Biomechanical Properties Of Corneal Stromal Cells And Tissues Investigated By Atomic Force Microscopy

The cornea is the primary refractive factor of the eye and possesses typical biologic mechanical properties of soft tissue.The effectiveness of corneal therapy highly depends on the biomechanical response of the periocular tissues to the applied treatment.The biomechanical properties of the cornea are in urgent need of investigation.This thesis mainly includes two parts,one is to investigate the biomechanical properties of corneal stromal cells dependence on substrate.Taking corneal stromal cells as a model,corneal cells cultured on hard substrate,3D hydrogel and 2D hydrogel,respectively.Atomic Force Microscopy was used to characterize the morphological structure,elastic and viscoelastic properties of corneal stromal cells.AFM scanning showed that morphology of corneal stromal cells gradually expanded from fusiform to triangular on hard substrate,3D hydrogel and 2D hydrogel.The force curve obtained on the cell surface was fitted with the Hertz model for cellular elastic modulus.The power-law index indicating cellular rheology and was obtained by fitting force curve with power-law rheology model.The viscoelastic parameters of cells were obtained by fitting the stress relaxation curve and strain creep curve obtained on the cell surface with the generalized second-order Maxwell model.Through AFM characterization,it was concluded that cellular morphological and mechanical properties of corneal stromal cells highly depends on culturing substrates,in the perspective of,spreading area of cell morphology,elastic and viscoelastic modulus.This study provides the possibility of culturing corneal stromal cells in vitro to achieve their physiological state in vivo.The second is to explore the effect of myopia on corneal biomechanical properties.The human corneal stromal lens tissue obtained by Small Incision Lenticule Extraction(SMILE)surgery was used as a model.The lenses were divided into three groups according to the degree of myopia(mild myopia-3D<SE≤-0.50 D,moderate myopia-6D<SE≤-3D,severe myopia SE≤-6D,SE indicating Spherical Equivalent).The lens morphology and elastic properties were characterized by AFM,and the lens surface morphology was characterized by scanning electron microscope(SEM).Corvis ST experiment for traditional measurement of corneal biomechanics.Corvis ST data acquired preoperatively to obtain ocular biomechanical properties in macro-scale.The higher the degree of myopia,the weaker the elastic response of human corneal stroma to AFM probe is.The arrangement gap of collagen fibers on the cornea became larger and the diameter became thicker.A microstructural gradient from the mild,moderate to high myopia is found across the human corneal stroma.The stress strain index(SSI)obtained from Corvis ST experiment was weakly correlated with the degree of myopia.Through AFM characterization,myopia changes the corneal collagen arrangement of corneal stroma,as the gap between the fibers becomes larger,the fiber diameter becomes thicker.The corneal elastic modulus is reduced,indicating the ability to resist intraocular pressure to maintain the mechanical rigidity of the cornea is reduced.Therefore,the cornea is deformed,the eye axis is prominent,and myopia is formed.The corneal elastic modulus obtained by AFM is strongly correlated with the degree of myopia,stronger than that obtained from the Corvis ST experiment,indicating that AFM can be used more as a means to measure or evaluate the pathological changes of human cornea than Corvis ST.In this dissertation,the biomechanical properties of the cornea were investigated by atomic force microscopy at the cellular and tissue levels.Multi-scale interdisciplinary research was realized,combining mechanics with biology and medicine.