Convergent Evolution to Engineering: Multiscale Structures and Mechanics in Damage Tolerant Functional Bio-composite and Biomimetic Materials

Northwestern University Statement of Work PI: Horacio D. Espinosa Nanoscale tests: biomaterial characterization (from individual constituents to macroscopic samples) will be achieved through a series of in-situ tests using motorized and microelectromechanical system (MEMS)-based stages with simultaneous observation by electron microscopy or Raman spectroscopy. Under this project, we will employ the in-situ electron microscopy techniques developed by Espinosa and co-workers to perform nanoscale tests that will allow direct visualization of biomaterial constituents’ deformation and failure. For the case of rod-like or plate-like constituents, tests will be carried out within a field emission SEM. For the case of polymer constituents, and in view that they can be damaged when imaged by an electron beam, we will perform Raman spectroscopy tests using a combined AFM/Raman microscope. These tests will allow an independent chemo-mechanical characterization of constituents. Raman spectroscopy has proven highly sensitive to specimen stress, defect density, atomics structure and degree of constituent alignment. With a spatial resolution of 200 nm, confocal Raman will provide spatial mapping of these characteristics along the length of the samples. Thus by performing tensile tests of rod-like or plate-like constituents using the same loading stages (motorized and MEMS-based) within a confocal Raman spectroscopy system, the characterization will be greatly enriched. Polarized illumination will be used to characterize the degree of molecular alignment within the specimens prior and during tensile loading. Pull-out tests: To obtain additional insights into interfacial and interphase properties, fracture surfaces of biomaterial specimens will be investigated. In the event that nanocrystals dangle sufficiently far from the surface, to permit contact between an AFM cantilever tip and an individual nanocrystal, nanoscale pullout tests will be conducted to characteri