Platelet adhesion to polyurethane urea under pulsatile flow conditions

Abstract

Platelet adhesion to a polyurethane urea surface is a precursor to thrombus formation within blood-contacting cardiovascular devices, and platelets have been found to adhere strongly to polyurethane surfaces below a shear rate of approximately 500 s(-1). The aim of the current work is to determine the properties of platelet adhesion to the polyurethane urea surface as a function of time-varying shear exposure. A rotating disk system was used to study the influence of steady and pulsatile flow conditions (e.g., cardiac inflow and sawtooth waveforms) for platelet adhesion to the biomaterial surface. All experiments were conducted with the same root mean square angular rotation velocity (29.63 rad/s) and waveform period. The disk was rotated in platelet-rich bovine plasma for 2 h, with adhesion quantified by confocal microscopy measurements of immunofluorescently labeled bovine platelets. Platelet adhesion under pulsating flow was found to decay exponentially with increasing shear rate. Adhesion levels were found to depend upon peak platelet flux and shear rate, regardless of rotational waveform. In combination with flow measurements, these results may be useful for predicting regions susceptible to thrombus formation within ventricular assist devices.

Keywords: Fluid dynamics; Platelet adhesion; Polyurethane; Pulsatile flow; Rotating disk; Shear stress.

Figure 1

A) Schematic representation of the RDS setup and the scribed metal mounting surface for the smooth PUU material. The disk is rotated by an applied voltage waveform from a function generator. Confocal images (0.011187 mm²) are taken at each radial intersection. Image modified from Milner et al. B) Angular velocity (rad/s) for experimental waveforms over the course of one 700 ms period.

Figure 2

Adhesion coefficient plotted versus shear rate calculated from peak angular velocity. The flux is also calculated based upon peak angular velocity.