AbioCor Heart System

Foreword We have been asked to research a biomedical device and present our findings as well as propose a design recommendation for the device. In response to this task, we chose the AbioCor Replacement Heart System and conducted detailed research on the device. This report contains relevant background information and a thorough physical description of the components and functions of the AbioCor Replacement Heart System in addition to materials used in the device, alternative systems to the device, limitations of the device, and current research in this field. The report also contains our proposed design recommendation to improve the AbioCor System. The purpose of this report is to present our findings to readers in an effective manner. Summary The AbioCor Replacement Heart System is a solution for end stage heart failure. End stage heart failure is a severe condition that affects the heart’s ability to pump blood throughout the body. Over 100,000 patients each year suffer from end stage heart failure and will die if a donor heart is not readily available. Unfortunately, there are only 2,000 donor hearts available each year in the United States, creating a huge need for an alternative solution [1]. The AbioCor System is designed to permanently replace the hearts of patients suffering from end stage heart failure. Artificial hearts have been under development for over fifty years. The Jarvik-7 Total Artificial Heart and the Akutsu III Total Artificial Heart are two predecessors to the AbioCor System, sustaining patients for short periods of time until a donor heart became available. However, both of these earlier artificial hearts were limited by their external console size and skin-piercing connection wires. The AbioCor System consists of three interconnected systems: the power system, the control system, and the pumping system. The power system consists of an external battery, internal battery, external TET, and an internal TET. The power system receives power from either the external battery or an electrical outlet. The external TET transfers power from the electrical outlet or external battery pack wirelessly to the internal TET. The internal TET then transmits the power to the pumping and control system. The internal battery pack can provide power for up to 45 minutes if it is the only source of energy available. The control system consists of an internal sensor, an internal controller, an external console, and the Patient Carried Electronics (PCE). These components work in conjunction to make sure the AbioCor functions properly. The PCE and the console communicate wirelessly with the internal controller to maintain the AbioCor System. Finally, the pumping system consists of the thoracic unit. The thoracic unit replaces the natural heart of the patient and is responsible for pumping blood. A small rotary motor pumps hydraulic fluid, causing the contraction of Angioflex® membrane. The inflation and deflation of this membrane causes blood to pump through the device. These three systems work together to replace the failed heart of a patient [2]. Although the AbioCor System is an effective treatment for end stage heart failure, there are alternative devices available for combating this disease, including the Jarvik 2000 Left Ventricle Assist System and CardioWest Heart. Like all cardiac support devices, the AbioCor has its limitations, including a large internal component, limited length of patient sustainment, limited battery life, and incidences of internal bleeding. Further development of artificial hearts continues with the AbioCor II, designed to address the AbioCor’s limitations, and the Carmat Heart. In response to the limitations of the AbioCor System, we propose replacing the external battery with a fuel cell to increase battery life. The AbioCor Replacement Heart System is designed to sustain patients with end stage heart failure. Every year over 100,000 people in the United States will die from end stage heart failure because a donor heart is not available [1]. The AbioCor System is designed to permanently replace a damaged heart. In order to fully describe the AbioCor System, this document gives a brief background on the anatomy and physiology of a healthy heart, medical problems that lead to heart failure, previous attempts of heart replacement, and a technical description of the AbioCor System. Brief Description of the Heart The heart is the center of the cardiovascular system and is responsible for pumping blood throughout the body. The average adult’s heart is about the size of a clenched fist. Despite its relatively small size, the heart has a tremendous capacity for work. The average heart pumps about 30 times its weight in blood each minute [3]. Over an average lifetime, the heart beats well over 3 billion times [4]. 