title: Biomechanics of the anterior human corneal tissue investigated with atomic force microscopy.
abstract: OBJECTIVE
  To investigate the biomechanics of the anterior human corneal stroma using atomic force microscopy (AFM).
  
  
  METHODS
  AFM measurements were performed in liquid on the anterior stroma of human corneas, after gently removing the epithelium, using an atomic force microscope in the force spectroscopy mode. Rectangular silicon cantilevers with tip radius of 10 nm and spring elastic constants of 25- and 33-N/m were used. Each specimen was subjected to increasing loads up to a maximum of 2.7 μN with scan speeds ranging between 3- and 95-μm/s. The anterior stromal hysteresis during the extension-retraction cycle was quantified as a function of the application load and scan rate. The elastic modulus of the anterior stroma was determined by fitting force curve data to the Sneddon model.
  
  
  RESULTS
  The anterior stroma exhibited significant viscoelasticity at micrometric level: asymmetry in the curve loading-unloading response with considerable hysteresis dependent both on the application load and scan rate (P < 0.01). The mean elastic modulus ranged between 1.14 and 2.63 MPa and was constant over the range of indentation depths between 1.0 and 2.7 μm in the stroma.
  
  
  CONCLUSIONS
  At microscale level, the mechanical response of the most anterior stroma is complex and nonlinear. The microstructure (fibers' packing, number of cross-links, water content) and the combination of elastic (collagen fibers) and viscous (matrix) components of the tissue influence the type of viscoelastic response. Efforts in modeling the biomechanics of human corneal tissue at micrometric level are needed.
authors.affiliation: IRCCS (Istituto Ricerca e Cura a Carattere Scientifico) G B Bietti, Rome, Italy. mlombardo@visioeng.it
authors.forename: Marco
authors.initials: M
authors.lastname: Lombardo
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Lombardo
authors.forename: Giovanni
authors.initials: G
authors.lastname: Carbone
authors.forename: Maria P
authors.initials: MP
authors.lastname: De Santo
authors.forename: Riccardo
authors.initials: R
authors.lastname: Barberi
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Serrao
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D002452:Cell Count; D003319:Corneal Stroma / Q000166:cytology / Q000502:physiology*; D055119:Elastic Modulus / Q000502:physiology; D004548:Elasticity / Q000502:physiology*; D004728:Endothelium, Corneal / Q000166:cytology; D006801:Humans; D018625:Microscopy, Atomic Force; D013314:Stress, Mechanical