Afshar, Ayda; (2023) Using Pressurised Spinning to Fabricate Multifunctional and Binary Polymeric Fibres for Biomedical Applications. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Healthcare applications have long made use of biomaterials, which are continually evolving. Tissue engineering, wound healing, and biomedical engineering have each been revolutionised by biomaterials. Polymeric properties and manufacturing procedures have been researched, fabricated, and characterised for their performance. The first part of this work has addressed the demand for suitable polymer-based nanodelivery system with antimicrobial properties to overcome challenges in wound care. Polyethylene oxide (PEO) has attracted considerable interest in biomedical applications due to its non-toxicity, hydrophilicity and biocompatibility. Pressurised gyration (PG) was utilised as a technique to fabricate water-soluble PEO nanofibre meshes incorporated with two different types of de novo antimicrobial peptides (AMPs), M2 and AMP2, using distilled water. The effect of varying applied PG working pressure, along with the impact on the fibre diameter and morphology was reported. At 0.3 MPa, nanofibre meshes ranging in the diameters of 200-250 nm were successfully manufactured, and significant bacterial viability against Staphylococcus epidermidis was achieved utilising AMP2 peptides at 105 µg/ mL. Nanofibres were tuned for the rapid release of peptides which represent a viable biologically active solution to next-generation wound dressings. The subsequent section of this study focused on a novel fabrication of biomaterial-based nanomaterial-polymeric fibre scaffold composites using polycaprolactone (PCL) incorporated with in situ mineralised montmorillonite nanoclay (MMT-Clay) and hydroxyapatite nanoclay (HAP MMT-Clay) which can serve as non-union bone defect fillers for bone tissue regeneration. Scaffolds are physical substrates for cell attachment, proliferation, and differentiation, ultimately leading to the regeneration of tissues. As a biomaterial for scaffold production, PCL provides various advantages, including tuneable biodegradation and relatively high mechanical toughness. Using the PG process, PCL HAP-Clay and PCL HAP MMT-Clay fibres were successfully generated at 2-5 w/w %. The 3D nanoclay PCL fibre scaffolds were able to enhance bone tissue growth, cell viability, and proliferation. It was demonstrated that the polymer fibre scaffolds were biocompatible, and the mesenchymal stem cells (MSCs) and osteoblasts were able to thrive and differentiate on the fibre scaffold composites. A significant increase in cell viability, osteogenic differentiation, extracellular matrix (ECM) formation, and collagen formation were observed with the PCL HAP MMT-Clay fibre scaffolds (5 w/w %) compared to the control PCL fibres. Further, the intracellular alkaline phosphatase (ALP) levels were increased with PCL HAP MMT-Clay fibre scaffolds, indicative of enhanced osteogenic differentiation of MSCs. This research demonstrated a promising outlook for the future of manufacturable composite nanoclay polymer fibres incorporated as scaffolds for bone tissue engineering applications. Although singular polymeric fibres performed significantly as functional biomaterials, they were not without limitations. Binary polymer systems allow modification of individual materials and create an optimum combination of both polymer properties with advanced biomedical engineering capabilities. Thus, PEO and PCL were combined in a blend system in the ratios of 14:1-1:4 dissolved in chloroform and pressure-spun into fibre composites. The resulting polymer solutions were characterised for their rheology and surface tension properties. Scanning electron microscopy (SEM) was utilised to analyse the influence of increasing PEO ratio in the binary PCL:PEO polymer systems and achieved controllable morphologies and topographies. It was observed that an increase in PEO ratio resulted in a decrease in the average fibre diameters, ranging at 3.4 ± 1.8 µm – 1.5 ± 0.4 µm. Binary fibre composites were subjected to swelling test, having been immersed in deionised water for 15-60 min, and the impact of PEO on swelling behaviour was analysed using an optical microscopy. The comparison of solution properties, morphology, and swelling behaviour resulted in the establishment of an optimised binary polymer composition. Caffeine (CAF) was integrated into singular PEO, PCL and optimised binary PCL:PEO polymer systems. Fourier transform infrared (FTIR) spectroscopy was performed on all fibre composites to detect the presence of individual materials. In-vitro drug release studies were performed on PEO-CAF, PCL-CAF, and PCL:PEO-CAF fibre composites to further evaluate the efficacy of various polymer systems and their promise for biomedical applications. During the 24-96 h incubation period, PEO possessed a rapid release profile of 47–67 % due to its hydrophilic nature. While the rapid wetting and dissolution characteristics of PEO-CAF composites offer multiple advantages for certain applications, they impose limitations for other drug delivery systems, making PEO composites undesirable on their own. The swift dissolution can result in a rapid release of CAF, resulting in an instantaneous period of action. In situations requiring sustained drug release over an extended period of time, such behaviour may be unfavourable. PCL displayed a slower and more sustained release profile of 39–55 % attributed to its hydrophobicity, slow degradation rate, and resistance to water penetration. However, due to the presence of PEO in the binary polymer matrix, the PCL:PEO composites achieved an improved CAF release profile of 44–58 %. This study demonstrated that the binary polymer system offers an intriguing strategy for tailored polymer properties by overcoming the shortcomings of individual materials. This is an innovative PG-based blend system that can be utilised to create scaffolds for heterogeneous tissue engineering, remarkable therapeutic release, and antimicrobial attributes.

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