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Expanded polytetrafluoroethylene (ePTFE) is used as a support for artificial corneas. Implanted in corneas, most of the time this polymer is colonized by corneal host cells. The absence of colonization often coincides with extrusion of the polymer. Therefore, we decided to introduce keratocytes into ePTFE in vitro before implantation. Because keratocytes do not spontaneously enter ePTFE, we used several chemoattractants, separately and in a mixture, to stimulate the penetration of cultured keratocytes into the polymer. The influence of the passage number on cell penetration was also studied. No significant differences were observed up to the seventh passage, although seventh-passage cells penetrated somewhat more slowly than younger cells. Satisfactory results were obtained with four of the tested chemotactic factors: IL-6, type alpha transforming growth factor (TGF-alpha), platelet derived growth factor isoform BB (PDGF-BB), and fibroblast growth factor-2 (FGF-2). Under our experimental conditions, two to more than six million keratocytes entered the polymer discs with a volume of 706.5 mm(3) in the presence of these four chemoattractants. TGF-alpha was the most efficient and was selected for further in vitro and in vivo studies., (Copyright 2001 John Wiley & Sons, Inc. J Biomed Mater Res 56: 487--493, 2001)

An amorphous and transparent form of Teflon is proposed as a coating of polymethylmethacrylate (PMMA) intraocular lenses (IOLs), rendering them highly hydrophobic. We used an organ culture method to evaluate cell adhesion, proliferation, and migration on Teflon-coated IOLs. Corneal explants from 14-day-old chicken embryos were placed on a semisolid culture medium and covered with uncoated PMMA (n = 36) and Teflon-coated PMMA (n = 36) IOLs and two controls, Thermanox (n = 84) and latex (n = 36). After incubation (7 days at 37 degrees C), a digital imaging system was used to measure the areas of the cell migration layers on the materials. The cells were then removed with tripsin-ethylenediaminetetraacetic acid and the cells detached at times up to 75 min were counted (Coulter(R) Multisizer System). The values were used to construct a cell disconnecting curve for each material. The areas of cell migration layers on uncoated and Teflon-coated IOLs were significantly different (p <.05). Cell disconnecting curves demonstrated that cells adhered less strongly to Teflon-coated IOLs than to the other materials. This organ culture method demonstrated that the coating of PMMA IOLs with Teflon AF(R) is correlated with antiadhesive and antiproliferative properties., (Copyright 1999 John Wiley & Sons, Inc.)

To investigate the effects of focal implantation of expanded polytetrafluoroethylene (e-PTFE) episcleral implants (i.e., explants or exoplants) on surrounding ocular tissues, an experimental and histopathological study was performed. Twenty-seven Fauve de Bourgogne rabbits eyes were implanted for a period of 3-11 months with oval-shaped e-PTFE episcleral implants. A newly formed capsule constantly encased the implants. Affected by the only two severe complications observed, 2 eyes had an endocapsular acute inflammation and could not be included in the study. Finally, 25 eyes were studied histopathologically. Neither intrusion nor extrusion of episcleral implants was observed. Other changes were related to implant characteristics. The inner surface of the capsule was often covered with numerous giant cells attesting to a foreign-body granuloma developed against the irregular outline of the episcleral implants. The porosity of the material was closely related to its surface irregularity, and also allowed its colonization by a fibrovascular and inflammatory tissue mainly in its peripheral layers. Under episcleral implants, sclera was both thinned and invaginated. Expanded PTFE hydrophobia was the other factor that might have suscitated granuloma. These microscopic changes are in contrast with an overall good apparent experimental tolerance to the material. However, additional studies on the long term behavior of this material would be helpful., (Copyright 1999 John Wiley & Sons, Inc.)

Polymethylmethacrylate (PMMA) intraocular lenses (IOLs) were coated with Teflon AF, an amorphous, transparent Teflon, to render them highly hydrophobic. Teflon-coated PMMA IOLs were immersed in culture medium for 30 days at 37 degrees C. Four concentrations of the IOL leachables, 2 concentrations of a toxic control (phenol), and complete liquid culture medium (nontoxic control) were incubated for 24 h in a 96-well plate containing confluent L-929 fibroblasts. The cytotoxic effect of each solution on the fibroblasts was quantitatively assessed by measuring the uptake of neutral red by the viable cells. After the extraction of the neutral red using 1% acetic acid-50% ethanol, the optical densities were measured with a microplate reader at 550 nm. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to analyze the surfaces of the IOLs. Only the optical densities in the wells containing fibroblasts that had been in contact with the phenol solutions were significantly lower than those in the wells incubated with the nontoxic control solution (p < 0.01). There were no signs of surface alteration by SEM, apart from some crystals on the IOLs. The crystals were composed of Na and Cl, as demonstrated by XPS. Aqueous extractables from the Teflon-coated IOLs produced no cytotoxic effects in the neutral red assay used., (Copyright 1999 John Wiley & Sons, Inc.)

