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Polytetrafluoroethylene (PTFE) was treated in a low-power plasma using a series of feed gases (O 2 , Ar, N 2 and NH 3 ) and the resulting surface modifications were evaluated by x-ray photoelectron spectroscopy, static secondary ion mass spectroscopy, dynamic contact angle measurements and atomic force microscopy. All plasma treatments caused light etching, but the nature and extent of chemical modification varied considerably. Fluorine depletion of the surface was affected most efficiently by Ar and least effectively by O 2 plasma. New functionalities were introduced to the surface either from plasma derivatives of the feed gases or by post-treatment exposure to moist air; Ar, N 2 and NH 3 were more effective than O 2 in this respect. The wettability of virgin and plasma-treated materials in phosphate-buffered saline solution (PBS) and 1-bromonaphthalene was studied, and the observations are discussed in a framework that correlates contact-angle hysteresis with surface chemistry in a semi-quantitative manner. In Part II of this work, further changes of the surface chemistry and wettability of virgin and plasma-treated materials arising due to storage in PBS or air are described.

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In order to ascertain the tamponade effect of air and silicone oil we examined the contact angles subtended by ex vivo human retina, Teflon and Perspex to find a suitable experimental material which would mimic the surface properties of the retina at a three-phase interface. Using the captive bubble technique to measure the contact angle, it was found that air subtended a larger contact angle (38.8 degrees) with the retina than did silicone oil (18.2 degrees). On coating the Perspex surface with protein (PCP), it was observed that the surface properties were modified such that PCP subtended contact angles with air (43.0 degrees) and silicone oil (16.4 degrees) similar to those subtended by ex vivo human retina. Using PCP as an experimental material that mimics ex vivo human retina, spherical chambers were employed in order to examine qualitatively and to quantify the arc of contact obtained with air and silicone oil. It was found that air gave a greater arc of contact for the same percentage fill than silicone oil.

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This study investigates the biocompatibility of polypyrrole, a conducting polymer, and comments on its potential as an effective guidance channel for the regeneration of nervous tissue. The polymer was prepared in our laboratories by an electro-polymerization process. Pyrrole is placed in an electrolyte and when a potential is applied polypyrrole is deposited at the anode. After polymerization the polypyrrole is easily removed from the anode. Extraction in methanol for a period of 1 week was carried out to remove residual electrolyte. The biocompatibility of the material was assessed in vitro and in vivo. The response of two cell lines growing in contact with the polymer was evaluated. L929 mouse fibroblast and neuro2a neuroblastoma cells contacted the polypyrrole in a specially constructed cell culture chamber which allowed a controlled current to pass through the material. In vivo, the material was evaluated following implantation into a rat model.Furthermore, the effect of charge on the cell lines was examined using the same cell culture chamber, but substituting platinum wire for the polypyrrole. Finally, the polypyrrole was deposited directly onto the platinum wire and introduced to the cell culture chamber. The results demonstrate that the polypyrrole is cytocompatible in vitro if prepared by appropriate extraction techniques. In vivo there was only a minimal tissue response after 4 weeks in situ. The cell culture chamber model proved successful and allowed a current up to 1 mA to be applied across the polypyrrole or platinum wire while in contact with both cell lines. Some evidence of toxicity was evident when a current of 1 mA was applied across the polymer for periods up to 96 h. However, it is clear from these experiments that polypyrrole can be an effective medium for carrying current in a biological environment.