title: Understanding of the viscoelastic response of the human corneal stroma induced by riboflavin/UV-a cross-linking at the nano level.
abstract: OBJECTIVE
  To investigate the viscoelastic changes of the human cornea induced by riboflavin/UV-A cross-linking using Atomic Force Microscopy (AFM) at the nano level.
  
  
  METHODS
  Seven eye bank donor corneas were investigated, after gently removing the epithelium, using a commercial AFM in the force spectroscopy mode. Silicon cantilevers with tip radius of 10 nm and spring elastic constants between 26- and 86-N/m were used to probe the viscoelastic properties of the anterior stroma up to 3 µm indentation depth. Five specimens were tested before and after riboflavin/UV-A cross-linking; the other two specimens were chemically cross-linked using glutaraldehyde 2.5% solution and used as controls. The Young's modulus (E) and the hysteresis (H) of the corneal stroma were quantified as a function of the application load and scan rate.
  
  
  RESULTS
  The Young's modulus increased by a mean of 1.1-1.5 times after riboflavin/UV-A cross-linking (P<0.05). A higher increase of E, by a mean of 1.5-2.6 times, was found in chemically cross-linked specimens using glutaraldehyde 2.5% (P<0.05). The hysteresis decreased, by a mean of 0.9-1.5 times, in all specimens after riboflavin/UV-A cross-linking (P<0.05). A substantial decrease of H, ranging between 2.6 and 3.5 times with respect to baseline values, was observed in glutaraldehyde-treated corneas (P<0.05).
  
  
  CONCLUSIONS
  The present study provides the first evidence that riboflavin/UV-A cross-linking induces changes of the viscoelastic properties of the cornea at the scale of stromal molecular interactions.
authors.affiliation: Department of Physics, University of Calabria, Ponte P. Bucci, Cubo 33B, 87036, Rende, Italy; Consiglio Nazionale delle Ricerche, Istituto di Processi Chimico-Fisici, Unit of Support Cosenza, Ponte P. Bucci, Cubo 33B, 87036, Rende Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Labate
authors.affiliation: Department of Physics, University of Calabria, Ponte P. Bucci, Cubo 33B, 87036, Rende, Italy; Consiglio Nazionale delle Ricerche, Istituto di Processi Chimico-Fisici, Unit of Support Cosenza, Ponte P. Bucci, Cubo 33B, 87036, Rende Italy.
authors.forename: Maria Penelope
authors.initials: MP
authors.lastname: De Santo
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto di Processi Chimico-Fisici, Viale Stagno D'Alcontres 37, 98158, Messina, Italy; Vision Engineering Italy srl, Via Adda 7, 00198 Rome, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Lombardo
authors.affiliation: Fondazione G.B. Bietti IRCCS, Via Livenza 3, 00198 Rome, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Lombardo
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D003319:Corneal Stroma / Q000473:pathology / Q000502:physiology*; D055119:Elastic Modulus; D006801:Humans; D007640:Keratoconus / Q000532:radiotherapy; D018625:Microscopy, Atomic Force; D008875:Middle Aged; D049329:Nanostructures; D017319:Photosensitizing Agents / Q000494:pharmacology*; D012256:Riboflavin / Q000494:pharmacology*; D014467:Ultraviolet Therapy; D014783:Viscosity
chemical_list: D017319:Photosensitizing Agents; D012256:Riboflavin
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