ARLINGTON, Va., Nov. 26, 2003 --- A Whitaker investigator has moved tissue engineering a step forward by successfully using a single population of adult stem cells to grow a knob of jawbone as a potential medical implant.

Associate Professor Jeremy Mao, Ph.D., D.D.S., of the University of Illinois at Chicago used the stem cells to cultivate both the bony and cartilage-like elements of a critical part of the ball-and-socket joint that connects the jaw with the skull at the base of the ear.

Disorders of this temporomandibular joint (TMJ) are a source of pain and discomfort for about 30 million Americans. Degenerative diseases of the TMJ can require joint replacement, a procedure hampered by too few donors, possible rejection by the immune system, and other inherent complications.

Attempts to produce a tissue-engineered replacment have met with some measures of success. These have individually seeded bone-shaped scaffolds with mature bony cells or cartilage-like cells, which then take hold and grow.

A more realistic approach for joint replacement would be to seed a scaffold with adult stem cells taken from the patient. These cells would give rise to cell types responsible for both bone and cartilage tissue. The cells could be placed in a scaffold to grow into the correct three-dimensional structure, and then returned to the body as an implant without fear of triggering an immune response. Mao's study demonstrated that this approach may, in fact, be possible.

The experiments were conducted in rats, starting with a sample of bone marrow taken from two animals. The marrow was processed to obtain stem cells, which were loaded into four polyurethane molds shaped like the ball part (condyle) of a human temporomandibular joint. In three of the scaffolds, cells were given chemical treatments to encourage their growth. The fourth was left untreated as a control. All four scaffolds were implanted in the back of a mouse and allowed to grow for eight weeks.

When the tissue-engineered structures were removed from the mouse, they had developed into condyles with two layers of cartilage- and bone-like elements, closely resembling the natural tissues. But there is more to be done.

For one thing, the potential implants had grown a relatively even distribution of bony cells and cartilage-like cells, raising the question of whether this or some other proportion of cells is most desirable. Other technical issues, such as the strength and durability of the engineered tissue, also must be addressed before medical applications can be considered.

"Nevertheless, the present findings represent a proof of concept for further development of tissue-engineered mandibular condyles," Mao and coauthor Adel Al-Hadlaq, a graduate student, reported in the Nov. 20 issue of the Biomaterials & Bioengineering Section of the Journal of Dental Research.

Mao's research was supported, in part, by a 2001 Whitaker Foundation Biomedical Engineering Research Grant.

Contact:
Frank Blanchard, The Whitaker Foundation
Jeremy Mao, University of Illinois at Chicago