Tris hydroxymethyl aminomethane

The adhesion of the non-crosslinked and thermally crosslinked carriers to artificial skin (VitroSkin^® N-19, IMS Inc., Cape Coral, FL, USA) was tested with TA.XTplus Texture Analyser (Stable Micro Systems, Surrey, UK) equipped with a mucoadhesion rig and a cylinder delrin^® probe (⌀ = 10 mm) at ambient conditions. A method developed by Tamm et al. [42 (link)] was used in a slightly modified format. Shortly, circular samples (⌀ = 11 mm) of the carriers were prepared and attached to the probe with an adhesive double-sided tape (Scotch™, 3M, Livonia, MI, USA). Simulated wound fluid (200 µL/sample) was pipetted on the artificial skin before the measurement. The simulated wound fluid contained 2% bovine serum albumin (Sigma-Aldrich, St Louis, MO, USA), 0.02 M CaCl₂·2H₂O (Merck, Darmstadt, Germany), 0.4 M NaCl (Sigma-Aldrich, St Louis, MO, USA), 0.08 M tris(hydroxymethyl)-aminomethane (Merck, Darmstadt, Germany) and purified water [43 (link)]. The testing conditions were set as follows: pre-test speed 0.5 mm/s, test speed 0.5 mm/s, post-test speed 5 mm/s, applied force 1 N, return distance 100 mm, contact time 60 s, and trigger force 0.05 N. Scotch™ adhesive double-sided tape and commercial wound dressing Aquacel™ (ConvaTec Inc., Reading, UK) were used as references.

Albumin (albumin egg powder, max. 8% moisture), hydrochloric acid (35–38%, d = 1.19 g/mL), potassium dihydrogen phosphate and calcium chloride were purchased in Avantor Performance Materials Poland S.A. (Gliwice, Poland). Potassium phosphate, phosphate buffered saline (PBS, form: Tablet) and tris (hydroxymethyl) aminomethane (≥99.8%, ACS reagent) were bought in Merck (Darmstadt, Germany). Alpha-MEM and the normal human dermal fibroblast cell line (NHDF) were purchased in Lonza (Lonza, Warsaw, Poland). Fetal bovine serum (FBS) was from Biomedia (EuroClone by Biomedica, Piaseczno, Poland). MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) was from Sigma-Aldrich (Poznan, Poland). All reagents were applied without further purification.

As buffer substances, sodium hydrogen carbonate and tris(hydroxymethyl)-aminomethane (both Merck KGaA, Darmstadt, Germany) were used. Tris–hydrochloride was obtained from PanReac AppliChem (Darmstadt, Germany). Sodium carbonate was obtained from Sigma-Aldrich (St. Louis, MO, USA). The PEG with a median molecular mass of 6000 was obtained from Merck KGaA (Darmstadt, Germany). All buffers were prepared with a concentration of 50 mM. For this, the appropriate amounts of associated buffer components were weighed and dissolved in $dd{H}_{2}O$ . The desired pH was achieved by varying the amount of acid and basic component for each buffer. For the 40 $\%$  (w/w) PEG 6000 and 50 $\%$  (w/w) PEG 6000 stock solution, the buffer components were first dissolved in $dd{H}_{2}O$ followed by adding the appropriate amount of PEG 6000.