A Nanoparticle Ink Allowing the High Precision Visualization of Tissue Engineered Scaffolds by MRI.

Hydrogels are widely used as cell scaffolds in several biomedical applications. Once implanted in vivo, cell scaffolds must often be visualized, and monitored overtime. However, cell scaffolds appear poorly contrasted in most biomedical imaging modalities such as magnetic resonance imaging (MRI). MRI is the imaging technique of choice for high-resolution visualization of low-density, water-rich tissues. Attempts to enhance hydrogel contrast in MRI are performed with "negative" contrast agents that produce several image artifacts impeding the delineation of the implant's contours. In this study, a magnetic ink based on ultra-small iron oxide nanoparticles (USPIONs; <5 nm diameter cores) is developed and integrated into biocompatible alginate hydrogel used in cell scaffolding applications. Relaxometric properties of the magnetic hydrogel are measured, as well as biocompatibility and MR-visibility (T1 -weighted mode; in vitro and in vivo). A 2-week MR follow-up study is performed in the mouse model, demonstrating no image artifacts, and the retention of "positive" contrast overtime, which allows very precise delineation of tissue grafts with MRI. Finally, a 3D-contouring procedure developed to facilitate graft delineation and geometrical conformity assessment is applied on an inverted template alginate pore network. This proof-of-concept establishes the possibility to reveal precisely engineered hydrogel structures using this USPIONs ink high-visibility approach.

Effect of Solvent on the Mechanical and Structural Properties of N-Alkyldiamide Organogels.

Here, we study organogels prepared thanks to a new organogelator, the N-oleyldiamide molecule, which shows a remarkable propensity to gelify a large scope of solvents, from aprotic to high protic solvents. The solvent plays a key role in the formation and stability of supramolecular self-assemblies. However, the understanding and the control of its effects can be complex as many parameters are a priori involved. This study aims to understand the effect of solvent on the structures of organogels and on their final mechanical properties. Five solvent classes have been selected ranking from low protic to high protic, according to the Hansen H-bond parameter δh. The solvent proticity appears to be one of the main parameters that affect the organogel internal structure and therefore the final rheological properties. For a given organogelator fraction, the terminal elastic modulus measured by oscillatory rheology is observed to increase significantly with the Hansen H-bond solvent parameter δh. Materials of different mechanical properties are then shown to display various structures, which are investigated thanks to cryo-SEM. Besides, wide-angle X-ray scattering (WAXS) has been used to probe the gelator organization at the molecular scale with regard to the solvent nature, to understand the supramolecular self-assembly of this promising molecule.

Actin Depolymerization in Dedifferentiated Liver Sinusoidal Endothelial Cells Promotes Fenestrae Re-Formation.

Liver sinusoidal endothelial cells (LSECs) possess fenestrae, which are key for the exchange between blood and hepatocytes. Alterations in their number or diameter have important implications for hepatic function in liver diseases. They are lost early in the development of hepatic fibrosis through a process called capillarization. In this study, we aimed to demonstrate whether in vitro dedifferentiated LSECs that have lost fenestrae are able to re-form these structures. Using stimulated emission depletion super-resolution microscopy in combination with transmission electron microscopy, we analyzed fenestrae formation in a model mimicking the capillarization process in vitro. Actin is known to be involved in fenestrae regulation in differentiated LSECs. Using cytochalasin D, an actin-depolymerizing agent, we demonstrated that dedifferentiated LSECs remain capable of forming fenestrae. Conclusion: We provide a new insight into the complex role of actin in fenestrae formation and in the control of their size and show that LSEC fenestrae re-formation is possible, suggesting that this process could be used during fibrosis regression to try to restore exchanges and hepatocyte functions.

Sugar glass fugitive ink loaded with calcium chloride for the rapid casting of alginate scaffold designs.

Alginate-based hydrogels are widely used for the development of biomedical scaffolds in regenerative medicine. The use of sugar glass as a sacrificial template for fluidic channels fabrication within alginate scaffolds remains a challenge because of the premature dissolution of sugar by the water contained in the alginate as well as the relatively slow internal gelation rate of the alginate. Here, a new and simple method, based on a sugar glass fugitive ink loaded with calcium chloride to build sacrificial molds, is presented. We used a dual calcium cross-linking process by adding this highly soluble calcium source in the printed sugar, thus allowing the rapid gelation of a thin membrane of alginate around the sugar construct, followed by the addition of calcium carbonate and gluconic acid δ-lactone to complete the process. This innovative technique results in the rapid formation of "on-demand" alginate hydrogel with complex fluidic channels that could be used in biomedical applications such as highly vascularized scaffolds promoting pathways for nutrients and oxygen to the cells.

