Ultrasonic Welding of Novel Carbon/ Elium® Thermoplastic Composites with Flat and Integrated Energy Directors: Lap Shear Characterisation and Fractographic Investigation.

The current research work presents a first attempt to investigate the welding attributes of Elium® thermoplastic resin and the fusion bonding using ultrafast ultrasonic welding technique. The integrated energy director (ED) polymer-matrix composites (PMCs) panel manufacturing was carried out using the Resin Transfer Moulding (RTM) technique and the scheme is deduced to manufacture a bubble-free panel. Integrated ED configurations and flat specimens with Elium® film of different thickness at the interface were investigated for ultrasonic welding optimization. Optimised weld time for integrated ED and flat Elium® panels with film (0.5 mm thick) configuration was found to be 1 s and 5.5 s, respectively. The ED integrated configuration showed the best welding results with a lap shear strength of 18.68 MPa. The morphological assessment has shown significant plastic deformation of Elium® resin and the shear cusps formation, which enhances the welding strength. This research has the potential to open up an excellent and automated way of joining Elium® composite parts in automotive, wind turbines, sports, and many other industrial applications.

Investigation on Ultrasonic Welding Attributes of Novel Carbon/Elium® Composites.

Joining large and complex polymer-matrix composite structures is becoming increasingly important in industries such as automobiles, aerospace, sports, wind turbines, and others. Ultrasonic welding is an ultra-fast joining process and also provides excellent joint quality as a cost-effective alternative to other joining processes. This research aims at investigating the welding characteristics of novel methyl methacrylate Elium®, a liquid thermoplastic resin. Elium® is the first of its kind of thermoplastic resin, which is curable at room temperature and is suitable for mass production processes. The welding characteristics of Elium® composites were investigated by optimizing the welding parameters with specially designed integrated energy directors (ED) and manufactured using the Resin transfer molding process. The results showed a 23% higher lap shear strength for ultrasonically welded composite joints when compared to the adhesively bonded joints. The optimized welding time for the ultrasonic welded joint was found to be 1.5 s whereas it was 10 min for the adhesively bonded joint. Fractographic analysis showed the significant plastic deformation and shear cusps formation on the fractured surface, which are typical characteristics for strong interfacial bonding.

Unaffected contractility of diaphragm muscle fibers in humans on mechanical ventilation.

Several studies have indicated that diaphragm dysfunction develops in patients on mechanical ventilation (MV). Here, we tested the hypothesis that the contractility of sarcomeres, i.e., the smallest contractile unit in muscle, is affected in humans on MV. To this end, we compared diaphragm muscle fibers of nine brain-dead organ donors (cases) that had been on MV for 26 ± 5 h with diaphragm muscle fibers from nine patients (controls) undergoing surgery for lung cancer that had been on MV for less than 2 h. In each diaphragm specimen we determined 1) muscle fiber cross-sectional area in cryosections by immunohistochemical methods and 2) the contractile performance of permeabilized single muscle fibers by means of maximum specific force, kinetics of cross-bridge cycling by rate of tension redevelopment, myosin heavy chain content and concentration, and calcium sensitivity of force of slow-twitch and fast-twitch muscle fibers. In case subjects, we noted no statistically significant decrease in outcomes compared with controls in slow-twitch or fast-twitch muscle fibers. These observations indicate that 26 h of MV of humans is not invariably associated with changes in the contractile performance of sarcomeres in the diaphragm.

Assembly of metal nanoparticles into nanogaps.

The directed assembly of nanoparticles and nanoscale materials onto specific locations of a surface is one of the major challenges in nanotechnology. Here we present a simple and scalable method and model for the assembly of nanoparticles in between electrical leads. Gold nanoparticles, 20 nm in diameter, were assembled inside electrical gaps ranging from 15 to 150 nm with the use of positive ac dielectrophoresis. In this method, an alternating current is used to create a gradient of electrical field that attracts particles in between the two leads used to create the potential. Assembly is achieved when dielectrophoretic forces exceed thermal and electrostatic forces; the use of anchoring molecules, present in the gap, improves the final assembly stability. We demonstrate with both experiment and theory that nanoparticle assembly inside the gap is controlled by the applied voltage and the gap size. Experimental evidence and modeling suggest that a gap-size-dependent threshold voltage must be overcome before particle assembly is realized. Assembly results as a function of frequency and time are also presented. Assembly of fewer than 10 isolated particles in a gap is demonstrated. Preliminary electrical characterization reveals that stable conductance of the assembled particles can be achieved.

