Comprehensive Characterization of Grafted Expanded Poly(tetrafluoroethylene) for Medical Applications

Abstract

Successful implantation of any biomaterial depends on its mechanical, architectural, and surface properties. Materials with good bulk properties seldom possess the appropriate surface characteristics required for good biointegration. The present study investigates the results of surface modification of a highly porous, fully fluorinated polymeric substrate, expanded poly(tetrafluoroethylene) (ePTFE), with a view to improving the surface bioactivity and hence ultimately its biointegration. Modification involved gamma irradiation-induced graft copolymerization with the monomers monoacryloxyethyl phosphate (MAEP) and methacryloxyethyl phosphate (MOEP) in various solvent systems (water, methanol, methyl ethyl ketone, and mixtures thereof). In order to determine the penetration depth of the graft copolymer into the pores and/or the bulk of the ePTFE membranes, angle-dependent X-ray photoelectron spectroscopy (XPS) and magnetic resonance imaging (MRI) were used. It was found that the penetration depth was critically affected by the choice of monomer and solvent as well as by the technique used to remove dissolved oxygen from the grafting mixture: nitrogen degassing versus vacuum. Difficulties due to the porous nature of the membranes in establishing the lateral position of the graft copolymers were largely overcome by combining data from microattenuated total reflectance Fourier transfer infrared (μ-ATR-FTIR) mapping and time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging. Results show that the large variation in graft heterogeneity found between different samples is largely an effect of the underlying substrate and choice of monomer. The results from this study provide the necessary knowledge and experimental data to control both the graft copolymer lateral position and depth of penetration in these porous ePTFE membranes.

Calcium ion‐mediated grafting of a phosphate‐containing monomer

“…This was attributed to the poor wetting of ePTFE by the acrylate monomer solution. 27 The fact that we do see some grafting throughout the membrane in this study indicates that grafting can, at least to some extent, occur in thin membranes most probably by a grafting front-like mechanism.…”

“…Contact angle measurements were performed on a custom-built instrument which has been described in detail previously. 27 MilliQ water drops (5 lL) were placed on the surface of the sample using a 50-lL glass flattipped syringe and images of the drop captured and analyzed by Scion Image processing software. The advancing angles (h A ) were measured by successive 5 lL additions of water to a total of 20 lL.…”

“…24 The results of grafting MAEP in methanol onto a Gore ePTFE membrane found that while the graft copolymer was distributed in a patchy manner, as evaluated by micro-ATR mapping, ToF-SIMS revealed that the grafting had occurred both on the fibril and island regions. 27 In all of these studies, it is clear that the graft copolymer never completely covers the membrane surface.…”

“…The penetration of the PMAEP graft copolymer in a Gore ePTFE membrane (thickness 1 mm) has previously been evaluated using MRI. 27 Regardless of whether grafting was done in water or in methanol, the graft copolymer was only observed on the outer surface of the membrane. This was attributed to the poor wetting of ePTFE by the acrylate monomer solution.…”

Grafting of acrylic acid‐co‐itaconic acid onto ePTFE and characterization of water uptake by the graft copolymers

“…30 MilliQ water drops (5 lL) were placed on the surface of the sample using a 50 lL glass flat-tipped syringe and images of the drop captured and analyzed by Scion Image processing software. The advancing angles (h A ) were measured by successive 5 lL additions of water to a total of 20 lL.…”