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Home , Celluloid, DuPont (1802–2017), Hermann Staudinger, John Dalton, Polymer chemistry, Polymer science

This article was published in 1999 and has not been updated or revised.

P O LYM ERS AN D PEO PLE

n April 1997 Dr. Frank Baker, an emerge n c y straddle the boundary between living and nonliving— medicine specialist from the Chicago area, took like Frank Baker’s artificial skin—are beginning to sug- I pa r t in a clinical trial to test a form of arti f i c i a l gest exciting possibilities for improving human hea lth. ski n for t r ea t i n g in su li n -d epen d en t di a bet i cs whose t i ssu e Behind these developments lies more than 150 years ha d been degra ded by the secondar y effects of chronic high of pr og r ess in r es e a rch by hu ndreds of scientists blood sugar. Baker, who has had diabetes for more than as well as more than a century of res e a r ch i n four decades, wa s in danger of losing a foot because of and or gan transplants. As described in the following ha r d-to-heal skin ulcers. For him the trial results were ar ticle, which highlights the work of only a few of many close to mir a culou s: the la bor a tor y- g r own skin d idn ’t res e a rchers, the pa th to recen t a dva n ces in moder n med- just cover and protect his wound, it released chemicals ical treatment began with the investigations of scientists that caused his own tissue to grow back much faster. in t e r ested in a better ba sic u ndersta ndin g of chemistr y As Baker put it, the artificial skin “saved my foot.” and biology. The material that worked this medical wonder was synthesized from , long molecular chains for me d by the chemical bonding of many small of one Sor t i n g O u t N a t u re or more types. Most people are probably more familiar with polymers in the form of the that make up Humanity has a long history of trying to under- such everyday products as food containers, bubble stand the substance and structure of the physical wrap packing, and videotape. But polymers also are world around us, whether by simple observation or found everyw h e r e in n a tu re. Wood, a n ima l a n d veg- experimental manipulation. In ancient Greece, for eta ble s, bone, a n d hor n a re polymer s, for exa m ple, example, Aristotle concluded that all materials were as is the deoxyribonucleic (DNA) inside the cell made up of combinations of only four elements: air, nucleus and the membrane that separates one cell from earth, fire, and water. During the Middle Ages, an o t h e r . Indeed, when the alchemists tried in vain to polymer industr y bega n in the convert common into nineteenth century, it made gold. By the late eighteenth materials that we r e der ived century, had begun fr om n a t u r a l po l y m e r s — ar tificial from plant , for instance. Artificial skin grown in the Eventually the industry began laboratory on scaffolding made syn t hesi zi n g n ew m a t er i a ls, of lon g cha in molecu les ca lled su ch a s n ylon , t ha t r ep l a c e d polymers can help heal the wounds of pa tients with ulcers natural materials and were ca u sed by poor blood cir cu la - made without natural pre- tion. (Photo courtesy of cu r sor s. Toda y pr od u ct s t ha t Organogenesis Inc.)

