Smart biomaterials have become a highly developed and investigated field of interest in the last decades. One field of smart biomaterials are polyelectrolyte multilayer films (PEM) made of poly-L-lysine (PLL) and hyaluronic acid (HA). Potential applications of (PLL/HA)n films are located in drug delivery systems (1) and cell adsorption. These applications require a better understanding and control of their mechanical properties, especially separation between elastic and viscous properties.
Mechanical properties of PEM's were determined by using scanning- and colloidal-probe atomic force microscopy (cp-AFM). Elastic properties were determined by single force measurements in liquid at different pH, ionic strength and temperature. While the measured apparent Young's modulus is around 50 kPa for neutral pH, it decreases either by changing the pH to higher/lower values or by increasing the ionic strength. Furthermore separation of pure elastic from viscoelastic properties was determined via creep compliance, stress relaxation and dynamic force measurements, showing a strong viscous behaviour with multiple relaxation mechanisms (3).
(1) Volodkin, D. V.; Larionova, N. I.; Sukhorukov, G. B. Biomacromolecules 2004, 5, 1962 – 1972.
(2) Decher, G. Science 1997, 277, 1232 – 1237.
(3) Üzüm, C.; Hellwig, J.; Madaboosi, N.; Volodkin, D.; v. Klitzing, R. Beilstein J. Nanotechnol. 2012, 3, 778–788.
Hellwig@tu-berlin.de
