentration in air was measured in a thermal water spa used as a hydrotherapy centre in Tunisia. The associated health risk for employees and patients due to the inhalation of (222)Rn and its progeny was estimated. A protection scheme for the employees of the spas has been designed. Results show that the (222)Rn concentration varies in the range 33-589 Bq m(-3). The (222)Rn concentrations measured in the present study show lower values in comparison to those reported for thermal spas in other countries. The (222)Rn concentration in different rooms of the spa depends mainly on the ventilation rate. A model based on a dosimetric approach was adopted to estimate the radon risk considering the (222)Rn concentration, the time spent in the spa, and the radioactive equilibrium factor F. The annual effective dose was found to vary between 0.2 and 1.7 mSv for workers while the range for patients was from 2.8 x 10(-4) to 1.1 x 10(-4) mSv. These values are within the ICRP recommended values.

Natural radioactive nuclides in some Tunisian thermo-mineral springs.

Radioactivity in some Tunisian thermo-mineral springs (11 hot mineral springs and one cold spring) has been determined for the first time in Tunisia using radiochemical separation procedures. The obtained results show that 238U activity concentrations vary between 1.5 and about 43 mBq/l. The measured activities of 234U and 226Ra range from 1.1 to about 82.2 mBq/l and 34-3,900 mBq/l. respectively. The radioactive disequilibria in these waters are in excess of concentration of 234U compared to that of 238U. The 226Ra/234U activity ratios are high and in the range of 9.0-691.0). U, Th and Ra activities are similar to those published for other non-polluted regions of the world. Radioactivity in the only cold mineral water from Aïn Oktor is very low, and thus health hazards due to the consumption of this water are not expected.