Wang, Yuexin; (2025) Design and fabrication of thermo-responsive electrospun micro/nano fibres. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In recent years, there has been a surge in interest in stimuli-responsive nanocarriers, which have the potential for targeted delivery of various bioactive compounds in the pharmaceutical and biomedical fields. The background details to the project are set out in detail in Chapter 1. In Chapter 2, formulations have been investigated based on poly(Nisopropylacrylamide) (PNIPAM) and polycaprolactone (PCL). PNIPAm/PCL nanofibre scaffolds were produced via electrospinning, showing biocompatibility and temperature-responsive behaviour. The PNIPAM/PCL combination gave more rapid drug release rates at elevated temperatures, despite PNIPAM being known for its lower critical solution temperature behaviour. There was also minimal difference in the release profiles at 37 and 43 ºC, indicating that the application of local hyperthermia would likely not be suitable to trigger accelerated drug release. Nonetheless, PNIPAM/PCL nanofibre scaffolds remained stable, biocompatible, and exhibited temperatureresponsive characteristics in cell culture, making them potentially suitable for applications including tissue engineering. Next the upper critical solution temperature (UCST) polymer poly(acrylamideco- acrylonitrile) (AAm-AN) was explored. Two systems with different molecular weight and monomer ratios were prepared and fully characterised in Chapter 3. The two materials were termed AAm-AN1 (MW 114 kDa, UCST 34.3 ºC) and AAm-AN2 (higher AN content; MW 243 kDa, UCST 41.2 °C). Chapter 4 then explores electrospun formulations based on AAm-AN1 and PCL. Uniform fibres with the drug largely molecularly dispersed in the polymer carrier were generated. Temperature-sensitive behaviour was observed in the drug release profiles, with dissolution rates increasing with higher buffer temperatures. However, there was again minimal differences seen between 37°C and 43°C. in Chapter 5, mono-axial and coaxial electrospinning of AAm-AN 2 with PCL was performed. Carmofur and methotrexate were loaded in the systems as model drugs, and cylindrical fibres obtained. As in previous chapters, in most cases the fibres comprise amorphous solid dispersions. Both the monoaxial and coaxial systems give heat-responsive drug release during dissolution tests, with much clearer differentiation in behaviour between 37 and 34 ºC than in previous chapters. In vitro cell culture studies demonstrated non-toxicity of the placebo fibres to healthy cells but that the drug-loaded fibres were highly toxic to cancerous cells. The thesis finishes with a conclusion and future work in Chapter 6. In summary, this study successfully develops temperature-sensitive nanofibres using thermo-responsive polymers, showcasing their potential for advanced drug release and tissue engineering applications.

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