title: Formulation and rheological evaluation of ethosome-loaded carbopol hydrogel for transdermal application.
abstract: OBJECTIVE
  To select a suitable ethosome-loaded Carbopol hydrogel formulation, specifically tailored for transdermal application that exhibits (i) plastic flow with yield stress of approximately 50-80 Pa at low polymer concentration, (ii) relatively frequency independent elastic (G') and viscous (G″) properties and (iii) thermal stability.
  
  
  METHODS
  Carbopol (C71, C934, C941, C971 or C974) hydrogels were prepared by dispersing Carbopol in distilled water followed neutralization by sodium hydroxide. The effects of Carbopol grade, Carbopol concentration, ethosome addition and temperature on flow (yield stress and viscosity) and viscoelastic (G' and G″) properties of Carbopol hydrogel were evaluated. Based on the aforementioned rheological properties evaluated, suitable ethosome-loaded Carbopol hydrogel was selected. In-vitro permeation studies of diclofenac using rat skin were further conducted on ethosome-loaded Carbopol hydrogel along with diclofenac-loaded ethosomal formulation as control.
  
  
  RESULTS
  Based on preliminary screening, C934, C971 and C974 grades were selected and further evaluated for flow and viscoelastic properties. It was observed that ethosome-loaded C974 hydrogel at concentration of 0.50 and 0.75% w/w, respectively, demonstrated acceptable plastic flow with distinct yield stress and a frequency independent G' and G″. Furthermore, the flow and viscoelastic properties were maintained at the 4, 25 and 32 °C. The results from in vitro skin permeation studies indicate that ethosome-loaded C974 hydrogel at 0.5% w/w polymer concentration exhibited similar skin permeation as that of ethosomal formulation.
  
  
  CONCLUSIONS
  The results indicate that suitable rheological properties of C974 could facilitate in achieving desired skin permeation of diclofenac while acting as an efficient carrier system for ethosomal vesicles.
authors.affiliation: a College of Pharmacy and Health Sciences, St. John's University , Queens , NY , USA.
authors.forename: Shashank
authors.initials: S
authors.lastname: Jain
authors.affiliation: a College of Pharmacy and Health Sciences, St. John's University , Queens , NY , USA.
authors.forename: Niketkumar
authors.initials: N
authors.lastname: Patel
authors.affiliation: a College of Pharmacy and Health Sciences, St. John's University , Queens , NY , USA.
authors.forename: Parshotam
authors.initials: P
authors.lastname: Madan
authors.affiliation: a College of Pharmacy and Health Sciences, St. John's University , Queens , NY , USA.
authors.forename: Senshang
authors.initials: S
authors.lastname: Lin
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000279:Administration, Cutaneous; D000818:Animals; D002626:Chemistry, Pharmaceutical / Q000379:methods; D004008:Diclofenac / Q000737:chemistry; D005079:Excipients / Q000737:chemistry; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000737:chemistry*; D008297:Male; D010539:Permeability; D051381:Rats; D017207:Rats, Sprague-Dawley; D012212:Rheology; D012867:Skin / Q000378:metabolism; D012869:Skin Absorption / Q000502:physiology; D014783:Viscosity
chemical_list: D000180:Acrylic Resins; D005079:Excipients; C006912:carboxypolymethylene; D004008:Diclofenac; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate
keywords: Elastic modulus; lipid based vesicles; skin permeation; viscoelastic modulus; viscosity; yield stress