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

Biomaterials have become integral to healthcare, with their applications evolving continuously. They have driven significant advancements in wound healing, tissue engineering and biomedical engineering. Extensive research has been conducted on the properties of polymers and the optimisation of manufacturing processes to enhance their performance. This work has facilitated the optimisation, fabrication and characterisation of advanced biomaterials tailored for improved biomedical applications. The first part of this work has focused on developing a polymer-based nanodelivery system with antimicrobial properties to address the pressing demand for effective wound care solutions. Polyethylene oxide (PEO) has garnered significant interest in biomedical applications owing to its non-toxicity, hydrophilicity, and biocompatibility. Pressurised gyration (PG) was employed as a spinning method to fabricate water-soluble PEO nanofibre meshes incorporating two distinct types of de novo antimicrobial peptides (AMPs), M2 and AMP2, using distilled water. The effect of varying applied PG working pressure on fibre diameter and morphology was reported. At 0.3 MPa, nanofibre meshes ranging in the diameters of 200–250 nm was successfully manufactured, demonstrating significant bacterial viability against Staphylococcus epidermidis using AMP2 peptides at 105 µg/ mL. The nanofibres were optimised for the rapid release of peptides, providing a promising biologically active solution for next-generation wound dressings. This research highlights the potential of AMP-incorporated nanofibres as effective antimicrobial nanodelivery systems, further advancing the role of biomaterials in tissue engineering and wound care. The subsequent section of this study investigated the novel fabrication of biomaterial-based nanomaterial-polymeric fibre composite scaffolds using polycaprolactone (PCL) integrated with in situ mineralised montmorillonite nanoclay (MMT–Clay) and hydroxyapatite nanoclay (HAP MMT–Clay), serving as non-union bone defect fillers for bone tissue regeneration. Scaffolds act as physical platforms that support cell attachment, proliferation, and differentiation, promoting tissue regeneration. PCL is an excellent biomaterial for scaffold fabrication due to its tuneable biodegradability, high mechanical strength, and capacity to replicate the microenvironment of native tissue. Utilising the PG process, PCL HAP–Clay and PCL HAP MMT–Clay fibres were successfully generated at 2–5 w/w %. The 3D nanoclay PCL composite scaffolds subsequently enhanced bone tissue formation, cell viability, and proliferation, indicating their potential in bone tissue engineering. The polymer fibre scaffolds exhibited excellent biocompatibility, facilitating the growth and differentiation of mesenchymal stem cells (MSCs) and osteoblasts. Notably, the PCL HAP MMT–Clay fibre scaffolds (5 w/w %) significantly increased cell viability, osteogenic differentiation, extracellular matrix (ECM) formation, and collagen synthesis compared to control PCL fibres. Additionally, the intracellular alkaline phosphatase (ALP) levels were increased in the presence of PCL HAP MMT–Clay composite scaffolds, indicating improved osteogenic differentiation of MSCs. These findings highlight the potential of manufacturable composite nanoclay-polymer fibres as promising scaffolds for bone tissue engineering applications, offering new outlooks for regenerative medicine. While singular polymeric fibres demonstrated considerable efficacy as functional biomaterials, they also possessed limitations. Binary polymer systems enable the modification of each material, resulting in an optimal combination of polymer properties and enhanced capabilities in biomedical engineering. Consequently, PEO and PCL were combined in a blend system at ratios of 14:1–1:4, dissolved in chloroform, and pressure-spun into fibre composites. The resulting polymer solutions were characterised for their rheological and surface tension properties. Scanning electron microscopy (SEM) was employed to examine the effects of increasing the PEO ratio in the binary PCL:PEO polymer systems, resulting in controllable morphologies and topographies. It was noted that an increase in the PEO ratio resulted in a decrease in the average fibre diameters, which ranged from 3.4 ± 1.8 µm–1.5 ± 0.4 µm. Binary fibre composites were subjected to swelling tests after being immersed in deionised water for 15–60 min, with the effect of PEO on swelling behaviour assessed using an optical microscopy. The evaluation of solution properties, morphology, and swelling behaviour led to the identification of an optimised binary polymer formulation. Ibuprofen (IBP) was integrated into singular PEO, PCL and optimised PCL:PEO formulations. Fourier transform infrared (FTIR) spectroscopy was conducted on all fibre composites to identify the presence of individual materials. In vitro drug release studies were carried out on PEO–IBP, PCL–IBP, and PCL:PEO–IBP fibre composites to further assess the efficacy of the different polymer systems and their potential for biomedical engineering. In vitro studies on PEO–IBP exhibited an instant release rate of 90 % in 40 s, attributed to the polymer’s hydrophilic nature. While the rapid wetting and dissolution characteristics of PEO–IBP composites provide benefits for certain applications, they pose challenges for applications needing controlled release, rendering PEO composites less suitable on their own. The swift dissolution leads to a rapid release of IBP, resulting in an immediate period of action, which may be undesirable in situations that require sustained drug release over longer duration. In contrast, PCL–IBP and PCL:PEO–IBP exhibited a sustained release of 87–96 % over 72 h, respectively. This study illustrates that the binary polymer system provides a compelling approach for optimising polymer properties by addressing the limitations of individual materials. This innovative PG-based blend system can be utilised to develop scaffolds for heterogeneous tissue engineering, facilitating effective therapeutic release and exhibiting antimicrobial properties.

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