We present the dc performance of a high-quantum-efficiency GaNAsSb/GaAs p-i-n waveguide photodetector. GaNAsSb with N and Sb contents of 3.3% and 8%, respectively, is sandwiched by AlGaAs/GaAs cladding layers. Two types of device epilayer structures, i.e., with and without AlGaAs cladding layer, show high responsivity values of 0.72 and 0.55 A/W, respectively, at a reverse bias voltage of 10 V and a wavelength of 1.3 μm. These correspond to internal quantum efficiencies of 96.7% and 73.9%, respectively. A linear increase in photocurrent with an increase in optical power up to 8 mW and also a high reverse breakdown voltage of -16.6 V were obtained.

The authors report the demonstration of high-speed GaNAsSb/GaAs p-i -n waveguide photodetector grown by molecular beam epitaxy technique. A 0.4- m-thick GaNAsSb core layer with 3.3% of N and 8% of Sb for detection wavelength over 1.3 m is sandwiched by GaAs and AlGaAs cladding layers. The device exhibits a record value of cutoff frequency of 16.5 GHz.

We present the dc performance of a high-quantum-efficiency GaNAsSb/GaAs p-i-n waveguide photodetector. GaNAsSb with N and Sb contents of 3.3% and 8%, respectively, is sandwiched by AlGaAs/GaAs cladding layers. Two types of device epilayer structures, i.e., with and without AlGaAs cladding layer, show high responsivity values of 0.72 and 0.55 A/W, respectively, at a reverse bias voltage of 10 V and a wavelength of 1.3 mu m. These correspond to internal quantum efficiencies of 96.7% and 73.9%, respectively. A linear increase in photocurrent with an increase in optical power up to 8 mW and also a high reverse breakdown voltage of -16.6 V were obtained.

This paper reports on an easy and quick planarization and passivation technique of III–V compound semiconductor compatible with nanoscale devices. Vertical etching requires good sidewalls passivation to reduce drastically the leakage current and to obtain a good planarization of the devices for metal connection. This novel technique offers the capability to planarize all the different compounds in the entire wafer independently of the height of the structure to be connected. This method uses the HSQ properties (fluidity, solidification to silica film by using O2 plasma treatment, negative tone e-beam lithography resist, low-k dielectric, etc.) to planarize and to passivate all the devices at once. We applied this quick and easy method to InP digital optical switches. We demonstrated photonic switches with high yield (>90%), high breakdown voltage (>30V), low ohmic contact resistance (8Ω) and a low leakage current (21pA/μm2 for 5V reversed bias).

Platelet adhesion to subendothelial types I and III collagens exposed upon vascular injury plays a crucial role in hemostasis and thrombosis. We previously identified a KOGEOGPK sequence (O for hydroxyproline) within type III collagen interacting with platelets, and demonstrated a strong inhibitory effect of the KOGEOGPK peptide on human platelet interactions with type III collagen in vitro. In the present study, we tested the antithrombotic effect of KOGEOGPK in vivo. In a mouse model of pulmonary thromboembolism induced by intravenous injection of type III collagen and epinephrine, prior administration of 80 mg/kg KOGEOGPK reduced by 50% the size of thrombi embolized in lungs, compared to vehicle-treated mice (p < 0.0001). In a mouse model of photochemically induced lesion of caecum venules and arterioles, intravenous injection of 80 mg/kg KOGEOGPK decreased by 76% the occurrence of arteriole occlusion 45 min after vascular injury (p < 0.05). A moderate antithrombotic effect of KOGEOGPK was also observed in the injured venules. In addition, intracardiac injection of KOGEOGPK had no effect on the tail bleeding time. These findings demonstrate a substantial contribution of platelet interactions with the type III collagen-related KOGEOGPK sequence in thrombus formation in vivo with preferential involvement in arterial thrombosis.

InGaAsP/InP micro-waveguides are fabricated by a deep (>3 mum) Reactive Ion Etching. The devices losses are measured by the Fabry-Perot technique for guide width contained between 10 mum and 0.5 mum. The measured losses range from 2 dB/mm to 14 dB/mm. (C) 2004 Wiley Periodicals, Inc.

