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At least 361 records · Page 20Linked to original sources
PubMed1995

Electrical stimulation of bone nonunion with the presence of a gap.

A total of 22 established nonunions was treated with a capacitively-coupled electrical signal. A gap of 0.5 cm or more between the fragments was present in all of these nonunions. After an average of 26 weeks of treatment with capacitive coupling, radiographic assessment showed solid bone union in 72.7% of the cases. The results were better when the fracture site was metaphyseal. When the site was diaphyseal, bone healing was mainly achieved by bone trabeculae invading the gap. When the site was metaphyseal, healing occurred by the formation of a peripheral callus. The results were not affected by the presence of infection. In 8 of the cases osteomyelitis occurred, but all healed.

Adolescent↗
PubMed2002

Amiloride-sensitive sodium current in everted Ambystoma initial collecting tubule: short-term insulin effects.

Whole cell patch-clamp techniques were used to investigate amiloride-sensitive sodium conductance (G(Na)) in the everted initial collecting tubule of Ambystoma. Accessibility to both the apical and basolateral membranes made this preparation ideal for studying the regulation of sodium transport by insulin. G(Na) accounted for 20% of total cell conductance (G(T)) under control conditions. A resting membrane potential of -75 +/- 2 mV (n = 7) together with the fact that G(T) is stable with time suggested that the cells studied were viable. Measurements of capacitance and use of a known uncoupling agent, heptanol, suggested that cells were not electrically coupled. Thus the values of G(T) and G(Na) represented individual principal cells. Exposure of the basolateral membrane to insulin (1 mU/ml) for 10-60 min significantly (P < 0.05) increased the normalized G(Na) [1.2 +/- 0.3 nS (n = 6) vs. 2.0 +/- 0.4 nS (n = 6)]. Cell-attached patch-clamp techniques were used to further elucidate the mechanism by which insulin increases amiloride-sensitive epithelial sodium channel (ENaC) activity. In the presence of insulin there was no apparent change in either the number of active levels/patch or the conductance of ENaC. The open probability increased significantly (P < 0.01) from 0.21 +/- 0.04 (n = 6) to 0.46 +/- 0.07 (n = 6). Thus application of insulin enhanced sodium reabsorption by increasing the fraction of time the channel spent in the open state.

Ambystoma↗
PubMed2004

Determination of cell capacitance using the exact empirical solution of partial differential Y/partial differential Cm and its phase angle.

Measures of membrane capacitance offer insight into a variety of cellular processes. Unfortunately, popular methodologies rely on model simplifications that sensitize them to interference from inevitable changes in resistive components of the traditional cell-clamp model. Here I report on a novel method to measure membrane capacitance that disposes of the usual simplifications and assumptions, yet is immune to such interference and works on the millisecond timescale. It is based on the exact empirical determination of the elusive partial derivative, partial differential Y/partial differential C(m), which heretofore had been approximated. Furthermore, I illustrate how this method extends to the vesicle fusion problem by permitting the determination of partial differential Y(v)/partial differential C(v), thereby providing estimates of fusion pore conductance and vesicle capacitance. Finally, I provide simulation examples and physiological examples of how the method can be used to study processes that are routinely interrogated by measures of membrane capacitance.

Algorithms↗
PubMedDate not supplied

Use of electrical bone stimulation in spinal fusion.

Spinal fusion is commonly done to manage deformity, restore stability, and eliminate excessive motion at specific spinal levels. Pseudarthrosis limits the clinical success of spinal fusion. Three types of electrical stimulation, which is used to manage non-union in long bones, recently have been applied in an attempt to enhance the rate of spinal fusion. Direct current electrical stimulation is internal and thus eliminates dependence on patient compliance. Pulsed electromagnetic fields and capacitively coupled electrical stimulation are external techniques that require patient compliance but do not have the increased risk associated with implantable devices. Firm conclusions about efficacy are difficult to establish because of inconsistencies in both determining a reliable, reproducible end point for fusion and in incorporating the effect of patient parameters. Most data indicate a positive effect for use of direct current stimulation, but further studies are necessary to determine its appropriateness as an adjuvant to spinal fusion.

Animals↗
PubMed2025

Ambient-Stable and Resilient Glycerogel Electrolytes for Flexible Solid-State Supercapacitors.

