All solvents and chemicals used in this study were purchased at Fisher Scientific (Schwerte, Germany), Carl Roth (Karlsruhe, Germany), VWR (Darmstadt, Germany) or Sigma-Aldrich (Steinheim, Germany). Water was purified with a Purelab flex 2 system (ELGA LabWater Veolia Water Technologies, Celle, Germany). Cell culture media and supplements were obtained from PAN-Biotech GmbH (Aidenbach, Germany), Merck (Darmstadt, Germany) and Thermo Fisher Scientific (Dreieich, Germany). Hordenine with a purity ≥ 97% was purchased from Sigma-Aldrich (Steinheim, Germany).
Rat tail collagen was isolated according to a previous protocol by Franke and co-workers [17 (link)] with some modifications. After cleaning and sterilizing the rat tails in 70% (v/v) ethanol for 30 min, the rat tails were clamped at the tail end with hemostatic forceps, bent, and the collagen fibers were obtained by slowly pulling them out. The collagen fibers were then incubated with sterile 0.1% acetic acid for 24 h at 4°C to dissolve them. The suspension was centrifugated at 5000 rpm for 30 min, and the supernatant was collected. The pellet was mixed with 0.1% acetic acid, centrifugated, and the supernatants combined. Finally, the protein concentration of the solution was determined.
Rat tail collagen was isolated according to a previous protocol by Franke and co-workers [17 (link)] with some modifications. After cleaning and sterilizing the rat tails in 70% (v/v) ethanol for 30 min, the rat tails were clamped at the tail end with hemostatic forceps, bent, and the collagen fibers were obtained by slowly pulling them out. The collagen fibers were then incubated with sterile 0.1% acetic acid for 24 h at 4°C to dissolve them. The suspension was centrifugated at 5000 rpm for 30 min, and the supernatant was collected. The pellet was mixed with 0.1% acetic acid, centrifugated, and the supernatants combined. Finally, the protein concentration of the solution was determined.