Self-healing metallopolymers: From the biological model to synthetic materials

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The aim of the project is to develop bio-inspired self-healing metallopolymers based on mussel byssal threads as a biological archetype. Countless biological materials possess an adaptive self-healing response that increases the material lifetime and promotes survival of the organism. A deeper understanding of the underlying design paradigms of such natural role models at the chemical level up through higher length scales has a strong potential to inspire the development of self-healing polymers. Mussel byssus threads, for example, are protein-based biological metal-containing macromolecules that have gained much attention in recent years due to their intrinsic and autonomic self-healing abilities in the absence of living cells. Early efforts to mimic this remarkable material have shown promise; however, realizing fully functional self-healing polymers requires a deeper understanding of the structure-function properties on a chemical (molecular) level. Recent evidence demonstrates that healing in byssal threads depends on hierarchically-structured, polymer (protein) building blocks that possess reversibly breakable histidine-metal cross-links. This project brings together biochemistry and polymer chemistry to determine the structural and chemical design criteria essential to healing with the goal of integrating these principles into a synthetic polymer system. The proposed work on the biological model system consists of an in vitro chemical, structural and mechanical investigation of metal-binding peptide domains that have been previously implicated in the healing behavior of byssal threads. Additionally, studies on the assembly behavior of extracted byssal proteins will be performed, which will ideally provide inspiration for polymer processing. These studies will provide vital information and specific parameters on the structural and hierarchical order and the binding motifs that will be directly applied and utilized for the design of synthetic polymers (based on hierarchically-structured polymers with histidine). The resulting bio-inspired materials will be investigated in detail with the same methods applied for their biological counterparts in order to assess the degree to which biological concepts have been transferred. This approach will enable the direct comparison of the natural and synthetic materials under the same measurement conditions, which will furthermore allow an independent verification of biological structure-function hypotheses. Importantly, the synthetic system is more amenable to variations and alterations not possible in the biological system, which will permit the further exploration of structure-property relationships. Successful completion of the proposed project requires the close interaction of both partners and involves a synergistic exchange of ideas, competencies and characterization techniques, which will ultimately culminate in a hierarchically structured polymeric material possessing intrinsic healing behaviors.