Biomaterial-dependent neutrophil mobility and phagocytosis of bacteria in the mechanism of cardiovascular implant infection

Infection is a potentially serious complication and a major impediment to the long-term clinical success of implanted cardiovascular devices. This thesis examined the hypothesis that foreign-body biomaterials and surface-associated host proteins cause attenuations in neutrophil mobility and phagocytosis that increase the probability for cardiovascular implant-related infection. Reduced neutrophil mobility and phagocytosis may prevent access and effective killing of bacteria, giving the bacteria sufficient opportunity to produce a biofilm.; To address the hypothesis, microscopic methods were used to provide quantitative comparisons of neutrophil mobility and phagocytic function on materials with different surface properties.; To test human neutrophil mobility, three materials were selected. These materials include a clinically relevant polyurethane (Chronoflex AR), a hydrophobic model surface consisting of an octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM), and a glass reference material. Surface dependent neutrophil mobility was evaluated by time-lapse optical microscopy, confocal microscopy and atomic force microscopy (AFM). Our results show that material surface properties and surface adsorbed proteins are important in neutrophil mobility induced by N-formylmethionyl-leucyl-phenylalanine (fMLP) stimulation. Without plasma protein adsorption, neutrophil mobility increased with increasing material surface hydrophobicity from glass, to polyurethane to OTS. With plasma protein adsorption, neutrophil mobility decreased with increasing material surface hydrophobicity from glass, Polyurethane to OTS surfaces. The decrease in neutrophil mobility under stimulation was directly related to increased cell spreading on the material substrates.; Neutrophil phagocytosis of Staphylococcus epidermidis on the three materials was recorded using time-lapse optical microscopy and compared based on the rate of bacteria ingestion. The morphology of adherent neutrophils was analyzed by fluorescence confocal microscopy. Our results show that on the materials without adsorbed plasma protein, neutrophil phagocytic ability increases from hydrophilic glass to hydrophobic OTS. In the presence of adsorbed plasma protein, neutrophil phagocytic ability increased on all the three materials, but was highest on the polyurethane. The results suggest that material surface properties and the surface adsorbed plasma proteins significantly affect phagocytic ability of surface adherent neutrophils.; The results from this thesis may be of value in designing biomaterials surface that improve bactericidal function of neutrophil and reduce implant-associated infection.