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Surface modification of poly(ethylene-co-vinyl alcohol) (EVA). Part I. Introduction of carboxyl groups and immobilization of collagen.

To enhance the surface biocompatibility of poly(ethylene-co-vinyl alcohol) (EVA) and high-density polyethylene (HDPE), carboxyl groups were introduced by ozone exposure. Type I collagen was immobilized onto the surface through polyion complexing. The carboxyl groups on the EVA were characterized by electron spectroscopy for chemical analysis and neutralization. The amounts of the carboxylic group and collagen increased with increases in time and temperature of exposure. Water-soluble fragments were produced by ozone exposure to EVA, and they acted as collagen crosslinkers. The differences in charge distribution of carboxyl groups affected the amount of collagen immobilization. Graft polymerization of acrylic acid was also carried out onto EVA and HDPE surfaces. The amount of collagen immobilized by graft polymerization was much higher than that by ozone exposure despite the introduction of almost the same amounts of carboxylic groups. It was suggested that the negative charge distribution influences the amount of collagen immobilized onto films.