N A T I O N A L A C A D E M Y O F S C I E N C E S synthesizing and breaking down chemicals in an effort to determine their fundamental components. Early in the nineteenth century, English John , Launching the Polymer observing that chemicals would combine only in Industry specific ratios, concluded that matter was made of indivisible “” (a concept first proposed by the In 1870, four years before the structure of the Greek philosopher in about 400 BC). carbon was elucidated, American inventor John Nineteenth-century chemists also determined that Wesley H yatt won a contest to find a material for it was possible to synthesize so-called organic com- billiard balls to replace ivory—then as now in short pounds, once believed to be made only in living orga n - supply. Hyatt’s prize-winning contribution was cellu - is m s , from inorganic chemicals. loid, based on cellulose, a polymer that is the basic Even as chemists pursued their investigations into structural material of plant cell walls. It was the start the nature of nature, inventors were creating new of the polymer industry. Hyatt treated cellulose materials by treating natural substances with various nitrate, or guncotton—an explosive material made chemicals at elevated temperatures and . by exposing cotton plant to nitric and sulfuric In 1839, American inventor Charles Goodyear discov- —with alcohol and . What he got was a ered a technique, which he called , for hard, shiny material that could be molded when hot. manipulating the properties of the sap from rubber Cheap and uniform in consistency, this new material trees by treating it with heat and . The process did indeed replace ivory in billiard balls. Occasionally converted a gummy, springy material used mainly to though, when the celluloid billiard balls collided, they erase (“rub out”) into a dry, tough, elastic material created a small detonation like a firecracker because that would make automobile possible—and of the explosive nature of cellulose nitrate, which eventually a transportation revolution. is related to trinitrotoluene (TNT) in composition. Investigators working at the theoretical level were Celluloid also replaced horn in combs, found wide equally productive, arriving at a series of independent use in housewares, and was made into the first flexible realizations that would eventually lay the foundation . In 1887, Count Hilaire de for the polymer industry. In 1858, German chemist Chardonnet created a related product when he Friedrich Kekulé developed the framework for under- learned to spin cellulose nitrate into Chardonnet , standing the struc t u r e of organic molecules when he the first to enter production and a showed that a carbon atom can form chemical bonds forerunner of , , and Dacron. with up to four other atoms and that multiple carbon Both celluloid and Chardonnet silk were polymers atoms can join together to create long chains—a dis- c reated by altering natural polymers. The first tru l y co v er y also made at about the same time by Scottish synthetic polymer did not come along until 1909, chemist Archibald S. Couper. Then, in 1874, Jacobus when American inventor treated phe- van’t Hoff of the Netherlands and Joseph Le Bel of nol, or carbolic acid, another derivative of coal tar, France independently suggested that the carbon atom’s with the pre s e rvative under heat and four bonds are arranged so that they point at the cor- p re s s u re. His product, , was hard, immune ners of a tetrahedron, or pyramid. Since carbon atoms to harsh chemicals, electrically insulating, and heat ar e the framework for natural and artificial polymers, the resistant—characteristics that made it useful for a two discoveries would in time furnish a three - d i m e n - myriad of household goods and electrical part s . sional pi c t u r e of the molecular struc t u r e of polymers. Soon Bakelite was being used to make tools, machines, and cookingware. A key discovery in the late was that the ca r bon a tom ca n for m bonds with up to four ot her a t oms, ea ch ma r kin g Explains Polymers on e cor n er of a t et r a he - dron, or pyramid. Many The rapid success of Bakelite sparked a flurry ca r bon a toms ca n bon d, of synthesis investigations and innovations in both forming long molecular cha in s, or polymer s, in America and Europe. As the financial stakes rose, possible combinations that the hit-or-miss garage inventor’s approach that had number in the billions. dominated the industry gave way to more systematic

