INDIANAPOLIS - Robert S. Langer describes the ultimate medical implant: Human cells, removed from a patient's body, are reproduced using special polymers to form an ear, replacement cartilage, a chest cavity, perhaps part of a skull. Other polymers deliver chemotherapy and other medicine directly to the area inside a body, slowly releasing it over a period of weeks, even years.
Langer, a 47-year-old professor of chemical and biomedical engineering at Massachusetts Institute of Technology, won the Society of Plastics Engineers' top honor, the International Award. He took the audience deep inside the human body during a May 8 speech at SPE's Annual Technical Conference.
A chemical engineer, Langer became interested in the ability of polymers to carry medicine in 1974 while at a post-doctoral MIT position at Boston Massachusetts General Hospital. At the time, scientists thought that polymers would not be able to release large-molecule drug agents, such as proteins.
At first, Langer recalled, ``It was really just academic interest. But what happened was, about eight years later, the early 1980s, this whole area of biotechnology and genetic engineering came forth.''
Emerging large-molecule drugs posed problems because they would be destroyed if swallowed and cannot be delivered with a skin patch, he said. Injected drugs often have too quick a life-span inside the body when a slower release is needed.
``What became clear in the 1980s is that if you wanted to use some of these molecules on a chronic basis, it would be very important to have a way to deliver them in an unaltered form and yet protect them from harm,'' Langer said.
Introducing Langer was his former Massachusetts Institute of Technology classmate, Nicholas Peppas, a Purdue University professor of chemical engineering.
``Bob was the first one to really come up with these new devices, these new systems, for the delivery of these macromolecules,'' Peppas said. ``That was the beginning of a magnificent scientific career.''
Langer has posted amazing numbers for a polymer scientist not yet 50 years old. Many of his 130-plus patents have been licensed by leading biomaterials companies. He has written more than 400 articles.
His early-morning speech featured slides depicting molecules -comforting sights for the top-level polymer scientists who populate any Annual Technical Con-ference. But other slides ventured into unfamiliar territory of brain surgery and misshapen lab rats.
Clearly, Langer was not talking about off-the-shelf polyethylene. These are polymers engineered to do their biomedically specific job. Langer drew laughs when he told how the general implant industry too often takes an off-the-shelf approach, picking familiar materials. Designers of the first artificial heart, looking for a long-life, flexible material, selected the polymer used in women's girdles.
``It's still used today, 29 years later. But sometimes when the blood hits the surface of the heart, the ladies' girdle material forms a clot and the patient gets a stroke. And yet if we think about it, perhaps it's not that surprising that something designed to be a ladies' girdle might not be the perfect thing to put in the body.''
Of the materials in breast implants, he said: ``One of those is a lubricant, another, a mattress stuffing. You can kind of see the logic of how all this evolved.''
One solution for drug delivery could be biodegradable polymers. For example, doctors now deliver the cancer drug BCNU intravenously to brain cancer patients. But the harsh chemotherapy drug can ravage
other parts of the body.
Langer said a biodegradable polymer was developed to release BCNU over four weeks, then disappear. After a brain tumor is removed, the surgeon lines the cavity around the brain with dime-shaped discs containing the medicine, delivering it right to the correct spot.
Polymers also are central to the emerging field of tissue engineering, actually growing tissue using human cells, biochemicals and synthetic materials into living implants that function inside the body.
Langer showed a slide of a 12-year-old boy with only a small amount of chest structure to protect his heart. Doctors fashioned a new chest for him. Another depicted tissue formed in a mold shaped like an ear.
Some of the research involves polymers with specific amino acids to control cell growth, he said.
``We can take almost any cell type, grow them in a bioreactor, then ultimately place them in the patient to make a new tissue,'' he said.
