Cysteamine

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).

Analytical grade reagents gold chloride trihydrate (HAuCl₄·3H₂O), N-hydroxysuccinimide (C₄H₅NO₃), sodium tetrahydroborate (NaBH₄), polyethylene glycol (PEG), bleomycin (BLM) and cysteamine (~95%) were obtained from (Alfa Aesar, China), (1-ethyl-3-(3-dimethylaminopropyl)-carbodimide hydrochloride) (EDC) and ethanol were purchased from (Aladdin Reagent, China). Doxorubicin was purchased from the Iranian Red Crescent Society. All stock solutions were prepared in purified water (Milli-Q Plus 185 Water Purifier, USA) having a resistivity close to 18 MΩ.cm. Experiments were conducted at room temperature. All reagents were used as provided, unless otherwise stated.