The amount and distribution of hyaluronan in a PTFE polymer used to support an artificial cornea implanted in the rabbit cornea were determined. The findings were used to describe the polymer-corneal stroma interface and the reason for the translucence and wettability of this originally opaque and hydrophobic biomaterial. PTFE disks (6 mm in diameter, 0.2 mm thick, 50 microns in pore size) were implanted after a free-hand intralamellar dissection. The corneas were removed 15 days, 1 month, and 3 months after implantation. The hyaluronan content of pepsin-solubilized corneal stromal extracts and its distribution (7 microns cryostat sections) were investigated using an alkaline phosphatase-linked hyaluronectin assay that specifically detects nanogram amounts of hyaluronan. A PTFE polymer implant caused large, transient increases in hyaluronan density in the implanted stroma. The presence of amphiphilic hyaluronan in the polymer 15 days post implantation probably produced translucence and wettability of this opaque, hydrophobic implant despite the absence of cells. The hyaluronan density in the PTFE polymer increased considerably during the first month and then decreased to stabilize at a moderate level by the third month. These changes in hyaluronan density parallel the invasion of the polymer by inflammatory cells during the first month and the subsequent replacement of these cells by fibroblasts. The PTFE polymer is a good interface that is compatible with the native corneal stroma, and our results indicate that hyaluronan, because of its amphiphilic character, plays a major role in the polymer wettability and translucence and in the production of typical corneal extracellular matrix within the pores of the polymer.

Microporous polymers have great potential for the production of corneal keratoprosthetic devices. Keratocytes invade the pores of expanded polytetrafluoroethylene implants (ePTFE) and collagen synthesis occurs. This ePTFE becomes translucent after its implantation in the stroma of rabbit cornea. The rate and density of cell growth within this polymer depends on the implant thickness, pore size, and its placement in the cornea. We have investigated the influence of the polymer permeability on the collagen and protein contents ePTFE implants. Rabbit corneal stroma were implanted with ePTFE disks (6 mm in diameter) by intralamellar keratoplasty. The implanted polymers were removed from the stroma after 3 to 6 months. The collagen and protein contents were determined after pepsin solubilization. The collagen content of the high-permeability implant was 3.7-fold greater than that of the low-permeability implant 3 months after implantation and 2.4-fold greater after 6 months. The total protein content of the high-permeability implant was 2.5-fold greater than that of low-permeability implant at 3 months and was the same after 6 months. The collagen-to-protein ratio was 68% in the high-permeability implants, and thus similar to that of normal corneal stroma. Thus, high polymer permeability increased both the rate and density of the corneal extracellular matrix ingrowth.

An implant of porous expanded polytetrafluoroethylene (PTFE) in the corneal stroma allows fast cell colonization and can become translucent. We studied the behavior of the same polymer implanted in the anterior chamber of the rabbit eye and sutured to the posterior surface of the cornea. The expanded tetrafluoroethylene was provided as 200-micron thick sheets in 3 pore diameters (20, 50 and 80 microns). Disks (5 mm) were implanted in the anterior chambers of 20 rabbits and sutured to the posterior surface of the cornea. Histological and ultrastructural studies were performed after 3 and 4 months. Quantimetry was done on TEM images to analyze the fibrillar structure of the intercellular matrix inside and around the implanted polymer. The material was well tolerated. In all cases there was mild central corneal edema, which disappeared after 1 month. Mild neovascularization occurred in five cases, decreasing after 1 month. The polymer became translucent after 8 days. Keratocytes from the corneal stroma colonized the implant via breaks in the Descemet's membrane along the sutures. Quantimetry showed three types of fibrils inside and beside the polymer. Corneal endothelial cells regenerated over the fibroblasts and the polymer. This fluorocarbon polymer implanted in the anterior chamber and sutured to the posterior surface of the cornea was well tolerated, and there was real incorporation, with keratocytes producing collagen fibrils inside the polymer and endothelial cells forming a posterior cell monolayer. This is promising for the development of a keratoprothesis with posterior fixation.