A comparison of front-end amplifiers for tetrapolar bioimpedance measurements

Many commercial benchtop impedance analyzers are incapable of acquiring accurate tetrapolar measurements, when large electrode contact impedances are present, as in bioimpedance measurements using electrodes with micrometer-sized features. External front-end amplifiers can help overcome this issue and provide high common-mode rejection ratio (CMRR) and input impedance. Several discrete component-based topologies are proposed in the literature. In this article, these are compared with new alternatives with regard to their performance in measuring known loads in the presence of electrode contact impedance models, to emulate tetrapolar bioimpedance measurements. These models are derived from bipolar impedance measurements taken from the electrodes of a tetrapolar bioimpedance sensor. Comparison with other electrode models used in the literature established that this is a good and challenging model for bioimpedance front-end amplifier evaluation. Among the examined amplifiers, one of the best performances is achieved with one of the proposed topologies based on a custom front-end with no external resistors (AD8066/AD8130). Under the specific testing conditions, it achieved an uncalibrated worst-case absolute measurement deviation of 4.4% magnitude and 4° at 20 Hz, and 2.2% and 7° at 1 MHz accordingly with loads between 10 Ω and 10 kg. Finally, the practical use of the front-end with the impedance analyzer is demonstrated in the characterization of the bioimpedance sensor, in saline solutions of varying conductivities (2.5-20 mS/cm) to obtain its cell constant. This article serves as a guide for evaluating and choosing front-end amplifiers for tetrapolar bioimpedance measurements both with and without impedance analyzers for practical/clinical applications and material/sensor characterization

Arrays of Nano-Electromechanical Biosensors Functionalized by Microcontact Printing

The biofunctionalization of nanoelectromechanical structures is critical for the development of new classes of biosensors displaying improved performances and higher-level of integration. We propose a modified microcontact printing method for the functionalization and passivation of large arrays of nanocantilevers in a single, self-aligned step. Using fluorescence microscopy and resonant frequency measurements, we demonstrate (1) the bioactivity and the anti-fouling property of deposited antibodies and BSA molecules and (2) the preservation of the nanostructures' mechanical integrity.Comment: 20 pages, 5 figure

Lateral Flow Test (LFT) detects cell-free microRNAs predictive of preterm birth directly from human plasma

Despite extensive research toward the development of point-of-care nucleic acid tests (POC NATs) for the detection of microRNAs (miRs) from liquid biopsies, major hurdles remain including the strict requirement for extensive off-chip sample preprocessing. Herein, a nucleic acid lateral flow test (NALFT) is reported on that enables the direct detection of endogenous miRs from as little as 3 μL of plasma without the requirement for any enzyme-catalyzed target amplification or complex miR extraction steps. This is achieved through integration of a denaturing hydrogel composite material onto the LFT, allowing for near-instantaneous on-chip release of miRs from their carriers (extracellular vesicles or transport proteins) prior to detection. This next-generation LFT is sensitive enough to detect endogenous concentrations of miR-150-5p, a predictive biomarker for preterm birth (PTB) found deregulated in maternal blood from as early as 12th week of pregnancy. Herein, a key step is represented toward a first bedside test for risk-stratification during pregnancy by predicting true outcome at a very early stage. More generally, the universal and versatile nature of this novel sample preprocessing platform can further improve the robustness of existing NALFTs and facilitate their application at the POC

Elucidation of the Role of Carbon Nanotube Patterns on the Development of Cultured Neuronal Cells.

Carbon nanotubes (CNTs) promise various novel neural biomedical applications for interfacing neurons with electronic devices or to design appropriate biomaterials for tissue regeneration. In this study, we use a new methodology to pattern SiO2 cell culture surfaces with double-walled carbon nanotubes (DWNTs). In contrast to homogeneous surfaces, patterned surfaces allow us to investigate new phenomena about the interactions between neural cells and CNTs. Our results demonstrate that thin layers of DWNTs can serve as effective substrates for neural cell culture. Growing neurons sense the physical and chemical properties of the local substrate in a contact-dependent manner and retrieve essential guidance cues. Cells exhibit comparable adhesion and differentiation scores on homogeneous CNT layers and on a homogeneous control SiO2 surface. Conversely, on patterned surfaces, it is found that cells preferentially grow on CNT patterns and that neurites are guided by micrometric CNT patterns. To further elucidate this observation, we investigate the interactions between CNTs and proteins that are contained in the cell culture medium by using quartz crystal microbalance measurements. Finally, we show that protein adsorption is enhanced on CNT features and that this effect is thickness dependent. CNTs seem to act as a sponge for culture medium elements, possibly explaining the selectivity in cell growth localization and differentiation

