Glyoxal crosslinking of electro-responsive alginate-based hydrogels: Effects on the properties

To improve the features of alginate-based hydrogels in physiological conditions, Ca²⁺-crosslinked semi-interpenetrated hydrogels formed by poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid and alginate (PEDOT/Alg) were subjected to a treatment with glyoxal to form a dual ionic/covalent network. The covalent network density was systematically varied by considering different glyoxalization times (t_G). The content of Ca²⁺ was significantly higher for the untreated hydrogel than for the glyoxalized ones, while the properties of the hydrogels were found to largely depend on t_G. The porosity and swelling capacity decreased with increasing t_G, while the stiffness and electrical conductance retention capacity increased with t_G. The potentiodynamic response of the hydrogels notably depended on the amount of conformational restraints introduced by the glyoxal, which is a very short crosslinker. Thus, the re-accommodation of the polymer chains during the cyclic potential scans became more difficult with increasing number of covalent crosslinks. This information was used to improve the performance of untreated PEDOT/Alg as electrochemical sensor of hydrogen peroxide by simply applying a t_G of 5 min. Overall, the control of the properties of glyoxalized hydrogels through t_G is very advantageous and can be used as an on-demand strategy to improve the performance of such materials depending on the application.