Surface Characterization and Platelet Adhesion Studies of Plasma-Carboxylated Polyethylene

Abstract

Carboxyl groups were incorporated onto low-density polyethylene (LDPE) by carbon dioxide (CO 2) plasma modification, ammonia (NH 3) plasma modification with subsequent β-propiolactone (C 3H 4O 2) chemical grafting, and allylamine (CH 2=CHCH 2NH 2) plasma polymerization with subsequent β-propiolactone chemical grafting. ESCA and contact-angle experiments indicated that the hydrophilicity of the carbon dioxide plasma treated LDPE decreased with time due to the diffusion of the hydrophilic oxygen-containing functional groups away from the surface regions and/or the loss of the low molecular weight polar fragments. In contrast, the surface hydrophilicity of the β-propiolactone carboxylated ammonia and allylamine plasma treated LDPE determined by contact angle experiments was stable with time, but ESCA experiments showed that surface oxygen atomic concentration increased with time because of extensive post-plasma-treatment oxidation in air. The surface nitrogen atomic concentrations of both kinds of β-propiolactone carboxylated materials decreased with time due to diffusion of the nitrogen-containing functional groups into the bulk of the materials and/or the loss of the low molecular weight fragments to the environment. The blood compatibility of the carboxylated materials was examined by in vitro canine platelet adhesion as assessed by SEM. All three types of the plasma modified materials were more platelet reactive than the control LDPE base which suggests these materials are thrombogenic.