Hemocompatible Coatings for Metallic Cardiovascular Components, 18-9021

Principal Investigators
Kathryn A. Dannemann
James H. Arps
Susan W. Zogbi

Inclusive Dates: 04/01/97 - Current

Background - Cardiovascular implant (e.g. artificial hearts, heart valves, stents) procedures are being performed at an ever-increasing rate. It is estimated that the clinical application of materials in contact with the bloodstream exceeds one million devices per year. The materials in these devices have severe hemocompatibility requirements to ensure that the device is not rejected and that adverse clotting or blood flow responses are avoided. Stainless steel and titanium alloys are most commonly used in these procedures. Although the biocompatibility of these materials has been demonstrated, they are not necessarily hemocompatible. Hence, there is a strong need, particularly in cardiovascular implant and stent applications, for a biocompatible, blood-compatible material that will not induce blood clotting or form a calcified scale.

Approach - The goal of this project is to develop blood-compatible coatings for metallic components used in cardiovascular applications. A specific objective of the research is to deposit candidate hemocompatible coatings onto currently used biocompatible metal alloys (e.g. Ti-6Al-4V and 316 stainless steel) using the SwRI ion beam surface modification facility. Techniques for coating deposition include ion beam-assisted deposition (IBAD), ion sputtering, ion implantation, and sequential evaporation of solid materials. The coating compositions for investigation are variants of the Ti-Zr-Nb/Ta system. The blood compatibility of these coatings will be characterized and compared with current optimum performing mechanical heart valve materials, such as pyrolytic carbon. Compositional analyses of promising coatings will be used to establish the performance characteristics and to assess the potential suitability for use of these coatings in vivo.

Accomplishments - Various coatings were deposited on 316L stainless steel and Ti-6Al-4V substrates. Elemental and alloy coatings of Ti, Zr, Nb and Ta are being investigated. In addition, diamond-like carbon coatings were deposited for use as a comparative standard for the blood compatibility tests. Several techniques were used to apply the coatings, including sputtering, electron beam vapor deposition (EB-PVD) of a solid source material, and ion implantation techniques. The IBAD (i.e. EB-PVD) and sputtered coatings were approximately 0.5 micrometer thick.

Coating compositions were confirmed by Auger and energy-dispersive X-ray spectroscopy. Contact-angle measurements with human blood revealed that all coated samples performed better than bare titanium. Initial blood compatibility tests were conducted using an SwRI-designed and fabricated experimental blood flow system. Subsequent blood compatibility tests were performed using a protein absorption technique that used radiolabeled proteins (i.e. albumin and fibrinogen). Differences in protein adsorption of ¹²⁵I-labeled albumin were measured for the coatings of interest, implying differences in thrombogenicity. Additional tests are planned using ¹³¹I-labeled fibrinogen.

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