title: Evaluation of Heating and Shearing on the Viscoelastic Properties of Calcium Hydroxyapatite Used in Injection Laryngoplasty.
abstract: OBJECTIVE
  To compare the viscoelastic properties of calcium hydroxyapatite (CaHA) to carboxymethylcellulose (CMC) injectables used for injection laryngoplasty and determine if they are affected by heating and shearing.
  
  
  METHODS
  Experimental.
  
  
  METHODS
  University laboratory.
  
  
  METHODS
  Vocal fold injection laryngoplasty with CaHA is oftentimes challenging due to the amount of pressure necessary to push the injectate through a needle. Anecdotal techniques, such as heating the product, have been suggested to facilitate injection. The viscoelastic properties of CaHA and CMC were measured with a rheometer. The effects of heating and shearing on sample viscoelasticity were recorded.
  
  
  RESULTS
  CaHA was 9.5 times more viscous than CMC (43,100 vs 4540 Pa·s). Heating temporarily decreased the viscosity of CaHA by 32%. However, it also caused the viscosity to subsequently increase after time. Shearing of CaHA reduced its viscosity by 26%. Heating and shearing together temporarily reduced the viscosity of CaHA by 52%.
  
  
  CONCLUSIONS
  A combination of heating and shearing had a more profound effect than heating or shearing alone on the viscosity of CaHA, potentially making it easier to inject temporarily. Long-term and in vivo studies are required to further analyze the effect of heating and shearing on CaHA injectables.
authors.affiliation: University Voice and Swallowing Center, Department of Otolaryngology-Head and Neck Surgery, University of California, Irvine School of Medicine, Irvine, California, USA.
authors.forename: Hossein
authors.initials: H
authors.lastname: Mahboubi
authors.affiliation: Department of Chemical Engineering and Materials Science, University of California Irvine, Irvine, California, USA.
authors.forename: Ali
authors.initials: A
authors.lastname: Mohraz
authors.affiliation: University Voice and Swallowing Center, Department of Otolaryngology-Head and Neck Surgery, University of California, Irvine School of Medicine, Irvine, California, USA verma@uci.edu.
authors.forename: Sunil P
authors.initials: SP
authors.lastname: Verma
mesh_terms: D002266:Carboxymethylcellulose Sodium / Q000737:chemistry* / Q000627:therapeutic use; D017886:Durapatite / Q000737:chemistry* / Q000627:therapeutic use; D004548:Elasticity; D006361:Heating; D006801:Humans; D058753:Laryngoplasty / Q000379:methods*; D012212:Rheology; D014783:Viscosity
chemical_list: D017886:Durapatite; D002266:Carboxymethylcellulose Sodium
keywords: Radiesse Voice; Radiesse Voice Gel; calcium hydroxyapatite; viscoelastic properties; vocal fold injection