Source: https://www.researchgate.net/profile/Benoit-Minisini/publication/309887313_Stiff_IPN_Hydrogels_of_PolyAcrylamide_and_Alginate_Influence_of_the_Crosslinking_Ion's_Valence_on_Hydrogel's_Final_Properties/links/5842a49308ae8e63e623b7fb/Stiff-IPN-Hydrogels-of-PolyAcrylamide-and-Alginate-Influence-of-the-Crosslinking-Ions-Valence-on-Hydrogels-Final-Properties.pdf