Barbara James

The incorporation of strontium and zinc into a calcium-silicon ceramic for bone tissue engineering.

In this study we developed novel scaffolds through the controlled substitution and incorporation of strontium and zinc into a calcium-silicon system to form Sr-Hardystonite (Sr-Ca(2)ZnSi(2)O(7), Sr-HT). The physical and biological properties of Sr-HT were compared to Hardystonite (Ca(2)ZnSi(2)O(7)) [HT]. We showed that Sr-HT scaffolds are porous with interconnected porous network (interconnectivity: 99%) and large pore size (300-500 microm) and an overall porosity of 78%, combined with a relatively high compressive strength (2.16+/-0.52 MPa). These properties are essential for enhancing bone ingrowth in load-bearing applications. Sr-HT ceramic scaffolds induced the attachment and differentiation of human bone derived cells (HOB), compared to that for the HT scaffolds. Sr-HT scaffolds enhanced expression of alkaline phosphatase, Runx-2, osteopontin, osteocalcin and bone sialoprotein. The in vivo osteoconductivity of the scaffolds was assessed at 3 and 6 weeks following implantation in tibial bone defects in rats. Histological staining revealed rapid new growth of bone into the pores of the 3D scaffolds with the Sr-HT and HT, relative to the beta-tricalcium phosphate (beta-TCP). In vivo, HT and Sr-HT produced distinct differences in the patterns of degradation of the materials, and their association with TRAP positive osteoclast-like cells with HT appearing more resistant compared to both Sr-HT and beta-TCP.

The effect of the addition of noble gases on H- production in a dc filament discharge in hydrogen

The effect of the addition of helium, neon, argon and xenon on the production of negative hydrogen ions in a magnetically confined dc filament discharge has been investigated. The addition of helium and neon produces effects not significantly different from an equivalent increase in the hydrogen pressure. The addition of argon and low fractions of xenon produces significant increases in the negative-ion density for hydrogen pressures close to 1 mTorr. The addition of argon and xenon, by increasing the electron density and decreasing the electron temperature, achieves conditions closer to optimum for negative-ion production. The largest enhancement occurs with argon and it is suggested that a resonant energy exchange between excited argon atoms and hydrogen molecules is a contributing factor.

The “nicotinic” and “muscarinic” receptors of the urinary bladder of the guinea-pig

The action of acetylcholine and nicotine on the urinary bladder of the guinea‐pig has been examined using three techniques of physiological denervation. Nicotine was neurogenic and equiactive concentrations of acetylcholine were myogenic. Whilst acetylcholine has both “muscarinic” and “nicotinic” effects on the guinea‐pig bladder, the concentration required to stimulate the nicotinic receptors was approximately 100 times that required for the muscarinic receptors. These results indicate that the nicotinic receptors are confined to nervous tissue, and do not support the suggestion that there might be non‐neuronal nicotinic receptors in the bladder musculature of the guinea‐pig. The possibility of a non‐cholinergic component in the post‐ganglionic parasympathetic fibres to the bladder should still be considered.

Langmuir probe study of a titanium pulsed filtered cathodic arc discharge

A Langmuir probe has been used to make measurements of plasma parameters as a function of time at the substrate position in a magnetically-filtered pulsed cathodic arc discharge. Electron density, ne, and effective electron temperature, Teff, were calculated as a function of time from the I–V curves. The Druyvesteyn method was used to determine the electron energy distribution. Ion density was calculated using the assumption of plasma quasi-neutrality and an average ion charge state. Results show that over the plateau region (350–600 µs) of the pulse, the electron energy distribution is Maxwellian with Teff = Te = (10 ± 1) eV. During the rise and fall times of the pulse, the electron energy distribution is non-Maxwellian with an effective temperature of up to 15 to 20 eV during the rise time and ~7 eV during the fall time. The electron density during the plateau is ne = (3.0–6.0 ± 0.5) × 1017 m−3.

