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PubMed2003

Electrochemical deposition of hydroxyapatite with vinyl acetate on titanium implants.

A novel approach to electrochemical processing of hydroxyapatite (HA) coating was explored. Vinyl acetate was added in the electrolytes of calcium and phosphorous in order to improve the adhesion between HA coating and titanium substrate. X-ray powder diffractometer (XRD) spectra indicated that the vinyl acetate did not interfere with the deposition of HA on the surface of titanium cathodes. X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) results revealed that both vinyl acetate and HA were deposited on the titanium cathodes. The vinyl acetate changed the HA crystalline morphology in the deposition layer. The shape and growth direction of the HA crystals in the coating with vinyl acetate differed from those of HA deposition along. The addition of vinyl acetate increased the coating strength considerably, even though further improvement is needed for clinical applications. Moreover, a preliminary study of the bioactivity showed that osteoblastic cells exhibited higher cell proliferation potential on the HA/vinyl acetate coating than on that of pure HA.

Adhesiveness↗
PubMed2004

Electrochemical properties of suprastructures galvanically coupled to a titanium implant.

In recent years, dental implants have been widely used for the aesthetic and functional restoration of edentulous patients. Dental implants and restorative alloys are required with high corrosion resistance. Suprastructures and implants of different compositions in electrical contact may develop galvanic or coupled corrosion problems. In addition to galvanic corrosion, crevice and pitting corrosion may occur in the marginal gap between dental implant assemblies. In this study, gold, silver-palladium, cobalt-chromium, and nickel-chromium suprastructures were used to investigate their galvanic and crevice corrosion characteristics in combination with titanium (Ti) implants. Potentiodynamic and potentiostatic testing were performed in artificial saliva at 37 degrees C. Potentiodynamic testing was carried out at the potential scan rate of 1 mV/s in the range of -600-1600 mV (SCE). Potentiostatic testing was performed with an open-circuit potential and current densities at -250, 0, and 250 mV (SCE) in artificial saliva. After electrochemical testing, surface morphologies and cross-sections were examined using micrographs of the samples. Potentiodynamic test results indicated that suprastructure/Ti implant couples produced passive current densities in the range of 0.5-12 microA/cm(2); Ti abutment/Ti implant and gold/Ti implant couples exhibited relatively low passive current densities; Co-Cr/Ti implant couples the highest. Co-Cr and Ni-Cr/Ti implant couples showed breakdown potentials of 700 and 570 mV (SCE), respectively. The open-circuit potentials of silver, Ti abutment, gold, Ni-Cr, and Co-Cr/Ti implant couples were -93.2 +/- 93.9, -123.7 +/- 58.8, -140.0 +/- 80.6, -223.5 +/- 35.1, and -312.7 +/- 29.8 mV (SCE), respectively, and did not change with immersion time. The couples exhibited cathodic current densities at -250 mV (SCE); in particular, gold and silver alloys showed high cathodic current densities of -3.18 and -6.63 microA/cm(2), respectively. At 250 mV (SCE), Ti abutment/Ti implant couples exhibited a minimum current density of 9.48 x 10(-2) microA/cm(2), but gold, Ni-Cr, Co-Cr, and silver/Ti implant couples exhibited 0.313, 1.27, 5.60, and 8.06 microA/cm(2), respectively. All couples exhibited relatively low current densities at 0 mV (SCE). Photomicrographs after electrochemical testing showed crevice or pitting corrosion in the marginal gap and at the suprastructure surface. Although of the tested samples Co-Cr/Ti implant couples showed the possibility of galvanic corrosion, its degree was not significant. However, it should be borne in mind that galvanic corrosion can accelerate localized corrosion, such as crevice or pitting corrosion.

Alloys↗
PubMed1989

Studies of refractory carbides, nitrides, and borides as the thermionic emitters for electron microscopy.

Thermionic emission properties of several kinds of refractory carbides, nitrides, and borides of the transition metals in the form of powder were investigated with a newly developed measuring device and evaluated by the figure of merit defined as the ratio of the effective work function to the working temperature at which the vapor pressure becomes 1 x 10(-5) Torr. There are several materials whose thermionic emission properties are better than those of tungsten or compatible to those of tungsten among the carbides and borides, such as TaC, HfC, ZrC, LaB6, and CeB6, as judged by the figure of merit. New preparation methods for carburization, nitriding, and boriding of the wires of matrix metals and alloys were successfully developed for using these materials as the cathode of the electron microscope. Other necessary techniques such as spot welding and electrolytic etching were also developed. From the brightness characteristics, it was found that some of carbides, carbide solid solutions, and borides such as HfC, ZrC (Ta0.8-0.7Hf0.2-0.3)C, TaB2, and HfB2 are very good emitters comparable to LaB6. It is emphasized that the work functions of the carbide-solid solutions (Ta0.8Hf0.2)C and (Ta0.7Hf0.3)C, which have low rates of evaporation at high temperature, show no remarkable rise as compared with that of HfC, so that their figures of merit are better than that of HfC. Feasibility of providing good cathodes with HfC and (Ta0.8Hf0.2)C tips was demonstrated by taking high-resolution electron micrographs.

