Biomedical subjects

Brij M Moudgil

Publications and source records attributed to Brij M Moudgil.

12 recordsLinked to original sources

PubMed2006

Effect of the chain-length compatibility of surfactants and mechanical properties of mixed micelles on surfaces.

Force/distance curves for silicon nitride tip/flat silica or alumina coated by a layer of mixed micelles of cationic/anionic surfactant are measured by using AFM. Mixtures of SDS/C(n)TAB (with molecular ratios of 3:1 and 20:1) and C(n)TAB/SDS (with molecular ratio of 85:15) were used for alumina and silica substrates, respectively. The number of carbon atoms per C(n)TAB molecule, n, was in the range of 8 to 16. On the basis of the force/distance curves, the elastic modulus, E, and yield strength, Y, of surface micelles are calculated. It is shown that in surfactant mixtures containing SDS the maximal repulsive force (the barrier F(bar)) at which the tip punctured the micelles, as well as the magnitudes of E and Y, attained the maximal values for C(12)TAB ( i.e., when the hydrocarbon chain lengths of two oppositely charged surfactants are the same). Obviously, it can be related to the highest density structure of these micelles. Note that the literature data for the surface micelles from pure C(n)TAB solutions demonstrate a monotonic dependence of F(bar), E, and Y on n in the range of n = 8-16, whereas the oppositely charged mixed surfactant systems yield much higher values of F(bar), E, and Y than does an equivalent chain length from the homologue series plots. The results obtained for mechanical characteristics of mixed micelles at the surface are compared with the results for the relaxation time, tau(2), that characterizes the lifetime (and therefore structure) of the bulk micelles. Both the dependence of F(bar), E, and Y on n for the surface mixed micelles and tau(2) on n for the bulk mixed micelles demonstrate a maximum at n = 12 for the C(n)TAB + SDS system. This correlation between properties of the surface and bulk micelles suggests that the mechanical properties of the surface micelles are largely determined by the interactions between surfactant molecules with surfactant-substrate interactions playing a secondary role.

Journal Article↗

PubMed2006

Research strategies for safety evaluation of nanomaterials. Part VI. Characterization of nanoscale particles for toxicological evaluation.

To properly assign mechanisms or causes for toxic effects of nanoscale materials, their properties and characteristics both outside and within the biological environment must be well understood. Scientists have many tools for studying the size, shape, and surface properties of particulates outside of the physiological environment; however, it is difficult to measure many of these same properties in situ without perturbing the environment, leading to spurious findings. Characterizing nanoparticle systems in situ can be further complicated by an organism's active clearance, defense, and/or immune responses. As toxicologists begin to examine nanomaterials in a systematic fashion, there is consensus that a series of guidelines or recommended practices is necessary for basic characterization of nanomaterials. These recommended practices should be developed jointly by physical scientists skilled in nano characterization and biological scientists experienced in toxicology research. In this article, basic nanoparticle characterization techniques are discussed, along with the some of the issues and implications associated with measuring nanoparticle properties and their interactions with biological systems. Recommendations regarding how best to approach nanomaterial characterization include using proper sampling and measurement techniques, forming multidisciplinary teams, and making measurements as close to the biological action point as possible.

Drug Evaluation, Preclinical↗

PubMed2005

Capillary forces between two spheres with a fixed volume liquid bridge: theory and experiment.

Capillary forces are commonly encountered in nature because of the spontaneous condensation of liquid from surrounding vapor, leading to the formation of a liquid bridge. In most cases, the advent of capillary forces by condensation leads to undesirable events such as an increase in the strength of granules, which leads to flow problems and/or caking of powder samples. The prediction and control of the magnitude of capillary forces is necessary for eliminating or minimizing these undesirable events. The capillary force as a function of the separation distance, for a liquid bridge with a fixed volume in a sphere/plate geometry, was calculated using different expressions reported previously. These relationships were developed earlier, either on the basis of the total energy of two solid surfaces interacting through the liquid and the ambient vapor or by direct calculation of the force as a result of the differential gas pressure across the liquid bridge. It is shown that the results obtained using these methodologies (total energy or differential pressure) agree, confirming that a total-energy-based approach is applicable, despite the thermodynamic nonequilibrium conditions of a fixed volume bridge rupture process. On the basis of the formulas for the capillary force between a sphere and a plane surface, equations for the calculation of the capillary force between two spheres are derived in this study. Experimental measurements using an atomic force microscope (AFM) validate the formulas developed. The most common approach for transforming interaction force or energy from that of sphere/plate geometry to that of sphere/sphere geometry is the Derjaguin approximation. However, a comparison of the theoretical formulas derived in this study for the interaction of two spheres with those for sphere/plate geometry shows that the Derjaguin approximation is only valid at zero separation distance. This study attempts to explain the inapplicability of the Derjaguin approximation at larger separation distances. In particular, the area of a liquid bridge changes with the separation distance, H, and thereby does not permit the application of the "integral method," as used in the Derjaguin approximation.

