Micro and Nanosystems - Volume 9, Issue 2, 2017

Background: RF MEMS switches can be used in radars, wireless systems, communication systems, phase shifters and switch matrices in order to achieve low power consumption, high isolation, small size and weight. Objective: This paper reports a low actuation voltage Capacitive Shunt RF MEMS Switch with two flexures, based on rotated serpentine spring concept. Method: The switch is designed on a CPW line with an impedance of 50 Ω. The dielectric is used is silicon nitrate with the thickness of 0.1 μm. Also, a cantilever beam switch and a switch with the serpentine spring structure based on meanders are simulated with the Comsol software and compared with the proposed switch. Conclusion: The results show actuation voltages of 15.89 V, 10 V and 7.755 V for the cantilever beam structure, serpentine spring structure and the proposed switch, respectively. RF scattering parameters are simulated by HFSS. Result: The results show that the return loss is -0.18 at 9.3GHz and the isolation is -37 dB at 9.3 GHz.

Background: Curcumin constitutes 80% of the curcuminoids (4 - 5%) of the rhizomes of Curcuma longa L. and saffron. This polyphenol regulates various targets through direct interaction or modulation of gene expression. Despite well documented clinical benefits in colon disorders and safety profile, curcumin has limited pharmaceutical role owing to reduced water solubility, instability in alkaline condition, enzymatic degradation, high metabolism and systemic clearance, hence poor bioavailability (<1%). This demands administration of multiple and larger doses (0.4-8 gm) of curcumin to achieve intended therapeutic benefits. Several strategies have been explored to enhance curcumin delivery to the colonic tissues including microencapsulation using nondigestible polysaccharides developed as bioresponsive drug delivery systems. The aim of the study was to formulate casein-chitosan microparticles of curcumin. Methods: In Accordance with 32 factorial design, total 9 formulations were prepared to optimize curcumin loaded microparticles using coacervation by polyelectrolyte complexation. Microparticles collected from the slurry were dried at 300C for 6 h and stored in an air tight container. % Drug loading of the formulations was assessed by UV spectroscopy at 425 nm. Average particle size and yield were determined by optical microscopy and gravimetry respectively. % Swelling and release prolfiles in SGF and SIF containing 0.2% tween 80 were plotted. Drug polymer interactions were assessed by FTIR spectroscopy and Differential scanning colorimetry. Morphology of microparticles was recorded by scanning electron microscopy. Results and Conclusions: Formulation 4 turned out to be the best microparticulate system prepared using 0.5% casein and 0.25% chitosan. This formulation exhibited yield of 98% ± 4.9, average particle size of 251 ± 12μ, drug loading (%) 10.8 ± 2, encapsulation efficiency of 95 ± 3.2% with good color, appearance, texture and flow properties by subjective assessment. This formulation can be scaled up conveniently for industrial production. Release behavior demonstrated that release rate of curcumin at pH 1.2 was relatively more than that in pH 7.4 for formulations 4 & 7. Release profile is in agreement with swelling profile at the two chosen pH. Formulation 4 found to be most optimum with reference to all the parameters tested - yield, particle size, encapsulation efficiency, swelling behavior, sustenance of release, curcumin - polymer compatibility by FTIR and DSC, formation of microcapsules by SEM images. Formulation 4 has released nearly 18% of its pay load in the first two hours at SGF and 25% in SIF at the end of 24 hours implying approximately 75% of curcumin cargo is available for delivery in the colonic region after transit through stomach and small intestine.

Background: A three-layered structure for solar cell model is designed. We consider a LHM film bounded by a glass superstrate and silicon/or silicon nitride substrate. Objective: The aim of this paper is to study transmittance, reflectance and absorptance in a three-layers structure composed of a glass superstrate and LHM middle layer; and as a substrate, we will be using silicon which is one of the widely used materials to enhance light absorption in multilayer structures. We will also be alternating between silicon and silicon nitride substrates to show their influence on the optical parameters. Method: Our analysis is based on the transfer matrix approach, which is a very powerful algorithm for optical parameters calculation in multilayer structures. The transmittance, reflectance and absorptance are formulated at some specific incidence angles, computed numerically as functions of the incident frequency and finally plotted using MATLAB software. Results: Numerical results provide an extremely high absorption for a specific left-handed material. Thus, absorptance near 100% can be theoretically achieved within an ultra broad band if the negative index layer is sandwiched in a specifically designed structure. Conclusion: It is shown that the proposed structures lead to absorptance improvement over wide ranges of frequency and incidence angles. It has been also noticed that the absorptance in a LHM between a glass cover and a silicon substrate, is better than the absorptance in a LHM between a glass cover and a silicon nitride substrate. With adjustable LHM layer thicknesses and for exact values of the refractive index, we can achieve high values of the absorptance coefficient that can reach 100%. These proposed structures can be designed and fabricated with existing and future nanotechnology to produce high efficiency solar cell devices.

