Citric acid h2o

L-aspartic acid (Sigma-Aldrich, UK), 1,4-diaminobutane (DAB) (Sigma-Aldrich, ≥99%), cysteamine (CYSE) (Sigma-Aldrich, UK), cystamine (CYS) (Sigma-Aldrich, UK), dimethylformamide (DMF) (VWR International, USA), dimethylsulfoxide (DMSO) (Sigma-Aldrich), o-phosphoric acid (VWR), imidazole (ACS reagent, ≥99%, Sigma-Aldrich), citric-acid*H₂O (ACS reagent, ≥99.9%, VWR), sodium chloride (99–100.5%, Sigma-Aldrich), phosphate buffer saline (PBS) (Tablet, Sigma), D,L-dithiotreitol (DTT) (Sigma), 5,5 dithio bis-(2-nitrobenzoic acid) (Sigma, ≥98%, USA), L-cystein (Sigma, ≥97%, USA), Humidified incubator (Nuaire, USA), 100 mm tissue culture dishes (Orange Scientific, Belgium), 48 well plates (Sigma-Aldrich, USA), low cell binding 96 well plates (Nunc, Denmark), Eagle’s Medium Alfa minimal essential medium (αMEM) (Gibco, USA), fetal bovine serum (FBS, Gibco, USA), L-glutamine (Gibco, USA), penicillin and streptomycin (Gibco, USA), L-ascorbic acid 2-phosphate (Sigma-Aldrich, USA), beta-glycerophosphate (Sigma-Aldrich, USA), dexamethasone (Sigma-Aldrich, USA), WST-1 [2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium] (Roche, Switzerland), Vybrant DiD (Molecular Probes, USA), 2-Amino-2-Methyl-1-Propanol buffer (Sigma-Aldrich, USA), Alkaline Phosphatase Yellow (pNPP) Liquid Substrate System (Sigma-Aldrich, USA).

For ¹H-NMR characterization, the PSI-DA polymers were treated with the same materials, i.e., pH = 8 imidazole buffer (imidazole: ACS reagent, ≥99%, Sigma-Aldrich, Budapest, Hungary), citric-acid*H₂O (ACS reagent, ≥99.9%, VWR), sodium chloride (99–100%, Sigma-Aldrich) that were used for hydrolyzation of PSI-based gels into PASP gels. All ¹H NMR spectra were obtained using a JEOL SC400 spectrometer (JEOL Ltd., Riken, Tokyo, Japan) operating at 400 MHz. Then, 25 mg of polymer powders were dissolved in 0.6 mL of D₂O in 5 mm NMR tubes. All spectra were recorded at 23.5 °C ± 0.5 °C and tetramethylsilane was used as an internal standard. The pulse angle was 45°, and a 2 s delay was applied with 8 kHz spectral width, while 16 K data points and 16 scans were done at each measurement. To evaluate spectra, the ACD/Labs NMR software was used.

L-aspartic acid (Sigma-Aldrich, Darmstadt, Germany), dimethylformamide (DMF) (VWR International, Radnor, PA, USA), dimethylsulfoxide (DMSO) (Sigma-Aldrich, Darmstadt, Germany), nutrient broth (Fluka Analytical, Charlotte, North Carolina, USA), o-phosphoric acid (VWR International, Radnor, PA, USA), phosphate buffer saline (PBS) (Sigma-Aldrich, Darmstadt, Germany), imidazole (ACS reagent, ≥99%, Sigma-Aldrich, Darmstadt, Germany), citric-acid*H2O (ACS reagent, ≥99.9%, VWR International, Radnor, PA, USA), sodium-chloride (99-100.5%, Sigma-Aldrich, Darmstadt, Germany), minimum essential medium (MEM) (Gibco, Waltham, MA, USA), fetal bovine serum (FBS, Gibco, Waltham, MA, USA), L-glutamine (Gibco, Waltham, MA, USA), non-essential amino acids (NEAA, Gibco, Waltham, MA, USA), penicillin-streptomycin mixture (Gibco, Waltham, MA, USA), trypsin/EDTA (Gibco, Waltham, MA, USA), 2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium (WST-1 cell proliferation reagent, Roche, Basel, Switzerland). All the chemicals were of analytical grade and used as received. For the aqueous solutions, ultrapure water (ZeneerPower I Water Purification System, Human Corporation, Seoul, South-Korea) was used.