Highly Modular Protein Polymers for Multivalent Display, Liquid Crystalline Bacillary Polymers and Hydrogels for in Situ Tissue Engineering

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The de novo design of bio-inspired materials with precisely controlled properties is challenging, but has potential applications in nano-biotechnology. Applications range from nanometer scaled assemblies to three-dimensional scaffolds for tissue engineering. Genetic engineering of protein-based polymers offers distinct advantages over traditionally synthesized polymers, de novo proteins can be produced with tremendous control over protein structure and properties. This enables the design of macromolecular materials with controlled structure while maintaining features of natural proteins. Molecular biology techniques were applied to create protein families that can be used as building blocks for the self-assembly of liquid crystalline materials, as multivalent scaffolds, and as tissue engineering hydrogels for regenerative medicine. In the first section, a biosynthetic strategy was developed to prepare a new class of self-assembled macromolecules - dendronized protein polymers (DPPs) - that have well-defined cylindrical shapes with controlled molecular dimensions. The DPPs consisted of an alpha-helical polypeptide core that determined the molecular length (L) surrounded by grafted wedge-shaped dendrons that controlled the diameter (D). The DPPs self-assemble to form highly ordered liquid crystalline (LC) phases, where the type of LC ordering is controlled by DPP aspect ratio (L/D) and concentration. This biophysical study of entropically-driven colloidal self-assembly shows the utility of combining biological and chemical synthetic tools towards preparation of new macromolecular blocks for nanoscale engineering. In section two, a class of modular high-molecular weight protein polymers were constructed that can be derivatized with bioactive domains to create a multivalent scaffold. In addition, the inherent monodispersity of the protein polymer building blocks allowed for accurate determination of the bioactive domain valencies. Furthermore, these protein polymers were enzymatically crosslinked into hydrogels with controlled viscoelastic properties and bioactivity. Rheological studies indicated an in situ liquid-to-gel transition within minutes and the bulk material properties were affected by crosslink density and number, and gel composition. By combining these strategies, this new class of gelling materials can be tailored to have a range of bulk properties and can be easily decorated with bioactive domains for in situ tissue engineering.

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  • 09/14/2018
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