In vivo evaluation of antithrombogenicity and surface analysis of ion-implanted silicone rubber

The chemical and physical structure of ion-implanted silicone rubbers has been studied in order to analyze their blood compatibility such as reduction of platelet accumulation owing to ion implantation. H⁺₂, He⁺, C⁺, O⁺, O⁺₂, N⁺, N⁺₂, Ne⁺, Na⁺, Ar⁺, K⁺, and Kr⁺ ion implantations were performed at an energy of 150 keV with fluences between 1 × 10¹⁷ and 3 × 10¹⁷ ions/cm² at room temperature. Results of FT-IR-ATR showed that ion implantation broke the original chemical bond to form new radicals such as OH, >C = O, SiH, and CH₂. The formation of these radicals depended on the ion species employed: >C = O formation by O⁺ or O⁺₂ implantation and formation of amines by N⁺ or N⁺₂ implantation. The results of Raman spectroscopy showed that ion implantation always produced a peak at near 1500 cm⁻¹, although the intensity of this peak was dependent on the ion species. The light ions like H⁺₂ and He⁺ were more effective than heavy ions in producing this peak, and O⁺₂ implantation was the most effective on producing amorphous carbon. These results indicated that >C = O and amorphous carbon, generated by O⁺₂ implantation, may improve the antithrombogenicity. The antithrombogenicity was tested by the superior vena cava (SVC) indwelling method for two days in rats with in-111-tropolone-platelets, and by the inferior vena cava (IVC) indwelling method for periods of 1–4 weeks in dogs. Results of the SVC indwelling method showed that platelet accumulation on H⁺₂ and O⁺₂ implanted specimens decreased. In particular 1 × 10¹⁷ O⁺₂/cm² implantation caused both accumulation onto specimens and the SVC to decrease. Macroscopic views of the ion-implanted IVC specimens in dogs revealed little thrombus formation. It is concluded that ion implantation into silicone rod is a useful technique to improve its antithrombogenicity.