Early implant healing: promotion of platelet activation and cytokine release by topographical, chemical and biomimetical titanium surface modifications in vitro

Objectives: Platelet releasate has been shown to promote osteogenetic cell proliferation and differentiation. Topography and chemistry of biomaterials have high impact on platelet activation. More specifically, the bioactive cell adhesive peptide sequence ArgGlyAsp (RGD) triggers platelet activation mediated by the aIIb beta 3 integrin receptor. Accordingly, topographical, chemical and biomimetical (immobilized RGD peptide) modifications of titanium (Ti) surfaces may enhance early platelet activation and bony healing of implants. Therefore, the aim of the study was to evaluate platelet activation with subsequent platelet-derived cytokine release by accordingly modified Ti surfaces. Materials and methods: Pre-treated (PT; mean roughness [Ra]=0.04 mu m, contact angle [CA]=91 degrees), acid-etched (A, Ra=0.83 mu m, CA=106 degrees), large grit-sandblasted, acid-etched (SLA, Ra=3.2 mu m, CA=109 degrees) as well as hydrophilically modified acid-etched (modA, Ra=0.83 mu m, CA=0) and modified large grit-sandblasted, acid-etched (modSLA, Ra=3.2 mu m; CA=0 degrees) titanium surfaces were investigated. Additionally, RGD peptides were chemically immobilized on PT, A and SLA surfaces (PT-RGD [CA=18 degrees], A-RGD [CA=0 degrees], SLA-RGD [CA=0 degrees]). The different Ti surfaces were incubated with platelet concentrate of three healthy volunteers at room temperature for 15 min and for 30 min. High thrombogenous collagen served as the control group. Out of the supernatant, platelet consumption was assessed via platelet count (PC). Cytokine release was quantified via the level of platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF). Results: After 15 min, especially the rough SLA surface showed a strong decrease in PC and a strong increase in VEGF and PDGF levels. After 30 min, high platelet consumption as well as high levels of VEGF and PDGF were measured for unspecifically modified (modA) and especially for biomimetic, specifically modified (PT-RGD, A-RGD) surfaces, indicating a delayed effect of the surface modifications on platelet activation. Discussion: Modifications of surface roughness modifications appear to influence early platelet activation and cytokine release after 15 min whereas surface chemistry modifications with increased hydrophilic properties and surface modifications via RGD peptide on plainer surfaces lead to a further, more specific promotion of platelet activation and degranulation after 30 min. The observed effect could be valuable for critical clinical situations like compromised bone sites.