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Researchers have substantiated the fact that hyaluronic acids from different sources have the same primary structure, but their molecular weight is slightly different. For example, the HA molecular weight in the bovine vitreous body is lower, which is 104~105 Dalton, while the HA molecular weight in the umbilical cord and rooster crown is higher, which is 106~107 Dalton.

HA has a strong ability to retain water, so it can keep eyes, joints, and skin tissues moist and lubricated. As HA has a long molecular chain, it has been widely used clinically, such as in osteoarthritis, tissue filling, and ophthalmic surgery. The molecular weight of HA is closely related to the hydrodynamic volume. In fact, HA molecular weight is often calculated by measuring the intrinsic viscosity. The relationship between the intrinsic viscosity and the molecular weight follows the Mark-Houwink formula.

[η]=KMα

This formula shows the dependency relationship between the intrinsic viscosity of the polymer and its relative molecular weight. [η] is the intrinsic viscosity. K and α are constants, whose values depend on the nature and temperature of the polymer and solvent. M is the average molecular weight.

The rheological properties of HA are manifested in its viscosity, elasticity, and pseudo-plasticity. These properties are HA-unique. Although other mucopolysaccharides can form viscous solutions at high concentrations, they cannot form a viscous polymer network. The properties of the HA solution depend on the molecular weight of HA, the concentration, and the pH of the solution.

At low concentrations, hyaluronic acid molecules are entangled with each other to form a network structure, and the HA solution exhibits unique viscoelasticity and pseudo-plasticity of the water-soluble polymer at low concentrations. When the concentration increases, the HA molecular domain decreases, and the molecular motion is limited, making the solution viscous and elastic.

Hyaluronan (HA) is a ubiquitous constituent of extracellular matrices and has two main characteristics: physicochemical properties and cell biological functions. The physicochemical properties of HA are viscosity, elasticity, lubrication, and a high capacity for holding water.