The nitrodibenzofuran chromophore: a new caging group for ultra-efficient photolysis in living cells.

Photochemical uncaging of bio-active molecules was introduced in 1977, but since then, there has been no substantial improvement in the properties of generic caging chromophores. We have developed a new chromophore, nitrodibenzofuran (NDBF) for ultra-efficient uncaging of second messengers inside cells. Photolysis of a NDBF derivative of EGTA (caged calcium) is about 16-160 times more efficient than photolysis of the most widely used caged compounds (the quantum yield of photolysis is 0.7 and the extinction coefficient is 18,400 M(-1) cm(-1)). Ultraviolet (UV)-laser photolysis of NDBF-EGTA:Ca(2+) rapidly released Ca(2+) (rate of 20,000 s(-1)) and initiated contraction of skinned guinea pig cardiac muscle. NDBF-EGTA has a two-photon cross-section of approximately 0.6 GM and two-photon photolysis induced localized Ca(2+)-induced Ca(2+) release from the sarcoplasmic recticulum of intact cardiac myocytes. Thus, the NDBF chromophore has great promise as a generic and photochemically efficient protecting group for both one- and two-photon uncaging in living cells.

Kinetics of cardiac thin-filament activation probed by fluorescence polarization of rhodamine-labeled troponin C in skinned guinea pig trabeculae.

A genetically engineered cardiac TnC mutant labeled at Cys-84 with tetramethylrhodamine-5-iodoacetamide dihydroiodide was passively exchanged for the endogenous form in skinned guinea pig trabeculae. The extent of exchange averaged nearly 70%, quantified by protein microarray of individual trabeculae. The uniformity of its distribution was verified by confocal microscopy. Fluorescence polarization, giving probe angle and its dispersion relative to the fiber long axis, was monitored simultaneously with isometric tension. Probe angle reflects underlying cTnC orientation. In steady-state experiments, rigor cross-bridges and Ca2+ with vanadate to inhibit cross-bridge formation produce a similar change in probe orientation as that observed with cycling cross-bridges (no Vi). Changes in probe angle were found at [Ca2+] well below those required to generate tension. Cross-bridges increased the Ca2+ dependence of angle change (cooperativity). Strong cross-bridge formation enhanced Ca2+ sensitivity and was required for full change in probe position. At submaximal [Ca2+], the thin filament regulatory system may act in a coordinated fashion, with the probe orientation of Ca2+-bound cTnC significantly affected by Ca2+ binding at neighboring regulatory units. The time course of the probe angle change and tension after photolytic release [Ca2+] by laser photolysis of NP-EGTA was Ca2+ sensitive and biphasic: a rapid component approximately 10 times faster than that of tension and a slower rate similar to that of tension. The fast component likely represents steps closely associated with Ca2+ binding to site II of cTnC, whereas the slow component may arise from cross-bridge feedback. These results suggest that the thin filament activation rate does not limit the tension time course in cardiac muscle.

Tuning caged calcium: photolabile analogues of EGTA with improved optical and chelation properties.

The physico-chemical properties of several Ca(2+)-selective, photolabile chelators are described. These molecules have been developed as part of an effort to produce a caged Ca(2+) that improved upon the Ca(2+) chelation properties and light absorption capability of nitrophenyl-EGTA (NP-EGTA). Four dimethoxy-ortho-nitrophenyl derivatives of EGTA (called DMNPE-1 through -4), and one analogue of EGTA (DMNPE-5) have been characterized, each of which is bisected upon irradiation. One of these cages has a higher affinity than NP-EGTA: DMNPE-4 has a K(d) for Ca(2+) of 48 nm at pH 7.2 (19 nM at pH 7.4). Furthermore, this cage has a large extinction coefficient of 5120 M(-1)cm(-1) at 350 nm (cf. 975 M(-1)cm(-1) for NP-EGTA). The other physico-chemical properties of DMNPE-4 are: quantum yield of photolysis of 0.09; bipasic Ca(2+) release kinetics (70% released with a rate of about 48,000 s(-1) and 30% at 1.5s(-1)) and photoproducts that bind Ca(2+) with very low affinity (K(d) in the range of 2mM, pH 7.2), hence most of the bound Ca(2+) is released rapidly and efficiently upon photolysis. Thus, DMNPE-4 has a unique combination of properties that make it an extremely effective Ca(2+) cage.

