Characteristics of HA Dermal Fillers

Hyaluronic acid (HA) dermal fillers are popular for facial rejuvenation, with various products and technologies available.
Understanding basic characteristics and rheology helps in selecting suitable products for different indications and patient factors.

Introduction

HA is found in biological fluids and tissues, offering unique properties for medical applications.
HA dermal fillers are widely used in aesthetic medicine due to their immediate results and reversibility via enzymatic digestion.

Viscoelastic Properties: G*, G’, G”, and ? describe overall viscoelasticity, elasticity, viscosity, and their ratio, respectively.
Elastic Modulus (G’): Measures the gel’s resistance to distortion under pressure.
Viscous Modulus (G”): Indicates the flow properties of the gel.
Viscosity (Complex Viscosity): Determines the fluid phase’s resistance to shearing forces.
Cohesivity: Degree of attraction between cross-linked HA units, impacting gel behaviour post-implantation.
Cross-linking: Creation of bonds between HA strands to improve mechanical properties and longevity.
HA Concentration: Higher concentrations lead to greater volume expansion and possibly increased longevity.
Water Absorption: HA’s hydrophilic nature influences its ability to absorb water post-injection.
Particle Size and Distribution: Influence extrusion force and product placement control.
Biphasic and Monophasic Gels: Contain different combinations of cross-linked and non-cross-linked HA.
Polydensified Dermal Fillers: Single-phase HA with continuous cross-linking, producing a cohesive gel matrix.

Understanding these properties helps in selecting the right product for each indication and patient, ensuring optimal aesthetic outcomes.
No single property can dictate filler choice; a comprehensive consideration of all properties is essential.