Platelet adhesion to vascular collagens is an essential step in the initiation of hemostasis and thrombosis. Several platelet receptors interact with type I and type III collagens, including GP Ia/IIa and GP VI. We recently described a new platelet receptor (TIIICBP) specific for a type III collagen-related primary binding sequence, the KOGEOGPK octapeptide. Here, we characterize platelet adhesion to the immobilized octapeptide and demonstrate that this adhesion 1) is Ca2+ and Mg2+ independent, suggesting a noninvolvement of GP Ia/IIa; 2) is not inhibited by an antibody against GP VI; and 3) triggers platelet protein tyrosine phosphorylation. Whereas TXA2 has minimal effects, released ADP via only P2Y12 potentiates platelet adhesion to the octapeptide. Octapeptide-induced platelet adhesion triggers platelet signaling through tyrosine phosphorylation of the 68 kDa subunit of TIIICBP, Syk, PLCgamma2, and FAK. Tyrosine phosphorylation of the FcR gamma-chain and LAT is also observed but to a lesser extent than with type III collagen, suggesting the requirement of GP VI for full tyrosine phosphorylation of FcR gamma-chain and LAT. The present study provides evidence for a critical role for the type III collagen-related KOGEOGPK octapeptide in mediating platelet adhesion and signaling, and consequently in platelet-collagen interactions.-

Thrombospondin-1 (TSP-1) is an adhesive glycoprotein which, when secreted from alpha-granules of activated platelets, can bind to the cell surface and participate in platelet aggregate formation. In this study, we show that thrombin activation leads to the rapid and specific association of a large amount of secreted alpha-granular TSP-1 with the actin cytoskeleton. This cytoskeletal association of TSP-1 was correlated with platelet secretion, but not aggregation. and was inhibited by cytochalasin D. an inhibitor of actin polymerization. Association of TSP-1 with the actin cytoskeleton was mediated by membrane receptors. as shown by using MAII, a TSP-1-specific monoclonal antibody that inhibited both TSP-1 surface binding to activated platelets and cytoskeletal association. TSP-1 and its potential membrane receptors, e.g. alphaIIbbeta3 integrin, CD36 and CD47, concomitantly associated with the actin cytoskeleton. However, studies on platelets from a patient with type I Glanzmann's thrombasthenia lacking alphaIIbbeta3 and another with barely detectable CD36 showed normal TSP-1 surface expression and association with the actin cytoskeleton. Likewise, no involvement of CD47 in TSP-1 association with the actin cytoskeleton could be inferred from experiments with control platelets using the function-blocking anti-CD47 antibody B6H12. Finally, assembly of signalling complexes. as observed through translocation of tyrosine-phosphorylated proteins and kinases to the actin cytoskeleton, was found to occur in concert with cytoskeletal association of TSP-1. in control platelets as well as in thrombasthenic and CD36-deficient platelets. Our results imply a role for the actin cytoskeleton in the membrane-surface expression process of TSP-1 molecules and suggest a possible coupling of TSP-1 receptors to signalling events occurring independently of alphaIIbbeta3 or CD36. These results provide new insights into the link between surface-bound TSP-1 and the contractile actin microfilament system which may promote platelet aggregate cohesion.

The macromolecular composition of the extracellular matrix (ECM) produced by the human microvascular endothelial cell line (HMEC-1) was determined by ELISA and its thrombogenicity was studied in blood perfusion assays. Results were compared with those obtained with the ECM produced by human umbilical vein endothelial cells (HUVEC). The HMEC-1's ECM contains collagen type IV, fibronectin, laminin and thrombospondin, but no detectable levels of collagen types I, III and VI, or von Willebrand factor (vWF), whereas all these components were found in the ECM synthesized by HUVEC. HMEC-1's ECM was perfused with low-molecular-weight heparin-anticoagulated blood at two wall shear rates (650/s and 2,600/s), representative of moderate and high arterial wall shear rates, in parallel plate flow chambers for 5 min. This resulted in the formation of large platelet aggregates, compared to essentially a monolayer of adherent platelets on HUVEC's ECM. Interestingly, large thrombi were formed at 2,600/s when HMEC-1's ECM was perfused with the blood of a patient with severe type III von Willebrand disease lacking both plasma and platelet vWF, indicating that vWF was not absolutely required for thrombus formation on this matrix. Thrombin generated on the HMEC-1's ECM contributed importantly to the large platelet thrombi formed, shown by performing blood perfusion experiments in the presence of thrombin inhibitors. Our results indicate that 1) platelet adhesion and aggregate formation on a subendothelium may occur at a high shear rate (2600/s) without the participation of collagen types I, III and VI, and vWF; and 2) the HMEC-1 cell line may prove useful for in vitro studies of the thrombogenic properties of microvascular subendothelium which in most cases does not contain fibrillar collagens and vWF.

