A layered modular polymeric <Emphasis Type="Italic">μ</Emphasis>-valve suitable for lab-on-foil: design,fabrication, and characterization

Cost-effective fabrication of microfluidic networks require that all components have to be manufactured with up-scalable processes such as reel-to-reel fabrication of foil-based devices. A microvalve design must take into account functional requirements together with manufacturing feasibilities. Here we present the development of a modular polymeric laser structured microvalve. The complete valve structure is designed to be used in a bendable lab-in-foil system. The modular microvalve design consists of three layers: an actuator layer, an interfacing membrane, and a passive microchannel layer to be separately fabricated and then stacked. Different actuator layer concepts are compared out of which a thermal actuation scheme generating sufficient stroke using phase changing paraffin is chosen. The passive layer is designed with a shallow and sufficiently smooth spherical cavity that acts as the valve seat from which paraffin material can reliably retract during solidification. The shape and dimensions of the shallow cavity are derived from the natural membrane deflection and from the channel cross section. It is not essential that all the paraffin within the actuator cavity to be molten for valve closure allowing a high degree of assembly tolerance and inherent sealing of actuator cavity. All the module layers in the current prototype are structured using 3D laser fabrication processes but mass-fabrication methods like reel-to-reel hot-embossing are foreseen as well. A prototype microvalve stack was assembled with a thickness of 1.1 mm which could be further reduced to meet the requirements of extremely flexible lab-on-foil systems. The closed valve is tested up to a pressure of 3 kPa without any measurable leakage. The dynamics of valve closure is evaluated by a new optical characterization method based on image processing of color micrograph sequences taken from the transparent valve.     

Uterine leiomyomata--a feature of acromegaly

In order to assess the prevalence of leiomyomata in patients diagnosed with acromegaly, files of all women so diagnosed were obtained (n = 25). Eight of these patients had undergone hysterectomy. In eight of the remaining patients, assessment of the uterus was performed by gynaecological examination and transvaginal ultrasound. The prevalence of leiomyomata was 81% (13/16) in patients who had undergone hysterectomy (8/8) or who underwent gynaecological examination (5/8). In conclusion, the very high prevalence of leiomyomata in patients diagnosed with acromegaly warrants the inclusion of growth hormone excess as a cause of leiomyomata. Leiomyomata are a feature of the organomegalic syndrome associated with acromegaly.     

Apoptosis of neutrophils

Cercarial behavior patterns were examined in 4 species of frog lung flukes (Haematoloechus spp.). Cercariae of Haematoloechus complexus, Haematoloechus medioplexus, Haematoloechus longiplexus, and Haematoloechus varioplexus were exposed to 3 species of experimental arthropods and an inanimate control. The number of cercariae attached to an experimental host at 5 min postexposure was recorded. Haematoloechus longiplexus and H. complexus cercariae attached to experimental hosts at higher rates than cercariae of H. medioplexus and H. varioplexus. Cercariae of H. longiplexus attached to experimental hosts in approximately the same numbers as H. complexus, but H. longiplexus penetrated only damselfly naiads, and only at the base of the zygopteran caudal gills. Cercariae of H. complexus, a second intermediate host generalist, were able to penetrate and enter several arthropod species at the intersegmental membranes. Haematoloechus medioplexus and H. varioplexus are restricted to development in dragonfly naiads and cercariae rarely attached to and never penetrated experimental hosts. These behavioral patterns dictate the range of hosts suitable for metacercarial development of H. complexus, H. longiplexus, H. medioplexus, and H. varioplexus. The evolution of disparate patterns of behavior among the cercariae of these 4 congeners has directly affected subsequent patterns of transmission to the definitive host.     

Locating objects in wide-area systems

Locating mobile objects in a worldwide system requires a scalable location service. An object can be a telephone or a notebook computer, but also a software or data object, such as a file or an electronic document. Our service strictly separates an object's name from the addresses where it can be contacted. This is done by introducing a location-independent object handle. An object's name is bound to its unique object handle, which, in turn, is mapped to the addresses where the object can be contacted. To locate an object, we need only its object handle. We present a scalable location service based on a worldwide distributed search tree that adapts dynamically to an object's migration pattern to optimize lookups and updates     