440055035560Chambers of the Heart The heart is divided into four inner cavities called chambers. As Figure 1 shows, the upper two chambers are known as the left and right atria (the singular is atrium). The lower two chambers are called the left and right ventricles. The left ventricle is the largest and strongest chamber of the heart, followed by the right ventricle. The atria are the smallest and weakest chambers of the heart. Blood Vessels of the Heart Fig. 1 Diagram of the Heart[5]Veins and arteries, collectively called blood vessels, are connected to the four chambers. Veins carry blood towards the heart while arteries carry blood away from the heart. Figure 1 shows that the superior and inferior venae cavae (the singular is vena cava) are connected to the right atrium. The pulmonary trunk, which branches into the left and right pulmonary arteries, is connected to the right ventricle. The left and right pulmonary veins are connected to the left atrium. The aorta is connected to the left ventricle. The blood vessels allow the heart to move nutrient and oxygen-rich blood throughout the body. Valves of the Heart There are two types of valves in the heart: valves that separate atria from ventricles, or atrioventricular valves, and valves that separate blood vessels from ventricles, or semilunar valves. The tricuspid valve is an atrioventricular value that separates the right atrium from the right ventricle. The bicuspid (also called mitral) valve is also an atrioventricular valve that separates the left atrium from the left ventricle. The pulmonary semilunar valve lies between the pulmonary trunk and the right ventricle. The aortic semilunar valve separates the aorta from the left ventricle. These valves are designed to keep blood flowing in one direction. Blood Flow Through the Heart Fig. 2 Blood Flow through the Heart[4]-6985075565The heart pumps blood using a simple principle: as volume decreases, pressure increases. Figure 2 illustrates the cycle of blood flow through the heart. The chambers of the heart receive blood, pump the blood by contracting, and then relax to fill with blood again. Deoxygenated blood returning from the body enters the right atrium through the superior and inferior venae cavae. Then, an electrical impulse stimulates the right atrium to contract, increasing the pressure inside the atrium. The increased pressure forces the blood through the tricuspid valve into the right ventricle. Another electrical impulse stimulates the right ventricle to contract, pumping the blood through the pulmonary semilunar valve, into the pulmonary trunk and then through the pulmonary arteries to the lungs. The newly oxygenated blood returns through the pulmonary veins into the left atrium. The left atrium pumps the blood through the bicuspid valve into the left ventricle. Finally, the left ventricle contracts and sends the blood through the aortic valve and into the aorta. This description is of one isolated cycle of blood flow through the heart. Blood flow is continuous through the heart, so it is important to note that the atria simultaneously fill with blood as do the ventricles. Heart Failure Heart failure is a condition in which the heart is unable to pump enough blood to meet the body’s needs. In heart failure, the heart overworks itself by forming more muscle mass and pumping faster in an attempt to pump sufficient blood to the body. Over time, the heart becomes fatigued. At this point, heart failure worsens to end stage biventricular heart failure, the most severe type of heart failure, having an average prognosis (patient life expectancy) of a month [6]. 42640251200150Heart Disease Fig. 3 Diseased Artery[8]Heart failure is caused by heart disease. Heart disease can be either congenital (since birth) or acquired. Patients acquire heart disease over an extended period of time through unhealthy lifestyle choices, including poor diet and exercise, smoking, and drinking. The two most common types of heart disease are coronary heart disease and heart valve disease. Coronary Heart Disease Coronary heart disease occurs when plaque buildup clogs the arteries, limiting blood flow to the heart. As seen in Figure 3, atherosclerosis, the process of plaque buildup, causes coronary heart disease [7]. Plaque is a mixture of cholesterol, fat, calcium, and free radicals that travel through the blood stream. As a result of coronary heart disease, the heart cannot receive the proper amount of blood, causing the heart to work harder than normal. Heart Valve Disease Heart valve disease occurs when the valves in the heart are not functioning properly. In this malfunction, valves are unable to open or close in the proper manner. Heart valve disease can be caused in three ways: deterioration, endocarditis (an infection), or a preexisting problem from a birth defect. In heart valve disease, blood either leaks through an unclosed valve when it is not supposed to or a valve prevents blood from readily passing [9]. History and Development of the AbioCor Replacement Heart System Doctors have been using artificial hearts to combat heart failure for over fifty years. Over this time period, doctors have implanted numerous designs. These various artificial heart designs are distinguished