Development of "heparin-like" polymers using swift heavy ion and gamma radiation. I. Preparation and characterization of the materials.
The development of ideal antithrombogenic polymers, a major problem in biomaterials sciences, is a primary objective in the fields of cardiovascular prostheses, artificial hearts, and other devices. To decrease their thrombogenicity, which remains the major obstacle, we have developed polymeric materials endowed with a specific affinity for antithrombin III (ATIII) and thus able, like heparin, to catalyze the inhibition of thrombin by ATIII. Sulfonate and sulfonamide groups are introduced onto phenyl rings belonging to styrene residues, which are radiation grafted (using swift heavy ion and gamma radiation) onto poly(vinylidene difluoride) (PVDF) and also onto poly(vinylidene fluoride/hexafluoropropylene) [P(VDF-HFP)]. In contrast to gamma radiation, which leads to a homogeneous modification, the advantage of swift heavy ion grafting is that only small regions are modified; thus, the surface may present hydrophilic (corresponding to the modified areas) and hydrophobic microdomains (corresponding to the unmodified areas) of different sizes, depending on the absorbed dose and grafting yield. Surface topography and composition are characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Sulfur, sodium, fluorine, and carbon are determined by scanning electron microscopy combined with energy-dispersive X-ray analysis (SEM-EDXA). The amount of fluorine decreases as polystyrene (PS) is grafted, whatever the kind of radiation and polymer. When the polymers are functionalized, the amount of fluorine also decreases while sodium and sulfur appear. Functionalization seems to increase the roughness of the surface, and its area.