Influence of tyrosine phosphorylation on protein interaction with FcgammaRIIa

The cytoplasmic tail of Fc(gamma)RIIa present on human neutrophils shares with other antigen receptors a common amino acid sequence called ITAM (Immunoreceptor Tyrosine-based Activation Motif). After receptor ligation, the tyrosine residues within this motif become phosphorylated. We prepared a recombinant fusion protein of the cytoplasmic tail of Fc(gamma)RIIa (containing the ITAM) with glutathione-S-Transferase (GST-CT) to characterize the phosphorylation of Fc(gamma)RIIa and its ability to interact with other proteins involved in signal transduction. The GST-CT became phosphorylated in the presence of Lyn, Hck and Syk (immunoprecipitated from human neutrophils), but not in the presence of Fgr. Of the active kinases, only Lyn (mainly present in the membrane fraction) was found to associate with the GST-CT in the absence of ATP. This association was also observed in immunoprecipitates of Fc(gamma)RIIa from resting neutrophils, suggesting that Lyn might be the kinase responsible for the initial Fc(gamma)RIIa phosphorylation. Moreover, we observed specific association of Syk and the p85 subunit of PI 3-kinase after incubation of the GST-CT with neutrophil cytosol. This interaction was dependent on tyrosine phosphorylation of the GST-CT. Substitution of 269Tyr by Phe almost completely abolished tyrosine phosphorylation of the fusion protein. Substitution of either 253Tyr or 269Tyr eliminated Syk binding, but only 253Tyr appeared to be essential for p85 binding. We hypothesize that, upon activation, the membrane-associated Lyn is responsible for the initial tyrosine phosphorylation of Fc(gamma)RIIa, thus creating a docking site for Syk and PI 3-kinase.     

A reconfigurable superparamagnetic bead filter for microfluidic detection of bio-material

For a faster and more efficient sensing of highly diluted samples, up-concentration of biological species is often required. Within this framework, we here describe the design, fabrication and first experimental results of a compact microfluidic chip that uses the capture and release of micron-sized superparamagnetic beads for species up-concentration. The beads are captured out of the bypassing flow by soft-magnetic structures embedded in the microchannel that can be magnetized by an external field. Simulations of bead capture are reported for average flow speeds up to 50 mm/s that are equivalent to flow rates of 0.03 μl/s on a single channel. A comparison between the experimental results obtained with an average flow speed of 4.44 mm/s (flow rate of about 0.028 μl/s) and finite element method (FEM) simulations of the bead capture is shown. From the obtained results we can conclude that an up-scaled version of such a chip could easily scan fluids with flow rates above 1 μl/s.     

Essentially asymptotically stable homoclinic networks

Melbourne [An example of a nonasymptotically stable attractor, Nonlinearity 4(3) (1991), pp. 835–844] discusses an example of a robust heteroclinic network that is not asymptotically stable but which has the strong attracting property called essential asymptotic stability. We establish that this phenomenon is possible for homoclinic networks, where all heteroclinic trajectories are symmetry related. Moreover, we study a transverse bifurcation from an asymptotically stable to an essentially asymptotically stable homoclinic network. The essentially asymptotically stable homoclinic network turns out to attract all nearby points except those on codimension-one stable manifolds of equilibria outside the homoclinic network.     

Polycystic ovary syndrome - from gynaecological curiosity to multisystem endocrinopathy

In order to study the effect of cytochrome P-450 isozyme induction on the pharmacokinetics and metabolism of diltiazem (DTZ), male Sprague-Dawley rats weighing 300-600 g were randomly assigned to two groups. The enzyme induction group (n = 4) received phenobarbital 60 mg/kg i.p. once daily for 4 days, whereas the control group (n = 6) received normal saline for the same duration. Each rat then received a single oral dose of DTZ in solution (20 mg/kg). Blood samples (0.5 ml) were collected from each rat via an implanted polyethylene catheter (0.040" i.d.) in the right carotid artery at 0 (just before dosing), 0.25, 0.5, 1,2,3,4,6,8 and 10 h post-dose. Arterial plasma concentrations of DTZ and its metabolites M(A), M1, M2, M4 and M6 were determined by HPLC. Pharmacokinetics parameters were calculated using non-linear regression. The results showed that both mean Cmax and AUC of DTZ were lower (871.6 vs 79.8 ng/ml; 1171 vs 101.9 ng-h/ml), but the mean Cmax of the primary metabolites M1 and M(A) was higher after phenobarbital (M1 413.0 vs 648.9 ng/ml; M(A) 683.0 vs 814.8 ng/ml). The highest increase was seen in the mean Cmax and AUC of the secondary metabolite M2 (837.5 vs 2585.7 ng/ml; 3312.1 vs 13156.5 ng-h/ml). In contrast, plasma concentrations of the O-desmethylated metabolites M4 and M6 did not increase after phenobarbital. These results suggest that both deacetylation and N-demethylation of DTZ in rats are catalyzed by drug metabolizing enzymes inducible by phenobarbital.