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Poly(tetrafluoroethylene) (PTFE), a fully fluorinated linear thermoplastic polymer, and in particular the porous form expanded PTFE (ePTFE) has found widespread use in biomaterials application due to its properties of high toughness, nonadhesiveness and hydrophobicity. While it performs ideally for many applications, some challenges have been identified for its use in small diameter vascular grafts and as a tissue space-filler for cosmetic reconstructions where the implant interfaces with bone. For these applications modification of the surface of ePTFE has been investigated as a means to enhance its performance. This review will focus on the applications listed above and will detail methods of evaluating the biological response, methods used to enhance the surface properties of ePTFE, and how the modified materials have performed in their intended applications. This review will focus on work published from 2004 onwards.

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Expanded polytetrafluoroethylene, ePTFE, is an attractive material for use as the implant in facial reconstruction surgery because it is bioinert; however, its low surface energy does not facilitate a strong interfacial bond with bone and thus for some applications the surfaces need to be modified to enhance their bone-integration properties. The surface modification of ePTFE membranes with copolymers of acrylic acid (AA) and itaconic acid (IA) using in situ gamma radiation induced grafting has been studied. Solutions with AA mole fractions ranging from 0.4 to 1.0 have been investigated. Graft yields of 35-50% with water uptakes of greater than 300% were obtained using 3 mol L 21 aqueous solutions of the monomers and a total incident dose of 10 kGy. The grafts were characterized by Fourier transform infrared and X-ray photoelectron spectroscopy analyses and the compositional microstructure of the grafted copolymers was investigated. The water uptake by the grafted membranes displayed a complex dependence on polymer chemistry and topology.

Natural rubber latex (NRL) is a natural polymer with versatile properties.However, uncured NRL has low strength and limited practical use. Therefore, we utilized low-dose gamma irradiation to induce cross-linking in blended NRL/poly(styrene-block-isoprene-block-styrene) (SIS). Blends were prepared in various ratios, and the 70 NRL /30 SIS blend gave optimal mechanical properties. The 70 NRL /30 SIS blend was then irradiated from 4 to 16 kGy. An exposure of 12 kGy led to the highest tensile strength (4.49 MPa), Young's modulus (0.41 MPa), gel content (45%), and cross-link density (12.18 Â 10 À5 molÁcm À3 ).The results of study show irradiation has improved the crystallinity of the polymer blend, which has been determined by the formation of a new NRL crystal peak at 31.2 and the decrease of the crystallization temperature from 58 to 19 C due to strain-induced crystallization. Moreover, the radiation has trans-

In vitro mineralisation in simulated body fluid (SBF) of synthetic polymers continues to be an important area of research as the outcomes cannot be predicted. This study evaluates a series of ePTFE membranes grafted with carboxylate-containing copolymers, specifically using acrylic acid and itaconic acid for grafting. The samples differ with regards to graft density, carboxylate density and polymer topology. The type and amount of mineral produced in 1.5 × SBF was dependent on the sample characteristics as evident from XPS, SEM/EDX, and FTIR spectroscopy. It was found that the graft density affects the mineral phases that form and that low graft density appear to cause co-precipitation of calcium carbonate and calcium phosphate. Linear and branched graft copolymer topology led to hydroxyapatite mineralisation whereas crosslinked graft copolymers resulted in formation of a mixture of calcium-phosphate phases. This study demonstrates that in vitro mineralisation outcomes for carboxylate-containing graft copolymers are complex. The findings of this study have implications for the design of bioactive coatings and are important for understanding the bone-biomaterial interface.

Unilamellar liposomes composed of dipalmitoylphosphatidylcholine (DPPC