John C. Woodard

A novel textured surface for blood-contact

Blood-contacting surface modifications aimed at reduction of thromboembolic complications have included the texturing of surfaces so as to promote the formation of a stable pseudo-neointima. A technique has been developed whereby a textured surface consisting of regularly spaced micro-fibres was produced on a smooth base plane. Polyurethane vascular patches with and without the textured luminal surface were fabricated and implanted bilaterally in ovine carotid arteries for 1- and 3-week implantation periods (n = 6 per period). One of 6 arteries with textured patches in the 1-week group was occluded. All other arteries were patent. At 1 week, all patent textured patches had adherent thrombus covering the entire patch surface. By 3 weeks, the thrombus had organised to form a stable pseudo-neointima. Non-textured patches at 1 week had only partial surface coverage of thrombus. At 3 weeks, 4 of 6 non-textured patches had significant red thrombus in the lumen. At 3 weeks, there was also evidence of cellular migration from artery onto both textured and non-textured patches. These findings suggest that the major role of the textured surface was as a promoter of a stabilised thrombus base onto which subsequent cellular migration and tissue healing occurred more rapidly than onto a smooth polyurethane surface.

Effect of radial position on volume measurements using the conductance catheter

A finite-difference computer model has been used to determine the potential distributions arising from a dipole current source aligned parallel to the axis of bounding cylinders. The radial position of this source had large and nonlinear influence on the potentials along the dipole axis. The accuracy of the computer simulation was established from comparison with an analytic solution of a simple geometry. Measurements using a conductance catheter in saline-filled cylinders also demonstrated the dependence of the conductance on the radial position. The dependence of the potential distribution on the radial position of the dipole places limits on the ultimate accuracy of the conductance catheter technique when used for the measurement of ventricular volume. Radial movement of the catheter within the ventricular cavity, resulting in changes in the potential distribution, could explain some artefacts that appear on volume recordings from the conductance catheter.

Detecting Right Ventricular Volume Changes Using the Conductance Catheter

The purpose of this study was to assess the role of conductance catheter position within the right ventricle in obtaining adequate indications of phasic changes in ventricular volume. Possible applications of this lechnology are in rate responsive pacemakers and implantable defibrillators. The conductance catheter was placed in the right ventricle by cannulation of a jugular or femoral vein or a branch of the pulmonary artery. Position within the ventride was documented from biplane fluoroscopy. Stroke volume was perturbed by: bolus injection of blood, vagal stimulation, venous infusion of methylcholine chloride, or isoprenaline. Four criteria were used to assess the quality of volume signals: (1) volume signal phase relative to the electrocardiogram; (2) magnitude parity of volume change from each electrode pair; (3) freedom from artifact; and (4) indication of stroke volume change during interventions. Greyhound dogs of either sex (n = 33), weight 20–32 kg. A total of 236 recordings from 14 distinct catheter positions were analyzed. Catheter positions originating from a femoral cannulation and one position from the pulmonary artery gave markedly superior volume transduction compared to those from the jugular route. Although right ventricular volume transduction was possible from all catheter trajectories, those resulting from the femoral approach were clearly superior. In the right ventricle, the inability to transduce a sufficient proportion of ventricular volume, in concert with the potential sensitivity of the catheter to atrial volume changes, may seriously limit the potential of the conductance technique in the applications envisaged.

Right ventricular volumetry by catheter measurement of conductance.

The electrical conductivity of blood is sufficiently higher than that of myocardium to make feasible the detection of cardiac volume changes hy measurement of intraventricuiar fluid conductance. An eight‐electrode catheter was used to inject an aiternating current (100 μA or less, at 1500 Hz) via the two electrodes nearest the ventricular base and apex, then the resulting five voltage differences between adjacent pairs of the six intervening electrodes were measured. When current amplitude was held constant, the cross‐sectional area of the ventricuiar cavity slice defined hy planes perpendicular to the catheter through the relevant pair of electrodes was inversely proportional (to the first order) to the voltage difference. Measurement of multiple segments compensated for isovolumic cavity shape changes. The technique had previously been shown to measure left ventricular volume successfully, but the geometry of the right ventricle made this measurement more problematical. Using open‐chested, anesthetized greyhounds, we compared the catheter‐measured right ventricuiar volume change with stroke volume as measured by a pulmonary arterial electromagnetic blood flowmeter. With optimal catheter placement, good correlation between stroke volume and catheter‐measured volume changes was achieved when stroke volume was perturbed on a heat‐to‐heat hasis. In six data records from three dogs, involving two different means of varying stroke volume (rapid injection of blood and sinus node irritation), the correlations yielded r2 values between 0.82 and 0.98. The method detected ineffective (nonejecting) beats associated with normal‐appearing QRS complexes and was thus a more reliable indicator of cardiac mechanical function than an eiectrocardiogram.

