A high-repetition rate scheme for synchrotron-based picosecond laser pump/x-ray probe experiments on chemical and biological systems in solution

We present the extension of time-resolved optical pump/x-ray absorption spectroscopy (XAS) probe experiments towards data collection at MHz repetition rates. The use of a high-power picosecond laser operating at an integer fraction of the repetition rate of the storage ring allows exploitation of up to two orders of magnitude more x-ray photons than in previous schemes based on the use of kHz lasers. Consequently, we demonstrate an order of magnitude increase in the signal-to-noise of time-resolved XAS of molecular systems in solution. This makes it possible to investigate highly dilute samples at concentrations approaching physiological conditions for biological systems. The simplicity and compactness of the scheme allows for straightforward implementation at any synchrotron beamline and for a wide range of x-ray probe techniques, such as time-resolved diffraction or x-ray emission studies.     

In-Situ Simultaneous Measurement of Thickness,Elastic Moduli and Density of Thermal Sprayed WC-Co Coatings by Laser-Ultrasonics

A method for simultaneous nondestructive evaluation of WC-Co coating thickness, elastic moduli, and density is presented. The technique, known as laser-ultrasonics, is used to generate and detect surface acoustic waves in a noncontact and nondestructive manner. The surface acoustic wave velocity dependence on frequency is compared to a model and an optimization procedure is used to evaluate the coating properties. The results obtained demonstrate the ability of the technique to simultaneously determine such properties with a single and possibly in situ measurement.     

Development of osteoblast colonies on new bioactive coatings

The aging baby boomer population coupled with an increase in life expectancy is leading to a rising number of active elderly persons in occidental countries. As a result, the orthopedic implant industry is facing numerous challenges such as the need to extend implant life, reduce the incidence of revision surgery, and improve implant performance. This paper reports results of an investigation on the bioperformance of newly developed coating-substrate systems. Hydroxyapatite (HA) and nano-titania (nano-TiO₂) coatings were produced on Ti-6Al-4V and fiber reinforced polymer composite substrates. In vitro studies were conducted to determine the capacity of bioactive coatings developed to sustain osteoblast cells (fetal rat calvaria) adherence, growth, and differentiation. As revealed by scanning electron microscopy (SEM) observations and alkaline phosphatase activity, cell adhesion and proliferation demonstrated that HA coatings over a polymer composite are at least as good as HA coatings made over Ti-6Al-4V substrate in terms of osteoblast cell activity. Nano-TiO₂ coatings produced by high-velocity oxyfuel (HVOF) spraying led to different results. For short-term cell culture (4.5 and 24 h), the osteoblasts appeared more flattened when grown on nano-TiO₂ than on HA. The surface cell coverage after seven days of incubation was also more complete on nano-TiO₂ than HA. Preliminary results indicate that osteoblast activity after 15 days of incubation on nano-TiO₂ is equivalent to or greater than that observed on HA. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Magnitude and time course of microvascular obstruction and tissue injury after acute myocardial infarction

BACKGROUND: Microvascular obstruction within an area of myocardial infarction indicates worse functional recovery and a higher risk of postinfarction complications. After prolonged coronary occlusion, contrast-enhanced MRI identifies myocardial infarction as a hyperenhanced region containing a hypoenhanced core. Because the time course of microvascular obstruction after infarction/reperfusion is unknown, we examined whether microvascular obstruction reaches its full extent shortly after reperfusion or shows significant progression over the following 2 days. METHODS AND RESULTS: Seven dogs underwent 90-minute balloon occlusion of the left anterior descending coronary artery (LAD) followed by reflow. Gadolinium-DTPA-enhanced MRI performed at 2, 6, and 48 hours after reperfusion was compared with radioactive microsphere blood flow (MBF) measurements and myocardial staining to define microvascular obstruction (thioflavin S) and infarct size (triphenyltetrazolium chloride, TTC). The MRI hypoenhanced region increased 3-fold during 48 hours after reperfusion (3.2+/-1.8%, 6.7+/-4.4%, and 9.9+/-3.2% of left ventricular mass at 2, 6, and 48 hours, respectively, P<0.03) and correlated well with microvascular obstruction (MBF <50% of remote region, r=0.99 and thioflavin S, r=0.93). MRI hyperenhancement also increased (21.7+/-4.0%, 24.3+/-4.6%, and 28.8+/-5.1% at 2, 6, and 48 hours, P<0.006) and correlated well with infarct size by TTC (r=0.92). The microvascular obstruction/infarct size ratio increased from 13.0+/-4.8% to 22.6+/-8.9% and to 30.4+/-4.2% over 48 hours (P=0.024). CONCLUSION: The extent of microvascular obstruction and the infarct size increase significantly over the first 48 hours after myocardial infarction. These results are consistent with progressive microvascular and myocardial injury well beyond coronary occlusion and reflow.     

Spatial organization of peptide nanotubes for electrochemical devices

A novel biosensor for hydrogen peroxide was developed by combining the known properties of microperoxidase-11 (MP11) as an oxidation catalyst, and the interesting properties of diphenylalanine peptide nanotubes (PNTs) as a supporting matrix to allow a good bioelectrochemical interface. In this case, the synthesized MP11/PNTs were immobilized onto the ITO electrode surface via layer-by-layer (LBL) deposition, using poly(allylamine hydrochloride) (PAH) as positively charged polyelectrolyte layers. The PNTs provide a favorable microenvironment for MP11 to perform direct electron transfer to the electrode surface. The resulting electrodes showed a pair of well-defined redox peaks with formal potential at about −343 mV (versus SCE) in phosphate buffer solution (pH 7). The experimental results also demonstrated that the resulting biosensor exhibited good electrocatalytic activity to the reduction of H₂O₂ with a sensitivity of 9.43 μA cm⁻² mmol⁻¹ L, and a detection limit of 6 μmol L⁻¹ at the signal-to-noise ratio of 3. Moreover, we also observed that the peptides self-assembly can be influenced upon changing the pH of the solution. Alkaline solution appears to favor the packing of diphenylalanine nanotubes being closer than acidic or neutral conditions. The study proved that the combination of PNTs with MP11 is able to open new opportunities for the design of enzymatic biosensors with potential applications in practice.