Primary cell adhesion on RGD-functionalized and covalently crosslinked thin polyelectrolyte multilayer films

Polyelectrolyte multilayers (PEMs) are now widely used for biomedical applications. In this work, we investigated the primary osteoblast adhesion properties of PEMs of poly(L-lysine) (PLL), poly(L-glutamic acid) (PGA), poly(alginic acid) (Palg), and poly(galacturonic acid) (Pgal). In order to compensate for the poor adhesion of the as-synthesized films, two kinds of film modifications were achieved: a purely physical modification by film crosslinking, and a chemical modification by grafting a arginine-glycine-aspartic acid (RGD) peptide to PGA. Crosslinking was performed using a water-soluble carbodiimide in combination with N-hydroxysulfosuccinimide (sulfo-NHS) to induce amide formation. This reaction was followed by Fourier-transform IR spectroscopy. For film functionalization, a 15-amino-acid peptide was grafted to PGA and deposited as the top layer of the film. PLL/PGA, PLL/Palg, and PLL/Pgal films were crosslinked or functionalized. The films were tested for both short-term adhesion properties and long-term proliferation of primary osteoblasts. Whereas the effect of film crosslinking on short-term adhesion was moderate, it was much more important for the RGD-functionalized films. On the other hand, the long-term proliferation was the same or even higher for the crosslinked films as compared with the functionalized films. This effect was particularly enhanced for the PLL/Palg and PLL/Pgal films. Finally, we functionalized PLL/PGA that had been crosslinked prior to PGA-RGD deposition. These architectures exhibited even higher short-term adhesion and proliferation. These results clearly show the important role of the physical properties of the films, besides their chemical properties, for the modulation of primary cell-adhesion behavior.