Biomedical Engineering Reference
In-Depth Information
selection of coatings, TiN, DLC or heparin, should be carefully decided in
relation to the duration of clinical application. In addition, as mentioned, mostly
used covalent binding technology of heparin to the substance surface is rather
chemically complex (Sin et al., 2009).
Textured surface (bioactive)
Another bioactive surface coating is the textured surface coating. The first
application of textured surface was conducted by Bernhard et al. (1968). Decron
fibrils were applied with polyurethane adhesive to a silastic bladder of an
LVAD.
Whalen (1988) developed and examined two different textured surfaces
(polyurethane fibrils woven into a fabric and an integrally textured silicone
rubber surface with nonfibril geometry to silicone rubber substrates) as
alternatives to the polyester velour surface (Hall et al., 1967, 1968; Liotta et
al., 1996; Reichenbach et al., 2001) for chambers of artificial hearts. The study
showed that tissue fixation depended on the textured surface morphology. In
comparison with smooth surface silicone rubber, formation of tissue capsules
was thinner for both examined textured surfaces.
Synthetic polymer has been known as potential cause for thromboembolism.
Polyurethane vascular patches with textured luminal surface were produced to
diminish this problem and compared with non-textured polyurethane surface for
period of 1±3 weeks post-implantation (Fujisawa et al., 1999). The study
investigated the effect of controlled surface texture on the formation of blood-
compatible pseudo-neointima. The major finding of the study is that the
formation of a stabilized thrombus layer can be achieved only by having
textured surface on a substance. Another study suggested that the thickness of
pseudo-neointima can be handled by the ability to control the surface texturing
(Fujisawa et al., 2000). Three different lengths of microfibers, 25, 50 and
100m were produced on a polyurethane as shown in Fig. 8.3.
As an example of commercial use, the polyurethane diaphragm is textured
with integral fibrillar texture in HeartMate LVAD. This textured surface allows
a thin coagulum to be built, which leads to a neo-intimal surface. This neo-
intimal surface consists of acellular elements and progenitor cells that
differentiate into fibroblasts, myotibroblast, monocytes and endothelial cells.
Stable, thin layer biological neo-intimal remains without a large hanging flap of
tissue on the surface (Long, 2001). It prevents the connection of blood and the
material surface once it is formed. Therefore, this cellular matrix derived from
the blood offers remarkable thrombosis reduction and minimizes the need for
anticoagulants such as warfarin (Poirier, 1997a; Frazier et al., 2001).
Many methods are used to create a textured surface on a substrate, such as the
formation of sintered titanium microspheres on a titanium substrate (Dasse et al.,
1987; Graham et al., 1990). Excimer laser micromachining is utilized in order to
