2.1. Synthesis of Alginate Methacrylate (ALMA)

Medium viscosity alginate (MW ~ 260 kDa) was modified to include photocrosslinkable groups by reaction with methacrylic anhydride (MAAh) (both Sigma-Aldrich, St Louis, MO, USA). Alginate was dissolved in distilled water at 2 % and reacted with a 10-fold molar excess of MAAh over total alginate hydroxyl groups for 24 h on ice and under constant stirring [40]. The pH was regularly adjusted to 8 using 5 M NaOH. After the reaction period, insoluble MAAh was removed by centrifugation, followed by dialysis against deionized water using a 12 kDa MWCO cellulose dialysis membrane (Sigma-Aldrich) for 5–7 days. The pH of the dialyzed polymer solutions was adjusted to 7.4, after which they were lyophilized and stored at −20 °C protected from light and moisture.