title: Development of a novel anisotropic self-inflating tissue expander:  in vivo submucoperiosteal performance in the porcine hard palate.
abstract: BACKGROUND
  The advent of self-inflating hydrogel tissue expanders heralded a significant advance in the reconstructive potential of this technique. Their use, however, is limited by their uncontrolled isotropic (i.e., uniform in all directions) expansion.
  
  
  METHODS
  Anisotropy (i.e., directional dependence) was achieved by annealing a hydrogel copolymer of poly(methyl methacrylate-co-vinyl pyrrolidone) under a compressive load for a specified time period. The expansion ratio is dictated by the percentage of vinyl pyrrolidone content and the degree of compression. The expansion rate is modified by incorporating the polymer within a silicone membrane. The in vivo efficacy of differing prototype devices was investigated in juvenile pigs under United Kingdom Home Office Licence. The devices were implanted within a submucoperiosteal pocket in a total of six porcine palates; all were euthanized by 6 weeks after implantation. A longitudinal volumetric assessment of the expanded tissue was conducted, in addition to postmortem analysis of the bony and mucoperiosteal palatal elements.
  
  
  RESULTS
  Uncoated devices caused excessive soft-tissue expansion that resulted in mucoperiosteal ulceration, thus necessitating animal euthanasia. The silicone-coated devices produced controlled soft-tissue expansion over the 6-week study period. There was a statistically significant increase in the volume of expanded soft tissue with no evidence of a significant acute inflammatory response to the implant, although peri-implant capsule formation was observed. Attenuation of the bony palatal shelf was noted.
  
  
  CONCLUSIONS
  A unique anisotropic hydrogel device capable of controlled expansion has been developed that addresses a number of the shortcomings of the technology hitherto available.
authors.affiliation: Oxford, United Kingdom; and Atlanta, Ga. From the Department of Plastic and Reconstructive Surgery, Nuffield Department of Surgery, and the Nuffield Department of Anesthesia, University of Oxford, John Radcliffe Hospital; Department of Materials, University of Oxford; and Materials Science and Engineering, Georgia Institute of Technology.
authors.forename: Marc C
authors.initials: MC
authors.lastname: Swan
authors.forename: David G
authors.initials: DG
authors.lastname: Bucknall
authors.forename: Jan T
authors.initials: JT
authors.lastname: Czernuszka
authors.forename: David W
authors.initials: DW
authors.lastname: Pigott
authors.forename: Timothy E E
authors.initials: TEE
authors.lastname: Goodacre
mesh_terms: D000818:Animals; D016880:Anisotropy; D003761:Dental Impression Technique; D005260:Female; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D021362:Palate, Hard; D019904:Polymethyl Methacrylate; D011474:Prosthesis Design; D011760:Pyrrolidinones; D012828:Silicones; D013552:Swine; D015626:Tissue Expansion / Q000295:instrumentation / Q000379:methods*; D015625:Tissue Expansion Devices
chemical_list: D011760:Pyrrolidinones; D012828:Silicones; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D019904:Polymethyl Methacrylate