from one another by several important design characteristics: safety of device use, weight and size, the mobility they allow a patient, and length of time they can sustain the patient. Over time, artificial heart designs have advanced in these characteristics. Continuous-flow Pump Experimentation In the 1950s and 1960s, doctors began experimenting with continuous-flow pumps designed to pump enough blood to meet circulatory demand. These pumps supply blood in a continuous fashion, rather than in short bursts as a normal heart would pump [10]. In 1960, doctors conducted the most influential and successful experiment in which two continuous-flow pumps sustained an animal for twelve hours [10]. Continuous-flow pumps have been used in subsequent artificial hearts as a result of this success. 4956810121920Liotta Total Artificial Heart Fig. 4 Liotta Total Artificial Heart[11]The Liotta Total Artificial Heart is the first artificial heart and was implanted in 1969. As seen in Figure 4, the artificial heart replaces the heart’s ventricles and uses a pneumatic (air-driven) pump to push blood continuously through the body [11]. The Liotta connects to an external power unit with a control panel to adjust pumping rate and pressure [11]. Although it was considered a huge accomplishment at the time, this artificial heart has many flaws, such as the high risk of complication in its implantation. Furthermore, the Liotta requires the patient to be connected to the external power unit at all times; thus, the patient is immobile. Finally, the Liotta is designed to sustain patients temporarily, until a donor heart became available. Akutsu III Total Artificial Heart Fig. 5 Akutsu III TAH[12]952563500The Akutsu III Total Artificial Heart was first implanted in 1981. As seen in Figure 5, the Akutsu III implements two air-driven pumps in prosthetic ventricles, both very similar in design to the Liotta [12]. Externally, a pneumatic drive system pushes compressed air into the artificial heart to pump blood. The Akutsu III also relies on an external power system, which includes a back-up battery [12]. Although its power system includes the added safety feature of a back-up battery, the Akutsu III still faces many of the limitations as the Liotta. Like its predecessor, the Akutsu III was designed to sustain patients only until a donor heart became available. However, this artificial heart can only support a person for up to 55 hours while a donor heart can take over a year to become available. This device is also limited by its large external consoles, which make patients immobile. 484822529845Jarvik-7 Total Artificial Heart The use of the Jarvik-7 began in 1982. Pictured in Figure 6, the Jarvik-7 is very similar in design to the Akutsu III. The Jarvik-7 combines the Akutsu III’s external monitoring system and power system into one large device. This artificial heart system addresses some of the Akutsu III’s problems by implementing a back-up battery for patient transportation and having the ability to sustain patients for up to two years [13]. However, the Jarvik-7 still relies on skin-piercing wires and tubes to connect internal and external components, increasing risk of infection. Fig. 6 Jarvik-7 Total Artificial Heart[13] AbioCor System Addresses Limitations of Predecessors The AbioCor Replacement Heart System is the most advanced heart system to date. Its unique design, later discussed in detail, allows the AbioCor to be completely self-contained, reducing the risk of infection from skin-piercing wires [14]. Furthermore, a portable battery allows the patient to be independently active. As a result, the AbioCor System addresses all of the limitations of its predecessors. Figure 7. Layout of the AbioCor System[15] 3492500914400Basic Layout of the AbioCor System Figure 7 displays the layout of the AbioCor System, which includes the external and internal TET, thoracic unit, implanted controller, implanted battery, and the PCE (Patient carried electronics). -3175149860 The Patient-carried Electronics (PCE) 24003001531620Figure 8. The Patient-carried Electronics (PCE)[2]The patient-carried electronic system (Figure 8) is composed of essential technologies, including the batteries, the control module, and the external TET, that allow a patient to be mobile. The bag consists of two battery pairs and is connected to the PCE control module, a device that monitors the internal components of the AbioCor and alerts the patient of any problems. The PCE is also connected to the external TET and cable [2]. 