Riboflavin

Bovine pericardia from two to eight years old cattle (n = 5) were kindly provided by a local slaughterhouse (Vorwerk Podemus, Dresden, Germany). Pericardia were dissected and washed in PBS to remove the connective tissue. The SULEEI treatment [12 (link),13 (link)] was performed at the Fraunhofer Institute for Organic Electronics, Electron Beam, and Plasma Technology FEP (Dresden, Germany). Briefly, the bovine pericardia were at first decellularized according to Roosens et al. [32 (link)], secondly they were incubated in a 2% dextran solution (Carl Roth GmbH & Co. KG, Karlsruhe, Germany) containing 0.1% riboflavin (Serva Electrophoresis GmbH, Heidelberg, Germany) prior to UV irradiation to crosslink collagen fibers, and lastly the pericardia were sterilized by low-energy electron irradiation (Table 1). As a control material, conventionally GA-fixed bovine pericardia (in 0.625% GA in 4.863 g/l HEPES supplemented with 2.65 g/L MgCl₂*6 H₂O, 4.71 g/L NaCl, pH 7.4 for 3 h at room temperature) were prepared. Pericardial thickness was measured using a thickness gauge Model FD50 (Käfer Messuhrenfabrik GmbH and Co. KG, Villingen-Schwenningen, Germany).
Verification of the sample sterility performed as described before (incubation in a CASO bouillon (Carl Roth GmbH & Co. KG, Karlsruhe, Germany) at 30 °C for 14 days) was the basis for the sample implementation in this study [12 (link)].

Pericardial tissue was treated with 260 μM riboflavin (Serva, Germany) and 2% dextran T500 (Carl Roth, Germany) for at least 24 h. To prevent drying, samples were placed on filter paper immersed in riboflavin/dextran solution and irradiated with 570 mJ/cm² UV (320–480 nm) within 30 min.