4.2. Synthesis of Alginate Di-Aldehyde (ADA)

A partial oxidization of sodium alginate with sodium (meta) periodate (NaIO₄) as oxidizing agent was performed in order to obtain alginate dialdehyde (ADA). In brief, 10 g of alginate were dispersed in 50 mL of ethanol (99.8 %) and kept under stirring in dark conditions. Then, appropriate amounts of NaIO₄ (1.337, 2.003 or 2.674 g) were dissolved in 50 mL ultrapure water in the absence of light to achieve a corresponding oxidation degree of 13, 19 or 26%. The NaIO₄ solution was added dropwise to the stirring alginate suspension immediately upon dissolution. After 6 h of oxidation time, the reaction was quenched by the addition of 10 mL ethylene glycol while further stirring at room temperature (RT) for an additional 30 min. Finally, the suspension was left 10 min for sedimentation of the ADA product and the supernatant was decanted. For the purification of ADA, it was dialyzed against ultrapure water in containers holding a volume of 15 L. The water was replaced with fresh water daily, and dialysis tubes had a molecular weight cut-off of 6–8 kDa. After 5 days, the purified ADA solution was frozen for 72 h at −20 °C and subsequently lyophilized (ALPHA 1−2 LDplus, CHRIST Gefriertrocknungsanlagen, Harz, Germany) to obtain a dry product.