Monophasic vs Biphasic Fillers…. the real story!

Recently Biphasic fillers have been getting a bit of a bad rep on social media and as this is one of the hot topics online at the moment, we thought we would shed some light on the differences between the two types of filler, what makes them unique and finally come to a conclusion on which one is better and why!

What are Monophasic & Biphasic Fillers?

The majority of the fillers discussed here will be Hyaluronic Acid (HA) based fillers. This is an acid that is found naturally in our body already and is what holds the moisture in the body. The vast majority of dermal fillers are made from Hyaluronic Acid because of its biocompatibility as an injectable, and for its ability to be dissolved relatively safely should a patient experience a complication or be dissatisfied with treatment.

Despite these amazing properties, Hyaluronic Acid in its natural form cannot be directly injected into the skin because it will dissolve rapidly or spread. So the Hyaluronic Acid has to be processed to be thicker and there are several ways of achieving this. The thickness of the filler can be adjusted based on the area it is intended to treat and the structure of the filler can also be changed depending on the procedure.

Most fillers go through the same manufacturing process: a mixing process, a reaction phase, and a blending phase before the Hyaluronic Acid is washed and sterilised. The mixing phase is where most brands will make a change to form the unique aspect of their product.

The two main structures made in the reaction stage are monophasic and biphasic. A monophasic structure is when there are cross-links formed between Hyaluronic Acid chains, which makes a uniform gel-like structure. A Biphasic structure is when the Hyaluronic Acid is made to be gel-like as well as having free HA particles within the mixture which are not part of the crossed structure. This type of structure is not as smooth as monophasic but historically gives more volume.

How do they compare?

Longevity

Firstly let’s look at longevity. All the evidence up to today shows that there is no real difference between the longevity of Monophasic and Biphasic fillers over the initial 90-100 day period after initial injection. A study in 2016 at Oxford University conducted by 7 leading aesthetic doctors showed that over a 6 month period there was no discernable difference in the speed of breakdown of the different structures of Hyaluronic Acid when skin samples were taken at regular intervals over the 6 months. Subsequently, a 2017 clinical study at the University College of Medicine in Seoul showed that both monophasic and biphasic fillers performed almost identically over 24 weeks when treating deep nasolabial folds. What was interesting as that although both of these studies tested for the presence of hyaluronic acid in the tissue what they didn’t test for was the viability of the products to continue to deliver visable results after the first 6 months and initial research shows that this is one of the areas biphasic fillers start to fall behind monophasic fillers due lower levels of cohesiveness. 

Outcome: Draw (slight monophasic win)

Volume

This is where the two fillers start to differentiate themselves. A 2013 Korean study showed that monophasic fillers consistently produce noticeably more voluminous results due to their swelling principles and their ability to increase water swelling at the treatment site. Although there are some studies that show biphasic fillers provide great volumising power when treating areas such as jaw, the requirement to inject deeper than monophasic fillers of-sets any benefits.

Outcome: Win for Monophasic

Migration

The same 2013 Korean study showed that there was no measurable difference in migration levels between monophasic and biphasic fillers when injected into the mid to upper dermis. A separate 2019 study at the University of Madrid showed monophasic HA fillers are more cohesive, and may not migrate as much following injecting into deeper tissue levels due to the ability of the gel to resist compression/stretching. It’s worth adding that a 2011 study by the University of North Carolina by the American Skin Association showed similar results but to a lesser extent.

Outcome: Win for Monophasic (but only just)

Swelling

There have been several studies into the swelling effects of fillers with almost universally accepted outcomes. Monophasic fillers swell more, simple as that. The uniform lattice structure of the filler attracts water at a much higher degree than biphasic fillers and this might be something as a practitioner you’re looking for but for clients wanting a more natural look it’s something to be aware of.

Outcome: Draw

Aesthetic Result

UPDATE PENDING NEW RESEARCH.

Ease Of Injection (Pressure)

A 2013 study by the University College of Medicine in Seoul showed that biphasic fillers required less force to inject using a 27G needle when compared to 20mg/HA monophasic filler. A follow-up study showed that as the concentration of Hyaluronic Acid increased the pressure required to inject the monophasic filler also increased due to the high viscosity of the HA within the syringe.

Winner: Biphasic

In Conclusion

If you’ve not read the whole article and you’ve skipped to the good bit I would recommend reading each point as it shows that these two products made from the same material in two different ways can have vastly different properties.

But for those in a hurry…

Both fillers have their advantages and disadvantages.

Biphasic fillers:

The Good:

• Long-lasting
• Easier to inject due to lower pressure
• Potentially longer-lasting results in some cases
• Less swelling in some cases
• Can create natural results in fine lines and softer tissues like lips

The Bad:

• Not suitable for soft tissue areas such as lip augmentation or naso lines.
• Lower Cohesiveness so greater chance of migration
• Grainy texture
• Can sometimes naturally feel uneven in the skin especially on softer tissue.
• Not suitable for Russian lip technique due to uneven product consistency
• Rapid decline in long term performance six months plus

Monophasic fillers:

The Good:

• Good long-lasting results
• Noticeably more volume over extended periods of time
• Less chance of migration
• Perfect for sharp edges, and stiff lines or for injecting onto the bone or deep dermis
• If you want crisp Russian lines you will not get better results.

The Bad:

• Harder to inject in terms of pressure
• More swelling in some cases

As you can see in the summary there are some circumstances when a biphasic filler might be better for a client but in 99% of circumstances a monophasic filler is going to be the best option. 

Our personal recommendation is to use a monophasic filler in almost all situations unless you’re looking to achieve a natural or more youthful outcome. Monophasic fillers are also better suited to techniques such as tenting where you need a stiffer line of filler to pull the lip up and support the lip structure.