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Biomedical subjects

P E Donaldson

Publications and source records attributed to P E Donaldson.

At least 19 recordsLinked to original sources
PubMed1995

Aspects of silicone rubber as encapsulant for neurological prostheses. Part 2: Adhesion to binary oxides.

The paper presents some measurements of the hydrothermal stability of experimental adhesive joints in water at 100 degrees C. The joints are between one adhesive silicone rubber and ten metal or metal-oxide adherends, all combinations of interest to the neurological prosthesis maker. The probable adhesion mechanism is then considered, in the search for some parameter by which the experimental results could have been predicted. Evidence is produced that physical adsorption plays little or no part in the adhesion, but that hydrothermal stability seems to be a function of the adherend ionic charge. In pursuit of this idea, the valency, the Slater potential and the iso-electric point for the surface (IEPS) of the adherend are examined as possible prediction parameters. It is concluded that, at least in neutral and acidified water, the IEPS is a promising predictor, with the benefit that it is experimentally determinable for adherends of unknown composition. The most stable joints seem to occur when the charge density on the adherend has an optimum negative value.

Adhesiveness↗
PubMed1991

Aspects of silicone rubber as an encapsulant for neurological prostheses. Part 1. Osmosis.

Silicone rubber is not, at first sight, a promising material with which to encapsulate a piece of implantable microelectronics expected to last ten or twenty years. It is well known to be very permeable to water. In fact, if correctly applied, it performs very well for ten years, possibly longer. The paper considers the part played by osmosis in achieving satisfactory performance combined with simple technology.

Biomedical Engineering↗
PubMed1987

Power for neurological prostheses: a simple inductive R.F. link with improved performance.

A variety of methods has been used or proposed to stabilize the amplitude of signals received by implanted neurological prostheses from external equipment via R.F. inductive links of uncertain geometry. These include: use of Zener diodes, operation at critical coupling, operation inside a Helmholz pair, recoding amplitude data into time intervals or pulse trains and automatic adjustment of transmitter power to compensate for fluctuations in coupling coefficient. Rather surprisingly, a pair of inductively-coupled series-resonant circuits is inherently insensitive to variations in coupling coefficient over a wide range (e.g. 0.03-1.0) if the transmitter coil is part of a self-oscillator. Exploitation of this insensitivity may, in some applications, render the use of special amplitude-fixing strategems unnecessary.

Biomedical Engineering↗
PubMed1987

Twenty years of neurological prosthesis-making.

The UK Medical Research Council's Neurological Prosthesis Unit was formed on 1 October 1968. In this review, Peter Donaldson, who has been with the unit from the beginning, reflects on what seem to him to be the most important contributions to implant technology from the unit, and suggests some possible developments for the future.

Extremities↗
PubMed1986

Polychrest: a development system for radio-frequency-coupled implants.

Inductively-coupled neurological prosthetic implants may employ RF coils of unusual design (for example 'square' spiral inductors printed in thick-film ink on both sides of the alumina substrate) for which published empirical design equations are hard or impossible to find. 'Polychrest' enables the rapid experimental generation of ad hoc design data for RF-coupled energy-transfer systems, leading quickly to a working model which can be thoroughly studied and understood.

Energy Transfer↗