Abstract
Purpose :
Corneal reshaping by additive surgery presents several advantages over tissue removal, but many previous attempts for corneal inlays (CI) have failed due to lack of full biocompatibility, shifting current paradigms to allogeneic corneal tissue as a material alternative. We present a silk fibroin (SF) hydrogel, transparent, biocompatible, easily stored and with expected long-residency time as a material for CI and a model of the expected biomechanical response.
Methods :
SF was extracted from silkworm cocoons in water solution. HEMA and EGDMA (17:1) monomers were mixed with 0.6wt.% AIBN initiator, 3wt.% SF solution and polymerized at 60°C. The final material had an 80wt.% SF. We characterized material transparency (UV-Vis spectrophotometry), stability (in PBS and protease XIV 0.05U/mL at 37°C), and stiffness (uniaxial stretching). Material glucose diffusion coefficient (and of a control rabbit cornea) was measured in a custom two-chamber (10mg/mL glucose/PBS solution) at 24h. In vitro biocompatibility assays tested cytotoxicity, adhesion, growth and proliferation of human corneal fibroblasts and epithelial cells. A finite element (FE) model of the cornea and CI were used to predict corneal curvature change in response to the CI and ZEMAX ray tracing to predict the corresponding change in power.
Results :
The material is transparent (98%, 400-800nm), stable (at least 24 months in PBS and 17 months in protease). It has a 30-40MPa Young’s modulus and a glucose diffusion coefficient in the order of 10-7-10-8 cm2/s (rabbit cornea was 10-6 cm2/s). In the presence of the material, cell viability is >80%, with <40% cell adhesion. FE modelling of the corneal response to the CI allowed finding theoretical optimal parameters: central thickness of 15-30 μm, meniscus shape (6-8 mm curvature radii), 2-2.5 mm diameter and 100-150 μm depth implantation. With these material and geometrical parameters, we predicted at least 2D change in power.
Conclusions :
We have developed a SF-based material with prospective applications as a corneal inlay, with well-suited physical and in vitro biocompatibility properties. Computational models predict geometrical and optical corneal reshaping consistent with refractive and presbyopia correction needs. In vivo biocompatibility essays will determine the CI viability in living eyes.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.