Surface topography modulates initial platelet adhesion to titanium substrata

Abstract

The clinical success of implanted biomaterials such as dental implants is largely determined by the molecular signaling that occurs at the tissue-implant interface. The modification of surface topography is a widely-employed strategy for optimizing tissue integration with dental implants. However, little is known regarding the direct, cellular-level effects of substratum topography on platelet signaling and adhesion, despite these cells being the first to encounter the implant surface during surgical placement. Here we compared platelet adhesion and secretion on four (4) different titanium surfaces, notably, the modifications applied to commercially available dental implants: smooth (S) titanium; acid-etched (AE), sandblasted (SB) and a combined acid-etching/sandblasting procedure (SLA). Platelets were isolated from human blood, washed, and seeded on to the 4 test surfaces; platelet adhesion was quantified by microscopy. In addition, the secretion of critical molecules stored in platelet granules (platelet factor 4, PF4; soluble P-selectin, sCD62P; transforming growth factor-beta1, TGF-β1; platelet-derived growth factor-AB, PDGF-AB) was measured by enzyme-linked immunosorbent assay (ELISA) analysis of the supernatants. There was greater platelet adhesion to the rougher AE and SB surfaces, however, the concentration of the secreted growth factors was comparable on all surfaces. We conclude that while surface topography can be engineered to modulate initial platelet adhesion, granule secretion is likely regulated as a separate and independent process.

Keywords: Cell adhesion; Implant; Platelets; Surface topography.

Graphical abstract

Fig. 1

Topographical characterization of titanium (Ti) surface treatments. Scanning electron micrographs (SEM) taken at low magnification (500×, top panels) and high magnification (2000×, bottom panels) illustrate the microscopic features of the different surface treatments: acid-etching, sand-blasting and combined etching/blasting (SLA).

Fig. 2

Quantification of surface roughness by atomic force microscopy (AFM). A. The surface characteristics of the different test Ti surfaces were quantified by atomic force microscopy (AFM). B. Bar graph depicts the roughness average (Ra) of the 4 test surfaces, as determined by AFM. Data are mean ± SD.

Fig. 3

Platelet adhesion to Ti surfaces is modulated by surface topography. A. Confocal micrographs depict the F-actin staining (by FITC-phalloidin) of platelets adhering to smooth, acid-etched, sand-blasted or SLA titanium surfaces at the indicated time points. B. Bar graph depicts the mean number of platelets (per field of view) adhering to smooth Ti (white bars), acid-etched Ti (light grey bars), sand-blasted Ti (dark grey bars) and SLA-treated Ti (black bars). Data are mean ± SEM. *, p < 0.05; **, p < 0.001, based on ANOVA and Bonferroni post-hoc multiple comparison tests.

Fig. 4

Platelet secretion on Ti surfaces is unaffected by surface topography. Bar graphs depict the concentration of secreted platelet factor 4 (PF4) (A), transforming growth factor-beta1 (TGF-β1) (B), soluble P-selectin (sCD62P) (C), and platelet-derived growth factor-AB (PDGF-AB) (D) from human platelets on smooth Ti (white bars), acid-etched Ti (light grey bars), sand-blasted Ti (dark grey bars) and SLA-treated Ti (black bars). Data are mean ± SEM and represent a minimum of 3 independent experiments using blood from different donors.