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Biomedical subjects

S G Kazarian

Publications and source records attributed to S G Kazarian.

11 recordsLinked to original sources
PubMed2006

Applications of ATR-FTIR spectroscopic imaging to biomedical samples.

FTIR spectroscopic imaging in ATR (Attenuated Total Reflection) mode is a powerful tool for studying biomedical samples. This paper summarises recent advances in the applications of ATR-FTIR imaging to dissolution of pharmaceutical formulations and drug release. The use of two different ATR accessories to obtain chemical images of formulations in contact with water as a function of time is demonstrated. The innovative use of the diamond ATR accessory allowed in situ imaging of tablet compaction and dissolution. ATR-FTIR imaging was also applied to obtain images of the surface of skin and the spatial distribution of protein and lipid rich domains was obtained. Chemical images of cross-section of rabbit aorta were obtained using a diamond ATR accessory and the possibility of in situ imaging of arterial samples in contact with aqueous solution was demonstrated for the first time. This experiment opens an opportunity to image arterial samples in contact with solutions containing drug molecules. This approach may help in understanding the mechanisms of treatment of atherosclerosis.

Animals↗
PubMed2005

Fourier transform infrared imaging of human hair with a high spatial resolution without the use of a synchrotron.

The cross-section of a human hair has been imaged for the first time using the micro attenuated total reflection (ATR) Fourier transformed infrared (FT-IR) method in combination with a focal plane array (FPA) detector. A rigorous approach was applied to determine the spatial resolution, namely, measuring the distance over which the band absorbance changes from 95 to 5% of the maximum absorbance when passing through a sharp interface. The measured value for IR transmission was approximately 16 microm, while the value obtained using ATR imaging was approximately 5 microm. The enhanced spatial resolution achieved by this method allows the medulla of the hair (approximately 8 microm in diameter) to be imaged clearly without the need for a synchrotron source. The spatial resolution of transmission and ATR imaging is compared, and advantages of ATR imaging are discussed.

Amides↗
PubMed2004

Effects of particle size on near-wall depletion in mono-dispersed colloidal suspensions.

In this work we investigate the change in particle concentration near a solid boundary for colloidal dispersions in pressure driven flow, commonly referred to as wall depletion. In particular we determine the effect of Peclet number on the strength and spatial extent of the depleted layer. The change in concentration near the solid boundary is measured with attenuated total reflection infrared (ATR-IR) spectroscopy described previously (P.J.A. Hartman Kok et al., J. Rheol. 46 (2002) 481). The method is capable of measuring the concentration of particles at distances ranging from 0.2 to 1.0 mum from the boundary. The suspensions investigated consisted of mono-dispersed polystyrene particles in water. Particles of four different sizes were used, with radius, a, of 30, 54, 105, and 197 nm. (The ratio H/a was in the range 2500-17,000 with H being the height of the flow cell.) This enabled us to measure the wall depletion effect over a wide range of Peclet numbers, ranging from 0.01 to 45. We found that wall depletion was not significant for Peclet numbers smaller than unity. Estimates of the wall slip layer thickness obtained from rheological experiments were consistent with the results obtained by ATR-IR spectroscopy.

Journal Article↗
PubMed2004

Spectroscopic imaging of arteries and atherosclerotic plaques.

Fourier transform infrared (FTIR) spectroscopic imaging using a focal plane array detector has been used to study atherosclerotic arteries with a spatial resolution of 3-4 microm, i.e., at a level that is comparable with cellular dimensions. Such high spatial resolution is made possible using a micro-attenuated total reflection (ATR) germanium objective with a high refractive index and therefore high numerical aperture. This micro-ATR approach has enabled small structures within the vessel wall to be imaged for the first time by FTIR. Structures observed include the elastic lamellae of the tunica media and a heterogeneous distribution of small clusters of cholesterol esters within an atherosclerotic lesion, which may correspond to foam cells. A macro-ATR imaging method was also applied, which involves the use of a diamond macro-ATR accessory. This study of atherosclerosis is presented as an illustrative example of the wider potential of these ATR imaging approaches for cardiovascular medicine and biomedical applications.

