Ossification Osteoclast

Osteopontin (formerly known as bone sialoprotein I) binds tightly to hydroxyapatite in bone and thus forms an integral part of the mineralised matrix. It has been postulated to be a ligand for the vitronectin receptor, and this suggests a possible role of osteopontin in osteoclast attachment and function (Merry et al., 1993). Hence, it functions as a potent marker of ossification and consequently its expression serves to quantify the degree of mineralisation of bone tissue in contact with bioceramic materials including coatings. 

The formation and breakdown of bone are vital processes carried out by special cells. Mineralualion occurs in the osteoblasts, apparently involving alkaline phosphatase. The enzyme is especially abundant in areas of active ossification, while cartilage is free of it. The breakdown of bone in the osteoclasts serves to mobilize mineral material. The solubilization of apatite probably is a surface phenomenon, analogous to its formation. 

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