On the piezoelectricity of collagen–chitosan films

We studied the physicochemical, piezoelectric and dielectric properties of collagen–chitosan films, with regard to the development of new biomaterials which have potential applications in the coating of cardiovascular prostheses, support for cellular growth and in systems for controlled drug delivery. The piezoelectric strain tensor element d14, the elastic constant s55, and the relative permittivity ε11 were obtained for the collagen and collagen–chitosan films. Resonance measurement of the piezoelectric strain constant d14 of collagen gives 0.096 pC N−1, which is in good agreement with values reported in the literature, measured using other techniques. It was observed that addition of 15% of chitosan increased the piezoelectricity to 0.212 pC N−1. The frequency constant f L and the piezoelectric strain element d14, obtained for this sample, present the highest value for the samples under study (427.24 kHz m and 0.212 pC N−1). This value for the d14 element is of the same order as that obtained for bovine bone (d14 = 0.2 pC N−1) (T. G. Netto and R. L. Ziemmerman, Biophys. J., 1975, 15, 573), which is about one-tenth of the piezoelectric constant d11 of quartz crystal. Our results also show that the presence of chitosan contributes to an increase in the thermal stability of the collagen films, which is associated with an increase in the denaturation temperature of the collagen–chitosan samples compared with the collagen sample. We believe that the increase in the organization of the microscopic structure of the sample, results in an increase in the piezoelectricity. These high values for the frequency constant and piezoelectricity, give the possibility of using these films in electronic devices based on acoustic waves (e.g. surface acoustic wave devices (SAW)) which operate in the MHz frequency range using piezoelectric substrates.