Human acellular dermal matrix for corneal reinforcement: analysis of biocompatibility and mechanical properties

Purpose collagen constitutes the largest portion, more than 90%, of the cornea stroma, contributing to many characteristics
of the it, including physical strength and transparency. Corneal ectatic disorders are characterised by a marked local
thinning of stromal collagen. A material with good biocompatibility, strength integrity and transparency may display
potential for use in corneal reinforcement. An acellular dermal matrix (ADM) derived from human donor skin offers a biological collagen scaffold and could be an alternative. This research
is designed to assess the efficacy of ADM used as a reinforcement material in the rabbit cornea.

Methods ADM used was commercially available. Cell components and collagen structure of ADM were investigated by light microscopy
and transmission electron microscopy. ADMs transparency and biomechanics were evaluated. Then the ADM was made into
uniform size and implanted into rabbit corneal pocket. The properties of graft biocompatibility and transparency were
observed and recorded at 1 day, 12 weeks and 24 weeks post surgery. Keratocyte ingrowth and graft collagen changes were
investigated at the above time by microscopy(including picrosirius red staining). 24 weeks after implantation, the biomechanical properties were analysed by an
uniaxial tension test.

Results The graft showed good transparency after dehydration. Microscope observation indicated that the removal of cell
components in ADM was complete and that the dermal collagen structure was different from that of cornea with thicker
fibers tightly packed in bundles. But like cornea stroma, the dermal collagen fibers were uniform in both diameter
and interfiber distance. Twelve weeks after operation no inflammation and new vessel invasion could be identified,
and from that time the graft in the cornea pocket became clear and transparent. Light microscope observation showed
obvious keratocyte ingrowth in the graft 24 weeks post operation and part of the cornea/graft interface was unrecognizable.
Picrosirius red staining revealed great changes of collagen fibers in the graft after implantation with an increased green
color percentage. The biomechanical properties of ADM were much greater than the normal cornea(p<0.01). 24 weeks after operation, the graft showed lower mechanical properties than before operation(p<0.01). Though the mechanical parameters were higher than normal cornea, no significant difference could be identified.

Conclusion The biocompatibility, optical clarity, and mechanical properties of the ADM combined with its ability to induce
keratocyte ingrowth suggest that this new biomaterial offers important potential benefits for corneal tissue
reinforcement.