Inspired Chemistry for a Simple but Highly Effective Immobilization of Vascular Endothelial Growth Factor on Gallic Acid-functionalized Plasma Polymerized Film†

Biomolecules with thiol or amine groups can be easily covalently immobilized onto a material substrate equipped with quinone groups in a simple mild alkali buffer solution based on Schiff base and Michael addition reaction. In this study we report a novel two-step approach to creating a functional coating with abundant quinone groups for a facile immobilization of vascular endothelial growth factor (VEGF) in chemical mild phosphate buffered saline (PBS, pH = 7.4). This approach firstly involves the deposition of plasma polymerized allylamine (PPAam) thin coating onto a substrate to introduce the amine groups. Then gallic acid (3,4,5-trihydroxybenzoic acid, GA) is chosen to functionalize PPAam for introducing phenol groups through a water-soluble carbodiimide (WSC) coupling procedure. The results of infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and water contact angles reveal the effective conjugation of GA to PPAam and further immobilization of VEGF to GA functionalized PPAam. The results of quartz crystal microbalance equipped with dissipation monitoring (QCM-D) show that 120 ng · cm−2 of VEGF is successfully immobilized onto GA functionalized surface. The VEGF functionalized surface shows a significant enhancement of human umbilical vein endothelial cell (HUVEC) proliferation, revealing a good bioactivity of VEGF. This functional coating not only provides a novel facile strategy for the covalent immobilization of biomolecules in a chemical mild reaction condition, but also can be adapted for a wide range of materials without surface pretreatment.