Hemocompatibile Thin Films Assessed under Blood Flow Shear Forces.

The aim of this study was to minimize the risk of life-threatening thromboembolism in the ventricle through the use of a new biomimetic heart valve based on metal-polymer composites. Finite volume element simulations of blood adhesion to the material were carried out, encompassing radial flow and the cone and plane test together with determination of the effect of boundary conditions. Both tilt-disc and bicuspid valves do not have optimized blood flow due to their design based on rigid valve materials (leaflet made of pyrolytic carbon). The main objective was the development of materials with specific properties dedicated to contact with blood. Materials were evaluated by dynamic tests using blood, concentrates, and whole human blood. Hemostability tests under hydrodynamic conditions were related to the mechanical properties of thin-film materials obtained from tribological tests. The quality of the coatings was high enough to avoid damage to the coating even as they were exposed up to maximum loading. Analysis towards blood concentrates of the hydrogenated carbon sample and the nitrogen-doped hydrogenated carbon sample revealed that the interaction of the coating with erythrocytes was the strongest. Hemocompatibility evaluation under hydrodynamic conditions confirmed very good properties of the developed coatings.

Formation and Thermal Stability of the ω-Phase in Ti-Nb and Ti-Mo Alloys Subjected to HPT.

This paper discusses the features of ω-phase formation and its thermal stability depending on the phase composition, alloying element and the grain size of the initial microstructure of Ti-Nb and Ti-Mo alloys subjected to high-pressure torsion (HPT) deformation. In the case of two-phase Ti-3wt.% Nb and Ti-20wt.% Nb alloys with different volume fractions of α- and ß-phases, a complete ß→ω phase transformation and partial α→ω transformation were found. The dependence of the α→ω transformation on the concentration of the alloying element was determined: the greater content of Nb in the α-phase, the lower the amount of ω-phase that was formed from it. In the case of single-phase Ti-Mo alloys, it was found that the amount of ω-phase formed from the coarse-grained ß-phase of the Ti-18wt.% Mo alloy was less than the amount of the ω-phase formed from the fine α'-martensite of the Ti-2wt.% Mo alloy. This was despite the fact that the ω-phase is easier to form from the ß-phase than from the α- or α'-phase. It is possible that the grain size of the microstructure also affected the phase transformation, namely, the fine martensitic plates more easily gain deformation and overcome the critical shear stresses necessary for the phase transformation. It was also found that the thermal stability of the ω-phase in the Ti-Nb and Ti-Mo alloys increased with the increasing concentration of Nb or Mo.

Experimental and numerical analysis of blood flow in roughness impact-R test.

PURPOSE: The present paper covers simulation of blood flow in a roughness impact-R test model to anticipate the hemodynamic conditions of adhesion of blood elements to the modified surface. It was performed using numerical modelling of this process. The aim of these simulations was to create a surface morphology that stimulates the adhesion of blood elements to the surface of base plate of impact-R test. METHODS: The morphology of base plate of impact-R test was developed using a vacuum powder sintering of commercial purity titanium powder (CP-Ti) on Ti6Al7Nb substrate. The finite volume method (FVM) and disperse particle method (DPM) were applied to develop the target model of a roughness impact-R test. The morphology of modified surfaces was documented with digital microscope and SEM (scanning electron microscopy). RESULTS: The impact-R test developed using the two-phase blood model performed on regularly structured base plate resulted in shear stress values higher than the analogous for the model lacking such modification. The most significant reduction in maximum values of shear stress occurred in case of the DPM model and especially in the model with regular structures. CONCLUSIONS: The proposed models are very effective in modeling of the analysis of blood flow in roughness impact-R test.

(Ti,Al)O2 Whiskers Grown during Glow Discharge Nitriding of Ti-6Al-7Nb Alloy.

Plasma nitriding of titanium alloys is capable of effective surface hardening at temperatures significantly lower than gas nitriding, but at a cost of much stronger surface roughening. Especially interesting are treatments performed at the lower end of the temperature window used in such cases, as they are least damaging to highly polished parts. Therefore identifying the most characteristic defects is of high importance. The present work was aimed at identifying the nature of pin-point bumps formed at the glow discharged plasma nitrided Ti-6Al-7Nb alloy using plan-view scanning and cross-section transmission electron microscopy methods. It helped to establish that these main surface defects developed at the treated surface are (Ti,Al)O2 nano-whiskers of diameter from 20 nm to 40 nm, and length up to several hundreds of nanometers. The performed investigation confirmed that the surface imperfection introduced by plasma nitriding at the specified range should be of minor consequences to the mechanical properties of the treated material.

In vitro haemocompatibility assessment of acrylic acid deposited on solid, polyurethane substrate.

The main purpose of the work was to assess the haemocompatible properties of polyurethane discs with a modified surface dedicated to cardiovascular system regeneration. They were coated with acrylic acid-based material to inhibit the activation of the blood coagulation cascade. This coating improved the wettability of the material, leading to the prevention of protein adsorption on the surface. The blood-material interaction was analyzed in dynamic conditions with a specially designed tester, which helps to control blood-material interaction under high shear stress conditions. The corresponding numerical model of the tester was also developed by finite volume method (FVM). The 3D FVM model allows the determination of shear stresses applying different flow and boundary conditions representing blood-material interactions. The haemocompatibility analyses were performed through in vitro tests using a blood flow simulator. They revealed a low probability of activation of blood coagulation and low leukocyte activation. The original mechanical set-up to test the blood-material interaction helped to prove that acrylic acid-based coatings expressed good haemocompatible properties.