Objective: The aim of the current study was to develop stable submicronized formulation of budesonide (BUD) for pulmonary delivery to treat chronic inflammation associated with asthma. Method: Submicronized formulation was prepared by antisolvent nanoprecipitation method and freeze dried using mixture of cryoprotectants. The optimized DPI formulation contains 200 μg labelled dose of budesonide, 0.5% w/v of leutro F68 as a stabilizer, mannitol (2% w/v) in combination with sorbitol (0.5% w/v) and lactose (1.5% w/v) as cryoprotectant. Z-average diameter (433.93 ± 8.32 nm) and polydispersity index (0.204) of submicron particles suggested narrow size distribution and particle size uniformity. The solid state characterization revealed loss of crystallinity of BUD in the submicronized formulation. The submicronized particles exhibited a burst effect over the first few minutes followed by 72-90% release in 2-3 hrs, significantly higher (p < 0.01) compared to conventional micronized formulation and pure budesonide. The device removal efficiency and aerosolization efficiency of BUD were estimated for 10 mg samples (~200 μg BUD) of the submicronized DPI formulation, conventional micronized formulation and stock drug using the Twin-stage impinger (TSI). Total emitted dose (84.5%) for submicronized DPI formulation showed fairly good device BUD removal and aerosolization efficiency, regardless of the loaded BUD dose in the lactose blends. The physical stability study was performed at 25°C/60% RH (controlled) for 12 month and at 40°C/75% RH (accelerated) for 6 month. Result: At controlled condition, the formulation was found stable and no any significant change was observed in drug content, particle size, Fine Particle Dose (FPD) and emitted dose. Conclusion: The results suggest that developed submicronized formulation of BUD can be used for pulmonary drug delivery with successful landing of drug from mouth to lungs.

Background: MEMS piezoelectric accelerometers are used in many different applications. In Some applications, accelerometers have to measure the acceleration at high frequency ranges. Objective: Due to the inverse relation between their sensitivity and bandwidth, high-bandwidth accelerometers generally have low sensitivity. By increasing their sensitivity, these accelerometers can measure vibrations with low amplitudes in a wide frequency range. Method: In this study, a single axis piezoelectric accelerometer with sensitivity higher than conventional accelerometers is introduced for high-bandwidth applications. The behavior of this micro-accelerometer including its resonance mode shapes, proof mass displacement amplitude, and output characteristics, as well as its stress distribution, polarity, and the electric potential generated in the piezoelectric layer are also studied by the finite element method. In addition, an idea to have a three axis accelerometer with higher sensitivity is proposed. Results: The proposed single axis accelerometer has 0.54 mV/g sensitivity and 10 kHz bandwidth. The three axis accelerometer has 7e-3 mV/g sensitivity for acceleration in x-y plane with the same bandwidth. Conclusion: This study proposed a piezoelectric accelerometer (based on a membrane attached to a proof mass) for high bandwidth applications with a sensitivity double that of its similar counterparts. To evaluate the performance of the proposed model, its characteristics were compared with those of a piezoelectric accelerometer with a circular membrane cross section. Although both studied structures had identical spring stiffness and proof mass, we observed that the maximum stress developed in the membrane for the proposed model is more than the circular accelerometer under a same acceleration. Therefore, the electric potential generated via the piezoelectric layer was greater in the square accelerometer.

Background: The geometry of stent in expansion process has great influence on restenosis of pathological vessels. Objective: In this paper, the nonlinear finite element method is used to simulate the free expansion process of drug-eluting stents (DES). By analyzing the plastic strain nephograms at each stage in the process of stent deformation, the parameters of holes in the stent is determined. The major aim is to obtain the least tiny deformation occurred during the expansion process and then to guarantee the best drugloading property. Method: Based on the results of stent expansion, an axially heterogeneous stent structure is set up. Changing rule of uniformity characteristics of the stent during the expansion process is concluded and then suggestions about how to adjust rigidity of the stent edge are also presented. Result: It is shown that rigidity of the stent edge is a little lower than that of the inner part which is the major reason for dogboning phenomena. Based on this observation, an optimized type of DES with micro drug-loading holes is built up and analyzed in detail.

Background: Piezoelectric micro-power generator (PMPG) is used to scavenge mechanical vibration energy and convert it into electrical energy via piezoelectric effects. In tire-pressure monitoring system (TPMS), the utilization of PMPG eliminates the requirement for a traditional battery replacement. Objective: In this paper, a PMPG was designed and optimized in the frequency range of 900-1100 Hz. Method: A Taguchi optimization method based on Orthogonal arrays (OA) and signal-to-noise (S/N) ratio is used in order to design a PMPG that vibrates at 1 kHz. The PMPG model selected to be cantilever beam cross shape with seven control factors which are strip length, strip width, strip displacement from the origin, membrane material, piezo material, membrane thickness and piezo thickness. The resonance eigenfrequency and transient analysis are conducted for the optimized PMPG model using COMSOL Multiphysics software. Result: The analyzed results show that there are three main factors that play the major role in PMPG optimization. These factors are, in descending order, membrane thickness, strip displacement from the origin and strip width. The first resonance eigen frequency found at 1 kHz, with peak voltage of 0.012 V, and reached the steady state after 0.03 seconds. The PMPG presented in this work is able to power a large number of small electronic devices like TPMS at 1 KHz. Furthermore, this optimization method solved tuning problems associated with PMPG cross shape rectangular cantilever beam.

Objective: We develop a method for green synthesis of nanoparticles using date palme wood extract (Phoenix dactiferia L.) in a rapid and eco-friendly microwave-assisted synthesis from silver nitrate solution. Background: Green synthesis of metallic silver nanoparticles has attracted attention nowadays and as credible alternative to physical and chemical approaches that can be expensive and can also have toxic substances absorbed onto them. Method: Microwave parameters (irradiation time and power), woodextract and silver nitrate concentration were optimized. The UV-visible spectroscopy was used to monitor the silver nanoparticle formation through sampling at time intervals. Results: The formation of silver nanoparticles was apparently displayed within evidence of surface plasmon bands, phytosynthesized silver nanoparticles dimensions 20-60 nm were characterizedusing X-ray diffraction analysis and transmission electron microscopy (TEM). The particle sizes obtained from the widening of the XRD line were found to be about 39.57 nm, which is well correlated with that obtained from TEM. Application: Prepared silver nanoparticles were used as a catalyst for the reduction of 4-nitro phenol to 4-amino phenol. The green synthesized nanoparticles exhibited potent antibacterial activity against the pathogenic bacteria, as evidenced by their zones of inhibition.