E. Dalas

Calcification of porcine and human cardiac valves: testing of various inhibitors for antimineralization.

Despite distinct advantages over mechanical cardiac valve prostheses, the use of bioprosthetic valves remains limited, due to poor long-term durability, primarily as a result of tissue calcification. A novel in vitro, anticalcification process based on treatment of porcine and human heart valves with metallocene dichlorides, as well as with amino acids (phenylalanine, aspartic acid, glutamic acid), has been developed. This anticalcification process reduced mineralization of porcine and human valves up to 32% and 28%, respectively.

The effect of sodium alginate on the crystal growth of calcium carbonate

The effect of sodium alginate in supersaturated solutions of calcium carbonate was investigated under plethostatic conditions. The rates of crystal growth measured in the presence of sodium alginate at concentrations as low as 0.83 × 10-7mol dm-3 were drastically reduced. Kinetic analysis according to a Langmuir-type adsorption isotherm led to the calculation of an affinity constant Kaff = 999.8 × 10-4mol dm-3. The apparent order found from kinetic data was 3.0±0.2 suggesting a surface nucleation mechanism.

Hopping charge transport mechanisms in conducting polypyrrole: Studying the thermal degradation of the dielectric relaxation

Isotherms of the imaginary part of the permittivity from 10−2to2×106Hz from liquid nitrogen to room temperature for fresh and thermally aged specimens of conducting polypyrrole reveal a dielectric loss peak, which is affected by the reduction of conducting grains with aging. Charge trapping at the interfaces separating the conductive islands seems invalid. Thermal aging indicates that macroscopic conductivity and short range one have different aging evolution. The first (dc conductivity) is dominated by the tunneling of the carriers between neighboring grains through the intermediate insulating barriers, though the second (ac conductivity) is due to a backward-forward movement of the carriers and is controlled by the intrachain transport of them and their hopping between the chains.

Novel composites materials from functionalized polymers and silver coated titanium oxide capable for calcium phosphate induction, control of orthopedic biofilm infections: an “in vitro” study

Three copolymers containing the functional groups P=O, S=O and C=O were prepared, and upon the introduction in calcium phosphate aqueous solutions at physiological conditions, “in vitro” were induced the precipitation of calcium phosphate crystals. The investigation of the crystal growth process was done at constant supersaturation. It is suggested that the negative end of the above functional groups acts as the active site for nucleation of the inorganic phase. In order to obtain the copolymer further antimicrobial activity, titania (TiO2) nanocrystals were incorporated in the polymer matrix after silver coverage by UV radiation. The antimicrobial resistance of the composite material (copolymer-titania/Ag) was tested against Staphylococcus epidermidis (SEM), Staphylococcus aureus (SAM), Candida parapsilosis (CAM) and Pseudomonas aeruginosa (PAM), microorganisms, using cut parts of “π-plate” that covered with the above mentioned composite. The antimicrobial effect increased as the size of the nanocrystals TiO2/Ag decreased, the maximum achieved with the third polymer that contained also quartenary ammonium groups.

The crystallization of calcium carbonate on sodium cholate

Recent studies in the bibliography showed that calcium carbonate was the major constituent (77.8%) in gall stones, and the polymorph calcite was at 62.5% of the cases examined. The kinetics of crystallization of calcite on sodium cholate has been studied using the constant composition technique. Analysis of the initial rates as a function of the solution supersaturation, according to the classical nucleation theory, yielded a value of 33 mJ m-2 for the surface energy of the growing phase and a five-ion cluster, forming the critical nucleus. The apparent order for the calcite crystallization was found to be 4.5±0.7 indicative of a surface nucleation mechanism. The formation of calcite may be initiated through the interaction of Ca2+ ions with the negative end of the C=0 bond of the sodium cholate molecule.

Correlation between thickness, conductivity and thermal degradation mechanisms of PEDOT:PSS films

D.c. conductivity σ and thermal degradation measurements on PEDOT:PSS films of different thicknesses d = 50, 120 and 180 nm are reported. The experimental results are consistent with a hopping type carrier transport. For the films with thickness d = 50 nm, which consist of almost one single layer of PEDOT:PSS conductive grains, the conductivity and the heat aging are consistent with a hopping transport in a granular metal type structure. However, for films with d = 120 and 180 nm, in which many conductive grains constitute the film thickness, a completely different behaviour is exhibited. An explanation of this is proposed.