Implant Surface Topographies Alter Human Platelet Cell Adhesion and Activation

Implant surface microtopography may influence initial platelet adhesion and activation (Eckdhal, 2002). Objectives: Titanium surfaces were incubated with platelets to characterize binding and activation as a function of implant surface topography. Methods: Grade II cpTi disks were prepared through 1µm diamond polish or 600grit polished and then Al₂O₃ (50µm) grit blasted or prepared by large grit blasting and acid etch (SLA). Disks were coated with fibrinogen (1mg/mL, 1hr at 37°C) rinsed with PBS, and blocked with BSA. Glass disks were used as a control. Human whole blood was drawn and platelets retrieved, inactivated with PGE1 and apyrase, and reconstituted in tyrodes buffer. Approximately 2.5x10⁷ platelets, in CaCl₂-thrombin media with FITC-conjugated a2b1 and PE-conjugated P-selectin antibodies, were applied to the surface of each disk. Platelet-coated disks were incubated with the antibodies for 25min at 37°C in the dark. After incubation, disks were fixed and rinsed with PBS. Surface-bound platelets (a2b1) and platelet activation (P-selectin) were measured with a microplate reader. SEM was also used to characterize binding. (adhesion: n=3-4/group; repeated 3x) (activation: n=3/group; repeated 1x). Results: Platelet adhesion was highest on the smooth 1µm polished surface and decreased with increasing roughness on the grit blasted and etched surfaces evaluated. Platelet adhesion was significantly greater on the 1µm polished surface (1.3 fold greater [p<0.05] than 600g machined surface) and 4.7 fold greater than grit blasted surfaces (p<0.001). Titanium surfaces with roughened topographies had similar platelet adhesion (p>0.05). P-selectin activation studies demonstrated greater activation on the rougher surfaces relative to the number of adherent platelets. Ratios of activation/adhesion were greater on roughened surfaces (3.1-6.2) and less on 600g machined titanium (1.5) and polished 1µm titanium (1.3). Conclusions: Rougher titanium surface topographies resulted in reduced adhesion but enhanced activation of adherent platelets. Supported by: ITI Foundation (#209/2001, #284/2003) and AADR fellowship.