Collagen-poly(N-isopropylacrylamide)-based membranes for corneal stroma scaffolds

Purpose: To investigate the feasibility of using the biocompatibility of collagen-based blended biomaterials as cell-delivery systems in ocular surface reconstruction in vivo. Methods: Collagen-based composites that were blended with synthetic acrylamide-based polymers [poly(N-isopropylacrylamide), pNIPAAm] were transplanted into corneal pockets of white rabbits, with a 3-mm epithelial window. Epithelial cells were allowed to migrate onto the polymer. Transplanted eyes were examined daily for up to 30 days, after which animals; were killed for histologic examination. lm- munohistochemistry was performed for vimentin, a-smooth muscle actin (alpha-SMA), CD4, and CD8. Gold-chloride staining was performed to observe neuronal regrowth. Human amniotic membranes (AMs) and sham-operated corneas served as controls. All animals received topical antibiotics (levofloxacin) without the use of steroids or other immunosuppressive agents. Results: The pNIPAAm polymer allowed smooth epitheliatization of the cornea, which was similar to the epithelialization observed in sham controls and AM-transplanted eyes. Histology revealed that epithelium overlying the polymer was bundled into several layers, without the orientation observed with AM and sham controls. The polymer gradually thinned and was gradually replaced by host tissue. Vimentin- and alpha-SMA-positive cells were found in stromal pockets up to 1 month following polymer transplantation. These cells were responsible for slight subepithelial haze near the wound edge. CD4- and CD8-positive lymphocytes were also observed in the vicinity of the polymer. Gold-chloride staining showed nerve regrowth in the wound edge after 1 month and subepithelial branches after 3 months. Conclusion: Collagen-pNIPAAm blended polymers may he effective as biomaterials to be used in the early stages of lamellar stromal replacement.