Search

In order to improve water and oxygen barrier properties, the surface of two commercial medical grade polyurethane (PU) membranes (Chronoflex® AR-LT and Bionate® II) was modified by a spray deposited film of poly(ethylene-co-vinyl alcohol) (EVOH). The influence of the temperature, the deposited layer thickness and the EVOH ethylene group percentage (27%, 32%, and 44% for EVOH27, EVOH32, and EVOH44, respectively) on the barrier properties of the PU/EVOH multilayered membranes was investigated. The increase of the EVOH layer thickness leads to higher oxygen barrier properties (the highest barrier improvement factor of 412 was obtained). However, in case of the deposited layer thickness higher than 18 μm, microcracks appeared on the treated surface promote a significant loss of the barrier effect. Due to its higher crystallinity degree, EVOH27 provides a higher oxygen barrier effect compared to EVOH32 and EVOH44. On the contrary, an increase of the water barrier properties was observed with the increase of the percentage of ethylene groups. Moreover, the delamination of the EVOH layer was noted after water permeation, especially in case of EVOH44, which is the most hydrophobic layer. Nevertheless, significant decrease of the water and oxygen permeability of the modified PU membranes was achieved, thus showing the benefit of using the EVOH spray deposition for the biomedical application, which requires high performance material with flexible and barrier properties.

Heart failure is a progressive and often fatal pathology among the main causes of death in the world. An implantable total artificial heart (TAH) is an alternative to heart transplantation. Blood damage quantification is imperative to assess the behavior of an artificial ventricle and is strictly related to the hemodynamics, which can be investigated through numerical simulations. The aim of this study is to develop a computational model that can accurately reproduce the hemodynamics inside the left pumping chamber of an existing TAH (Carmat-TAH) together with the displacement of the leaflets of the biological aortic and mitral valves and the displacement of the pericardium-made membrane. The proposed modeling workflow combines fluid-structure interaction (FSI) simulations based on a fixed grid method with computational fluid dynamics (CFD). In particular, the kinematics of the valves is accounted for by means of a dynamic mesh technique in the CFD. The comparison between FSI- and CFD-calculated velocity fields confirmed that the presence of the valves in the CFD model is essential for realistically mimicking blood dynamics, with a percentage difference of 2% during systole phase and 13% during the diastole. The percentage of blood volume in the CFD simulation with a shear stress above the threshold of 50 Pa is less than 0.001%. In conclusion, the application of this workflow to the Carmat-TAH provided consistent results with previous clinical studies demonstrating its utility in calculating local hemodynamic quantities in the presence of complex moving boundaries.

The Carmat bioprosthetic total artificial heart (C-TAH) is a biventricular pump developed to minimize drawbacks of current mechanical assist devices and improve quality of life during support. This study aims to evaluate the safety of the hybrid membrane, which plays a pivotal role in this artificial heart. We investigated in particular its blood-contacting surface layer of bovine pericardial tissue, in terms of mechanical aging, risks of calcification, and impact of the hemodynamics shear stress inside the ventricles on blood components. Hybrid membranes were aged in a custom-designed endurance bench. Mechanical, physical and chemical properties were not significantly modified from 9 months up to 4 years of aging using a simulating process. Exploration of erosion areas did not show no risk of oil diffusion through the membrane. Blood contacting materials in the ventricular cavities were subcutaneously implanted in Wistar rats for 30 days as a model for calcification and demonstrated that the in-house anti-calcification pretreatment with Formaldehyde-Ethanol-Tween 80 was able to significantly reduce the calcium concentration from 132 μg/mg to 4.42 μg/mg (p < 0.001). Hemodynamic simulations with a computational model were used to reproduce shear stress in left and right ventricles and no significant stress was able to trigger hemolysis, platelet activation nor degradation of the von Willebrand factor multimers. Moreover, explanted hybrid membranes from patients included in the feasibility clinical study were analyzed confirming preclinical results with the absence of significant membrane calcification. At last, blood plasma bank analysis from the four patients implanted with C-TAH during the feasibility study showed no residual glutaraldehyde increase in plasma and confirmed hemodynamic simulation-based results with the absence of hemolysis and platelet activation associated with normal levels of plasma free hemoglobin and platelet microparticles after C-TAH implantation. These results on mechanical aging, calcification model and hemodynamic simulations predicted the safety of the hybrid membrane used in the C-TAH, and were confirmed in the feasibility study., Biomedical engineering; Bioengineering; Biophysics; Cardiology; Haematology; Total artificial heart; Bioprosthetic; Carmat; Hemocompatibility

International audience; The objective of this paper is to demonstrate the utility and relevance of the use of reliability allocation methodology in the design of reliability test plans for the qualification of new medical systems. This approach makes use of all of the information collected in the preliminary product development phases. Firstly, this methodology provides a resolution to optimizing the reliability allocation process for the design of a reliability test plan, with a view to cost containment and, secondly, demonstrates the applicability to the demanding constraints provided by the medical sector, and in particular, those in the field of Mechanical Heart Replacement Therapy. The Carmat Total Artificial Heart was the subject of this study, possibly the most demanding of reliability requirements, as it replaces the heart of patients with irreversible bi-ventricular heart failure and who are, consequently, totally reliable on the device for survival.

Polyurethane (PU) elastomers represent an important class of segmented copolymers. Thanks to many available chemical compositions, a rather broad range of chemical, physical, and biocompatible properties of PU can be obtained. These polymers are often characterized by high tensile and tear strength, elongation, fatigue life, and wear resistance. However, their relatively high permeability towards gases and water as well as their biocompatibility still limits the PU’s practical application, especially for biomedical use, for example, in implants and medical devices. In this review, the barrier and permeability properties of segmented PUs related to their chemical structure and physical and chemical properties have been discussed, including the latest developments and different approaches to improve the PU barrier properties.