3429000144780The External and Internal TET Figure 10. Internal TET[2]Figure 9. External TET[2]The external and internal TET (Figures 9 and 10) distinguishes the AbioCor System from other heart systems because it allows the external battery to power the internal components without the use of skin-piercing wires. The external TET converts electricity to electromagnetic waves through magnetic induction. The electromagnetic waves are then wirelessly transferred to the internal TET, which converts the waves back into electricity. The electricity is transmitted to the implanted controller to power the pump motor of the thoracic unit. The TET system helps eliminate the need for any sort of wires that penetrate the skin. This eliminates any possible infection that would come from wires that penetrate the skin [14]. The Battery System 44005502609850The internal and PCE batteries power the AbioCor System. The internal battery is surgically implanted in the patient’s abdomen [2]. Its purpose is to provide emergency power in the event that there is no external power being transferred into the body [2]. Even though the implanted battery is rarely used, it lasts only up to a year because of the body’s corrosive environment [2]. The PCE battery, which is located in the PCE bag, provides two hours per battery pair of mobile power. Together, the batteries allow a patient to be independently active. The Console Figure 11. The Console[2]The console (Figure 11) allows a doctor or physician to communicate with the AbioCor System. The console transmits a doctor’s adjustments to the internal controller through an internal antenna. Similar to the PCE control module, which will be explained in the next section, the console is able to receive status updates on the AbioCor System as a whole from the internal controller. The console also has the ability to alert the patient or doctor if there are any problems with the AbioCor System. The console provides electrical power to the external TET from an outlet as opposed to batteries from the PCE bag when a patient is moving around [2]. 3632200100330PCE Control Module Figure 12. The PCE Bag. The PCE control module is circled.[2]The PCE control module (circled in Figure 12) performs the same essential functions as the console, but it doesn’t allow a doctor or physician to make changes to the AbioCor System. However, the PCE control module also has the ability to connect to the batteries in the PCE bag, allowing a patient to go wherever he or she may want without having to worry about the AbioCor System [2]. Internal Controller The internal controller is a small computer unit, known as a microprocessor, which is connected to all the internal components of the AbioCor System. The internal controller is encased in titanium because of the metal’s biocompatibility. The purpose of the internal controller is to monitor the internal components of the AbioCor System, communicate with the PCE or the console unit, and control the rate at which the thoracic unit pumps blood [2]. The internal controller monitors the sensors located near the outflow valve of the thoracic unit [15]. These sensors measure the oxygen content of the blood. Based on the sensors’ measurements, the internal controller adjusts the pumping rate depending on the needs of the patients and the activities they are doing. In order to maintain proper functioning of the internal components, the internal controller communicates with the PCE or the console unit, depending on the power connection, to transmit information. The PCE or console unit will then notify the patient immediately of any issues with the internal components or the power supply. The internal control operates by a predetermined program or can be externally controlled by a clinician through the console system [2]. Thoracic unit Fig. 14 Thoracic Unit[18]1778005524500Fig. 13 AbioCor Installation[18]02286000The thoracic unit of the AbioCor replaces both of the patient’s ventricles. The thoracic unit is just over two pounds. Due to its necessary size to efficiently pump blood, it is too large to fit in the chest cavity of smaller patients such as children. The thoracic unit is made from titanium and a polyurethane blend called Angioflex™ to reduce the likeliness of clotting by being incredibly smooth. This smoothness gives blood less of a chance to cling to imperfections, lowering the chance of blood clots [16]. As Figure 13 shows, the thoracic unit is surgically implanted into the patient’s chest cavity after both ventricles have been removed. The thoracic unit is then connected to the right and left atria, the aorta, and the pulmonary artery. In order for blood to enter and exit from the unit, grafts must be sewed onto the right and left atria, the aorta, and pulmonary artery of the patient. They must also be sewed onto the thoracic unit’s four heart valves. These grafts then allow for the two arteries and the two atria to each be snapped onto the graft of one of the heart valves. The thoracic unit contains two motors: one controls the opening and closing of the heart valves and another powers the central rotary motor [17]. These hydraulic pumps are powered by electricity rather than pneumatics (air powered). As shown in Figure 14, the center of the thoracic unit contains a small rotary motor pumps hydraulic fluid between the Angioflex™ membranes in each of the artificial ventricles [17]. A rotating titanium ring controls the flow of this hydraulic fluid between each membrane. This process imitates muscle contraction of