The structure-property relationships of biological materials such as amyloid fibrils are important to developing therapeutic strategies for amyloid-related diseases. The mechanical characterization of biological materials can provide insight into such relationships. In this study, polymorphic human islet polypeptide (hIAPP) fibrils were constructed with molecular modeling, and a constant-force bending simulation was performed to characterize the different mechanical behaviors of polymorphic hIAPP protofibrils. Our simulation results showed that, owing to their different intramolecular interactions, the fracture times of polymorphic hIAPP protofibrils depend on polymorphic structures. (C) 2014 Elsevier B.V. All rights reserved.