Effect of metal ions with reducing properties on hydrogels containing catechol groups

The catechol group in mussel has been widely explored for the development of hydrogels due to its optimal adhesion with water. Although the development of the catechol hydrogels has made an extensive progress, however, there is still room for further exploration. In this study, the effect of metal ions on the catechol modified hydrogels was studied with respect to the mechanical properties. For this, a polymer network structure containing the catechol hydrogel and polyacrylamide networks has been designed. Fe3+ and Ag+ have been selected to form the redox pairs with catechol. The addition of metal ions in the double network hydrogel increases the crosslinking degree and hardness of the hydrogel, thus, indicating the tuning of the mechanical properties. For instance, the maximum elongation of CHCS-PAAM is noted to reach 259.6% after soaking in the ferric chloride solution for 15 min. Simultaneously, the coordination between the metal ions and catechol declines the superior adhesion nature of catechol. Due to the addition of metal ions, the conductivity of the double network hydrogels may also change. The insights into the effect of metal ions on the mechanical properties of the catechol double network hydrogels can help in developing the wearable skin sensors with a superior detection ability.