2 BEYON D DISCOVERY This article was published in 1999 and has not been updated or revised. efforts. No longer content simply to tinker with raw In 1920, German organic chemist materials and various processing conditions, scientists proposed began basic research designed to understand the mol- that the unusual strength and ela sticity of polymer s wa s du e to ecular structure of polymers. their great length and high molec- In 1920, the German chemist Hermann Staudinger, ular weight. (Photo of Hermann fascinated by the seemingly unique properties of poly- Staudinger courtesy of Institute mers, began investigating their behavior and chemical for Macromolecular Chemistr y, characteristics. Staudinger’s research suggested that Freiburg, Germany); (Diagram of a polymer , in t his ca se, polyet h - polymers are composed of long chain molecules ylene strands, courtesy of Biografx) of many identical or closely related chemical units. Moreover, he suggested that their unusual tensile strength and elasticity are a result of that great length or, in chemical terms, of their high molecular weight. Staudinger’s ideas may not sound especially radical today, but at the time he was ridiculed by his col- leagues in organic chemistr y, and his theories had little impact on the scientific community. Indeed, the existence of polymeric chain molecules was not accepted until 1928, when Kurt Meyer and H erman Mark, working for the German chemical trust I. G. Farben Industrie in Ludwigshafen, demonstrated their existence by examining the crystalline structure of polymers with x-rays. Many years later Staudinger was recognized for his efforts and persistence, when in 1953 he became the first polymer chemist to receive a . Staudinger’s key insights—that polymers are long chains of many small chemical units and that chain length plays a crucial role in determining physical pro p e r ties and behavior—pointed up the need for tools to assess molecular weight and thus chain length. One of the first tools was the ultracentrifuge, invented The Glory Years by the Swedish chemist . The ultra- centrifuge spins samples at very high speeds and can When nylon was introduced as a substitute for separate molecules according to their size. It can be silk in stockings in 1937, the new material—strong, used to estimate both the size of the molecules and cheap, and easy to work with—became an unqualified the distribution of sizes in a given polymer sample. commercial hit. The instant success of nylon fibers By the end of the 1920s, armed with better tools and , the first , taught the and better theories, polymer scientists were making polymer industry an important lesson—that basic dramatic breakthroughs. In 1928, the DuPont research can lead to products that can replace natural Corporation hired chemist Wallace Hume Carothers materials. It can also eventually lead to Nobel prizes. to build new kinds of polymers in a new laboratory of Stanford University received one for his dedicated to basic research. To test Staudinger’s still- career contributions to while working controversial theor y, Carothers carefully joined small in both academic and industrial laboratories. Flory organic compounds into long chains and examined was instrumental in developing the theory of how the properties of his products. He found that collec- polymer molecules behave, especially through mathe- tions of very long chain molecules produced stiffer, matical and statistical analysis of the shape and prop- stronger, and denser materials. By 1930, Carothers’s erties of polymer chains. systematic synthetic approach was bearing fruit as The 1930s were the glory years for the develop- he came up with a new class of polymers called ment of new synthetic polymers, producing polyvinyl polyamides, or “.” These polymers could be chloride (PVC), , melted and drawn into a remarkably strong fiber. (Teflon), and , which together would

N A TIONAL ACADEMY OF 3 This article was published in 1999 and has not been updated or revised. revolutionize the fabric, , houseware, packag- sizes of very long polymers. Polymer scientists used ing, and insulation industries. These new materials this knowledge to analyze the artificial rub b e r . Modern bore no resemblance to their raw materials (which versions of his technique are invaluable to res e a rc h e r s we r e commonly oil or natural ) and were celebrated characterizing complex molecules. for their very artificiality. Because many of these polymers became malleable when heated, they came to be called “plastics” from the Greek word meaning “able to be molded.” Another important development beginning in the Polymers from Petroleum late 1930s and 1940s was the large-scale production of Although both the science and technology of ar tificial rub b e r , spurred by the booming automobile polymers had advanced remarkably by the early in d u s t r y and the military demands of World War II. 1950s, formidable challenges remained to be sur- By 1930, two new forms of artificial rubber had been mounted. Because of the abundant supply and low developed in Germa n y , both based on the petrol e u m cost of their component petroleum-derived building by p r oduct butadiene. As tensions grew in Europe, the blocks or “,” hydrocarbon polymers con- U.S. government recognized the vulnerability of the taining only carbon (C) and hydrogen (H) atoms nation’s rubber supply and in 1941 established the represented a potentially highly useful class of sub- Rubber Reserve Company to produce 10,000 tons of stances. Particularly attractive targets were polymers rubber annually. By the middle of 1942 the prod u c - of the smallest and most abundant such monomers, tion goal had soared to 850,000 tons annually in and propylene (containing two and three response to the Japanese occupation of the East carbon atoms, res p e c t i v e l y ) . The general ability of Indies, whose vast rubber tree plantations had supplied such molecules, containing pairs of carbon atoms the world with the raw material for rub b e r . Polymer connected by “double bonds,” to join together to fo r m scientists and engineers worked together to develop long chains (see figure opposite) had long been rec o g - a variety of new processes to meet wartime demands. nized (a familiar example being polystyrene). Ho w e v e r , One of the most important was a light-scattering tech- in the case of ethylene and propylene this presented a nique developed by of Cornell University, formidable challenge. The “” of ethyl- who used it to determine the molecular weight and ene had been accomplished, but only at undesirably

Timeline This timeline shows the chain of research that led to an understanding of polymers and the development of some of their medical uses.

