Artificial Epithelium Research Articles

Physiological response of the cornea to an artificial epithelium

The effect of epithelial removal and absence upon stromal hydration and thickness was studied in rabbits, cats, and humans. The epithelium was replaced with a methyl-methacrylate contact lens, affixed to the denuded stroma by cyanoacrylate adhesive. In rabbits, stromal thickness and hydration showed an increase from the day of lens application. After 20 days, the stromal sodium concentration remained unchanged, but potassium levels had decreased, supporting the histological observation of some degradation of anterior keratocytes. Cats tolerated the lens quite well, with normal stromal thickness being maintained as long as the seal around the lens was complete. Humans exhibited excellent tolerance to the procedure, with a stable stromal thickness being maintained for up to 6 months, to date. In view of the success in replacing the epithelial layer of the cornea with an intert impermeable barrier, such as a contact lens, it appears likely that the epithelium is not required, beyond its fluid barrier characteristics, to maintain normal thickness and hydration of the corneal stroma in cats and humans.

Artificial membranes for corneal surgery.

AbstractThe most commonly used synthetic polymers in corneal implants are reviewed from the viewpoint of their properties and tissue tolerance. Special attention is given to the properties of these materials in in regard to their application as artificial corneal epithelium and endothelium. It is postulated that an ideal artificial corneal membrane must exhibit, as closely as possible, the physical properties and the functional characteristics of the natural membrane. Of all the known artificial materials, homogeneous hydrogels seem to offer the best possibilities as membranes for corneal surgery. Three types of hydrogels were investigated. Poly(2‐hydroxyethyl methacrylate) (PHEMA) and poly(glyceryl methacrylate) (PGMA) are covalently linked tridimensional nonionic networks. The third type of hydrogel has multiple ionic crosslinks and belongs to the family of the polyelectrolyte complex hydrogels, made by reacting poly(vinylbenzyl‐trimethylammonium chloride) with sodium poly(styrenesulfonate). The acrylic hydrogels are very well tolerated by living tissues, but the polyelectrolyte complexes gave inconsistent results. Membranes of either type were made having permeability to water similar to that of the corneal layers. Most hydrogels are friable and do not hold sutures; this difficulty was solved by attaching the hydrogels are friable and do not hold sutures; this difficulty was solved by attaching the hydrogel membrane to the cornea by means of alkyl cyanoacrylate adhesives. n‐Heptyl and n‐butyl 2‐cyanoacrylate gave very good results in this application.

Evaluation of adhesives for corneal surgery.

Methyl, n-butyl, and n-heptyl 2-cyanoacrylates and silicone adhesive (Dow Corning, Type A) were tested in animal eyes. Corneal perforations were sealed with n-butyl and n-heptyl 2-cyanoacrylates where the adhesive remained in place long enough for the tissue to heal behind it. Synthetic membranes were glued with cyanoacrylate adhesives to the corneal stroma, serving as artificial epithelium and as artificial endothelium. Using silicone adhesive, silicone rubber membranes were attached to dried corneal stroma where bonding was moderately strong even after rehydration of the cornea.