Synthetic scleral reinforcement materials. III. Changes in surface and bulk physical properties

Abstract

Changes in the physical properties of polymer materials during implantation in the biological environment can directly affect the ultimate performance of the polymer and/or device. We implanted four types of extraocular bands (porous, solid, composite, and patched) made from 11 types of materials in rabbit eyes and examined the changes in the physical strength and polymer structure of the implanted bands in terms of tensile strength measurements, creep analysis, and attenuated total internal reflectance--Fourier transform infrared spectroscopy (ATR-FTIR) at intervals up to 18 months after implantation. Most of the materials showed increases in tensile strength over the first 6 months in situ in the rabbit eye, followed by significant decreases between 6 and 18 months. Polymer bands that had been implanted for 18 months generally exhibited less creep behavior than unimplanted controls; for most of the bands, creep values ranged from 0% to 10% of the original length. ATR-FTIR of the solid bands and surface coatings showed protein deposition on all of the materials examined, with silicone materials and coatings least affected. Thirty-degree ATR-FTIR scans detected significant changes in the polymer structure for two of the band types: one solid (polyether urethane) and one porous (porous polyacrylate). In general, expanded polytetrafluoroethylene was the most stable in terms of tensile strength and creep. The least stable bands (composite bands made with porous polyurethane) were those that had undergone hydrolytic and/or oxidative degradation and chain scission of the polymer or alteration of the bond between the two materials making up the composite. These changes in physical properties and polymer structure observed after 18 months of implantation support the idea that polymer implant materials should be followed closely over several years in vivo to determine their suitability prior to use in humans.

Effects of poly(2-hydroxyethyl methacrylate) and poly(vinyl-pyrrolidone) hydrogel implants on myopic and normal chick sclera

“…For these high-risk eyes, the only available treatment is donor scleral graft reinforcement surgery (Thompson, 1978; Avetisov et al, 1997), which is reserved for eyes exhibiting scleral creep, and is limited by access to suitable donor tissue. While a limited range of synthetic polymer scleral reinforcement materials have been developed (Jacob et al, 1997; Tarutta et al, 1999), they have not yet seen widespread clinical use. Ways of promoting collagen crosslinking to strengthen the sclera and so prevent eye elongation have also been explored (Wollensak and Spoerl, 2004; Paik et al, 2008), but there remain obstacles to their clinical application.…”

Scleral Cross-Linking Using Riboflavin UVA Irradiation for the Prevention of Myopia Progression in a Guinea Pig Model: Blocked Axial Extension and Altered Scleral Microstructure

“…[6, 7] Scleral strengthening surgery, such as polymeric gel injection or scleral reinforcement surgery,[8] where a donor sclera or silicone band is sutured onto the sclera at the back of the globe to prevent excessive eye globe extension, are highly invasive procedures that have been demonstrated to have limited success at halting myopic progression. [9] The sclera must first become biomechanically weaker before it can be stretched as a result of myopia. This is often caused by enzymes.…”

Safety evaluation of rabbit eyes on scleral collagen cross‐linking by riboflavin and ultraviolet A

“…Scleral biomechanical weakness and thinning are the main factors in the pathogenesis of this disease. Until now, several treatments of pathological myopia have been developed, such as injections of a polymeric composition under Tenon's capsule and the posterior scleral reinforcement surgery . Nevertheless, none of these methods can regenerate the internal structure of the weakened sclera.…”