Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100

have a major impact. One particular area of research is spinal cord injury, once thought to be totally incurable. In 1995, when the handsome actor Christopher Reeve suffered a severe spinal cord injury that left him totally paralyzed, there was no cure. However, in animal studies, great strides have been made in repairing the spinal cord with stem cells.
    For example, Stephen Davies of the University of Colorado has had impressive success in treating spinal cord injuries in rats. He says, “I conducted some experiments where we transplanted adult neurons directly into adult central nervous systems. Real Frankenstein experiments. To our great surprise, adult neurons were able to send new nerve fibers from one side of the brain to the other in just one week.” In treating spinal cord injury, it was widely thought that any attempt to repair the nerves would create great pain and distress as well. Davies found that a key type of nerve cell, called an astrocyte, occurs in two varieties, with different outcomes.
    Davies says, “By using the right astrocytes to repair spinal cord injuries, we have all the gains without the pain, while these other types of appear to provide the opposite—pain but no gain.” Moreover, the same techniques he is pioneering with stem cells will also work on victims of strokes and Alzheimer’s and Parkinson’s diseases, he believes.
    Since virtually every cell of the body can be created by altering embryonic stem cells, the possibilities are endless. However, Doris Taylor, director of the Center for Cardiovascular Repair at the University of Minnesota, cautions that much work has yet to be done. “ Embryonic stem cells represent the good, the bad, and the ugly. When they are good, they can be grown to large numbers in the lab and used to give rise to tissues, organs, or body parts. When they are bad, they don’t know when to stop growing and give rise to tumors. The ugly—well, we don’t understand all the cues, so we can’t control the outcome, and we aren’t ready to use them without more research in the lab,” she notes.
    This is one of the main problems facing stem cell research: the fact that these stem cells, without chemical cues from the environment, might continue to proliferate wildly until they become cancerous. Scientists now realize that the subtle chemical messages that travel between cells, telling them when and where to grow and stop growing, are just as important as the cell itself.
    Nonetheless, slow but real progress is being made, especially in animal studies. Taylor made headlines in 2008 when her team, for the first time in history, grew a beating mouse heart almost from scratch. Her team started with a mouse heart and dissolved the cells within that heart, leaving only the scaffolding, a heart-shaped matrix of proteins. Then they planted a mixture of heart stem cells into that matrix, and watched as the stem cells began to proliferate inside the scaffolding. Previously, scientists were able to grow individual heart cells in a petri dish. But this was the first time that an actual beating heart was grown in the laboratory.
    Growing the heart was also an exciting personal event for her. She said, “ It’s gorgeous . You can see the whole vascular tree, from arteries to the tiny veins that supply blood to every single heart cell.”
    There is also one part of the U.S. government that is keenly interested in making breakthroughs in the area of tissue engineering: the U.S. Army. In past wars, the death rate on the battlefield was appalling, with entire regiments and battalions decimated and many dying of wounds. Now rapid-response medical evacuation teams fly the wounded from Iraq and Afghanistan to Europe or the United States, where they receive top-notch medical care. The survival rate for GIs has skyrocketed. And so has the number of soldiers who have lost arms and limbs. As a consequence, the U.S. Army has made it a priority to find a way to grow back limbs.
    One breakthrough made by the Armed Forces Institute of Regenerative Medicine has been to use a radically new method of growing organs. Scientists have long known that salamanders have remarkable powers of regeneration, regrowing entire limbs after they are lost. These limbs grow back because salamander stem cells are stimulated to make new limbs. One theory that has borne fruit is being explored by Stephen Badylak of the University of Pittsburgh, who has successfully regrown fingertips. His team has