Use of controlled mechanical stimulation in vivo to induce cartilage layer formation on the surface of osteotomized bone.

A micromachine was used to study the response of mesenchymal tissue to mechanically controlled motion in vivo. The middle portion of the coccygeal vertebra of Fischer 344 rats was osteotomized, and continuous bending motion was applied for 4 weeks. The experimental groups were divided into two groups with higher sliding displacement applied at the osteotomized gap of group II. Hyaline cartilage tissue was generated at the osteotomized ends, and was predominantly formed on the side that extended during the bending motion. These newly formed tissues stained intensively with safranin O and toluidine blue, positively with immunostain for type II collagen, but negatively with immunostain for type I collagen. Articular cartilage-like tissues with a surface and a layer structure were obtained in group II, in which higher sliding motion was applied. Light and electron microscopy revealed morphological features similar to those of normal articular cartilage tissue in the superficial and middle zones of the tissues obtained in group II. Collagen fibrils in the superficial zone were found aligned parallel to the smooth surface. Although tidemark formation was not observed in the deep zone, the structure was much more natural than that of any other tissue-engineered cartilage reported to date. These results suggest that controlled sliding stimulation can elicit the generation of articular cartilage structure in vivo.