Enhancement of the growth of human endothelial cells by surface roughness at nanometer scale

This study investigated whether a nanometer scale of surface roughness could improve the adhesion and growth of human endothelial cells on a biomaterial surface. Different molecular weights or chain lengths of polyethylene glycol (PEG) were mixed and then grafted to a polyurethane (PU) surface, a model smooth surface, to form a nanometer (nm) scale of roughness for PU-PEG surfaces (PU-PEGmix) while PEG with a molecular weight of 2000 was also grafted to PU to form PU-PEG2000 for comparison. In addition, the concept was tested on cell-adhesive peptide Gly–Arg–Gly–Asp (GRGD) that was photochemically grafted to PU-PEGmix and PU-PEG2000 surfaces (e.g., PU-PEGmix-GRGD and PU-PEG2000-GRGD surfaces, respectively). To prepare GRGD-grafted PU-PEGmix and PU-PEG2000 surface, 0.025 of GRGD-SANPAH (N-Succinimidyl-6-[4′-azido-2′-nitrophenylamino]-hexanoate) solutions was grafted to PU-PEGmix and PU-PEG2000 by surface adsorption of the peptide and subsequent ultraviolet (UV) irradiation for photoreaction. The grafting efficiencies for GRGD to PU-PEGmix and PU-PEG2000 surfaces were about 67% for both surfaces, semi-quantitatively analyzed by an HPLC. The surface roughness, presented with a roughness parameter, Ra, and the topography of the tested surfaces were both measured and imaged by an atomic force microscope (AFM). Among the Ra values of the films, PU was the smoothest (e.g., Ra=1.53±0.20 nm, n=3) while PU-PEGmix was the roughest (e.g., Ra=39.79±10.48 nm, n=4). Moreover, Ra values for PU-PEGmix and PU-PEGmix-GRGD surfaces were about 20 nm larger than those for PU-PEG2000 and PU-PEG2000-GRGD, respectively, which were consistent with the topographies of the films. Human umbilical vein endothelial cells (HUVECs) were adhered and grown on the tested surfaces after 36 h of incubation. Among the films, HUVECʹs adhesion on the surface of PU-PEGmix-GRGD was the densest while that on the surface of PU-PEG2000 was the sparsest. Also, the adhesion and growth of HUVECs for the roughness surfaces were statistically significantly better than that of smooth surface for both GRGD grafted and un-grafted surfaces, respectively. The viability for the growth of HUVECs on the tested surfaces analyzed by MTT assay also confirmed the efficacy of the increased surface roughness. In conclusion, increased surface roughness of biomaterial surfaces even at 10–102 nm scale could enhance the adhesion and growth of HUVECs on roughness surfaces that could be useful for applications of tissue engineering.