▪ Abstract  The term bone refers to a family of materials, all of which are built up of mineralized collagen fibrils. They have highly complex structures, described in terms of up to 7 hierarchical levels of organization. These materials have evolved to fulfill a variety of mechanical functions, for which the structures are presumably fine-tuned. Matching structure to function is a challenge. Here we review the structure-mechanical relations at each of the hierarchical levels of organization, highlighting wherever possible both underlying strategies and gaps in our knowledge. The insights gained from the study of these fascinating materials are not only important biologically, but may well provide novel ideas that can be applied to the design of synthetic materials.

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We report the observation of single nanotube fragmentation, under tensile stresses, using nanotube-containing thin polymeric films. Similar fragmentation tests with single fibers instead of nanotubes are routinely performed to study the fiber-matrix stress transfer ability in fiber composite materials, and thus the efficiency and quality of composite interfaces. The multiwall nanotube-matrix stress transfer efficiency is estimated to be at least one order of magnitude larger than in conventional fiber-based composites.

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The force required to separate a carbon nanotube from a solid polymer matrix has been measured by performing reproducible nanopullout experiments using atomic force microscopy. The separation stress is found to be remarkably high, indicating that carbon nanotubes are effective at reinforcing a polymer. These results imply that the polymer matrix in close vicinity of the carbon nanotube is able to withstand stresses that would otherwise cause considerable yield in a bulk polymer specimen.

Microscale aggregate formation, resulting from high intrinsic filler attractions, is one of the major issues in nanocomposite preparation and processing. Herein, the dispersive effects achieved by a wide range of surface‐active agents, as well as surface oxidation and functionalization, are investigated. The aim of our research is to form a uniform, multiwalled carbon nanotube (MWNT) distribution in water‐soluble (poly(ethylene glycol)) and water‐insoluble (polypropylene) polymers. In order to understand the surface‐charge‐related stability of the treated nanotubes solutions, zeta‐potential measurements are applied. Quantification of the state of the MWNT dispersion is derived from particle‐size analysis, while visual characterization is based on optical and electron microscopy. To estimate the nucleating ability of the surface‐modified carbon nanotubes, the temperature of crystallization and the degree of crystallinity are calculated from differential scanning thermograms. Finally, we suggest general guidelines to produce uniform MWNT dispersions using a dispersive agent and/or surface treatment in water‐soluble and water‐insoluble polymers.

Nanocomposites based on semi‐crystalline poly(vinyl alcohol) (PVA) and well‐dispersed chemically functionalized single‐walled carbon nanotubes are combined through simple mixing. The interaction between the nanotubes and the polymer matrix is studied using optical and thermal methods. Significant enhancement of the mechanical properties is obtained for the functionalized‐nanotube‐based composites. These results imply that promoting nanotube dispersion and strong interfacial bonding through adequate functionalization of nanotubes improves the load transfer from the matrix to the reinforcing phase.