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Direct aspiration with large bore catheter as the first line option in treatment of acute Ischemic stroke (AIS) is a fast and effective technique with promising outcomes. In silico models are widely used for design and preclinical assessment of new developed devices and therapeutic methods. Accurate modelling of the mechanical behaviour of blood clot is a key factor in the design and simulation of aspiration devices. In this study we develop a new constitutive model which incorporates the unrecoverable plastic deformation of clots. The model is developed based on the deformation-induced microstructural changes in fibrin network, including the formation and dissociation of the cross-links between fibrin fibres. The model is calibrated using previously reported experimentally measured permanent clot deformation following uniaxial stretching. The calibrated plasticity model is then used to simulate aspiration thrombectomy. Results reveal that inclusion of permanent plastic deformation results in ~15 % increase in clot aspiration length at an applied aspiration pressure of 200 mmHg. The constitutive law developed in this study provides a basis for improved design and evaluation of novel aspiration catheters leading to increased first-pass revascularization rate.

In this paper, the effect of pitting corrosion on fatigue life and fretting fatigue of elastic stable intramedullary nails (ESINs) is investigated. To this end, using a crystal plasticity formulation, the behaviour of magnesium under large deformations is investigated by implementing a user defined material subroutine (UMAT) in the Abaqus/Standard finite element solver. Using data provided by SEM images, the approximate configurations of grains in the polycrystalline material are obtained. Adopting Mg-RE (73-2) as one of candidates for implant applications, the fatigue analysis is performed, and the results are compared to the experimental fatigue data for various strain amplitudes. Furthermore, the effect of pitting corrosion on the fatigue life of the material is investigated. It is shown that the maximum accumulated plastic slip occurs at the tip of a corrosion pit. This suggests a faster crack initiation rate on corroded magnesium specimens compared to non-corroded ones, under cyclic loading. Application of pitting corrosion before cyclic loading, causes a significant reduction in the predicted cycles to crack initiation, compared to the uncorroded case. However, the number of cycles to crack initiation is almost the same irrespective of the amount of mass loss due to corrosion. Next, by modelling the fretting fatigue of ESINs, it is demonstrated that plastic slip accumulates at both the contact surface and deeper into the grain microstructure. However, the maximum values of stress and accumulated plastic slip occur at the contact surface. While the grain geometry and orientation influence the location and magnitude of accumulated plastic slip. By modelling the fretting fatigue of the material with different amounts of corrosion, it is shown that the maximum accumulated plastic slip occurs at the contact surface for the case without corrosion, and also for different percentages of corrosion. Finally, the results of fretting fatigue simulation of ESINs show that corrosion significantly accelerates crack initiation due to fretting wear.

Mechanical thrombectomy can be significantly affected by the mechanical properties of the occluding thrombus. In this study we provide the first characterization of the volumetric behaviour of blood clots. We propose a new hyperelastic model for the volumetric and isochoric deformation of clot. We demonstrate that the proposed model provides significant improvements over established models in terms of accurate prediction of nonlinear stress-strain and volumetric behaviours of low and high haematocrit clots. We perform a rigorous investigation of the factors that govern clot occlusion of a tapered vessel. The motivation for such an analysis is two-fold: (i) the role of clot composition on the in-vivo occlusion location is an open clinical question that has significant implications for thrombectomy procedures; (ii) in-vitro measurement of occlusion location in an engineered tapered tube can be used as a quick and simple methodology to assess the mechanical properties/compositions of clots. Simulations demonstrate that both isochoric and volumetric behaviour of clots are key determinants of clot lodgement location, in addition to clot-vessel friction. The proposed formulation is shown to provide accurate predictions of in-vitro measurement of clot occlusion location in a silicone tapered vessel, in addition to accurately predicting the deformed shape of the clot.