Anubhav Tripathi

The measurement of the shear-induced particle and fluid tracer diffusivities in concentrated suspensions by a novel method

The shear-induced particle self-diffusivity in a concentrated suspension (20%–50% solids volume fraction) of non-colloidal spheres (90 [mu]m average diameter) was measured using a new correlation technique. This method is based on the correlation between the positions of tracer particles in successive images and can be used to determine the self-diffusivity in non-colloidal suspensions for different time scales. These self-diffusivities were measured in the velocity gradient and vorticity directions in a narrow-gap Couette device for values of the strain [gamma][Delta]t ranging from 0.05 to 0.5, where [gamma] is the applied shear rate and [Delta]t is the correlation time. In both directions, the diffusive displacements scaled linearly with [gamma][Delta]t over the range given above and the corresponding diffusivities were found to be in good agreement with the experimental results of Leighton & Acrivos (1987a) and of Phan & Leighton (1993), even though these earlier studies were performed at much larger values of [gamma][Delta]t. The self-diffusivity in the velocity gradient direction was found to be about 1.7 times larger than in the vorticity direction. The technique was also used to determine the shear-induced fluid tracer by measuring the mean square displacement of 31.5 [mu]m diameter tracer particles dispersed in concentrated suspensions (30%–50% solids volume fraction) of much larger spheres (325 [mu]m average diameter). These fluid diffusivities were found to be 0.7 times the corresponding particle diffusivities when both were scaled with [gamma] a2 (2a = 325 [mu]m).

Particle segregation in monodisperse sheared suspensions

It has been known for a long time that many mixtures of granular materials tend to segregate when tumbled in a rotating horizontal cylinder, with the different components separating into bands of relatively pure single concentration along the rotational axis [Mixing of Solids, Advances in Chemical Eng., edited by T. B. Drew and J. W. Hoopes (Academic Press, New York, 1952), Vol. 2, p. 211]. Here we report a phenomenon that seems to be analogous, but in suspensions of monodisperse neutrally buoyant spherical particles in a Newtonian liquid medium being sheared in a partially filled horizontal Couette device in which the suspension separates itself into alternating regions of high and low particle concentration along the length of the tube. The experiment is mostly qualitative, the aim at this stage being primarily to provide photographic evidence of a curious and as yet unexplained phenomenon.

Review of sunscreen and the emergence of non-conventional absorbers and their applications in ultraviolet protection

Protection against ultraviolet (UV) radiation is the major function of sunscreen lotions and UV‐protective coatings for vehicles, homes, equipment and clothing. Sunscreen formulations have been optimized to become protective over a broader spectrum of UV radiation and maintain greater photostability. They are comprised of organic and inorganic components that act as chemical and physical UV protectors, respectively. Some of the organic components are limited by their spectrum of protection and photostability. Studies using solid lipid nanoparticles, recently explored organic molecules, inorganic components and antioxidants attempt to further optimize UV protection. In this review, we examine traditional and emerging nanoparticle components and highlight novel ideas in UV protection which may provide pathways for future studies.

Surface-Tension-Induced Synthesis of Complex Particles Using Confined Polymeric Fluids†

Therefore, a novel methodology for the gen-eration of uniform particles with a large diversity of designmorphologies and physicochemical properties would be apromising platform for many advanced applications.Conventional approaches for the synthesis of polymericparticles with various shapes are self-assembly,

Microfluidic Sample Preparation for Medical Diagnostics

Fast and reliable diagnoses are invaluable in clinical care. Samples (e.g., blood, urine, and saliva) are collected and analyzed for various biomarkers to quickly and sensitively assess disease progression, monitor response to treatment, and determine a patients prognosis. Processing conventional samples entails many manual time-consuming steps. Consequently, clinical specimens must be processed by skilled technicians before antigens or nucleic acids are detected, and these are often present at dilute concentrations. Recently, several automated microchip technologies have been developed that potentially offer many advantages over traditional bench-top extraction methods. The smaller length scales and more refined transport mechanisms that characterize these microfluidic devices enable faster and more efficient biomarker enrichment and extraction. Additionally, they can be designed to perform multiple tests or experimental steps on one integrated, automated platform. This review explores the current research on microfluidic methods of sample preparation that are designed to aid diagnosis, and covers a broad spectrum of extraction techniques and designs for various types of samples and analytes.

Microfluidic Reactors for Diagnostics Applications

Diagnostic assays are an important part of health care, both in the clinic and in research laboratories. In addition to improving treatments and clinical outcomes, rapid and reliable diagnostics help track disease epidemiology, curb infectious outbreaks, and further the understanding of chronic illness. Disease markers such as antigens, RNA, and DNA are present at low concentrations in biological samples, such that the majority of diagnostic assays rely on an amplification reaction before detection is possible. Ideally, these amplification reactions would be sensitive, specific, inexpensive, rapid, integrated, and automated. Microfluidic technology currently in development offers many advantages over conventional benchtop reactions that help achieve these goals. The small reaction volumes and energy consumption make reactions cheaper and more efficient in a microfluidic reactor. Additionally, the channel architecture could be designed to perform multiple tests or experimental steps on one integrated, automated platform. This review explores the current research on microfluidic reactors designed to aid diagnostic applications, covering a broad spectrum of amplification techniques and designs.

