THE EFFECT OF SURFACE CHARGE ON ARTERIAL THROMBOSIS

• Main Author: HELMUS, MICHAEL NEVIN
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1980
• Subjects: Biomedical engineering; Biomedical research
• ISBN: 9798661682314

The influence of surface charge and wettability on thrombosis and its characterization was studied in arterial implants of random copolymers of poly (L-glutamic acid co-L-Leucine) with nominal compositions of 10, 20, 30, 40, and 50 mole % glutamic acid. Physical characterization of the polymer surfaces was made using the following techniques. Streaming potential measurements were used to determine the degree of surface ionization. The surface charge is dependent on the surface conentration of glutamic acid and its degree of ionization which is, in turn, a function of pH. The pK of the surface glutamic acid was determined to be 5.2; this occurred at a bulk pH of 6.5. Contact angles, measured with buffer drops at different pH, were used to characterize the hydrophobic and hydrophilic nature of the surface and the degree of chemical heterogeneity of the surface; the surface tension and polarity of the surfaces were determined from the contact angles with organic liquids and water. Other material characterization methods used included bulk swelling, differential interference contrast microscopy of the surface topology, and silver staining of carboxyl surface sites. Implants were fabricated for placement in the femoral and carotid arteries of dogs. The initial surface charge was controlled by preequilibration of the implants in buffers of pH 5.8, 6.5, or 7.5. Samples were implanted for two hours, four days, or seven days and the response was studied with SEM, TEM, and light microscopy. At the short implantation times, the area of the surface covered by the thrombus was a function of the material composition and pH. As the area covered by thrombus decreased, the number of spread white blood cells, individually adhered platelets, or the amount of bare area increased. Comparisons of the area of thrombus at two hours of implantation with the extent of copolymer surface ionization revealed the following trends. If the unionized glutamic acid content of the surface was greater than 10%, the entire surface was covered by thrombus and the degree of surface ionization played no role. If the unionized glutamic acid content of the surface was less than 10%, the surface area covered decreased linearly as the ionized glutamic acid content of the surface increased. Furthermore, the decreased heterogeneity of the surface correlated with a decreased amount of thrombus formation. When more than 10% of the total surface sites were ionized glutamic acid residues, there was no thrombus formed, and only formed elements adhered to the surface. Surfaces which were thrombus free at short implantation durations continued to remain so at 7 days post implantation. Thrombus covered surfaces tended to show decreased thrombus formation, in most cases, by 7 days post implantation. Endothelial-like cell development differed on thrombus covered and thrombus free implant surfaces. On surfaces covered by thrombus, endothelial-like cells covered large areas of the surface by 7 days post implantation; while on thrombus free surfaces large flattened cells, some of which formed confluent patches, covered only small areas of the implant surface.