In Vivo Biocompatibility of an Innovative Elastomer for Heart Assist Devices.

Cardiac surgical approaches require the development of new materials regardless of the polyurethanes used for pulsatile blood pumps; therefore, an innovative biomaterial, a copolymer of poly(ethylene terephthalate) and dimer fatty acid (dilinoleic acid) modified with D-glucitol, hereafter referred to as PET/DLA, has been developed, showing non-hemolytic and atrombogenic properties and resistance to biodegradation. The aim of this work was to evaluate in vivo inflammatory responses to intramuscular implantation of PET/DLA biomaterials of different compositions (hard to soft segments). Two copolymers containing 70 and 65 wt.% of hard segments, as in poly(ethylene terephthalate) and dilinoleic acid in soft segments modified with D-glucitol, were used for implantation tests to monitor tissue response. Medical grade polyurethanes Bionate II 90A and Bionate II 55 were used as reference materials. After euthanasia of animals (New Zealand White rabbits, n = 49), internal organs and tissues that contacted the material were collected for histopathological examination. The following parameters were determined: peripheral blood count, blood smear with May Grunwald-Giemsa staining, and serum C-reactive protein (CRPP). The healing process observed at the implantation site of the new materials after 12 weeks indicated normal progressive collagenization of the scar, with an indication of the inflammatory-resorptive process. The analysis of the chemical structure of explants 12 weeks after implantation showed good stability of the tested copolymers in contact with living tissues. Overall, the obtained results indicate great potential for PET/DLA in medical applications; however, final verification of its applicability as a structural material in prostheses is needed.

In-Vitro Biocompatibility and Hemocompatibility Study of New PET Copolyesters Intended for Heart Assist Devices.

(1) Background: The evaluation of ventricular assist devices requires the usage of biocompatible and chemically stable materials. The commonly used polyurethanes are characterized by versatile properties making them well suited for heart prostheses applications, but simultaneously they show low stability in biological environments. (2) Methods: An innovative material-copolymer of poly(ethylene-terephthalate) and dimer linoleic acid-with controlled and reproducible physico-mechanical and biological properties was developed for medical applications. Biocompatibility (cytotoxicity, surface thrombogenicity, hemolysis, and biodegradation) were evaluated. All results were compared to medical grade polyurethane currently used in the extracorporeal heart prostheses. (3) Results: No cytotoxicity was observed and no significant decrease of cells density as well as no cells growth reduction was noticed. Thrombogenicity analysis showed that the investigated copolymers have the thrombogenicity potential similar to medical grade polyurethane. No hemolysis was observed (the hemolytic index was under 2% according to ASTM 756-00 standard). These new materials revealed excellent chemical stability in simulated body fluid during 180 days aging. (4) Conclusions: The biodegradation analysis showed no changes in chemical structure, molecular weight distribution, good thermal stability, and no changes in surface morphology. Investigated copolymers revealed excellent biocompatibility and great potential as materials for blood contacting devices.

Surface modification of metallic materials designed for a new generation of artificial heart valves.

PURPOSE:: The main goal of this work was to develop haemocompatibile thin film materials dedicated to novel flexible mechanical heart valves intended for pulsatile ventricle assist devices. METHODS:: The studies performed have led to the selection of a material for the surface modification of the metallic scaffold. Haemocompatible, biofunctional, ultra-elastic, thin carbon-based coatings were proposed. The surface was designed to eliminate thrombogenic and microbial construction by a reduction in turbulence and sufficient washing of the biofunctional-adapted surfaces, thus allowing for extended use for temporary heart support. The article presents the influence of the mechanical properties of coatings and their influence on the haemocompatibility. In this study, we investigated a simplified model of the whole blood shear stress based on a cone and plate rotational viscometer. Several indices of platelet activation were analysed, including platelet and granulocyte-platelet aggregates, platelet activation markers and platelet-derived microparticles. RESULTS:: The shear stress induced a platelet aggregate count in the range from 2% to 30% of the CD61 positive cells. For polyurethane (PU), the average value of platelet aggregates was on the level of 7%. The analyses have demonstrated that the cytometric methods of the direct determination of platelet-derived microparticles in plasma are reproducible and reliable. Considering the generation of microparticles on the tested coatings under hydrodynamic conditions, the best properties were observed for the coating a-C:H,N. CONCLUSION:: The results indicate that a-C:H-based coatings with the thickness of 110 nm do not induce an immune response and do not influence the origin of platelet microparticle formation; thus, these type of coatings are the most promising for the parts which are planned to withstand blood contact under the high value of shear stress.

