The Effect of Direct Gas Fluorination on Medical Grade Poly(methyl methacrylate)

Abstract

Medical-grade poly(methyl methacrylate) (PMMA) is extensively employed in the fabrication of a variety of medical implants, including intraocular lenses (IOLs). However, a postoperative complication that leads to the failure of the implanted intraocular lenses has been recently identified. This process, termed calcification, occurs when calcium-containing deposits accumulate on the surface of the IOL. In this study direct gas fluorination was used to modify the surface of PMMA in an attempt to increase the service lifetime of the material in optical applications. PMMA discs exposed to a 20% fluorine/nitrogen gas mixture for 24 h were compared with untreated PMMA discs serving as control samples. Over time, both surface-fluorinated and untreated PMMA samples immersed in a simulated aqueous humour solution (SAHS) (pH 7.4, 35˚C) were used to carry out in vitro studies. Attenuated total refractive Infrared spectroscopy (ATR-IR) Scanning electron microscopy (SEM), coupled with Energy dispersive X-ray analysis (EDX), showed that calcium-containing surface deposits were less abundant on surface-fluorinated PMMA compared with the control samples, indicating that the fluorinated surface was acting as a barrier to the deposits. Gravimetric analysis data showed that the decreased rate of diffusion compared with that of a control sample was due to the fluorinated surface.

Sulfur Hexafluoride (SF6) Plasma Treatment of Medical Grade Poly(methyl methacrylate)

“…As the sodium percentages are consistently higher than that of chlorine, other sodium-containing deposits are likely to be present. In previous works regarding gas fluorinated PMMA samples immersed in SAH (8 weeks), the EDS analysis indicated the presence of sodium chloride crystallites but a negligible calcium deposition [10,30]. This previous result could be attributed to the concentration of NaCl in the SAH being > ×50 higher than that calcium and phosphate.…”

“…This hypothesis has been tested and its validity proved in previous works, where the direct surface plasma fluorination of PMMA IOLs employing F 2 or exploiting surface segregation of perfluoroalkyl chains effectively hinder the surface formation of inorganic-based deposits [9,10]. As discussed above, this was attributed to the barrier effect of the hydrophobic, fluorinated PMMA surface, which caused a slower rate of diffusion of water into the polymer network, compared with the untreated PMMA.…”

Surface Perfluoroalkyl Chains Segregation: A Tool for Reducing Calcium Deposits in Medical Grade Poly(Methyl Methacrylate)

“…In these lenses, a surface modification that can reduce the calcium containing deposits is particularly attractive since it can contribute to keeping down costs and avoiding the associated trauma of repeat surgeries to remove the opacified/calcified IOL. Surface fluorination, by specific surface chemical reactions, has been routinely applied to biomaterial surfaces to increase the biocompatibility of organic materials with the human body [15], and recently researchers have assessed the use of direct surface fluorination IOL using plasma techniques employing elemental fluorine [16]. In this latter case, although the plasma fluorination treatment is very aggressive, both the wettability of PMMA surfaces and calcium containing deposits are sensibly reduced.…”