Enhanced Biocompatibility of GPC by Silver Ion Implantation
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Enhanced Biocompatibility of GPC by Silver Ion Implantation 1 2 1 R. Zimmerman , I. Gürhan , C. Muntele1, and D. Ila , F. Özdal-Kurt3 and B. H. Sen4 Center for Irradiation of Materials, Alabama A&M University, Normal, AL 2 Ege University Faculty of Engineering, Department of Bioengineering, Izmir, Turkey 3 Celal Bayar University Faculty of Science and Arts, Department of Biology, Manisa, Turkey. 4 Ege University Faculty of Dentistry, Izmir, Turkey 1
ABSTRACT Biocompatible Glassy Polymeric Carbon (GPC) is used for artificial heart valves and in other biomedical applications. Although it is ideally suited for implants in the blood stream, tissue that normally forms around the moving parts of a GPC heart valve sometimes loses adhesion and creates embolisms downstream. Here we compare silver ion implantation and silver deposition, each of which strongly inhibits cell attachment on GPC. Inhibition of cell adhesion is a desirable improvement to current GPC cardiac implants. In vitro biocompatibility tests have been carried out with model cell lines to demonstrate that traces of silver can favorably influence the surface of GPC for biomedical applications.
INTRODUCTION Glassy Polymeric Carbon (GPC) is an outstanding and versatile biomaterial [1-5] owing to its electrical, mechanical and chemical properties, which include exceptional biocompatibility. The density (1.45 g/cm3) of GPC is significantly lower than that of graphite from which one may deduce a relative pore volume of about 35% although the material is among the most impermeable known. Its structure (figure 1) has intertwined graphene planes that enclose voids. Because there are no open bonds even at the surface, GPC is resistant to corrosion, even at high temperatures in air. The strength, durability and low density make GPC a favored material for the manufacture of replacement heart valves. However, the low adhesion at the interface with biological tissue [6] has the potential of creating an embolism when endothelial tissue that naturally encapsulates the implant is released into the blood stream. Greater tissue adhesion can be achieved by making the surface rough. The texture dimensions and chemical affinity of
15 µm
Figure 1: Transmission electron micrograph of Glassy Polymeric Carbon heat treated to 2500°C. The cross sectional dimensions of the ribbon like structures of the graphene layers are of the order of 15. Raman spectroscopy and TEM images suggest that amorphous carbon is present and is responsible for eliminating pore connectivity and making GPC non permeable.
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the surface should be adequate to allow strong adherence of tissue on the material surface. Alternatively, surface treatment by an appropriate ion implantation may be expected to inhibit cell growth or give the cells no adherence at all. The danger of embolism is eliminated if no tissue can form on critical implant surfaces. We have previously reported the use of oxygen ion bombardment to increase the surface roughness, to enhance cell
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