Micro and Nanosystems - Volume 7, Issue 1, 2015

Conventional microsystems including sensors and actuators are made of rigid materials such as silicon because of their origin from the microelectronics. However, most micro- and nanosytems found in the nature are made of soft materials allowing them to deform or even morph depending on the task and external environment. The deformability allows natural microsystems to exceed the performance of their rigid micromachined counterparts. Inspired by nature, recent research efforts have been focused on soft microsystems including sensors, actuators and microfluidic platforms, promising a completely new approach in engineering small systems with a broad range of applications.

We developed a low-cost and high-resolution micro-fabrication system that enables quick and inexpensive manufacturing of master molds for fabricating microfluidic devices via softlithography. The system utilizes ultraviolet light-emitting diodes as a light source and dry film photoresists as patterning materials. Compared to cleanroom methods of fabricating master molds, our system demonstrates several advantages, including the ability to process in ambient air environments and normal lighting conditions, low costs, ease of operation, and short processing time. Moreover, the system achieves feature resolutions of 30 μm, aspect ratios larger than 1, and sidewall angles larger than 80o, which meet the requirements of a variety of microfluidic applications.

The objective of present investigation was to develop and evaluate Nanoparticulate Periodontal Drug Delivery System (NPDDS) for local delivery of metronidazole benzoate with combination processing method. Dichloromethane, acetone and ethanol were utilized in combination with, HPMC E15 LV, HPC LF and gelusire 44/14, formulation stabilizers to develop NPDDS. A specific DOE was selected to study the effects and interactions of stabilizers and solvent mixture on particle size distribution and other relevant formulation characterization parameters. We have considered four independent variables X1, X2, X3 and Z4 are HPMC E15 LV, (HPC-LF), Gelusire 44/14 and Solvent mixture, respectively. DOE was used in this investigation to map the system and thus to approximate the Mean particle size (MPS) (Y1), Drug release at 30 minute (%) (Y(30 min)) (Y2), and time for 50% drug release [t50%] (Y3) to find an optimal range of experimental conditions. A two step production process, including combination of high speed homogenization and wet media milling technique was developed. Formulation stabilizer gelusire 44/14 has shown prominent effect over MPS, Y(30 min), and t50%. Overall effect of factors over the responses is graphically represented by the ternary plots.

A new approach for manufacturing of porous and amorphous silicon is presented. The electrochemistry and the rare behaviour of Si were examined with cathodic etching conditions under coulostatic pulse polarization in aqueous buffer solutions. Compared to the usual situation of the etching process here the pores were made by pulse polarizing the silicon electrodes cathodically in aqueous alkaline solution instead of typical anodic etching with highly acidic conditions of hydrofluoric acid combined with aqueous or organic solvents. According to this research, some interesting results were noticed. Therefore, it seems obvious that there is still the possibility to find new ways of forming pores and porous silicon with peculiar features and with possible interest of applications. The porous silicon manufacturing process also has an effect on the types of the pores formed. In the paper a new way of formation of porous silicon is described. The features, structures and manufacturing processes of the pores are analysed and possible reaction mechanism of the pore formation is proposed. In addition, the Si-electrolyte contact itself has an interesting science and technology features. Presented manufacturing process can be abused for instance in sensor platform applications.

Nanogap electrodes fabricated from metals separated by a distance on nanometer scale have gained tremendous acceptance in various fields of applications and essential elements of nanoscale biosensor transducers and electrochemical sensing element. Electrical conduction of nanogap is typically deternimed by the characteristics of its electron transport molecules and mainly conducted through current-voltage (I-V) measurements. However, due to capacitively shifting behavior of the nanogap device as a result of atomic agintation by the increase in frequency, it is difficult to measure two devices of the same configuration that produce exact behavior. In order to understand these fundamentals, three gap electrodes of three different materials were fabricated and tested for their impedance behavior to identify sensitive and stable atomic configuration mode for maximum detection throughput.

