L aspartic acid

For the synthesis of the polymers, L-aspartic acid (Merck, extra pure), phosphoric acid (Sigma Aldrich, 99%), cysteamine (Acros Organics, 95%), N,N-dimethylethylenediamine (Sigma Aldrich, 95%), ethyl acetate (Reanal Hungary, a.r.), acetone (Reanal Hungary, a.r.), and N,N-dimethylformamide (DMF) were used without further purification. To mimic the oxidative effect on the ocular surface, 20% w/w 1 M NaBrO₃ was used as model oxidant in the formulations. A phosphate-buffered saline (PBS) solution of pH = 7.4 was prepared by dissolving 8 g dm⁻³ NaCl, 0.2 g dm⁻³ KCl, 1.44 g dm⁻³ Na₂HPO₄·2H₂O, and 0.12 g dm⁻³ KH₂PO₄ in distilled water, with the pH being adjusted with 0.1 M HCl. Lacrimal fluid of pH = 7.4 was prepared by dissolving 2.2 g dm⁻³ NaHCO₃, 6.26 g dm⁻³ NaCl, 1.79 g dm⁻³ KCl, 96.4 mg dm⁻ MgCl₂·6H₂O, and 73.5 mg dm⁻³ CaCl₂·H₂O in distilled water, with the pH being adjusted with 1 M HCl. Mucin (porcine gastric mucin type II) was purchased from Sigma Aldrich. Mucin dispersions were prepared with simulated lacrimal fluid and stirred for 8 h. As reference system eye drop formulation from the market was used, consisting of dextran, hypromellose, benzalkonium chloride, EDTA, KCl, NaCl, and water for injection, with the pH being adjusted with HCl and NaOH. Sodium hyaluronate (HA) (MW: 4350 kDa) was purchased from RichterGedeon Ltd. (Budapest, Hungary).

Chitosan (low molecular weight 50,000–190,000 Da; deacetylation degree 75–85%), diacrylate poly(ethylene glycol) (crosslinker, Mn = 700 g/mol), 2-hydroxy-2-methylpropiophenone (photoinitiator, d = 1.077 g/mol, 97%, Mw = 164.2 g/mol) and L-aspartic acid (≥98%) were purchased in Merck (Darmstadt, Germany). Starch (natural potato-Starch) was bought in Avantor Performance Materials Poland S.A. (Gliwice, Poland). All reagents were applied without further purification.

l-aspartic acid (extra pure, 99.5%) was purchased from Merck, crystalline phosphoric acid (99%) was bought from Sigma-Aldrich. Cysteamine (95%), dibutylamine (HPLC grade, 99%), dithiothreitol (99%), N,N-dimethylformamide (for analysis, 99.8%) and sodium bromate (99%) were purchased from Reanal Hungary. 6-monodeoxy-6-monoamino-beta-cyclodextrin hydrochloride (MABCD) was obtained as a gift from CycloLab Cyclodextrin Research and Development Laboratory Ltd. (Budapest, Hungary). In the gel formulation, phosphate-buffered saline (PBS) solution of pH = 7.4 was prepared by dissolving 8 g dm⁻³ NaCl, 0.2 g dm⁻³ KCl, 1.44 g dm⁻³ Na₂HPO₄·2H₂O and 0.12 g dm⁻³ KH₂PO₄ in distilled water, the pH was adjusted with 0.1 M HCl. In the mucoadhesive measurements, mucin (porcine gastric mucin type II) was purchased from Sigma-Aldrich, mucin dispersions were prepared with PBS, stirred for 1 h and left for overnight in a refrigerator. The active agent prednisolone was obtained as a gift from TEVA Hungary Ltd. (Gödöllő, Hungary).