Control of the self-assembly and properties of quaternized dextran/heparin polyelectrolyte multilayer films by the degree of dextran substitution

The layer-by-layer (LbL) assembly of polyelectrolyte multilayer films offers a versatile approach to construct ultrathin films with controlled nanostructures and functionalities. The properties of LbL assemblies are strongly influenced by the intrinsic properties of the polyelectrolytes and the assembly conditions. In this study, we investigated the effect of charge content, concentration, deposition time, and molecular weight of polyelectrolytes on the formation and stability of LbL films composed of quaternized dextran (QDex) with varying degrees of substitution (DS) (30%-90%) and heparin (Hep). Surface plasmon resonance analysis revealed that the introduction of a QDex/tannic acid anchoring bilayer effectively reduced the desorption occurring during the deposition of both strong polyelectrolytes, resulting in continuous, exponential growth of QDex/Hep LbL films. The mass deposition increased with increasing DS of QDex, particularly when the QDex concentration and deposition time were optimized. The quartz crystal microbalance with dissipation (QCM-D) monitoring revealed that increasing DS of QDex led to LbL films with progressively higher apparent elastic modulus and viscosity, indicating a transition from soft, water-rich networks to more rigid, cohesive, and less dissipative structures due to enhanced electrostatic interactions (proved by isothermal titration calorimetry) and reduced chain mobility. Furthermore, spectroscopic ellipsometry analysis of 20-bilayer QDex/Hep assemblies deposited on real silica substrates confirmed the increase in film thickness with increasing DS of QDex, especially after the formation of nine QDex/Hep bilayers, where the film structure became more stable. The obtained findings provide detailed insights into the precise control of film growth and stability, which are essential for potential applications in tissue engineering and biomaterial field.