A bioinspired 3D micro-structure for graphene-based bacteria sensing

Nature is a great source of inspiration for the development of solutions for biomedical problems. We present a novel biosensor design utilizing two-photon polymerisation and graphene to fabricate an enhanced biosensing platform for the detection of motile bacteria. A cage comprising venous valve-inspired directional micro-structure is fabricated around graphene-based sensing electronics. The asymmetric 3D micro-structure promotes motile cells to swim from outside the cage towards the inner-most chamber, resulting in concentrated bacteria surrounding the central sensing region, thus enhancing the sensing signal. The concentrating effect is proved across a range of cell cultures - from 101 CFU/ml to 109 CFU/ml. Fluorescence analysis shows a 3.38–3.5 times enhanced signal. pH sensor presents a 2.14–3.08 times enhancement via the detection of cellar metabolite. Electrical measurements demonstrate an 8.8–26.7 times enhanced current. The proposed platform provides a new way of leveraging bio-inspired 3D printing and 2D materials for the development of sensing devices for biomedical applications

Liquid seal for compact micro-piston actuation at capillary tip

Actuators at the tip of a sub-millimetric catheter could facilitatein vivointer-ventional procedures at cellular scales by enabling tissue biopsy, manipulationor supporting active micro-optics. However the dominance of frictional forcesat this scale makes classical mechanism problematic. In this paper, we reportthe design of a micro-scale piston, with a maximum dimension of 150μm,fabricated with two-photon lithography onto the tip of 140μm diameter cap-illaries. An oil drop method is used to create a seal between the piston andthe cylinder which prevents any leakage below 185 mbar pressure differencewhile providing lubricated friction between moving parts. This piston gener-ates forces that increase linearly with pressure up to 130μN without breakingthe liquid seal. The practical value of the design is demonstrated with its inte-gration with a micro-gripper that can grasp, move and release 50μm micro-spheres. Such a mechanism opens the way to micron-size catheter actuation

Finite element modeling of abradable materials – Identification of plastic parameters and issues on minimum hardness against coating's thickness

Abradable materials are used to decrease the gas consumption of aircraft engines by minimizing the gap between the blade tips and the stator. The key idea consists in using the blades themselves to machine the gap on the abradable coating. The best compromise between soft and hard coating properties has to be reached to avoid blades wear and prevent coating erosion by gas flux and particles. The plastic parameters of abradable coating were identified by using an optimization process directly connected to FEA. The first order optimization method (conjugate gradient strategy + golden section algorithm) was applied to achieve the optimal solution. A good agreement was found between experimental and numerical results. The plastic parameters were used to study the hardness variability of abradable materials with the coating thickness. Surprisingly, a minimum hardness value was found while it was expected that hardness should be always decreasing with thickness. It has been demonstrated that this minimum is produced by the boundary conditions influence on hardness measurement. This research work was completed within the Seal-Coat project funded by the European Commission under the FP5 Growth Program

Middle-term effects of education programme in chronic low back pain patients to an adherence to physical activity: A randomized controlled trial.

International audienceObjectiveThis study was to measure the impact of an education programme in Chronic Low Back Pain (CLBP) patients on their changing behaviour; particularly on the resumption or maintenance of physical activity (PA) at three and six months after care.MethodsA two-group, randomised controlled clinical trial was conducted on 68 patients as the control group (CG) and 68 as the experimental group (EG). All patients benefited from a four-week multidisciplinary programme, with an educative programme for the EG. The dropouts of patients during the follow-up period and the PA level were measured at three and six months after the end of care.ResultsAt 3-months, the EG presented a significant higher level of physical activity (91% of EG versus 77% of CG, p < 0.001) and at six months, this group presented a lower dropout rate than CG (60% of EG versus 73% of CG, p = 0.017).ConclusionThe educative programme, added to a multidisciplinary care plan, can improve adherence to the care programme and the continuum of PA.Practice implicationsAdd an educative programme focused on motivation, physical activity, stress management and daily activities seems necessary to accompany CLBP patient towards the maintenance of a regular PA