"Drug-delivering" biopolymer – Caf1

Abstract

The thesis explores biopolymer-based hydrogel in the ever-growing “drug delivery” field – an approach to deliver pharmaceutical compounds to their targeted sites safely and effectively by tailoring the carrier for specific applications. This work reports the initial finding of Caf1 as a drug delivery vehicle to deliver drug molecules. Caf1 is a biopolymer produced by Yersinia pestis, the bacterium known for bubonic plague. The biopolymer act as a cloak for the bacterium shielding it from macrophages, and it has properties close to the extracellular matrix, which makes the material ideal for drug delivery due to its biocompatibility. A Caf1 protein polymer comprises several Caf1 subunits (monomers) linked together via donor strand exchange, where one subunit donates its N-terminal -strand for acceptance on the adjacent subunit to form a polymer chain. This key mechanism is unique from this class of protein. Herein, this thesis investigates the usability of crosslinked Caf1 hydrogels for drug delivery applications and the associated challenges that comes with it. Chapter 1 explores the use of biopolymers for drug delivery in literature and proposes strategies that utilise Caf1 polymer for “drug delivery” purposes. Chapter 2 explores the methodology to afford Caf1 hydrogel suitable for uploading model drugs from small molecules to large biomolecules and analyses the subsequence release profiles to further understand the mechanism that took place. Further, this work proposes several drug-loading approaches for loading biomolecules by utilising the unique reversible nature of Caf1 protein linkages where the Caf1 protein linkage can undergo thermal unfolding and reform. Chapter 3 proposes a stimulus-responsiveness mechanism for Caf1 hydrogel by modifying native Caf1 polymer with cysteine residues, inducing a cleavable disulfide bridge within the hydrogel network, which will lead to the release of the model drug. Further, this chapter investigates a novel mosaic hydrogel consisting of two types of Caf1 subunit containing both Caf1WT and Caf1Cys subunits to improve the mechanical properties of a stimulus-responsiveness Caf1 hydrogel. Chapter 4 describes the term “nanogel” and exploits synthetic approaches to form such Caf1 nanogels, that can be functionalised with specific groups for specific application purposes. In conclusion, these findings laid a fundamental bedrock for the consequent development of Caf1 polymer; for release kinetics, drug loading, stimuli-responsive and nanoparticles, which showcases the versatility of Caf1 as an exciting novel material for biomedical purposes