Polyurethanes bearing pendant amino acids: fibrinogen adsorption and coagulant properties

Segmented polyurethanes based on 4,4'-diphenylmethane diisocyanate and polypropylene oxide and chain extended with a sulfonated diamine were derivatized by reaction of sulfonate groups in the polymer with amino acids. The chemical composition of the derivatized polymers was determined by elemental analysis. Tensile stress-strain measurements indicated a slight increase in modulus and elongation with incorporation of amino acids. Water uptake at room temperature showed little change following derivatization, but at 70 degrees C increased significantly. Water contact angles were not influenced by the presence of amino acids, but electron spectroscopy for chemical analysis data showed an increase in hard segment content in the near-surface layers so that bulk and surface compositions were more nearly the same in the amino-acid-containing materials. Fibrinogen adsorption from plasma, shown previously to be high on the sulfonated polyurethanes, was reduced by derivatization, due probably to the decrease in free sulfonate content. Thrombin times of plasma in contact with these materials were essentially the same for the derivatized and underivatized materials.