Polish researchers are at the forefront of a worldwide effort to design innovative artificial ventricles to assist the heart, and they are also working on an artificial heart implantable into the patient's body.

Researchers at the Artificial Heart Laboratory of the Cardiac Surgery Development Foundation in the southern city of Zabrze have designed the PolVAD ventricular assist device that paves the way to developing assist devices of much greater long-term durability than those used so far. This innovative design has won some major awards, including the Grand Prix at the 53rd Brussels Eureka World Exhibition of Innovation, Research and New Technology in 2004, and a Gold Medal at the 104th International Concours-Lépine invention show in 2005 held as part of the Foire de Paris international fair.

Until recently ventricular assist devices were made from an elastic plastic-polyurethane. It is one of the polymers most biocompatible with the human body and resistant to degradation. However, after years of work, a micro-crack may appear on the surface of the material, triggering a process of calcification or blood clotting. The problem is the same as with ordinary arteriosclerosis. Thrombotic material is spread across the body and clots may appear. As a result, researchers have been looking for a way to increase the durability of artificial ventricles in contact with blood, which is a chemically-aggressive environment.

New to the world

The Zabrze-based team, headed by Prof. Zbigniew Religa, now health minister in Jarosław Kaczyński's government, has found a solution to the problem. The researchers coated the internal and external surface of the ventricle with a layer of crystalline titanium and its compounds. The combination of polyurethane and titanium turned out to be an innovative design on a global scale. For the first time, a single device combines the advantages of the elasticity of the working components, which enables an unobstructed and close-to-physiological blood flow, and the durability of titanium, the most biocompatible and biodegradation-resistant material used in implants.

The titanium nanolayer not only ensures excellent biocompatibility but also offers hope for long-term durability of the ventricles. A transplanted heart, a biological substitute for artificial ventricles, is capable of working efficiently in the host's body for 20-25 years. Meanwhile, ventricles used today can only survive for around five years.

The problem of biocompatibility of implants in the human body is multi-faceted. The point is not only to make sure that the implant is harmless to humans but also to check any kind of impact of the implant's surface on the biological environment. Titanium is the second most biocompatible material after carbon. And it was with carbon that the researchers at the Artificial Heart Laboratory experimented first. Unfortunately, carbon beams used to destroy polyurethane surface. Nor did the researchers manage to adapt for their purpose the nanodiamond technology that has been successfully used in orthopedic and dental implants. This is because metal surfaces can only be coated with diamond nanolayers for the time being. In this situation, they decided to start experimenting with titanium and its compounds. Ultimately, by means of laser ablation, they succeeded in coating a whole artificial ventricle with this metal, while at the same time all parts of the ventricle retained excellent elasticity. Initially, there were fears that, with this kind of mechanical work, titanium, as a crystalline material, would tend to brittle, crack or come off. However, it turned out that the layer excellently adhered to the elastic surface and changed shape along with it. This is a real breakthrough and a starting point for the development of truly durable ventricular assist devices.

Nanotechnology is key

Researchers at the Cardiac Surgery Development Foundation say that nanotechnology is one of the crucial issues in work on developing ventricular assist devices. This explains why the project was carried out in cooperation with the Institute of Metallurgy and Materials Science of the Polish Academy of Sciences in Cracow, where materials tests were made. Assistance also came from specialists at the Joanneum Research Forschungsgesellschaft mbH Laser Center in Leoben, Austria, who took care of the technology for depositing a titanium nanolayer on polyurethane.

In fact, there are several layers. The one consisting of pure titanium is a buffer layer, on which a layer, or layers, of titanium nitride is/are deposited. The composition, number and thickness of individual layers are still subject to research. The researchers are thinking of conducting tests with titanium carbon nitride or perhaps even pure carbon. At present, research is under way to optimize this coating.

One thing is certain: the Zabrze designers were the first in the world to succeed in coating an elastic surface with metal and keep it elastic. While it is still unclear how long it will remain resistant to biodegradation, it is known that a heart prosthesis should be durable in the long run.

