Exploring HA Filler Longevity

Dr Ciara Abbott provides an introduction to HA filler longevity and gives advice to practitioners on product selection for longer-lasting results

The question of how long dermal fillers last is one that patients and practitioners alike wish to know the answer to. Multiple filler treatment options are currently available to help create revolumisation and facial rejuvenation, including hyaluronic acid (HA), poly-L-Lactic acid (PLLA), calcium hydroxyapatite (CaHA), polymethylmethacrylate and autologous fat transfers. HA is the most commonly used facial dermal filler in aesthetic medicine, due to its biocompatibility, safety, reliability and reversibility.1 With the ever-increasing number of new HA fillers now available on the market, and longevity of these products is an important area for discussion amongst injectors.2 In this article, we will be focussing on what the research says about the factors affecting filler longevity in patients, with an overview to provide a structured approach for practitioners in their choice of product and how they can inform patients regarding expectations relating to longevity.

What is longevity, and why does it matter?

It is generally considered that the ideal dermal filler:3

• Is safe and easy to administer • Can produce reliable and reproducible results with few, if any, local adverse events • Provides longevity (lasting between nine-18 months or more) • Affordable to both the patient and the practitioner

When we speak about longevity, we are referring to the amount of time that one would expect the filler to be active and provide results for the patient. For the patients, longevity matters for several reasons: post-procedure downtime, such as bruising, potential discomfort of undergoing filler procedures and of course the financial implications. In general, patients would prefer not to have to undergo a procedure repeatedly every few months if they can instead choose to have just an annual treatment. Fundamentally, patients wish to ensure their filler procedure produces a long-lasting aesthetic result.

What factors impact HA filler longevity?

After injection, HA filler will integrate with the tissue before being broken down over time and eliminated from the body. How long this process takes varies. This is usually anywhere between three and 12 months, however some retrospective imaging studies have highlighted some HA fillers lasting for more than two years and, as discussed below, practitioners in the industry are highlighting that HA fillers are lasting longer than we think.4,5 Many factors impact filler longevity, including the rheological characteristics of the product used (for example, particle size, the concentration of HA within the product and the level of cross-linking), the indication the product is being used for (such as how dynamic that area is) and patient-specific biological responses and lifestyle.6-9

Rheological properties

Cross-linking In its pure state, the HA molecule is present in nearly all species, including bacteria and mammals, and is considered immunologically inert.4,10-11 Due to its physicochemical properties, HA is one of the most hygroscopic molecules in nature, and hydrated HA can contain up to 1,000-fold more water than its own weight.8,12 This makes it an appealing choice from a biocompatibility perspective. However, in this pure state, the half-life of the HA molecule is just 24-48 hours.9 Therefore, to create longevity, HA dermal fillers are cross-linked to form a viscous gel that delays degradation.4,9,13 Cross-linked fillers are classified as monophasic or biphasic. Monophasic fillers consist of a homogeneous mixture of high- and low-molecular-weight HA, making their application easier.15 Biphasic fillers have cross-linked particles of HA dispersed in a non-cross-linked HA vehicle.6,14-16 The most used cross-linking materials are divinyl sulfone, 1,4-butanediol diglycidyl ether (BDDE) and p-phenylene bisethyl carbodiimide, which are refined to reduce risk of sensitivity.3 Cross-linking is known to reduce a product’s degradation rate, and therefore the degree of cross-linking denotes the mechanical strength of the product and directly represents a measure of its longevity.17

Research has highlighted that biphasic cross-linked HA fillers show greater rheological stability than monophasic fillers. It is thought that due to their increased level of cross-linking, they exhibit greater durability, have a lower propensity to be homogeneously distributed throughout the injected area and are able to withstand compressive forces when passing through a needle.7,18,19 This therefore produces the clinically longer-lasting results of biphasic products, compared to monophasic.3

Viscosity, cohesivity and elasticity The other major factors that impact filler longevity are the viscosity, cohesivity and elastic modulus of a product. In addition, a study by Park et al. showed that a significant factor determining the degradation of HA particles is the gel swelling ratio, which is related to the particle structure of the gel.7

There is a large spectrum of HA filler products available in the UK, with different gel properties designed for specific indications, and it is important for practitioners to understand the intrinsic differences in these properties so that they can choose the correct product for the correct tissue plane and treatment indication. It is thought that the firmer the product, or the greater the G prime (G’), the more volumising potential and therefore the longer it may last.21 For example, if you’re using a lighter, less cross-linked HA for superficial tissue application, results are likely to remain for closer to six months than 12. Alternatively, with a firmer HA with a greater G’ for significant tissue projection, it is more likely results will last for between 12-18 months.17,20

