Hemocompatibility and safety of the Carmat Total Artifical Heart hybrid membrane

Abstract

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.

Keywords: Bioengineering; Biomedical engineering; Biophysics; Bioprosthetic; Cardiology; Carmat; Haematology; Hemocompatibility; Total artificial heart.

Figure 1

Endurance bench and measures of compliance. A: Schematic view of the endurance bench used for membranes aging test, description of the different components of the bench test used for validation of membrane resistance: 1) PBS Kathon reservoir; 2) Glass dome; 3) Pressure sensor; 4) Pressure sensor; 5) Pressure sensor; 6) Hydraulic pump; 7) Bench test chamber filled by PBS with Kathon; 8) Metallic tank; 9) Silicon oil supply; 10) Silicon oil reservoir; 11) Hydraulic actuator filled with silicon oil; *) C-TAH hybrid membranes.B: Kinetic of volume-loss to evaluate the variation of the membrane compliance after endurance test in percentage. Group 1 is the low number of cycles aging group (black) with membranes A, B, C and D; Group 2 is the high number of cycles aging group (red) with membranes E, F, G, H, I and J.

Figure 2

Physical tests to evaluate the aging of the membranes. A: Measures of the glass transition temperatures obtained by Differential Scanning Calorimeter for the membranes, separated in Group 1: low number of cycles aging group (black) with membranes A, B, C and D; and Group 2: high number of cycles aging group (red) with membranes E, F, G, H, I and J. B: Infrared Absorption Spectra of one membrane for each of the 5 amount of cycles (membranes B, C, E, H, and J) and the non-aged control membrane; peaks are corresponding to-NH absorbing at 3321 cm⁻¹ (1), two –CH2 at 2937 cm⁻¹ (2) and 2862 cm⁻¹ (3) of the carbon chain, –C=O at 1739 cm⁻¹ (4),C=C of the aromatic at 1592 cm⁻¹ (5), C–C of the aromatic at 1403 cm⁻¹ (6), C–O–C of the carbonate function C–O–C=O at 1251 cm⁻¹(7), C–O at 1110 cm⁻¹ (8), C–O–C of the urethane function C–O–C=O at 1068 cm⁻¹ (8).

Figure 3

Surface exploration and permeability. A: Reconstruction using Electronic Microscopic images investigating the two erosion zones on the PU membrane: contact zone on the left corresponding to the zone in contact with the PEEK, and working zone on the right in contact with the oil. B: Cross sectional view of a schematic representation of the disposition of the hybrid membrane inside the C-TAH, with the two erosion areas: the working zone and the contact zone. C: Topographic mapping of the surface of one erosion area on the left, with the topographic profile acquired during exploration of the erosion on the right. D: Raman spectroscopy one membrane, PU wavelengh = 1618 cm⁻¹; silicon oil wavelengh = 491 cm⁻¹, Z profile assessing the absence of silicon oil inside the PU membrane. E: Gas Chromatography coupled with Mass Spectrometry performed on the aging solution of PBS-Kathon used in the endurance bench. Brown: positive control of silicon oil; Black: negative control of non-aged PBS-Kathon; Purple: PBS-Kathon used for the aging of the membrane C; Blue: PBS-Kathon used for the aging of the membrane D.

Figure 4

In-vivo calcification test. A: Picture of subcutaneous membrane explant on a Wistar rat after euthanasia. B: Diagram of the calcium concentration (in μg/mg) in the different membranes: pericardium without anti-calcification treatment as positive control, Pericardium with anti-calcification (FET) treatment and ePTFE.

Figure 5

Simulation results. A: Histogram repartition of the shear stress (Pa) inside left ventricle and B: right ventricle occurring on one cycle of contraction at nominal pressure and flow. The Y-axis represents the percentage of blood volume, the X-axis the shear stress with a step of 0.02 Pa per column. C: Graph of the mean cumulated shear stress during one cycle of contraction in the left ventricle and D: right ventricle. The graph represents the envelop of the histogram repartition graph, The Y axis is the mean percentage of blood volume subject to a shear stress superior to the X axis corresponding value.

Figure 6

Results from feasibility clinical trial. A: 3D acquisition of the calcification for the hybrid membrane of the patient 3 of the clinical trial, with the corresponding views in cross sections, obtained by X-Ray microtomography. B: Plasma glutaraldehyde quantification before and after C-TAH implantation for the last three patients by LC-MS/MS. Values for patient 2 (blue), patient 3 (green) and patient 4 (red) are presented between pre-implant day and 269 days post implantation. C: Mean values of the plasma free hemoglobin for the first three patients after C-TAH implantation using spectrophotometry at specific wavelengths. D: Mean platelets microvesicles CD41 (in Annexin V positives MV) values for the first three patients of the clinical trial before (white) and after (light grey) C-TAH implantation, and compared to the values observed in five HeartMate II patients (dark grey).