Hydrogel electrolytes are increasingly used for flexible solid-state supercapacitors emerged as promising power sources due to their similarity to aqueous electrolytes. However, their performance is limited by evaporation or freezing in challenging weather, restricting their practical applications. This study introduces a flexible glycerogel electrolyte with antidrying and antifreezing properties, offering exceptional durability under harsh conditions. Inspired by the role of glycerol and electrolytes in electrodermal activity of biological tissue, eco-friendly NaCl and hygroscopic glycerol are incorporated into a stretchable hydrogel matrix. The resulting glycerogel electrolyte retained hydration in the open air for 180 days. It also exhibited stable conductivity under extreme temperatures (-20 to 60 &#xb0;C) and low-pressure conditions (&#x223c;2.4 kPa). A fibrous solid-state supercapacitor assembled using carbon nanotube yarns delivered a maximum gravimetric capacitance of 148 F&#xb7;g-1 at 0.5 A&#xb7;g-1. Notably, the device maintained 94%, 86%, and 90% of its initial capacitance after 30 days of exposure to -20 &#xb0;C, 60 &#xb0;C, and low-pressure conditions, respectively, without encapsulation. To demonstrate practical utility, this fibrous supercapacitor was integrated into the ear loop of a facial mask, enabling heat-induced sanitization that killed 99.999% of bacterial cells. This glycerogel electrolyte provides a sustainable, versatile solution for powering future wearable electronic devices across diverse environmental conditions.

Electric Capacitance↗
PubMed2002

High-speed pressure clamp.

We built a high-speed, pneumatic pressure clamp to stimulate patch-clamped membranes mechanically. The key control element is a newly designed differential valve that uses a single, nickel-plated piezoelectric bending element to control both pressure and vacuum. To minimize response time, the valve body was designed with minimum dead volume. The result is improved response time and stability with a threefold decrease in actuation latency. Tight valve clearances minimize the steady-state air flow, permitting us to use small resonant-piston pumps to supply pressure and vacuum. To protect the valve from water contamination in the event of a broken pipette, an optical sensor detects water entering the valve and increases pressure rapidly to clear the system. The open-loop time constant for pressure is 2.5 ms for a 100-mmHg step, and the closed-loop settling time is 500-600 micros. Valve actuation latency is 120 micros. The system performance is illustrated for mechanically induced changes in patch capacitance.

Animals↗
PubMed2003

Capacitative calcium influx and intracellular pH cross-talk in human platelets.

This study focuses on the potential interrelationships between changes in pH and capacitative calcium entry in stimulated platelets and on the participation of SOCs in the control of intracellular pH (pH(i)). Extracellular acidification reduces the Mn(2+) entry, measured by the slope of the quenching of FURA 2 fluorescence at the isoemissive wavelength of 360 nm. In thrombin-stimulated platelets Mn(2+) entry is reduced by acidosis (pH(o) = 6.89) to 17 +/- 4% of control (pH(o) = 7.32). In platelets treated with thapsigargin (TG) to induce the opening of store-operated channels (SOCs) the rate of quenching was reduced by acidosis to 31 +/- 5 % of control. Calcium entry was measured as the peak of [Ca(2+)](i) response to extracellular calcium readmission after mobilization of calcium from intracellular stores. Changes in pH(o) of platelet suspension media markedly alters the calcium entry evoked by thrombin that reach a 16 +/- 6 % of control in acidosis (pH(o) = 6.89) and 150 +/- 15% of control in alkalosis (pH(o) = 7.62). The SERCA inhibitor TG was used to study the effect of pH(o) on Ca(2+) influx. Acidosis decreases and alkalosis increases the capacitative calcium entry to 22 +/- 4 % and 129 +/- 1% of control respectively. These changes in pH(o) also produced changes in pH(i). Treatment of platelets with titrated solutions of trimethylamine causes intracellular alkalinization without changes in pH(o) increasing the capacitative calcium entry to 120 +/- 5%. TG itself produces an intracellular alkalinization that is further increased by calcium entry. Blockage of the Na(+)/H(+) exchanger reverted TG effect on pH(i) without changes in capacitative calcium entry.

Blood Platelets↗
PubMed1992

[Electrical stimulation in the treatment of osteoporosis in sciatic denervated rat tibia].

