Comparative experiments for in vivo fibroplasia and biological stability of four porous polymers intended for use in the Seoul-type keratoprosthesis

Abstract

Aims: To evaluate in vivo fibroplasia and biological stability of porous polymers intended for use in the Seoul-type keratoprosthesis (S-KPro). Methods: Four porous polymers (polypropylene, two kinds of polyethylene terephthalate (PE70 and PE50), and polyurethane) were investigated. Discs of polymers were inserted into the corneal stroma of rabbits for a 2 and 5 month period. Corneal oedema and neovascularisation were evaluated. The fibroplasia and collagen deposition were examined under light and transmission electron microscopy. S-KPros, whose skirt was made of four types of polymer, were implanted into the rabbits' eyes. The retention time and complications were evaluated. Results: Neovascularisation and corneal oedema were found in all of the disc inserted eyes, but the corneal oedema subsided within 2 months in most of the eyes. The mean number of fibroblasts increased significantly in polypropylene and PE50 disc inserted eyes compared with polyurethane disc inserted eyes. Plentiful collagen deposition was also found in both polypropylene and PE50 disc inserted eyes. Mean retention time in the polypropylene SK-Pro implanted eyes was longer than that of the other eyes (20.7 weeks). The PE70 skirt induced corneal melting around the prosthesis. Conclusion: Polypropylene encourages fibroblast ingrowth and shows good biological stability when used as a skirt material in S-KPro.T he most common problem associated with keratoprosthesis (KPro) implantation results from an inadequate integration between the peripheral edge of the device and the residual rim of the host cornea. From the time that Barber first examined cellular ingrowth into the carbon fibre Teflon composite Propoplast in interlamellar pockets, 1 many different materials intended for use in a KPro have been evaluated as to their biocompatibility, especially with respect to fibroplasia. 2-5The Seoul-type keratoprosthesis (S-KPro) which is composed of a PMMA cylinder and a porous polymer skirt is being developed in our laboratory.6 A major characteristic of the S-KPro is a double fixed design, which includes the anchoring sutures of a skirt to the cornea and ab internal scleral fixation of the haptics, which synergistically improves the mechanical biostability (Fig 1). Therefore, the skirt, which is anchored to the cornea, does not need to serve as a strong support. An adequate coaptation with the surrounding cornea is emphasised in our model rather than a role as a support. We are currently attempting to find a material that enhances fibroblast migration even though it may have low tensile strength. Initially, polyurethane was used for the S-KPro skirt, because the fabrication of its pore size is easily controlled to allow fibroblast invasion.7 However, the polyurethane skirt was found to degenerate in a keratoprosthetic human eye after a long period. Therefore, we tried to find another porous material, which is biologically stable and allows more fibroblast invasion than polyurethane. Our goal was to compare the biological response, especially the fi...

Femtosecond Laser-Assisted Intracorneal Keratoprosthesis Implantation

“…5,6,10 However, as technology moves forward, new-generation 2-piece keratoprostheses may also offer the advantages of improved biointegration, ability to measure intraocular pressure, reduced retroprosthetic membrane formation, and increased visual field. [27][28][29][30][31][32] The FDA has recently approved the AlphaCor intracorneal keratoprosthesis for marketing in the United States. Multicenter clinical trials have been in progress for more than 3 years in Australia and Southeast Asia with outcomes reported in 45 patients.…”

Progress in the development of a corneal replacement: keratoprostheses and tissue-engineered corneas

“…However, despite sufficient biocolonization shown in the animal models, skirt exposure was observed in all human eyes. These differences may be due to the effects of the tear film, abnormal fibroblasts in diseased human eyes or enhanced regenerative capabilities of rabbit corneal cells versus those of humans [14,34]. Similar to other devices, the surgical outcome was dependent on the preoperative diagnosis [34].…”

“…No retroprosthetic membranes were observed in the short term, possibly due to the long optic shape, infusion of heparin and/or surface modification of the PMMA with polyethylene glycol to reduce cell adhesion [34,35]. For the first seven human cases, polypropylene was chosen for a skirt material due to improved fibroblast ingrowth and collagen deposition shown in animal studies [14], and better long-term mechanical integrity compared with polyurethane in human eyes [34]. At 25 months' follow-up, the devices were well tolerated in six patients and, despite loosening at the corneal anchorage point, the haptic fixation maintained stability [34].…”

“…The cellular response to the implant material is a key design consideration, and it is now generally thought that the material should be biocompatible and encourage colonization by host stromal cells for integration into the surrounding tissue and limiting inflammation [9,13]. While vascularization has been suggested to improve healing and survival of adjacent corneal tissue by provision of nutrients and proteolytic enzyme inhibitors [14,15], more research into the effects of the degree of vascularization of a host cornea on a device is needed, as vascularization is often an indication of increased inflammation…”

Amniotic membrane immobilized poly(vinyl alcohol) hybrid polymer as an artificial cornea scaffold that supports a stratified and differentiated corneal epithelium

“…The development of a stable keratoprosthesis (KPros) may be a solution towards solving this problem. Several models of Kpros are already in clinical use [1][2][3][4][5] , and 2 models are currently approved by the FDA 2,6 . The stability of Kpros was greatly enhanced by the design of a porous skirt that allowed the integration of host corneal tissue into prosthetic peripheral region 7 .…”