Influence of modified extracellular matrices on TI6AL4V implants on binding and release of VEGF

Besides osteoconductive and osteoinductive signals, angiogenesis plays a crucial role in bone development and regeneration and consequently in the integration of implants. Therefore we investigated in this study the binding and release behaviour of vascular endothelial growth factor (VEGF) from Ti6Al4V surfaces coated with 3-dimensional collageneous matrices, some additionally modified with heparin. The heparin was incorporated using different methods: a) adsorptive immobilization b) crosslinking with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) or c) incorporating during self-assembly of fibrils followed by cross-linking. For unmodified samples, maximum VEGF adsorption was reached with 85 ng VEGF/cm(2). On all 3d-collagen coated surfaces studied (with or without heparin), no saturation could be observed in the range of 0-256 ng VEGF/cm(2).Improved release kinetics were observed for the modified coatings. The initial burst of VEGF within the first 24 h was diminished. From the third day of delivery heparinized matrices showed a higher release of VEGF than the pure collagen matrix and the unmodified reference surface, respectively. In vitro, the proliferation of human dermal microvascular endothelial cells was increased with released VEGF from all investigated samples compared to a VEGF-free control. After 7 days highest increases in cell numbers were observed with solutions from heparinized matrices. It is concluded that functionalization of Ti6Al4V surfaces with heparinized collageneous matrices and VEGF leads to advantageous properties concerning the impact on angiogenesis and thus may improve bone regeneration in the microenvironment of implants.