In Silico And Experimental Mechanical Characterization Of A New Corneal Implant For The Treatment Of Keratoconus

A novel therapeutic corneal implant to reshape deformed corneas in patients with keratoconus (KC) has been developed and characterized experimentally and computationally in terms of mechanical properties. The GROSSO® implant is the world's first nitinol corneal implant to treat KC by restoring the physiological curvature of the cornea. Two potentially critical situations are investigated. The first is a 90° bending of two opposite edges of the dome-shaped device, an operation involved in the minimally invasive implantation of the device in the patient’s intracorneal pocket. The second is a vertical crushing of the device to test the strength of the device and provide information on possible impacts occurring in daily use of the device. 

PoliTo^BIOMed Lab, Department of Mechanical and Aerospace Engineering, Politecnico di Torino, and Recornea srl.

The computational model of the GROSSO® implant was reconstructed from micro-computed tomographic acquisitions (Phoenix v|tome|x m, resolution: 1µm) of the actual GROSSO® implant. The mechanical behavior of the nitinol alloy was modelled by implementing a super-elastic constitutive law with material parameters obtained from experimental tensile tests, which also determined the strain value at which permanent plastic deformation occurs. Finite-element analyses of the bending and crushing simulations were performed in Abaqus (Dassault Systèmes Simulia Corp.) to obtain the reaction force (RF) exerted by the device, maximum principal stress and maximum principal strain undergone by the device, verifying the absence of permanent deformations. 

The maximum principal strain reached by the device in the bending simulation is 6.9%, while the maximum principal stress is 620 MPa, and the RF is 0.19 N. The crushing simulation indicated a maximum principal stress value of 519 MPa, a maximum strain value of 3.8% and an RF of 0.71 N. The developed computational tool is currently being validated through experimental replication of the bending and crushing simulations. Preliminary experimental results on the bending of the device confirmed the order of magnitude of the RF.

The novel GROSSO® implant provides adequate mechanical stability without incurring in permanent deformations. These results appear promising in view of providing a predictable clinical outcome to KC patients. The developed computational tool allows to explore different device design, cost-effectively predicting the mechanical properties at the macroscale, and the compliance to relevant standards or regulatory requirements. The interaction between the device and corneal tissue will be modelled by digitally generating KC corneal anatomies to evaluate the anatomical fitting and the reshaping effect imposed by the device. FINANCIAL DISCLOSURE: EL and KM are employees of Recornea Srl. Horizon 2020 project HUMANeye (GA 878719) is acknowledged.