Silk : a biopolymer for engineering nanoparticles

Student thesis: Doctoral Thesis

Abstract

Silk from Bombyx mori has a robust clinical track record for load bearing applications. It was hypothesized that the biopolymer silk would also have the potential to generate nanoparticles. Therefore, the aim of this thesis was to manufacture and assess these silk nanoparticles for drug delivery. First, silk nanoparticles were produced from aqueous silk stock by nanoprecipitation. The resulting nanoparticles were then surface grafted with polyethylene glycol (PEG), yielding nano-sized particles (104 to 116 nm) with a negative zeta potential (-56 to -46 mV). PEGylated silk nanoparticles showed a reduced macrophage response, high aqueous stability but low drug loading capacity. The drug loaded PEGylated silk nanoparticles showed improved cytotoxicity, cellular uptake and intracellular dynamics in cancer cells (Chapter 2). Next, the fate of native and PEGylated silk nanoparticles during various enzyme treatments was investigated to demonstrate the elimination of nanoparticles after administration. Native and PEGylated silk nanoparticles were degraded in protease enzymes in vitro, but showed faster degradation in protease XIV (degraded after a 1-day treatment) and slower degradation in papain and ex vivo lysosomal enzymes (degraded after a 5-day treatment) (Chapter 3). Next, the NanoAssemblrTM microfluidic system was exploited to manufacture silk nanoparticles. Silk nanoparticles were generated using the commercial microfluidic chip that allowed rapid mixing of both the aqueous silk solution and the organic solvent.This microfluidic system allowed tuning of silk nanoparticle characteristics through adjusting processing parameters such as the total flow rate, the total flow rate ratio and solvent selection (Chapter 4). Finally, computational modelling was applied to better understand the impact of silk conformation and its subsequent interaction with the model drug doxorubicin at the atomic level. Well-tempered metadynamics, an enhanced sampling method for molecular dynamics simulations was used to explore the free energy surface of an amorphous-crystalline silk model structure in water. Next, silk with optimised secondary structures were used to study the interaction of the model drug doxorubicin at both pH 4 and 7.4. Here, the N-terminus was the predominant domain responsible for drug loading and release (Chapter 5). Overall, this thesis demonstrated that silk is a versatile biopolymer to generate nanoparticles for drug delivery (Chapter 6).
Date of Award12 Apr 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorPhilipp Seib (Supervisor) & Blair Johnston (Supervisor)

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