Cell and protein compatibility of parylene-C surfaces

Parylene-C, which is traditionally used to coat implantable devices, has emerged as a promising material to generate miniaturized devices due to its unique mechanical properties and inertness. In this paper we compared the surface properties and cell and protein compatibility of parylene-C relative to other commonly used BioMEMS materials. We evaluated the surface hydrophobicity and roughness of parylene-C and compared these results to those of tissue culture-treated polystyrene, poly(dimethylsiloxane) (PDMS), and glass. We also treated parylene-C and PDMS with air plasma, and coated the surfaces with fibronectin to demonstrate that biochemical treatments modify the surface properties of parylene-C. Although plasma treatment caused both parylene-C and PDMS to become hydrophilic, only parylene-C substrates retained their hydrophilic properties over time. Furthermore, parylene-C substrates display a higher degree of nanoscale surface roughness (>20 nm) than the other substrates. We also examined the level of BSA and IgG protein adsorption on various surfaces and found that surface plasma treatment decreased the degree of protein adsorption on both PDMS and parylene-C substrates. After testing the degree of cell adhesion and spreading of two mammalian cell types, NIH-3T3 fibroblasts and AML-12 hepatocytes, we found that the adhesion of both cell types to surface-treated parylene-C variants were comparable to standard tissue culture substrates, such as polystyrene. Overall, these results indicate that parylene-C, along with its surface-treated variants, could potentially be a useful material for fabricating cell-based microdevices.     

Generation of dynamic temporal and spatial concentration gradients using microfluidic devices

This paper describes a microfluidic approach to generate dynamic temporal and spatial concentration gradients using a single microfluidic device. Compared to a previously described method that produced a single fixed gradient shape for each device, this approach combines a simple "mixer module" with gradient generating network to control and manipulate a number of different gradient shapes. The gradient profile is determined by the configuration of fluidic inputs as well as the design of microchannel network. By controlling the relative flow rates of the fluidic inputs using separate syringe pumps, the resulting composition of the inlets that feed the gradient generator can be dynamically controlled to generate temporal and spatial gradients. To demonstrate the concept and illustrate this approach, examples of devices that generate (1) temporal gradients of homogeneous concentrations, (2) linear gradients with dynamically controlled slope, baseline, and direction, and (3) nonlinear gradients with controlled nonlinearity are shown and their limitations are described.     

Preconcentration in static and dynamic extractive separations

Possibilities of the preconcentration of solutes in liquid-liquid extraction have been investigated from the point of view of transport processes in two models. It was found that the multistage dynamic (flow) column operation with a stationary extracting phase containing solutes to be separated enables to obtain higher preconcentrations than the one-stage static (batch) process with a factor available to reach its maximum value of 2 for separations approaching 100 percent extraction. The theoretical considerations were confirmed in the separation of¹³¹I from aqueous solutions.Presented at the Conference on the Separation of Ionic Solutes, SIS '85, Smolenice, Czechoslovakia, September 2–6, 1985.     

Electrodeposition of microstructures using a patterned anode

In this paper we report the transfer of micro-scale patterns by electrodeposition on to substrates without requiring them to be coated with a photoresist mask. This approach makes uses of a patterned tool which is placed in close proximity to the substrate in an electrochemical reactor. With an appropriate choice of electrochemical parameters, electrodeposition can be confined to regions corresponding to the exposed regions of the tool. Experiments indicate that the electrodeposition of copper features on to conductive substrates is possible using this approach. Copper lines of 100 μm width have been successfully replicated, but with some increase in dimension due to current spreading. This effect can be minimised by reducing the inter-electrode gap and employing an electrolyte with a low conductivity. It is also demonstrated that the tool can be used to pattern multiple substrates.     

Analysis of aggregates of human immunoglobulin G using size-exclusion chromatography,static and dynamic light scattering

Large aggregates (Mr: 10(6)-10(7) g/mol) of human immunoglobulins are present in extremely small concentrations in IgG preparations (<0.1%). Traces of large protein aggregates cannot be determined by conventional size-exclusion chromatography (SEC) using UV detection due to limitations in sensitivity. The conventional analysis of IgG by SEC is limited to dimers and oligomers. Using light scattering it is possible to determine significant differences concerning the aggregate composition and the extent of protein aggregation in samples of different process steps. Two different pilot preparations were analyzed by SEC with UV and static light scattering detection and compared to dynamic light scattering in the batch mode. The change of large aggregates could be monitored and data were corroborated by dynamic light scattering.     

