Biocompatible Lipid‐Coated Persistent Luminescent Nanoparticles for In Vivo Imaging of Dendritic Cell Migration

Dendritic cell (DC)‐based vaccines for immunotherapy have already achieved promising results in the last decade. To further improve current treatment protocols and enhance the therapeutic outcome, noninvasive in vivo tracking of DCs remains of crucial importance. Persistent luminescent nanoparticles (PLNPs) are inorganic materials which show an afterglow for hours after the optical excitation has ceased. If the afterglow is in the near‐infrared, the emission of injected particles can be tracked in vivo. However, stability and toxicity issues limit the use of bare PLNPs for biological applications. Therefore, appropriate surface functionalization is needed to improve their biocompatibility. In this study, it is demonstrated that near‐infrared light emitting LiGa₅O₈:Cr³⁺ nanoparticles can be functionalized with a biocompatible lipid coating which provides them with outstanding stability in biological media. In vitro experiments show efficient uptake, absence of cytotoxicity even at very high particle concentrations, and no adverse effects on the maturation potential of DCs. DCs labeled with lipid‐coated LiGa₅O₈:Cr³⁺ nanoparticles injected in mice can be imaged over days, confirming efficient in vivo migration to the popliteal lymph node. Together the results show that lipid coated LiGa₅O₈:Cr³⁺ nanoparticles possess excellent possibilities for further use in research and development of DC based vaccines.     

Deep SiC etching with RIE

SiC is currently an important topic in power devices. This new technology leads to lower power losses, faster switching, and higher working temperature. The design of SiC power devices requires the integration of edge termination techniques to obtain a high blocking voltage. The mesa structure approach is one well-established method. It could be used alone or in combination with a Junction Termination Extension (JTE). The mesa consists of a structure that removes material around the pn-junction. Due to the strong Si–C bonds, conventional chemical–wet etching solutions are inefficient on SiC, so plasma methods are required to etch SiC.The presented work is based on the use of an RIE reactor with an SF₆/ O₂ plasma. Its geometry structure and parameters were optimized. An etch rate of 0.35 μm/min was obtained without any trenching phenomenon. Trenches deeper than 10 μm deep were realized with a nickel etching mask that shows a high selectivity. AFM analysis revealed an etched surface as smooth as the initial one.     

Crystallization and glass properties of pentitols

Thermodynamic and dynamic data of the four pentitols, xylitol, adonitol, l-arabitol and d-arabitol, measured by temperature modulated DSC (TMDSC) in the crystalline and amorphous states are presented. The properties of the supercooled liquids clearly show two distinct kinds of thermal behaviors with regard to their aptitude to crystallize. The capacity of the TMDSC technique to characterize both the molecular mobility and the thermal behavior is used to analyze the stability of the supercooled liquid state of the compounds. The comparison between the pentitols shows that the crystallization processes are mainly dominated by the interfacial energy rather than by a competition between the thermodynamic driving force and the molecular mobility. This revised version was published online in July 2006 with corrections to the Cover Date.     

Onset of slow dynamics in difluorotetrachloroethane glassy crystal

Complementary neutron spin-echo and x-ray experiments and molecular-dynamics simulations have been performed on difluorotetrachloroethane (CFCl2-CFCl2) glassy crystal. Static, single-molecule reorientational dynamics and collective dynamics properties are investigated. Our results confirm the strong analogy between molecular liquids and plastic crystals. The orientational disorder is characterized at different temperatures and a change in the nature of rotational dynamics is observed. A careful check of the rotational diffusion model is performed using self-angular correlation functions Cl with high l values and compared to results obtained on molecular liquids composed of A-B dumbbells. Below the crossover temperature at which slow dynamics emerge, we show that some scaling predictions of the mode coupling theory hold and that alpha-relaxation times and nonergodicity parameters are controlled by the nontrivial static correlations.     

Transformations of crystalline sugars upon milling

In this paper we compare the solid-state transformations upon room temperature milling of four sugars: lactose, trehalose, mannitol and sorbitol. The two disaccharides (lactose and trehalose) are found to undergo a direct transformation from crystal to glass while the two sugar alcohols (mannitol and sorbitol) are found to undergo polymorphic transformations. The origin of these different behaviors is discussed and ascribed to the relative position of the glass transition temperature (T _g) of the amorphous states with respect to the milling temperature. This point was also finely studied through co-milling experiments of lactose and mannitol. These two compounds having their glass transition respectively above and below room temperature the T _g of the mixture can be conveniently tuned on either side of the milling temperature by varying the concentrations.     

