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In order to replace or repair small diameter arteries in patients suffering from peripheral vasculardisease, for example, for coronary artery bypass or below the knee femoral/popliteal bypass, thecurrent "gold standard" for the choice of material involves the patients own tissue such as theinternal mammary artery/or saphenous vein.However, there are certain shortcomings with theseautologous vessels, such as problems of inappropriate size for certain procedures, unacceptablevaricosities for different veins and unavailability of supply in chronic patients.Current syntheticpolymer graft materials, such as poly(ethyleneterephthalate) (polyester-PET) or expandedpolytetrafluoroethylene (ePTFE-Goretex(R)), inevitably fail due to thrombosis (clot formation) orintimal hyperplasia most likely caused by compliance mismatch.Natural polymers, such as silkfibroin, have long been used as implantable surgical sutures, and recent reports from our groupand others have demonstrated that it has acceptable mechanical properties and patency rates foruse as a vascular substitute in animal models.However, fibroin is believed to contribute to thedamage of red blood cells, and in order to be used as an implantable vascular prosthesis itshemocompatibility needs to be improved.This study has taken two sequential steps to address thisproblem.First, in order to create a positively charged surface on the clean silk fibroin fabric (SFF),a 3 and 5 layers of polyelectrolyte surface deposition layer-by-layer technique was used with thepositive counterion poly(allylamine hydrochloride)(PAH) and the negative counterionpoly(acrylic acid)(PAA).Second, negatively charged low molecular weight heparin (LMWH) withand without activation with 1-ethyl-3-(dimethylaminopropyl) carbodiimide hydrochloride (EDC)and N-hydroxysuccinimide (NHS) was then immobilized on these positively charged self-assembled surfaces. The effectiveness of the alkali degumming treatment for raw silk fabric was confirmedqualitatively using picric acid and carmine staining (PACS).Fibroin selectively adsorbs picric acidmolecules in alkaline solution, generating a yellow color, whereas, both carmine (red color) andpicric acid (yellow color) adhere to sericin producing a deep red identifiable coloration.In addition,the accumulation of sericin gum on the virgin silk fabric surface was readily visualized by SEMmicrographs compared to the SFF which showed a smooth surface which confirmed theeffectiveness of the degumming process.Additional gravimetric measurements, representing aquantitative assessment of the degumming process, attributed a weight loss of 25.5％ to thedegummed silk fabric. The presence of heparin was confirmed with Alcian Blue staining, a toluidine blue assay, energydispersive X-ray analysis and XPS (X-ray photoelectron spectroscopy) analysis. Surface modified and immobilized silk fibroin fabrics showed an evident difference anduniformity in color under light microscopy between the untreated and modified samples whenstained with of Alcian Blue solution.This result confirmed the presence of an activeglycosaminoglycan (GAG), namely heparin, and indicated that it was uniformly distributed overthe surface of the modified fibroin fabrics. According to the toluidine blue assay, the average heparin content was found to lie in the range10.65 μg/cm2 to15.34 μg/cm2.In order to confirm the presence of heparin molecule on themodified SFF surfaces, both sulfur (S) and sodium (Na) peaks were identified by XPS and EDXanalyses. Increased roughness and hydrophilicity of the modified surfaces were characterized by scanningelectron microscopy (SEM), atomic force microscopy (AFM) and water contact anglemeasurements.SEM microphotographs confirmed that the surface of the control silk fibroin fibersappeared to be smooth with axially aligned striations.On the other hand, the surfaces of themodified fibroin fibers changed from being smooth to being irregular and rough.The 3 and 5 layersof polyelectrolyte deposition and heparin immobilization added a raised globular appearance onthe fibroin fiber surface.The irregular distribution of discrete "hills and valleys" suggests that thepolyelectrolyte distribution was not applied evenly across the whole fiber surface.In some areasthe discrete globular regions combined and fused together to form a more extensive modifiedsurface. AFM analysis showed that before modification, the top view of the fibroin fiber surface appearedto be comparatively smooth.However, after modification, the fiber surfaces became more unevenwith many convex protrusions separated by pits or valleys, suggesting that the polyelectrolytedeposition created irregular clusters of condensation on the fibers surface.The contact angle testresults indicated ensured that the modified SFFs had significantly increased hydrophilicity.Themechanical properties in terms of bursting strength test and the thermal performance as measuredby thermogravimetric analysis (TGA) revealed that the modification process caused no reductionin bursting strength and resulted in a marginally higher thermal stability. The polyelectrolytes deposition and heparin immobilization surface treatment also generatedimprovements in the biological performance.The modified SFF surfaces were found to have anegligible hemolytic effect, reduced protein adsorption and platelet adhesion and a higherconcentration of free hemoglobin measured by a kinetic clotting time test.Furthermore, the surfacetreated with the 5 layer deposition procedure gave an enhanced performance compared to the 3layer self-assembly technique.Given the success of these preliminary results, it is anticipated thatthis novel approach to surface modification and heparin immobilization will demonstrate long termpatency in during in vivo animal trials of small caliber silk fibroin vascular grafts.