Chondrogenesis in periosteal explants. An organ culture model for in vitro study.

Periosteal grafts have chondrogenic potential and have been used to repair defects in articular cartilage. We studied the effects of the culture conditions and of transforming growth factor-beta 1 on chondrogenesis in rabbit periosteal explants that were cultured in vitro. A total of 390 periosteal explants were obtained from the anteromedial sides of the proximal parts of the tibiae of eleven rabbits that were two weeks, two months, or six months old. The culture medium (alpha minimum essential medium or Dulbecco minimum essential medium) contained fetal calf serum, with or without transforming growth factor-beta 1, at a concentration of one or ten nanograms per milliliter for the first two weeks of culture. Three hundred and twenty-one explants were submerged in liquid medium and sixty-nine were suspended in an agarose gel; they were then evaluated histochemically, histomorphometrically, and by collagen-typing. In the media without agarose, in the presence of ten nanograms of transforming growth factor-beta 1 per milliliter, chondrogenesis was commonly seen after two to four weeks with use of safranin-O staining and histomorphometry. In the agarose gels, chondrogenesis from the periosteum was observed at four and six weeks and was enhanced by the presence of one or ten nanograms of transforming growth factor-beta 1 per milliliter. The combination of agarose with transforming growth factor-beta 1 most favored the formation of cartilage, which was maximum at six weeks in the presence of ten nanograms of transforming growth factor-beta 1 per milliliter. Under these conditions, chondrogenesis occurred in almost every explant, with 50 +/- 30 per cent of the tissue being composed of cartilage. Type-II collagen was present in the explants that had undergone chondrogenesis.