Open Access

Show Abstract ▼

Abstract: Stimuli-responsive polymeric vesicles offer a versatile platform for mimicking dynamic cell-like behaviors for synthetic cell applications. In this study, thermally responsive polymeric droplets derived from poly(ethylene oxide)-poly(butylene oxide) (PEO-PBO) polymersomes, aiming to create synthetic cell models that mimic key biological functions are developed. Upon heating, the nanoscale vesicles undergo fusion, transforming into sponge-like microscale droplets enriched with membrane features. By modulating the temperature, these droplets display dynamic properties such as contractility, temperature-induced fusion, and cargo trapping, including small molecules and bacteria, thereby demonstrating their ability to dynamically interface with biological entities. The findings demonstrate the potential of our sponge-like droplets in synthetic cell applications, contributing to the understanding of PEO-PBO polymersomes’ unique characteristics, expanding the capabilities of synthetic cell structures, and representing an exciting possibility for advancing soft matter engineering to cell-like behaviors.

Show Abstract ▼

Abstract: Geopolymers are promising materials for safe immobilisation and disposal of complex radioactive waste streams. This work investigates the effect of Sr incorporation and alkali-activator chemistry on 1) geopolymer chemistry, phase assemblage and nanostructure, 2) chemical binding mechanism of Sr2+ into the aluminosilicate framework of (N,K)-A-S-H gels in geopolymers, and 3) mass transport of Sr2+ during leaching, using high-field solid-state nuclear magnetic resonance spectroscopy and synchrotron-based X-ray absorption spectroscopy measurements. All geopolymers studied comprise a fully polymerised, X-ray amorphous Al-rich (N,K)-A-S-H type gel. Si exists predominantly in tetrahedral Q4(4Al) and Q4(3Al) sites and Al exists in tetrahedral sites, resulting in a net negative charge that is balanced by Na+ and/or K+ in extra-framework sites. Sr2+ was incorporated into extra-framework sites within (N,K)-A-S-H gels, without altering the local structure of the aluminosilicate framework by directly substituting for both Na+ and K+ in charge-balancing sites to form a (N,K,Sr)-A-S-H gel, at loadings equal to or below Sr/Na = 0.005. Above this limit, SrCO3 is formed, and the geopolymers simultaneously chemically bind Sr within a (N,Sr,K)-A-S-H gel, and physically encapsulate excess Sr as SrCO3. These findings have significant implications for use of geopolymers as materials for encapsulation and/or immobilisation of radioactive waste containing 90Sr.

Show Abstract ▼

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.

Open Access

Show Abstract ▼

Abstract: Laser powder bed fusion (LPBF) of Polyamide 12 (PA12) using a near-infra-red (NIR) beam is largely unexplored; therefore, the beam-matter interaction, evolution mechanisms of the melt pool and defects remain unclear. Here, we employed a combination of in situ synchrotron X-ray imaging, ex situ materials characterisation techniques, and high-fidelity process simulations to study these behaviours during LPBF of PA12. Our results demonstrate that the NIR absorption of PA12 can be improved by 600 times through powder surface modification with C, P and Al species. In situ X-ray images reveal that the PA12 powders undergo melting, viscous merging, volume expansion, warping, solidification, and shrinkage before forming a solid track. Our results uncover the bubble evolution mechanisms during LPBF of PA12. During laser scanning, the high-energy laser beam produces organic substances/vapours which are trapped inside bubbles during viscous merging. These bubbles continue to shrink due to vapour condensation as the polymer cools under a cooling rate range of 200 - 600 K s−1. Using the collected data, we have developed a data-driven bubble shrinkage criterion to predict the bubble shrinkage coefficient using the bubble half-life, improving the build quality of LPBF polymeric parts.

Open Access

Show Abstract ▼

Abstract: A series of novel chain-extended polyurethanes (CEPUs) featuring degradable sulfonyl ethyl urethane chain-extenders that permit degradation under base-triggered conditions to afford “debond-on-demand” elastomeric adhesives are reported. Exposure of the CEPUs to tetra-butylammonium fluoride (TBAF) triggered the degradation of the sulfonyl ethyl urethane chain-extenders. Lap shear adhesion tests of the CEPUs exposed to TBAF revealed reductions in shear strength of up to 65% for both aluminum and glass substrates, from 2.18 to 0.76 MPa and from 1.13 to 0.52 MPa, respectively. The selective depolymerization of these polymers makes them suitable candidates as debondable binders for inkjet inks and coatings, enabling removal of inks and adhesive residues from substrates before they enter the recycling process, to prevent surface contaminants decreasing the quality of the recycled material.