Accelerated Poisson-Boltzmann calculations for static and dynamic systems

We report here an efficient implementation of the finite difference Poisson-Boltzmann solvent model based on the Modified Incomplete Cholsky Conjugate Gradient algorithm, which gives rather impressive performance for both static and dynamic systems. This is achieved by implementing the algorithm with Eisenstat's two optimizations, utilizing the electrostatic update in simulations, and applying prudent approximations, including: relaxing the convergence criterion, not updating Poisson-Boltzmann-related forces every step, and using electrostatic focusing. It is also possible to markedly accelerate the supporting routines that are used to set up the calculations and to obtain energies and forces. The resulting finite difference Poisson-Boltzmann method delivers efficiency comparable to the distance-dependent dielectric model for a system tested, HIV Protease, making it a strong candidate for solution-phase molecular dynamics simulations. Further, the finite difference method includes all intrasolute electrostatic interactions, whereas the distance dependent dielectric calculations use a 15-A cutoff. The speed of our numerical finite difference method is comparable to that of the pair-wise Generalized Born approximation to the Poisson-Boltzmann method.     

Controlling drop size and polydispersity using chemically patterned surfaces

We explore numerically the feasibility of using chemical patterning to control the size and polydispersity of micrometer-scale drops. The simulations suggest that it is possible to sort drops by size or wetting properties by using an array of hydrophilic stripes of different widths. We also demonstrate that monodisperse drops can be generated by exploiting the pinning of a drop on a hydrophilic stripe. Our results follow from using a lattice Boltzmann algorithm to solve the hydrodynamic equations of motion of the drops and demonstrate the applicability of this approach as a design tool for micofluidic devices with chemically patterned surfaces.     

Evaluation of the molecular static and dynamic first hyperpolarizabilities

By considering two prototypical π‐conjugated compounds, several technical aspects associated with the evaluation of the first hyperpolarizabilities have been addressed in this article, that is, (i) the automatization of the Romberg's scheme to improve the numerical accuracy in the finite field method, (ii) the evaluation of the frequency dispersion at correlated levels using approximate schemes, and (iii) the deviations from Kleinman's symmetry conditions. It results from this study that accurate numerical derivatives can be obtained by resorting to the Romberg's method and by analyzing the Romberg's table in terms of two quantities, the field error and the iteration error. Indeed, the resulting first hyperpolarizability values are in close agreement with those obtained using an analytical differentiation procedure. The reliability of the multiplicative and additive approximate schemes to describe the frequency dispersion at correlated levels from using HF (Hartree‐Fock) frequency dispersion has been confirmed to be limited to large wavelengths or far‐from‐resonance wavelength regions. Kleinman's symmetry conditions have been assessed, showing that for off‐diagonal components of these two π‐conjugated compounds, the deviations could be substantial. Nevertheless, good accuracy can be achieved for experimentally related quantities like β_HRS because the diagonal tensor components are dominant. © 2014 Wiley Periodicals, Inc.     

Removal of nanoparticles from plain and patterned surfaces using nanobubbles

It is the aim of this paper to quantitatively characterize the capability of surface nanobubbles for surface cleaning, i.e., removal of nanodimensioned polystyrene particles from the surface. We adopt two types of substrates: plain and nanopatterned (trench/ridge) silicon wafer. The method used to generate nanobubbles on the surfaces is the so-called alcohol-water exchange process (use water to flush a surface that is already covered by alcohol). It is revealed that nanobubbles are generated on both surfaces, and have a remarkably high coverage on the nanopatterns. In particular, we show that nanoparticles are-in the event of nanobubble occurrence-removed efficiently from both surfaces. The result is compared with other bubble-free wet cleaning techniques, i.e., water rinsing, alcohol rinsing, and water-alcohol exchange process (use alcohol to flush a water-covered surface, generating no nanobubbles) which all cause no or very limited removal of nanoparticles. Scanning electron microscopy (SEM) and helium ion microscopy (HIM) are employed for surface inspection. Nanobubble formation and the following nanoparticle removal are monitored with atomic force microscopy (AFM) operated in liquid, allowing for visualization of the two events.     

