Coalescence and counterflow of droplets on needle electrode with negative corona discharge

The coalescence of droplets on the discharge electrode surface in high humidity environments has rarely been studied, which may affect discharge characteristics. Meanwhile, directional transport of droplets is of great significance for many applications ranging from fluidic processing to thermal management. Here, corona discharge in needle-plate electrode is adopted to explore the coalescence rule of droplets attached on the discharge electrode surface in high-humidity environment, and realize the counterflow of droplets. The experimental results show that the amount of coalesced droplets on the needle electrode surface reaches the maximum under -7.5 kV at relative humidity ~ 94% and ambient temperature ~ 20 ℃. When the applied voltage increases from -6 kV to -11 kV, the droplet moves up 2.76 mm in 5 s. The size of attached droplet depends on the balance of coalescence and evaporation. The coalescence is mainly attributed to the dielectrophoretic force caused by the high electric field gradient. The evaporation is related with the ionic wind generated by the corona discharge. As for the counterflow phenomenon of droplet, we speculate that the high concentration gradient of positive ions near the needle electrode provides a driving force for the negatively charged droplets. Meanwhile, the electrons and negative ions below the needle tip offer a repulsive force to the droplet. The shape and moving direction of the droplet attached on the needle surface can be manipulated by changing the voltage applied to the needle electrode, which shows the potential application value in realizing self-cleaning of electrode, liquid lens and so on.

A floating 5-µm-diameter needle-electrode on the tissue for damage-reduced chronic neuronal recording in mice

Microelectrode technology is essential in electrophysiology and has made contributions to neuroscience as well as to medical applications. However, it is necessary to minimize tissue damage associated with needle-like electrode...

Simulation and Experimental Investigation of a Hollow, Bipolar Needle Electrode

Localized impedance measurements at the needle tip identifying the present tissue type could aid clinicians in needle procedures. To assess the sensitivity field of a hollow, bipolar needle electrode, a 3D finite element approach using COMSOL Multiphysics was chosen. The simulated bipolar needle electrode consists of two hypodermic needles (17 G and 23 G) with an insulating layer of polytetrafluoroethylene (PTFE) in between. Impedance values were recorded while steadily increasing the insertion depth of the needle electrode in a layered tissue structure of skin (dermis), fat, and blood. Simulation results reveal a highly local sensitivity volume around the needle tip that can be approximated by half a tri-axial ellipsoid with elliptic radii of 0.735 mm, 2.886 mm, and 1.774 mm. A comparison with simulated and measured impedance values shows great correspondence.

Surface Electromyography for Identification of Pre-Phonatory Activity

Surface electrode EMG is an established method for studying biomechanical activity. It has not been well studied in detecting laryngeal biomechanical activity of pre-phonatory onset. Our aims were to compare the sensitivity of surface EMG in identifying pre-phonatory laryngeal activity to needle electrode laryngeal EMG and to compare the pre-phonatory period in patients with adductor laryngeal dystonia (ADLD) with that in controls. ADLD patients (n = 10) undergoing needle LEMG prior to Botox injection and participants with normal voices (n = 6) were recruited. Surface EMG electrodes were placed over the cricoid ring and thyrohyoid membrane. Needle EMG electrodes were inserted into the thyroarytenoid muscle. EMG and auditory output samples were collected during phonation onset. Tracings were de-identified and evaluated. Measurements of time from onset in change of the amplitude and motor unit frequency on the interference pattern to onset of phonation were calculated by two blinded raters. 42 of 71 patient and 40 of 50 control tracings were available for analysis. Correlation for pre-phonatory time between electrode configuration was 0.70 for patients, 0.64 for controls and 0.79 for all the data combined. Inter-rater correlation was 0.97 for needle and 0.96 for surface electrodes. ADLD patients had a longer pre-phonatory time than control subjects by 169.48ms with surface electrode and 140.23ms with needle electrode (p < 0.001). Surface EMG demonstrates equal reliability as Needle EMG in detecting pre-phonatory activity in controls and subjects. Patients with ADLD have a significantly prolonged pre-phonatory period when compared with controls.

Dielectrophoretic Manipulation of Cell Transfection Efficiency During Electroporation Using a Center Needle Electrode

Long duration electric pulses are frequently used to facilitate DNA electrotransfer into cells and tissues, while electroporation pulses can be combined with electrophoresis to maximize the transfection efficiency. In this work, we present the dielectrophoresis (DEP)-assisted methodology for electrotransfer of plasmid DNA (3.5 kbp pmaxGFP) into mammalian cells (CHO-K1). A prototype of an electroporation cuvette with center needle electrode for DEP-assisted transfection is presented resulting in a 1.4-fold of transfection efficiency increase compared to the electroporation-only procedure (1.4 kV/cm × 100 µs × 8). The efficiency of transfection has been compared between three DEP frequencies of 1, 100, and 1 MHz. Lastly, the effects of exposure time (1, 3, and 5 min) during the DEP application step have been determined. It is concluded that the proposed methodology and exposure setup allow a significant improvement of transfection efficiency and could be used as an alternative to the currently popular electrotransfection techniques.