1920s 1 9 3 0 Germans develop 1 8 3 9 Kurt Meyer and Herman Mark two types of synthetic Charles Goodyear 1 8 7 0 use x-rays to examine the rubber (Buna-S invents the process of John Wesley Hyatt mar- internal structure of cellulose 1 9 0 9 and Buna-N) from vulcanization, which kets celluloid, a plastic and other polymers, providing Leo Baekeland butadiene, a makes rubber into a made of chemically convincing evidence of the creates Bakelite, petroleum byproduct. dry, tough, springy modified cellulose, also multiunit structure of some the first completely material. called cellulose nitrate. molecules. synthetic plastic.

Late 1920s 1 8 5 8 1 9 2 0 Wallace Hume Carothers 1 8 8 7 Chemists Friedrich Kekulé Hermann Staudinger proposes that and his research group Count Hilaire de and Archibald Couper polymers are long chains of smaller at DuPont synthesize and Chardonnet introduces a show that organic units that repeat themselves hun- develop applications for way to spin of molecules are made up dreds or thousands of times. He synthetic , cellulose nitrate into of carbon atoms combined later receives a Nobel Prize for neoprenes, and nylons. Chardonnet silk, the first chemically into different his research on the synthesis and synthetic fiber. shapes. properties of polymers.

This article was published in 1999 and has not been updated or revised. wa y , because the chains were longer and more linear, had greatly superior pro p e rties such as stre n g t h , h a rdness, and chemical inertness, making them very useful for many applications. Building on Ziegler’s discovery, Italian chemist , working at the Milan Polytechnic Institute, demonstrated that similar catalysts were effe c - tive for the polymerization of propylene. Furth e rm o re , with such “Ziegler-Natta catalysts” it was possible to achieve exquisite control of the chain length and struc - tu r es of the resulting polymers and, th e re b y , of their prop e r ties. Among other rem a r k a b l e Polymerization of ethylene and propylene to and achievements of this class of catalysts was the synthesis polypropylene. of a polymer that is identical to natural rub b e r . Industrial applications of “Ziegler-Natta catalysts” high temperatures and pres s u res, yielding polymers we r e realized almost immediately and with various whose prop e r ties left much to be desired. The poly- subsequent refinements continue to expand. Tod a y , merization of propylene remained to be achieved. polyethylene produced with such catalysts is the In 1953, while engaged in basic re s e a rch on the la r gest volume plastic material and, together with reactions of compounds containing aluminum-carbon po l y p r opylene, accounts for about half of the U.S.’s bonds, the German chemist , working cu r rent annual 80 billion pound production of plastics at the Max Planck Institute for Coal Research in and . The uses of polyethylene and polyprop y - Mulheim, discovered that adding salts of cert a i n lene extend to virtually every facet of industry and other metals such as titanium or zirconium to these daily life, including building and construction materials, c o mpounds resulted in highly active “catalysts” containers, toys, sporting goods, electronic appliances, (substances that speed up chemical reactions) for textiles, carpets and medical products. In many of the polymerization of ethylene under relatively mild these applications polymers replace other substances, conditions. Fu rt h e rm o r e, the polymers formed in this such as glass and metals, but their distinctive prop e rt i e s

1 9 6 3 1 9 4 0 s Edward Schmitt and 1 9 8 6 1 9 9 7 Langer and Joseph Vacanti Peter Debye develops Rocco Polistina file Clinical trials show that demonstrate that liver cells a light-scattering tech- a patent for the first artificial skin can heal grown on a plastic framework nique for measuring the absorbable synthetic diabetic skin ulcers, can function after being trans- molecular weight of sutures, made of establishing the poten- planted into animals, opening large polymers. polyglycolic acid, tial clinical feasibility the door to the new field of a key plastic in tissue of tissue . engineering. tissue engineering.

