High-Throughput Micro-Debubblers for Bubble Removal with Sub-Microliter Dead Volume

We present the fabrication and evaluation of microdebubblers that are able to remove large bubbles while keeping a very low dead volume. The devices use a polytetrafluoroethylene membrane that is permeable to air in order to filter air bubbles out of an aqueous sample. The dead volume of the devices is less than one microliter, but bubbles as large as 60 microliters can be removed. This simple solution can be very useful for microfluidic devices for chemical or biological analysis that suffer from channel clogging due to the presence of bubbles in their sample. One embodiment is particularly suited for buffer solutions with living cells

The rod and hole paradox re-examined

In the rod and hole paradox as described by Rindler (1961 Am. J. Phys. 29 365–6) ('length contraction paradox'), a rigid rod moves at high speed over a table towards a hole of the same size. A bystander expects the rod to fall into the hole, but a co-moving observer expects it to pass unhindered over the hole. According to the accepted solution as first described in that paper, the entire rod must fall somewhat into the hole and therefore cannot remain rigid when the hole moves underneath it. We present an improved approach that is based on retardation due to speed of stress propagation, and in which proper stiffness is not affected. After showing how to solve the similar but simpler car and hole paradox, we find with the same approach that the rod as depicted in Rindler's paper will not fall into the hole as was claimed and that it may pass practically unhindered over it

Efficacy of pulsed electromagnetic fields and electromagnetic fields tuned to the ion cyclotron resonance frequency of Ca2+ on chondrogenic differentiation

Previous studies provide strong evidence for the therapeutic effect of electromagnetic fields (EMFs) on different tissues including cartilage. Diverse exposure parameters applied in scientific reports and the unknown interacting mechanism of EMF with biological systems make EMF studies challenging. In 1985, Liboff proposed that when magnetic fields are tuned to the cyclotron resonance frequencies of critical ions, the motion of ions through cell membranes is enhanced, and thus biological effects appear. Such exposure system consists of a weak alternating magnetic field (B-1) in the presence of a static magnetic field (B-0) and depends on the relationship between the magnitudes of B-0 and B-1 and the angular frequency omega. The purpose of the present study is to determine the chondrogenic potential of EMF with regards to pulsed EMF (PEMF) and the ion cyclotron resonance (ICR) theory. We used different stimulating systems to generate EMFs in which cells are either stimulated with ubiquitous PEMF parameters, frequently reported, or parameters tuned to satisfy the ICR for Ca2+ (including negative and positive control groups). Chondrogenesis was analysed after 3 weeks of treatment. Cell stimulation under the ICR condition showed positive results in the context of glycosaminoglycans and type II collagen synthesis. In contrast, the other electromagnetically stimulated groups showed no changes compared with the control groups. Furthermore, gene expression assays revealed an increase in the expression of chondrogenic markers (COL2A1, SOX9, and ACAN) in the ICR group. These results suggest that the Ca2+ ICR condition can be an effective factor in inducing chondrogenesis

Study of micro-glow discharges as ion sources for ion mobility spectrometry

We develop a microionizer as the ion source in a miniaturized spectrometerlike gas analyzer, operating at atmospheric pressure. Several options for the ionizing principle were considered. The application of dc glow discharge in a microsystem was studied in detail and first devices were fabricated and tested. We obtained stable dc plasmas in micromachined electrode gaps from 1 to 50 mum width, at pressures up to 10(5) Pa in various gases. With 1 and 3 mum gaps, stable glow was achieved at atmospheric pressure in Ar and N-2, respectively. In a macrosystem, we extracted ions from a dc glow discharge and controlled the ion flow with a grid. (C) 2003 American Vacuum Society

Effect of the surface charge on ion transport through nanoslits

A description of ion transport through geometrically defined nanoslits is presented. It is characterized by the effective surface charge density and was obtained by impedance spectroscopy measurements of electrolytes with different physico-chemical properties. The fluid channels were fabricated in a Pyrex-Pyrex field assisted bonding process with an intermediate layer of amorphous silicon. The height of the nanoslits was defined by the 50 nm thickness of the amorphous silicon layer. Two microfluidic channels, containing electrodes for the characterization of the nanoslits, maintained fresh liquid on both sides of the nanoapertures. By changing the KCl concentration of the electrolyte, a conductance plateau (in log-log scale) was observed due to the dominance of the effective surface charge density, resulting in an excess of mobile counterions in the nanoslits at low salt concentrations. The effective surface charge density of the Pyrex nanoslits could be modified by changing the pH of the solution. It was verified that at higher pH values the nanoslit conductance increased. Field-effect experiments allowed changing the effective surface charge density as well. The polarity of the external voltage could be chosen such that the effective surface charge density was increased or decreased, resulting in a higher or lower nanoslit conductance. This regulation of ionic flow can be exploited for the fabrication of nanofluidic device

Direct localised measurement of electrical resistivity profile in rat and embryonic chick retinas using a microprobe

We report an alternative technique to perform a direct and local measurement of electrical resistivities in a layered retinal tissue. Information on resistivity changes along the depth in a retina is important for modelling retinal stimulation by retinal prostheses. Existing techniques for resistivity-depth profiling have the drawbacks of a complicated experimental setup, a less localised resistivity probing and/or lower stability for measurements. We employed a flexible microprobe to measure local resistivity with bipolar impedance spectroscopy at various depths in isolated rat and chick embryo retinas for the first time. Small electrode spacing permitted high resolution measurements and the probe flexibility contributed to stable resistivity profiling. The resistivity was directly calculated based on the resistive part of the impedance measured with the Peak Resistance Frequency (PRF) methodology. The resistivity-depth profiles for both rat and chick embryo models are in accordance with previous mammalian and avian studies in literature. We demonstrate that the measured resistivity at each depth has its own PRF signature. Resistivity profiles obtained with our setup provide the basis for the construction of an electric model of the retina. This model can be used to predict variations in parameters related to retinal stimulation and especially in the design and optimisation of efficient retinal implants

A high-performance silicon micropump for disposable drug delivery systems

This paper describes the design, fabrication and experimental results of a new, low cost, high-performance silicon micropump developed for a disposable drug delivery system. The pump chip demonstrates linear and accurate (+/-5%) pumping characteristics for flow rates up to 2 ml/h with intrinsic insensitivity to external conditions. The stroke volume of 160 nl is maintained constant by the implementation of a double limiter acting on the pumping membrane. The actuator is dissociated from the pump chip. The chip is a stack of three layers, two Pyrex wafers anodically bonded to the central silicon wafer. The technology is based on the use of SOI technology, silicon DRIE and the sacrificial etch of the buried oxide in order to release the structures. The result is a small size chip, suitable for cost-effective manufacturing in high volume. The micropump chip is integrated into the industrial development of a miniature external insulin pump for diabetes care