Even with the limited tools available now, devices that function as part of the body are rapidly emerging. The vascular stent provides an excellent example with which to illustrate the present state and future prospects of bioengineering.

We all know arteries become clogged; debris accumulates on the inside of the blood vessel and flow is reduced. Untreated, the constriction can ultimately block the flow of blood to part of your body. If the blockage is in a coronary artery, a blood vessel that feeds the heart muscle itself, it is deadly.

The early bioengineering solution was to pry the constriction open with a procedure called a balloon angioplasty. The limitations of this approach are obvious. When you force something open, especially something with the limited flexibility of a hardened vessel wall, there are problems. Frequently, the vessel would relapse to its constricted state. So an improved engineering concept was developed. Open the constriction and simultaneously implant a structure to hold it open: the stent.

A coronary or vascular stent is a small slotted metal cylinder mounted on a balloon catheter, a long flexible tube capped by an expandable tip. When your pipe gets clogged, this catheter is inserted into your artery and snaked along until the balloon portion is at the site of the constriction. Then the balloon is inflated and deflated a number of times while, simultaneously, the metal stent expands and is pressed into the inner wall of the artery. The standard stent looks something like a tubular wire fence with flat, fat wires. It expands along with the balloon but then retains its larger diameter when the catheter is removed.

A stent is basically a plumbing device for the repair of a collapsed piece of pipe. It is also representative of the state of the art in applied bioengineering available on the market today. And, like computer displays and cellphones, stents have already undergone several product generations. Early stage enhancements were designed mainly to improve delivery and placement accuracy, or to eliminate potential catastrophes such as structural collapse or the formation of blood clots. A major bioengineering challenge has been to develop materials with sufficient tensile strength to hold the vessel open but malleable enough to be placed in the vessel with a minimum of damage to surrounding tissue.

Tissue damage as a result of stent placement calls for improved design specs. Not coincidentally, these new designs place us on the road to Homo technicus. Recently the FDA approved a "drug eluting" stent. This stent is metal with a plastic coating impregnated with a specific pharmaceutical. So it is a true hybrid: part device, part drug. The first compound incorporated into a drug-eluting stent was selected to reduce the regrowth of tissue into the region of the opened vessel, a process called restenosis. When wire is driven into the tissue of the vessel wall some cells are ruptured and others are mashed. The result is inflammation and wound healing. If too much tissue is produced, it re-clogs the vessel. From a bioengineering standpoint having the stent release a drug to inhibit restenosis is an excellent device modification.

Future drug-eluting stents will contain multiple active ingredients. The elution process will be refined so that the timing and amount of active ingredient that enters the tissue, the "elution profile," will be controlled with greater precision. Design specs will continue to be upgraded via the sequential timed release of a complex mixture of natural and synthetic chemicals to control the response of the wounded tissue. Further enhancement will involve attaching small protein molecules directly onto the stent surface to signal adjacent cells. Bioengineers call this molecular decoration.

Molecular decoration camouflages a nonbiological material in order to mimic a biological material. This type of strategy has been designated biomimetics. A protein-decorated, drug-eluting stent is one of the first true hybrid biomaterials: part biological, part synthetic. One small step for Homo technicus. Drug-eluting stents and their progeny will speak the language of the cell well enough to stimulate production of smooth endothelial cells on the inner surface of the stent, in effect growing a brand-new vessel surface. In later designs the stent itself will biodegrade after stimulating the growth of complete replacement vasculature. In this final design, we will have engineered tissue that will be in better shape than the rest of the vessel. In the process of therapeutic life-saving we will have generated a rejuvenated biosystem component.

This brings us to what I call the First Law of Biomimetics:

With respect to bioengineering there is no border between life-saving and life-enhancing technology.

The First Law of Biomimetics will drive Homo sapiens to the point of speciation. Practically speaking, bioengineers will adopt the tools of nanofabrication to fix our damaged parts and will then offer us enhanced parts. If we simply follow this road to its logical end we reach a point when the organism has so many modifications it just doesn't qualify as Homo sapiens anymore. A new species will emerge that differs both in psychology (software) and chemistry (hardware). The name Homo technicus does not imply any biological relationship but a fusion at the molecular and atomic level. For Homo technicus the difference between DNA and silicon will be no more significant than the difference between protein and DNA is to Homo sapiens. After all, our own bodies contain a wide range of structural materials, from the ceramic in bone to the organic polymer collagen in skin.

How will the First Law of Biomimetics drive Homo sapiens to speciation? The answer is that we will demand it. Many of the changes that technology offers are subject to interpretation, but few object to an increase in the quality and length of human life. When baby boomers say that their children can reasonably expect to live to be 85, we are talking about productive and active years, not the ways in which their deaths will be prolonged.

In our generation we expect, not hope, that biotechnology will bring an end to age-associated cognitive problems such as Alzheimer's and senile dementia. Within a generation or two we expect, not hope, that we will have hip and knee implants that function as well as or better than the worn-out originals. And, of course, we expect a cure for cancer. Or, more correctly, cures for cancers. Cancer is the ultimate "bad boy" of molecular biology because it comprises a multiplicity of diseases resulting from inappropriate gene expression -- the wrong permutation of the genetic code acting out at the wrong time in the wrong place. That is why a Normandy Beach frontal assault on cancer will not work. Like terrorist cells, cancer cells have multiple manifestos, multiple strategies, and an array of weapons at their disposal. Nevertheless we expect, not hope, that a complete understanding of the human genome and cellular function will enable us to deal with each particular cancer on its own terms.

Our increase in life expectancy is, of course, multivariate in nature; it is the result of enhanced medical care, improved nutrition (from advanced agricultural and food-manufacturing technologies), and the general techno-sheltering we receive from the wear and tear of direct interaction with the environment. But the greatest strides are expected to emerge from biotechnology and bioengineering. While bioethics per se thrives on slippery slopes shaded by the sinister foliage of death or dysfunctional biology, I am not aware of significant societal objection to medical advances that unambiguously enhance life. Say you need a heart transplant. Just to make the argument clean, we will assume the heart was grown in culture using your skin cells via tissue engineering. No embryonic stem cells need apply. Your surgeon comes in smiling and says, "Look, not only will this transplant save your life, but the new heart will also pump more efficiently and last longer than your original." Who among us would object?

We expect these advances and we will not be disappointed. Staying with the stent as our example, a dozen product generations down the road will see targeted stem cells injected into the bloodstream that will hunt down damaged vasculature, attach to the target site, and replace or repair the damage through tissue regeneration. This will be minimally invasive. "Minimally invasive" is what bioengineers want because that is what you and I want. Who among us would not prefer a virtual colonoscopy? But in the end our real desire is for a colon, lung or liver that has no possibility of developing diseases or disorders, and we will get it. The ultimate therapy is never having to need therapy. Bioengineers are looking for zero failure rates and this, in turn, means engineered tissues that are not limited to the design evolved by random variation followed by natural selection.

Recent Stories