Cartilage in fetal development

In embryogenesis

Embryogenesis

Embryogenesis is the process by which the embryo is formed and develops, until it develops into a fetus.Embryogenesis starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote...

, the skeletal system is derived from the mesoderm germ layer. Chondrification (also known as chondrogenesis) is the process by which cartilage is formed from condensed mesenchyme

Mesenchyme

Mesenchyme, or mesenchymal connective tissue, is a type of undifferentiated loose connective tissue that is derived mostly from mesoderm, although some are derived from other germ layers; e.g. some mesenchyme is derived from neural crest cells and thus originates from the ectoderm...

 tissue, which differentiates into chondrocytes and begins secreting the molecules that form the extracellular matrix.

Early in fetal development, the greater part of the skeleton is cartilaginous. This temporary cartilage is gradually replaced by bone (Endochondral ossification

Endochondral ossification

Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike intramembranous ossification, which is the other process by which bone tissue is created, cartilage is present during endochondral...

), a process that ends at puberty. In contrast, the cartilage in the joints remains unossified during the whole of life and is, therefore, permanent.

Mineralization

Adult hyaline articular cartilage is progressively mineralized

Mineralization (biology)

In biology, mineralization refers to the process where an organic substance is converted to an inorganic substance.This may also be a normal biological process which takes place during the life of an organism such as the formation of bone tissue or egg shells, largely with calcium.This term may...

 at the junction between cartilage and bone. It is then termed articular calcified cartilage. A mineralization front advances through the base of the hyaline articular cartilage at a rate dependent on cartilage load and shear stress. Intermittent variations in the rate of advance and mineral deposition density of the mineralizing front, lead to multiple "tidemarks" in the articular calcified cartilage.

Adult articular calcified cartilage is penetrated by vascular buds, and new bone produced in the vascular space in a process similar to endochondral ossification

Endochondral ossification

Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike intramembranous ossification, which is the other process by which bone tissue is created, cartilage is present during endochondral...

 at the physis

Physis

Physis is a Greek theological, philosophical, and scientific term usually translated into English as "nature."In The Odyssey, Homer uses the word once , referring to the intrinsic way of growth of a particular species of plant. In the pre-Socratic philosophers it developed a complex of other...

. A cement line demarcates articular calcified cartilage from subchondral bone.

Repair

Once damaged

Articular cartilage damage

Cartilage structures and functions can be damaged. Such damage can result from a variety of causes, such as a bad fall or traumatic sport-accident, previous knee injuries or wear and tear over time...

, cartilage has limited repair capabilities. Because chondrocytes are bound in lacunae

Lacuna (histology)

In histology, a lacuna is a small space containing an osteocyte in bone or chondrocyte in cartilage.-Bone:The Lacuna are situated between the lamella, and consist of a number of oblong spaces. In an ordinary microscopic section, viewed by transmitted light, they appear as fusiform opaque spots...

, they cannot migrate to damaged areas. Also, because hyaline cartilage does not have a blood supply, the deposition of new matrix is slow. Damaged hyaline cartilage is usually replaced by fibrocartilage scar tissue. Over the last years, surgeons and scientists have elaborated a series of cartilage repair procedures

Articular cartilage repair

The aim of an articular cartilage repair treatment is to restore the surface of an articular joint's hyaline cartilage. Over the last decades, surgeons and researchers have been working hard to elaborate surgical cartilage repair interventions...

 that help to postpone the need for joint replacement.

In a 1994 trial, Swedish doctors repaired damaged knee joints by implanting cells cultured from the patient's own cartilage. In 1999 US chemists created an artificial liquid cartilage for use in repairing torn tissue. The cartilage is injected into a wound or damaged joint and will harden with exposure to ultraviolet light.

Synthetic Cartilage

Researchers say their lubricating layers of "molecular brushes" can outperform nature under the highest pressures encountered within joints, with potentially important implications for joint replacement surgery.
Each 60-nanometre-long brush filament has a polymer backbone from which small molecular groups stick out. Those synthetic groups are very similar to the lipids found in cell membranes.

"In a watery environment, each of these molecular groups attracts up to 25 water molecules through electrostatic forces, so the filament as a whole develops a slick watery sheath. These sheathes ensure that the brushes are lubricated as they rub past each other, even when firmly pressed together to mimic the pressures at bone joints."

Known as double-network hydrogels, the incredible strength of these new materials was a happy surprise when first discovered by researchers at Hokkaido in 2003. Most conventionally prepared hydrogels - materials that are 80 to 90 percent water held in a polymer network - easily break apart like a gelatin. The Japanese team serendipitously discovered that the addition of a second polymer to the gel made them so tough that they rivaled cartilage - tissue which can withstand the abuse of hundreds of pounds of pressure.

Sulfation

The SLC26A2

SLC26A2

The SLC26A2 protein is a member of the solute carrier family. In humans, this transporter is encoded by the SLC26A2 gene.- Function :The diastrophic dysplasia sulfate transporter is a transmembrane glycoprotein implicated in the pathogenesis of several human chondrodysplasias...

 is a sulfate transporter. Defects result in several forms of osteochondrodysplasia

Osteochondrodysplasia

Osteochondrodysplasia is a general term for a disorder of the development of bone and cartilage .-Achondroplasia:Achondroplasia is a type of autosomal dominant genetic disorder that is a common cause ofdwarfism...

.