Biocompatible Nanoparticles Trigger Rapid Bacteria Clustering

This study reveals an exciting phenomenon of stimulated bacteria clustering. Rapid aggregation and microbial arrest are shown to occur in Escherichia coli solutions of neutral pH when chitosan nanoparticles with positive zeta potential are added. Because chitosan nanoparticles can easily be dispersed in aqueous buffers, the rapid clustering phenomenon requires only minuscule nanoparticle concentrations and will be critical in developing new methods for extricating bacterial pathogens. This work establishes the dominant role of electrostatic attraction in bacteria‐nanoparticle interactions by varying the nanoparticle zeta potential from highly positive to strongly negative values, and by exploring concentration effects. For strongly negative nanoparticles, no clusters form, while aggregates are small and loose at intermediate conditions. In addition, optical density measurements indicate that over 90% of the suspended bacteria flocculate within seconds of being mixed with chitosan nanoparticles of a highly positive surface charge. Finally, the nanoparticles are significantly more efficient as a clustering agent compared to an equal mass of molecular chitosan in solution, as the bacteria‐nanoparticle clusters formed are substantially larger. The bacteria‐nanoparticle aggregation effect demonstrated here promises a rapid separation method for aiding pathogen detection and for flocculation of bacteria in fermentation processes.

Multilayer spheroids to quantify drug uptake and diffusion in 3D.

There is a need for new quantitative in vitro models of drug uptake and diffusion to help assess drug toxicity/efficacy as well as new more predictive models for drug discovery. We report a three-dimensional (3D) multilayer spheroid model and a new algorithm to quantitatively study uptake and inward diffusion of fluorescent calcein via gap junction intercellular communication (GJIC). When incubated with calcein-AM, a substrate of the efflux transporter P-glycoprotein (Pgp), spheroids from a variety of cell types accumulated calcein over time. Accumulation decreased in spheroids overexpressing Pgp (HEK-MDR) and was increased in the presence of Pgp inhibitors (verapamil, loperamide, cyclosporin A). Inward diffusion of calcein was negligible in spheroids that lacked GJIC (OVCAR-3, SK-OV-3) and was reduced in the presence of an inhibitor of GJIC (carbenoxolone). In addition to inhibiting Pgp, verapamil and loperamide, but not cyclosporin A, inhibited inward diffusion of calcein, suggesting that they also inhibit GJIC. The dose response curves of verapamil’s inhibition of Pgp and GJIC were similar (IC50: 8 μM). The method is amenable to many different cell types and may serve as a quantitative 3D model that more accurately replicates in vivo barriers to drug uptake and diffusion.

Micron-Scale Droplet Deposition on a Hydrophobic Surface Using a Retreating Syringe

Droplet deposition onto a hydrophobic surface is studied experimentally and numerically. A wide range of droplet sizes can result from the same syringe, depending strongly on the needle retraction speed. Three regimes are identified according to the motion of the contact line. In region I, at slow retraction speeds, the contact line expands and large droplets can be achieved. In region II, at moderate needle speeds, a quasicylindrical liquid bridge forms resulting in drops approximately the size of the needle. Finally, at high speeds (region III), the contact line retracts and droplets much smaller than the syringe diameter are observed. Scaling arguments are presented identifying the dominant mechanisms in each regime. Results from nonlinear numerical simulations agree well with the experiments, although the accuracy of the predictions is limited by inadequate models for the behavior of the dynamic contact angle.

Localization of magnetic pills

Numerous therapeutics demonstrate optimal absorption or activity at specific sites in the gastrointestinal (GI) tract. Yet, safe, effective pill retention within a desired region of the GI remains an elusive goal. We report a safe, effective method for localizing magnetic pills. To ensure safety and efficacy, we monitor and regulate attractive forces between a magnetic pill and an external magnet, while visualizing internal dose motion in real time using biplanar videofluoroscopy. Real-time monitoring yields direct visual confirmation of localization completely noninvasively, providing a platform for investigating the therapeutic benefits imparted by localized oral delivery of new and existing drugs. Additionally, we report the in vitro measurements and calculations that enabled prediction of successful magnetic localization in the rat small intestines for 12 h. The designed system for predicting and achieving successful magnetic localization can readily be applied to any area of the GI tract within any species, including humans. The described system represents a significant step forward in the ability to localize magnetic pills safely and effectively anywhere within the GI tract. What our magnetic pill localization strategy adds to the state of the art, if used as an oral drug delivery system, is the ability to monitor the force exerted by the pill on the tissue and to locate the magnetic pill within the test subject all in real time. This advance ensures both safety and efficacy of magnetic localization during the potential oral administration of any magnetic pill-based delivery system.