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Biomedical subjects

A Danesh

Publications and source records attributed to A Danesh.

6 recordsLinked to original sources
PubMed2001

An in situ dissolution study of aspirin crystal planes (100) and (001) by atomic force microscopy.

PURPOSE: To observe in situ and on individual aspirin crystal faces the comparative rates and processes of dissolution of the dominant faces. METHODS: The kinetics of the dissolution rate of two aspirin crystal planes (001) and (100) under 0.05M HCl are studied in situ at room temperature using Atomic Force Microscopy. The dissolution process of each crystal plane was followed by observed changes in topographic features. RESULTS: The results revealed that crystal plane (001) dissolves by receding step edges, and has a dissolution rate of 0.45 nm s(-1). Conversely. plane (100) displays crystal terrace sinking at an average rate of 2.93 nm s(-1). Calculated intrinsic dissolution values (g s(-1) cm(-2)) for planes (001) and (100) are 1.37 x 10(-7) gs(-1) cm(-2) and 8.36 x 10(-7) gs(-1) cm(-2), respectively. CONCLUSIONS: These values indicate that the rate of flux of material from plane (100) is approximately six times greater than that from plane (001), under 0.05M HCl. Interpretation of the data, based upon intrinsic dissolution rates and dissolution rate velocities, correlate with reported variations in the dissolution behavior of commercial aspirin products. These observations illustrate the suitability of the technique for characterizing the dissolution behavior of crystalline drugs.

Aspirin↗
PubMed2000

Surface characterization of aspirin crystal planes by dynamic chemical force microscopy.

Tapping mode (TM) atomic force microscopy (AFM) has been applied in a novel fashion to characterize and distinguish the (001) and (100) surfaces of individual aspirin crystals. The surface characterization was achieved by amplitude-phase, distance (a-p,d) measurements employing gold-coated AFM probes functionalized with self-assembled monolayers (SAM). Experiments using model probes coated with -CH3 and -COOH terminated SAMs have been performed on the two aspirin crystal planes (001) and (100). Results indicate that the hydrophobic -CH3 terminated AFM probes had a greater degree of interaction with the crystal plane (001), whereas the -COOH terminated AFM probes had a larger interaction with the crystal plane (100). Interpretation of these data, based upon the chemistries of the probes, correlates with current understanding of the crystal surface chemistry derived from X-ray diffraction data and dissolution rate studies.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2000

Discrimination of polymorphic forms of a drug product by localized thermal analysis.

In chemical processing, it is important to distinguish between and identify polymorphic forms. We demonstrate the novel use of scanning thermal microscopy (SThM) and localized thermal analysis to distinguish and identify polymorphic forms of the drug cimetidine. These forms cannot be resolved by classical bulk thermal analysis. SThM reveals a sample consisting of a 50 : 50 mixture of the polymorphs contains regions of different thermal conductivity, corresponding to the different polymorphs. Localized thermal analysis of small volumes of pure polymorphic samples (approximately 50 microm3) shows that the origin of the thermal conductivity contrast lies, at least in part, with the presence of a surface water layer on the more hydrophilic polymorph.

Chemistry, Pharmaceutical↗
PubMed1992

Proper use of gastrointestinal tract to achieve continent urinary diversion in 73 patients.

Different segments of the gastrointestinal tract have been used to reconstruct the bladder and all have been reviewed in regard to achieving urinary continence. In 53 patients with detubularized ileocecal cystoplasty, the continence rate, both during the day and night, was 88%, while 95% of the patients were continent during the daytime. In nine patients in whom an ileocecal continent reservoir was made, 100% had dry stoma on intermittent catheterization, both during the day and night. We conclude that detubularization of the right colon has a significant effect in achieving urinary control and making a good low pressure pouch. This has helped us to avoid conduits with their inherent problems. Also, the right colon by virtue of the ileocecal valve has good versatility for use in both anti-incontinence or anti-reflux procedures as needed.

Adolescent↗