TITLE:
Evaluation of Rheometry Amplitude Sweep Cross-Over Point as an Index of Flexibility for HA Fillers
AUTHORS:
Åke Öhrlund
KEYWORDS:
HA Fillers, Rheology, xStrain, Flexibility
JOURNAL NAME:
Journal of Cosmetics, Dermatological Sciences and Applications,
Vol.8 No.2,
June
21,
2018
ABSTRACT: Background: The
majority of studies published on rheology of hyaluronic acid (HA) fillers have
focused on results from frequency sweeps within the linear viscoelastic region
(LVR), i.e. at nearly static
conditions. To study the properties and behavior of HA fillers at more dynamic
conditions, it is necessary to go outside the LVR. Objective: Evaluation of the G’/G’’ cross-over point from the amplitude sweep is suggested
as a manner to estimate the flexibility of HA fillers. Materials and methods: Rheological
properties of 7 HA fillers were measured in an amplitude sweep from 0.1% to
10000% strain at 1 Hz, using an Anton Paar MCR 301, a PP-25 measuring system
with a gap of 1 mm at 25℃ and a 30-min relaxation time. The cross-over point
was evaluated for stress, strain and G (G’ and G’’ identical), the values
denoted xStrain, xStress and xG. Results: The
xStrain values spanned from below 1000% to
above 2000% for the products based on the Optimal Balance Technology (OBT)? (in the
US, XpresHAn Technology?), compared to below 100% for the products based on the
NASHA? technology. Conclusions: Measurement
of the flexibility provides a more complete picture of the rheological
properties of HA fillers as a complement to firmness measured as G’. The test
results show that the Restylane family of products covers a large range in flexibility,
and that the flexibility can be estimated using xStrain derived from the
amplitude sweep.