Osteoporosis in the sciatic-denervated rat tibia was reversed with a capacitively coupled electrical field. In the reversal of a previously established osteoporosis, a statistically significant enhancement of wet weight, dry weight, ashed weight, ultimate strength, cortical area, cortical thickness and a concomitant decrease in cortical porosity occurred in the stimulated, denervated tibiae of the experimental animals compared with the nonstimulated, denervated tibiae of the control animals. A 60 Hz symmetrical sinewave signal was effective in reversing osteoporosis at 10 V peak to peak. Reversal of a well-established osteoporosis in laboratory animals has not been reported previously.

Animals↗
PubMed2005

Acoustic coupling in capacitive microfabricated ultrasonic transducers: modeling and experiments.

In the design of low-frequency transducer arrays for active sonar systems, the acoustic interactions that occur between the transducer elements have received much attention. Because of these interactions, the acoustic loading on each transducer depends on its position in the array, and the radiated acoustic power may vary considerably from one element to another. Capacitive microfabricated ultrasonic transducers (CMUT) are made of a two-dimensional array of metallized micromembranes, all electrically connected in parallel, and driven into flexural motion by the electrostatic force produced by an applied voltage. The mechanical impedance of these membranes is typically much lower than the acoustic impedance of water. In our investigations of acoustic coupling in CMUTs, interaction effects between the membranes in immersion were observed, similar to those reported in sonar arrays. Because CMUTs have many promising applications in the field of medical ultrasound imaging, understanding of cross-coupling mechanisms and acoustic interaction effects is especially important for reducing cross-talk between array elements, which can produce artifacts and degrade image quality. In this paper, we report a finite-element study of acoustic interactions in CMUTs and experimental results obtained by laser interferometry measurements. The good agreement found between finite element modeling (FEM) results and optical displacement measurements demonstrates that acoustic interactions through the liquid represent a major source of cross coupling in CMUTs.

Acoustics↗
PubMed1957

The membrane capacitance of the sea urchin egg.

1. The surface of the unfertilized sea urchin egg is folded and the folds are reversibly eliminated by exposing the egg to hypotonic sea water. If the plasma membrane is outside the layer of cortical granules, unfolding may explain why the membrane capacitance per unit area decreases (and does not increase) when a sea urchin egg is put into hypotonic sea water. 2. The degree of surface folding markedly increases after fertilization, which provides an explanation for the increase in membrane capacitance per unit area observed after fertilization. 3. The percentage reduction in membrane folding in fertilized eggs after immersion in hypotonic sea water is probably sufficient to explain the decrease in membrane capacitance per unit area observed in these conditions.

Animals↗
PubMed2003

A novel STM-assisted microwave microscope with capacitance and loss imaging capability.

We report a new technique of scanning capacitance microscopy at microwave frequencies. A near field scanning microwave microscope probe is kept at a constant height of about 1 nm above the sample with the help of scanning tunneling microscope (STM) feedback. The microwaves are incident onto the sample through a coaxial resonator that is terminated at one end with a sharp tip (the same tip is used to conduct STM), and capacitively coupled to a feedback circuit and microwave source at the other end. The feedback circuit keeps the source locked onto the resonance frequency of the resonator and outputs the frequency shift and quality factor change due to property variations of the sample. The spatial resolution due to capacitance variations is congruent with 2.5 nm. The microwave microscope is sensitive to sample sheet resistance, as demonstrated through measurements on a doped silicon sample. We develop a quantitative transmission line model treating the tip to sample interaction as a series combination of capacitance and sheet resistance in the sample.

Algorithms↗
PubMed2002

Deviations of capacitive and inductive loops in the electrochemical impedance of a dissolving iron electrode.

The electrochemical impedance of an iron electrode often shows the capacitive and inductive loops on the complex plane. The capacitive loop originates from the time constant of the charge transfer resistance and the electric double layer capacitance. The inductive loop is explained by Faradaic processes involving the reaction intermediate. In some cases, these loops deviate from a true semicircle. In this paper, the origins and curve-fitting methods for the deviated loops of electrochemical impedance are discussed. The constant phase element (CPE) was used to present the deviation of the capacitive loop instead of electric double layer capacitance. The reaction rate constants, which are a function of the frequency, are proposed for the Faradaic impedance to present the deviated inductive loop.

Journal Article↗