Fabrication of patterned nanofibrous mats using direct-write electrospinning

Due to the numerous advantages of nanofibers, there is a strong demand in various fields for nanofibrous structures fabricated by electrospinning. However, the process is currently beset by troublesome limitations with respect to geometric and morphological control of electrospun nanofibrous mats. This study presents a direct-write electrospinning process and apparatus with improved focusing and scanning functionalities for the fabrication of various patterned thick mats and nanofibrous patterns with high geometric fidelity, supported by a number of experimental results. Consequently, various patterned nanofibrous mats were fabricated using the developed method. Additionally, the fabricated mat was successfully used for cell patterning as a bioengineering application. The proposed method is expected to significantly improve the properties and functionalities of nanofibrous mats in a variety of applications.     

Electrophoresis in microfabricated devices using photopolymerized polyacrylamide gels and electrode-defined sample injection

Microfabrication techniques have become increasingly popular in the development of the next generation of DNA analysis systems. While significant progress has been reported by many researchers, complete microfabricated integrated DNA analysis devices are still in the earliest stages of development. Most miniaturized analysis systems have incorporated noncross-linked polymer solutions as the separation medium of choice and the operation of these systems necessitates the use of high electric fields and long separation lengths. In this paper, we present two techniques that may help alleviate this problem and accelerate the development of the so-called 'lab-on-a-chip' systems. We present the use of photodefinable polyacrylamide gels as a sieving medium for DNA electrophoresis. These gels offer the significant advantages of faster curing times, locally controlled gel interface, and simpler handling over chemically polymerized gels. We also introduce an electrode-defined sample compaction and injection technique. This technique helps achieve sample compaction without migration into the gel and offers significant control over the size and application of the sample plug. The use of these technologies for double-stranded DNA separations in microfabricated separation systems is demonstrated.     

Generation of discharges in dynamic foam for oxidants formation using various types of electrodes

An innovatory apparatus for the discharge generation in foaming conditions was constructed. The main goal of the research was to obtain various kinds of oxidants, useful in Advanced Oxidation Processes (AOP) in one compact reactor, potentially even in the treated medium. Such an application of dynamic foam, created without the addition of surfactant has not been investigated as yet. To find the optimum conditions for the efficient foam generation and the discharge development and moreover, to assure the presence of oxidants in sufficient concentrations several electrode materials and electrode set-ups were tested. The experiments were done in the metal plate-to-metal plate, metal plate-to-dielectric plate, needles-to-metal plate and needles-to-dielectric plate electrodes’ set-ups. The discharge gap space ranged from 4 mm in the case of plate-to-plate electrodes to 7 mm in the case of needles-to-plate electrodes. Generally, the highest oxidants’ concentrations at the highest comparable gas flow rate were obtained in the needles-to-dielectric plate arrangement, where 521 and 875 ppm of gaseous ozone, 0.36 and 0.5 mg dm⁻³ of dissolved ozone and 59 and 62 mg dm⁻³ of hydrogen peroxide were obtained at 14 kV of applied voltage and at 5 dm³ min⁻¹ of the substrate gas flow in air and oxygen, respectively. The presence of OH radicals was confirmed by the spectroscopic measurements. The larger gap size was more advantageous from the foam formation point of view and the dielectric layer assured more uniform spatial discharge development between the electrodes.     

Site-selective chemical etching of silicon using patterned silver catalyst

Si convex arrays and Si hole arrays with ordered periodicities were fabricated by the site-selective chemical etching of a Si substrate using patterned Ag nanoparticles as a catalyst. Ag particles were deposited selectively on the Si substrate by a combination of colloidal crystal templating, hydrophobic treatment and subsequent electroless plating. The obtained Ag patterns were of two different types: network-like honeycomb and isolated-island microarrays. The transfer of ordered patterns fabricated by Ag plating onto the Si substrate could be achieved by the selective chemical etching of a Ag-coated Si area using Ag particles as the etching catalyst. On the basis of this process, it is possible to fabricate negative and positive patterns by changing the arrangement of deposited Ag patterns.     

Variational calculation of static and dynamic vibrational nonlinear optical properties

The vibrational configuration interaction method used to obtain static vibrational (hyper)polarizabilities is extended to dynamic nonlinear optical properties in the infinite optical frequency approximation. Illustrative calculations are carried out on H(2)O and NH(3). The former molecule is weakly anharmonic while the latter contains a strongly anharmonic umbrella mode. The effect on vibrational (hyper)polarizabilities due to various truncations of the potential energy and property surfaces involved in the calculation are examined.     

