Hierarchically organized nanostructured TiO2 for photocatalysis applications.

A template-free process for the synthesis of nanocrystalline TiO2 hierarchical microstructures by reactive pulsed laser deposition (PLD) is here presented. By a proper choice of deposition parameters a fine control over the morphology of TiO2 microstructures is demonstrated, going from classical compact/columnar films to a dense forest of distinct hierarchical assemblies of ultrafine nanoparticles (<10 nm), up to a more disordered, aerogel-type structure. Correspondingly, the film density varies with respect to bulk TiO2 anatase, with a degree of porosity going from 48% to over 90%. These structures are stable with respect to heat treatment at 400 degrees C, which results in crystalline ordering but not in morphological changes down to the nanoscale. Both as deposited and annealed films exhibit very promising photocatalytic properties, even superior to standard Degussa-P25 powder, as demonstrated by the degradation of stearic acid as a model molecule. The observed kinetics are correlated to the peculiar morphology of the PLD grown material. We show that the 3D multiscale hierarchical morphology enhances reaction kinetics and creates an ideal environment for mass transport and photon absorption, maximizing the surface area-to-volume ratio while at the same time providing readily accessible porosity through the large inter-tree spaces that act as distributing channels. The reported strategy provides a versatile technique to fabricate high aspect ratio 3D titania microstructures through a hierarchical assembly of ultrafine nanoparticles. Beyond photocatalytic and catalytic applications, this kind of material could be of interest for those applications where high surface-to-volume and efficient mass transport are required at the same time.

Materials characterization of explanted mechanical heart valves and comparison to patients' clinical data.

In the present study, twelve explanted mechanical heart valves (MHVs)with pyrolitic carbon tilting disc and 14 bileaflet MHVs were analyzed to investigate the effects of material properties on valve performance and patients' general health conditions. Optical and scanning electron microscopy was used to investigate material imperfections, wear patterns or damages to housing and occluder components. All analyzed tilting disc valves exhibited wear effects, particularly due to abrasion and impact to both disc and housing. Wear of pyrolitic carbon disc and housing did not influence their in vivo performance. In the bileaflet MHVs, breakaway of the pyrolitic carbon coating sometimes caused malfunctioning and required surgical retrieval of the valve. In all cases, occurrence of clinical symptoms was more likely when wear effects were located in critical areas. The study supports a correlation between the properties of the MHVs material and patients' symptoms.

Decreased bacterial adhesion to surface-treated titanium.

Osteointegrative dental implants are widely used in implantology for their well-known excellent performance once implanted in the host. Remarkable bacterial colonization along the transgingival region may result in a progressive loss of adhesion at gum-implant interface and an increase of the bone area exposed to pathogens. This phenomenon may negatively effect the osteointegration process and cause, in the most severe cases, implant failure. The presence of bacteria at implant site affect the growth of new bone tissue and consequently, the achievement of a mechanically stable bone-implant interface, key parameters for a suitable implant osteointegration. In the present work, a novel surface treatment has been developed and optimized in order to convert the amorphous titanium oxide in a crystalline layer enriched in anatase capable of providing not only antibacterial properties but also of stimulating the precipitation of apatite when placed in simulated body fluid. The collected data have shown that the tested treatment results in a crystalline anatase-type titanium oxide layer able to provide a remarkable decrease in bacterial attachment without negatively effecting cell metabolic activity. In conclusion, the surface modification treatment analyzed in the present study might be an elegant way to reduce the risk of bacterial adhesion and increase the lifetime of the transgingival component in the osteointegrated dental implant.

Physico-chemical observations on a failed Greenfield vena cava filter.

A Greenfield vena cava filter for the prevention of thromboembolism failed in vivo due to the displacement of 2 of the 6 legs and their subsequent break. The explanted stainless steel filter was analyzed with an electron microscope and energy dispersion system in order to assess the reason for the break. Fatigue and corrosion of the metal were responsible for the failure.