Surface characterization and ex vivo blood compatibility study of plasmamodified small diameter tubing: effect of sulphur dioxide and hexamethyl-disiloxane plasmas

The development of a small diameter artificial vascular graft or prosthesis is limited by rapid thrombus formation and subsequent embolization upon blood contact. Plasma surface modification was employed to modify the inner surface of small diameter low density polyethylene (LDPE) tubing without varying the outer surface chemistry and physical properties of the tubing. A sulphur dioxide (SO2) plasma was used to form sulphonate functionality on the surface. In addition, a hexamethyl-disiloxane (HMDSO) plasma and different gas flow ratios of SO2-HMDSO gas mixture plasmas were used to form ultrathin polysiloxane-like coatings inside the LDPE tubing. X-ray photoelectron spectroscopy (XPS) indicated that the inner surface of the tubing can be modified uniformly with this treatment. In addition, XPS results showed that the percentage of sulphur atoms bound to two or three oxygen atoms (sulphone or sulphonate) increased with the SO2-HMDSO mass flow rate ratio. The blood compatibility of the plasma-modified model materials was evaluated using an ex vivo canine arteriovenous shunt model. Similar thrombogenicity was observed comparing the untreated control and the surfaces modified by HMDSO plasma and SO2-HMDSO gas mixture plasmas, despite the differences in surface chemistry. The SO2 plasma-modified surface, which is the most hydrophilic as measured by the captive bubble contact angle measurement technique, was more thrombogenic than the untreated control. This may be attributed to the combined effect of the surface chemistry and surface hydrophilicity.