Mechanical property and in vitro biocompatibility of brushite cement modified by polyethylene glycol

Brushite (dicalcium phosphate dihydrate, DCPD) cement, owing to its high solubility in physiological condition and ability to guide new bone formation, is widely used to treat bone defects. In the present study, we have evaluated the effects of poly ethylene glycol (PEG) addition on the setting time, compressive strength and in vitro biocompatibility of brushite cement. The brushite cements were prepared by mixing β-tricalcium phosphate [β-TCP, Ca₃(PO₄)₂] and monocalcium phosphate monohydrate [MCPM, Ca(H₂PO₄)₂ ? H₂O]. PEG was introduced at 2.0 and 5.0 wt% with the liquid. Introduction of PEG resulted in marginal increase in both initial and final setting time, however, significantly affected the compressive strength. Effects of PEG incorporation on in vitro biocompatibility of brushite cements were studied by using human fetal osteoblast cells (hFOB) cells. Field emission scanning electron microscope (FESEM) images and immunohistochemical analysis indicated that pure and PEG incorporated brushite cement facilitates cell adhesion, proliferation and differentiation. Fewer cells expressed vinculin protein with increased PEG content in the cement. Cell proliferation was found to decrease with increased PEG concentration while the cell differentiation increased with PEG content. Our results provide a better understanding of in vitro biocompatibility of PEG added brushite cements that can be used to customize the cement compositions based on application need.     

A microfabricated sensor for thin dielectric layers

We describe a sensor for the measurement of thin dielectric layers capable of operation in a variety of environments. The sensor is obtained by microfabricating a capacitor with interleaved aluminum fingers, exposed to the dielectric to be measured. In particular, the device can measure thin layers of solid frozen from a liquid or gaseous medium. Sensitivity to single atomic layers is achievable in many configurations and, by utilizing fast, high sensitivity capacitance readout in a feedback system onto environmental parameters; coatings of few layers can be dynamically maintained. We discuss the design, readout, and calibration of several versions of the device optimized in different ways. We specifically dwell on the case in which atomically thin solid xenon layers are grown and stabilized, in cryogenic conditions, from a liquid xenon bath.     

Interfacing microfluidics to LDI-MS by automatic robotic spotting

We developed a method of interfacing microfluidics with mass spectrometry (MS) using a robotic spotting system to automate the contact spotting process. We demonstrate that direct and automated spotting of analyte from multichannel microfluidic chips to a custom microstructured MALDI target plate was a simple, robust, and high-throughput method for interfacing parallel microchannels using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Using thermoplastic cyclic olefin copolymer (COC) polymer microfluidic chips containing eight parallel 100 μm × 46 μm microchannels connected to a single input port, spotting volume repeatability and MALDI-MS signal uniformity are evaluated for a panel of sample peptides. The COC microfluidic chips were fabricated by hot embossing and solvent bonding techniques followed by chip dicing to create open ends for MS interfacing. Using the automatic robotic spotting approach, microfluidic chip-based reversed-phase liquid chromatography (RPLC) separations were interfaced with electrochemically etched nanofilament silicon (nSi) target substrate, demonstrating the potential of this approach toward chip-based microfluidic separation coupled with matrix-free laser desorption/ionization mass spectrometry.     

Microfabricated sequential-leaf time-delay mechanisms

Arrays of micromechanical sequential-leaf time-delay mechanisms based on SOI/DRIE technology have been designed, fabricated, and characterized. The devices were designed as elements of a larger fuzing system for rifled munitions, in which a passive timing mechanism triggers at a predetermined rotational speed, followed by a desired delay time before the next element of the munition fuzing train is activated. Analytical models for the micromechanical timing mechanisms have been developed, and a variety of designs were simulated from the linear and nonlinear models, and using dynamics simulation software. Fabricated mechanism arrays designed to initiate switching at centrifugal accelerations from 44 to 263 g were characterized using a high-speed camera, with delay times of between 0.67 and 0.95 ms achieved for single elements within the arrays. Measured delay times and switching accelerations follow predicted trends based on analytical and numerical models.     

Piezoelectric Disk Resonators Based on Epitaxial AlGaAs Films

A new design for anisotropic piezoelectric disk resonators is demonstrated using single-crystal Al_0.3Ga_0.7As films. The shape of the disk resonator is based on the velocity propagation profile of the elastic wave in the plane of the piezoelectric film, with lateral dimensions scaled to the half wavelength of the desired resonance frequency. The resonators are designed with supports which emulate free-free boundary conditions. Prototype resonators are fabricated using a three-layer Al_0.3Ga_0.7As heterostructure containing silicon-doped electrodes and an undoped piezoelectric Al_0.3Ga _0.7As layer. Quality factors as high as 11 200 are measured in air for a 23.25 MHz fundamental resonant mode, with a corresponding motional resistance of 1.67 kOmega. A finite-element model for the resonator design is also described. Simulation results agree well with both theoretical calculations and experimental data     

Electron microscopical study of the Fleisher ring

The Fleischer ring of keratoconus was studied with the transmission electron microscope in four corneal buttons. The ring was characterized by accumulations of ferritin particles in the widened intercellular spaces and/or in the cytoplasmic vacuoles of the corneal epithelium. Both changes were prominent in basal layers in three cases; in one case, ferritin-containing vacuoles were noted in wing cell layers. Ferritin particles were also scattered over the corneal epithelium in all cases. For comparison, normal human corneas and conjunctivas were studied. Ferritin particles were scattered over the corneal epithelium and throughout the basal cells of the conjunctiva. They were not found in corneal stroma or endothelium. In conjunctival stroma, numerous ferritin particles were observed in the cytoplasm of some macrophages. Possible origin of these particles and the cause of their deposition are discussed.     

Visualizing the Growth and Dynamics of Liquid‐Ordered Domains During Lipid Bilayer Folding in a Microfluidic Chip

A microfluidic platform enabling optical monitoring of bilayer lipid membrane formation by a new monolayer folding process is described. The thermoplastic chips integrate dried lipid films that are rehydrated by microfluidic perfusion, which enables delivery of lipid‐laden air bubbles across a membrane‐supporting aperture. As in traditional Montal–Mueller bilayer formation, lipid monolayers are delivered independently to each side of the aperture, thereby allowing asymmetric lipid composition in the resulting bilayer to be achieved. Confocal microscopy is used to image the monolayer folding process, and reveals the growth and dynamics of asymmetric liquid‐ordered domains during bilayer stabilization.     

Piezoelectric Al/sub 0.3/Ga/sub 0.7/As longitudinal mode bar resonators

This paper reports the modeling, fabrication, and experimental characterization of piezoelectric longitudinal mode bar resonators based on thin film single crystal Al/sub 0.3/Ga/sub 0.7/ As. Fabricated resonators with lengths ranging from 1000 /spl mu/m to 100 /spl mu/m have been characterized for operation in their first five odd longitudinal modes. Resonance frequencies range from 2.5 to 75 MHz, with quality factors up to 25 390 at 21.8 MHz in vacuum. Power handling capacity as high as -2.6 dBm is demonstrated at 18.8 MHz. Motional resistance and temperature stability of the resonators are also evaluated.     

Modeling and optimal design of piezoelectric cantilevermicroactuators

A novel model is described for predicting the static behavior of a piezoelectric cantilever actuator with an arbitrary configuration of elastic and piezoelectric layers. The model is compared to deflection measurements obtained from 500-μm-long ZnO cantilever actuators fabricated by surface micromachining. Modeled and experimental results demonstrate the utility of the model for optimizing device design. A discussion of design considerations and optimization of device performance is presented