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Biomedical subjects

R Tawashi

Publications and source records attributed to R Tawashi.

At least 19 recordsLinked to original sources
PubMed1991

Calcium oxalate crystal growth in the presence of mucin.

Using interfacially-controlled crystallization and gel diffusion crystallization methods, calcium oxalate monohydrate (COM), dihydrate (COD) and trihydrate (COT) crystals were grown by the slow diffusion of reacting ions in the presence of mucin. It was demonstrated that mucin in the growth media dramatically affected the size, habit, surface structure, thermodynamic stability and phase transition kinetics of hydrated calcium oxalate crystals. The results obtained revealed that mucin as a glycoprotein model controlled the growth of COT and COD single crystals as well as cluster formation. Growth inhibition of specific crystal faces and phase transition retardation occurred in its presence. The data confirmed that glycoproteins are more than just adhesive materials, enhancing crystal aggregation in stone formation.

Calcium Oxalate↗
PubMed1991

The study of the surface geometry of renal stone fragments after shock wave and ultrasound disintegration.

Computerized image analysis was used for characterizing the irregular boundaries of calcium oxalate stone fragments resulting from shock wave and ultrasound disintegration. The complexity of the contour of the fragments was determined to evaluate the surface roughness of the rugged profile of the samples. Crack propagation on the crystal surface of the mineral phase was studied using fractal geometry. A significant difference was observed in the boundary variation of the calcium oxalate stone fragments treated by shock wave and ultrasound. Crack propagation in the mineral phase crystal was found to depend on the method of fragmentation used. There is also an experimental evidence that the surface topography of the stone fragments produced by shock wave depends on the microhardness of the stone material.

Calcium Oxalate↗
PubMed1990

Effect of surface geometry and morphic features on the flow characteristics of microsphere suspensions.

In this paper we present a study on the effect of surface ruggedness of microspheres on the rheological behavior of their suspensions. For this purpose, different types of ragweed pollen grains were selected as models of natural microspheres. A computer-image processing system based on Fourier and fractal analysis of the contour was used to quantitate the micromorphology and surface roughness. The viscosity of suspensions, prepared by the dispersion of the different types of microspheres in heavy liquid paraffin, was determined. It was found that an increase in surface roughness causes an increase in the viscosity of the suspension. Additional resistance to flow could be attributed to internal friction within the suspension due to an increase in the area of contact (during collision or aggregation) among the microspheres, and between microspheres and liquid environment. These findings suggest that the surface geometry of solid particles (e.g., microcapsules, beads, and microspheres) could have a significant effect on the performance of these microparticles in suspension.

Fourier Analysis↗
PubMed1990

Surface phase transition of hydrated calcium oxalate crystal in the presence of normal and stone-formers' urine.

Crystals of calcium oxalate monohydrate (COM), dihydrate (COD) and trihydrate (COT) were grown by slow diffusion of reacting ions from solutions using interfacially controlled crystallization. Phase transition of COT to COD and COM, and COD to COM were studied on single crystal by X-ray diffraction analysis of the same crystal before and after exposure to normal and stone formers' urine. Phase transition on the surface of single crystals has been demonstrated by SEM energy dispersive X-ray microanalysis using windowless detector, and scanning Auger electron microprobe. Data obtained in this study offer direct experimental evidence for phase transformation on the surface of the hydrated calcium oxalate single crystal. In presence of normal urine the surface of COT single crystal undergoes transformation into COD and in presence of recurrent calcium oxalate stone former's urine surface transformation to COM takes place.

Calcium Oxalate↗
PubMed1989

Surface studies of calcium oxalate dihydrate single crystals during dissolution in the presence of stone-formers' urine.

Dissolution of calcium oxalate dihydrate (COD) single crystals was studied at different pH levels and in different dilutions of stone formers' (SF) urine. The Fourier descriptors of the contour were determined during dissolution of COD using a quantitative morphological technique. The surface ruggedness of COD single crystals was determined from fractal analysis. The results obtained were compared with COD single crystals behavior in different dilutions of normal urine previously reported. The shape parameters and surface geometry of the dissolving COD crystals were significantly different in normal and SF urine. The data suggest that the shape descriptors and fractal geometry is likely to be a potential factor in identifying the urine of stone formers.

Calcinosis↗
PubMed1988

Application of fractal dimension to the study of the surface ruggedness of granular solids and excipients.

This report describes the use of fractal analysis in the study of the surface ruggedness of pharmaceutical solids. A comparison of the fractal dimension of granules and excipients prepared by different techniques revealed a possible correlation between the physical behavior of these granules and their surface geometry. The applications of the proposed tool in the study of the surface geometry of pharmaceutical bulk solids are discussed.

Chemical Phenomena↗
PubMed1987

Surface studies of calcium oxalate dihydrate single crystals during dissolution in the presence of urine.

Single crystals of Calcium Oxalate Dihydrate (COD) were grown from solution under controlled release of the reacting ions. Dissolution of COD was studied at different pH levels and in different dilutions of urine. The descriptors of the contour were determined during dissolution of COD using a quantitative morphological technique. The shape parameters and surface ruggedness were determined from Fourier and fractal analysis. The results obtained give quantitative information on the dissolution kinetics and the surface geometry of COD crystals in normal and diluted urine. Dissolution inhibition and morphological changes of COD crystals during dissolution were attributed to selective adsorption of urine non-ionic macromolecules on the crystal stepped surface. Surface etching of COD was found to depend on urine dilution and time of incubation. The data obtained suggest that the geometric structure of the surface is likely to be a potential factor in understanding crystal aggregation in stone formation.