1 9 3 0 s Paul Flory develops a mathe- 1 9 5 3 1 9 7 5 1 9 9 6 matical theory to explain the Karl Ziegler discovers Robert Langer and M. Judah The U. S. Food and Drug creation of polymer networks catalysts for polymer- Folkman use polymers to isolate Administration approves “in which polymer form ization of ethylene. chemicals that stop the formation of polymer wafer implants cross-links and become, like Giulio Natta synthe- blood vessels, suggesting a new way for treating brain cancer. rubber, elastic.” Flory would sizes polypropylene. to attack cancer. These studies also receive a Nobel Prize for his Their discoveries establish the feasibility of controlled lifetime contributions to were recognized by release of . polymer in 1974. a Nobel Prize.

This article was published in 1999 and has not been updated or revised. also have given rise to entirely new applications, many diseases of the heart, liver, and kidney actually including medical uses. involved failures of these organs, and they were initiat- In 1963, the was awarde d ing effo r ts to replace damaged organs with healthy to Ziegler and Natta “for their discoveries in the field ones. H owever, the body’s immune cells—which are of the chemistry and technology of high polymers.” In designed to seek out and destroy any foreign tissue— his acceptance speech, recalling the circumstances of his ar e unable, for example, to distinguish between an pioneering discovery and the scientific obstacles that unwanted bacterial infection and a much-desired trans- had to be overcome, Ziegler went on to say: planted kidney. Although some early drugs, such as “But a much more formidable impediment might co rt i c o s t e r oids, azothropine, and 6-merca p t o p u r i n e , have presented itself. In order to illustrate this, I must helped in combating rejection, the problem began to elaborate on the paradox that the critical concluding fade only after 1969, when Swiss microbiologist Jean stages of the investigations I have reported took place Bo r el discovered that a soil fungus, cyclosporin A, in an institute for ‘coal research.’ When I was called would selectively interfe r e with the specific immune to the Institute for Coal Research in 1943, I was dis- cells that drive the rejection reaction. The 1983 turbed by the objectives implied in its name. I was ap p r oval of cyclosporin A by the U.S. Food and Drug afraid I would have to switch over to the considera- Administration (FDA) gave transplant surgeons a tool tion of assigned problems in applied chemistry. Since that has since saved the lives of thousands of patients ethylene was available in the Ruhr for coke manufac- with heart, liver, or kidney failure. ture, the search for a new polyethylene process, for example, could certainly have represented such a problem. Today I know for certain, however, and I suspected at the time, that any attempt to strive for a set goal at the very beginning would have completely Designer Polymers dried up the springs of my creative activity.” Cyclosporin A encouraged a wave of transplants and also helped set the stage for the current rise in “tissue engineering,” as scientists call the construction of whole artificial organs. Transplant surgeons, Working with Nature who no longer lost patients because of the rejection of their transplants, now were faced with a new As new applications for polymers were being frustration—losing patients for lack of donor organs. found, some re s e a rchers wondered whether they One of those frustrated doctors was Joseph Vacanti could also play a role in the human body, perhaps at Boston’s Children’s Hospital, home of the first in repairing or replacing body tissues and cart i l a g e . The idea was not entirely new. The natural polymer collagen, found in animal connective tissue, had been used as surgeon’s thread for more than 2,500 years. And as early as the 1860s, an artificial poly- mer called collodion, invented a decade earlier by the French chemist Louis Ménard, was used as a liquid dressing for minor wounds. Collodion, made f rom a of cellulose nitrate in alcohol and e t h e r, formed a film that could be peeled off after the wound healed. The excellent barrier pro p- e rties of polymers were also central to an experiment in 1933 by Italian biologist Vincenzo Bisceglie, who implanted tumor cells encased in a nitro c e l l u l o s e membrane in a guinea pig. The cells survived, pro- Physician Joseph Vacanti (left) and chemical engineer tected by the membrane against attack by the host Robert Langer joined forces in the early 1980s in an effort to create artificial tissues. Within a few years they had animal’s immune cells. grown liver cells on a polymer framework, giving rise to Meanwhile, the question of contending with the the field of tissue engineering. (Photo of Vacanti courtesy body’s immune system was becoming a critical one in of C ha r les Va ca n t i, of La n ger cou r t esy of R ober t La n ger ) . medicine. Scientists were beginning to recognize that

