title: The cross-linked biopolymer hyaluronic acid as an artificial vitreous substitute.
abstract: OBJECTIVE
  Biopolymers are promising substances in the development of a new vitreous substitute to overcome the drawbacks associated with current hydrophobic tamponade materials.
  
  
  METHODS
  Different hydrogels were assembled by cross-linking hyaluronic acid either with adipic dihydrazide (ADH) by carboxylation with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDCI) after hydrazation or by photocrosslinking with UV-light and N-vinyl-pyrrolidinone. The refractive index and rheologic properties of the obtained gels were investigated. To quantify the degradation of the hydrogels over time, free hyaluronic acid was measured photometrically by means of the degradation product uronic acid. For biocompatibility testing, the hydrogels were applied on top of cultured retinal pigment epithelial (RPE) cells and analyzed by the cell viability, MTT, and alamar blue viability cytotoxicity assays and flow cytometry, with Annexin V-FITC and propidium iodide co-staining. The in vivo biocompatibility of the hydrogels was tested in vitrectomized rabbit eyes for up to 6 weeks.
  
  
  RESULTS
  The synthesized hydrogels were all clear and transparent and had a refractive index similar to human vitreous. The rheologic measurements suggested sufficient viscosity and elasticity for intraocular use. Quantification of the degradation products revealed only a small decay of the gels over 1 month. However, the ADH cross-linked hydrogels induced mild cytotoxicity in the RPE cells. The UV cross-linked hydrogels showed no toxicity or induction of apoptosis. In vivo the UV cross-linked biogels remained in place for 6 weeks, and electrophysiology and histology showed excellent tissue biocompatibility.
  
  
  CONCLUSIONS
  Biopolymers based on UV cross-linked hyaluronic acid may be promising vitreous substitutes.
authors.affiliation: Section Experimental Ophthalmic Surgery, Department of Ophthalmology, Eberhard-Karls University Tübingen, Tübingen, Germany.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Schramm
authors.forename: Martin S
authors.initials: MS
authors.lastname: Spitzer
authors.forename: Sigrid
authors.initials: S
authors.lastname: Henke-Fahle
authors.forename: Gabriele
authors.initials: G
authors.lastname: Steinmetz
authors.forename: Kai
authors.initials: K
authors.lastname: Januschowski
authors.forename: Peter
authors.initials: P
authors.lastname: Heiduschka
authors.forename: Jürgen
authors.initials: J
authors.lastname: Geis-Gerstorfer
authors.forename: Tilo
authors.initials: T
authors.lastname: Biedermann
authors.forename: Karl U
authors.initials: KU
authors.lastname: Bartz-Schmidt
authors.forename: Peter
authors.initials: P
authors.lastname: Szurman
mesh_terms: D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry*; D001704:Biopolymers / Q000737:chemistry; D003432:Cross-Linking Reagents / Q000737:chemistry*; D005123:Eye / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D006820:Hyaluronic Acid / Q000737:chemistry*; D020100:Hydrogels / Q000737:chemistry; D008422:Materials Testing; D019736:Prostheses and Implants; D011817:Rabbits; D014783:Viscosity; D014822:Vitreous Body
chemical_list: D001672:Biocompatible Materials; D001704:Biopolymers; D003432:Cross-Linking Reagents; D020100:Hydrogels; D006820:Hyaluronic Acid