A study that used histology and three-dimensional imaging of hyaluronic acid fillers in a mouse model reveals that lifting capacity depends on more than G prime.
Chicago - A new study shows for the first time in vivo that the concept of G prime alone fails to explain fully the lifting capacity of dermal fillers.
As the filler market expands, says Vic Narurkar, M.D., many questions remain regarding what parameters give these products their lifting capacity, and how these products behave in vivo postinjection. Dr. Narurkar is chair of dermatology at California Pacific Medical Center, director and founder of the Bay Area Laser Institute, San Francisco, and a co-founder of Cosmetic Bootcamp.
In the former area, "There's a myth going around that the higher the G prime, the better a filler will lift. But it has never been demonstrated in a living organism. It's all been a theoretical proposition based on rheology," he says.
To better address this issue, Dr. Narurkar and colleagues compared the histological and moldability characteristics of the following three hyaluronic acid (HA) fillers in a mouse model: Juvéderm Voluma XC (Allergan), Juvéderm Ultra Plus (Allergan) and Perlane (Medicis). More specifically, investigators used three-dimensional imaging and histology to measure these factors at various time points through 12 weeks postinjection.
Immediately postinjection, all three products were moldable. However, Voluma XC resisted deformation thereafter compared to Perlane and Juvéderm Ultra Plus. In addition, throughout the 12 weeks, Voluma provided a greater lift compared to the other fillers. (Shumate G, Narurkar V, Van Epps D, et al. Abstract presented at: American Society for Dermatologic Surgery Annual Meeting. Oct. 3-6, 2013. Chicago.).
Histologically, "Unlike the other HAs and some of the other fillers, Voluma actually intercollates between the tissues." This ability stems from its proprietary Vycross technology, which combines longer HA chains having a high molecular weight with shorter chains that have a lower molecular weight, he says. "Therefore, how the different fillers are manufactured also impacts their ability to interact with tissue. Our study demonstrated this for the first time in vivo, as opposed to in vitro."
Conversely, he says that after injection, "The other fillers examined remained in the form of globules. The ability to intercollate gives Voluma its ability to lift. Voluma also has a lower G prime than the other fillers studied. But it lifts better than any of the fillers currently approved by the FDA. We know this not only from the histology study, but also from our experience in the clinical trial, and now in practice," adds Dr. Narurkar, who was a principal investigator in the product's pivotal phase 3 trial.
"These findings completely shatter the notion that the higher the G prime, the greater the ability to lift. Rather, it's a complex interaction between G prime, cohesivity and other parameters. Relying purely on one factor to determine the lifting capacity of a filler is highly inaccurate. This completely changes the way we think of the ability of dermal fillers to lift, and potentially their duration as well."
Dr. Narurkar says he was somewhat surprised by the study's results. "Dermatologists had been living under the dogma that the higher the G prime of a filler, the better its ability to lift. However, collagen has a very high G prime, but it doesn't lift. We've all been almost brainwashed into thinking that only G prime contributes to lifting capacity. And we now know better."
Even before the introduction of Juvéderm Voluma, he says, "We were looking at fillers that may not have a high G prime but are able to lift well. We knew that lifting capacity involved a complex interaction."
Similarly, he says that filler duration involves more than G prime and viscosity, as was previously believed. "In this regard, Voluma is the only filler that has the ability to last for up to two years after a single injection," as was shown in the product's pivotal clinical trial.
At press time, the comparative study conducted by Dr. Narurkar and colleagues was ongoing. These investigators plan to compare the in vivo qualities of other fillers in similar fashion, while also attempting to correlate clinical findings regarding Voluma with the structural characteristics revealed by the study's first phase.
Disclosures: Dr. Narurkar has performed clinical trials for Allergan and Merz.