Journal Article↗

PubMed2005

Rapid and effective labeling of brain tissue using TAT-conjugated CdS:Mn/ZnS quantum dots.

TAT (a cell penetrating peptide)-conjugated CdSratioMn/ZnS quantum dots (Qdots), intra-arterially delivered to a rat brain, rapidly (within a few minutes) labeled the brain tissue without manipulating the blood-brain-barrier (BBB). Qdot loading was sufficiently high that it allowed a gross fluorescent visualization of the whole rat brain using a low power hand-held UV lamp. Histological data clearly showed that TAT-conjugated Qdots migrated beyond the endothelial cell line and reached the brain parenchyma. Qdots without TAT did not label the brain tissue confirming the fact that TAT peptide was necessary to overcome the BBB. The present study clearly demonstrated the possibility of delivering a large amount of Qdot-based imaging agents to the brain tissue.

Animals↗

PubMed2005

Folate conjugated fluorescent silica nanoparticles for labeling neoplastic cells.

We describe a novel technique of using fluorescent silica nanoparticles (FSNPs) to detect over-expressed folate receptors, as typical for certain malignancies (metastatic adenocarcinoma, pituitary adenoma and others). Using Stöber's method with some modification, 135 nm size FSNPs were synthesized by a hydrolysis and co-condensation reaction of tetraethylorthosilicate (TEOS), fluorescein labeled (3-aminopropyl)triethoxysilane (APTS) and a water-dispersible silane reagent, (3-trihydroxysilyl)propyl methylphosphonate (THPMP) in the presence of ammonium hydroxide catalyst. Folic acid (folate) was covalently attached to the amine modified FSNPs by a carbodiimide coupling reaction. The characterization of folate-FSNPs was performed using a variety of spectroscopic (UV-VIS and fluorescence), microscopic (transmission electron microscopy, TEM) and light scattering techniques. Folate conjugated FSNPs were then targeted to human squamous cancer cells (SCC-9). Laser scanning confocal images successfully demonstrated the labeling of SCC-9 cells and the efficacy of FSNP based detection system.

Biomarkers, Tumor↗

PubMed2005

Fluorescent nanoparticle probes for cancer imaging.

Optical imaging technique has strong potential for sensitive cancer diagnosis, particularly at the early stage of cancer development. This is a sensitive, non-invasive, non-ionizing (clinically safe) and relatively inexpensive technique. Cancer imaging with optical technique however greatly relies upon the use of sensitive and stable optical probes. Unlike the traditional organic fluorescent probes, fluorescent nanoparticle probes such as dye-doped nanoparticles and quantum dots (Qdots) are bright and photostable. Fluorescent nanoparticle probes are shown to be very effective for sensitive cancer imaging with greater success in the cellular level. However, cancer imaging in an in vivo setup has been recently realized. There are several challenges in developing fluorescent nanoparticle probes for in vivo cancer imaging applications. In this review, we will discuss various aspects of nanoparticle design, synthesis, surface functionalization for bioconjugation and cancer cell targeting. A brief overview of in vivo cancer imaging with Qdots will also be presented.

Diagnostic Imaging↗

PubMed2005

Adsorption density of spherical cetyltrimethylammonium bromide (CTAB) micelles at a silica/silicon surface.

In situ Fourier transform infrared internal reflection spectroscopy (FT-IR/IRS) was used to calculate the adsorption density values for spherical cetyltrimethylammonium bromide (CTAB) micelles at the silica/silicon (SiO2/Si) surface based on a previously developed adsorption density equation. Recent advances in atomic force microscopy (AFM) imaging methodology have led to the ability to image surface micelles, which was not possible previously. These AFM images have been used to independently calculate adsorption density values through offline fast Fourier transform (FFT) analysis. The adsorption density values measured from in situ FT-IR/IRS spectra and from AFM images showed good agreement and provide further validation of the FT-IR/IRS adsorption density equation in the low concentration range.

