title: Rheological, mechanical, and bioadhesive behavior of hydrogels to optimize skin delivery systems.
abstract: BACKGROUND
  Hydrogels are widely used for cutaneous formulations; thereby comparing the bioadhesive properties of polymers with a view to prolong the residence time of topical drugs on the skin would be very useful to design novel topical drug delivery systems.
  
  
  OBJECTIVE
  The objective of this study was to correlate data from rheological studies and texture profile analysis, with bioadhesion on the skin.
  
  
  METHODS
  Polyacrylic acid polymers used were carbomer homopolymer type A (C971) and type B (C974), and polycarbophil (PP) dispersed in water at various concentrations (0.1, 0.5, 1.0, 1.5, 2.0, 3.0, 5.0%, w/v). Rheological, texture, and bioadhesive properties were determined to compare the hydrogels.
  
  
  RESULTS
  Rheological analysis showed that all samples exhibited pseudoplastic behavior with thixotropy. Texture profile analysis showed that compressibility, hardness, and adhesiveness of the hydrogels were dependent on the polymer concentration, and the cohesion values were high. Bioadhesion of C974 and PP at 0.5 and 2% was of the same magnitude, while all samples of C971 had lower values. The bioadhesion of 5% C974 was the highest, while that 5% PP was lower, possibly because PP showed the greatest hardness and this rigidity may decrease the interaction of the polymer with the skin.
  
  
  CONCLUSIONS
  A comprehensive comparative rheological and textural analyses of several polymers for topical systems were undertaken in terms of their bioadhesion. Therefore, it is possible to conclude that these polymers can be used for optimization of drug delivery systems on the skin.
authors.affiliation: School of Pharmaceutical Sciences, State University of São Paulo, UNESP, Rodovia Araraquara/Jaú Km 1 , Araraquara, SP , Brazil.
authors.forename: Flávia Chiva
authors.initials: FC
authors.lastname: Carvalho
authors.forename: Giovana
authors.initials: G
authors.lastname: Calixto
authors.forename: Ilka Narita
authors.initials: IN
authors.lastname: Hatakeyama
authors.forename: Gabriela Marielli
authors.initials: GM
authors.lastname: Luz
authors.forename: Maria Palmira Daflon
authors.initials: MP
authors.lastname: Gremião
authors.forename: Marlus
authors.initials: M
authors.lastname: Chorilli
mesh_terms: D000179:Acrylates / Q000737:chemistry; D000180:Acrylic Resins / Q000737:chemistry*; D000268:Adhesiveness; D000279:Administration, Cutaneous; D000818:Animals; D055598:Chemical Phenomena; D003879:Dermatologic Agents / Q000008:administration & dosage / Q000737:chemistry*; D016503:Drug Delivery Systems; D004423:Ear; D055119:Elastic Modulus; D006244:Hardness; D020100:Hydrogels; D055595:Mechanical Phenomena; D014677:Pharmaceutical Vehicles / Q000737:chemistry*; D012867:Skin / Q000737:chemistry*; D034421:Sus scrofa; D014783:Viscosity
chemical_list: D000179:Acrylates; D000180:Acrylic Resins; D003879:Dermatologic Agents; D020100:Hydrogels; D014677:Pharmaceutical Vehicles; C492577:carbopol 971P; C117167:carbopol 974P NF; C030312:calcium polycarbophil