Osteocytes are one of the four kinds of bone cells. Due to derivation from osteoblasts, these cells are highly specialized in nature and are responsible for the maintenance of the bony matrix. Specially built with innate proteins that help them to survive in hypoxic conditions, osteocytes maintain biomineralization. Not only do osteocytes contribute to bone mass via controlling osteoblast and osteoclast activity, but these cells act as main players in phosphate metabolism. Osteocytic necrosis is caused due to pathologic conditions such as osteoarthritis and osteoporosis, leading to developing skeletal fragility and dysfunctional signal repair and/or microdamage. Immobilization-induced hypoxia and glucocorticoid treatment may also lead to osteocytic necrosis or apoptosis. Osteocytes react to implant biomaterials in dynamic ways and are currently under active stem-cell research for trauma care and bone remodeling purposes.[1]

Osteocyte resides within the lacunae located between the lamellae of the matrix. Each lacuna consists of one osteocyte. Osteocytes are flat, almond-shaped in the structure; they have a depth of about 7 micrometers and length of about 15 micrometers. The cell body diameter ranges from 5 to 20 micrometers and may obtain 40 to 60 processes per cell within a cellular distance of 20 to 30 micrometers. A mature osteocyte holds a single nucleus, which has a membrane and one or two nucleoli. The nucleus usually exists toward the vascular side of the surface. These cells exhibit a predominantly reduced Golgi complex and rough endoplasmic reticulum. These specialized structures also exhibit a more condensed nuclear chromatin. Osteocytes compose an extensive connecting syncytial network with small dendritic, or cytoplasmic, processes taking place in canaliculi. Osteocytes have expanded longevity and are long-living by nature.[2][3]

Nutrient exchange involving osteocytes may nourish a chain of approximately 15 cells. Processes involving adjacent cells allow contact with gap junctions; molecules pass intracellularly via these structures. The small amount of extracellular substance between the bone matrix and osteocytes may instigate a few molecular exchanges between blood vessels and osteocytes. Osteocytes are actively involved in the perseverance of the bony matrix; osteocytic necrosis leads to resorption of the bony matrix. Despite their inert qualities, osteocytes perform molecular modification and synthesis along with signal transmission over long distances. After a bone fracture, for instance, osteocytic glutamate transporters compose nerve growth factors, proving their ability to sense and transfer information. Matured osteocytes are the most common cells in bone tissues, and the majority of receptor activities involved with bone function are available in these cells. Osteocytic necrosis also leads to trabecular bone decay, decreased bone formation, and malfunctioning loading.

Osteocytes also control osteoblastic and osteoclastic activities within a basic multicellular unit (BMU), a transient anatomic structure for insulating bone remodeling. Osteocytic proteins like sclerostin contribute to mineral metabolism aside from other molecules such as  MEPE, FGF-23, PHEX, and DMP-1, which help to regulate phosphate and biomineralization. Osteocytes also regulate bone mass and act as an essential endocrine regulator of phosphate metabolism.[4][5][6]

Medical scientists typically use trabecular bone samples from the anterior iliac crest, as this sample can be collected from healthy patients as surgical waste material from procedures like the sinus floor elevation surgery. Creating human osteocyte culture is a tedious process: firstly, researchers collect the sample in sterile phosphate-based saline (PBS) with antimicrobial agents. They wash the biopsy materials three times using phosphate-buffered saline and then allocate the biopsy samples to a petri dish. They use a 23 scalpel to fragment the trabecular bone from the original sample in a PBS-treated petri dish.

Afterward, they use a 10 blade to divide the trabecular bone pieces into 1 to 2 mm square samples. In serum-free DMEM, they make 2 mg ml^−1 collagenase II solution and filter the solution with a 0.2 um filter unit. They place the bone fragments inside a 50 ml centrifuge tube, which is premixed with collagenase II and mix properly. They incubate those fragments using collagenase II for two hours at 37 degrees C inside a rocking water bath to clean any existing adhering cells on top of the bone surfaces. They then wash those samples with DMEM consisting of 10% serum made off fetal Clone I.

A subdivision phase follows: they submerge the bone samples into another petri dish; they then divide them into equal sections weighing about 100 mg. They transfer those portions into wells of a culture plate (12 wells suggested); the samples are treated with cCM. After incubating the samples at 37 degrees C with 5% CO2 overnight, they wash the samples with PBS 4 or 5 times the next day, followed by a repetition of the overnight treatments. The medium is replenished twice a week, and the process continues for seven days. At the preparation period, the scientists continue to add cytokines, hormones, chemicals, etc. into the osteocytic culture; osteocytic signaling factors are also measured in this modified culture medium. The additional analysis derives from the collection of total RNA from the samples using triazole.[7]