a normal heart, achieving continuous blood flow. Alternatives Systems and Techniques Although the AbioCor System is an effective treatment for end stage heart failure, doctors use other biomedical systems as well to combat this disease. Depending on each individual patient’s condition, doctors may use Left Ventricle Assist Systems (LVAS) or a different artificial heart. Similar to artificial hearts, LVAS are also designed to provide cardiac support to the patient. Both LVAS and total artificial hearts are fully implanted in the body. However, unlike artifical hearts, LVAS do not replace the heart. Furthermore, LVAS supplement the native heart by optimizing blood flow output from the heart while total artifical hearts pump all of the patient’s blood (Hoenicke). Both devices are treatments of heart failure and end stage heart failure. Doctors select the appropriate biomedical system depending on the patient’s condition. Two of the most advanced LVAS are the Jarvik 2000 and the Penn State LionHeart™. The two most advanced and implanted artificial hearts are the AbioCor System and the CardioWest Heart. Jarvik 2000 Figure SEQ Figure \* ARABIC 15. Jarvik 2000 [25]4051300354330The Jarvik 2000 is a LVAS designed to sustain patients with heart failure for short-term periods or permanently. The device consists of three main parts: the internal axial flow pump, the external controller, and the battery. The internal axial flow pump is implanted inside the left ventricle of heart, where it uses a spinning rotor to propel blood from the left ventricle to the aorta [20]. Meanwhile, the heart continues to pump naturally, pushing the extra volume of blood sent by the Jarvik 2000 to the rest of the body. Generating an average pump flow rate of 5 liters per minute, the internal axial pump of the Jarvik 2000 magnifies the blood output of the heart [25]. As seen in Figure 15, the internal pump speed is connected to the external controller through a skin-piercing wire. The external controller is small and allows the patient to manually adjust blood flow rate of the internal pump depending on the patient’s activity level. This control unit also alerts the patient of any device malfunctions [20]. Finally, the internal pump and external controller are both powered by the Jarvik 2000’s battery. A power cable connects the implanted pump to its wearable battery and controls through the abdominal wall [20]. This external battery can power the Jarvik 2000 for 8 to 10 hours. The external components, including the external controller and the battery, weigh less than three pounds. Advantages and Disadvantages of the Jarvik 2000 In comparison to the AbioCor System, the Jarvik 2000 has three main advantages: a smaller and lighter internal component, a smaller and lighter external controller, and longer battery life. Because the Jarvik 2000 does not replace the heart, the device’s internal component is extrememly light, weighing only 85 grams, and small [25]. A smaller internal component allows doctors to use the Jarvik 2000 in more pateints, while the AbioCor System’s size limits its candidate patients. Furthermore, the Jarvik 2000’s smaller and lighter external controller and longer battery life makes patients more mobile and less restrained by their medical condition. On the other hand, the Jarvik 2000 does not replace the heart. In the event of an entirely failed heart, the Jarvik 2000 cannot be used as a treatment. The use of skin-piercing wires in the Jarvik 2000 is also a disadvantage because pierced skin increases the risk of infection. The AbioCor System, however, is completely self-contained and eliminates this risk. Penn State LionHeart™ The Penn State LionHeart™ is the first fully self-contained LVAS, designed to sustain patients suffering from severe heart failure for both short-term and long-term periods. The LionHeart™ consists of internal components and external components. There are three internal components: the blood pump, motor controller, and internal coil. There are two external components: the battery pack and system monitor [19]. The LionHeart™ uses the same TET system as the AbioCor System to transfer power non-invasively through the intact skin to power the internal components. In fact, the LionHeart™ is essentially the LVAS equivalent of the AbioCor System. The internal pump is implanted in the abdomen near the ribs. Advantages and Disadvantages of the Penn State LionHeart™ Because the Penn State LionHeart™ resembles the AbioCor System so much, the two biomedical devices share the same advantages and disadvantages. Both devices are relatively large in size and weigh nearly triple the size of a human heart, making both devices unsuitable for smaller patients. On the other hand, both devices are completely self-contained, eliminating the risk of life-threatening infections from skin-piercing wires in previous devices. CardioWest Heart 43307003175The CardioWest Heart is an artificial heart that consists of two ventricles and an external driver and console system. These