Molecular stability, mechanical properties, surface characteristics and sterility of biodegradable polyurethanes treated with low-temperature plasma

Biodegradable medical polyurethanes with varying hydrophilic-to-hydrophobic segment ratios based on hydrophilic poly(ethylene oxide) and hydrophobic poly(c-caprolactone) diol, were treated with low-temperature, low-pressure plasmas of hydrogen peroxide, oxygen, carbon dioxide and ammonia. All samples treated with hydrogen peroxide plasma were sterile, while samples treated with oxygen, carbon dioxide and ammonia plasmas were nonsterile. The treatment caused a 7% drop in molecular weight and a 15% reduction in tensile strength for polyurethanes with a higher content of the hydrophobic segment; and a 27% reduction of molecular weight and a 20% decrease in tensile strength for the most hydrophilic materials. The hydrogen peroxide plasma extensively etched the surface of the materials, this being accompanied by a significant, 100-200% increase in the surface roughness. In contrast, the oxygen, carbon dioxide and ammonia plasma reduced the surface roughness of most hydrophilic PEO-PCL70-30 material, but minimally affected the surfaces of the remaining polymers. The hydrogen peroxide and oxygen plasmas increased the surface content of oxygen and decreased the content of nitrogen and carbon. The carbon dioxide plasma increased the carbon content, but decreased the oxygen and nitrogen content. The ammonia plasma decreased the nitrogen content, increased the carbon content and decreased the oxygen content. The surface contact angles slightly decreased for polyurethanes treated with oxygen and hydrogen peroxide plasmas, and increased for the samples treated with ammonia and carbon dioxide plasmas. Plasma treatment minimally affected the thermal characteristics of polyurethanes. (C) 2002 Elsevier Science Ltd. All rights reserved.