Hyaluronic Acid in Modern Cosmetic and Reconstructive Surgery - Hyaluronic Acid for Biomedical and Pharmaceutical Applications - page 139

thousands of disaccharide units, residues of glucuronic acid and
N -acetylglucosamine [5]. In vivo , all carboxylic groups of the
glucoronic acid are ionised, providing molecular polarisation,
hydrophilicity and increased solubility in water ( Figure 7.1 ). Due to
its polar nature, it provides increased hydration and moisturisation
in the matrix of the skin (dermis). It can bind to water molecules and
increase its weight by 1,000 times and its volume by 18-20 times.
Its hydrophilic nature acts as cell lubricant, decreasing the damage
caused by friction between cells [6].

OH OH

O

O O

O HO

HO O

OH

NH

O n

Figure 7.1 The repeat unit of HA

The half-life of HA ranges from 12-24 h in both the dermis and
the epidermis. The presence of HA in epithelial tissues promotes
keratinocyte proliferation and increases the presence of retinoic acid,
causing skin hydration. HA interaction with CD44 antigen drives
collagen synthesis and normal skin function. Present in the ECM of
basal keratinocytes, HA is critical to the structural integrity of the
dermal collagen matrix.

HA is isolated either from animal (bovine/porcine) or non-animal
(bacterial) sources. The majority of the HA fillers used in aesthetic
plastic surgery are non-animal derived, mainly made by bacterial