Multilayered carbon films for tribological applications

Recent work has shown that for nano-layered structures consisting of two materials, an effect may be shown in which the elastic modulus and fracture toughness depend on the period of the structure. In this paper we create carbon multilayer structures by two methods using cathodic arc deposition with pulsed bias applied to the substrate. The multilayers are created in one class of structures simply by interrupting the deposition to form relaxed layers. In the other class of structures, the pulse bias conditions are varied periodically. The in-service performance of the structures is assessed by impact-enhanced pin-on-disc wear testing and indentation hardness. The structures are examined using bright field and dark field transmission electron microscopy. A 10 nm non-convergent electron probe was used for the micro-diffraction studies. A model for the structure of the interfaces between the relaxed layers and the as-deposited material, including evidence of preferred orientation is presented.

Carbon coating of Ti-6Al-4V for reduced wear in combined impact and sliding applications

Abstract A range of carbon coatings with different hardness and modulus was compared for wear and frictional behaviours using one-side-carbon-coated Ti-6Al-4V alloy couples tested under conditions of combined impact and sliding contact. Carbon films with hardness over 10 GPa were found to cause far greater volume loss of the uncoated counterpart, and the volume loss was approximately proportional to the extent of hardness deviation above 10 GPa. The coefficient of friction was shown to correlate positively with coating hardness. The tendency of a softer coating to possess a greater sp2 or graphite-like content provides more effective solid lubrication in a wet environment, hence minimising both wear and friction. The corresponding low film modulus also provides an optimal structural integrity of the composite system by minimising the elastic modulus mismatch between the film and the underlying substrate.

Acute cellular interaction with textured surfaces in blood contact

Textured blood-contacting surfaces can promote the formation of a blood-compatible pseudo-neointima. We hypothesized that by controlling the surface texturing, the pseudo-neointima thickness could be controlled. The hypothesis was tested experimentally by fabricating the polyurethane textured surfaces with three different fiber lengths, and exposing them simultaneously to the flowing blood in an ovine ex vivo carotid-jugular series shunt for periods up to 4 h. The textured surface consisted of regularly spaced tapered micro-fibers of defined length on a smooth base-plane surface. Because of the simple surface topography, detailed computational fluid-dynamic modeling of the surface could be obtained as a parallel study. Experimental results showed that white cell was the predominant cell type deposited on the textured surfaces, whereas macroscopic thrombus formation occurred only in one of nine blood-contacting experiments. White cell density on the textured base-plane surface was subsequently quantified by image-analyzing the electron micrographs of blood-contacted textured surfaces. The statistical analysis of cell densities on individual textured surfaces showed effects of wall shear stress on the textured base plane (which was obtained from the fluid-dynamic modeling), the longitudinal position of the test section in the series shunt, and blood-contact time.

A novel pin-on-apparatus

A novel pin-on-disk apparatus was developed that provides a repetitive impact loading between periods of sliding through alternate lifting and dropping of a spring-suspended spinning disk, away from, and onto, a spring-supported pin, respectively. The combination of the repetitive impact loading and sliding achieved in the apparatus was able to induce film adhesion failure of a thin film coated disk within 20 min, which, in the absence of the impact loading, would have survived the test due to the adequate sliding wear resistance. The impact/sliding pin-on-disk apparatus developed is therefore a useful means of predicting the sliding wear resistance and film adhesion of a coated system simultaneously.

Fluid Dynamics of a Textured Blood-Contacting Surface

This study examined the fluid dynamics of a textured blood-contacting surface using a computational fluid-dynamic modeling technique. The texture consisted of a regular array of microfibers of length 50 or 100 microm, spaced 100 microm apart, projecting perpendicularly to the surface. The results showed that the surface texture served as a flow-retarding solid boundary for a laminar viscous flow, resulting in a lowered wall shear stress on the hase-plane surface. However, the maximum wall shear stress on the fibers was much higher than the shear stress on the nontextured phase plane. At all fractions of fiber height down past 10 microm, the permeability of the textured region greatly exceeded the analytically predictable permeability of an equivalent array of infinite-height fihers. The lowered suiface shear stress appears to explain in part the enhanced deposition of formed blood elements on the textured surface.

Erratum to “A novel pin-on-disk apparatus” [Wear 254 (2003) 111–119]

Erratum to “A novel pin-on-disk apparatus” [Wear 254 (2003) 111–119] Naoki Fujisawa a,∗, Natalie L. James b, Richard N. Tarrant c, David R. McKenzie c, John C. Woodard b, Michael V. Swain a,1 a Biomaterials Science Research Unit, Faculties of Dentistry and Engineering, University of Sydney, Suite G11, National Innovation Centre, Australian Technology Park, Eveleigh, NSW 1430, Australia b VentrAssist Division, Ventracor Limited, 126 Greville Street, Chatswood, NSW 2067, Australia c Department of Applied and Plasma Physics, School of Physics, University of Sydney, Sydney, NSW 2006, Australia