Demonstration of sutureless fixation of silk fibroin based corneal bandages ex vivo and in vivo

Abstract

Purpose : Standard-of-care treatment for corneal abrasions consists of suturing amniotic membrane (AM) to the cornea. We have developed silk fibroin (SF) corneal bandages and a light-initiated fixation method that overcomes the potential allograft rejection, opacity, and scarcity of the AM, as well as need for sutures. We demonstrate the method and the optimization of photobonding parameters in a rabbit eye model ex vivo and in vivo.

Methods : SF was extracted from silkworm cocoons in water solution. 3% SF with 5% polyethylene glycol (PEG) solution was cast at 25⁰C and 40% relative humidity. PEG acts as a crosslinker and porogen. Membranes were characterized by Fourier transform infrared spectroscopy (FTIR), cut into 8x10 mm strips with rounded corners and soaked in 0.01% Rose Bengal photosensitizer for 10min. Experiments were performed on corneal strips from 4 enucleated eyes and on 7 eyes in vivo, in a New Zealand rabbit model. Irradiation was carried out with 532nm collimated green laser light (0.15W/cm² irradiance for 6.6min). Ex vivo, stained strip membranes were placed on corneal strips and irradiated. 24h post-treatment, the photobonding strength was characterized by uniaxial stretching. In vivo, stained membranes were placed on a pupil-centered vertical rectangular deepithelialized area of the same size. An opaque mask covered the limbus and the pupil leaving a rim of 2mm on either side of the bandage for irradiation. Animal follow up (0-15days) included clinical signs, neovessels formation, and membrane stability, bonding and transparency.

Results : Membranes showed 35-40μm thickness, 10.4±1.8MPa Young's modulus, >1 month stability in PBS and 24h in protease XIV. In corneas ex vivo, bonding force was 1.37 ± 0.24N/cm². In vivo, the SF membranes remained bonded >1 week in 85% of the rabbits, and corneas showed no sign of edema. The membranes were fully transparent (no RB in the non-irradiated area) 10 days after bonding. Neovessels were observed superiorly, without reaching the optical area.

Conclusions : We have developed SF-based corneal bandages as alternative to AM dressing, and a photobonding paradigm that produces firm suture-less fixation to the cornea both ex vivo and in vivo. The procedure has proved safe and stable over time. Fine-tuning of some fabrication parameters (decreased membrane thickness or increased permeability) could eliminate the neovascularization found in some eyes.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.