Multi-scale force spectroscopy was applied to measure unfolding properties and the internal domain structure of Bombyx mori silk fibroin. We demonstrated that the complex multi-domain sequence and block design in this protein can be directly related to multi-stage unfolding behavior of the specific regions through the use of force extension measurements. These new findings suggest relationships between polymer block chemistry and mechanical features, as origins of the remarkable mechanical properties of native silk fibers in general. We observed multiple consequential unfolding of hydrophilic and hydrophobic domains with characteristics that can be directly related to known molecular dimensions of the protein backbones. Future screening and selection approaches can be envisioned to exploit this approach to optimize specific material functional features for both biopolymers and synthetic polymers in relation to sequence chemistry, a capability not currently available. (c) 2006 Elsevier Ltd. All rights reserved.