Pericardial scaffolds have a wide spectrum of clinical applications ranging from patches for vascular reconstruction and abdominal wall defects to bioprosthetic heart valves. The current gold standard of tissue preparation involves disinfection and cross-linking using glutaraldehyde. However, glutaraldehyde-associated toxicity as well as rapid calcification and premature graft failure represent the major modes of failure.1 Therefore, a variety of alternative strategies for tissue conservation have been pursued. However, none of those strategies has substituted glutaraldehyde as the method of choice yet. Furthermore, safe sterilization procedures that are nondetrimental to the tissue's functionality are scarce. We have developed a novel procedure to stabilize and sterilize (S) acellular pericardial scaffolds combining photo-initiated ultraviolet cross-linking (U) with low-energy electron irradiation (LEEI). This SULEEI procedure avoids the use of glutaraldehyde and utilizes LEEI as effective sterilization method. A bioburden of 5.1 × 105 ± 4.6 × 105 viable bacteria could be successfully inactivated by SULEEI treatment applying a surface dose of 30.6 ± 2.8 kGy. By challenging high-density polyethylene foil stacks with >106 Bacillus pumilus spores in different depths and modeling the dose distribution within the scaffolds, a maximum sample thickness of 175 μm was determined for successful sterilization. Moreover, SULEEI treatment appeared nondetrimental to the ultimate tensile strength (17.6 ± 8.6 MPa vs. 17.4 ± 9.6 MPa) of the scaffolds compared with glutaraldehyde-treated pericardia. Cell number and overall metabolic activity of human endothelial cells were significantly higher on SULEEI-treated pericardia compared with control samples. In contrast, no cell proliferation could be detected on glutaraldehyde-treated pericardia. Thus, the SULEEI procedure may be a promising novel procedure for glutaraldehyde-free tissue preparation for pericardium-based tissue transplants and tissue engineering.Impact StatementPericardium-based tissue transplantation is a lifesaving treatment. Commercial glutaraldehyde-treated pericardial tissue exhibits cytotoxicity, which is associated with the accelerated graft failure. Replacement of glutaraldehyde has been suggested to overcome those drawbacks. In this study, we report a toxin-free method that combines tissue stabilization with a terminal sterilization. Our data indicate that the SULEEI procedure, which is part of an issued patent, may be a promising first step toward glutaraldehyde-free pericardium-based tissue transplants. Thus, our results may contribute to improving cardiovascular treatment strategies.

Background Bovine pericardium is the major natural source of patches and aortic valve substitutes in cardiac repair procedures. However, long-term tissue durability and biocompatibility issues lead to degeneration (e.g., calcification) that requires reoperation. Tissue preparation strategies, including glutaraldehyde fixation, are reasons for the deterioration of pericardial tissues. We describe a pretreatment procedure involving sterilization and cross-linking combined with ultraviolet (UV) irradiation and low-energy electron irradiation (SULEEI). This innovative, glutaraldehyde-free protocol improves the mechanical aspects and biocompatibility of porcine pericardium patches. Methods We adopted the SULEEI protocol, which combines decellularization, sterilization, and cross-linking, along with UV irradiation and low-energy electron irradiation, to pretreat bovine pericardium. Biomechanics, such as ultimate tensile strength and elasticity, were investigated by comparing SULEEI-treated tissue with glutaraldehyde-fixed analogues, clinical patch materials, and an aortic valve substitute. Histomorphological and cellular aspects were investigated by histology, DNA content analysis, and degradability. Results Mechanical parameters, including ultimate tensile strength, elasticity (Young's modulus), and suture retention strength, were similar for SULEEI-treated and clinically applied bovine pericardium. The SULEEI-treated tissues showed well-preserved histoarchitecture that resembled all pericardial tissues investigated. Fiber density did not differ significantly. DNA content after the SULEEI procedure was reduced to less than 10% of the original tissue material, and more than 50% of the SULEEI-treated pericardium was digested by collagenase. Conclusion The SULEEI procedure represents a new treatment protocol for the preparation of patches and aortic valve prostheses from bovine pericardial tissue. The avoidance of glutaraldehyde fixation may lessen the tissue degeneration processes in cardiac repair patches and valve prostheses.