Artificial Organs: Corneas from Calf Skin

Though few people outside medicine and biology know the word, collagen is one of the most important constituents of the human body, making up 30% of its protein. In bone and tooth enamel, its long chains of molecules serve the same purpose as that of steel reinforcing rods in concrete. In mobile tissues' such as tendons, arteries and heart valves, they are like flexible steel wires. And despite the unfamiliarity of its name, collagen (from the Greek kolla, or glue, and pronounced col-uh-jen) has been popular in the humblest homes for centuries. When the hides and bones of animals are boiled down, they yield that denatured but widely used form of collagen, gelatin.

In theory, so versatile a natural body component should be ideal for replacing corneas, blood vessels, valves, and perhaps even whole organs. But practical considerations have long frustrated theory. In humans, animal collagen almost certainly would trigger inflammatory reactions and rejection mechanisms. Now, through the unlikely partnership of a Japanese shoe-leather company, which was making sausage casings on the side, and the Rogosin Laboratories of the New York Hospital-Cornell Medical Center, it looks as though animal collagen may yet become the ideal material for many medical uses.

Cut the Tails. X-ray studies reveal natural collagen as three strands of molecules twisted together like rope. The strands are short, and many have to be joined end to end to make up the body's long collagen fibers. Dr. Tomio Nishihara, a physical chemist who heads research for the Japan Leather Co., and Dr. Francis O. Schmitt of the Massachusetts Institute of Technology, thought there must be something on the ends of the basic molecules that enabled them to couple. Dr. Albert L. Rubin and an M.I.T. team set about testing the theory. They found that each collagen strand has a tail or tails consisting of smaller protein molecules that determine the linkages. Cut off the tails, and what remains is short strands of colla gen that can be recombined in almost any desired "weave," shape or thickness, and with varying degrees of softness or hardness. More important, when the tails are cut off, the collagen molecules lose most of their power to set off allergic reactions.

For its reconstituted collagen, the Japan Leather Co. uses odds and ends of calf skin left over when the hides have been cut for making shoes. After weeks of soaking and washing hide in various chemicals, including enzymes, to remove the linkage tails, Dr. Nishihara pours collagen into thin sheets resembling cellophane. The resulting membrane makes fine, easily digestible sausage casing. It also gave the Rogosin Labs' Dr. Rubin and Dr. Kurt Stenzel an idea for its first medical application—use in the artificial kidney, which has a filter membrane of sausage-casing cellophane. In laboratory glassware the collagen membrane has already done a better filtering job than cellophane; specially prepared collagen sheets will now be tested in artificial kidneys for animals in the laboratory.