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peer-reviewed, The full text of this article will not be available in ULIR until the embargo expires on the 22/06/2020, This is a pre-print of an article that was published in " Computers In Biology And Medicine" for the final version please see http://dx.doi.org/10.1016/j.compbiomed.2019.103337, Planning and practice of surgical procedures can be improved through the use of modelling. This study provides an insight into the biopsy needle (i.e. hollow cannula) and needle-tissue interactions using a modelling approach, thus enabling the optimization of needle-tip designs not only for training but also for the planning of surgical procedures. Simulations of needle insertion into agar gel were performed using a Coupled Eulerian-Lagrangian (CEL) based finite element (FE) analysis, adapted for large deformation and tissue fracture. The experimental work covers needle insertion into 3% agar gel using a needle with a beveled tip of various angles, to assess the validity of the simulation. The simulated needle deflection and insertion force for two needles (i.e. Needle 1 with 18° bevel angle and Needle 2 with 27° bevel angle) were compared with corresponding experimental results. The contact stress (i.e. contact pressure) on the needles from the agar gel during the insertion of the needles were also studied. Observations indicate that varying the needle bevel angle from 27° to 18° results in a decrease of the peak force (i.e. puncture force) and an increase in needle deflection. Quantitatively, the percentage errors between the experimental data and the FE model for the total insertion force along the z-direction (i.e. Z Force) for Needle 1 and 2 were 4% and 4.8% (p > 0.05), respectively. Similarly, needle deflection percentage errors along the x-z plane were 5.7% and 10% respectively. Therefore, the forces and needle deflection values predicted by the simulation are a close approximation of the experimental model, validating the Coupled Eulerian-Lagrangian based FE model. Thus, providing an experimentally validated model for biopsy and cytology needle design in silico that has the potential to replace the current build and break approach of needle design used by manufacturers., peer-reviewed

peer-reviewed, In this thesis, validated Finite Element (FE) models for a viscoelastic braided stent are created, to investigate the mechanical behaviour of the stent subjected to crimping and to predict the stent’s radial forces. The research is focused on developing and validating two linear viscoelastic material models: one for Polydioxanone, a biodegradable polymer and one for Nitinol, a Nickel Titanium shape memory alloy. Both models are developed using Abaqus, a commercial FE software package. The existing analytical model is corrected and adapted to include the braiding angle as opposed to the pitch angle. The model is also extended by introducing additional design information such as the mandrel design to enable correct fabrication, the braid cover factor and the condition in which the braid is in jammed state. A tensile test and tensile creep experiment are performed on the polymer monofilament in order to characterise its viscoelastic response. Data acquired are used to calibrate the polymer material model. Two experiments are performed on the Nitinol material: a uniaxial tensile test to capture its superelasticplastic behaviour and a Discrete Scanning Calorimeter analysis to investigate its transformation temperatures. Data acquired alongside creep data available in the literature are used to calibrate the Nitinol viscoelastic material model. Finally, both viscoelastic configurations of the FE models for the braided stent used in a crimping simulation are validated experimentally on in-house built prototypes. The outcomes of the study demonstrate the great benefits in using FE analysis to assess the mechanical behaviour of a viscoelastic braided stent during crimping. The viscoelastic material model developed for Polydioxanone shows an improvement in the accuracy of the stent’s mechanical behaviour in comparison to a purely elastic material model. The viscoelastic model developed for Nitinol predicts the radial resistive forces more accurately; however, overall, the sup

peer-reviewed, In this thesis, validated Finite Element (FE) models for a viscoelastic braided stent are created, to investigate the mechanical behaviour of the stent subjected to crimping and to predict the stent’s radial forces. The research is focused on developing and validating two linear viscoelastic material models: one for Polydioxanone, a biodegradable polymer and one for Nitinol, a Nickel Titanium shape memory alloy. Both models are developed using Abaqus, a commercial FE software package. The existing analytical model is corrected and adapted to include the braiding angle as opposed to the pitch angle. The model is also extended by introducing additional design information such as the mandrel design to enable correct fabrication, the braid cover factor and the condition in which the braid is in jammed state. A tensile test and tensile creep experiment are performed on the polymer monofilament in order to characterise its viscoelastic response. Data acquired are used to calibrate the polymer material model. Two experiments are performed on the Nitinol material: a uniaxial tensile test to capture its superelasticplastic behaviour and a Discrete Scanning Calorimeter analysis to investigate its transformation temperatures. Data acquired alongside creep data available in the literature are used to calibrate the Nitinol viscoelastic material model. Finally, both viscoelastic configurations of the FE models for the braided stent used in a crimping simulation are validated experimentally on in-house built prototypes. The outcomes of the study demonstrate the great benefits in using FE analysis to assess the mechanical behaviour of a viscoelastic braided stent during crimping. The viscoelastic material model developed for Polydioxanone shows an improvement in the accuracy of the stent’s mechanical behaviour in comparison to a purely elastic material model. The viscoelastic model developed for Nitinol predicts the radial resistive forces more accurately; however, overall, the sup