Boranes↗
PubMed1987

Coexpression of distinct eye- and liver-specific LDH isozymes in cichlid fish.

In a recent electrophoretic survey of lactate dehydrogenase (LDH) in neotropical cichlid fishes (Perciformes, Cichlidae) we have discovered several species in which a cathodal liver-specific isozyme is expressed along with the highly-anodal eye-specific isozyme (LDH-C4) typically encountered in perciform fishes. We believe this fourth, liver-specific LDH isozyme to be real and not artifactual since homogenization of fresh liver from one of these species, the Basketmouth cichlid (Acaronia nassa), in either of two nondenaturing detergents or in the presence of the protease inhibitor phenylmethylsulfonylfluoride affects neither the presence nor mobility of this cathodal band. Moreover, it continues to be expressed in the captively bred F1 of these same wild fish. The discovery of several fish species, like the Basketmouth, in which biochemically distinct eye- and liver-specific LDH isozymes are coexpressed, is discussed in light of the currently accepted hypothesis that these two isozymes are encoded by a single locus (LDH-C) which has undergone divergent tissue expression in several other major teleost groups. Preliminary characterization of the liver-specific isozyme relative to the eye-specific LDH-C4 in the Basketmouth cichlid with respect to thermolability and NADH-induced binding to oxamate-sepharose columns suggests that the eye- and liver-specific LDH isozymes are biochemically quite distinct in this fish and that they are probably encoded by two distinct loci.

Animals↗
PubMed1985

Temporal course of bone formation in response to constant direct current stimulation.

Reactive, post-traumatic bone formation in response to intramedullary insertion of a polytetrafluorethylene-coated, 28 gauge stainless steel wire was compared with the sequential bone formation seen in response to an identical intramedullary stainless steel cathode delivering 20 microA constant direct current. Animals were studied at days 1, 2, 3, 4, 5, 7, 9, 11, 14, 17, and 21 after wire insertion. Point count analysis revealed progressive bone formation beginning as early as day 3 on the constant direct current-stimulated side, progressing steadily through day 21. Control tibia, however, began to show bone formation on day 5 with peaking at day 9 and subsequent bone resorption. The osteogenic response at the 20 microA cathode was statistically elevated above that seen at the control on days 11, 17, and 21.

Animals↗
PubMed1988

Changes in bioelectric potentials on bone associated with direct current stimulation of osteogenesis.

This study was designed to determine whether changes occur in the bioelectric potentials on bone during and after bone stimulation with a 20-microA direct current (DC) and whether the variations in bioelectric potentials are related to the variations in bone formation. The bioelectric potentials were recorded at different times on the rabbit distal tibial surface, during (current-on state) and after (current-off state) DC stimulation with a cathode implanted within the medullary canal. The new bone formed at the end of the experiment was quantitated and related to the bioelectric potentials recorded at current-on and current-off states, respectively. Direct current stimulation resulted in electronegative potential spike centered on the cathode tip while current was applied. After electrical stimulation was turned off, the residual potentials at the end of the experiment did not significantly differ from the initial values. Conversely, the time sequence of the changes was significantly different from the control to the experimental group. The variations in the induced potentials at current-on state were significantly related to the variations in bone formation. This study suggests the existence of a relationship among bioelectric potentials, DC stimulation, and osteogenesis.

Animals↗
PubMed2003

In vitro transdermal iontophoretic delivery of leuprolide-mechanisms under constant voltage application.

