Regulation of angiogenesis during osseointegration by titanium surface microstructure and energy

Rough titanium (Ti) surface microarchitecture and high surface energy have been shown to increase osteoblast differentiation, and this response occurs through signaling via the alpha(2)beta(1) integrin. However, clinical success of implanted materials is dependent not only upon osseointegration but also on neovascularization in the peri-implant bone. Here we tested the hypothesis that Ti surface microtopography and energy interact via alpha(2)beta(1) signaling to regulate the expression of angiogenic growth factors. Primary human osteoblasts (HOB), MG63 cells and MG63 cells silenced for alpha(2) integrin were cultured on Ti disks with different surface microtopographies and energies. Secreted levels of vascular endothelial growth factor-A (VEGF-A), basic fibroblast growth factor (FGF-2), epidermal growth factor (EGF), and angiopoietin-1 (Ang-1) were measured. VEGF-A increased 170% and 250% in MG63 cultures, and 178% and 435% in HOB cultures on SLA and modSLA substrates, respectively. In MG63 cultures, FGF-2 levels increased 20 and 40-fold while EGF increased 4 and 6-fold on SLA and modSLA surfaces. These factors were undetectable in HOB cultures. Ang-1 levels were unchanged on all surfaces.Media from modSLA MG63 cultures induced more rapid differentiation of endothelial cells and this effect was inhibited by anti-VEGF-A antibodies. Treatment of MG63 cells with 1 alpha,25(OH)(2)D3 enhanced levels of VEGF-A on SLA and modSLA.Silencing the alpha(2) integrin subunit increased VEGF-A levels and decreased FGF-2 levels. These results show that Ti surface microtopography and energy modulate secretion of angiogenic growth factors by osteoblasts and that this regulation is mediated at least partially via alpha(2)beta(1) integrin signaling.