Polyelectrolyte Multilayers with a Tunable Young's Modulus:  Influence of Film Stiffness on Cell Adhesion

Abstract

Mechanical properties of model and natural gels have recently been demonstrated to play an important role in various cellular processes such as adhesion, proliferation, and differentiation, besides events triggered by chemical ligands. Understanding the biomaterial/cell interface is particularly important in many tissue engineering applications and in implant surgery. One of the final goals would be to control cellular processes precisely at the biomaterial surface and to guide tissue regeneration. In this work, we investigate the substrate mechanical effect on cell adhesion for thin polyelectrolyte multilayer (PEM) films, which can be easily deposited on any type of material. The films were cross linked by means of a water-soluble carbodiimide (EDC), and the film elastic modulus was determined using the AFM nanoindentation technique with a colloidal probe. The Young's modulus could be varied over 2 orders of magnitude (from 3 to 400 kPa) for wet poly(L-lysine)/hyaluronan (PLL/HA) films by changing the EDC concentration. The chemical changes upon cross linking were characterized by means of Fourier transform infrared spectroscopy (FTIR). We demonstrated that the adhesion and spreading of human chondrosarcoma cells directly depend on the Young's modulus. These data indicate that, besides the chemical properties of the polyelectrolytes, the substrate mechanics of PEM films is an important parameter influencing cell adhesion and that PEM offer a new way to prepare thin films of tunable mechanical properties with large potential biomedical applications including drug release.

Engineering Muscle Tissues on Microstructured Polyelectrolyte Multilayer Films

“…Before the buildup of films, the PDMS substrates were oxidized by oxygen plasma in a microwave downstream etcher (Plassys) at 1500 W power for 10 s. The films were prepared as previously described 25 with an automated dipping machine (Dipping Robot DR3; Kierstein GmbH) on PDMS pieces or on 14 mm-diameter glass slides (VWR Scientific), used here as control substrates. PLL at 0.5 mg/mL, HA at 1 mg/mL, and polyethyleneimine (as precursor layer) at 2 mg/mL were dissolved in an HEPES-NaCl buffer (20 mM HEPES and 0.15 M NaCl at pH 7.4).…”

“…During (PLL/ HA) 12 film buildup, all the rinsing steps were performed with a rinsing solution (0.15 M NaCl, pH 6.5). After buildup, the films were cross-linked following a previously published protocol 25 using EDC and sulfo-NHS. EDC was used at various concentrations (10,30,70, or 100 mg/mL), while sulfo-NHS was kept constant at 11 mg/mL.…”

“…25 The adhesion of C2C12 on stiff films (EDC70, EDC100) was effective, as cells exhibit a characteristic fibroblastic morphology; whereas on softer films (EDC30), cells remain round and exhibit a preference for cell-cell interactions (Supplementary Fig. S1; Supplementary Data are available online at www.liebertpub.com/ tea).…”

“…The mechanical properties of the (PLL/HA) 12 films were modified by chemical crosslinking 25 and myoblast adhesion, spreading, proliferation, and differentiation were examined. Young's modulus of the films can be varied between several tens of kPa to about 400 kPa depending on the concentration of the cross-linker, 22 which is much softer than glass (*50 GPa).…”

Hyaluronan-dependent pericellular matrix☆

“…The stiffness of crosslinked hyaluronan gels is important for cellular adhesion and spreading in bioengineering applications [108]. This suggests that local variations in Young's modulus of the native pericellular matrix may dictate its inherent signal transduction potential, whether it promotes cell adhesion and spreading, or promotes cell detachment and rounding, or contributes to the metastatic potential of cancer cells.…”