Monophasic and biphasic fillers: what they mean
Quick facts
- Definition
- Classification of cross-linked hyaluronic acid gels by how the gel is structured during manufacturing.
- Monophasic
- Homogeneous, continuous cross-linked hyaluronic acid gel, with no separate particles.
- Biphasic
- Cross-linked hyaluronic acid particles, sized by sieving, suspended in non-cross-linked hyaluronic acid.
- What changes
- In general, monophasic gels are more cohesive; biphasic gels tend to be firmer and less cohesive.
- Point of attention
- It is a simplification: real behavior depends on each product's rheology, not just its phase.
Monophasic and biphasic are two ways of classifying cross-linked hyaluronic acid gels according to the structure the gel takes on during manufacturing. Monophasic is a continuous, homogeneous gel. Biphasic is made of cross-linked gel particles, separated by size, suspended in non-cross-linked hyaluronic acid, which acts as a lubricant for injection.
How is each gel made?
Both start from the same principle: hyaluronic acid chains linked to each other by cross-linking, which gives the gel firmness and durability. The difference lies in what happens next.
| Aspect | Monophasic | Biphasic |
|---|---|---|
| Structure | Single, continuous gel | Gel particles in a liquid medium |
| Decisive step | Homogenization of the cross-linked gel | Fragmentation and sieving of particles by size |
| Free phase | Little or none, depending on the product | Non-cross-linked hyaluronic acid as a carrier |
| Cohesivity | Generally higher | Generally lower |
| Firmness (G prime) | Variable, from soft to firm | Generally higher |
| Behavior in tissue | Tends to spread evenly | Tends to stay where it was placed, like "blocks" |
Some monophasic gels go through more than one cross-linking step, which creates regions of different density within the same gel. That is why the literature sometimes subdivides monophasic gels, but the general logic holds.
Why does this classification matter in facial harmonization?
It helps explain why there are different gels for different areas:
- Projection and structure (chin, jaw angle, cheekbone): call for a gel that withstands tissue pressure. Firm biphasic gels and monophasic gels with high firmness and cohesivity appear in these indications.
- Thin skin and high-movement areas (lips, eye area): usually call for softer gels that blend in without forming relief.
- Particle size in biphasic gels: larger particles are usually indicated for deeper planes; fine particles, for more superficial planes.
How do you use this information when choosing a product?
Read the manufacturer's data sheet and use only products registered with Anvisa (Brazil's health regulator). Compare properties measured under the same conditions, when available, and consider the area, skin thickness, intended plane and clinical experience with the product. The comparison between cross-linked and free gels is in cross-linked and non-cross-linked hyaluronic acid, and the area-by-area logic is in hyaluronic acid by area.
Both types are degradable by hyaluronidase, which should always be available whenever hyaluronic acid is used. The response to the enzyme may vary with the degree of cross-linking and the gel's structure.
Also called: monophasic gel, biphasic gel, single-phase filler, particulate filler.
Frequently asked questions
What is the difference between monophasic and biphasic hyaluronic acid?
Monophasic is a continuous, homogeneous cross-linked hyaluronic acid gel. Biphasic is made of cross-linked gel particles, sieved by size, suspended in free hyaluronic acid that acts as a carrier for the injection.
Is a biphasic filler better for projection?
Biphasic fillers tend to have a higher G prime and are therefore associated with projection and support, but there are firm, cohesive monophasic fillers with good projection capacity. The choice depends on the data sheet, the area and the goal, at the professional's discretion.