Researchers comparing the intradermal durability of three hyaluronic acid filler types—biphasic, monophasic monodensified, and monophasic polydensified—report that, at six months post intradermal injection, biphasic and monophasic monodensified fillers were more durable than the monophasic polydensified filler.
Adilson da Costa, M.D., MS.c., Ph.D., lead author of the study published in the Aesthetic Surgery Journal, says this research offers physicians a comprehensive review of the differences among biphasic, monophasic monodensified and monophasic polydensified fillers, as well as insight about the manufacturing process of these three categories of HA fillers, which directly impacts the durability of the fillers in the skin.
Biphasic fillers have cross-linked particles of HA dispersed in a non-cross-linked HA vehicle; therefore, the HA is heterogeneous, according to Dr. Costa.
Monophasic fillers consist of a homogeneous mixture of high and low-molecular-weight HA, making their application easier, according to Dr. da Costa.
Monophasic fillers may be further categorized as monodensified, in which cross-linking occurs after homogeneous mixing, or polydensified, when cross-linking occurs separately, before the mixture is produced, according to Dr. da Costa.
Choosing the Right Filler
Armed with the knowledge of which biphasic HA fillers have the best durability, physicians can better differentiate the best HA filler for their patients based on several factors, including cost-benefit aspects, according to Dr. da Costa, a tenured professor in the Ph.D. and MS.c. programs at State of Sao Paulo Workers' Welfare Institute, Sao Paulo, Brazil.
“Indeed, this is the first histological study to evaluate the durability in humans of one representative HA filler from each category for six months,” Dr. da Costa says.
Dr. Costa and colleagues studied 25 volunteers, who received injections of three different fillers in the dermis of the right lumbar region. One of the volunteers dropped out for personal reasons, according to Dr. da Costa.
Researchers injected equal amounts of the fillers into three different sites—in the same column—yielding nine points of application in each patient. They biopsied each line on days 2, 92 and 184. The skin samples were analyzed histologically, and the presence or absence of these fillers was verified by a dermatopathologist, according to Dr. da Costa.
During a period of 182 days post injections, the researchers found that the amount of biphasic decreased by 12.5%; the monophasic monodensified decreased by 25% and the monophasic polydensified filler decreased by 62.5%.
The reduction in the biphasic product’s histologic presence was not statistically significant over six months, when researchers compared days 92 versus 2, 182 versus 92, and 182 versus 2.
“Interestingly, the histological presence of the biphasic and monophasic monodensified fillers was statistically similar throughout the trial,” Dr. da Costa says. “Furthermore, the amount of monophasic polydensified filler was equal to that of the monophasic monodensified filler at three months after injection, but the amount of monophasic monodensified filler remaining after six months exceeded that of the monophasic polydensified filler.”
In summary, Dr. Costa says, the durability of the dermal biphasic HA-based filler was similar to that of the monophasic monodensified filler—both of which were superior to the monophasic polydensified filler.
The three filler types are classified as cross-linked fillers, meaning they have intermolecular bonds—mainly, divinyl sulfone, 1,4-butanediol diglycidyl ether (BDDE), or p-phenylene bisethyl carbodiimide—which make stability and durability higher when injected into dermis, he says.
“Physicians consider cross-linked HA fillers as ‘heavier’ injectables, and they are the most common fillers used worldwide,” Dr. da Costa says.
Disclosure: Dr. da Costa is a Scientific Board Member at Sinclair Pharma England (London, UK) and the Global, Latin American, and Brazilian Alliance to Improve Outcomes in Acne (which are sponsored by Galderma).