The transdermal iontophoretic delivery of Leuprolide, a nonapeptide LHRH agonist was studied with the aim of understanding the mechanisms of iontophoresis. Permeation studies were carried out at pH 4.5 and 7.2, at which the average ionic valence of the drug molecule was roughly 2 and 1, respectively. Heat-separated human epidermal membrane was subjected to constant voltage within the range of 250 to 1000 mV during the iontophoretic phase. Iontophoretic enhancement at pH 7.2 was greater than at 4.5. A model for iontophoretic enhancement was developed that takes into consideration the membrane alterations caused by iontophoresis depicted as increased porosity and the permeation through lipid pathways of the stratum corneum. Model-based evaluation yielded that first, the porosity increased with the applied voltage to as much as three times the original at 1000 mV. Second, the lipid pathways contributed approx. 20% to the total permeation during the passive phase. Third, the electro-osmotic flow contributed significantly to the enhancement and its direction was from anode to cathode at pH 7.2 and the opposite at pH 4.5. The magnitude of the electro-osmotic flow was at pH 4.5 somewhat lower than at pH 7.2. Addition of a negatively charged water soluble peptide, Acetyl leucine leucinolyl phosphate as an adjuvant led to twofold increase in the enhancement factor at pH 4.5 and a decrease in the magnitude of the electro-osmotic flow from cathode to anode. Repeated iontophoretic applications of 250 mV on the same skin specimen resulted in same enhancement every time and did not cause any barrier alterations when applied for 1 h every 24 h, which was not the case if the duration between the two iontophoretic applications was only 3 h.

Administration, Cutaneous↗
PubMed2006

Electromigration of ions across the skin: determination and prediction of transport numbers.

In iontophoresis, an electric field across the skin induces electromigration of exogenously applied and endogenously present ions. The approach can be used to improve dramatically drug delivery by elimination of competing co-ions in the externally applied formulation, as this maximizes the fraction of current carried by (i.e., the transport number of) the drug. In this study, the dependence of the transport number on the nature of the ions present at the anode and cathode was examined using 12 different combinations of ions (4 cations x 3 anions). Cationic transport numbers (t(C+) (o)) were a function of their inherent mobilities and depended upon those of the single anion at the cathode; however, t(C+) (o) was independent of the counter-ion concentration. The extensive data obtained agreed well, furthermore, with a theoretical framework previously developed for this so-called "single-ion" situation. In addition, there was a strong correlation between ionic transport numbers in the skin and those in aqueous solution, which are easily estimated from measurements of ionic mobility. It follows that it should be possible, from the framework developed here, to establish a predictive tool, combining theory with simple experiments, for the optimization of iontophoretic drug delivery.

Acetates↗
PubMed1978

Differential pulse polarographic determination of clorazepate monopotassium and dipotassium.

Polarographic investigation of clorazepate monopotassium and dipotassium showed two cathodic waves at about -1.28 and -1.66 v. The cathodic wave associated with clorazepate monopotassium or dipotassium at about -1.66 v was a pH-independent, diffusion-controlled wave. This wave was used to develop a specific stability-indicating procedure for clorazepate monopotassium and dipotassium in the presence of their degradation products, namely, nordiazepam, 2-amino-5-chlorobenzophenone, and glycine. The method involves a 10(-2) M LiOH-10(-1) M LiCl extraction of the active ingredient from the formulation, filtration, dilution with the same supporting electrolyte, and then use of the standard addition technique for drug quantitation in capsules. Typical fomulation excipients did not interfere with the analysis. Accuracy and precision of the procedure were 99.55 +/- 0.68%.

Anti-Anxiety Agents↗
PubMed1987

Characterization of the permselective properties of excised human skin during iontophoresis.

The iontophoretic and passive transport of [3H]mannitol, 22Na+, 36Cl-, and 45Ca++ across excised human cadaver skin was studied using diffusion cells. The anode (+) was placed in the side of the diffusion cell facing the epidermis and the cathode (-) was placed in the side facing the dermis, and current densities at 0, 0.078, 0.16, and 0.23 mA.cm-2 were investigated. The results showed that mannitol and Na+ were transported preferentially by anodal (+) iontophoresis, Cl- was transported by cathodal (-) iontophoresis, and all respective fluxes were approximately proportional to the applied current density. When the skin was present as a membrane barrier between the two diffusion cell chambers the voltage induced flux of Na+ was found to be higher than its free solution value, and that of Cl- was lower. Taken together these results suggest that the skin is a permselective membrane and exists with an "apparent" net negative charge at the free solution pH of 7.4. During iontophoresis this permselectivity leads to current-induced volume flow, which provides a primary mechanism for the transport for a polar uncharged molecule such as mannitol. When Ca++ is substituted for Na+ on the side of the diffusion cell facing the epidermis, the Cl- flux from the dermal side is enhanced with a portion of the remaining charge being carried by Ca++. The mannitol flux from the epidermal side was decreased under these conditions. This implies that Ca++ alters the anion/cation flux ratio in the excised tissue, possibly by binding to fixed negative charges in the membrane, with the result that the volume flow is decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Effects of argon laser irradiation on polar excitations in frog sciatic nerve.