Activation kinetics of skinned cardiac muscle by laser photolysis of nitrophenyl-EGTA.

The kinetics of Ca(2+)-induced contractions of chemically skinned guinea pig trabeculae was studied using laser photolysis of NP-EGTA. The amount of free Ca(2+) released was altered by varying the output from a frequency-doubled ruby laser focused on the trabeculae, while maintaining constant total [NP-EGTA] and [Ca(2+)]. The time courses of the rise in stiffness and tension were biexponential at 23 degrees C, pH 7.1, and 200 mM ionic strength. At full activation (pCa < 5.0), the rates of the rapid phase of the stiffness and tension rise were 56 +/- 7 s(-1) (n = 7) and 48 +/- 6 s(-1) (n = 11) while the amplitudes were 21 +/- 2 and 23 +/- 3%, respectively. These rates had similar dependencies on final [Ca(2+)] achieved by photolysis: 43 and 50 s(-1) per pCa unit, respectively, over a range of [Ca(2+)] producing from 15% to 90% of maximal isometric tension. At all [Ca(2+)], the rise in stiffness initially was faster than that of tension. The maximal rates for the slower components of the rise in stiffness and tension were 4.1 +/- 0.8 and 6.2 +/- 1.0 s(-1). The rate of this slower phase exhibited significantly less Ca(2+) sensitivity, 1 and 4 s(-1) per pCa unit for stiffness and tension, respectively. These data, along with previous studies indicating that the force-generating step in the cross-bridge cycle of cardiac muscle is marginally sensitive to [Ca(2+)], suggest a mechanism of regulation in which Ca(2+) controls the attachment step in the cross-bridge cycle via a rapid equilibrium with the thin filament activation state. Myosin kinetics sets the time course for the rise in stiffness and force generation with the biexponential nature of the mechanical responses to steps in [Ca(2+)] arising from a shift to slower cross-bridge kinetics as the number of strongly bound cross-bridges increases.

Morphology control in self-assembled monolayers written by dip pen nanolithography.

Here, we describe the effect of writing speed in dip pen nanolithography on the morphology (height and density) of self-assembled monolayers of alkanethiols on gold surfaces. The analysis of atomic force microscopy images of written monolayers shows that molecules assemble according to a nucleation and growth mechanism. Slow writing speeds lead to dense monolayers that can be used either to direct the self-assembly of metal nanoparticles or as masks for selective etching of conductive gold nanowires.

Stretch-induced calcium release in smooth muscle.

Smooth muscle cells undergo substantial increases in length, passively stretching during increases in intraluminal pressure in vessels and hollow organs. Active contractile responses to counteract increased transmural pressure were first described almost a century ago (Bayliss, 1902) and several mechanisms have been advanced to explain this phenomenon. We report here that elongation of smooth muscle cells results in ryanodine receptor-mediated Ca(2+) release in individual myocytes. Mechanical elongation of isolated, single urinary bladder myocytes to approximately 120% of slack length (DeltaL = 20) evoked Ca(2+) release from intracellular stores in the form of single Ca(2+) sparks and propagated Ca(2+) waves. Ca(2+) release was not due to calcium-induced calcium release, as release was observed in Ca(2+)-free extracellular solution and when free Ca(2+) ions in the cytosol were strongly buffered to prevent increases in [Ca(2+)](i). Stretch-induced calcium release (SICR) was not affected by inhibition of InsP(3)R-mediated Ca(2+) release, but was completely blocked by ryanodine. Release occurred in the absence of previously reported stretch-activated currents; however, SICR evoked calcium-activated chloride currents in the form of transient inward currents, suggesting a regulatory mechanism for the generation of spontaneous currents in smooth muscle. SICR was also observed in individual myocytes during stretch of intact urinary bladder smooth muscle segments. Thus, longitudinal stretch of smooth muscle cells induces Ca(2+) release through gating of RYR. SICR may be an important component of the physiological response to increases in luminal pressure in smooth muscle tissues.