Biocompatibility of a Novel Interpenetrating Hydrogel Polymer

Abstract

Purpose: : Laser corneal surgery has been a successful modality to correct refractive errors. However, the corneal induced changes are irreversible and for certain patients there is a risk of iatrogenic keraectasia and regression. Refractive corneal inlays offer a reversible alternative but have had limited success due to issues with corneal biocompatibility. We have previously shown the high nutrient permeability and high mechanical strength of a novel interpenetrating (IPN) hydrogel polymer. The aim of this project was to examine the biocompatibility of this polymer.

Methods: : Hydrogels consisting of poly(ethylene glycol)(PEG) interpenetrated by poly(acrylic acid)(PAA) were manufactured using a previously described technique. They were lathed to a 30 micron thickness. NZ white rabbits underwent corneal inlay surgery. Implants were inserted using a manual pocket incision. Rabbits (n=10) were followed up by anterior segment optical coherence tomography (ASOCT), slit lamp photography and keratometry. Rabbits were sacrificed at 2 months, 4 months and 6 months. Histological examination and electron microscopy was performed on the cornea.

Results: : Three animals were sacrificed at each of the above time points. Following surgery, ASOCT confirmed that the implants were placed at a mean depth of 75% of total corneal thickness. There was swelling of the anterior lamella which settled by one month postop. There was no thinning of the anterior lamella on ASOCT up to 6 months postop. There was no significant difference in mean keratometry compared to preoperative levels. Slit-lamp photography showed no stromal inflammation or implant vascularization. Histological examination showed normal stromal and epithelial architecture. Electron microscopy showed activated keratocytes at 2 months that settled by 4 months. Ultra-structural epithelial architecture was maintained throughout follow up.

Conclusions: : This novel interpenetrating hydrogel polymer showed good biocompatibility in an animal model of corneal inlay surgery. There was no stromal thinning or inflammation up to 6 months follow up. IPN hydrogel polymers may be considered as a biomaterial for corneal inlays.

Keywords: keratoprostheses • wound healing • refractive surgery: other technologies