G Prime (G'): What It Means in Hyaluronic Acid
G prime, written G', is the elastic modulus of a gel. Put simply, it measures how much the product resists being deformed and returns to its shape after being pressed. In orofacial harmonization it is used as an indicator of the firmness of hyaluronic acid: the higher the G prime, the firmer the gel and the greater its ability to lift tissue.
G prime depends mainly on cross-linking, HA concentration and particle size. It is measured in the lab (rheometry), in pascals, and appears in technical materials and articles that compare products.
How does G prime guide the choice for each area?
As a general rule of thumb:
| Need | Gel profile |
|---|---|
| Projection over bone, such as the chin, cheekbone and jaw | Higher G prime, firmer gel |
| Areas of movement and thin skin, such as the lips and periorbital region | Lower G prime, softer gel |
This is a reference, not a hard rule. Cohesivity, water-binding capacity and how the product behaves in the tissue also matter, and values measured by different methods are not comparable across manufacturers.
Why does it matter for the result?
A very firm gel in an area of movement can become palpable or visible; a very soft gel in a supporting area can spread and fail to give the projection you want. The choice of product is up to the qualified professional, after assessment and based on the package insert.
Also called: G', elastic modulus, modulus of elasticity.
Frequently asked questions
Is a high G prime always better?
No. A high G prime means a firmer gel, suited to projection over supporting structures. In lips and thin-skinned areas, softer gels are usually preferred.