Undoped and Fe-doped TiO2 nanotubes were fabricated by hydrothermally treating the solgel- derived undoped and Fe-doped TiO2 nanoparticles in a KOH aqueous solution. The light absorption edge the nanotubes extended to visible light region of ~449 nm at a maximal Fe molar content (3.86 %). Correspondingly, the optical bandgap narrowed to ~2.76 eV. The sunlight-excited degradation rate of methyl orange aqueous solution on the nanotubes increased as increasing Fe-doping content and initial solution pH. The photodegradation followed pseudo-first order reaction kinetics. The pseudo-kinetic rate constant increased from 0.133 to 0.513 h-1 as the increase of Fe content and initial pH. A maximal value was achieved at Fe molar content of 3.86 % and initial solution pH=9. The measurement of oxidation-reduction potential revealed a dominant reductive photocatalytic behavior of the nanotubes. The mechanism of enhancing photocatalysis of TiO2 nanotubes by Fe-doping was proposed.

To observe the effect of Polycaprolactone on Nateglinide release from its nanoparticulate dosage form, the drug and polymer were dissolved in mixture of organic solvent. This solution was homogenized with high speed followed by high pressure homogenizer in surfactant containing aqueous solution. The obtained nanoparticles after solvent evaporation and freeze drying were characterized for particle size, zeta potential, X-ray diffraction, encapsulation efficiency, in-vitro dissolution and drug release kinetics. The developed nanoparticles are in size range of 142.53±6.42 nm to 281.34±3.48 nm. The zeta potential value of most encapsulated formulation batch was +30.2. Nateglinide is crystalline in nature with 86.1% crystallinity but the developed encapsulated nanoparticles showed decrease in crystallinity up to 32.5%. The results showed that the drug released was increased gradually from first hour (7.06±0.24%) to 10^th hour (23.13±0.25%) and after that it released in controlled manner up to 24 hours (27.63±1.82%). Polycaprolactone controlled the release of Nateglinide efficiently up to 24 hours. From the release kinetic models it was observed that the dissolution pattern follows Higuchi model.

Green synthesis of nanomaterials finds the edge over chemical methods due to its environmental compatibility. The present study deals with the green synthesis of silver (AgNPs) nanoparticles using the aqueous extract of Alstonia scholaris without any catalyst, template, surfactant or any intermediate. The method was well controlled using ultrasonic cavitation so as to facilitate the high level of dispersion with an increase in rate of reaction. AgNPs was synthesized using silver nitrate in aqueous extract of Alstonia scholaris as a reducing agent. The size of AgNPs can be tuned using significant variation in reaction parameters. The as-synthesized nanomaterials were characterized using UV-visible spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM), Field emission scanning electron microscope (FE-SEM) and Fourier transform infra-red spectroscopy. The optimized condition produces the AgNPs of size ~15-38 nm. The presence of aldehydic and ketonic compounds (alkaloids, flavonoids, pinocarvone and cryptone) potentially acts as reducing as well as stabilizing agents. Moreover, reduction of silver nitrate under controlled ultrasonication shows the implosive collapsing of bubbles, which results in attaining a very high temperature of solution with fast cooling at RT. Due to this uniform dispersion there are less chances of agglomeration of nanoparticles.

Polyimide (PI) is a high performance polymer material with excellent thermal stability and electrical insulation property. However, the low thermal conductivity of PI limits its wider application. Graphene (GNS) is ideal filler because of its incredible physical and chemical properties to reinforce the thermal and mechanical performance of polymer based matrix. In this work, we report an effective method using in situ polymerization to prepare graphene/polyimide (GNS/PI) and graphene oxide/ polyimide (GNO/PI) composite films with good thermal properties. When the content of GNS is 0.75%, the thermal conductivity value of GNS/PI film reaches 0.1375 W/m.k, which is 47.1% higher than pure PI film. This approach shows a potential application in microelectronics and aircraft industries and can be further investigated and optimized.

We present the use of impedance monitoring to determine the geometrical characteristics and the ionic concentration of droplets in a microchannel. A compact impedance monitoring system is developed based on an embedded computer that can provide an adjustable excitation signal from 2 KHz to 2 MHz. Aqueous droplets are continuously formed by hydrodynamic focusing and then directed into a primary channel for monitoring with embedded electrodes in a microfluidic chip. With the monitoring system, the correlation between the electrical amplitude and the ionic concentration in droplets is investigated and the correlation coefficient is 0.98. Moveover the dependency of the impedance response on the geometrical features of droplet is analyzed. According to the experimental results, an algorithm for the quantitative estimation of droplet length is established. Compared with the results from optical microscopy, the relative difference of the estimated droplet length is less than 10%.