Objective: To determine the reliability of a delay in the microscopic examination of synovial fluid (SF) to detect and identify crystals. Methods: Ninety one SF samples were examined, 31 with monosodium urate (MSU) crystals, 30 with crystals of calcium pyrophosphate dihydrate (CPPD), and 30 containing no crystals. The specimens were stored with EDTA, sodium heparin, and without anticoagulant at 4ºC before examination at 24 and 72 hours with ordinary and polarised light microscopy. Another aliquot of the same samples was stored in a plastic container without anticoagulant at −80°C and examined after two months. Results: When the samples stored at 4ºC were re-examined after 24 hours, intracellular crystals of MSU were seen in 90/93 (97%) cases where they had been identified previously and 89/93 (96%) cases after 72 hours. Similarly, CPPD crystals were identified in 90/90 (100%) and 87/90 (97%) cases after 24 and 72 hours. Examination of the samples stored at −80°C showed intracellular MSU crystals in 25/31 (81%) of cases and CPPD crystals in 25/30 (83%). No crystals were seen in any sample which had previously been diagnosed as crystal-free. Conclusions: Deferred microscopic examination of refrigerated or deep frozen SF provides a strong probability of detecting MSU or CPPD crystals if these are present initially.

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The surface of the oxide layers formed after oxidation in air at 750• C of three titanium alloys has been characterized by several techniques. The investigated alloys were Ti-7Nb-6Al, Ti-13Nb-13Zr and Ti-15Zr-4Nb, with potential applications as biomaterials. XPS experiments showed that, after 24 h exposure, the surface of the Ti-7Nb-6Al alloy is mainly formed of Al 2 O 3 , with a minor presence of TiO 2 , and absence of Nb oxide. On the other hand, the surface of both Ti-Nb-Zr alloys is mainly composed of TiO 2 , with some amount of ZrO 2 and Nb 2 O 5 . An enrichment of the Nb signal is observed in both samples with respect to the bulk composition. The topography and surface morphology of the oxidized alloys were investigated by atomic force microscopy. A more regular surface topography was observed for the Ti-7Nb-6Al alloy than for the Ti-Nb-Zr alloys and, consequently, a higher potentiality in biomedical applications. Finally, in order to get in-depth information of the oxide scale, Rutherford backscattering spectroscopy experiments were also performed. The results obtained with this technique confirm those obtained by XPS, and can help to understand the mechanism and kinetics of the oxide film formation.

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A novel technique based in the combination of vapor silanization and chemical vapor deposition, hereafter referred to as activated vapor silanization (AVS), is shown to be an effective biofunctionalization technique. The AVS process results in thin organic films with a high surface amine concentration when deposited on substrates with different chemical characteristics, such as silicon, porous silicon, or gold. Chemical characterization shows that the films are composed of carbon (hydrocarbon, C-Si, C-C), silicon (different oxidation states), nitrogen (primary and secondary amines), oxygen, and hydrogen. Relevantly, the amines are also distributed along the film thickness, ensuring functionality even after some degradation of the films. AVS films behave practically as monocrystalline silicon substrates under loading-unloading tests. In addition, the AVS films behave as permeable membranes for molecules smaller than 5 Å, and the amine surface concentration is estimated to be 8 NH 2 /nm 2 for molecules of about 12 Å, which is three times higher than that obtained with standard silanization procedures.