The rheological characterisation of typical injection implants based on hyaluronic acid for contour correction

Systematic rheological characterisation of several injection implants based on hyaluronic acid (Belotero^®, Teosyal^®, Glytone^® and Juvéderm^® brands) has been carried out. All these dermal fillers are viscoelastic media with the storage modulus exceeding the loss modulus. So at low deformations, they are gel-like materials, but at increasing shear stress, they can flow demonstrating typical non-Newtonian behaviour. In some cases, though not always, the yield stress is expressed rather clearly. The application of the technique of large amplitude oscillation shear (LAOS) allowed us to distinguish two groups of rheological behaviour characterised by shear thinning or strain overshoot. The Belotero^® fillers belong to the first group. Similar strong changes in the storage and loss moduli as a function of frequency and fuzzy yielding are characteristic of these materials. The Teosyal^® and Juvéderm^® Voluma filler belong to the second group. Their typical rheological features are existence of the minimum for the frequency dependence of the loss modulus and clearly expressed the yield stress. The Glytone^® and Juvéderm^® Ultra fillers occupy the intermediate position. When the dermal fillers of the second group were diluted, they demonstrated effects similar to the phase separation. As a result of the rheological characterisation, some assumptions have been advanced regarding correlations between the objective rheological parameters of dermal fillers and conditions of their application.