The adhesion of primary osteoblastic cells on top of biocompatible polyelectrolyte multilayer (PEM) films was investigated for native films and after changing the films properties either with a chemical stimulus (film functionalization), with a mechanical stimulus (film cross-linking), or with both stimuli combined. For the functionalization, a 15 amino acid peptide containing a –RGD- (-Arg-Gly-Asp) sequence was grafted to poly(L-glutamic) acid and deposited on top of poly(L-lysine)/poly(L-glutamic) (PLL/PGA), PLL/Poly(alginic), and PLL/Poly(galacturonic) films. The film buildup and the adsorption of the PGA-RGD was followed by Optical Waveguide Lightmode Spectroscopy and by Atomic Force Microscopy. The mechanical stimulus was achieved by crosslinking the films with a water soluble carbodiimide (EDC) in combination with N-hydroxysulfo-succinimide (sulfo-NHS) to induce amide formation. Fourier Transform Infrared Spectroscopy evidenced the conversion of amine and carboxylic groups into amide groups.
The alkaline phosphatase (ALP) activity test was used to assess osteoblast adhesion and proliferation on top of the different films over a period of eight days in culture. Whereas the native films are poorly adherent, the RGD-functionalized films exhibit an increased short time adhesion. The native films could also be successfully cross-linked thereby dramatically enhancing cell proliferation. The cells did not react similarly on the different types of films investigated : the cross-linked (PLL/Palg) and (PLL/Pgal) films were much more efficient than the native or functionalized films in terms of proliferation. On the other hand, for the (PLL/PGA) films, functionalization and film cross-linking had a similar long term effect. Very interestingly, for these latter films, both stimuli could be combined.