We have evaluated the relative contribution of the adhesive ligands, von Willebrand factor (vWF), fibrinogen (Fg) and thrombospondin (TSP), all surface-expressed on washed platelets (WP) activated with a threshold thrombin concentration (approximately 0.04 U/ml), to platelet microaggregation (PA) at shear rates (G) from 300-2000 s(-1). In suspensions of thrombin-activated WP sheared immediately (tau0), all three ligands were required for optimal aggregation at all G, as shown by a 50-70% inhibition of capture efficiencies of PA (measured from initial rates of PA), by antibodies (Abs) directed against each protein. This aggregation involved both GPIb and GPIIbIIIa, as indicated by approximately 80% and 100% inhibition by Ab 6D1 and Ab 10E5, respectively. For WP preexposed to thrombin for 10 min to ensure maximal surface expression of secreted ligands and activated GPIIbIIIa (tau0), vWF was predominantly required at all G (63-75% inhibition by anti-vWF Ab), together with TSP (35-50% inhibition by anti-TSP Ab). Under these conditions, Fg was extensively converted to fibrin, so that fibrin, rather than Fg, could participate in microaggregation, with GPIb less required than GPIIbIIIa as indicated by a 30-60% inhibition by Ab 6D1 as compared to 100% inhibition by Ab 10E5. Our results show that interactions between multiple ligands and receptors favour microaggregation depending on shear and thrombin activation conditions.

SummaryTIIICBP is a new platelet receptor involved in platelet-type III collagen and platelet-subendothelium interactions. This receptor is composed of a doublet of 72-68 kDa proteins. In this study, the major protein (68 kDa) was purified and used to produce monoclonal antibodies. One of these antibodies, 7F4, binds to platelets as confirmed by flow cytometry. 7F4 inhibited platelet contact, spreading and aggregation induced by type III collagen. Under flow conditions, 7F4 prevented platelet interactions with type III collagen, endothelial cell matrix and the KOGEOGPK type III collagen octapeptide: the specific sequence recognized by TIIICBP. On the other hand, 7F4 had no effect on platelet-type I collagen interactions. TIIICBP was also detected on lymphocytes, granulocytes and monocytes. TIIICBP was expressed on endothelial cells and fibroblasts but not on smooth-muscle cells. These results show that TIIICBP is expressed on several cell types and participates in cell adhesion to the subendothelium.

Thrombospondin-l (TSP) may, after secretion from platelet Lu granules, participate in platelet aggregation, but its mode of action is poorly understood. We evaluated the capacity of TSP to form inter-platelet crossbridges through its interaction with fibrinogen (Fg), using either Fg-coated beads or Fg bound to the activated GPIIbIIIa integrin (GPIIbIIIa*) immobilized on beads or on activated fixed platelets (AFP), i.e. in a system free of platelet signaling and secretion mechanisms. Aggregation at physiological shear rates (100-2000 s(-1)) was studied in a microcouette device and monitored by flow cytometry. Soluble TSP bound to and induced aggregation of Fg-coated beads dose-dependently, which could be blocked by the amino-terminal heparin-binding domain of TSP, TSP18. Soluble TSP did not bind to GPIIbIIIa*- coated beads or AFP, unless they were preincubated with Fg. The interaction of soluble TSP with Fg-GPIIbIIIa'''-coated beads or Fg-AFP resulted in the formation of aggregates via Fg-TSP-Fg cross-bridges, as demonstrated in a system where direct cross-bridges mediated by GPIIbIIIa*'-Fg on one particle and free GPIIbIIIa* on a second particle were blocked by the RGD mimetic Ro 44-9885. Soluble TSP increased the efficiency of Fg-mediated aggregation of AFP by 30-110% over all shear rates and GPIIbIIIa* occupancies evaluated. Surprisingly, TSP binding to Fg already bound to its GPIIbIIIa* receptor appears to block the ability of this occupied Fg to recognize another GPIIbIIIa* receptor, but this TSP can indeed cross-bridge to another Fg molecule on a second platelet. Finally, TSP-coated beads could directly coaggregate at shear rates from 100 to 2000 s(-1). Our studies provide a model for the contribution of secreted TSP in reinforcing inter-platelet interactions in flowing blood, through direct Fg-TSP-Fg and TSP-TSP cross-bridges.