Emergency HeartWare Ventricular Assist Device (HVAD) exchange due to pump thrombosis using minimally invasive technique.

Left ventricular assist device (LVAD) thrombosis remains a dreadful complication of mechanical circulatory support, with an incidence of 8-12% depending on the pump type and patient's comorbidities. Fibrinolysis may be considered early in pump thrombosis, but when contraindicated a pump exchange remains the only alternative. This short report documents an emergency LVAD exchange in a 55-year-old man who underwent LVAD (HeartWare Inc) implantation in 2013 as a bridge to transplantation. Four months after the initial surgery, he suffered from a hemorrhagic stroke despite properly managed anticoagulation. On February 17th, 2017 he was re-admitted with LVAD pump thrombosis. As fibrinolysis was contraindicated, an emergency pump exchange was performed via a limited thoracic incision in order to minimize surgical trauma, reduce intraoperative complications and facilitate immediate post-operative recovery. This report documents the very first LVAD pump exchange as well as the first one performed via a minimally invasive approach in Poland.

Athrombogenic hydrogel coatings for medical devices--Examination of biological properties.

In the article the authors present hydrogel coatings prepared from polyvinylpyrrolidone (PVP) macromolecules, which are chemically bonded to polyurethane (PU) substrate. The coating is designed to improve the surface hemocompatibility of blood-contacting medical devices. The coating was characterized in terms of physical properties (swelling ratio, hydrogel density, surface morphology, coating thickness, coating durability). In order to examine surface hemocompatibility, the materials were contacted with whole human blood under arterial flow simulated conditions followed by calculation of platelet consumption and the number of platelet aggregates. Samples were also contacted with platelet-poor plasma; the number of surface-adsorbed fibrinogen molecules was measured using ELISA assay. Finally, the inflammatory reaction after implantation was assessed, using New Zealand rabbits. The designed coating is characterized by high water content and excellent durability in aqueous environment - over a 35-day period, no significant changes in coating thickness were observed. Experiments with blood proved twice the reduction in adsorption of serum-derived fibrinogen together with a moderate reduction in the number of platelet aggregates formed during the contact of the material with blood. The analysis of an inflammatory reaction after the implantation confirmed high biocompatibility of the fabricated materials - studies have shown no toxic effects of the implanted material on the surrounding animal tissues.

Digital image correlation of coated and uncoated Religa Heart_Ext ventricular assist device.

The digital image correlation is used to estimate influence of deposited heamocompatible coatings (gold and titanium nitride) on mechanical response of ventricular assist device Religa Heart_Ext made of Bionate II (thermoplastic polycarbonate urethane) under working conditions by comparison of the coated Religa Heart_Ext with uncoated Religa Heart_Ext. The DIC is applied for experimental investigation of the strains and displacements distribution on external surface of the blood chamber of ventricular assist device during loading. The experiment was conducted in a hydraulic system with water at operating temperatures of 25 and 37 °C, as well as under static pressures: 80, 120, 180, 220 and 280 mmHg, and static underpressures: -25, -45, -75 mmHg. The subsequent images were taken after stabilization of pressure on a set level. The applied research method shows that the nano-coating of 30 nm in thickness significantly affects deformation of the blood chamber of Religa Heart_Ext in macro scale. The proposed composition of coatings increases strain on external surface of the ventricular assist device.

Numerical modelling and verification of Polish ventricular assist device.

The developed multiscale model of blood chamber of POLVAD (Polish ventricular assist device) was introduced. The tension test for polymer and digital image correlation (DIC) were performed for verification of the strains and displacements obtained in the numerical model of POLVAD_EXT. The numerical simulations were carried out in conditions given in the experiment to compare the results obtained on external surfaces of blood chamber of the POLVAD_EXT. The examined polymer applied in the POLVADs is sensitive to changes of temperature and this observation is considered in all prepared numerical models. The comparison of experimental and numerical results shows acceptable coincidence. There are some heterogeneous distributions of strains in experiment with respect to analysis of computed parameters. The comparison of two versions of blood chambers (POLVAD and POLVAD_EXT) in numerical analysis shows that POLVAD_EXT construction is better with respect to analysis of strain and stress. The maximum values of computed parameters are located in the regions between connectors on the internal surfaces of blood chambers of POLVAD.