The next few decades will see competition between regenerative medicine and prosthetic design in the construction of replacement organs. At some point in the future the two will merge, most likely after a molecular nanotechnology industry emerges and becomes capable of manufacturing designs as complex and reliable as evolved cell biology. There are attempts today to build bioartificial organ substitutes that combine tissue and machinery, but designing artificial organs remains an undertaking still in its infancy, beset with challenges:
One of the biggest problems with ventricular assist devices (VADs), as well as with existing artificial hearts, is that they can damage the blood. Through shear stress, delicate platelets - whose function is to stop bleeding in normal situations - can become "activated," causing thrombosis or clots, which can lead to stroke or heart attack. It's the reason why patients require comprehensive anti-coagulation medication, which can have problematic side effects as well. Red blood cells can also be damaged by the high shear stresses caused by pumps and leach hemoglobin, causing more problems.
So how should an artificial heart pump blood? Should it run continuously at a steady rate, or pulsate like a real heart? Should it be made of synthetics, organic materials, or a combination of both? Currently most VADs rely on centrifugal or axial flow pumps to circulate blood via a rotary impeller, much like a sump pump moves water out of a flooded basement. These pumps rotate at high speeds - 5,000 to 10,000 rpms - in order to circulate in a minute the approximately 5 liters of blood in a human body. But all that pressure can cause problems. "It's like the force that's coming out of a water hose, and these poor little, innocent platelets are very sensitive to turbulence."
Researchers came up with the idea of using a completely different kind of pump, one that uses a peristaltic pumping mechanism - a far more gentle way of moving fluid. Peristaltic pumps rely on a symmetrical contraction and relaxation motion to generate a wave down a tube. It's basically how your gastrointestinal system transports food through the intestines. Peristaltic pumps are already used in heart/lung blood machines to circulate blood in and out of a patient during open-heart surgeries, but they have never been used in VADs or in artificial hearts.
Another challenge for researchers is trying to map the brain-heart connection. When you're lying down and want to get up, your brain tells the heart to beat faster, to pump more blood. Your body simply reacts. But how will a person's nervous system involuntarily control an artificial heart? "The classic example is a baseball player at the plate who isn't really doing anything. But as soon as the pitcher throws the ball, a dozen different things occur automatically. Blood flow increases, there's a rush of adrenaline. It doesn't look like he's doing anything, but the body reacts to that stimulus in a way that's profoundly different than just sitting there. The mechanical heart wouldn't care that here comes a 90 mph pitch. But we want it to care. We want it to know the difference." If an artificial heart contained enough organic material, could the body's neurological pathways reconnect with it?