Generation of complex, static solution gradients in microfluidic channels

A microfluidic device is used to generate a complex gradient of diffusible molecules in a static solution. The gradient is precise and steady both in space and in time. This device, made from poly(dimethylsiloxane), consists of three layers. The molecules in reservoirs on the top layer diffuse through the flat middle layer of hydrogel and reach an equilibrium distribution. Microfluidic channels on the bottom layer that are in close contact with the hydrogel contain free solution that has concentration gradients based on the gradient in the gel. The gradient profile in the channel can be designed to have an arbitrary form (within the range of the existing gradient in the hydrogel) by controlling the local direction of the channel at each point.     

Effect of static and dynamic disorder on exciton mobility in oligothiophenes

The polarized optical absorption spectra of different quaterthiophene single crystals in the energy region of the exciton bands originating from the first molecular transition are reported as measured in the temperatures ranging from 7 to 140 K. The intrinsic higher mobility of the b-polarized 0-0 a(u) exciton both with respect to its replicas and to the a-polarized structures is demonstrated in high quality crystals at the lowest temperatures. The influence of structural disorder on mobility is discussed considering, for the different samples, the measured lineshape and linewidth of the absorption peaks, and the relative lineshift and intensity ratio between the 0-0 a(u) line and its first replica at the lowest temperature. The influence of dynamic disorder is discussed considering the lineshape and linewidth of the measured peaks as a function of temperature for both polarizations in the framework of the exciton-phonon coupling theory.     

Computational insight into the static and dynamic polarizabilities of aluminum nanoclusters

The static and dynamic polarizabilities for the lowest-energy structures of pure aluminum clusters up to 31 atoms have been investigated systematically within the framework of density functional theory. The size evolution of several electronic properties such as ionization potential, electron affinity, the energy gap between the highest occupied molecular orbital and lowest unoccupied molecular orbital, and chemical hardness have also been discussed for aluminum clusters. Our primary focus in this article, however, has been upon the study of polarizability of aluminum clusters, although we also looked at the role of other electronic properties. From the energetics point of view, the relative stability of aluminum clusters at different sizes is studied in terms of the calculated second-order difference in the total energy of cluster and fragmentation energy, exhibiting that the magic numbers of stabilities are n = 7, 13, and 20. Moreover, the minimum polarizability principle is used to characterize the stability of aluminum clusters. The results show that polarizabilities and electronic properties can reflect obviously the stability of clusters. Electronically, the size dependence of ionization potential and electron affinity of clusters is determined. On the basis of the Wood and Perdew model these quantities converge asymptotically to the value of the bulk aluminum work function.     

Fluidic shear-assisted formation of actuating multilamellar lipid tubes using microfabricated nozzle array device

Molecular self-assemblies exhibiting automatic motions have received much attention as potential artificial models of living organisms. We have developed a microfluidic picolitre nozzle-array device to form multilamellar lipid tubes (MLTs) under fluidic shear stress, which transformed into different two patterns (yarn-balls and double-helixes) and also exhibited unique self-actuation behaviors.     

Chiral analysis of neurotransmitters using cyclodextrin-modified capillary electrophoresis equipped with microfabricated interdigitated electrodes

We present cyclodextrin-modified capillary electrophoresis equipped with a microfabricated chip consisting of an array of eight interdigitated microband platinum electrodes (IDs) for simultaneous analysis of three chiral models: epinephrine, norepinephrine and isoproterenol. The IDE chip, positioned very close to the capillary outlet, served as an amplification/detection system. Emerging neurotransmitters at the IDE surface were oxidized at +1.1 V by seven electrodes of the array and then detected by the remaining electrode, poised at +0.0 V. There was an amplification effect on the detecting electrode owing to the recycle between the reduced and oxidized forms of the optical isomers at the electrode surface. The detecting "amplification" current response was governed by the applied potential, the detecting electrode position, the number of adjacent electrodes used for recycling and the distance between the oxidative and reductive electrodes. The six chiral forms of the three neurotransmitters were resolved using 25 mM heptakis(2,6,di-o-methyl)-beta-cyclodextrin with a detection limit of approximately 5 microM. The scheme detected a reduced compound at a reducing potential instead of conventional oxidation detection to alleviate electrode fouling and electroactive interferences. The concurrent oxidation/reduction detection of compounds also facilitated and ascertained peak identification as interfering compounds were unlikely to have the same oxidative/reductive characteristics and mobilities as the analytes of interrogation.