Previous studies using whole blood perfusion through flow chambers have suggested that unactivated platelets can adhere to surface immobilized fibrinogen (Fg). However, the red blood cells needed for surface delivery of the platelets may activate platelets by released adenosine diphosphate (ADP). Our studies of coaggregation of unactivated or ADP-activated platelets with Fg-coated latex beads in flowing suspensions show that only preactivated platelets can adhere to Fg-coated surfaces.

The degradation of extracellular matrix (ECM) adhesive glycoproteins, fibronectin (FN), thrombospondin (TSP) and von Willebrand factor (vWF), by human leukocyte cathepsin G and elastase, and by plasmin or thrombin, was analysed by immunoblotting after incubation of physiologic doses of the proteases with confluent human umbilical vein endothelial cells. Elastase induced an almost complete disappearance of intact FN, TSP, and vWF from the ECM at 0.02 units/ml within 5 minutes of incubation at 37°C. Plasmin (0.2 units/ml) was also active on all three substrates, whereas cathepsin G (0.2 units/ml) had a preferential effect on TSP. Most remarkably, these degradations occurred with no apparent change in endothelial cell morphology, as shown by phase-contrast microscopy. In contrast, thrombin (0.2 units/ml) had no apparent proteolytic action on ECM glycoproteins, where it induced cell retraction and rounding. The release of adhesive glycoproteins from the ECM was accompanied by the detection of proteolytic fragments in the conditioned medium. Kinetic studies indicated that proteolysis started within minutes and proceeded for at least 1 hour. TSP was extremely sensitive to degradation by all enzymes except thrombin, whereas vWF released from the ECM was more resistant to proteolysis than constitutively secreted vWF, and FN was poorly degraded by plasmin. Our results indicate that serine proteinases, locally produced during inflammation and/or thrombolysis, can release extracellular matrix components and generate proteolytic fragments with potential biological activities.

The kinetics of adhesion of platelets to fibrinogen (Fg) immobilized on polystyrene latex beads (Fg-beads) was determined in suspensions undergoing Couette flow at well-defined homogeneous shear rates. The efficiency of platelet adhesion to Fg-beads was compared for ADP-activated versus "resting" platelets. The effects of the shear rate (100–2000 s−1), Fg density on the beads (24–2882 Fg/μm2), the concentration of ADP used to activate the platelets, and the presence of soluble fibrinogen were assessed. "Resting" platelets did not specifically adhere to Fg-beads at levels detectable with our methodology. The apparent efficiency of platelet adhesion to Fg-beads readily correlated with the proportion of platelets "quantally" activated by doses of ADP, i.e., only ADP-activated platelets appeared to adhere to Fg-beads, with a maximal adhesion efficiency of 6–10% at shear rates of 100–300 s−1, decreasing with increasing shear rates up to 2000 s−1. The adhesion efficiency was found to decrease by only threefold when decreasing the density of Fg at the surface of the beads by 100-fold, with only moderate decreases in the presence of physiologic concentrations of soluble Fg. These adhesive interactions were also compared using activated GPIIbIIIa-coated beads. Our studies provide novel model particles for studying platelet adhesion relevant to hemostasis and thrombosis, and show how the state of activation of the platelet and the local flow conditions regulate Fg-dependent adhesion.

The adhesion of a human microvascular endothelial cell line to its own matrix was studied in comparison with adhesion of the same cells to fibronectin or thrombospondin-1. These endothelial cells adhered preferentially to their matrix whereas an equal cell number was attached to fibronectin or thrombospondin-1. The adhesion of cells to thrombospondin-1 was mediated by the N-terminal heparin binding domain of thrombospondin-1 as shown by the use of a recombinant fragment, N18. Cells adhering to their matrix displayed a morphology and a cytoskeleton organization very similar to that observed in vivo with an apical immunostaining for actin stress fibers and a fine basal labeling for vinculin. Cells on fibronectin were extensively spread and rapidly assembled stress fibers and focal contacts. Cells adherent to thrombospondin-1 presented large lamellae rich in actin but devoid of vinculin and only few actin fibers were observed. Depending on the substratum used, adhering endothelial cells displayed also different tyrosine phosphorylation patterns on electrophoresis. Our observations indicate that endothelial cells adhering to their matrix present an activation state intermediate between that induced by a "hyperadhesive" protein like fibronectin and that generated by a moderate, indeed anti-adhesive, protein like thrombospondin-1.