Dynamics of the amorphous and crystalline alpha-, gamma-phases of indomethacin

Crystallization processes in indomethacin can be observed below Tg leading to different forms depending on the thermal treatment: a rapid and deep quench below Tg leads to the metastable alpha-phase and a slow cooling close to Tg gives rise to the stable gamma-phase. To understand this atypical behavior, we have studied the molecular mobility of the amorphous and crystalline forms of indomethacin by dielectric relaxation and 1H NMR spectroscopy. Two relaxations were detected in the glassy state obtained from the deeply quenched liquid. One, also present in the gamma-phase, was attributed to local rotations. The other one, of very low amplitude, was attributed to the Johari-Goldstein relaxation. The results allowed to discuss the relationship between these two relaxation processes and the crystallization properties of amorphous indomethacin.     

Two-color pump-probe experiments in helium using high-order harmonics

A pump-probe technique has been applied for measuring the lifetimes and absolute photoionization cross-sections of excited He states. The 1s2p ¹P and 1s3p ¹P states of He are excited by using the 13th and the 14th harmonic, respectively, of a tunable 70 ps dye laser generated in a Kr gas jet. The states are ionized after a varying time delay, by absorption of probe photons with energies between 1.6 and 4.5 eV. Lifetimes of τ(1s2p) = 0.57 ns and τ(1s3p) = 1.76 ns are determined with a precision of about 15%. A significant enhancement of the number of ions present in the lifetime curves at zero time delay for pressures above 6×10^-5 mbar is attributed to direct two-photon ionization of He in combination with AC Stark broadening of the excited state and absorption of the XUV light in the medium. Absolute photoionization cross-sections from the He 1s2p ¹P and He 1s3p ¹P states in the threshold region are determined by measuring the saturation of the ionization process with a precision of ∼ 25%. In addition, the variation of the relative orientation between the polarization vectors of the pump and probe beams enables the determination of partial photoionization cross-sections. Received 3 June 2002 / Received in final form 14 August 2002 Published online 22 October 2002 RID="a" ID="a"Present address: Department of Biophysics, Leiden University, 2333 CA Leiden, The Netherlands. RID="b" ID="b"Present address: Continuum Electro-Optics Inc., 3150 Central Expressway, Santa Clara, CA 95051, USA. RID="c" ID="c"Present address: CEA/DRECAM/SPAM, CEN Saclay, 91105 Gif-sur-Yvette, France. RID="d" ID="d"Present address: Department of Physics, National University of Rwanda, Butare, Rwanda. RID="e" ID="e"Present address: CELIA, Université Bordeaux 1, 33405 Talence, France. RID="f" ID="f"Present address: MAX-Lab, Lund University, Box 118, 221 00 Lund, Sweden. RID="g" ID="g"e-mail: anne.lhuillier@fysik.lth.se     

Does the interaction potential determine both the fragility of a liquid and the vibrational properties of its glassy state?

By performing molecular dynamics simulations of binary Lennard-Jones systems with three different potentials, we show that the increase of anharmonicity and capacity for intermolecular coupling of the potential is the cause of (i) the increase of kinetic fragility and nonexponentiality in the liquid state, and (ii) the T(g)-scaled temperature dependence of the nonergodicity parameter determined by the vibrations at low temperatures in the glassy state. Naturally, these parameters correlate with each other, as observed experimentally by T. Scopigno et al. [Science 302, 849 (2003)]     

Contribution of Temperature Modulated DSC® to the Study of the Molecular Mobility in Glass Forming Pharmaceutical Systems

The temperature modulated differential scanning calorimetry (MDSC^®) technique has been used to characterise the low frequency molecular mobility of indomethacin and maltitol just above their respective calorimetric glass transition temperatureT _g. Analysis has been made using the concept of complex specific heat. Spectroscopic information are thus obtained through the temperature dependence of the isochronal real and imaginary parts C′ and C″. This gives access to the fragility index m and the stretched exponent β. The comparison with dielectric spectroscopy has been performed to check the coherence of spectroscopic information. Measurements on maltitol enable to demonstrate the useful complementarity of the technique when the low frequencies dielectric relaxations are occulted by the presence of conductors default.     

Interactions underpinning the plasticization of a polymer matrix: a dynamic and structural analysis of DMP-plasticized cellulose acetate

This work establishes that the plasticization effect of a classical petrochemical plasticizer, dimethyl phthalate (DMP), on a polymer matrix, cellulose acetate (CA), is due to the development of intermolecular interactions of dipolar type. Plasticized cellulose acetate films are studied with regard to the interactions between the polymer and plasticizer at the macroscopic scale by thermogravimetric analysis and differential scanning calorimetry. At the molecular level, Fourier transform infrared spectroscopy and dielectric relaxation spectroscopy are used to elucidate the nature of interactions that are responsible for the plasticizing effects. These static and dynamic complementary analyses evidenced that DMP does not establish H-bonding interactions with the polymer chains of cellulose acetate but rather weaker interactions of dipolar type. These dipole–dipole interactions that develop between acetyl side groups of CA and the ester phthalate moieties of DMP increase the overall mobility of CA chains and also locally influence the molecular mobility and the water uptake tendency.