Platelet Adhesion to Heparin-Bonded and Heparin-Free Surfaces

Abstract

Polyether polyurethanes containing positive charges in the backbone or in the side chains were synthesized from commercially available diisocyanates. These cationic polyurethanes were reacted with sodium heparin to yield polyurethane heparin complexes (heparin content: 16%) soluble in specific organic solvent systems. The homogeneous solutions were used to produce thromboresistant coatings on commercial tubing.

In order to evaluate the thromboresistance of the coated and uncoated surfaces, tubing sections were inserted into a beagle chronic A-V shunt and the rate of platelet deposition was determined by the electron scanning microscope technique.

A plot of the number of platelets as a function of time on heparinized tubing shows that the buildup rate is just in the first 30 min, reaching a saturation limit of about 6 × 10⁵ platelets/cm² at about 60 min. On commercial polyurethane the rate of platelet deposition is considerably faster.

Platelets adhering to a silicone surface seem to exhibit initially a different appearance to those on a polyurethane surface. A flaking-off phenomenon was observed leaving a platelet-free silicone surface to which new platelets adhere with time.