Cross-Linking of Hyaluronic Acid: What It Is

Cross-linking is the chemical process that bonds the chains of hyaluronic acid to each other, forming a three-dimensional network. Without it, injected HA would be broken down by the body within a few days. With it, the gel resists the tissue's enzymes and free radicals for months.

Cross-linking is done with a chemical agent that creates bridges between the molecules. After the process, the manufacturer purifies the gel to remove the excess of that agent. The degree of cross-linking, the HA concentration and the technology used vary considerably between products and lines.

What does cross-linking change in practice?

The degree of cross-linking influences several properties of the gel:

• Firmness and projection capacity, which relate to G prime.
• Cohesivity, that is, how well the gel stays together after injection.
• Water absorption after application, which may increase initial swelling in some products.
• Duration, although it also depends on the region, the volume and the patient.

That is why each product line usually has different gels for lips, folds, cheekbone and chin. The choice belongs to the qualified professional, based on the indication, the injection plan and the package insert.

What about hyaluronidase?

Even when cross-linked, the gel is still hyaluronic acid, and so it can be broken down by hyaluronidase. More heavily cross-linked gels may need more enzyme or more time to respond, which reinforces the importance of having a defined protocol.

Also called: cross-linking, crosslinked bonding.