Rheologic properties of soft tissue fillers and implications for clinical use

Abstract

Background: The use of injectable soft-tissue fillers has become an essential tool in esthetic rejuvenation. Rheology, the study of flow of matter, helps to understand the function of these products. Aims: The purpose of this article is to review the rheologic properties of soft-tissue fillers currently available in the United States and to evaluate how these properties relate to clinical performance. Methods: This article explains basic rheologic terms and describes how rheologic properties of specific soft-tissue fillers affect filler performance. Results: The currently available soft-tissue fillers have unique rheologic and physicochemical properties that influence performance and cosmetic outcome. These properties determine that filler product is most appropriate based on degree of soft-tissue defect and anatomic location. Conclusion: It is imperative for physicians to have an in-depth understanding of the rheologic properties of soft-tissue fillers in order to appropriately select and utilize these products for the desired cosmetic outcome.

Rheologic and Physicochemical Characteristics of Hyaluronic Acid Fillers: Overview and Relationship to Product Performance

“… 13 Rheology, the study of the way a material deforms and reacts under mechanical stress, allows for this assessment. 18 Four rheologic parameters may be used as the primary measures of a gel's viscoelastic properties: G* (a measure of the overall viscoelastic properties), G′ (a measure of the elastic properties), G″ (a measure of the viscous properties), and tan δ (tan delta, a measure of the ratio of the elastic to viscous properties). 7 17 19 20 Using a rheometer, a twisting force is applied to a gel between two plates to measure these parameters 12 ( Fig.…”

“… 11 17 20 Tan δ >1 signifies a mostly viscous filler, whereas tan δ <1 indicates a mostly elastic filler. 18 Most HA crosslinked fillers have tan δ <1 (i.e., G′ > G″). 17 While tan δ allows an understanding of whether the filler is more elastic or more viscous, it is important to note that it does not provide information on the actual magnitudes of G′ and G″.…”

Hyaluronan Hydrogels for Injection in Superficial Dermal Layers: An In Vitro Characterization to Compare Performance and Unravel the Scientific Basis of Their Indication

“…Considering that gel-projection capacity is related to its stiffness, G' (Storage Modulus) has long been the only parameter considered in selecting the most suitable gel for the specific clinical need. A more recent approach has been extended to the whole fluido-dynamic gel behavior as well as to its sensitivity to enzymatic and radical degradation and to other properties (e.g., hydration capacity, cohesivity) [1,[5][6][7][8][14][15][16][17][18][19][20][21][22][23][24][25]. All of the latter features are known to contribute to the in vivo effect after injection and/or over time, and they are therefore generally studied to predict relative in vivo performance and to provide clinicians with valuable information to select treatments and optimize outcome [1,[5][6][7][8][14][15][16][17][18][19][20][21][22][23][24][25].…”

“…Former studies and literature report extensively analyzed volumetric gels and compared available formulations, suggesting opportunities toward design optimization, and supporting their appropriate selection and use [1,[5][6][7][8][14][15][16][17][18][19][20][21][22][23][24][25]. On the contrary, no similar studies have been carried out so far to scientifically assist this recent "skinboosting" approach.…”

Application Status of Sacrificial Biomaterials in 3D Bioprinting

“…The advantages of this ‘bioink’ were bio-friendliness and rheologic. Thick composite hydrogel structures were obtained through the media adsorbable on the living cells [ 136 , 137 , 138 , 139 ].…”