ventricles are implanted separately to replace diseased ventricles. As seen in Figure 16, the ventricles connect to the external driver through two skin-piercing tubes (one from each ventricle). The driver is pneumatic, providing pulses of air and vacuum to the ventricles that make the artifical heart pump [27]. When a patient exercises and blood vessels contract, increased blood enters the artificial ventricles which in turn pumps more blood to meet the patient’s circulatory demand. The external driver system also serves as a console system, allowing the patient to adjust blood flow rate. Figure 16. Cardiowest [27]Advantages and Disadvantages of the CardioWest Heart The CardioWest is smaller in size than the AbioCor System, allowing the CardioWest Heart to fit in more patients. Furthermore, the CardioWest heart uses two separate ventricles, making implantation surgery safer and easier [22]. However, unlike the AbioCor System, the CardioWest Heart is not desgiend to permanently replace the heart. The CardioWest also relies on skin-piercing tubes, which risks infection in the patient. Limitations of the Current System Like its competitors, the AbioCor System also has several limitations: a large thoracic unit, limited patient sustainment, limited battery life, and incidences of blood clot formation. The large thoracic unit is too large to fit in the majority of patients’ chest cavities; in fact, only 50% men and very few women are large enough to be eligible for an AbioCor System [23]. As a result, the majority of Americans suffering from end stage heart failure cannot use the AbioCor System because of its size. The AbioCor System has also only been successful in sustaining a patient for one to two years on average. The battery life is another limitation of the AbioCor System, requiring recharging every four hours. The batteries’ constant need for recharging is an inconvinience to the patient. Finally, some users of the AbioCor System have experienced blood clot formation due to the device. If not immediately treated, a blood clot can result in death of the patient. The occurance of blood clot formation in its users also limits the AbioCor System. Current Research and Development The development of the AbioCor System and alternative biomedical systems simmilar to the AbioCor System is considered a huge accomplishment in biotechnology development and heart failure treatment. However, research on heart failure treatments and further development of artificial hearts continues. Doctors and engineers continue this research in hopes of further improving current systems and generating new treatments for heart failure. Two main areas of current research and devopment are improved artificial hearts, such as the AbioCor II and Carmat heart, and tissue engineering. 3841750111125AbioCor II Replacement Heart System Figure 17. AbioCor II Heart [31]Abiomed is currently developing a predecesor to the Abiocor System – the AbioCor II Replacement Heart System, designed to address many of the AbioCor System’s limitations. Although the AbioCor II is still in clinical testing, Abiomed plans to address the following problems of the AbioCor System in the AbioCor II System: the size and weight of the thoracic unit, blood clotting, and length of patient sustainment. The grapefruit-sized AbioCor System weighs about two pounds, making it too large to be implanted in the majority of patients. In fact, the AbioCor System is suitable to fit in only 50% of men and 20% of women [22]. In response to this problem, the AbioCor II System will be 30% smaller than its predecesor [23]. The AbioCor System also has caused incidents of blood clot formation in several patients. As a result, Abiomed is investigating new polymers and biosynthetic materials for the AbioCor II to decrease the likelihood of clot formation in patients [22]. Finally, the AbioCor System is designed to sustain patients for up to 18 months. The AbioCor II is designed to last 5 years. Carmat Heart Figure 18. Carmat Heart [32]33528001555750Created by EADS, an aerospace company, the Carmat Heart is a total artificial heart designed to sustain patients suffering from end stage heart failure indefinitely. The artificial heart consists of two ventricles, each with a pump, making the Carmat heart more similar to a human heart than the AbioCor heart. Furthermore, the AbioCor system had several cases of blood clotting in patients. In response to this concern, the membrane of the Carmat’s implanted unit is composed of a combination of polymers and biological materials, made of chemically treated animal tissue, minimizing blood clotting incidents and increasing biocompatibility [28]. The Carmat Heart System also implements innovative internal software. The internal software automatically adjusts the pumps’ speed based on the patient’s level of exertion, an improvement from the Jarvik 2000’s manual pump rate controller. In addition, the internal software also monitors the Carmat Heart and diagnosing any problems, sparring patients from frequent