Navigating Networks: The Translation of Single Molecule Properties to Multi-Molecular Hierarchical Protein Networks

Hierarchical networks of semi-flexible biopolymers are ubiquitous in nature and are fascinating for their paradoxical combination of extraordinary mechanical strength and ability to grow, reshape and adapt to their environment. These biological hierarchical networks serve as inspiration for novel bio-mimic/bio-inspired materials. However, despite the ubiquity of these systems in nature it remains a fundamental challenge in soft matter physics and network theory to relate the properties of an individual building block to the collective response of a network of building blocks. Here, we utilise folded globular protein-based hydrogels constructed from maltose binding protein (MBP) and bovine serum albumin (BSA) to investigate the translation of single molecule stability and force lability, respectively, to the architectural and mechanical properties of a protein network. To achieve this, we employ a multi-modal cross length-scale characterisation approach, combining circular dichroism (CD), small-angle scattering (SAS), and rheology. Using this combined approach, we show that the single molecule stability of the building block translates to the mechanical strength of the network and that in situ force-induced unfolding is crucial in defining the architecture of folded protein networks. Furthermore, we have deconvoluted the contributions of building block thermodynamic and mechanical stabilities, illustrating that different types of stability have distinct roles in defining network properties.
This thesis has demonstrated the importance of the building block stability on network structural and mechanical properties and the necessity of a multi-modal cross-length scale approach. Furthermore, our work has shown that consideration of only the cross-linking network is not sufficient to produce a complete theory connecting the behaviour of a single building block to the collective behaviour of a network of building blocks. This is an important step in understanding, providing insight into fundamental hierarchical mechanics and a novel route to develop and tune new biomaterials for future applications.