Hemocompatible Coatings for Metallic Cardiovascular Components, 18-9021

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

Inclusive Dates: 04/01/97 - 06/30/00

Background - Cardiovascular implants (e.g., artificial hearts, substitute heart valves, stents, pacemaker casings, and leads) use various biomaterials in contact with blood. The materials utilized in these devices have unique hemocompatibility requirements to ensure that the device is not rejected and that adverse thrombogenic (clotting) or hemodynamic (blood flow) responses are avoided. Stainless steel and titanium alloys are most commonly used. Although the biocompatibility of these materials has been demonstrated, they are not necessarily hemocompatible. While attempts have been made to reduce thromboembolic phenomena, there is a continuing need for a biocompatible, blood-compatible material that will not induce blood clotting or form a calcified scale.

Approach - The objective of this project was to assess the blood compatibility of a range of vacuum-deposited coatings for metallic components used in cardiovascular applications. The SwRI ion surface modification facility was utilized to produce candidate hemocompatible coatings. Coating trials were primarily directed toward dopant elements that could improve the blood compatibility of Ti. Two of the alloy constituents investigated, Nb and Zr, were selected based on literature findings that indicate these elements do not produce adverse tissue reactions. Flat coupon samples of Ti-6Al-4V and 316L stainless steel were treated by several methods, including: magnetron sputtering, ion beam-assisted deposition (IBAD), ion implantation, and sequential evaporation of solid materials. Promising coatings were characterized to determine coating composition, extent of adherence, and wettability. Simulated in vitro tests were employed to evaluate the hemocompatibility of the coatings. The results were compared with materials currently used in medical devices.

Accomplishments - Non-equilibrium Ti-based metallic coatings were produced using various ion beam processing techniques. In addition, diamond-like carbon coatings were deposited for use as a comparative standard for the blood compatibility tests. Coatings with the lowest oxygen contents were achieved using magnetron sputtering. Coating thicknesses ranged from 100 nanometers to 5 micrometers, depending on the deposition technique. Coating and surface compositions were confirmed by Auger electron spectroscopy and energy-dispersive X-ray spectroscopy. Contact-angle measurements with human blood revealed that all the coated samples performed better than bare Ti. Initial blood compatibility tests were conducted using an experimental blood flow system, designed and fabricated at SwRI. Flow-tested samples were evaluated by scanning electron microscopy to determine the extent of platelet adhesion. Results from blood flow loop trials revealed no significant differences among the coated surfaces. A protein absorption technique, using radiolabeled albumin and fibrinogen, was implemented later in the program as a quantitative means of distinguishing the relative blood compatibility of the coatings. Results of these studies showed antithrombogenic potential for some of the surfaces containing Zr, though the surface-treated samples did not show a statistically significant difference relative to untreated control samples. The absence of a significant blood compatibility effect may be related to surface texture or the extent of oxidation of the coatings.

Materials Research and Structural Mechanics Program
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