Improved hemocompatibility of silk fibroin fabric using layer-by-layer polyelectrolyte deposition and heparin immobilization

Silk fibroin has long been used as implantable surgical sutures and it has acceptable mechanical properties and patency rates in animal models and in clinical end-uses. However, fibroin has been shown to be hemolytic and can cause damage to red blood cells. So to be used as an implantable vascular prosthesis its hemocompatibility needs to be improved. This study has taken two sequential steps to address this problem. First, to create a positively charged layer on the fibroin fibers' surface, a 1.5 and 2.5 bilayers polyelectrolyte surface deposition layer-by-layer technique was used with the positive counterion poly(allylamine hydrochloride) and the negative counterion poly(acrylic acid). Second, negatively charged low molecular weight heparin was then immobilized on these positively charged self-assembled surfaces. The presence of the heparin was confirmed with Alcian Blue staining and a toluidine blue assay, and the increased roughness and hydrophilicity of the modified surfaces were characterized by scanning electron microscopy, contact angle measurements, and atomic force microscopy. In addition, a negligible hemolytic effect, reduced protein adsorption, and a higher concentration of free hemoglobin measured by a kinetic clotting time test were found to be enhanced with the use of 2.5 bilayers compared to the 1.5 bilayers self-assembly technique. Given the success of these preliminary results, it is anticipated that this novel approach of surface modification and heparin immobilization will demonstrate long-term patency during future animal trials of small caliber silk fibroin vascular grafts. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40772.