BACKGROUND AND OBJECTIVES: Since the mechanisms underlying the effects of low-power laser irradiation on the nervous system remain unclear, we examined whether such irradiation can influence ionic channels of the nerve membrane using the law of polar excitation in isolated frog sciatic nerve. STUDY DESIGN/MATERIALS AND METHODS: Using 43 frogs (Xenopus laevis), nerve preparations were stimulated at 0.5/second using a 10-millisecond pulse at supramaximal intensity. Ar+ laser irradiation (457, 488, 514 nm; 50, 75, 100 mW) was applied for 30 minutes to the portion between the anode and cathode stimulating electrodes. RESULTS AND CONCLUSIONS: Ar+ laser irradiations (457, 488 nm; 50 mW) blocked the generation of anode-break-excitation, rather than cathode-make-excitation. Such a selective effect occurred when applying a blocker of hyperpolarization-activated cation current (Ih) channel, ZD7288. Ar+ laser irradiation may influence Na+ channels in addition to Ih channels.

Action Potentials↗
PubMed1990

A comparison of magnetic and electrical stimulation of spinal nerves.

The utility of the magnetic coil for stimulation of the cervical spinal nerves was compared to electrical stimulation by a monopolar needle cathode placed onto the spinal lamina in six volunteers. No statistical difference in average amplitudes or areas of evoked CMAPs was found although the size of the magnetic coil evoked potentials was less at C7-8 in several subjects. Electrical stimulation resulted in depolarization at a more proximal site. Electrical stimulation was associated with more discomfort, especially at C5-6. We conclude that electrical stimulation using a monopolar needle as the cathode is the superior technique for the clinical electrophysiologic study of the proximal brachial plexus and cervical spinal nerves.

Action Potentials↗
PubMed1995

Electric field-directed growth and branching of cultured frog nerves: effects of aminoglycosides and polycations.

The direction and rate of earliest nerve growth are critical determinants of neuronal architecture. One extrinsic cue that influences these parameters is a small direct current electric field, although the underlying mechanisms are unclear. We have studied the orientation, rate of growth, and branching behavior of embryonic Xenopus spinal neurites exposed to aminoglycoside antibiotics, to raised external cations, to applied direct current electric fields, and to combinations of these treatments. Field-induced cathodal turning and cathodal branching of neurites were blocked by the aminoglycosides, by raised extracellular calcium ([Ca2+]0) and by raised extracellular magnesium ([Mg2+]0). Neomycin together with high external Ca2+, by contrast, induced a reversal in the polarity of turning and branching, with neurites reorienting and branching more frequently anodally. Aminoglycosides decreased neurite growth rates, and for neomycin this was partially reversed by high external Ca2+. Raised [Ca2+]0 alone but not raised [Mg2+]0 altered growth rates in a field-strength dependent manner. Modulation of membrane surface charge may underlie altered galvanotropic orientation and branching. Such an effect is insufficient to explain the changes in growth rates, which may result from additional perturbations to Ca2+ influx and inositol phospholipid metabolism.

Animals↗
PubMed2003

Combined infrared multiphoton dissociation and electron capture dissociation with a hollow electron beam in Fourier transform ion cyclotron resonance mass spectrometry.

An electron injection system based on an indirectly heated ring-shaped dispenser cathode has been developed and installed in a 7 Tesla Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. This new hardware design allows high-rate electron capture dissociation (ECD) to be carried out by a hollow electron beam coaxial with the ion cyclotron resonance (ICR) trap. Infrared multiphoton dissociation (IRMPD) can also be performed with an on-axis IR-laser beam passing through a hole at the centre of the dispenser cathode. Electron and photon irradiation times of the order of 100 ms are required for efficient ECD and IRMPD, respectively. As ECD and IRMPD generate fragments of different types (mostly c, z and b, y, respectively), complementary structural information that improves the characterization of peptides and proteins by FTICR mass spectrometry can be obtained. The developed technique enables the consecutive or simultaneous use of the ECD and IRMPD methods within a single FTICR experimental sequence and on the same ensemble of trapped ions in multistage tandem (MS/MS/MS or MS(n)) mass spectrometry. Flexible changing between ECD and IRMPD should present advantages for the analysis of protein digests separated by liquid chromatography prior to FTICRMS. Furthermore, ion activation by either electron or laser irradiation prior to, as well as after, dissociation by IRMPD or ECD increases the efficiency of ion fragmentation, including the w-type fragment ion formation, and improves sequencing of peptides with multiple disulfide bridges. The developed instrumental configuration is essential for combined ECD and IRMPD on FTICR mass spectrometers with limited access into the ICR trap.

