Semi-interpenetrated polymer networks of hyaluronic acid modified with poly(aspartic acid)

New hydrogels based on entrapped poly(aspartic acid) (PAS) into hyaluronic acid (HA) crosslinked network were obtained to improve the sensitive characteristics, especially the pH responsiveness of the hyaluronic gels. The interactions between the macromolecular chains were sustained by rheological test, zeta potential, and hydrodynamic diameter and conductivity determinations. In situ and static evaluation of zeta potential indicated a substantially decreases of electrokinetic potential of HA/PAS mixture solutions interpreted due to the electrostatic complexation between polypeptide and polysaccharide causing a decrease in electrostatic free energy of the system. Similar, the positive deviation from the ideal additive observed on the logarithmic graphical representation of relative viscosity corresponds to the presence of the intermolecular bonds between the macromolecular chains. The spectral analysis confirmed the hydrogels formation, while the rheological measurements of HA/PAS semi-IPN have shown formation of structured network with physical links between the polymeric copartners. The SEM microphotographs presented a homogeneous porous structures with spherical formations ordered at high concentration of PAS. The superabsorbent character of PAS is evidenced by the maximum swelling degree reached at high value of pH and high PAS content. With an advantageous decreasing of residual mass and convenient straightening for thermal stability up to 60 °C compared with hyaluronic gels, the improved properties are explicated.