Richard B. Beard

Biocompatibility considerations at stimulating electrode interfaces

The choice of biocompatible stimulating electrodes for various biomedical applications varies with the type of electrode-tissue interface, biomolecules present, electrolyte background, preparation of electrode, interfacial potential, current density, electrode material, porosity, geometry, and inflammatory response. Illustrative examples are given to demonstrate the importance of these parameters. Topics discussed are: A) DC electrodes applied to partially keratinized epithelial membranes; B) Variation of the electrical impedance and biocompatibility of stimulating electrodes with electrode potential and surrounding pH; C) Influence of electrode geometry, porosity and pore size on biocompatibility; D) Body defense mechanisms at the sites of implantable stimulating electrodes; E) Thrombus formation at stimulating electrode interfaces and F) Sterilization of electrodes to ensure biocompatibility.

Linear AC Electrode Polarization Impedance at Smooth Noble Metal Interfaces

The linear A. C. electrode polarization impedance of polished platinum has been analyzed on the basis of the rate determining mechanism of the oxygen electrode. The impedance has been found to follow the frequency dependence predicted by an adsorption of the electroactive species. The effects of D. C. potential and specific adsorption of anions have been studied and their effect on the electrode polarization impedance is in agreement with the adsorption mechanism.

Dielectric relaxation of the micelle forming anionic paraffin chain salt sodium dodecyl sulfate

Abstract Dielectric measurements on a micelle-forming material such as an ionic paraffin chain salt, sodium dodecyl sulfate, SDS, illustrate that there is a dielectric dispersion above the critical micelle concentration, CMC. The dielectric increment varies linearly with the SDS concentration while the relaxation time for the dispersion remains relatively constant over a wide range of concentration. The dispersion is attributed to a shell of bound water around the hydrocarbon core of the micelle. The large constant dielectric decrement produces for the assumed inhomogeneous models a large amount of bound water.

Development of antimicrobial and antithrombogenic coatings for inside and outside of medical catheters

Abstract Catheter-related infections are costly problems for hospitals around the world. Protection of the body against infection involves not only the immune system, but also the integrity of the external skin and internal mucosal surface. Catheters, introduced from the outside into the interior of the body, breach this important defense and lay the patient open to the risk of infection. It is believed that the surface characteristics of the polymers used in todays catheters are, to a large degree, responsible for this. In particular, the surface roughness, the hydrophobic nature of the surface and the ability of certain types of common bacteria to attach to and metabolize on the polymers are at fault. Interestingly, prior to the 1950s, when venous access required the use of rigid stainless steel needles, catheter infection was a minor problem. This has led us to develop various metal coatings (e.g. Ag, Pt, etc.) both for inside and outside of even the smallest catheter of 1 mm in diameter. Electroless deposition has been used for silver coating of both inside and outside of catheters, while hollow cathode magnetron and vacuum arc deposition have been used for outside coating. High-quality adherent metallic films have been deposited on Teflon, polyimide and latex substrates. Both biological and animal tests have shown the excellent antimicrobial and good mechanical durability of these films. The fabrication processes, results of thin film characterizations and investigations of antimicrobial effects are discussed. The biocompatibility of the chosen metals is also addressed.

Fabrication and Evaluation of Cathode and Anode Materials for Implantable Hybrid Cells

The power output of flexible zinc and aluminum anodes in a plastic binder compared favorably with that of pure metals used in previous implantable hybrid cells. Cathodes of platinum and palladium black in a polyvinyl chloride binder compared well with cathodes of platinum black in teflon. In-vivo and in-vitro measurements on palladium black cathodes with a polyvinyl chloride binder indicate that they perform better than the platinum black cathodes using plastic binders. A spreading resistance measurement correlated with the catalytic activity of the cathode. Modified galvanostatic and spreading resistance measurements were used in in-vitro studies to evaluate the fabricated cathodes.

Porous Cathodes for Implantable Hybrid Cells

The in vivo power output of implantable power sources using porous platinum- or palladium-black cathodes is approximately four to five times greater than ones using commercially available cathodes of platinum black dispersed in Teflon. Porous electrodes produce a much lower foreign-body reaction than electrodes with plastic binders. Comparison of BET surface-area measurements for the powders and compacted electrodes illustrate that there is an approximate 20-percent decrease in surface area following compaction. The particle size, distribution, and shape of the powders were studied with the aid of scanning electromicrographs. In vitro galvanostatic measurements were made on the implantable power sources to study the electrochemical activity before implantation.

Dielectric response of human melanoma cells on the surface of polymeric chemoattractants

The influences of dielectric properties on the malignant cell adhesion and migration have been investigated. The Wistar Melanomas, primary (WM793) and metastatic (WM1205), respectively, were chosen as the model cell lines because of their pleomorphic and invasive characteristics, and the dielectric relaxation frequencies of the cells were determined using the impedance spectroscopy. Both WM793 and WM1205 showed the enhanced adhesion and the interesting changes in their morphology under the dielectric stimulations. However, it was found that the changed conditions of cell adhesion due to dielectric relaxation did not influence the migrational behavior of the cells.

Polarization and Corrosion Studies of Porous and Solid Anodes for Implantable Power-Generating Electrodes

An implantable power source for driving a pacemaker consisting of a hybrid cell utilizing a sacrificial porous aluminum anode and a catalytic cathode for reducing oxygen is considered. Porous aluminum anodes show a significant improvement in polarization over a solid aluminum anode under in vitro transient operating conditions found with certain types of pacemakers. However, the in vivo transient behavior of porous aluminum anodes is only slightly better than solid aluminum anodes. Using in vivo and in vitro linear polarization studies, the corrosion of solid aluminum has been determined to be more than an order of magnitude less than that of solid zinc. The weight loss of aluminum due to corrosion is less than 3.0 percent that of the aluminum needed to supply the faradaic current to the pacemaker. A hybrid cell consisting of an aluminum anode and a porous palladium-black cathode has powered a commercially available pacemaker. Further histopathologic evaluation of tissues surrounding anodes is needed before selecting either zinc or aluminum as an anode material.

Corrosion and Histopathological Studies on Anode Materials for Implantable Power Sources

The biocompatibility and corrosion resistance of various materials for use as sacrificial anodes in in vivo hybrid fuel cells were studied. Aluminium, zinc, and magnesium alloy AZ31B were studied, and the results are discussed.

Comparison of photonic and electromagnetic effects on the human leukocyte

The dielectric and magnetic influence on human cells have been widely studied previously by the authors. Recently, the effects of energy in the visible electromagnetic spectrum have been investigated. In this subsequent study, the photonic effects on the in vitro migration of the polymorphonuclear and mononuclear leukocytes are compared with the corresponding electromagnetic field effects. Dielectric spectra of the polymorph in the 300 KHz to 400 KHz and 700 KHz to 800 KHz range have been measured. At frequencies of 350 KHz and 720 KHz an increase in the migration of the polymorphonuclear leukocyte have been observed. This stimulation was attributed to the charges on the nuclear surface. Recent preliminary data have shown a similar increased migration in the 20 MHz range. Photonic studies have indicated an enhanced migration for the polymorphonuclear leukocytes at a wavelength of 660 nm (red) and an inhibited migration at 565 nm (green). The photonic effects were postulated to be the results of a biochemical interaction rather than a membranous surface charge displacement secondary to an electric field. The migration of the white blood cells were measurement via the Boyden chamber technique and expressed in terms of a cytokinetic index which expresses the cellular movement independent of its environmental concentration gradient.