Hemocompatible Coatings for Metallic
Cardiovascular Components, 18-9021
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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
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