Cl 1000l uv crosslinker

Gelatin methacryloyl (gelMA) was synthesized according to a previously published protocol, as used as a platform to produce hydrogels for 3D tissue culture (Melchels et al., 2014 (link)). Briefly, gelatin type A (obtained from porcine skin; Sigma-Aldrich) in PBS was functionalized with methacrylic anhydride groups to achieve an 80% degree of functionalization of the available primary amines. Subsequently, a 10% w/v solution of gelMA was supplemented with 0.1% w/v 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959; BASF, Ludwigshafen, Germany) as a photoinitiator. AuCPCs of each donor were expanded to passage 4 and were encapsulated in the hydrogel at a density of 1.5 × 10⁷ cells/mL at 37°C. The cell-laden gel was cast into a custom-made Teflon™ mold and subsequently subjected to UV-radiation for 15 minutes (wavelength λ = 365 nm, intensity E = 7 mW/cm², at height of 12 cm; CL-1000L UV Crosslinker, UVP, UK) to allow free-radical polymerization crosslinking of the hydrogel, producing cylindrical samples (diameter = 6 mm, height = 2 mm). As controls, cell-free hydrogel samples were prepared under the same conditions. All samples were cultured in chondrogenic differentiation medium for 1, 28 and 56 days at 37°C and 5% CO² and receiving fresh media 3 times per week.