trips to the hospital for check-ups [28]. Like the AbioCor System, the Carmat Heart System will not rely on skin-piercing wires to power its components. Instead, the Carmat Heart System will incorporate an internal battery for emergency use and an external battery. EADS plans to use either a TET energy-transfer technology to power the internal components from the external battery pack or use a titanium receiver implanted in the skull that would channel energy send through the skin [29]. EADS also plans to incorporate fuel cell technology in the Carmat System’s external battery to produce an extended battery life of 5 to 14 hours (timesonline.co.uk). Like other artificial hearts, the main limitation of the Carmat Heart will be its size. Currently, the device can fit in 70% of males and a small percentage of females, a problem EADS plans to further address [30]. Although the Carmat Heart System integrates many innovative ideas and new technologies, the Carmat Heart System still has not began clinical trial testing in Europe; thus, the commercial release of this device is still a ways off. Tissue Engineering Along with further artificial heart development, doctors are experimenting with tissue engineering as an alternative solution to heart failure with the ultimate goal of regrowing a failed heart. One popular idea is the use of nanotechnology to create hundreds of microsized electromagnetic motors to replace a failing heart. This unit would be powered by a TET system simmilar to that of the AbioCor [22]. Furthermore, a team of doctors at MIT is experimenting with a biodegradable scaffold that can be used to guide the orientation of culture heart cells; ideally, the heart cells will be orientated into a new heart [26]. Although tissue engineerign research is still in preliminary phases, the ability to regrow failed hearts would be an effective and long-term solution to heart failure if plausible. Design Recommendation The AbioCor System’s external batteries only last about four hours on a charge and are a significant limitation in the design of the AbioCor. Patients can perform fewer activities and are greatly inconvenienced because of the short battery life. We have one recommendation that will significantly increase the battery life of the AbioCor System and give patients more freedom and a better quality of life. We propose that solid oxide fuel cells replace the AbioCor System’s external battery. Overview of the Solid Oxide Fuel Cell A solid oxide fuel cell (SOFC) is a device that controls chemical reactions to create electric current. The SOFC takes advantage of hydrogen and oxygen’s natural reactivity in these chemical reactions. The main fuel used in the SOFC is either propane or butane gas and is the source of hydrogen atoms in the oxygen-hydrogen reaction. Oxygen-containing air is the source of oxygen atoms in this reaction. 390525061595Description of the Solid Oxide Fuel Cell The design of the SOFC is essential for its function [34]. As Figure 19 shows, the SOFC is made up of four components: a permeable cathode and anode, an impermeable electrolyte, and a circuit. The cathode and anode are on either side of the electrolyte and the circuit is connected to the cathode and anode. Four vents leading into and out of the SOFC allow for the chemical reactions to take place. Function of the Solid Oxide Fuel Cell Figure SEQ Figure \* ARABIC 19: Solid Oxide Fuel Cell [33]The SOFC takes advantage of oxygen and hydrogen’s natural reactivity to create an electric current. Figure 19 schematically demonstrates this energy-converting chemical process. Oxygen (air) enters one vent and flows along the cathode. The oxygen molecules permeate through the cathode and hit the cathode-electrolyte surface. The cathode-electrolyte surface catalytically splits the oxygen molecules into oxygen ions. These oxygen ions diffuse through the electrolyte and hit the anode-electrolyte surface. Fuel (propane or butane) enters through another vent and flows along the anode surface. The fuel permeates through the anode and hits the anode-electrolyte surface. The fuel and oxygen ions react on the anode-electrolyte surface, producing water molecules and electrons. The circuit directs the electrons, as an electric current, to provide power. Advantages of the Solid Oxide Fuel Cell The SOFC has three main advantages over batteries. It is a better source of energy than a battery, creates almost no pollution, and uses readily available fuels. In a recent test run, a solid oxide fuel powered an unmanned aerial vehicle (UAV). The SOFC powered the UAV for 12 hours, while the standard battery lasted for only 30 minutes. The SOFC releases small amounts of water and carbon dioxide as byproducts in the chemical reaction. Most attractive about this device is its use of common materials as fuel. Propane gas is available around the world and oxygen (in air) is obviously very common. 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AbioCor Heart System

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