Micro and Nanosystems - Volume 3, Issue 1, 2011

The aim of the present investigation was to evaluate the potential application of microemulsions in topical drug delivery loading terbinafine hydrochloride. The pseudo-ternary phase diagrams were developed for various microemulsion formulations composed of cottonseed oil (oil phase), Tween 80 (surfactant) and ethanol (cosurfactant). Composition of microemulsion systems was optimized using simplex lattice design including the concentrations of surfactant, cosurfactant and water (independent variables) and the amount of drug released in first hour and t50% (response variables). The physicochemical properties of the optimized microemulsion, microemulsions incorporated into1% carbopol 974P gel base and the invitro drug diffusin of terbinafine hydrochloride from the gels prepared with microemulsions were also investigated. The results showed that the optimized microemusion formulation was composed of cottonseed oil (10%, w/w), Tween 80 (15%,w/w), ethanol (30%, w/w) and water (45%, w/w). The mean globule diameter was 65.56 nm. The conclusion was that the release controlling ability of microemulsion containing gel formulations was significantly improved in comparison to commercial cream.

Micropumps with varying nozzle-diffuser geometry and actuations are being explored for many drug delivery applications. Power consumption and reliability become very critical in the realization of these micropumps. In this study, the performance of a micropump consisting of three nozzle/diffuser elements designed and fabricated from PDMS material and actuated on top by a reciprocal motor was evaluated. The performance characteristics related to the flow rate obtained from testing demonstrated the efficiency of the micropump. The results obtained illustrate the relationship between actuation frequency and fluid flow through the micropump. The effects of fluid viscosity and actuator location were also investigated and the results are presented and discussed.

Nano TiO2 as a potential photocatalyst has been widely studied and used in many fields including environmental decontamination, sterilization and fuel cells. Some efforts, including improvements by doping, synthesis technique and operation parameter, have been made to enhance its performance. In this paper, the new progresses in these studies have been reviewed.

Due to their small size, low energy consumption, low cost and long life-time, MEMS (Micro-electromechanical Systems) vibratory gyroscopes have attracted tremendous interest among researchers. In this paper, a novel bulk-micromachined electrostatic comb-driven, differential capacitance sensing MEMS vibratory gyroscope based on glass-silicon-glass sandwich-structure is proposed. The novel structure eliminates the parasitic capacitances of the gyroscope, which greatly eases the signal sensing. Furthermore, due to the device structure design, the sensing vibration is not coupled to the driving vibration, which improves the device stability. In the driving mode, the gyroscope is activated to vibrate along X axis by electrostatic comb driving. If there is angular velocity along Y axis, the central mass experiences Coriolis force along Z axis which activates the sensing vibration of the central mass along Z axis. The size of the driving beams and sensing beams are carefully chosen to reduce the frequency mismatch between driving and sensing modes, which increases the gyroscope sensitivity. The working principle and dynamic analysis of this gyroscope are given and a set of optimized design parameters are derived based on the analysis. ANSYS FEM simulation is used to find out the device frequency and verify the theoretical prediction. The fabrication flow of the MEMS gyroscope is also proposed. The proposed MEMS gyroscope can be used for inertial sensing in automobile, aerospace, and consumer products.

Nanoscale devices traditionally rely on external, macroscopic voltage sources to establish their electrostatic potentials and fields ( e.g., batteries, fuel cells, power supplies). This study explores a general method by which potentials and fields can be established in situ using solid-state effects inherent in devices themselves. Endogenous electrostatic potentials (EEP) and endogenous electric fields (EEF) are created via physical junctions between metals or semiconductors having dissimilar chemical potentials for their mobile charge carriers. When expressed at the boundaries of materials, especially across narrow gaps, these EEPs and EEFs could have broad utility in nanotechnology. The magnitudes of EEPs are limited to about 4.5V; however, at the nanoscale EEFs can be as intense as any achievable using external biasing, while obviating the need for external voltage sources and electrical leads. Endogenous potentials and fields can be sustained indefinitely without power consumption and can regenerate quickly at system boundaries. In this paper the theory of EEPs and EEFs is introduced in the context of several potential nanotechnological applications, including charged particle optics and chemical catalysis; sorting and filtering of dielectric nanoparticles; spectroscopy of dipolar molecules; and the actuation of NEMS and MEMS.

