Bone metabolism is a dynamic equilibrium process between osteoclast bone resorption and osteoblast bone formation. Osteoblasts are responsible for the synthesis, secretion, and mineralization of bone matrix, and are the controllers of the activation or termination of bone reconstruction, which plays an important role in the trauma repair of bone tissues, the growth and development of bone tissues, and the balance of bone mass, and it is the main focus of the research on osteoporosis, fractures, and other bone diseases. Osteoblast differentiation is the premise and foundation of its dominant bone formation, and its most basic biological characteristics in the process of osteogenic differentiation are bone matrix synthesis, secretion, mineralization and maturation, and the mineralized nodule is the sign of osteoblast differentiation and maturation, and it is also the main morphological manifestation of osteoblasts exercising their osteogenic function, and observation of osteoblasts mineralized nodule is one of the commonly used means of researching the osteoblasts' differentiation.

The commonly used methods for staining mineralized nodules of osteoblasts are tetracycline and alizarin red S. Tetracycline staining method uses tetracycline to form fluorescent phosphate complexes with calcium salts in mineralized nodules, which can be observed by fluorescence microscope.