Surface activation of polyetheretherketone (PEEK) and formation of calcium phosphate coatings by precipitation

Plasma activation of polyetheretherketone (PEEK) surfaces and the influence on coating formation in a supersaturated calcium phosphate solution was investigated in this study. It was observed that plasma treatment in a N2/O2 plasma had a significant effect on the wettability of the PEEK surface. The contact angle decreased from 85° to 25° after plasma treatment. Cell culture testing with osteoblastic cell lines showed plasma activation not to be disadvantageous to cell viability. X-ray photoelectron spectroscopy (XPS) analysis was performed to characterize the chemical composition of the PEEK surfaces. It was observed that the O1s intensity increased with plasma activation time. At the C1s peak the appearance of a shoulder at higher binding energies was observed. Coating of PEEK was performed in a supersaturated calcium phosphate solution. Coating thicknesses of up to 50 μm were achieved after 24 days of immersion. Plasma activation followed by nucleation in a highly saturated hydroxyapatite solution had a positive effect on the growth rate of the layer on PEEK. Chemical analysis revealed that the coating consists of a carbonate-containing calcium phosphat

Iodine, Hemin and Heminester as Oxidants in a Synthesis of ATP from ADP and Pi Mediated by Thiols and Disulfides

The conversion of oxidation energy into the energy-rich phosphoryl linkage of ATP has been demonstrated in a system consisting of the tertiary-butylammonium salts of ADP and Pi in pyridine and utilising several mercapto carboxylic acids or their disulfides as mediators and iodine or hemin or hemindimethyl ester as oxidants. Iodine with several thiols in 1:1 molar proportions produces relatively poor yields of ATP (1.5–5.4%) which can be considerably increased (10–15%) when the corresponding disulfides are used, whereas a thioether (N-acetylmethionine) had no effect. This led to the conclusion that disulfides are better substrates and accordingly much higher amounts of ATP were formed from all thiols on using a two-fold amount of oxidant (up to 25.6%). Taking this into account a mechanism has been formulated in which the formation of a phosphorylating species, RS-OPO3H2, is assumed to be formed from disulfides. Hemin and (less efficiently) its dimethyl ester used as oxidants also give rise to the formation of ATP in our system, but only under aerobic conditions. Here optimal yields (up to 16.7%) were obtained with thioglycolate or its disulfide as mediators, a thioether (N-acetylmethionine) being almost ineffective, and no difference in efficiency between thiol acid and disulfide was observed at a hemin: sulfur ratio of 1:1. The yields depend in some way on the hemin: S ratio, lower values giving higher amounts of ATP on oxidation of the mercapto compound, but not of its disulfide. Therefore a reaction mechanism different from that of iodine must be presumed. The formation of the same phosphorylating species as above has been assumed to occur preferently with a thiol and to a lesser extent with a disulfide. The role of oxygen is still rather obscure, for it can not be determined whether it is the terminal electron acceptor or electron carrier. A catalytic participation of hemin could not be demonstrated, perhaps on account of the slow autoxidation rate of the ferrous heme iron

Surface activation of polyetheretherketone (PEEK) and formation of calcium phosphate coatings by precipitation

ISSN:0957-4530ISSN:1573-483