In this paper, the heat transfer characteristics of a thermal flow sensor are investigated experimentally and numerically. Deionized water (DI-water) is employed as the working fluid. Operation mode with a constant heater temperature is considered in our experiment. The main part of the thermal flow sensor is a cylindrical copper heater. A Laser Induced Fluorescence (LIF) method is used to measure the full temperature field of the fluid in a microchannel. A specific number of flows were studied to allow investigation of the temperature distribution in a microchannel. The flow direction and velocity can be predicted based on the temperature distribution. A numerical simulation of conjugate forced convection- conduction heat transfer has been employed to investigate the predicted heat transfer processes in the thermal flow sensor. The measured temperature profiles along the central axis of the microchannel and the temperature differences between two positions upstream and downstream at different flow rates were compared with the numerical simulation results. Since the simulation and experimental measurements agree, the results show that the LIF method is suitable for temperature characterization on a microscale and confirms satisfactory characterization of the thermal flow sensor utilized here.

This paper numerically studies the equilibrium shape of a sessile droplet with moving contact lines. The Navier- Stokes equation was solved through the finite volume method on a Cartesian staggered grid. The level-set method was used to track free surface of the immiscible two-phase, gas and liquid. The Navier boundary condition is enforced on the entire solid surface away from the triple contact line to remove the force singularity. The continuum model formulated by Ren and E was used near the contact line [1]. Our code was validated by comparing it with other numerical results, and gave a lower mass loss of less than 2%. The method can easily be extended to a three dimensional model. Droplet spreading and recoiling were calculated and discussed with the presented numerical methods. Both two-dimensional and threedimensional simulation results agree well with experimental observations.

This paper reports the investigation on the process of thermally mediated droplet formation at a microfluidic Tjunction. The temperature field generated by an integrated heater causes changes in properties of the fluids and affects the droplet formation process. The droplet formation process is formulated in this paper as an incompressible immiscible twophase flow problem. The motion of the two-phases is strongly coupled by interfacial conditions, which are governed by the three-dimensional Navier-Stokes and the energy equations. The interface or the droplet surface is described by a narrow- band particle level-set method. The numerical solutions of the problem are obtained with finite volume method on a staggered mesh and validated with the experiment data on droplet formation in the dripping regime of a T-junction. The combined effect of the temperature-dependent viscosities and interfacial tension of the fluids results in a larger droplet at elevated temperature. The effectiveness of the penetration of temperature field induced by different heater geometries that resulted in different incremental change in droplet size over a temperature range is discussed.

Gold hollow nanospheres (GHNs) were synthesized by using various stoichiometric ratios of chloroauric acid and cobalt nanoparticles as sacrificial templates through redox reaction of sodium borohydride. The self-assembly and crystallization process of GHNs were represented. The size of GHNs was dependent on the concentration of sodium citrate, sodium borohydride, and chloroauric acid. The composition of hollow nanospheres was analyzed for each growth strategy. It was notable that the core of the nanoshells contains significant traces of Co elements. The surface plasmon resonance peak of these hollow nanospheres shifts over 140 nm with varying nanostructure sizes. The GHNs are extremely useful for various molecular sensing applications.

The present study demonstrates that nanosphere lithography and electro-polymerization can be successfully combined to produce bioactive protein nanoarrays. In particular, we describe a method to produce well-defined nanoarrays of polypyrrole functionalized with biomolecules. The nanoarrayed surfaces were fabricated on gold coated surface plasmon resonance prisms by first creating silicon oxide or polyethylene oxide nanotemplate using nanosphere lithography. The nanotemplate was subsequently used to grow bio-functionalized polypyrrole nanoarrays by electrocopolymerization. Atomic force microscopy analysis showed that the fabricated surfaces have a well-organized 2D hexagonal geometry with nanoscale dimensions. The biological activity of the bio-functionalized polypyrrole was assessed by surface plasmon resonance detection. The results showed that the immobilized biomolecules within the nanoarrayed polypyrrole films had the necessary bioactivity for successful molecular recognition. Moreover the detection signals normalized to the bioactive area were increased by a factor 5 as compared to non-structured bio-functionalized polypyrrole in the nanoarrayed surfaces using polyethylene oxide.