Biofunctionalization of surfaces to minimize undesirable effects in cardiovascular assistance devices.

BACKGROUND: The reactivity of blood with non-endothelial surface is a challenge for long-term Ventricular Assist Devices development, usually made with pure titanium, which despite of being inert, low density and high mechanical resistance it does not avoid the thrombogenic responses. Here we tested a modification on the titanium surface with Laser Induced Periodic Surface Structures followed by Diamond Like Carbon (DLC) coating in different thicknesses to customize the wettability profile by changing the surface energy of the titanium. METHODS: Four different surfaces were proposed: (1) Pure Titanium as Reference Material (RM), (2) Textured as Test Sample (TS), (3) Textured with DLC 0.3µm as (TSA) and (4) Textured with 2.4µm DLC as (TSB). A single implant was positioned in the abdominal aorta of Wistar rats and the effects of hemodynamic interaction were evaluated without anticoagulant drugs. RESULTS: After twelve weeks, the implants were extracted and subjected to qualitative analysis by Scanning Electron Microscopy under low vacuum and X-ray Energy Dispersion. The regions that remained in contact with the wall of the aorta showed encapsulation of the endothelial tissue. TSB implants, although superhydrophilic, have proven that the DLC coating inhibits the adhesion of biological material, prevents abrasive wear and delamination, as observed in the TS and TSA implants. Pseudo- neointimal layers were heterogeneously identified in higher concentration on Test Surfaces.

A strategy for designing of customized electromechanical actuators of blood pumps.

Congestive heart failure is a pathology of global incidence that affects millions of people worldwide. When the heart weakens and fails to pump blood at physiological rates commensurate with the requirements of tissues, two main alternatives are cardiac transplant and ventricular assist devices (VADs). This article presents the design strategy for development of a customized VAD electromagnetic actuator. Electromagnetic actuator is a brushless direct current motor customized to drive the pump impeller by permanent magnets located in rotor-stator coupling. In this case, ceramic pivot bearings support the VAD impeller. Electronic circuitry controls rotation switching current in stator coils. The proposed methodology consisted of analytical numerical design, tridimensional computational modeling, numerical simulations using Maxwell software, actuator prototyping, and validation in the dynamometer. The axial flow actuator was chosen by its size and high power density compared to the radial flow type. First step consisted of estimating the required torque to drive the pump. Torque was estimated at 2100 rpm and mean current of 0.5 A. Numerical analysis using finite element method mapped vectors and fields to build stator coils and actuator assemblage. After tests in the dynamometer, experimental results were compared with numerical simulation and validated the proposed model. In conclusion, the proposed methodology for designing of VAD electromechanical actuator was considered satisfactory in terms of data consistency, feasibility, and reliability.

Magnetic suspension of the rotor of a ventricular assist device of mixed flow type.

This work presents results of preliminary studies concerning application of magnetic bearing in a ventricular assist device (VAD) being developed by Dante Pazzanese Institute of Cardiology-IDPC (São Paulo, Brazil). The VAD-IDPC has a novel architecture that distinguishes from other known VADs. In this, the rotor has a conical geometry with spiral impellers, showing characteristics that are intermediate between a centrifugal VAD and an axial VAD. The effectiveness of this new type of blood pumping principle was showed by tests and by using it in heart surgery for external blood circulation. However, the developed VAD uses a combination of ball bearings and mechanical seals, limiting the life for some 10 h, making impossible its long-term use or its use as an implantable VAD. As a part of development of an implantable VAD, this work aims at the replacement of ball bearings by a magnetic bearing. The most important magnetic bearing principles are studied and the magnetic bearing developed by Escola Politécnica of São Paulo University (EPUSP-MB) is elected because of its very simple architecture. Besides presenting the principle of the EPUSP-MB, this work presents one possible alternative for applying the EPUSP-MB in the IDPC-VAD.