Internal composition versus the mechanical properties of polyelectrolyte multilayer films: the influence of chemical cross-linking.
Different types of polyelectrolyte multilayer films composed of poly(L-lysine)/hyaluronan (PLL/HA), chitosan/hyaluronan (CHI/HA) and poly(allylamine hydrochloride)/poly(L-glutamic acid) (PAH/PGA) have been investigated for their internal composition, including water content, ion pairing, and ability to be covalently cross-linked, as well as for their mechanical properties. Film buildup under physiological conditions was monitored by the quartz crystal microbalance with dissipation monitoring (QCM-D) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), which allows unambiguous quantification of the different groups present in the polyelectrolytes. (PAH/PGA) films emerged as the most dense films with the lowest hydration (29%) and the highest COO(-) molar density. In addition, PAH is greatly in excess in these films (3 PAH monomers per PGA monomer). The formation of amide bonds during film cross-linking using the water-soluble carbodiimide EDC was also investigated. All of the films could be cross-linked in a tunable manner, but PAH/PGA exhibited the highest absolute number of amide bonds created, approximately 7 times more than for (PLL/HA) and (CHI/HA) films. The Young's modulus E of the films measured by AFM nanoindentation was shown to vary over 1 to 2 orders of magnitude for the different systems. Interestingly, a linear relationship between E and the density of the covalent cross-links created was observed for (PLL/HA) and (CHI/HA) films whereas (PGA/PAH) films exhibited biphasic behavior. The mean distance between covalent cross-links was estimated to be approximately 11 nm for (PLL/HA) and (CHI/HA) films and only approximately 6 nm for (PAH/PGA) films for the maximum EDC concentration tested (100 mg/mL).
Boudou
Thomas
T
Minatec, Grenoble Institute of Technology and LMGP, F-38016 Grenoble Cedex, France.
Crouzier
Thomas
T
Auzély-Velty
Rachel
R
Glinel
Karine
K
Picart
Catherine
C
D000577:Amides; D002234:Carbodiimides; D003432:Cross-Linking Reagents / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D019563:Mechanics; D008567:Membranes, Artificial; D015394:Molecular Structure; D011108:Polymers / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D000577:Amides; D002234:Carbodiimides; D003432:Cross-Linking Reagents; D007477:Ions; D008567:Membranes, Artificial; D011108:Polymers; D014867:Water