a synthetic polymer with a long biodegradation period - polycaprolactone ( poly ( e - caprolactone ( pcl ) is used to fabricate vascular graft scaffolds due to its suitable and well - known mechanical properties ( flexibility and strength ). moreover , this polymer is biocompatible and bioresistant , the degradation rate of pcl fibers , spun by electrospinning , is from three months up to a year . this pcl degradation rate contributes to the long - term support of the necessary mechanical graft properties to grow into functional native vessel ; the polymer &# 39 ; s hydrolytic degradation and blood vessel regeneration are concomitant and coordinated in time . no toxic substances are formed as a result of the biodegradation : water and caproic acid . the electrospining technique used to fabricate scaffolds enables to spin micro - and nanofibers and porous structures from polymer solutions and melts . this method relates to fiber fabrication within a strong electric field generated between two electrodes bearing electrical charges of opposite polarity , with one electrode being placed into the spinning polymer solution or melt , the other being attached to a metal collector . vascular graft scaffolds are produced on the electrospinning apparatus , a polymer solution is loaded in a syringe , a metering pump attached to a plunger generates pressure at a given rate . an electrical potential is applied to a blunt - end needle attached to the syringe . the polymer is ejected from the tip , solidifies and leaves a fiber behind . the polymer fibers are captured on a rotating collector screen with the other attached electrode to comprise a porous material . the pores size do not exceed 20 μm in order to prevent bleeding through the prosthesis wall . the following parameters of electrospinning are used to produce vascular grafts : voltage — 10 - 50 kv , the flow rate of the polymer solution — 1 - 10 ml / h , the distance between the capillary and collection screen — 1 - 20 cm , motion of the target screen — about 10 - 300 / min polymer fibers are supplemented with biological molecules such as vascular endothelial growth factor ( vegf ), fibroblast growth factor beta ( b - fgf ), stromal derived factor - 1alpha ( sdf - 1α ) as well as heparin molecules during the electrospinning process . vegf incorporation into the scaffold structure contributes to its faster endothelialization , because this growth factor has been shown to play an important role in the regulation of endothelial cells migration and proliferation . in addition , bfgf is used for induction of endothelial cells and fibroblasts proliferation . sdf - 1αactivates autologous stem cells migration towards area of an injured segment , promoting its healing . the incorporation of heparin molecules into the matrix wall reduces the risk of the graft lumen thrombosis . the incorporation of these growth factors and heparin into the graft wall is performed by mixing the biodegradable polymer solution with the solution containing biological molecules in phosphate - buffered saline at a ratio of 20 : 1 , then the electrospinning is applied . since each type of biomolecules has its own impact on host &# 39 ; s cells , the proposed vascular graft may be composed of either one type of molecules or their combination . during the polymer biodegradation process the incorporated molecules are released into the surrounding tissues and perform their biological functions , such as stimulation and regulation of the native vessel growth . furthermore , the molecules attached to the polymer fibers have no contact with the external environment that ensures the long - term preservation of their functions promoting to perform grafts sterilization prior to the implantation . the utilization of polycaprolactone for a graft fabrication eliminates the immune response and allergic reactions caused by the implantation . continuous delivery of bioactive molecules into the surrounding tissues is ensured by the low rate of polymer biodegradation . the trial of the pcl vascular grafts was conducted in the louis stokes cleveland veterans affairs medical center , cleveland , ohio , usa . example 1 . vascular grafts ( internal diameter of 2 μm , thickness 100 μm ) composed of biodegradable polycaprolactone polymer ( pcl ) ( m = 80 . 000 ) were fabricated by electrospinning method and implanted in five male inbred wistar rats ( weight 400 - 450 g ). pcl - grafts were implanted in the abdominal aorta between the renal artery and the aortic bifurcation . after the clamps were removed , the blood flow through the grafts was assessed by doppler ultrasonography . after 6 weeks , the animals were euthanased , the anastomoses and graft performance were assessed by the histological examination of the samples stained with haematoxylin and eosin , mallory and van gieson technique . the histological examination of the graft lumen and anastomoses areas revealed the continuous layer of neointima . the inner surface of the seeded graft was covered with endothelial cells , most of which had enlarged hyperchromatic nuclei and decreased nuclear - cytoplasmic index compared to the endothelial cells of the own aorta . the graft was infiltrated by the cells of myofibroblasts and macrophages morphological features . collagen accumulation sites , rich in glycosaminoglycans , laminin and fibronectin , were detected on the whole graft surface . the macroscopic evaluation of the implanted graft in the perivascular tissue found no signs of bleeding . thus , the conducted trial reported the structures formation on the pcl grafts that mimic native blood vessels ; hence , these polymer substitutes appears to be promising for use in cardiovascular surgeries as a tissue - engineered vascular grafts .