Shear stress effects on bacterial adhesion, leukocyte adhesion, and leukocyte oxidative capacity on a polyetherurethane.

Infection of implanted cardiovascular biomaterials still occurs despite inherent host defense mechanisms. Using a rotating disk system, we investigated Staphylococcus epidermidis and polymorphonuclear leukocyte (PMN) adhesion to a polyetherurethane urea (PEUU-A') under shear stress (0-17.5 dynes/cm2) for time periods up to 6 h. In addition, the superoxide (SO) release capacity of PMNs after transient exposure to PEUU-A' under shear stress was determined. Bacterial adhesion in phosphate-buffered saline (PBS) showed a linear shear dependence, decreasing with increasing shear stress. Overall adhesion in PBS decreased with time. However, bacterial adhesion in 25% human serum was similar for all time points up to 360 min. Adhesion was observed at all shear levels, displaying no shear dependence. In contrast, PMN adhesion demonstrated a strong shear dependence similarly for times up to 240 min, decreasing sharply with increasing shear stress. Although PMNs preexposed to shear stress showed a slightly diminished SO release response compared to fresh cells for all stimuli, it was not statistically significant regardless of the stimulus. We conclude that circulating leukocytes are unable to adhere in regions of high shear which may contain adherent bacteria. In addition, exposure to PEUU-A' and shear stress (in the range 0-18 dynes/cm2) is insufficient to cause a depression in the oxidative response of PMNs.