The influence of early-phase remodeling events on the biomechanical properties of engineered vascular tissues

ObjectivesDuring the last decade, the use of ex vivo–derived materials designed as implant scaffolds has increased significantly. This is particularly so in the area of regenerative medicine, or tissue engineering, where the natural chemical and biomechanical properties have been shown to be advantageous. By focusing on detailed events that occur during early-phase remodeling processes, our objective was to detail progressive changes in graft biomechanics to further our understanding of these processes.MethodsA perfusion bioreactor system and acellular human umbilical veins were used as a model three-dimensional vascular scaffold on which human myofibroblasts were seeded and cultured under static or defined pulsatile conditions. Cell function in relation to graft mechanical properties was assessed.ResultsCells doubled in density from approximately 1 × 106 to 2 ± 0.4 × 106 cells/cm ringlet, whereas static cultures remained unchanged. The material's compressive stiffness and ultimate tensile strength remained unchanged in both static and dynamic systems. However the Young's modulus values increased significantly in the physiologic range, whereas in the failure range, a significant reduction (66%) was shown under dynamic conditions.ConclusionsAs pulse and flow conditions are modulated, complex mechanical changes are occurring that modify the elastic modulus differentially in both physiologic and failure ranges. Mechanical properties play an important role in graft patency, and a dynamic relationship between structure and function occurs during graft remodeling. These investigations have shown that as cells migrate into this ex vivo scaffold model, significant variation in material elasticity occurs that may have important implications in our understanding of early-stage vascular remodeling events.

Clinical RelevanceEngineering vessels that possess biomechanical properties are similar to natural arteries is an important research objective. Although we are beginning to understand the complex nature of tissue remodeling, little is currently known for how these early remodeling events influence the mechanical behavior of these tissues. These investigations characterized biomechanical changes that occur during early-phase remodeling events and compared the variation as a function of dynamic stimulation within an acellular human umbilical vein scaffold. Our findings showed that early remodeling events of these in vitro-engineered blood vessels have a significant effect on graft elasticity. These mechanical changes occur independently of ultimate tensile strength, suggesting early biomechanical changes may be an important marker for successful adaptation of engineered blood vessels.