A short-pulsed compact supersonic helium beam source for plasma diagnostics

A short-pulsed (less than 1 ms) compact supersonic helium beam source has been developed for plasma diagnostics purposes. The beam has been characterized experimentally and the results compared with calculations from a simple model that takes into account interaction between the supersonic beam and gas in the region between the nozzle and the skimmer. For a 200 μs driving pulse, a beam of density N > 1 × 1018 m−3 on the axis, a width of D  ≈  1 cm at a distance of 30 cm from the nozzle and a velocity v  ≈  1.8 × 103 m s−1 has been achieved.

Acute coronary stent thrombosis: Toward insights into possible mechanism using novel imaging methods

Acute coronary stent thrombosis: Toward insights into possible mechanism using novel imaging methods -

Spatial distribution of the pulsed neutral helium beam

A supersonic He beam source, which consists of a commercial pulse generator and a pulsed nozzle with a diameter of 0.8 mm, is fabricated. The helium beam is ejected from a pulsed nozzle, and then collimated through a skimmer. We observe that the helium density is inversely proportional to the square of the distance. At the longitudinal position of Y = 12 cm away from the nozzle, the atom densities of the helium beams of 8.4 × 1014 cm−3 (26 mTorr) and 6.1 × 1014 cm−3 (19 mTorr) are obtained for the nozzle backing pressure of 101 kPa and the gaps between the nozzle and the skimmer of D = 1 and 3 mm. Experimental data indicate that the radial width of the helium beam is around 64 mm at a position 19 cm away from the nozzle for D = 1 mm. In contrast, for D = 3 mm, the radial width of the helium atom beam is decreased to 44 mm.From the time shift of each peak, the speeds of the pulsed beams of 1.1 km s−1 at Y = 14 cm and 508 m s−1 at Y = 21 cm are also obtained. The background of signal due to gas diffusion at the position far from the nozzle is always larger than that at the position close to the nozzle. This suggests that the speed of the He beam is affected by He atom collision and gas diffusion.A high-density short-pulsed supersonic metastable helium beam was obtained. After discharge, a metastable density of 1.33 × 1011 cm−3 was obtained. Its fraction was up to 1.65 × 10−5.

A pinhole transmission grating spectrograph used in the characterization of the spatial distribution plasma x-ray spectrum

A pinhole transmission grating spectrograph has been used for measuring the soft x-ray spectrum from a laser-irradiated solid target plasma and gas-filled plasma focus. This spectrograph can be used together with a soft x-ray streak camera or a soft x-ray CCD detector for time-resolved studies. The spectrograph has provided a spatially resolved spectrum with a wavelength range of 0.3-50 nm. It is a cheap, compact and easily adjusted and has been used for both laser-produced plasma and plasma focus. Preliminary experimental results have been obtained for the plasma x-ray spectrum and the spatial structure both from the laser-produced plasma and the plasma focus.

Probable endothelisation of bare metal stent struts extending from the left main coronary into the aorta

Two post mortem images are presented of a 4.0 9 13 mm Vision bare metal stent, placed in a protected left main coronary artery in a 46 year old male 3 years prior to death from non-cardiac cause. These demonstrate proximal placement of the stent edge into the aorta, with the suggestion on visual inspection that a tissue layer covers the stent struts (Fig. 1a). After fixing, embedding, horizontally sectioning, staining with haematoxylin and eosin (H and E), and imaging according to previously described methods [1] a thin layer of H and E stained tissue surrounds the stent struts (Fig. 1b). Though proof of origin using specific endothelial cell markers has not been technically possible, this tissue appears to be continuous, extending from the left main ostium, and similar to that covering the most proximal stent struts that are completely free within the aorta. Together, these appearances suggest stent-strut endothelialisation (Fig. 1b, c, d). Left main stenting—both bare metal and drug eluting—is being explored as an alternative to coronary bypass surgery in selected cases [2]. While lack of stent-strut endothelialisation is probably a risk factor for stent thrombosis in stents placed entirely within the coronary vasculature [3], proximal stent placement with overlap into the aorta is proposed by some as a technique for left main stenting, without any data as to whether such stent struts undergo endothelialisation. These images suggest for the first time, that endothelialisation of bare metal stents in this context may indeed occur.