| The effects of plasma proteins, biomaterial surface characteristics, and platelets on Staphylococcus epidermidis strain RP62A adhesion to biomedical polymers were studied using the rotating disk system. The rotating disk system generated well-defined shear conditions, simulating the hemodynamics of normal human circulation. Bacterial adhesion was quantified by the adhesive coefficient, defined as the percentage of bacteria transported to the surface that becomes adherent. Polymers studied include National Heart, Lung, and Blood Institute (NHLBI) reference polyethylene and polydimethylsiloxane, Silastic{dollar}spcircler,{dollar} expanded polytetrafluoroethylene, Dacron{dollar}spcircler,{dollar} and argon plasma treated polyethylene.; In comparing adhesion studies conducted in phosphate buffered saline (PBS) and 1% solution of plasma proteins in PBS, staphylococcal adhesion to all of the polymers studied were reduced by the presence of adsorbed plasma proteins. This reduction was statistically significant across the entire range of shear stress studied. Surface modification of polyethylene by argon plasma treatment also reduced bacterial adhesion relative to the untreated polymer. In the presence of adsorbed plasma proteins, argon plasma treated polyethylene had the lowest adhesive coefficients of all of the materials tested. The result is consistent with thermodynamic analysis of the bacterial adhesion process, i.e., increasing polymer surface tension would reduce staphylococcal adhesion.; The highest adhesive coefficients were recorded for woven Dacron graft material. The surface topography of this biomaterial created turbulence under flow, resulting increased bacterial flux to the surface. Furthermore, significant number of bacteria were "adherent" via physical entrapment in the interstices of the fibers. For cases such as this, physical forces dominate and even overwhelm the thermodynamics of the adhesion process. In the same light, increasing shear stress reduces the number of adherent bacteria. However, even with argon plasma treatment polyethylene and adsorbed plasma proteins, the highest normal physiologic shear stress cannot detach all of the adherent bacteria.; In studying Staphylococcus epidermidis adhesion to polyethylene with heparin anticoagulated platelet-rich plasma, it was observed that surface-activated platelets, occupying only 4% of the disk surface, mediated the adhesion of 50% of the adherent bacteria. Repeating this study using sodium citrate as the anticoagulant, Staphylococcus epidermidis did not exhibit preferential adhesion to contact-activated platelets on the polymer surface. This suggests a calcium-mediated staphylococcal adhesion to platelets. The reduction of bacterial adhesion by adsorbed plasma proteins was unaffected by the choice of anticoagulant.; Thus our studies demonstrate that (1) increasing polymer surface tension by biologic or artificial surface modification effect a lower bacterial adhesion; (2) hemodynamic shear conditions in conjunction with surface topography may create physical forces that dominate the adhesion process; and (3) platelets are potent mediators of staphylococcal adhesion to biomaterial surface and this mechanism may be a calcium-dependent process. |
