A computational study of crimping and expansion of bioresorbable polymeric stents

This paper studied the mechanical performance of four bioresorbable PLLA stents, i.e., Absorb, Elixir, Igaki-Tamai and RevaMedical, during crimping and expansion using the finite element method. Abaqus CAE was used to create the geometrical models for the four stents. A tri-folded balloon was created using NX software. For the stents, elastic-plastic behaviour was used, with hardening implemented by considering the increase of yield stress with the plastic strain. The tri-folded balloon was treated as linear elastic. To simulate the crimping of stents, a set of 12 rigid plates were generated around the stents with a radially enforced displacement. During crimping, the stents were compressed from a diameter of 3 mm to 1.2 mm, with the maximum stress developed at both inner and outer sides of the U-bends. During expansion, the stent inner diameter increased to 3 mm at the peak pressure and then recoiled to different final diameters after balloon deflation due to different stent designs. The maximum stress was found again at the U-bends of stents. Diameter change, recoiling effect and radial strength/stiffness were also compared for the four stents to assess the effect of design variation on stent performance. The effect of loading rate on stent deformation was also simulated by considering the time-dependent plastic behaviour of polymeric material

Testing, characterization and modelling of mechanical behaviour of poly (lactic-acid) and poly (butylene succinate) blends

Background Significant amount of research, both experimental and numerical, has been conducted to study the mechanical behaviour of biodegradable polymer PL(L)A due to its wide range of applications. However, mechanical brittleness or poor elongation of PL(L)A has limited its applications considerably, particularly in the biomedical field. This study aims to study the potential in improving the ductility of PLA by blending with PBS in varied weight ratios. Methods The preparation of PLA and PBS blends, with various weight ratios, was achieved by melting and mixing technique at high temperature using HAAKE™ Rheomix OS Mixer. Differential Scanning Calorimetry (DSC) was applied to investigate the melting behaviour, crystallization and miscibility of the blends. Small dog-bone specimens, produced by compression moulding, were used to test mechanical properties under uniaxial tension. Moreover, an advanced viscoplastic model with nonlinear hardening variables was applied to simulate rate-dependent plastic deformation of PLA/PBS blends, with model parameters calibrated simultaneously against the tensile test data. Results Optical Microscopy showed that PBS composition aid with the crystallization of PLA. The elongation of PLA/PBS blends increased with the increase of PBS content, but with a compromise of tensile modulus and strength. An increase of strain rate led to enhanced stress response, demonstrating the time-dependent deformation nature of the material. Model simulations of time-dependent plastic deformation for PLA/PBS blends compared well with experimental results. Conclusions The crystallinity of PLA/PBS blends increased with the addition of PBS content. The brittleness of pure PLA can be improved by blending with ductile PBS using mechanical mixing technique, but with a loss of stiffness and strength. The tensile tests at different strain rates confirmed the time-dependent plastic deformation nature of the blends, i.e., viscoplasticity, which can be simulated by the Chaboche viscoplastic model with nonlinear hardening variables

A computational study of mechanical performance of bioresorbable polymeric stents with design variations

Purpose: The study compared the mechanical behavior of bioresorbable polymeric stents with various designs during deployment, and investigated their fatigue performance under pulsatile blood pressure loading. Methods: Finite element simulations have been carried out to compare the mechanical performance of four bioresorbable polymeric stents, i.e., Absorb, Elixir, Igaki-Tamai and RevaMedical, during deployment in diseased artery. Tri-folded balloon was modelled to expand the crimped stent onto the three-layered arterial wall with plaque. Cyclic diastolic-systolic pressure loading was applied to both stent and arterial wall to study fatigue behavior. Results: Stents with larger U-bend and longer axial strut demonstrate more flexibility but suffer from severe dogboning and recoiling effects. Stress concentrations in the stent, as well as in the plaque and artery, are higher for stents designed with increased rigidity such as those with smaller U-bends and shorter axial struts. Simulations of fatigue deformation for Elixir stent demonstrate that the U-bends, with high stress concentrations, have a potential risk of fatigue failure under pulsatile systolic-diastolic blood pressure as opposed to the counter metallic stents which are normally free of fatigue failure. Conclusion: The structural behaviour of bioresorbable polymeric stent is strongly affected by its design, in terms of expansion, dogboing, recoiling and stress distribution during the deployment process

Testing, characterization and modelling of mechanical behaviour of poly (lactic-acid) and poly (butylene succinate) blends

