Hydrogel Synthesis and Characterization

Acrylamide was purchased from MP Biomedicals LLC (France, purity ≥ 99%, Acrylamide acid <0.001%), lithium bromide (≥99%), sodium bromide (≥99%), sodium bicarbonate (≥99.5%), methacrylate anhydride (99%), N,N′-MethylenebisAcrylamide (MBAA, purity ≥ 99.5%), microcrystalline cellulose (MCC, size exclusion, ca 50 μm particle size), 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO, 98%), phenylboronate Acrylamide (PBAAm, 98%), phosphotungstic acid hydrate (PTA, ≤ 0.002% total nitrogen), 2,4,6-trimethylbenzoyl chloride (97%) were bought from Sigam-Aldrich (Germany). Dimethoxyphenylphosphine (97%), dopamine hydrochloride (99%) and 2-butanone (99%) were received from Alfa Aesar (Germany). Sodium hydroxide (99%), borax-NaOH buffer (pH = 10.00, accuracy: ± 0.02 pH, reference temperature 20 °C) and sodium hypochlorite solution (14%, active chlorine) were purchased from TH Geyer (Germany). DI water (conductivity <1 μS/cm, room temperature) was used in all steps and all solvents were used directly from TH Geyer (Germany) without further treatment. Dopamine methylacrylate (DMA) and lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) were prepared using the reported method^{54 (link),55 (link)}.