Characterisation and modelling of biodegradable biomedical fibres

Thesis

Biodegradable fibrous scaffolds offer a route for soft tissue repair by providing temporary mechanical support while eliminating the need for retrieval surgery. Among fabrication techniques, electrospinning enables the production of micro- and nanoscale fibrous architectures that resemble the hierarchical structure of native tendons and ligaments. The fabrication of continuous electrospun filaments further allows textile processing, such as braiding, to produce scaffolds with tailored mechanical properties. However, translating these materials into biomedical implants requires an understanding of their microstructure, mechanical behaviour, and stability under physiological and degradative conditions. This thesis addresses these challenges through a systematic experimental investigation of electrospun poly($\varepsilon$-caprolactone) filaments, combining thermal analysis, mechanical testing, topographical characterisation, and constitutive modelling. Mechanical characterisation using dynamic mechanical analysis and uniaxial tensile testing revealed an initially linear elastic response followed by plastic yielding with two-stage hardening, which was correlated with microstructural evolution observed via SEM, including fibre disentanglement, alignment, and stretching. A large-deformation viscoelastic–viscoplastic constitutive model was developed and shown to capture the filament response under non-monotonic loading. The measured mechanical response was found to depend strongly on the gripping configuration, highlighting implications on strain measurement accuracy and microstructural evolution. The thesis further examined degradation under combined thermal and mechanical loading, showing that pre-stretched filaments undergo molecular degradation over short time scales, with applied tensile loads accelerating the degradation rate. Degradation-induced microstructural changes increased stiffness and strength but reduced ductility with exposure time, demonstrating the coupling between mechanical loading, degradation kinetics, and evolving filament properties. To this end, this work establishes links between processing, structure, thermo-mechanical response, and degradation behaviour, informing the design of electrospun fibrous scaffolds for tendon and ligament repair.

Authors: Zanetti Ferreira, T

• DOI: 10.5287/ora-vy12bz9vg
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: mechanical characterisation; electrospinning; biomedical fibres; viscoelasticity; viscoplasticity; polycaprolactone
• Subjects: Engineering; Materials Science