Calcium Oxalate↗
PubMed1986

S.E.M. study of urease-induced crystalluria in the presence of hydroxamic derivatives.

The effect of 3 hydroxamic acid derivatives on urease-induced crystalluria was studied in vitro. Acetohydroxamic acid is more effective than salicylhydroxamic and gentisohydroxamic acids in inhibiting the kinetic of urease enzymatic reaction and in retarding the formation of struvite and apatite. Crystal deposits studied by scanning electron microscope (S.E.M.) and X-ray microanalysis indicated that acetohydroxamic acid favours the formation of large crystals of struvite, and less aggregation is observed. Salicyl and gentiso derivatives favour the formation of brushite together with struvite and apatite.

Apatites↗
PubMed1985

Tack behavior of coating solutions III.

The effect of finely divided solids on the tackiness of coating solutions was determined using a parallel-plate technique. Results demonstrated that the tackiness of coating solutions containing relatively low concentration of polymers augments with the increase in concentration and diminishes with the increasing particle size of finely divided solids. In contrast, the tackiness of coating solutions containing high concentrations of polymers is suppressed upon increasing the concentration and decreasing the size of finely divided solids.

Chemistry, Pharmaceutical↗
PubMed1985

The effect of pH and urine dilution on the electrophoretic mobility of uric acid crystals.

As a result of a continuing programme to understand better the uric acid stone treatment and prophylaxis, an investigation of the effect of pH and urine dilution on the surface charge of uric acid crystals was undertaken. A microelectrophoretic technique was employed to characterize the nature of the surface charge and the electrokinetics of uric acid crystals both in natural and synthetic urines under different conditions of pH and dilution. Both dilution and alkalization reduced the specific conductance of urine and increased the electrophoretic mobility (zeta potential) of uric acid crystals. The presence of cationic additives in diluted urine altered the zeta potential of uric acid crystals. Such findings suggest that proper control of the pH level and urine dilution as well as the surface charge at the solid-liquid interface represent an important factor in the uric acid stone prophylaxis.

Crystallization↗
PubMed1978

Methylene blue as an inhibitor of stone formation.

Kinetics of growth and dissolution of calcium oxalate monohydrate were examined in the presence of small concentrations of methylene blue. The data presented show moderate retardation in growth and dissolution rates. It was also found that methylene blue decreased the decalcification rate of calcium oxalate renal calculi. The implications of these findings in the treatment of urolithiasis are discussed.

Calcium↗
PubMed1978

Growth retardation of calcium oxalate by sodium copper chlorophyllin.

Earlier reports from our laboratories described the inhibitory effect of Mg++ and pyrophosphate on the dissolution and growth of calcium oxalate. In this report, growth of Ca oxalate in presence of very low concentration of chlorophyllin was followed by the Coulter counter and a multichannel analyser. The effect of chlorophyllin concentration on crystal formation was studied at different levels of supersaturation. A concentration of 0.1 microgram/ml produced a remarkable retardation of the induction period and the growth rate. The findings obtained in this study are discussed in the light of the crystal poisoning theory. Comparison was made between chlorophyllin and other growth inhibitors.

Calcium↗
PubMed1977

Calcite growth under controlled diffusion.

The growth of calcite was studied in a gelatin-gel medium under variable environmental conditions by 2 different methods. The results suggest that the organic matrix, the temperature, the diffusion fluctuation depending on ionic concentrations, and the presence of additives exert a fine control on the evolution of single crystals, polycrystalline aggregates, and highly structured concretions of calcite.

Calcification, Physiologic↗
PubMed1977

Scanning electron microscopic study of calcium oxalate concretions grown in gel system and calcium oxalate stones.

Calcium oxalate concretions grown in gelatin gel medium, and calcium oxalate renal stones were studied by polarized light and scanning electron microscopy. In both cases, the results obtained confirm that the surface crystals have random axial orientation and that the gross configuration seems to be determined by the fibrous organic matrix. In vitro concretions grown in the gelatin gel medium are more resistant to EDTA demineralization and to ultrasonic irradiation than calcium oxalate stones.

Calcium↗
PubMed1976

Retardation of dissolution and growth of calcium oxalate monohydrate.

The kinetics of dissolution and growth of calcium oxalate monohydrate were examined in the presence of small concentrations of pyrophosphate, chlorophyll, and other agents. Data presented show that the retardation in mass transport in both processes is controlled by the nature of the additive, its concentration, and the way the additives are combined in the dissolution medium. Dissolution was studied using a particle counter method, and growth was conducted in a gel system under the slow diffusion of the reacting ions. Results obtained show that chlorophyll is more active than other inhibitors studied and suggest a higher surface adsorption intensity on the primary sources of the crystal surface.

Chlorophyll↗
PubMed1975

Growth of calcium oxalate in gel systems.

Methods are described for growing calcium oxalate in silica and gelatin gels under different conditions. The results obtained indicate that, in silica gel, calcium oxalate grows into single individual crystals, twins, and rosettes. Bipyramidal calcium oxalate dihydrate crystals similar to those present in the urine of stone formers were prepared in the silica gel system. The gelatin gel offered a suitably structured substrate on which calcium oxalate monohydrate crystals grow into aggregates. The orientation pattern of calcium oxalate crystals suggests that the growth process is controlled by the stereospecificity of the gelatin medium supporting growth.

Calcium↗