Tissue-engineered osteochondral constructs in the shape of an articular condyle.
BACKGROUND
An entire articular condyle engineered from stem cells may provide an alternative therapeutic approach to total joint replacement. This study describes our continuing effort to optimize the chondrogenic and osteogenic differentiation from mesenchymal stem cells toward engineering articular condyles in vivo.


METHODS
Primary rat bone-marrow mesenchymal stem cells were induced to differentiate into chondrogenic and osteogenic lineages in vitro and were suspended in polyethylene glycol-based hydrogel. The hydrogel cell suspensions, each at a density of 20 x 10(6) cells/mL, were stratified into two separate layers that were molded into the shape and dimensions of an adult human cadaveric mandibular condyle by sequential photopolymerization. The osteochondral constructs fabricated in vitro were implanted in the dorsum of immunodeficient mice for twelve weeks.


RESULTS
De novo formation of articular condyles in the shape and dimensions of the adult human mandibular condyle occurred after a twelve-week period of in vivo implantation. Histological evaluation demonstrated two stratified layers of cartilaginous and osseous tissues, and yet there was mutual infiltration of cartilage-like and bone-like tissues into each other's territories. The cartilaginous portion was stained intensively to safranin O and expressed immunolocalized type-II collagen. Chondrocytes adjacent to the tissue-engineered osteochondral junction were enlarged and expressed type-X collagen, typical of hypertrophic chondrocytes. The osseous portion contained bone trabeculae-like structures and expressed immunolocalized type-I collagen, osteopontin, and osteonectin.


CONCLUSIONS
A cell encapsulation density of 20 million cells/mL with in vivo incubation for twelve weeks yields further tissue maturation and phenotypic growth of both cartilage-like and bone-like tissues in the tissue-engineered articular condyle.
Alhadlaq
Adel
A
Department of Anatomy, Tissue Engineering Laboratory, MC 841, University of Illinois at Chicago, 801 South Paulina Street, Chicago, Illinois 60612, USA.
Mao
Jeremy J
JJ
D000818:Animals; D002358:Cartilage, Articular / Q000166:cytology; D002452:Cell Count; D002454:Cell Differentiation / Q000502:physiology; D019902:Chondrocytes / Q000502:physiology*; D024042:Collagen Type I / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000502:physiology*; D010012:Osteogenesis / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D023822:Tissue Engineering / Q000379:methods*
D024042:Collagen Type I