It will be some time before the first man with an artificial heart walks down the street on artificial legs, breathing through an artificial lung, his blood coursing through long stretches of artificial artery, his metabolic poisons filtered by an internal artificial kidney, while he admires the landscape through artificial corneas in eyes filled with a chemical fluid the consistency of molasses. It may be that no one man will ever enjoy all these advantages of alloplasty-surgery in which foreign materials are used to replace the body’s natural parts. But it will not be long before many people are fitted with one or more of these devices.
For thousands of years, repair surgery was limited to such obvious and available materials as wood, bone and ivory-which the body is usually quick to reject. Then doctors turned to refined metals. But the current mush rooming of alloplasty had to await the proliferation of synthetic plastics. Most of the materials now favored are the polymers (basically familiar molecules in unfamiliar, complex arrangements), such as nylon, Dacron and Plexiglas. But even more widely useful are the silicones,* which may be solid or as gooey as engine oil.
In Brain & Heart. Even the hypersensitive brain is amenable to surgery and the implantation of certain plastics. Only ten years ago, a child who was born with or soon developed the condition known as hydrocephalus (water on the brain) was doomed to mental retardation or early death. Today, more than 80,000 youngsters have their brain-drain problem solved by an implanted Silastic tube.
The duct of Silastic (trade name for medical silicones made by Michigan’s Dow Corning Corp.) is 18 in. to 24 in. long, only 1/16-in. thick. It is led under the skin, behind the ear and down the neck to a point where it is spliced into the internal jugular vein. The excess brain fluid is thus dripped into the bloodstream, where the body readily disposes of it. Another Silastic preparation, which looks like a sheet of waxed paper, serves to correct a different type of brain problem: when part of the brain’s parchmentlike covering, the dura mater, is damaged or destroyed, the brain tissues and fluids are kept from bulging or leaking out by a Silastic sheet backed with Dacron.
In a still more delicate sealing-off operation, Tufts University’s Dr. Bertram Selverstone opens the skull of a patient who has an aneurysm on a brain artery. To seal or prevent a rupture, he sprays the artery with a plastic mixture which gives it a dry, thin coating like Saran wrap. Then Dr. Selverstone sprays on a second coat, using a new, quick-setting epoxy resin. The double coat has the desired toughness. And more than 100 patients are living with blowout patches in their brains.
Muscular and robust as it is, the heart is less tolerant of foreign materials. Washington Surgeon Charles Hufnagel overcame this intolerance in 1952, when he implanted the first artificial aortic valves, made of a Plexiglas ball in a Plexiglas sleeve. The ball has since been replaced by Silastic.
After the sleeve came a cage in which the silicone ball must bob up and down 40 million times a year without sticking, and Dow Coming’s Chemist Silas A. Braley says confidently: “The Silastic ball cannot stick.” The University of Oregon’s Dr. Albert Starr has installed 18 such valves in six patients -three apiece, replacing the aortic, mitral and tricuspid valves.
But any ball valve is rougher on blood cells than nature’s leaflet valves, so surgeons at the University of Wisconsin have developed butterfly valves of Teflon that come closer to the original in design. The demands on the plastic in such valves are tremendous: the leaflets must bend back and forth 40 million times a year. But so far, 39 patients have had them installed as replacements for aortic or mitral valves, and they are still working after as long as 20 months.
When the first entirely artificial heart is developed, it will probably be made of Silastic. This is the material that Houston’s Surgeon Michael E. DeBakey used for the closest approximation to such an organ ever tried in a human patient. It was a substitute for the left ventricle, the heart’s main pumping chamber, and it worked for 3½ days, until the patient died of other causes (TIME. Nov. 8, 1963).
Parts of major arteries, including the biggest of all, the aorta, are far easier to deal with. They are regularly replaced or bypassed with grafts of Dacron knit such as was used in surgery on the Duke of Windsor. Electrical pacemakers to regulate or replace the beat of a faltering heart have by now been implanted under the abdominal skin of 10,000 patients, with leads to their hearts; all these devices are encased in Silastic because of its inertness.
Filters & Glues. Artificial kidneys now in use are as big as a washing machine or an entire laundry, but medical engineers are making them ever smaller; they hope eventually to devise one that can actually be put inside the body. A hopeful lead comes from a plastic called polyvinyl pyrrolidone, now widely used as the setting agent in women’s hair sprays. PVP membranes pass chemicals between the blood and the cleansing water of the artificial kidney about three times as fast as the cellophane membranes now used. PVP has another advantage for an implantable kidney: like Silastic, it seems thoroughly compatible with the blood, and has little tendency to provoke clotting.
As a replacement for bone in 700,000 operations a year, surgeons will now have available a regular supply of calf bone, specially treated to remove all dangerous protein. E. R. Squibb & Sons this week announced the first U.S. Government approval of a sterilized calf bone, vacuum-packed, which can be stored at room temperature.
Screw-In Cornea. Ironically, the earliest attempt to use a primitive plastic involved one of the most intricate organs in the body. It was an 1853 attempt to replace the cornea of the eye, and it failed. Then the technique of human corneal transplants was developed, and the urgency of finding a plastic seemed to diminish. But human transplants do not stay clear in all cases. An imaginative ophthalmic surgeon, Dr. William Stone Jr., working first in Boston, then in Los Angeles, has devised a corrective corneal implant of plastic.
The outer part of the transplanted human cornea can be left in place, cloudy as it is. Dr. Stone removes most of the thickness in the center, and sets in place a narrow, artificial cornea made of polymethyl methacrylate surrounded by a Teflon skirt (see diagram). The very center of the device is threaded so that it can be moved in or out to adjust its optical characteristics. And if the patient should need further major surgery, the plug can be unscrewed all the way, giving the surgeon direct access to the inside of the eyeball. As for the inside, where the vitreous humor may become clouded or lost through injury, one surgeon is using a synthetic like molasses in January.
Many eye surgeons have learned to correct detachment of the retina by putting a plastic girdle around the eyeball and squeezing it back into shape. And Dr. Stone has implanted plastic tubes in the eyes of glaucoma patients at Massachusetts Eye and Ear Infirmary to remove the accumulation of fluid that causes high pressure inside the eyeball-and eventually blindness.
To replace relatively insensitive tissues and those that are easy to get at, plastic surgeons have a wide choice of materials. They carve Silastic sponge to the shape of a human ear and cover it with skin grafts. For men who have undergone castration because of cancer, there are artificial testicles of the same or a similar material. Artificial breasts are now made of a soft silicone-rubber sack that holds a silicone gel, and they have a backing of Dacron for attachment to the chest wall.
One of the few parts of the anatomy for which the inventive human brain foresees no possibility of a plastic replacement is the brain itself.
*Unknown in nature, these are similar to the innumerable “organic” (carbon-containing) compounds, but have the central chain of carbon atoms replaced by a silicon-oxygen chain. Common sand consists mainly of quartz, which is silicon dioxide.
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