Review Current Developments and Future Prospects for Heart Valve Replacement Therapy Asmeret G. Kidane, 1 Gaetano Burriesci, 2 Patricia Cornejo, 1,3 Audrey Dooley, 4 Sandip Sarkar, 1,3 Philipp Bonhoeffer, 5 Mohan Edirisinghe, 2 Alexander M. Seifalian 1,3 1 Biomaterial and Tissue Engineering Centre (BTEC), Academic Division of Surgery & Interventional Sciences, University College London, London, United Kingdom 2 Department of Mechanical Engineering, University College London, London, United Kingdom 3 Cardiovascular Haemodynamic Center, University College London, London, United Kingdom 4 Department of Biochemistry and Molecular Biology, University College London, London, United Kingdom 5 Cardiothoracic Unit, Institute of Child Health and Great Ormond Street Hospital for Children, London, United Kingdom Received 30 April 2007; revised 28 March 2008; accepted 9 April 2008 Published online 9 July 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.b.31151 Abstract: Valve replacement is the most common surgical treatment in patients with advanced valvular heart disease. Mechanical and bio-prostheses have been the traditional heart valve replacements in these patients. However, currently the heart valves for replacement therapy are imperfect and subject patients to one or more ongoing risks, including thrombosis, limited durability, and need for re-operations due to the lack of growth in pediatric populations. Furthermore, they require an open heart surgery, which is risky for elderly and young children who are too weak or ill to undergo major surgery. This article reviews the current state of the art of heart valve replacements in light of their potential clinical applications. In recent years polymeric materials have been widely studied as potential prosthetic heart valve material being designed to overcome the clinical problems associated with both mechanical and bio-prosthetic valves. The review also addresses the advances in polymer materials, tissue engineering approaches, and the development of percutaneous valve replacement technology and discusses the future prospects in these fields. ' 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 88B: 290–303, 2009 Keywords: heart valve replacement; polymers; tissue engineering; percutaneous heart valves INTRODUCTION Heart valve replacements are, at present, one of the most widely used prosthetic devices. Recent statistics show that in 2006 there were around 98,000 valve replacements in the USA and 195,300 outside the USA. 1 The most common valve operation is aortic valve replacement for aortic steno- sis or aortic insufficiency. The aortic valve regulates the blood supply to all of the major vessels of the body. In aor- tic stenosis, the aortic valve tightens or narrows, preventing blood from easily flowing through. With aortic insuffi- ciency, the aortic valve no longer adequately retains blood, allowing leakage through the valve back into the heart resulting in regurgitation of blood, which can lead to heart failure. The desirable prosthetic heart valve is considered to function in the same manner as the native organ, and to have a long-term durability together with high reliability, safety, and biocompatibility. There are two types of prosthetic heart valve, mechani- cal valves, which are made entirely of synthetic materials, such as plastics and metal and bio-prosthesis valves, which are taken from animal or human sources. Mechanical pros- thetic valves are divided into two kinds based on their flow patterns, those with lateral flow, such as the ball in cage valves and those with more central flow, such as the tilting disc and bileaflet valves. One of the major drawbacks, however, of currently available prosthetic heart valves is that mechanical heart valves require daily anticoagulant treatment because of an increased risk of thrombosis and thromboembolism. More- Correspondence to: A. M. Seifalian (e-mail: a.seifalian@ucl.ac.uk) Contract grant sponsor: Engineering and Physical Sciences Research Council; Contract grant number: EPSRC EP/D061555; Contract grant sponsor: British Heart Foundation. ' 2008 Wiley Periodicals, Inc. 290