A. F. Chandler-Temple

Comprehensive characterization of grafted expanded poly(tetrafluoroethylene) for medical applications

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.

Surface chemistry of grafted expanded poly(tetrafluoroethylene) membranes modifies the in vitro proinflammatory response in macrophages

A series of surface-modified expanded poly(tetrafluoroethylene) membranes showed varied levels of in vitro macrophage proinflammatory response. Membranes containing a mixture of phosphate and hydroxyl groups (as determined by X-ray photoelectron spectroscopy analysis) stimulate greater macrophage activation than samples containing a mixture of phosphate and carboxylic acid segments. The types of proteins that adsorbed irreversibly from serum onto the two samples with the highest and lowest cellular response were investigated using surface-matrix-assisted laser desorption ionisation time-of-flight mass spectrometry. Distinct differences in the number and type of proteins that adsorbed were observed between these samples. A correlation was found between the main protein components adsorbed onto the surfaces and the resulting in vitro proinflammatory response. This study strongly supports the hypothesis that the cellular response is not controlled directly by surface properties but is mediated by specific protein adsorption events. This in turn highlights the importance of better understanding and controlling the properties of intelligent surface-modified biomaterials.

Replacement materials for facial reconstruction at the soft tissue-bone interface

The challenges faced by any tissue repair and regeneration process resulting from either trauma or disease are many and complex. Although it is of course impossible to identify any one anatomical region as being the most demanding in this respect, the craniofacial region surely qualifies. The judicious choice of available, well-defined and tested repair materials to be used in the reconstruction process by the multi-disciplinary team of reconstructive surgeons is critical. This chapter addresses one aspect of facial reconstruction that has been less well addressed in the literature; namely the materials used to repair and regenerate soft tissue both in terms of fillers and in terms of materials used at the hard-soft tissue interface.

XPS analysis of oxide films on lead-free solders with trace additions of germanium and gallium

A sessile drop experiment involving slow heating and cooling of lead-free solder alloys under inert gas revealed segregation of trace elements to the sample surface. Addition of germanium or gallium to Sn-0.7Cu-0.05Ni alloys promoted a metallic lustre in samples, in contrast with the blue/purple colour of the parent alloy. Alloys with Ge or Ga additions showed oxidation resistance. Depth profiling of surfaces of sample alloys with Ge or Ga showed a significant concentration of these elements within the oxide film, which may be responsible for oxidation resistance of these alloys.