Effect of crystalline phase changes in titania (TiO2) nanotube coatings on platelet adhesion and activation

Objective: To explore the relationship between various crystalline phases of titania (TiO2) nanotube (TNT) coatings and platelet adhesion and activation. Methods: TNT coatings were fabricated on pure titanium foils by anodization and then randomly divided into four groups. Three groups were annealed at 350 degrees C, 450 degrees C and 550 degrees C in order to obtain different crystalline phases. The remaining group was not annealed and served as the control group. X-ray diffraction (XRD) was used to define the crystalline phases of different groups. Surface morphology, elemental composition, surface roughness, and contact angles were measured by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), laser scanning confocal microscopy (LSCM) and contact angle analysis, respectively. Platelets were cultured on the TNT coatings for 30 min and 60 min to assess the number, viability, distribution, and morphology of the adhered platelets. CD62P fluorescence expression and the amount of released platelet derived growth factor (PDGF) were detected to evaluate platelet activation. Results: The un-annealed TNT coatings were amorphous and part of TNT converted to anatase after the 350 degrees C annealing treatment. The quantity of anatase increased upon annealing at 450 degrees C and transformed to rutile at 550 degrees C. Nanotubes of all four groups maintained a well-ordered structure, but the wall thickness of the nanotubes increased from (11.874 +/- 1.660) nm for the un-annealed TNTs to (26.126 +/- 2.130) rim for the 550 degrees C annealed TNTs. The surface roughness of the 550 degrees C annealed TNT coatings was the lowest and the water contact angle was the largest at (28.117 +/- 1.182). The number and viability of adhered platelets after 30 min and 60 min were the highest on TNT coatings annealed at 450 degrees C. LSCM and SEM images revealed that the platelets that adhered on the 450 degrees C annealed TNT coatings aggregated, transformed, and spread most obviously. CD62P fluorescence expression results showed that the platelets on the 350 degrees C and 450 degrees C annealed TNT coating groups expressed the strongest fluorescence, followed by platelets on the 550 degrees C annealed group and the un-annealed group. The quantity of released PDGF was highest for the 450 degrees C annealed group at (4719 +/- 86) pg/mL, and lowest for the un-annealed group at (4241 +/- 74) pg/mL. Conclusion: Crystalline TNT coatings encourage improved platelet adhesion and activation over amprphous analogues. The TNT coatings annealed at 450 degrees C resulted in the most improved platelet behavior. The TNT crystalline phase was the predominant influencing factor in platelet adhesion and activation.