Ultra-stiff compressed collagen for corneal perforation patch graft realized by in situ photochemical crosslinking

Despite the potential of a collagen construct, consisting of a major extracellular matrix component of the native cornea, as a patch graft to treat the corneal perforation, there has still been difficulty in acquiring sufficient mechanical properties for clinical availability. This study developed a novel in situ photochemical crosslinking (IPC)-assisted collagen compression process, namely, the IPC-C² process, to significantly enhance the mechanical properties of the collagen construct for the development of a collagenous patch graft. For the first time, we found that compressed collagen construct was rapidly rehydrated in an aqueous solution, which inhibited effective riboflavin-mediated photochemical crosslinking for mechanical improvement. The IPC-C² process was designed to concurrently induce the physical compaction and photochemical crosslinking of a compressed collagen construct, thereby avoiding the loosening of collagen fibrillar structure during rehydration and ultimately improving crosslinking efficiency. Hence, the suggested IPC-C² process could fabricate a collagen construct with a high collagen density (∼120-280 mg ml^-1) and ∼10³-fold increased mechanical properties (an elastic modulus of up to ∼29 MPa and ultimate tensile strength of ∼8 MPa) compared with collagen gel. This construct can then be used as a clinically applicable collagenous patch graft. With sufficient mechanical strength for surgical suture and the controllable thickness for patient specificity, the potential of the fabricated IPC-compressed collagen construct for clinical applications was demonstrated by using an in vivo rabbit corneal perforation model. It effectively protected aqueous humor leakage and maintained the integrity of the eye globe without an additional complication.