Influence of Synthetic Polyelectrolytes on the Growth and Properties of Hyaluronan−Chitosan Multilayers

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Abstract
Both hyaluronan (HA) and chitosan (CHI) are biocompatible polysaccharide electrolytes. The multilayers formed by these polyelectrolytes alone are known to be rather soft and strongly viscoelastic. In this work we study multilayers formed by incorporating synthetic nonsaccharide polyelectrolytes such as polyallylamine (PAH) and poly(acrylic acid) (PAA) in various proportions into the HA/CHI layers. The buildup was followed on a quartz crystal resonator. Surface acoustic impedance recorded in these measurements, in suitable conditions, gives a spiral when plotted in the complex plane. The shape of this spiral depends on the viscoelasticity of the layer material and regularity of the growth process. We found that poly(acrylic acid) destroys the soft diffuse matrix formed by hyaluronan. It forms diffusion barriers when deposited sparsely between the layers. If its proportion is higher, the film growth adopts a linear buildup in the layer-by-layer process. The linear buildup of CHI/PAA reveals that the buildup regime of a multilayer film does not determine the viscoelastic properties of the film. Linearly and exponentially growing films may have very similar mechanical properties. Polyacrylic acid forms a kind of scaffold inside the film giving the natively soft hyaluronan/chitosan film more mechanical strength. The optimal combination gave more than 100-fold increase in the shear modulus.