Background Significant amount of research, both experimental and numerical, has been conducted to study the mechanical behaviour of biodegradable polymer PL(L)A due to its wide range of applications. However, mechanical brittleness or poor elongation of PL(L)A has limited its applications considerably, particularly in the biomedical field. This study aims to study the potential in improving the ductility of PLA by blending with PBS in varied weight ratios. Methods The preparation of PLA and PBS blends, with various weight ratios, was achieved by melting and mixing technique at high temperature using HAAKE™ Rheomix OS Mixer. Differential Scanning Calorimetry (DSC) was applied to investigate the melting behaviour, crystallization and miscibility of the blends. Small dog-bone specimens, produced by compression moulding, were used to test mechanical properties under uniaxial tension. Moreover, an advanced viscoplastic model with nonlinear hardening variables was applied to simulate rate-dependent plastic deformation of PLA/PBS blends, with model parameters calibrated simultaneously against the tensile test data. Results Optical Microscopy showed that PBS composition aid with the crystallization of PLA. The elongation of PLA/PBS blends increased with the increase of PBS content, but with a compromise of tensile modulus and strength. An increase of strain rate led to enhanced stress response, demonstrating the time-dependent deformation nature of the material. Model simulations of time-dependent plastic deformation for PLA/PBS blends compared well with experimental results. Conclusions The crystallinity of PLA/PBS blends increased with the addition of PBS content. The brittleness of pure PLA can be improved by blending with ductile PBS using mechanical mixing technique, but with a loss of stiffness and strength. The tensile tests at different strain rates confirmed the time-dependent plastic deformation nature of the blends, i.e., viscoplasticity, which can be simulated by the Chaboche viscoplastic model with nonlinear hardening variables

A PCA and ELM Based Adaptive Method for Channel Equalization in MFL Inspection

Magnetic flux leakage (MFL) as an efficient method for pipeline flaw detection plays important role in pipeline safety. This nondestructive test technique assesses the health of the buried pipeline. The signal is gathered by an array of hall-effect sensors disposed at the magnetic neutral plane of a pair of permanent magnet in the pipeline inspection gauge (PIG) clinging to the inner surface of the pipe wall. The magnetic flux measured by the sensors reflects the health condition of the pipe. The signal is influenced by not only the condition of the pipe, but also by the lift-off value of the sensors and various properties of electronic component. The consistency of the position of the sensors is almost never satisfied and each sensor measures differently. In this paper, a new scheme of channel equalization is proposed for MFL signal in order to correct sensor misalignments, which eventually improves accuracy of defect characterization. The algorithm proposed in this paper is adaptive to the effects of error on the disposition of the sensor due to manufacturing imperfections and movements of the sensors. The algorithm is tested by data acquired from an experimental pipeline. The results show the effectiveness of the proposed algorithm

New Developments in Aromatic Halogenation, Borylation, and Cyanation

Several green procedures have been developed for synthesizing functionalized aromatics: i) AuCl3-catalyzed halogenation of aromatic compounds, including aryl boronates; ii) Fe2O3-catalyzed direct aromatic C–H bond borylation; iii) Pd-catalyzed direct cyanation of indoles; iv) direct conversion of arylamines to pinacol boronates

Active sites engineering leads to exceptional ORR and OER bifunctionality in P,N Co-doped graphene frameworks

Bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly desirable for rechargeable metal-air batteries and regenerative fuel cells. However, the commercial oxygen electrocatalysts (mainly noble metal based) can only exhibit either ORR or OER activity, and also suffer from inherent cost and stability issues. It remains challenging to achieve efficient ORR and OER bifunctionality on a single catalyst. Metal-free structures offer relatively large scope for such bifunctionality to be enginnered within one catalyst, together with improved cost-effectiveness and durablility. Herein, by closely coupled computational design and experimental development, highly effective bifunctionality is achieved in a phosphorus and nitrogen co-doped graphene framework (PNGF) - with both ORR and OER activities reaching the theoretical limits of metal-free catalysts, superior to the noble metal counterparts in both (bi)functionality and durability. In particular, with the identification of active P-N sites for OER and N-doped sites for ORR , we successfully intensified such sites by one-pot synthesis to tailor the PNGF. The resulting catalyst reaches an ORR potential of 0.845 V vs. RHE at 3 mA cm-2 and an OER potential of 1.55 V vs. RHE at 10 mA cm-2, respectively. Its combined ORR and OER overpotential of 705 mV is significantly lower than those reported previously for metal-free bifunctional catalysts