Tissue Engineered Intervertebral Discs
Intervertebral discs are fibrous pieces of cartilage that lie between the vertebrae of the spinal cord [4]. They allow the spinal cord to move while
keeping it connected and in tact. Perhaps the most crucial function of the intervertebral discs is to absorb compression, stresses, and shock [4]. This helps the body deal with physically intensive activities such as walking, running, and lifting.
Each intervertebral disc consists of two distinct regions: the annulus fibrosus and the nucleus pulposus. The nucleus pulposus is the central-core part of the disc consisting of a loose gel-like matrix of fibers, and the annulus fibrosus is the outer ring of the disc consisting of strong fibrous tissue and cartilage [2, 5].
The role of the stiffer annulus fibrosus is to keep the vertebrae connected and to distribute forces across the entire area of the disc, insuring no extreme pressure points  develop. It consists of chondrocyte (cartilage creating) cells organized in a lamellar structure wound around the nucleus pulposus. It also has a very rich extracellular matrix (ECM) that contains large amounts of type I collagen, necessary to keep the disc strong and coherent. The ECM is also abundant in proteoglycans and glycosaminoglycans (GAGs), responsible for creating the cartilage-like material [2].
The role of the more jelly-like nucleus pulposus is to absorb shocks that the body experiences. This area has a significantly less chondrocyte cell density than the annulus fibrosus, but it contains much more ECM. The ECM of the nucleus pulposus is rich in type II collagen, as well as GAGs and proteoglycans like the annulus fibrosus [2]. It is also important to note that the entire intervertebral disc contains no blood vessels or neurons; it consists only of disc cells and ECM [2]. Because the intervertebral discs are constantly exposed to repeated stresses and shocks, they can often wear out and degrade. As will be seen in the next section, this can give rise to several painful medical conditions.
Intervertebral Disc Anatomy
Disc Anatomy
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