Vitreous body nature

Glass-ceramics are a family of materials that are polycrystalline in nature and are formed from the liquid or glassy state. A glass-ceramic article is made by the heat treatment of a vitreous body in two stages ... 

This is a landmark paper on the nature of the vitreous body, describing the mechanochemical (or double-network ) model. This model explains satisfactorily the correlations between some properties of the vitreous (composition, rheology, volume, cell population, transparency) and the physicochemical principles governing its stability (frictional interaction, expansion/contraction, the excluded-volume concept, and the molecular-sieve effect). 

The biosynthesis and turnover of HA were shown to decrease with age. This decrease is of major importance for the age related increase of several tissue and organ modifications as for instance in osteoarthritis, because of lack of protection against frictional erosion of articular cartilage and also retinal detachment due to the degradation of HA in the joints and the vitreous body in the eye. Wrinkling of the aging skin is also one of its consequences. The precise cellular nature of this age-dependent decline of HA biosynthesis remains to be more deeply investigated. 

Deposition techniques may also allow the fabrication of functional assemblies of incompatible components such as rod and coiling polymers. This is the case of high-performance composites and natural systems such as connective tissue or the vitreous body of the eye [9], Engineered systems may exhibit even greater stability than self-assembled ones since use of compatibilizers, fast quenching techniques, or covalent cross-linking may prevent or retard the dissipation of their organization. 

In 1934, Karl Meyer and his colleague John Palmer isolated a previously luiknown chemical substance from the vitreous body of cows eyes. They found that the substance contained two sugar molecules, one of which was uronic acid. For convenience, therefore, they proposed the name hyaluronic acid . The popular name is derived from hyalos , which is the Greek word for glass + uronic acid [8], At the time, they did not know that the substance which they had discovered would prove to be one of the most interesting and usefirl natural macromolecules. HA was first used commercially in 1942 when Endre Balazs applied for a patent to use it as a substitute for egg white in bakery products[9]. 

Vitreous silica (silica glass) is essentially a supercooled Hquid formed by fusion and subsequent cooling of crystalline silica. It is found ia nature ia fulgerites, ie, fused bodies resulting from lightning striking quart2 sand. 

Owing to their almost complete resistance to corrosion, stoneware and porcelain occupy a unique position as materials in the chemical industry. Stoneware bodies can be compounded from many different raw materials to give the properties required and to permit the manufacture of articles up to a considerable size. Porcelain, on the other hand, is not generally used for very large articles, but owing to its completely vitreous nature it normally shows a much greater resistance to corrosion than does stoneware. 

Hyaluronic acid is a naturally occurring polysaccharide that is widely distributed in body tissues and intracellular fluids, including the aqueous and vitreous humour, synovial fluid, and in the ground substance that surrounds cells (1). It is a high-molecular weight substance originally developed for use as a vitreous replacement. Although 98% of the product consists of water, it is very viscoelastic. 

Polymer gels can be of both natural and synthetic origin. Examples of natural gels are the cornea, the vitreous, and the connective tissues in our body. Examples of synthetic gels are sodium polyaaylate gels used in diapers and poly-(2-hydroxyethyl methacrylate) gels used in soft contact lenses. ... 

The only body part that has transparent materials in the human body is the eyeball. The cornea, lens and vitreous humor consist mainly of collagen and acidic mucopolysaccharides, which makes them gels. The attempt to use natural polymer gels as a cataract cure has met with limited success due to biocompatibility problems and long-term stability. On the otiier hand, if vitreous humor substances are replaced by artificial materials made of PVA hydrogel, the properties (transparency and refiactive index) are very like those of the vitreous humor. Hence, it is ideal as a replacement material [12]. 

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