Hyaluronic acid dermal fillers are the most common type of filler used, making up 92% of all dermal filler treatments in the United States. Widely used as a biomaterial, hyaluronic acid is valued for its biocompatibility, established safety profile, and excellent clinical performance.

What is cross-linking?

In its natural form, hyaluronic acid is rapidly turned over in the body, as such it has a short half-life of 24–48 hours in tissue. This makes hyaluronic acid, at first glance, a poor choice to be used as a dermal filler. To overcome this limitation however, the hyaluronic acid in most dermal fillers are stabilized by cross-linking the long linear hyaluronic acid chains with other compounds such as 1,4-butanedioldiglycidyl ether (BDDE) and suspended in a physiological or phosphate-buffered solution. This popular compound is used by Restylane, Belotero, and Juvederm.

The product is then processed either as a homogeneous gel or a suspension of particles in gel carriers. Cross-linked hyaluronic acid degrades at a slower rate in tissue compared to native hyaluronic acid, and affords better rheological properties to the formulation in order to function as a dermal filler. In general, the more highly cross-linked the hyaluronic acid molecules are, the more elastic and cohesive the gel is.

Hyaluronic acid technology

The various manufacturers of cross-linked hyaluronic acid dermal fillers use different technologies to make their products. As a result, there is a variety of dermal fillers available, which are differentiated by gel thickness, degree of cross-linkage, particle size, and chemical used in the cross-linking process. Depending on these properties, cosmetic injectables will be used for different concerns. For example, fillers with higher elasticity and cohesiveness are used for volumising and lifting while fillers indicated for filling fine lines and wrinkles will have lower elasticity and cohesivity. It is essential for the practitioner to familiarise themselves with the physical properties of the injectable in order to select what’s appropriate for the type and area of treatment for optimal results.