Summary: The aim of this study was to design new resin formulations for blood vessel substitutes with small inner diameter that can be 3D-printed by Additive Manufacturing (AM). Commercially available urethane oligomer acrylates as crosslinking agents (CAs) with different reactive diluents (RDs) and/or thiol chain transfer agents (CTAs) were examined. It could be shown that the properties of photopolymers of carefully selected CA/RD/CTA combinations can be varied in a wide range, also to fit with those of natural blood vessels. Moreover, these materials showed good biocompatibility in in-vitro cell culture tests with endothelial cells. A new method to assess the tear resistance of the new materials in comparison with natural blood vessels was designed and established. The tear resistance of the developed photopolymers already approaches those of natural material, although there is still need of improvement. The 3D-structuring of optimized resin system succeeded. Hence AM has proven to be an ideal tool to manufacture parts with the complex structure of natural blood vessels.
The mechanical properties of materials designated for vascular tissue replacement are of crucial importance. The elastic modulus, the tensile strength as well as the suture tear resistance have to be adjusted. Our approach is to use photopolymers for artificial vascular grafts. Via the layer-by-layer photopolymerization of suitable resin formulations as performed in additive manufacturing (AM) very complex structures are realizable. Hence AM offer the possibility to create cellular structures within the artificial grafts that might favor the ingrowth of new tissue. Commercially available urethane acrylates (UA) were chosen as base monomers since urethane groups are known to have good cell-adhesion behavior and poly-UAs show adequate mechanical performance. The mechanical properties of the photoelastomers can be tailored by addition of reactive diluents (e.g. 2-hydroxyethyl acrylate, HEA) and thiols (e.g. 3,6 dioxa-1,8-octane-dithiol) as chain transfer agents to comply with the mechanical properties of natural blood vessels. To examine the suture tear resistance a new testing method has been developed. Finally, a formulation containing 30 wt% UA and 70 wt% HEA complies with the mechanical properties of natural blood vessels, shows good biocompatibility in in-vitro tests and was successfully 3D-printed with digital light processing AM.
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