Controlled self-assembly of natural proteins into hierarchically structured functional materials

Change log
Kamada, Ayaka 

Protein self-assembly offers key strategies for nature to generate high-performance and multifunctional proteinaceous materials. Inspired by nature’s approach, there is growing interest in the exploitation of self-assembled protein structures as a basis of artificial protein materials. To this end, this thesis aims to gain a better understanding of the nanofibrillar self-assembly of natural proteins and to develop new methods to utilise self-assembled structures for novel protein materials. The approach demonstrated here enabled an enhanced level of control over multi-scale protein assembly, leading to the creation of functional protein hydrogels, fibres and films, making them suitable for a wide range of applications.

The first part of the thesis focuses on investigating the molecular self-assembly mechanism of silk fibroin, a natural protein used by silkworms to generate fibres. Through applying kinetic analysis, I demonstrated that the self-assembly process is dominated by a secondary process in which the formation of new fibrils is catalysed by the existing aggregates in an autocatalytic manner. In addition, I showed that hydrodynamic shear applied to protein molecules accelerates self-assembly by promoting primary nucleation. The results provided useful insights into nature’s strategies for controlling the assembly of proteins into materials.

The second part describes the fabrication of silk-inspired protein-based microfibres using nanofibrils obtained from a milk-derived protein, β-lactoglobulin. The fibres were generated using a miniaturized fluidic device, which enables precise control of the hydrodynamic forces applied to the nanofibrils and thus replicates the natural spinning process of silk. By varying the flow rates, the degree of nanofibril alignment was tuned, leading to an orientation index comparable to that of native silk. It was further confirmed that this increased level of alignment led to enhanced mechanical properties in the fibre.

The last part demonstrates a scalable method to induce and control the self-assembly of plant-derived proteins. Plant-derived proteins are attractive protein feedstocks as they can be sourced in a sustainable and low environmental impact manner. However, their poor water solubility poses fundamental challenges for controlling their self-assembly. The method developed in this project enables the dissolution of plant-derived proteins in aqueous solution with concentrations as high as 10w/v%, which can then undergo self-assembly into intermolecular β-sheet rich networks. The approach was further exploited to fabricate nanostructured hydrogels and films with advantageous mechanical and optical properties.

Knowles, Tuomas
Protein self-assembly, Protein nanofibrils, Bio-inspired materials, Biomimetics, Silk fibroin self-assembly, Microfluidics, Plant-based proteins
Doctor of Philosophy (PhD)
Awarding Institution
University of Cambridge
Murata Scholarship, Japan Student Services Organization, Heiwa Nakajima Foundation