6 BEYON D DISCOVERY This article was published in 1999 and has not been updated or revised. Roughly the size of a dime, biodegra da ble polymer wa fers (left) ca n be implanted in specific places in the brain after cancer surgery to deliver cancer - killing drugs at a controlled rate. The implanted wafers deliver drugs only to the brain (far right) rather than to the whole body. (Photos courtesy of Guilford Pharmaceuticals)

successful human organ transplant. In 1983, Vacanti Using PGA and similar polymers, Langer crafted began talking with his friend Robert Langer, a degradable and nondegradable polymer pellets into chemical engineer at the Massachusetts Institute of an intricate porous structure that allowed the slow Technology, about the feasibility of making an artifi- diffusion of large molecules. (This finding is the cial liver and possible other artificial tissues to save the foundation of much of today’s controlled drug deliv- lives of his young patients. ery technology.) Loaded with chemical messengers, It was a tall order. Nobody had built any kind of the pellets played a key role in Langer and Folkman’s working organ, let alone one as complex as the liver. 1975 discovery in cartilage of the first compound that In addressing this task, Langer called considerable blocks the formation of new blood vessels, thereby experience to bear on attacking the problem in a halting tumor growth. rational way. In the mid-1970s, he had developed In 1984, at about the same time he was some polymer systems for M. Judah Folkman of a p p roached by Joseph Vacanti, Langer teamed up Harvard University, who was then investigating the with Brem, a brain cancer surgeon at Johns role of new blood vessels in promoting the growth of Hopkins Medical Institutions, to test his new cancerous tumors, and was looking for a slow-release techniques using polymers against brain cancer. mechanism to release compounds that block the Although there were new tools for finding tumors, chemical messengers that control angiogenesis, the including computed tomography and magnetic re s- formation of new blood vessels. Langer discovered onance imaging scanners, the most malignant brain that polymers such as ethylene-vinyl acetate, which cancers remained largely untreatable. Cancer cells absorb very little water, could slowly deliver these remaining after the tumor’s removal were pro t e c t e d chemical messages. f rom chemotherapy drugs by the so called blood- One polymer that Langer eventually focused on brain barr i e r, which prevents a variety of blood- was polyglycolic acid, or PGA, which was also used b o rne chemicals from penetrating the brain. Bre m in synthetic degradable sutures and had reached the w o n d e red if polymers could slowly release cancer- market in 1970. PGA itself had been known since at killing drugs right where they were needed—in the least 1950, when Norton Higgins of DuPont patented brain itself. a three-step process for making it from glycolic acid Langer responded by designing surface-degrading by carefully manipulating temperature and pre s s u re . polymers that released medicines at a controlled rate. The patent Higgins filed did not mention medical In 1992, Brem and Michael Colvin, now director applications, but in 1963 Edward Schmitt and Rocco of the Duke Cancer Center, implanted drug-bearing Polistina of American Cyanamid Company filed a polymer wafers after brain surgery. The wafers patent for the formation of sutures from PGA. prolonged the lives of both experimental animals and When the sutures reached the market seven years human patients. Since the chemicals were released l a t e r, they were rapidly adopted as a strong, re l i a b l e , locally, they did not result in the systemic toxicity typ- and workable replacement for the traditional colla- ical of anticancer drugs. With FDA approval in 1996, gen-based absorbable sutures that surgeons had the wafers represent the first new treatment for brain used until then. cancer in 25 years. Similar slow-delivery systems are

