The structural and optical properties of type III human collagen biosynthetic corneal substitutes

Sally Hayes,Phillip Lewis,M Mirazul Islam,James Doutch,Thomas Sorensen,Tomas White,May Griffith,Keith M Meek

doi:10.1016/j.actbio.2015.07.009

Sally Hayes, Phillip Lewis + Show 6 more

Open Access

https://doi.org/10.1016/j.actbio.2015.07.009

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Abstract

The structural and optical properties of clinically biocompatible, cell-free hydrogels comprised of synthetically cross-linked and moulded recombinant human collagen type III (RHCIII) with and without the incorporation of 2-methacryloyloxyethyl phosphorylcholine (MPC) were assessed using transmission electron microscopy (TEM), X-ray scattering, spectroscopy and refractometry. These findings were examined alongside similarly obtained data from 21 human donor corneas. TEM demonstrated the presence of loosely bundled aggregates of fine collagen filaments within both RHCIII and RHCIII-MPC implants, which X-ray scattering showed to lack D-banding and be preferentially aligned in a uniaxial orientation throughout. This arrangement differs from the predominantly biaxial alignment of collagen fibrils that exists in the human cornea. By virtue of their high water content (90%), very fine collagen filaments (2–9nm) and lack of cells, the collagen hydrogels were found to transmit almost all incident light in the visible spectrum. They also transmitted a large proportion of UV light compared to the cornea which acts as an effective UV filter. Patients implanted with these hydrogels should be cautious about UV exposure prior to regrowth of the epithelium and in-growth of corneal cells into the implants.

Highlights

The intrinsic properties of the healthy cornea, namely its strength, transparency and precise curvature enable it to withstand external damage and resist intraocular pressure, whilst allowing it transmit over 95% of incoming light [1] and provide 70% of the focussing power of the eye
We have previously shown that corneal swelling does not alter the predominant orientation of collagen within the cornea, it does
All recombinant human collagen type III (RHCIII)-methacryloyloxyethyl phosphorylcholine (MPC) hydrogel sheets were between 88% and 90% hydrated at the time of examination and had an average refractive index of 1.334 ± 0.0003

Summary

Introduction

The intrinsic properties of the healthy cornea, namely its strength, transparency and precise curvature enable it to withstand external damage and resist intraocular pressure, whilst allowing it transmit over 95% of incoming light [1] and provide 70% of the focussing power of the eye. These properties are largely governed by the unique architecture of the corneal stroma, which measures approximately 500 lm in thickness and occupies 90%.

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