Factors Definitions

Viscous modulus (G”)

Cohesivity

Elastic modulus (G’) The inability to recover the original shape after shear deformation

The strength of the cross-linking adhesion forces that hold the individual HA units together

The ability to recover the original shape after shear deformation

Table 1: Definitions of some of the rheological properties influencing filler longevity

Anatomical placement

Areas of dynamic movement may also affect longevity. For example, perioral, nasolabial and the lips, where dynamic movement is continuous. Products with lower cohesivity would be preferable in these areas, and therefore may see lower timeframes for longevity (from six to nine months) due to shear and compression forces from surrounding mobile muscular structures.19 Unlike ‘static’ areas such as the temples or tear troughs, where there is very little movement, in these areas, HA is more likely to provide longer-lasting results (from nine-18 months). The area being treated therefore requires thoughtful product choice to ensure the right rheological properties are utilised to allow for ultimate longevity.21

Patient-specific factors

I have observed anecdotally in my own practice that external factors (including lifestyle) can impact the longevity of fillers and how quickly a patient metabolises them on an individual basis.14,21 For example, one of my patients is an ultra-marathon runner, with a low BMI, who has repeatedly displayed a shorter time frame in the aesthetic outcome of her filler procedures compared to other patients whom I have treated with the same product for the same clinical indication.

Extrinsic factors such as smoking, alcohol intake, UV exposure and even excessive exercise are known to deplete HA reserves and accelerate ageing due to free radical formation, but there are also intrinsic factors that need to be accounted for such as individual skin elasticity.22-23

Product selection

As an aesthetic practitioner, longevity is an important factor in choosing which brand to use and which product to select from within that brand for a specific indication. To provide the best outcomes for our patients, we should have a pallet of products to choose from, and it is our job to select the best product based on what that patient needs. Incorrect product choice in the wrong anatomical place will certainly have an effect on the longevity of results. In addition to this, managing patient expectations and having an open dialogue with patients regarding product choice is essential. For example, helping patients to understand that for significant jowl lifting or jawline augmentation, a product with a high G’ is usually required which will have longer-lasting results, versus soft and subtle lip augmentation with an HA with lower cohesivity and cross-linking, which the patient will need to understand is likely to last for less time.

In my practice, I primarily use the Belotero range. Belotero VOLUME is an extremely versatile product with an established tolerability and safety profile from the injection time and up to 18 months post-injection.24 For areas such as the tear troughs, I use the Teosyal Pursense Redensity 2, which lasts up to 18 months, and Juvéderm Volux for the jawline. This has been shown to last up to 24 months.17 Of course, there are many other suitable brands available.

Late-onset complications

Finding the optimal balance between longevity and safety is a priority. From a practitioner’s point of view, we should always think about what is safest for our patients; knowing that the product has a good safety profile and robust research behind it is important.

There are also long-term side effects to consider. The longer a filler lasts, the longer any potential side effects may impact your patient. With HA dermal fillers, long-term complications are minimal as the reversibility of HA makes complications more manageable and treatable. However, there is increasing evidence that HA fillers may be present in tissue for considerably longer than expected, and that late-onset complications associated with HA fillers can occur several years after their placement and well after their cosmetic effect has worn off.4,25-31 The advent of ultrasound scanning in aesthetics now allows practitioners to visualise filler that has been previously injected into patients and determine how long it is lasting.8 This is particularly useful in the management of complications, and has become widely adopted now due to advances in technology which have made handheld devices a reality. I predict this type of imaging will be key to future studies surrounding filler longevity and its significance to the treatments we provide.

Further research

HA dermal fillers are the most widely used dermal fillers due to their reversibility, and advances in their manufacturing means that practitioners now have longer-lasting products available to them. Individual patient needs, product selection and product placement is key in matching the right product to the right indication to minimise risk and maximise longevity.

Our understanding of how dermal fillers behave in the tissues, and, in turn, their longevity, is being enhanced now with the use of ultrasound scanning. While dermal fillers are generally thought to degrade after a maximum of 18-24 months, we are now seeing evidence that HA fillers can last significantly longer, long after their cosmetic effects have dissipated. Further research is being done on this, and we should continue to update our approaches accordingly.

Dr Ciara Abbott is the medical director and co-owner of Barstable Medical Clinic, Essex and has worked in the aesthetic industry for the last 11 years. Her clinic was shortlisted for Best Clinic South England 2017 at The Aesthetics Awards and she is an associate member of the British College of Aesthetic Medicine (BCAM). Abbott works as a trainer for Merz Aesthetics as a Merz Innovative Associates. Qual: MBBS, Bsc, MRCS(Eng), MRCGP

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