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MIMEFUN Report Summary

Project ID: 291364
Funded under: FP7-IDEAS-ERC
Country: Finland

Final Report Summary - MIMEFUN (Biomimetics for Functions and Responses)

To meet the demands for energy saving and to reduce the dependence from petroleum based products, materials scientists quest for ever more tunable, functional, lightweight and sustainable materials. Nature offers inspiration based on several concepts, ranging from excellent mechanical properties (e.g., a pearl of nacre and silk) to dynamic and responsive properties. However, biological materials involve major challenges due to their inherent complexity and also technical applicability. Biomimetics aims to combine the best aspects of the biological and man-made materials by mimicking the essential structures and functions of biological materials (hierarchical self-assembly and supramolecular interactions) using simpler, rationally designed, technologically relevant, and (most desirably) scalable ways. It is foreseen that biomimetic materials will have a major impact on materials science and within the next 10 years, and thus later on materials production and use.

Nature's generic strategy is to render its mechanically excellent materials. This process happens through self-assembly where the structural information that forms larger structures is "encoded" into the constituent units. Typically multicomponent structures with a high volume fraction of aligned reinforcing elements (leading to high stiffness) are embedded in a softer matrix. Under that matrix, deformation consumes fracture energy (leading to toughness). The latter aspect benefits from so-called sacrificial bonds. In Nature, such complex structures are formed by a slow growth process, which conflicts with the demand for rapid processing in technical applications.

In Mimefun, we developed nacre-mimetic materials based on commodity clays and polymers based on Nature's model of self-assembly and showed for the first time that the high toughness can be obtained with self-assembly of nanoscale reinforcing sheets for nacre-mimics. The findings pave the way for optimising the material for applications. We also developed characterization methods to study the early stages of fracture by using laser speckle imaging. The diagnostic method is foreseen to optimise the biomimetic materials. Another particularly promising material class we explored consists of nanocellulose materials, which are plant-based and have extraordinary mechanical properties and inherent sustainability. Self-assembled materials were developed based on nanocellulose, resulting in toughened nanocomposites with molecularly engineered sacrificial bonds; this approach also constructs their self-assemblies with block copolymers and nanoparticles for hierarchical structures and e.g. new optical properties. Finally, the collaboration between two ERC projects, Mimefun and Foldhalo, allowed us to develop concepts for a recently found halogen bonding to macromolecules. This now beneficially facilitates design and processing to control polymeric nanostructures and amyloids to template applications for devices.

A serendipitous finding was also made: The above self-assemblies are structures in which the energy is ideally minimised, that is, the structures are in equilibrium. Another form of self-assembly is due to energy dissipation, where energy is fed to allow structures and functions, such as feeding chemical energy in biological organisms. Due to their inherent challenges, dissipative self-assemblies have been less studied in materials science. Using ferrofluid droplets on biomimetic superhydrophobic surfaces, we observed equilibrium self-assemblies after exposing the surfaces to a static magnetic field. By imposing oscillating magnetic fields, we observed transitions to dissipative self-assemblies. The system creates new opportunities for fundamental studies related to dissipative systems and novel types of dissipative devices.

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