Magneto-mechanical actuation of barium-hexaferrite nanoplatelets for the disruption of phospholipid membranes.

HYPOTHESIS: The magneto-mechanical actuation (MMA) of magnetic nanoparticles with a low-frequency alternating magnetic field (AMF) can be used to destroy cancer cells. So far, MMA was tested on different cells using different nanoparticles and different field characteristics, which makes comparisons and any generalizations about the results of MMA difficult. In this paper we propose the use of giant unilamellar vesicles (GUVs) as a simple model system to study the effect of MMA on a closed lipid bilayer membrane, i.e., a basic building block of any cell. EXPERIMENTS: The GUVs were exposed to barium-hexaferrite nanoplatelets (NPLs, ~50 nm wide and 3 nm thick) with unique magnetic properties dominated by a permanent magnetic moment that is perpendicular to the platelet, at different concentrations (1-50 µg/mL) and pH values (4.2-7.4) of the aqueous suspension. The GUVs were observed with an optical microscope while being exposed to a uniaxial AMF (3-100 Hz, 2.2-10.6 mT). FINDINGS: When the NPLs were electrostatically attached to the GUV membranes, the MMA induced cyclic fluctuations of the GUVs' shape corresponding to the AMF frequency at the low NPL concentration (1 µm/mL), whereas the GUVs were bursting at the higher concentration (10 µg/mL). Theoretical considerations suggested that the bursting of the GUVs is a consequence of the local action of an assembly of several NPLs, rather than a collective effect of all the absorbed NPLs.

Lagging-Domain Model for Compensation of Hysteresis of xMR Sensors in Positioning Applications.

The hysteresis of magnetoresistive sensors remains a considerable cause of inaccuracy of positioning applications. The phenomena itself has been well studied and described by different physical and phenomenological models. Various biasing techniques have been proposed. However, the increased fabrication and computational price they require is undesirable. In this paper, a computational algorithm for the compensation of hysteresis of linear and rotary encoders is proposed. A lagging-domain model based on play operators is presented for prediction of hysteresis. The outlined procedure for the calibration of parameters allows the use of the algorithm for various types of encoders without knowing their exact material properties. The method was tested on different anisotropic magnetoresistive and tunneling magnetoresistive sensors. Results show that the impact of hysteresis was reduced by up to 90% without a significant increase of computational time or production costs.

A strip-type microthrottle pump: modeling, design and fabrication.

A novel design for a strip-type microthrottle pump with a rectangular actuator geometry is proposed, with more efficient chip surface consumption compared to existing micropumps with circular actuators. Due to the complex structure and operation of the proposed device, determination of detailed structural parameters is essential. Therefore, we developed an advanced, fully coupled 3D electro-fluid-solid mechanics simulation model in COMSOL that includes fluid inertial effects and a hyperelastic model for PDMS and no-slip boundary condition in fluid-wall interface. Numerical simulation resulted in accurate virtual prototyping of the proposed device only after inclusion of all mentioned effects. Here, we provide analysis of device operation at various frequencies which describes the basic pumping effects, role of excitation amplitude and backpressure and provides optimization of critical design parameters such as optimal position and height of the microthrottles. Micropump prototypes were then fabricated and characterized. Measured characteristics proved expected micropump operation, achieving maximal flow-rate 0.43 mL·min(-1) and maximal backpressure 12.4 kPa at 300 V excitation. Good agreement between simulation and measurements on fabricated devices confirmed the correctness of the developed simulation model.

Short-term repeatability of parameters extracted from radial displacement of muscle belly.

The aim of this study is to analyse the short-term repeatability of the parameters extracted from radial muscle belly response on a stimulation pulse. The method uses a prefixed tension of a displacement sensor tip to the muscle and is being developed for noninvasive and selective evaluation of skeletal muscle contraction properties. Five parameters were extracted and statistically evaluated from the measured displacement: maximal displacement, delay time, contraction time, sustain time and half relaxation time. Care has been taken to leave sufficient time between stimulation pulses in order to reduce the effect of muscle fatigue and a constant pre-tension was assured by controlled step motor in consecutive measurement by withdrawal and anew placement of the sensor to the muscle belly after each measurement. Intra-class correlation coefficient (ICC) and normalized squared error (NSEM) were used as measures of short-term repeatability and accuracy (precision) of the measurements while fatigue rate was evaluated using area ratio fatigue index and normalized slope. All five measured parameters have been found highly repeatable (ICC from 0.86 to 0.98) and can be measured with high precision (NSEM from 0.43 to 1.93). Maximal displacement and half relaxation time show largest influence to muscle fatigue rate and are also expected to be the best measure of the fatigue rate. This investigation should serve as an initial study of repeatability of the presented method that should help in subsequent investigations and use of the method.

Feasibility study for cell electroporation detection and separation by means of dielectrophoresis.

Electroporation is a phenomenon during which exposure of a cell to high voltage electric pulses results in a significant increase in its membrane permeability. Aside from the fact that after the electroporation the cell membrane becomes more permeable, the cells' geometrical and electrical properties change considerably. These changes enable use of the force on dielectric particles exposed to non-uniform electric field (dielectrophoresis) for separation of non-electroporated and electroporated cells. This paper reports the results of an attempt to separate non-electroporated and electroporated cells by means of dielectrophoresis. In several experiments we managed to separate the non-electroporated and electroporated cells suspended in a medium with conductivity 0.174 S/m by exposing them to a non-uniform electric field at a frequency of 2 MHz. The behaviour of electroporated cells exposed to dielectrophoresis raises the presumption that in addition to conductivity, considerable changes in membrane permittivity occur after the electroporation.

Modeling AC current conduction through a human tooth.

Impedance between the electrode inserted in a root canal of a human tooth and the outer electrode placed on the oral mucosa serves as a measure of the root canal length, a vital parameter necessary for efficient endodontic procedure in dentistry. For better understanding of current conduction through the tooth, the impedance has been measured on extracted teeth (in vitro) and further used to develop corresponding electrical lumped element models. For modeling the metal/solution interface and complex structure of the tooth, Fricke's constant phase elements are employed. More detailed insight into current conduction is given by numerical simulation. Numerical simulation demonstrates the influence on the impedance of several important parameters, such as dentin conductance, canal preparation, and solution conductance.

Numerical computation of impedances of a human tooth for estimation of the root canal length.

Alternative current (ac) current conduction through a human tooth has been investigated through numerical simulation. Numerical calculation of impedance between the file (electrode) inserted in the root canal of the tooth and the outer electrode enables investigation of the impedance method used in dentistry for evaluation of the root canal length. Simulations confirm the improved sensitivity of the impedance method using the results of multiple frequency measurements.