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Abstract: Ultrasound standing waves (USW) produce a force capable of displacing micrometer-sized free-flowing particles in a fluid, wherein this phenomenon is also referred to as acoustophoresis. However, the effect of acoustophoresis on dynamically changing and growing crystal networks is unclear. An example of such a system are monoglyceride (MG)-based oleogels, which are free-flowing lipids (e.g., vegetable oils) structured with a lipid-crystal network. In this work, we use MG oleogels as an example system to investigate the acoustophoretic effect on the structuration of a growing crystal network. For this purpose, multifaceted characterization is conducted utilizing optical and coded excitation scanning acoustic microscopy as well as small-angle X-ray scattering, respectively. The optical microscopy results show that USW produces local density differences of the structuring crystalline material and induces the orientation of the MG platelets. X-ray diffraction measurements confirm these findings and show a 23% average increase in MG platelet correlation length, which can be linked to platelet thickness, as well as an increase in the MG nanoplatelet surface smoothness. These findings produce a foundation for better understanding the effect of acoustophoresis in dynamically developing lipid-based materials and illuminate the mechanical changes that arise because of USW treatment.

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Abstract: A polysiloxane with tris-alkoxy-ended rod-like mesogenic side groups forms an unusually low-symmetry antiferrochiral liquid crystal, space group P1̅, consisting of distorted left- and right-handed double-helices containing alternating splay and twist sections. The unit cell contains two double-helical columns. On faster cooling, a closely related metastable orthorhombic structure is formed, symmetry Fddd, with 8 double helices per cell.

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Abstract: Mimicking the fibrous structures of meat is a significant challenge as natural plant protein assemblies lack the fibrous organisation ubiquitous in mammalian muscle tissues. In this work, wet-spun hydrogel fibres resembling the anisotropic fibrous microstructure of meat are fabricated using carboxymethyl cellulose as a model polysaccharide and sodium caseinate as a model protein which are crosslinked using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). Hydrogels and spun fibres were characterised using a combination of rheology (shear, oscillatory, and extensional), microscopy (light, polarised, and fluorescence), rheo-NMR, and X-ray diffraction. Examination of structuring behaviour under shear uncovered a relationship between enhanced biopolymer orientation along the fibre axis and a viscoelastic time-dependent ageing window for optimal hydrogel spinnability. This study provides novel rheological and structural insights into mechanisms of protein-polysaccharide assembly that may prove instrumental for development of tuneable fibres for applications in plant-based foods, tissue engineering, and biomaterials.

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Abstract: Low molecular weight gelators (LMWG) are promising candidates for biomaterials due to their unique properties such as their reversibility and ability to hold large volumes of solvent. However, issues can arise when attempting to gel these materials under conditions acceptable for cell culture. In this thesis, the aim was to develop and comprehensively characterise a LMWG system at physiological pH. We employ a variety of techniques to investigate these materials across different length scales. By doing so, we have highlighted the significance of such characterisation when developing novel non-covalent biomaterials. We outline how the dipeptide-based LMWG 2NapFF (diphenylalanine protected with a naphthalene group at the N-terminus) produces biocompatible hydrogels when crosslinked with ions present in cell culture media. We also explore the impact of heating and cooling the gelator solution prior to initiating gelation as well as the impact of adding PODS® (micron-scale proteins containing cargo molecules which are gradually released over prolonged peroids) to the system for functionalisation purposes. Our findings reveal that a heating and cooling cycle can be used to adjust the properties of the resulting network without changing the gelator itself. Moreover, it was found that PODS® had minimal effect on the properties of the hydrogel, indicating that they can enhance the bioactivity of the systems without altering the network structure. PODS Furthermore, we compare the 2NapFF hydrogels previously discussed to a Ureidopyrimidinone (UPy) supramolecular hydrogel system, consisting of a monofunctional building block and bifunctional crosslinker species. We explored the effects of combining these two systems, both with and without the UPy crosslinker. Our results show that the assembly of the combined systems is primarily driven by the UPy component. Furthermore, the UPy crosslinker plays a vital role in the self-sorting of the UPy and 2NapFF components. It was also revealed that for cells to adhere effectively, the bifunctional UPy subunit was crucial to produce a supportive network. In the final experimental chapter, we investigate the potential of the 2NapFF hydrogels crosslinked with cell culture media as bioinks for extrusion-based 3D printing. Through optimisation of the printing process, it was demonstrated that the type of media used to trigger gelation directly impacted the printability of the systems. As a result, the samples that consistently formed self-supporting structures were selected for printing macrophage cells, which remained viable within the gel after 24 hours. Bioprinting macrophages can be used in applications such as immune system and tumour microenvironment modeling.

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Abstract: Silica gels have a multitude of applications ranging from cosmetics and food science to oil and gas recovery. For proper design and application, it is important to have a thorough understanding of the underlying mechanisms of gel formation under different circumstances. The growth and structure of colloidal silica gels has been investigated using RheoSAXS to study the effect of silica concentration, NaCl concentration, temperature and shear rate. Additionally, SAXS in combination with a strong magnetic field has been applied to investigate the effect of magnetic microparticles and magnetic field on the development of the gel structure. Results indicate that the strongest effect on the gel kinetics are achieved by altering the activator concentration, here in the form of NaCl, followed by silica concentration and temperature. Small structural effects were also observed, with larger cluster sizes being produced at lower silica concentration and at higher NaCl concentration. Applying shear caused major changes both in structure as well as the macroscopic behavior of the silica, preventing the gel from reaching an arrested state, instead forming a viscous liquid. Applying a magnetic field appears to suppress the formation of larger clusters. The same effect is observed for increasing magnetic microparticle concentrations.