Mechanical characterization of silk derived vascular grafts for human arterial implantation Patrick Iyaselea, Eoghan M. Cunnanea, Katherine L. Lorentza, Justin S. Weinbauma, e, and David A. Vorpa, b, c, d, f, g Department of Bioengineering, bMcGowan Institute for Regenerative Medicine, cDepartment of Surgery, d Center for Vascular Remodeling and Regeneration, e Department of Pathology, fDepartment of Chemical and Petroleum Engineering, gDepartment of Cardiothoracic Surgery a
Patrick Iyasele is a Senior Bioengineer from Milwaukee, Wisconsin. He is pursuing a Ph.D. in Bioengineering with focus on cardiovascular tissue engineering. He is a Foundation board member for Pitt B.R.O.T.H.E.R.H.O.O.D and is highly active in the Pitt Excel Program. Patrick Iyasele
David A. Vorp, PhD
David A. Vorp, PhD, is the Associate Dean for Research at the Swanson School of Engineering. He is also John A. Swanson Professor of Bioengineering, with secondary appointments in the Department of Cardiothoracic Surgery, the Department of Surgery, the Department of Chemical and Petroleum Engineering, and the Clinical and Translational Science Institute at the University of Pittsburgh.
Significance Statement
Occluded blood vessels are commonly treated by revascularization surgery utilizing vascular grafts. Compliance mismatch between the native coronary artery and a vein autograft often leads to restenosis and failure of roughly half of all autografts implanted during revascularization surgery [1]. Due to the limited quantity of autografts and required invasive harvesting, tissue engineered vascular grafts (TEVGs) are being researched and developed as an alternative. This paper presents preliminary data that suggests silk TEVGs may be a suitable alternative as they have similar mechanical properties to native tissue at low strain ratios.
Category: Experimental research
Keywords: TEVG, Silk, Mechanical Testing, Tangential Modulus Abbreviations: TEVG- Tissue Engineered Vascular Graft
52 Undergraduate Research at the Swanson School of Engineering
Abstract
Coronary artery disease occurs from the narrowing and blockage of the vessels supplying blood to the heart, leading to reduced blood flow and tissue damage. The preferred treatment for occluded small diameter arteries is revascularization surgery utilizing vascular autografts including the saphenous vein or internal thoracic artery. However, such autografts are limited in quantity, may be of poor quality and require invasive surgery to harvest and utilize. Additionally, compliance mismatch from the native coronary artery with a vein autograft often leads to restenosis and failure of roughly half of all autografts implanted during bypass surgery [1]. Tissue engineered vascular grafts (TEVGs) are currently being studied and developed as alternatives. A successful TEVG should mimic the mechanical properties of native vessels to reduce failure due to compliance mismatching, therefore, the objective of this study was to calculate the tangential modulus of a bombyx mori (BM) silk derived TEVG and compare it to the tangential modulus of the native vessels it is intended to replace. A BM scaffold was seeded with human cells and analyzed by uniaxial extension testing along with two explanted sheep carotid arteries. This entailed cutting the tube into ring specimens and tensile testing five replicates, recording the stress-strain curve and calculating the tangential modulus. The BM silk TEVG had a similar tangential modulus to a native sheep carotid artery at low strain ratios (1.3) but was significantly lower at high strain ratios (1.9).
1. Introduction
Cardiovascular disease is the leading cause of death worldwide, with most deaths associated with coronary heart disease, cerebrovascular disease, peripheral arterial disease, and deep vein thrombosis. These diseases often occur from the narrowing and blockage of blood vessels leading to reduced blood flow and tissue damage due to inadequate nutrient supply [1]. The preferred treatment for occluded small diameter arteries (such as the coronary arteries) is revascularization surgery utilizing vascular grafts. During this surgery, a graft is used to replace or bypass the damaged or occluded vessel. Around 400,000 coronary artery bypass grafting (CABG) procedures are performed each year in the United States alone [2]. The saphenous vein and internal thoracic artery are commonly used for autografts but those are limited in quantity, may be of poor quality and require invasive surgery to harvest and utilize [1]. Compliance mismatch from the native coronary artery and a vein autograft leads to restenosis and failure of roughly half of all autografts implanted during bypass surgery [1]. Tissue engineered vascular grafts (TEVGs) are currently being studied and developed as alternatives. An ideal TEVG should mimic the mechanical properties of native tissues. Compliance mismatch from the native coronary artery and a vein autograft lead to restenosis and failure of roughly half of all autografts implanted during bypass surgery [1]. Tangential modulus has been a useful property to ascertain in this regard as it describes the stiffness of a material at certain mechanical strains that are experimentally tested during uniaxial
