Engines of Healing

The human body is a hyperexpressed, hyperdifferentiated organic compound. Its architecture is the byproduct of exquisite molecular craftsmanship. But at a gross level, the human body is fairly substandard in its complexity. There is no evidence that the retina is processing light and motion at a rate of ten million times per second. There brain does not advertise the fact that it has reconciled 100 trillion instructions in the time it has taken you to read this sentence. One hundred million Krebs cycles churn every time you swallow. They make no sound. Your suprachiasmatic nucleus does not tick. Your ribosomes do not hiss. Yet when something goes wrong in this gargantuan molecular factory, when a cell fails to divide or a protein fails to act, a surgeon wields a knife. A knife is 15,200 times the size of an average cell. This is similar to clipping your fingernails with a Boeing 747.

It is ludicrous, and yet it persists. For centuries, this molecular microcosm has been viewed as one Brobdingnagian lump of mass. Wounds are covered with band aids 12,000 times the size of a red blood cell. Optometrists prescribe eyeglasses 6,000 times the size of a retina. Cancer patients undergo radiation, a treatment that kills trillions of cells instead of one.

The human body is a composite of a billion billion molecules. If an ant is infecting a colony, it is much more economical to remove the ant than to destroy the entire colony. Applying this to the human body, it would make much more sense to target 10 infectious cells instead of 10 trillion. But medicine does not work this way. While physicists relentlessly probe the depths of matter, physicians are content to take a step back. Drugs are the physician’s only link to the cellular world, but drugs operate entirely without direction. Pills are chewed and swallowed and then left to their own devices in the body. Drugs do not seek out target cells and formulate a plan of attack. They roll around in the bloodstream until they bump into cells and stick to their surface. This molecular pinball is our only alternative to sutures, surgeries and lacerations. Until now.

Growth stages of gold-plated nanoshells. Courtesy of rqi.rice.edu

Ray Kurzweil called it GNR: the confluence of genetics, nanotechnology and robotics. It is the epoch in the race towards technological autonomy where physiology and physics merge, where medicine is no longer the study of patients, but the study of their molecules. [1] Medicine should be practiced with the eye of a physicist – cell by cell, tissue by tissue. Colonoscopies could be avoided by swallowing microstructures that find and disintegrate polyps. Collagen-like composites could reverse osteoporosis and heal broken bones. Nanostructures that recognize specific cell types would be enough to cure cancer. Twenty-two years after the landmark discovery of Buckminster fullerene (a ball-like carbon compound that revolutionized chemistry and materials science), nanotechnology is finally being directed towards our most valuable asset – the human body.

Nanoshells, developed by Dr. Naomi Halas at Rice University, are 100 nanometers in diameter, 10,000 times smaller than the period at the end of this sentence. Thirty nanoshells in a row would traverse the smallest capillary in the body. [2] Nanoshells are silica particles coated with gold islands. These “islands” eventually coalesce to form a gold shell. Popular Science writer Kevin Kelleher wrote that “today’s best cancer treatments destroy tumor cells with about as much precision as an atomic bomb.” Nanoshells offer an elegant solution. Because nanostructures can go places drugs cannot, nanoshells slip into the tumor via its blood vessels and steadily accumulate there. After several hours, a handheld laser is used to shine infrared light on the skin and kill the tumor cells without destroying the surrounding tissue. The “tuning” of nanoshells to respond to infrared light is achieved by varying the thickness of the gold shell. In mice, gold nanoshells resulted in 100 percent remission of all tumors. Nanoshells, unlike conventional cancer drugs, are also nontoxic.

By looking at tumors under an atomic lens, scientists were able to exploit the biological “water window” and leave the surrounding tissue intact. The infrared absorption range of gold nanoshells can also be used to facilitate laser tissue welding (LTW). This procedure can be used to repair tissue trauma in the liver, urinary tract, skin and nerves, and has significant advantages over traditional suturing. [3]

In corroboration of Ray Kurzweil’s theory of technological explosion (in particular, GNR), logarithmic plots show a 1,000-fold increase in the number of nanotechnology citations between 1992 and 2002. The average size of mechanical devices has decreased from 1 millimeter in 1965 to 10-5 millimeters in 2000. The cost of DNA sequencing has decreased from ten dollars a base pair in 1990 to a few pennies per base pair in 2004. [1] This exponential growth of technology has swept medicine in its wake. And the ramifications are limitless.

DNA Buckyballs. Courtesy of www.cornell.edu

Twenty-two years after the discovery of Buckminster fullerene, self-assembling buckyballs made of DNA instead of carbon are being tested as containers for drug delivery. Single-walled carbon nanotubes (SWNTs) are being used to shuttle cargo across the cellular membrane. Quantum dots are being used as fluorescent probes to label tumor vasculature. [4] Nanobelts and nanocantilevers, antibody-coated levers resembling microscopic diving boards, will line the blood vessels. Pathogens that roll by will strike the cantilever and cause it to vibrate at a characteristic frequency, providing a powerful ultra-small pathogen detector. [5] And while gold nanoshells are busy destroying stagnant tumors, magnetic nanoparticles are being developed to detect their metastasizing cells. [6] In a radical upheaval of scientific order, this is physics curing cancer.

The human body is a composite of a billion billion molecules – and each of them is finally being addressed. Those squeamish at the thought of swallowing nanomachines can take solace in the fact that one nanoshell is 10 million times smaller than a tablet of Advil – eliminating the need for water. The nanostructures described still operate without direction, however. Eventually, nanostructures will be guided by nanocomputers, inside or outside the body. Eric Drexler describes a central database two cubic microns across (2/1000 the volume of a cell) that could be placed inside every cell. This extent of nanotherapy might be overkill. Still, nanomedical devices do not leave scars, induce pain, or introduce side effects. [7]

At the present, medicine is still very much a game of macroscopic proportions. But as the GNR revolution rushes upon us, looking at the body with the eye of a physicist may be just what the doctor ordered.

References:

[1] Kurzweil, Ray. The Singularity is Near. Penguin Books Ltd 2005. 1 May 2007

[2] Brongersma, Mark. “Nanoshells: Gifts in a Gold Wrapper.” Nature Materials. Vol 2 2003. 1 May 2007

[3] Halas, N., et. al. Near Infrared Laser-Tissue Welding Using Nanoshells as an Exogenous
Absorber. Lasers in Surgery and Medicine 9999:1-7 2005. 1 May 2007

[4] Cai, W., et. al. Peptide-Labeled Near-Infrared Quantum Dots for Imaging Tumor Vasculature in Living Subjects. Nano Letters. 6(4) 669-676 2006. 1 May 2007

[5] Hughes, W.L., & Wang, Z.L. Nanobelts as Nanocantilevers. Applied Physics Letters, 82 (17)
2003. 1 May 2007

[6] Schwalbe, M., et. al. Improvement of the Separation of Tumor Cells from Peripheral Blood Cells using Magnetic Nanoparticles. J. Phys.: Condens. Matter 18. S2865-S2876. 2006. 1 May 2007

[7] Drexler, Eric. Engines of Creation: The Coming Era of Nanotechnology. Random House. New York, New York. 1987. 1 May 2007