Adsorption↗

PubMed2004

TAT conjugated, FITC doped silica nanoparticles for bioimaging applications.

Water-in-oil (w/o) microemulsion synthesis of 70 nm size monodisperse TAT (a cell penetrating peptide, CPP) conjugated, FITC (fluorescein isothiocyanate) doped silica nanoparticles (TAT-FSNPs) is reported; human lung adenocarcinoma (A549) cells (in vitro) and rat brain tissue (in vivo) were successfully labeled using TAT-FSNPs.

Animals↗

PubMed2004

Pluronic microemulsions as nanoreservoirs for extraction of bupivacaine from normal saline.

We hypothesized that custom-designed microemulsions would effectively scavenge compounds from bulk media. Pluronic-based oil-in-water microemulsions were synthesized that efficiently reduced the free concentration of the local anesthetic bupivacaine in 0.9% NaCl. Both the molecular nature and concentration of the constituents in the microemulsions significantly affected extraction efficiencies. Pluronic F127-based microemulsions extracted bupivacaine more efficiently than microemulsions synthesized using other Pluronic surfactants (L44, L62, L64, F77, F87, F88, P104). Extraction was markedly increased by addition of fatty acid sodium salts due to greater oil/water interface area, increased columbic interaction between bupivacaine and fatty acids sodium salt, and greater surface activity. These data suggest that oil-in-water microemulsions may be an effective agent to treat cardiotoxicity caused by bupivacaine or other lipophilic drugs.

Bupivacaine↗

PubMed2004

Mechanical and thermodynamic properties of surfactant aggregates at the solid-liquid interface.

Surfactants are widely used to stabilize colloidal systems in a variety of industrial applications through the formation of self-assembled aggregates at the solid-liquid interface. Previous studies have reported that the control of surfactant-mediated slurry stability can be achieved through the manipulation of surfactant chain length and concentration. However, a fundamental understanding of the mechanical and energetic properties of these aggregates, which may aid in the molecular-level design of these systems, is still lacking. In this study, experimentally measured force/distance curves between an atomic force microscope (AFM) tip and self-assembled surfactant aggregates on mica or silica substrates at concentrations higher than the bulk critical micelle concentration (CMC) were used to determine their mechanical and thermodynamic properties. The experimental curves were fitted to a model which describes the interaction between a hard sphere (tip) and a soft substrate (surfactant structures) based on a modified Hertz theory for the case of a thin elastic layer on a rigid substrate. The calculated mechanical properties were found to be in the same order of magnitude as those reported for rubber-like materials (e.g., polydimethylsiloxane (PDMS)). By integrating the force/distance curves, the energy required for breaking the surface aggregates was also calculated. These values are close to those reported for bulk-micelle formation.

Journal Article↗

PubMed2003

Role of interaction forces in controlling the stability and polishing performance of CMP slurries.

Chemical mechanical polishing (CMP) is an essential step in metal and dielectric planarization in multilayer microelectronic device fabrication. In the CMP process it is necessary to minimize the extent of surface defect formation while maintaining good planarity and optimal material removal rates. These requirements are met through the control of chemical and mechanical interactions during the polishing process by engineering the slurry chemistry, particulate properties, and stability. In this study, the performance of surfactant-stabilized silica CMP slurries at high pH and high ionic strengths are investigated with particular emphasis on the particle-particle and particle-substrate interactions. It is shown that for the design of consistently high performing slurries, stability of abrasive particles must be achieved under the dynamic processing conditions of CMP while maintaining sufficient pad-particle-wafer interactions.

Journal Article↗

PubMed2002

Capillary forces between surfaces with nanoscale roughness.

The flow and adhesion behavior of fine powders (approx. less than 10 microm) is significantly affected by the magnitude of attractive interparticle forces. Hence, the relative humidity and magnitude of capillary forces are critical parameters in the processing of these materials. In this investigation, approximate theoretical formulae are developed to predict the magnitude and onset of capillary adhesion between a smooth adhering particle and a surface with roughness on the nanometer scale. Experimental adhesion values between a variety of surfaces are measured via atomic force microscopy and are found to validate theoretical predictions.

Journal Article↗