Dec. 1, 2003 Researchers at the University of Illinois at Chicago have successfully turned adult stem cells into bone and cartilage, forming the ball structure of a joint found in the human jaw with its characteristic shape and tissue composition.
Tested so far only in animals, the tissue-engineering procedure to create a human-shaped articular condyle could be used one day to regenerate the ball structure of joints in the jaw, knee and hip that have been lost to injury or diseases such as arthritis.
"This represents the first time a human-shaped articular condyle with both cartilage- and bone-like tissues was grown from a single population of adult stem cells," said Jeremy Mao, director of the tissue engineering laboratory at UIC and associate professor of bioengineering and orthodontics.
"Our ultimate goal is to create a condyle that is biologically viable -- a living tissue construct that integrates with existing bone and functions like the natural joint."
To create the articular condyle, Mao and Adel Alhadlaq, a doctoral student in anatomy and cell biology, used adult mesenchymal stem cells taken from the bone marrow of rats. Bone marrow is the inner, spongy tissue of long bones like the femur and tibia, the leg bones.
Under certain conditions, mesenchymal stem cells, present in a number of adult tissues, can potentially differentiate into virtually any kind of connective tissue -- including tendons, skeletal muscle, teeth, ligaments, cartilage and bone.
Using chemical substances and growth factors, the scientists induced the adult stem cells to develop into cells capable of producing cartilage and bone.
The cells were then stratified into two integrated layers, encapsulated in a biocompatible gel-like material, and shaped into an articular condyle using a mold made from the temporomandibular or jaw joint of a human cadaver.
After several weeks, Mao and his colleagues found that the tissue-engineered structures retained the molded shape of the human mandibular condyle, with bone-like tissue underneath and a layer of cartilage-like tissue on top -- an arrangement similar to that of a natural articular condyle.
Moreover, multiple tests confirmed that the newly grown tissues were indeed bone and cartilage, having the characteristic microscopic components: for bone, a matrix of collagen with deposits of calcium salts, and for cartilage, collagen and large amounts of substances called proteoglycans.
Mao stressed that much additional work is needed before tissue-engineered condyles are ready for therapeutic use in patients suffering from osteoarthritis, rheumatoid arthritis, injuries or congenital anomalies.
Nevertheless, he believes that with further refinements, the procedure could one day be adopted for total hip and knee replacements.
"Our findings represent a proof of concept for further development of tissue-engineered condyles," Mao said.
The first in a series of reports on the tissue-engineered articular condyle will be published as a rapid communication in the December issue of the Journal of Dental Research.
Mao's tissue engineering laboratory is funded by multiple grants from the National Institutes of Health and the Whitaker Foundation.
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