A characterisation of the structural and optical Properties of Type III collagen biosynthetic corneal implants

Abstract

Purpose: To characterize the structural and optical properties of bioengineered, immune compatible corneal implants which have been shown to promote endogenous regeneration of the epithelium, stroma and nerves.

Methods: Biosynthetic corneal implants were fabricated from freeze-dried recombinant human collagen type III (RHCIII), with (n = 3) and without (n = 3) the incorporation of 2-methacryloyloxyethyl phosphocholine (MPC). Their structural characteristics were examined using a combination of transmission electron microscopy (TEM) and high-angle x-ray scattering, to produce information about the organisation of collagen within the implants at both the fibrillar and molecular level. Spectroscopy was used to determine the light transmission properties of the implants between the range of 230 and 1100nm. All measured parameters were examined alongside similar data obtained from human corneas (n = 18).

Results: TEM demonstrated the presence of loosely bundled aggregates of fine collagen filaments within both RHCIII and RHCIII-MPC implants, which high-angle x-ray scattering showed to be preferentially aligned in a uniaxial orientation throughout. This arrangement differs from the predominantly biaxial alignment of collagen that exists in the human cornea. The implants, which had a water content of 90%, were found to transmit 90-96% of incident light in the visible spectrum but also a large proportion of UV light (up to 70% of UVB and 48% UVC). This is in contrast to the human cornea which acts as an effective UV light filter.

Conclusions: The structure of the implants differs substantially from that of the human cornea but both share a high level of transparency to visible light. The transparency of the implant may be attributed to its high water content and narrow collagen filaments. Patients grafted with these implants should be cautious about UV exposure, particularly in the period prior to epithelial regrowth.