Maintenance service

Heart prostheses are electromechanical devices that require servicing like any other device of this kind. The point is to make sure that maintenance is not done too frequently because each time it involves the need to perform a surgery.

Another area of research conducted at the Artificial Heart Laboratory is connected with efforts to enable the replacement of ventricles or their components through minimally invasive surgery. The designers do not want to use the same technology as that applied by their American counterparts, whose fully implantable ventricular assist devices have been implanted in around 100 people around the world. The American-designed artificial heart includes everything that is needed in such an artificial organ: a blood pump, a drive mechanism, a control system and a power supply system. A major surgery involving full breastbone incision is needed to replace any component of the pump or its drive system.

The goal of the work being conducted at the Cardiac Surgery Development Foundation is to separate the artificial heart's systems. The design is supposed to enable the surgeon to access each system independently so that they can be serviced by means of minimally invasive procedures. Particularly important is the location of the power supply system. For the time being, the heart is powered with a battery that has to be recharged from time to time.

Moreover, the American artificial heart is made of titanium and is heavy-it weighs 1.5 kilograms. The Zabrze researchers are convinced that the working components of the ventricle should be soft and flexible, which means they should be made of plastic. This is why the Polish invention, which won an award at the Brussels exhibition, is so significant. The American-designed ventricular assist device, used in patients since 1999, and the self-contained total artificial heart, implanted experimentally since 2000, are the only fully implantable, or intracorporeal, prostheses.

Life-giving pump

Extracorporeal ventricular assist devices, in which all of the key parts are outside the patient's body, have been used in Poland for several years now. More than 150 patients have benefited from them so far. They are intended for use in patients waiting for a transplant or those whose hearts have to be temporarily assisted to allow them to heal.

For several years now specialists at the Cardiac Surgery Development Foundation have been developing increasingly modern versions of drive mechanisms for extracorporeal ventricular assist devices. The most recent one is the POLPDU-402 with a totally independent pneumatic supply system that allows for independent operation without the need to use the hospital's pneumatic supply network.

The research project under way in Zabrze is focused on intracorporeal ventricles, or ventricles implanted into the body, to make the patient independent of external connections with specialist equipment and enable them to get out of bed. One such design is the ventricular assist device drive mechanism placed on a trolley, which enables the patient to move and continue their therapy outside the hospital. But the ultimate goal are devices that are either partially or fully implantable. The award-winning polyurethane-titanium ventricle marks an important stage in this program.

The Grand Prix for the PolVAD is not the only award that the Zabrze-based Cardiac Surgery Development Foundation brought home from the Brussels exhibition. The foundation also received a Gold Medal with Distinction and the Cup of the Technipol Science and Technology Association of Russia. Prof. Religa received the Commander's Cross of the Order of Invention, which was conferred on him by the Highest Commission of Awards of the Kingdom of Belgium.

Other devices developed at the foundation's Artificial Heart Laboratory have also won major awards. Among other designs, the Zabrze specialists have developed a pneumatic system for mechanical circulatory assistance, POLCAS, which won awards at the 5th European Forum of Competitive Technology TEC'96 in Grenoble, the 2nd Techno Messe Kansai in Osaka in 1997, and the Intertechnology'98 fair in Łódź. The POLHIVAD, a prototype of a fully implantable electrohydraulic left ventricular assist device, claimed a gold medal at the 6th London International Inventions Fair in 1998. The device enables long-term treatment of heart failure and secures the time needed for pharmacological therapy or the selection of an optimal organ for transplantation.

The Artificial Heart Laboratory designs and tests mechanical circulatory assist systems, and it also introduces them into clinical practice. The head of the laboratory is Roman Kustosz, a graduate of the Silesian University of Technology Department of Automation and Mechanics. His main interest is in medical electronics.

Ewa Dereń