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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., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The present study has two major purposes: firstly, to investigate whether the analytical model proposed by Jedwab and Clerc for assessing the mechanical behaviour of an open ends metallic braided stent is applicable to the looped ends stent design and secondly, to compare the response of the two stent designs subjected to radial compression. We use finite element analysis to evaluate the performance of the two braided stents emulating well established designs: WALLSTENT and WallFlex. We validate the WALLSTENT model analytically. We perform a radial crimping simulation and evaluate the radial forces and stresses induced. This study confirms the validity of using the analytical model in the biomechanical analysis of the WALLSTENT design. However, in case of the WallFlex design, a major difference in the results can be observed in the levels of radial forces and wire peak stresses, justifying the decision of using a different alloy in the fabrication of the WallFlex design., (Copyright © 2017 Elsevier Ltd. All rights reserved.)