Animals↗
PubMed2003

Confocal Raman microscopy of supercritical fluid dyeing of polymers.

Supercritical CO2 was used as a medium to introduce azo-dyes into polymers (PMMA and PET). Confocal Raman microscopy has been applied using dry metallurgical and oil objectives to measure the concentration of dye as a function of distance from the surface to the core of the polymer samples. A significant gradient of dye concentration normal to the surface, down to the depth of ca. 100 microm, has been observed. In addition, cross-sections of cut dyed polymer samples have been analysed using a conventional mapping approach. The comparison between confocal depth and conventional mapping approaches has demonstrated that the use of the oil objective can provide reliable qualitative information on dye distribution in these systems. These confocal Raman experiments demonstrate the potential of this method in applications to polymeric materials processed with supercritical fluids.

Journal Article↗
PubMed2003

New opportunities in micro- and macro-attenuated total reflection infrared spectroscopic imaging: spatial resolution and sampling versatility.

New opportunities exist to obtain chemical images using attenuated total reflection infrared (ATR-IR) spectroscopy. This paper shows the feasibility of obtaining FT-IR images with a spatial resolution of at least 3-4 microm using a Ge ATR objective coupled with an infrared microscope. The improved spatial resolution compared to FT-IR images obtained by the transmission method is due to the high refractive index of the ATR crystal, which gives a high numerical aperture and hence, a higher spatial resolution. FT-IR imaging with a conventional diamond ATR accessory has been investigated. This is the first time that FT-IR imaging is reported using such a versatile accessory based on a diamond ATR crystal. These results showed that a spatial resolution up to 13 microm can be achieved without the use of infrared microscope objectives. One advantage of the diamond element is that it allows pressure to be applied and hence, good contact to be obtained over the whole field of view.

Crystallography↗
PubMed2002

Spectroscopy of polymer/drug formulations processed with supercritical fluids: in situ ATR-IR and Raman study of impregnation of ibuprofen into PVP.

In situ ATR (attenuated total reflectance)-IR spectroscopy has been used to study poly(vinylpyrrolidone) (PVP) films subjected to a solution of ibuprofen in supercritical CO2. The process of impregnation of ibuprofen into PVP has been monitored in situ. It has been shown that the supercritical fluid impregnation process results in ibuprofen being molecularly dispersed in a polymer matrix with ibuprofen molecules interacting with the C=O group of PVP. Raman spectra of ibuprofen impregnated into PVP from supercritical fluid solution have also been measured and compared with the Raman spectra of crystalline ibuprofen. ATR-IR spectroscopy has also revealed specific interactions between the C=O groups of PVP and CO2. Impregnation of ibuprofen into PVP makes the C=O groups of PVP less available for interactions with CO2. It has also been demonstrated that the presence of ibuprofen in PVP also affects sorption of water into PVP.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

Membrane transport of hydrocortisone acetate from supersaturated solutions; the role of polymers.

Permeation of hydrocortisone acetate (HA) from supersaturated solutions was studied across a model silicone membrane. Supersaturated solutions were prepared using the cosolvent technique with propylene glycol and water (or aqueous polymer solutions) as the cosolvents. In the absence of the polymer, the flux of HA was similar at all degrees of saturation and was not significantly different from the value obtained for a saturated solution. Flux enhancement, as a result of supersaturation, was observed with all the polymers. The flux increased with increasing polymer concentration, reached a maximum and decreased at higher polymer percentages. The amount of polymer required for maximum enhancement differed for each polymer. The decrease of flux at high polymer concentrations is attributed to changes in microviscosity and a marginal increase in solubility. The infrared spectroscopic and differential scanning calorimetry data suggest that HA-polymer interactions occurred through hydrogen bonding thus explaining the proposed mechanism of the anti-nucleant properties of the polymers.

Biological Transport↗