[Keratoprosthesis design and biological response to a synthetic cornea].

OBJECTIVE: To evaluate the biological response to three different designs of synthetic cornea in vivo. METHODS: All devices consist of a transparent center and a porous blown periphery. Thirty-five devices were implanted into 35 rabbits' corneas and followed up to more than 6 months. Rabbit corneal stromal cells were inoculated onto the anterior surface of the synthetic cornea and cultured in vitro for one week before the operation. The anterior surface of the optic center hydrogel was modified with radio frequency (rf)-argon plasma treatment. RESULTS: Fibroplasia occurred 2 weeks after surgery and collagen was detected by 28 days. The anterior chamber was normal without detectable leakage of aqueous humor. Basic fibroblast growth factor (bFGF) was detected at the interface between the device and the tissue by 42 days. CONCLUSIONS: It is demonstrated that rabbit limbal epithelial cells can migrate onto the synthetic cornea in vivo.

In vivo comparison of three different porous materials intended for use in a keratoprosthesis.

AIM: The goal was to compare the biological response of the corneal stroma with three porous materials: a melt blown microfibre web of polybutylene:polypropylene (80:20); a polyester spun laced fabric (polyethylene terephthalate), and an expanded polytetrafluoroethylene. Fifty per cent of each of the materials were modified using argon radio frequency. METHODS: Discs (6 mm in diameter) were inserted into interlamellar stromal pockets and followed for a period of 12 weeks. Clinical evaluations were performed weekly. At 6 and 12 weeks, fibroplasia and the distribution of matrix proteins and growth factors (bFGF and TGF-beta) were evaluated immunohistochemically. The characterisation of glycosaminoglycans was determined after selective extraction and digestion. RESULTS: The response to the disc resembled that of a wound with a decrease in keratan sulphate and an increase in dermatan sulphate. Pretreatment of the disc reduced corneal oedema and neovascularisation. Heparan sulphate, not normally detected in the corneal stroma, was detected in the region immediately surrounding the disc and in the discs of some materials. The presence of glycosaminoglycans and collagens in the disc indicated that cells had migrated into the disc and deposited a complex matrix in all three materials. The collagen response was not surface specific. bFGF and TGF-beta were detected in the region between the disc and the stroma in the polybutylene material and became diffuse with time. CONCLUSION: Fibroplasia occurred most rapidly into the polyester discs but was accompanied by a large number of inflammatory cells. While the distribution of collagens was not altered by the material, the expression and distribution of growth factors was material dependent. bFGF was expressed transiently and occurred before that of TGF-beta. It is predicted that the transient expression of growth factors mediates the regulation of matrix proteins.

Plasma surface modification of artificial corneas for optimal epithelialization.

We have demonstrated that the optimal surface treatment of a polyvinylalcoholcopolymer hydrogel for epithelial cell migration and proliferation is an argon radio frequency (rf) plasma treatment. The surface chemistry of the material was determined prior to each cellular evaluation, allowing us to compare the biological response with a known surface chemistry. The cellular response was carried out in a consistent manner a minimum of three separate runs. We found that the optimal conditions required culturing the cells under constant rotation. Cells became confluent on argon-plasma-treated surfaces coated under several different reactions pressures, and after 2 weeks they became multilayered. Our experiments demonstrated that cells proliferated and extracellular matrix and adhesion proteins were present only when the surface was treated with an argon rf plasma; acetone- and ammonia-treated surfaces did not yield the desired results. Organ culture experiments further demonstrated the efficacy of the argon-treated surfaces. In these experiments, intact keratoprosthetic devices with modified hydrogel surfaces were implanted into rabbit corneas. The excised corneas containing the devices were cultured, and 3 weeks later, using confocal laser scanning microscopy, confluent epithelium was detected on the modified hydrogel surface. This is the first demonstration that rabbit limbal epithelial cells can migrate onto a synthetic cornea containing a modified hydrogel-treated surface and form a confluent surface of epithelium.

Advances in polyvinyl alcohol hydrogel keratoprostheses: protection against ultraviolet light and fabrication by a molding process.

Our goal was to: 1) modify poly(vinyl alcohol) hydrogels intended for use in a synthetic cornea to absorb ultraviolet light and 2) develop molding procedures for the fabrication of the device. Two ultraviolet light-absorbing monomers were incorporated by copolymerization. The resulting hydrogels protected against ultraviolet light, were not toxic to corneal fibroblasts, and the protection did not diminish during prolonged aqueous exposure. A novel keratoprosthesis molding procedure was developed that made use of the phase transition properties of mixtures of poly(vinyl-trifluoroacetate) and acetonitrile. In this procedure the keratoprosthesis was shaped and a fibrous skirt was bonded to it in a single operation. Composite keratoprostheses were designed and prepared for in vivo testing.

Implantation of a synthetic cornea: design, development and biological response.

Our goal was to evaluate 3 different designs of synthetic corneas in vivo. All devices had a transparent hydrogel center molded to a porous peripheral skirt. Over 30 devices were implanted into rabbits and followed for up to 6 months. The devices were preseeded with rabbit stromal fibroblasts, which enhanced the rate of fibroplasia. The anterior surface of the hydrogel was modified using argon rf plasma treatments. Clinical examinations were performed, and histological analyses were conducted on tissue throughout the time course. Our optimal model ranged from 4.5 to 6 mm and had an extended porous skirt increasing the surface area for fibroplasia and ultimate anchorage of the device. Fibroplasia occurred in this model, and collagen was detected by 28 days. The anterior chamber was normal with no detectable leakage of aqueous humor. Glycosaminoglycans were detected and followed the time course outlined previously when porous material itself was inserted into the stroma. We present the first demonstration that rabbit limbal epithelial cells can migrate onto the synthetic cornea in vivo.