Animals↗
PubMed2003

Nonaqueous magnesium electrochemistry and its application in secondary batteries.

A revolution in modern electronics has led to the miniaturization and evolution of many portable devices, such as cellular telephones and laptop computers, since the 1980s. This has led to an increasing demand for new and compatible energy storage technologies. Furthermore, a growing awareness of pollution issues has provided a strong impetus for the science and technology community to develop alternatives with ever-higher energy densities, with the ultimate goal of being able to propel electric vehicles. Magnesium's thermodynamic properties make this metal a natural candidate for utilization as an anode in high-energy-density, rechargeable battery systems. We report herein on the results of extensive studies on magnesium anodes and magnesium insertion electrodes in nonaqueous electrolyte solutions. Novel, rechargeable nonaqueous magnesium battery systems were developed based on the research. This work had two major challenges: one was to develop electrolyte solutions with especially high anodic stability in which magnesium anodes can function at a high level of cycling efficiency; the other was to develop a cathode that can reversibly intercalate Mg ions in these electrolyte systems. The new magnesium batteries consist of Mg metal anodes, an electrolyte with a general structure of Mg(AlX(3-n)R(n)R')(2) (R',R = alkyl groups, X = halide) in ethereal solutions (e.g., tetrahydrofuran, polyethers of the "glyme" family), and Chevrel phases of MgMo(3)S(4) stoichiometry as highly reversible cathodes. With their practical energy density expected to be >60 Wh/Kg, the battery systems can be cycled thousands of times with almost no capacity fading. The batteries are an environmentally friendly alternative to lead-acid and nickel-cadmium batteries and are composed of abundant, inexpensive, and nonpoisonous materials. The batteries are expected to provide superior results in large devices that require high-energy density, high cycle life, a high degree of safety, and low-cost components. Further developments in this field are in active progress.

Journal Article↗
PubMed1995

Effect of separation conditions on automated isoelectric focusing of carbohydrate-deficient transferrin and other human isotransferrins using the PhastSystem.

To investigate the effect of automated isoelectric focusing conditions in the PhastSystem, e.g., the point of sample application, prerun and separation times, and minimized gels on isotransferrin band pattern, human sera were analyzed with native transferrin iron load, after iron saturation or iron depletion in vitro. Varying the focusing conditions we found (i) Point of sample application (anode, middle of the gel, cathode) strongly affected transferrin iron loss. It was greatest at the anode and least at the cathode. (ii) Without prerun, distinct transferrin iron loss also occurred. A short prerun time prevented iron loss, but increasing it did not improve transferrin iron load stability as stated by others. (iii) An inappropriately long separation time inevitably yielded iron loss. In conclusion, inappropriate isoelectric focusing conditions strongly affect iron load stability of isotransferrins (obviously via low pH within the gel), resulting in transferrin iron release and cofocusing of isotransferrins with different sialic acid or iron contents. For determination of carbohydrate-deficient transferrin, such conditions resulted in overestimation of the marker of chronic alcohol abuse. Our findings may be of guiding importance for isoelectric focusing of protein-ligand complexes. We recommend the procedure described for development of isoelectric focusing of protein-ligand complexes.

Carbohydrates↗
PubMed1994

Effect of carboxyterminal modification on the oligomeric structure of human beta hemoglobin.

A broad beta chain band region containing multiple components was observed with both native beta and Des(His-146, Tyr-145) beta chains following isoelectric focusing on agarose gels (pH 6.0-8.0). In contrast to the tetramer-monomer system of beta chains, a distinct separation of three components (tetramer, dimer and monomer) was seen for Des(His-146, Tyr-145) beta chains indicative of an oligomeric structural beta model with a stable dimer species. Protein dilution (500 to 15.6 microM in heme) amplified the more cathodic (presumably dimeric and monomeric) components of these chains, and titration with partner alpha chains resulted in a selective depletion of the monomer (most cathodic) component which could be quantitatively correlated with assembly of the hemoglobin tetramer.

Crystallography, X-Ray↗
PubMed1995

Calcium channel subtypes and intracellular calcium stores modulate electric field-stimulated and -oriented nerve growth.

In culture, embryonic spinal neurites from Xenopus laevis show striking growth responses to steady dc electric fields, at a time when endogenous electric fields of similar size impinge on the developing nervous system. A high proportion of cultured neurites reorient, with both turning and branching directed cathodally. Neurite growth rates are increased and growth is differential (faster cathodally than anodally). Voltage-dependent calcium channels and calcium release from intracellular stores are shown to control these events. However, the pharmacological sensitivities of these phenomena differ, indicating different control mechanisms.

Animals↗