General Comments From The Dermatology And Cosmetic Perspectives

The nature moisture of skin is attributed to its HA content. The critical property of HA is its ability to retain water, more than any known synthetic or naturally occurring compound. Even at very low concentrations, aqueous solutions of HA have very high viscosity.

The advantage of using HA in cosmetic preparations was recognized very soon after its discovery. Difficulties in preparing large enough amounts of HA free of contaminating glycoproteins, lipids, and other tissue materials prevented its convenient use in commercial preparations including its use in cosmetics. Initially, HA was isolated from rooster combs. This HA was highly purified, and used in ophthalmology as a viscoelastic to replace fluid loss following cataract surgery. The revolution in biotechnology and molecular genetics made it possible more recently to engineer bacteria with augmented HA production, by amplifying the HA synthase gene. This generates a material much lower in molecular weight that has the additional disadvantage of frequent contamination by residual bacterial pyrogens. Such HA, processed from vast fermentation of engineered bacteria has reduced the price of HA drastically, bringing the price into a range that is reasonable for its use in cosmetics. However, this genetically engineered HA of bacterial origin is not of sufficient purity for injectional use.

Many of the cosmetic preparations than contain HA have a concentration -g of 0.025 to 0.050%, sufficient to give the preparations a very smooth and viscous |

feel. Such solutions, applied to the skin form hydrated films that hold water for considerable periods, and confer the properties of a moisturizer.

Currently, research is underway to modify HA in such a way as to make <

it more stable and to confer very specific properties. Another direction in such research is to combine it with other materials, such as chondroitin sulfate and modified sugar polymers, to simulate more closely the associations that HA has in its natural state in vertebrate tissues. Since the low molecular size HA fragments are highly angiogenic, defining the optimal size of the HA polymer for cosmetic purposes is also a major goal of such research.

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