Numerical investigation on epi-off crosslinking effects on porcine corneas
- PDF / 2,226,562 Bytes
- 17 Pages / 595.276 x 790.866 pts Page_size
- 42 Downloads / 208 Views
ORIGINAL PAPER
Numerical investigation on epi-off crosslinking effects on porcine corneas Aram Cornaggia 1
&
Federica Boschetti 2
&
Cosimo Mazzotta 3,4
&
Anna Pandolfi 5
Received: 29 September 2020 / Accepted: 2 November 2020 / Published online: 25 November 2020 # The Author(s) 2020
Abstract Experimental inflation tests, conducted on 90 pig corneas before and after corneal collagen crosslinking (CXL) treatment, are simulated with the finite element method. The experimental sample consists of five groups of corneas treated with different UV-A irradiation times (2.5, 5, 10, 15, and 20 min) at constant irradiance 9 mW/cm2. The linear elastic shell theory is used to estimate the equivalent material stiffness of the corneas, revealing that it increases with the exposure time in CXL corneas. In the view of numerical simulations, a simple mechanical model assuming piecewise constant elastic modulus across the corneal thickness is introduced, to estimate the effective increment of the material stiffness in the anterior stroma and the effective depth of the stiffness increment. The two effective quantities are used in the finite element models to simulate the post-CXL tests. Numerical models are able to describe the mechanical effects of CXL in the cornea. The increment of equivalent material stiffness has to be ascribed to a localized increment of the material stiffness in the anterior layers of the cornea, while the posterior layers preserve the original material stiffness. According to the simplified model, the increment of the material stiffness of the anterior cornea increases with the irradiation dose, while the effective reinforcement depth decreases with the irradiation dose. This trend, predicted by a simple mechanical model by imposing equilibrium and compatibility, has been verified by the numerical calculations that captured the global mechanical response of the corneas in untreated and post-CXL conditions. Keywords Crosslinking . Numerical simulations . Beam equivalent . Linear shell theory . Porcine corneas . Identification procedures
1 Introduction The cornea is organized into five principal layers: the epithelium, the Bowman lamina, the stroma, the Descemet lamina, and the endothelium, in order from anterior to posterior surfaces [1]. The stroma, the carrying structure of the cornea, is composed of a matrix of elastin and proteoglycans embedding collagen fibrils, organized into a highly specialized hierarchical architecture enabled by chemical bonds (crosslink) able to provide the necessary mechanical stiffness and to shape the curvature of the lens [2]. In contrast with the prevalent isotropic distribution of the collagen fibrils observed within the anterior third of the thickness, in the deepest layers of the stroma, the collagen fibrils show preferential directions along the nasal-temporal (NT) and superiorinferior (SI) meridians [3, 4].
* Anna Pandolfi [email protected] 1
Department of Engineering and Applied Sciences, University of Bergamo, Dalmine, Italy
2
Department of Chemistry, M
Data Loading...
