The applications of heparin in vascular tissue engineering.

Cardiovascular diseases, among all diseases, are taking the most victims worldwide. Coronary artery occlusion, takes responsibility of about 30% of the yearly global deaths in the world (Heart Disease and Stroke Statistics 2017 At-a-Glance, 2017), raising the need for viable substitutes for cardiovascular tissues. Depending on a number of factors, blocked coronary arteries are now being replaced by autografts or stents. Since the autografts, as the gold standard coronary artery replacements, are not available in adequate quality and quantity, the demand for small diameter vascular substitute comparable to native vessels is rapidly growing. Synthetic grafts have been successfully approved for developing vascular replacements but regarding the special conditions in small-caliber vessels, their use is limited to large-diameter vascular tissue engineering. The major problems associated with the vascular tissue engineered grafts are thrombosis and intimal hyperplasia. Heparin, a negatively charged natural polysaccharide has been used in fabricating vascular grafts since it prevents protein fouling on the surfaces and most importantly, impeding thrombosis. Herein, we focused on heparin, as a multifunctional bioactive molecule that not only serves as an anticoagulant with frequent clinical use but also acts as an anti-inflammatory and angiogenic regulatory substance. We summarized heparin incorporation into stents and grafts and their applicability to restrain restenosis. Also, the applications of heparinzation of biomaterials and heparin mimetic polymers and different approaches invoked to improve heparin bioactivity have been reviewed. We summarized the methods of adding heparin to matrices as they were explained in the literature. We reviewed how heparin influences the biocompatibility of the scaffolds and discussed new advances about using heparin in small-diameter vascular tissue engineering.