Fall 2006 - College of Dental Medicine - Columbia University

whether this or some other proportion of cells ismost desirable.” And, even though microscopicexamination of slices taken from the completedcondyles showed tissues similar to natural bone andcartilage, which expressed genes and producedchemicals characteristic of its tissue, as well as showinga normal increase of bone tissue calcium contentover time, Dr. Mao realized that the engineeredcondyles were not sturdy enough to replacecondyles in human patients. He described them asbeing “about as strong as those found in newbornbabies,” and added that “the strength and durabilityof the engineered tissue must be addressed beforemedical applications can be considered.” To increasemechanical strength in the condyles, Dr. Mao proposesadministering additional slow-release chemicalgrowth factors to the cells, thereby promoting furthertissue growth and maturation. A secondapproach applies mechanical stresses to cells at varioustimes during production of the condyle. “Welaboratory can be put to good use in the manufacturingof soft tissue to supplant deficiencies causedby disease, surgery, or trauma in craniofacial regionsand other areas of the body.Dr. Mao’s studies demonstrate that in comingdecades scientists may be able to seed a threedimensionalscaffold with a patient’s own adult stemcells, thereby generating cell types for both boneand cartilage tissue that could build an entirely newjaw, knee, or hip for someone who has lost thesestructures to disease or injury. The completedbody part could then be returned to the body as animplant without fear of triggering an immuneresponse.plan to mechanically stress the stem cells while theyare still in cell culture and then later mechanicallystress the osteoblasts and chondroblasts locatedwithin the gel,” says Dr. Mao. “These treatments mayincrease the rate of tissue formation and strengthenthe extracellular matrix between the cells.”In the course of developing the mandibular condyle,Dr. Mao also grew human soft tissue from stemcells. His explanation for this approach was that thesame cells he used to engineer the cartilage in histemporomandibular joint also make adipose tissue,or – fat! As he points out, fat cells produced in theIllustrations of the engineeredneogenesis of a human-shapedmandibular condyle from mesenchymalstem cells on pp. 8 and9 (courtesy of Jeremy Mao, DDS,PhD and Journal of DentalResearch, 85 (11) November2006); and details from anengraving of the human mandibleby John Hunter (1728-1793),Natural History of the HumanTeeth, London 1771, on pp. 6 and8 (courtesy of Archives and SpecialCollection,Augustus C. LongHealth Sciences Library, ColumbiaUniversity Medical Center).primus2006 09