351. Confining, Stretching and Aligning Fibrillar Biopolymers
- Author
-
Smith, Kathleen Beth, Mezzenga, Raffaele, and Isa, Lucio
- Subjects
Material sciences ,Technology (applied sciences) ,Physics ,cellulose nanofibrils ,polymer physics ,Life sciences ,amyloid fibrils ,ddc:570 ,AFM (atomic force microscopy) ,ddc:530 ,ddc:600 - Abstract
The main focus of this thesis lies on confining and/or pulling on two important biopolymers, i.e. cellulose nanofibrils (CNF) and amyloid fibrils. The results of these studies have implications for understanding in vivo biopolymer systems, improving the engineering of novel green materials, and furthering concepts in polymer physics. The first chapter introduces the reader to the motivations behind this work, as well as provides background information on CNF and amyloid fibrils and on the major polymer physics theories needed to devise experiments and simulations. In the second chapter, an experiment to study CNF under weak rectangular confinement is displayed. CNF were adsorbed into slits, previously obtained by thermal scanning probe nanolithography. Atomic force microscopy (AFM) coupled with single-molecule statistics allowed me to observe the alignment and self-folding of CNF under confinement. Simulations confirmed that the slits were not simply selecting a preexisting fibril population, but that the CNF were folding upon themselves as a result of the confinement. In addition, a kink preferential bending direction and an inverse correlation between kink angle and number of kinks, i.e. the fewer kinks the higher the angle, were noted. The combination of these observations provides further evidence that the kinks are a result of mechanical breaking. In the third chapter, an experiment to study subtle interplay between concurrent pulling and confinement of amyloid fibrils is explained. This was achieved by pulling the fibrils into a microcapillary device. AFM allowed a detailed single molecule statistics of the system. These results indicated that the extension of the fibrils was force- or confinement dominated at short and large length scales, respectively. This was in contrast to the order of the system, which was confinement-dominated at all length scales. Simulations both confirmed this result and brought to light the existence of other regimes. Therefore displaying the potential to tailor the system through the fine-tuning of the contribution of either effect. This data may in addition help understand in vivo amyloid phenomena in blood vessels, as well as other physiological occurrences involving the stretching and confining of semi-flexible biopolymers. The fourth chapter focuses on a technique to deposit gradients of amyloid fibrils from the liquid-liquid interface while under simultaneous compression, thus imposing macroscopic confinement. Orientation was induced perpendicularly to the compression, from isotropic to nematic. Reproducible transitions, from a monolayer to a bilayer and from a bilayer to a multilayer, were observed. This method brings forth an approach to overcome the engineering challenge associated with manipulating sticky amyloid fibrils. It further shows great potential for investigating amyloid aggregation at interfaces, which is of great relevance for understanding the propagation of certain amyloid fibril-related diseases. In conclusion, confinement successfully produced alignment, independently of the polymer and of the length scale. The effects of confinement can be modulated by adding a pulling force to the system. These experiments may not only be valid for CNF and amyloids, but show great potential for investigating divers biopolymers.
- Published
- 2019
- Full Text
- View/download PDF