STED microscopy: A simplified method for liver sinusoidal endothelial fenestrae analysis.

BACKGROUND INFORMATION: Liver sinusoidal endothelial cells (LSECs) possess fenestrae, open transcellular pores with an average diameter of 100 nm. These fenestrae allow for the exchange between blood and hepatocytes. Alterations in their number or diameter in liver diseases have important implications for hepatic microcirculation and function. Although decades of studies, fenestrae are still observed into fixed cells and we have poor knowledge of their dynamics. RESULTS: Using stimulated emission depletion (STED) super-resolution microscopy, we have established a faster and simplest method to observe and quantify fenestrae. Indeed, using cytochalasin D, an actin depolymerising agent known to promote fenestrae formation, we measure the increase of fenestrae number. We adapted this methodology to develop an automated method to study fenestrae dynamics. Moreover, with two-colour STED analysis, we have shown that this approach could be useful to study LSECs fenestrae molecular composition. CONCLUSIONS: Our approach demonstrates that STED microscopy is suitable for LSEC fenestrae study. SIGNIFICANCE: This new way of analysing LSEC fenestrae will allow for expedited investigation of their dynamics, molecular composition and functions to better understand their function in liver pathophysiology.

Anisotropic Metal Deposition on TiO2 Particles by Electric-Field-Induced Charge Separation.

Deposition of metals on TiO2 semiconductor particles (M-TiO2 ) results in hybrid Janus objects combining the properties of both materials. One of the techniques proposed to generate Janus particles is bipolar electrochemistry (BPE). The concept can be applied in a straightforward way for the site-selective modification of conducting particles, but is much less obvious to use for semiconductors. Herein we report the bulk synthesis of anisotropic M-TiO2 particles based on the synergy of BPE and photochemistry, allowing the intrinsic limitations, when they are used separately, to be overcome. When applying electric fields during irradiation, electrons and holes can be efficiently separated, thus breaking the symmetry of particles by modifying them selectively and in a wireless way on one side with either gold or platinum. Such hybrid materials are an important first step towards high-performance designer catalyst particles, for example for photosplitting of water.

Using STED and ELSM confocal microscopy for a better knowledge of fused silica polished glass interface.

Characteristics and nature of close surface defects existing in fused silica polished optical surfaces were explored. Samples were deliberately scratched using a modified polishing process in presence of different fluorescent dyes. Various techniques including Epi-fluorescence Laser Scanning Mode (ELSM) or STimulated Emission Depletion (STED) confocal microscopy were used to measure and quantify scratches that are sometimes embedded under the polished layer. We show using a non-destructive technique that depth of the modified region extends far below the surface. Moreover cracks of 120 nm width can be present ten micrometers below the surface.

Initiation of laser-induced damage sites in fused silica optical components.

Significant improvement in the polishing process of fused silica optical components has increased their lifetimes at 351 nm. Nevertheless, for large laser facilities like the LaserMegaJoule (LMJ), zero defect optical components are not yet available. Therefore, a damage mitigation technique has been developed to prevent the growth of the laser-initiated damage sites. Because of the difficulty to produce mitigated sites with sufficiently large depth, the initial morphology of damage to mitigate is a critical issue. The aim of this work is to determine laser parameters (pulse duration, fluence) which permit us to initiate damage sites in accordance with our mitigation process. Confocal microscopy is used to observe damage sites that have sub-surface cracks and consequently to measure precisely the diameter and the depth of the area to mitigate.

Novel diode-pumped infrared tunable laser system for multi-photon microscopy.

We report on a novel laser source, emitting high energy (20 nanoJoule) femtosecond pulses, in a broad spectrum (250 nm). This source is easily tuned from 950 to 1200 nm, without any laser adjustment, and delivers sub-300 femtosecond pulses with a 10-nm spectral width.