New Biomaterial May Replace Arteries, Knee Cartilage

The biomaterial is unique for several reasons, researchers said. It is biocompatible with body tissue because of its attraction to water; researchers can adjust its mechanical strength as needed; it is compliant like normal body tissue; and it is made from an organic polymer, rather than silicone.

Researchers have completed initial laboratory testing, secured investors for a private start-up company to produce and market the biomaterial, and are now beginning the five- to seven-year process toward obtaining approval from the Food and Drug Administration. That process will include testing in humans.

"The goal is to get the medical implant out to help patients," said lead inventor Dr. David Ku, a professor of mechanical engineering at Georgia Tech and a professor of surgery at Emory University. "But we first need to make sure it's very safe to patients and that it benefits them."

A patent has been allowed on the material, a hydrogel called "Salubria." Its name is derived from the Latin words for "safe" and "healthy." Georgia Tech Research Corporation and Ku will hold the patent, which is expected to be formally granted this spring by the U.S. Patent Office.

Salubria has a high water content, making it similar to, and thus biocompatible with, human tissue, Ku said. It is also unique for three other properties. It is an organic polymer, rather than being made from silicone, which is suspect in inflammatory disorders in breast implant patients. Second, it has enough mechanical strength that it will not burst under normal physiological conditions. And Salubria has enough elasticity and compliance that it will pulsate in rhythm with the heart under normal physiological conditions.

"When people touch samples of Salubria in its vascular graft (artery replacement) form, they describe it as noodle-like or similar to calamari (squid)," Ku said. " I think it feels very much like an artery. As a knee cartilage replacement, Salubria looks and feels like the white, shiny cartilage at the top of a drumstick."

To date, tests in rats, dogs and sheep show that Salubria is biocompatible: Platelets do not adhere to it in significant quantities, and thus the chance of blood clots is greatly reduced, Ku explained. Such has been the problem with Dacron, which surgeons have used for artery replacement in the abdomen and legs since its development in the 1950s. Other evidence of Salubria's biocompatibility is that it allows new cells to grow on it, effectively making it part of the body, Ku said.

Proof-of-concept studies showed Salubria's potential for use in artery replacement, including those in the heart because of its mechanical strength. Also, Salubria shows great promise for meeting the large demand for knee cartilage replacement in patients suffering from sports injuries, rheumatoid arthritis and osteoarthritis, Ku said. "Salubria acts like a shock absorber or water bag between bones in patients with arthritis or sports injuries to the knee," he added.

In addition these studies suggest Salubria can serve as a nerve guide to create a physical bridge that could dramatically increase the speed at which severed nerves heal. "This ability to speed the healing process could eventually help patients with spinal cord injuries, like (actor) Christopher Reeve's, to walk again," Ku said.

As an implantable drug delivery system, Salubria may work for many drugs, such as insulin and morphine, that need to be injected, Ku said. Its advantage for such is that it is hydrophilic (attracted to water), rather than hydrophobic (resisted by water) like the silicone used in the implantable contraceptive Norplant.

Proof-of-concept studies will continue as Ku tries to improve the biomaterial and broaden its application, he said.

It was a long road to reach the point at which Salubria now stands, Ku said. For eight years, he had been using Dacron and a material similar to Teflon to replace arteries in patients at Emory. But Ku was dissatisfied with these materials because they only last about two years, and thus require additional surgeries to replace failed grafts.

So Ku, who has doctoral degrees in mechanical engineering and medicine, took this clinical problem and posed it as an engineering problem, he explained. Hoping to find a new biomaterial, Ku contacted other university researchers, but no one could produce enough to implant. So Ku turned to his own laboratory at Georgia Tech to formulate a new material, one very similar in nature to human tissue. After about two years of research, Ku and his students developed Salubria in 1996. In February 1998, he started Restore Therapeutics, the Atlanta-based corporation that holds the exclusive license to produce and market Salubria.

Ku is grateful for what he calls Georgia Tech's vigorous movement toward technology transfer. The university is developing technology transfer models based on what other universities, such as Stanford, have successfully done. Georgia Tech is using licensing mechanisms and exploring ways for granting researchers seed funding for proof-of-concept studies.

In fact, Ku received $49,000 in such funding from the Georgia Tech-based Advanced Technology Development Center's (ATDC) Faculty Research Commercialization Program in fiscal year 1998. The grant and ATDC's business advice helped him start Restore Therapeutics. Georgia Tech, along with private investors, hold equity in Restore Therapeutics. The company has six members.

"Most professors are not business people," Ku said. "Without this sort of technology transfer assistance, a lot of useful technology would never make it to market."