Variation of Polyelectrolyte Film Stiffness by Photo-Cross-Linking: A New Way To Control Cell Adhesion

Abstract

We report on the preparation of polyelectrolyte films based on biopolymers whose nanomechanical properties can be tuned by photo-cross-linking. Cationic poly(L-lysine) was layer-by-layer assembled with anionic hyaluronan (HA) derivatives modified by photoreactive vinylbenzyl (VB) groups. The study of the multilayer buildup by quartz crystal microbalance with dissipation monitoring showed that the presence of VB groups does not influence significantly the multilayer growth. Then the VB-modified HA incorporated into the films was cross-linked upon UV irradiation. UV spectroscopy measurements showed that the cross-linking rate of the multilayers increases with the amount of VB groups grafted onto HA chains. Force measurements performed by atomic force microscopy with a colloidal probe proved that the rigidity of the cross-linked films increases with the grafting degree of HA chains and consequently the number of cross-links. Cell culture assays performed on non-cross-linked and photo-cross-linked films with myoblast cells demonstrated that cell adhesion and proliferation are considerably improved with increasing film rigidity.

Layer-by-Layer Assembly of Biopolyelectrolytes onto Thermo/pH-Responsive Micro/Nano-Gels

“…Thus, it was proposed that derivatives with long chains and high DS had an irregular internal structure, with hydrophobic nanodomains coexisting with hydrophilic domains. Similar behaviour was reported for VB-g-HA/PLL, where the mean surface roughness of the systems increased from 0.3 to 9 nm when the grafting degree rose from 14% to 37% [29]. …”

“…Vinylbenzene(VB)-modified HA derivatives were synthesized by grafting different amounts of VB onto the carboxylic acid groups of HA via an esterification reaction [29]. HA salt (in its acid form) and VB were dissolved in dimethyl sulfoxide (DMSO) at 40 °C, and the reaction was continued under magnetic stirring for 48 h. Then, a concentrated aqueous solution of NaCl was added to change the obtained VB-grafted HA into the sodium salt form that was precipitated in acetone.…”

“…The hollow microcapsules were then washed with NaCl solution several times and incubated in EDC solution for 6 h to obtain shell crosslinked microcapsules. A very similar procedure was used to assemble PLL onto VB and hydrazide-modified HA, but in this case the pH was set at 7.4 [29,30]. …”

“…In this function the cantilever oscillates at its resonant frequency at room temperature in air, and as it is brought to the sample surface it is caused to deflect according to Hooke’s law, with the deflection normally measured by a “ beam bounce ” method, with the computed deflections used to generate a surface topography map. The nanomechanical properties of thin films such as LbL constructions can also be tested using AFM by changing the cantilever probe to a sphere tip and applying it as a type of microindenter [29]. …”

“…The mechanical properties of VB- g -HA/PLL films were analysed by Pozos-Vazquez et al [29] using AFM nano-indentation. The comparison of force-indentation curves for samples with grafting degrees from 14% to 37% (Figure 16e) revealed that the stiffness of the multilayers increased with the grafting degree.…”