Cells cartilage forming

The family of connective-tissue cells includes fibroblasts, chondrocytes (cartilage cells), and osteoblasts (bone-forming cells). They are specialized to secrete extracellular proteins, particularly collagens, and mineral substances, which they use to build up the extracellular matrix (see p. 346). By contrast, osteoclasts dissolve bone matter again by secreting and collagenases (see p. 342). 

Endochondral ossification is the gradual replacement of cartilage by bone during development. This process is responsible for formation of most of the skeleton of vertebrate animals. In this process, actively dividing bone-forming cells (osteoblasts) arise in regions of cartilage called ossification centers. The osteoblasts then develop into osteocytes, which are mature bone cells embedded in the calcified (hardened) part of the bone known as the matrix. 

The size of the cartilage formed in the experimental bioabsorbable implants increased over a period of about 7 weeks after which time it remained stable. The growth appeared histologically to be at the expense of the fibrous tissue initially seen and associated at least temporally with a decrease in neovascularization and resolution of the mild inflammatory response originally noted. There was a decrease in inflammatory response, as evidenced by decreases in the number of polymorphonuclear leukocytes and giant cells, which correlated with the disappearance of the polymers. Very little evidence of either inflammatory response or polymer remnants were seen after 7 weeks when using bioabsorbable material, while moderate inflammation and minimal cartilage formation was noted in the nonabsorbable implants after this period of time. 

Similar events take place in postembryonic development during both endochondral longitudinal bone growth at the epiphysis and unstable fracture healing Cartilage is replaced by bone forming cells (Anderson, 1974). 

Setton and Chilkoti applied ELPs as a three-dimensional matrix to entrap chondrocytes. In their study, ELP[VsG3A2-90] with a transition temperature of 35°C at 50 mg/mL in PBS was used. This biopolymer can be used to generate a suspension with cells, which upon injection into a defect site will form a scaffold. They showed that in vitro the resulting ELP gel supported the viability of chondrocytes and the synthesis and accumulation of cartilage-specific extracellular matrix material. This suggested that ELPs indeed could be used for in situ formation... 

The latter issue was addressed more recently by Hamilton et al. who developed a trilayer composite consisting of CPP, articular cartilage (CEP), and NP tissue [125]. By sequential seeding of chondrocytes onto the CPP surface followed 2 weeks later by seeding NP cells onto the matrix produced by the chondrocytes, the authors were able to form a tissue composite construct. Although it appeared that the NP cells were able to maintain a rounded morphology, the interfacial shear load required to... 

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