Catalyst-assisted hydride vapor phase epitaxy of GaN nanowires: exceptional length and constant rod-like shape capability.

The hydride vapor phase epitaxy (HVPE) process exhibits unexpected properties when growing GaN semiconductor nanowires (NWs). With respect to the classical well-known methods such as metal organic vapor phase epitaxy and molecular beam epitaxy, this near-equilibrium process based on hot wall reactor technology enables the synthesis of nanowires with a constant cylinder shape over unusual length. Catalyst-assisted HVPE shows a record short time process (less than 20 min) coupled to very low precursor consumption. NWs are grown at a fast solidification rate (50 µm h(-1)), facilitated by the high decomposition frequency of the chloride molecules involved in the HVPE process as element III precursors. In this work growth temperature and V/III ratio were investigated to determine the growth mechanism which led to such long NWs. Analysis based on the Ni-Ga phase diagram and the growth kinetics of near-equilibrium HVPE is proposed.

Fast growth synthesis of GaAs nanowires with exceptional length.

We report the first synthesis of GaAs nanowires (NWs) by Au-assisted vapor-liquid-solid (VLS) growth in the novel hydride vapor phase epitaxy (HVPE) environment. Forty micrometer long rodlike <111> monocrystalline GaAs nanowires exhibiting a cubic zinc blende structure were grown in 15 min with a mean density of 10(6) cm(-2). The synthesis of such long figures in such a short duration could be explained by the growth physics of near-equilibrium HVPE. VLS-HVPE is mainly based on solidification after direct and continuous feeding of the arsenious and GaCl growth precursors through the Au-Ga liquid catalyst. Fast solidification (170 microm/h) is then assisted by the high decomposition frequency of GaCl. This predominant feeding through the liquid-solid interface with no mass and kinetic hindrance favors axial rather than radial growth, leading to twin-free nanowires with a constant cylinder shape over unusual length. The achievement of GaAs NWs several tens of micrometers long showing a high surface to volume ratio may open the field of III-V wires, as already addressed with ultralong Si nanowires.

Induction of LFA-1 independent human B cell proliferation and differentiation by binding of CD40 with its ligand.

Engagement of CD40 on resting B cells in the presence of IL-4 triggers B cell proliferation, differentiation and homotypic adhesion. This study was designed to investigate the role of LFA-1/ICAM-1 interactions in homotypic adhesion and proliferation of CD40-activated human B lymphocytes. Freshly isolated B cells were cultured in vitro in the presence of IL-4 and of L cells expressing CD40L, the CD40 ligand. The addition to the culture medium of LFA-1 and ICAM-1 antibodies inhibited homotypic B lymphocyte adhesion. However, these antibodies failed to affect B lymphocyte proliferation and antibody production. These results indicate that aggregation and proliferation are independent events although both induced by CD40 activation.

Use of hu-IgG-SCID mice to evaluate the in vivo stability of human monoclonal IgG antibodies.

Human and in vitro modified mAbs such as humanized rodent mAbs and immunotoxins are now considered for a variety of applications in humans. The adequate in vivo stability of these Ig preparations is not easily predicted from in vitro studies and may be essential for many therapeutic applications. In this study, we report the development and characterization of an in vivo model for testing this parameter using SCID mice containing a physiological concentration of human IgG (hu-IgG-SCID). The model was tested with several IgG1 and IgG3 human mAbs reacting with the human Rh(D) red cell antigen. It is known that human IgG have a shorter half-life in SCID mice than in humans. However, our results showed that the half-life of IgG3 mAbs (1.5 +/- 0.5 days) was much shorter than the one of IgG1 mAbs (5.8 +/- 1.4 days), indicating that the relative stability of IgG1 and IgG3 human mAbs in hu-IgG-SCID mice is similar to the one previously reported in humans (21 days vs. 7 days respectively). The IgG catabolism rate in humans is known to be inversely proportional to serum IgG concentrations. Accordingly, the dilution of the mAbs in a large excess (200-fold) of human IgG was found to be an important parameter of the hu-IgG-SCID mouse model since much longer (3-4-fold) mAb half-lives were obtained in the presence of a lower dose or in the absence of co-injected human IgG. This study show the usefulness of this animal model for the evaluation of human antibody stability in an in vivo environment.