Hamid Nayeb-Hashemi


Ahmet Umit Coskun

Date of Award


Date Accepted


Degree Grantor

Northeastern University

Degree Level


Degree Name

Master of Science

Department or Academic Unit

College of Engineering. Department of Mechanical and Industrial Engineering.


angioflex, bisphosphonate, calcification, polyurethane heart valve

Subject Categories

Heart valve prosthesis--Technological innovations, Polyurethanes in medicine


Mechanical Engineering


Heart valve related disease is a significant cause of mortality worldwide and in severe cases requires the patient to undergo a heart valve replacement surgery. The available heart valve prostheses on the market are mechanical and biological substitutes. However, both types of available heart valves have negative side-effects because they are fabricated from foreign materials. Mechanical heart valves have proven to be very durable, but are susceptible to thrombosis and thromboembolism and necessitate long-term anticoagulation therapy. On the other hand, bioprosthetic valves require little or no anticoagulation; however, the underlying problem with them is a limited life because of structural changes such as leaflet wear and calcification leading to valve failure. This study focuses on polyurethane as a potential material for prosthetic heart valves which is biocompatible, flexible and can withstand many cycles of stress and deformation before failure. The main objective of this study was to address the issue of calcification of polyurethane heart valve prostheses which require lower anticoagulation levels than mechanical valves, yet offer the potential for reduced calcification and increased durability when compared to tissue valves. The valve leaflets are fabricated from Angioflex®, a proprietary polyetherurethane material that has been successfully and clinically evaluated by ABIOMED, Inc. In the first phase of this study, a series of accelerated in vitro experiments were performed on the Angioflex® heart valves when subjected to a synthetic calcification solution. Results showed that these types of polyurethane have the potential to be considered as heart valve substitute material with significantly lower levels of calcification deposits compared to tissue valves. Another outcome of these studies was to evaluate the calcification resistance of bisphosphonate modified Angioflex® valves. Bisphosphonates are a class of drugs that are considered to enhance the calcification resistance of polymers once covalently bonded to the bulk of the material. However, our test's results showed that, although bisphosphonate-modified Angioflex® valves showed lower levels of calcification compared to tissue valves, but they are not superior to Angioflex® valves. It has also been suggested that surface defects, shear and mechanical stresses are contributing factors in the calcification process. In the second phase of this study, a number of experiments were performed to evaluate the effect of surface irregularities (such as roughness and cracks) and flow shear rate on the calcification process in the absence of any source of mechanical stresses. Results showed that even in the absence of mechanical stresses a polymeric surface gets calcified and all the above mentioned factors directly affect the calcification process. Roughness, cracks and low shear rate promote the calcification. Calcification process under steady flow rate and no mechanical stresses occurs mostly on the surface of the polymer rather than being a subsurface phenomenon.

Document Type

Master's Thesis

Rights Holder

Parnian Boloori Zadeh

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