pH-induced changes in the fabrication of multilayers of poly(acrylic acid) and chitosan: fabrication, properties and test as drug storing and delivery system

EDUARDO GUZMAN; JESICA CAVALLO; RAQUEL CHULIÁ-JORDÁN; CESAR G. GOMEZ; MIRIAM C. STRUMIA; FRANCISCO ORTEGA; RAMÓN RUBIO

LANGMUIR

AMER CHEMICAL SOC

Año: 2011 vol. 27 p. 6836 - 6845

0743-7463

Multilayers of poly(acrylic acid), PAA, and chitosan, CHI, have been built by the layer-by-layer (LbL) method from aqueous solutions at different pH values and analyzed by the dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The results showed that under all of the assembly conditions considered the growth of the films is nonlinear. The thickness of the PAA layers increases as the pH of the assembling solutions decreases, whereas the adsorption of CHI is almost unaffected by the pH conditions. The comparison of the thickness obtained by D-QCM and by ellipsometry has allowed us to calculate the water content of the films, showing that the multilayers are highly hydrated, with an average water content higher than 20%. The analysis of D-QCM data has provided high-frequency values of the complex shear modulus that are in the megapascal range and shows a transition from mainly viscous to mainly elastic behavior for the added PAA layers, depending on the pH. The monomer surface density in each layer (obtained from the combination of ellipsometry and differential refractive index measurements) indicated that the monomer density depends on the assembly conditions. It was found that the adsorption kinetics is a bimodal process, with characteristic times that depend on the number and nature of the layers. Finally, the possibility of using of thesemultilayers as a drug storage and delivery system has been evaluated.