title: The science of hyaluronic acid dermal fillers.
abstract: BACKGROUND
  The use of injectable materials for soft-tissue augmentation has been increasing in the United States, reflecting the introduction of new hyaluronic acid (HA)-based dermal fillers. HA dermal fillers vary widely in their physical and chemical characteristics and many variables contribute to their overall performance. This article explains the basic science of HA and describes how the physical properties of HA dermal fillers may influence clinical outcomes.
  The chemical composition of disaccharide HA monomers, and how they form polymer chains and are crosslinked into gels for dermal fillers are described.
  Key concepts and properties relevant to the production and performance of HA dermal fillers, such as the degree of crosslinking, gel hardness, gel consistency, viscosity, extrusion force, HA concentration, and extent of hydration are explained. New formulations of HA dermal fillers that have recently been approved by the US Food and Drug Administration differ from currently available HA fillers and may provide enhanced ease of extrusion and persistence over previous fillers.
  
  
  CONCLUSIONS
  Knowledge of the chemical and physical blueprint of HA dermal fillers may help physicians in choosing the appropriate HA dermal filler for facial enhancements. This, together with appropriate injector training and injection experience, should lead to results that ultimately will benefit patients.
authors.affiliation: University of California Santa Barbara, Santa Barbara, California, USA. Tezel_Ahmet@allergan.com
authors.forename: Ahmet
authors.initials: A
authors.lastname: Tezel
authors.forename: Glenn H
authors.initials: GH
authors.lastname: Fredrickson
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry* / Q000627:therapeutic use; D003357:Cosmetic Techniques; D004548:Elasticity; D006801:Humans; D006820:Hyaluronic Acid / Q000737:chemistry* / Q000627:therapeutic use; D010316:Particle Size; D011108:Polymers / Q000737:chemistry; D012060:Rejuvenation; D015595:Skin Aging; D014783:Viscosity
chemical_list: D001672:Biocompatible Materials; D011108:Polymers; D006820:Hyaluronic Acid