N A TIONAL ACADEMY OF SCIENCES 7

This article was published in 1999 and has not been updated or revised. cord repairs, bone or cartilage cells for joint repairs, pancreatic cells to make insulin for diabetics, and liver cells to make livers for transplantation. Through all of these efforts by many kinds of scientists, several facts stand out. The path from need to benefit travels through many areas of science and technology and depends crucially on the insights pro- vided by basic research. The first polymer inventors made progress by transforming natural materials in hit-or-miss fashion, but their work greatly accelerated after basic researchers clarified the fundamental char- A scanning electron micrograph reveals cells growing on long acteristics, such as the relation between size or molec- polymer fibers, the first step in creating artificial tissues. ular weight and physical properties, that govern the (Photo courtesy of Robert Langer) behavior of polymers. Similarly, the progress in medicine and biology that gave birth to organ trans- now being used to treat prostate cancer, endometrio- plantation still relies on basic research into the role sis, and severe bone infections. of chemical messengers, genetic codes, and cellular All these efforts laid the groundwork for function. As polymer science and materials engineer- researchers’ continuing search for a framework for ing join forces with biology and medicine to produce growing replacement body parts and organs, such as these modern miracles, we again see how interdiscipli- livers. By now scientists had learned that human cells nary collaboration and essential basic and applied grown on flat plates did not produce the normal array res e a r ch remain the true source of benefits as simple— of , while cells grown on three-dimensional and profound—as a living tissue that can be created in scaffolds had relatively normal . At first the laboratory. the best results were obtained from PGA, but since the best source of fibrous PGA in 1984 was degrad- able sutures, hours were spent unwinding sutures to This article has not been updated or revised since transform the fibers into meshlike plastic scaffolds to its original date of publication. The article from which this support liver cells. Still, by 1986, liver cells on plastic account was adapted was written by science writer David J. frameworks were surviving and functioning after Tenenbaum, with the assistance of Drs. Frank DiSesa, transplantation into animals, laying the groundwork Robert L. Kruse, Rober t S. Langer, Robert W. Lenz, for using polymer scaffolds to create a variety of tis- William J. MacKnight, Jeffery L. Platt, Bruce Rosen, Richard Stein, Walter H. Stockmayer, Edwin L. sues, from bone to cartilage to skin. Thomas, Valerie A. Wilcox, Charles A. Vacanti, The polymer scaffolds, made with nonwoven and William Vining, for Beyond Discovery™: The fabric techniques borrowed from the textile industry, Path from Research to Human Benefit, a project of the have now been used to grow at least 25 types of cells National Academy of Sciences. in animals or people and have thus become a kind of generic framework for artificial organs. Biotechnology The Academy, located in Washington, D.C., is a firms are using the scaffolds to make artificial skin for soci et y of d i st i n gu i shed schola r s en ga ged i n sci en t i fi c treating diabetic ulcers and severe burns. They multi- and engineering research, dedicated to the use of ply living cells in culture (from tissue that is normally science and technology for the public welfare. discarded during surgery), and then “seed” the cells For more than a century it has provided on the polymer scaffold. Applied to the patient’s independent, objective scientific advice to the wound, the material protects against deadly infection nation. and loss. More important, the cells it carries Funding for this article was provided by the Camille release chemical growth factors, signals that stimulate and Henry Dreyfus Foundation, Inc. and the National normal cellular growth at the wound site. These Academy of Sciences. chemicals account for the roughly 60 percent improvement in healing that diabetics like Frank Baker experience with artificial skin. As tissue engi- neers look to the future, they are talking about using polymer scaffolds to grow nerve cells for use in spinal © 1999 by the National Academy of Sciences N ovember 1999

8 BEYON D DISCOVERY

This article was published in 1999 and has not been updated or revised.