Assembly of heparin and type IV collagen onto titanium surface and the effect of assembled layer numbers on the behavior of endothelial progenitor cells

Negatively charged heparin and positively charged type IV collagen were assembled onto titanium surface by a layer-by-layer (LBL) self-assembly technique. Based on this approach, this work mainly investigated the effect of modified surface and assembled layer numbers on the behavior of endothelial progenitor cells (EPCs). Titanium was firstly activated by NaOH solution to generate a negatively charged hydroxyl-rich surface for subsequently poly-L-lysine (PLL) electrostatically binding and thereby formed positively charged amino group modified surface. Then the negatively charged heparin and the positively charged type IV collagen were alternately assembled onto the PLL coated titanium surface to form the functional multilayer via intermolecular electrostatically interaction. The change of the surface chemical composition after each step was detected by Fourier transform infrared spectroscopy. The total amount of assembled heparin was determined by toluidine blue assay. The surface topography and hydrophilic/hydrophobic property of the functional multilayer sample was investigated by atomic force microscopy and water contact angle measurement, respectively. The experiment results showed that heparin and type IV collagen were successfully assembled onto material surface. In compared with the controlled titanium surface, the biofunctional multilayer surface significantly improved endothelial progenitor cells (EPCs) adhesion. Meanwhile, with increasing of the assembled layer numbers, the biological behaviors of the endothelial progenitor cells were obviously improved, such as better adhesion, more accelerating growth and proliferation. It was due to the amount of IV collagen increasing.