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.

Ultrasound pulse-echo reflection from test object cylindrical reflectors.

This paper is a first attempt at answering the question of which strong reflectors are most useful in ultrasound test objects. A planar reflector placed in the transducer far field has demonstrated potential as a standard reference reflector for pulse-echo ultrasound studies. Measurements of echo temporal voltage waveform and frequency spectrum from various metallic and plastic cylindrical reflectors were performed and compared to the results obtained with the planar reflector. Relatively undistorted echos were obtained from metallic cylinders when the condition lambda > 3D was obeyed, as well as large attenuating plastic cylinders when the condition lambda << D was obeyed. Consideration of these results along with mechanical and corrosion data leads to the identification of thin stainless steel type 302, nickel and molybdenum wires, as well as thick Oilon Pv 80 rods as potentially good reflectors for ultrasound test objects. The observed mechanical resonant frequencies of metallic cylinders has been shown to be potentially useful as a temperature-independent frequency standard in suitably designed test objects. The potential use of thin Teflon cylinders for transducer axial resolution measurement has been demonstrated.