Controlled interfacial assembly of 2D curved colloidal crystals and jammed shells

Assembly of colloidal particles on fluid interfaces is a promising technique for synthesizing two-dimensional micro-crystalline materials useful in fields as diverse as biomedicine1, materials science2, mineral flotation3 and food processing4. Current approaches rely on bulk emulsification methods, require further chemical and thermal treatments, and are restrictive with respect to the materials employed5-9. The development of methods that exploit the great potential of interfacial assembly for producing tailored materials have been hampered by the lack of understanding of the assembly process. Here we report a microfluidic method that allows direct visualization and understanding of the dynamics of colloidal crystal growth on curved interfaces. The crystals are periodically ejected to form stable jammed shells, which we refer to as colloidal armour. We propose that the energetic barriers to interfacial crystal growth and organization can be overcome by targeted delivery of colloidal particles through hydrodynamic flows. Our method allows an unprecedented degree of control over armour composition, size and stability.Comment: 18 pages, 5 figure

Unique Properties of Eukaryote-Type Actin and Profilin Horizontally Transferred to Cyanobacteria

A eukaryote-type actin and its binding protein profilin encoded on a genomic island in the cyanobacterium Microcystis aeruginosa PCC 7806 co-localize to form a hollow, spherical enclosure occupying a considerable intracellular space as shown by in vivo fluorescence microscopy. Biochemical and biophysical characterization reveals key differences between these proteins and their eukaryotic homologs. Small-angle X-ray scattering shows that the actin assembles into elongated, filamentous polymers which can be visualized microscopically with fluorescent phalloidin. Whereas rabbit actin forms thin cylindrical filaments about 100 µm in length, cyanobacterial actin polymers resemble a ribbon, arrest polymerization at 5-10 µm and tend to form irregular multi-strand assemblies. While eukaryotic profilin is a specific actin monomer binding protein, cyanobacterial profilin shows the unprecedented property of decorating actin filaments. Electron micrographs show that cyanobacterial profilin stimulates actin filament bundling and stabilizes their lateral alignment into heteropolymeric sheets from which the observed hollow enclosure may be formed. We hypothesize that adaptation to the confined space of a bacterial cell devoid of binding proteins usually regulating actin polymerization in eukaryotes has driven the co-evolution of cyanobacterial actin and profilin, giving rise to an intracellular entity

Long-term effect of ventral root re-implantation on motoneuron survival following spinal root avulsion in adult rat

We have previously reported that re-implantation of ventral root can enhance motoneuron (MN) survival up to 6 weeks after root avulsion and surviving motoneurons can regenerate their axons into the re-implanted root. The aim of the present study is to investigate the long-term survival effect of root re-implantation. Axonal regeneration and myelination are also studied. Following root avulsion and re-implantation, animals in all groups were allowed to survival for 3, 6 or 12 months. Regenerating MNs were retrogradely labeled by fluorescent dye. In root re-implanted animals, about 60-70% of injured motoneurons survived up to 12 months after injury, while only 20% survival were found in the control animals. About 80% of the surviving motoneurons were found to regenerate their axons into the re-implanted ventral root. By 3 weeks after avulsion, myelin degeneration was widely spread throughout the lesioned ventral roots. In re-implantation groups, at 3 and 6 weeks after treatment, scattered Schwann cell myelinated axons within the demyelinated regions were observed. At 6 and 12 months after treatment, numerous thinly oligodendrocyte-myelinated axons were mixed with Schwann cell myelinated axons. Compared with the normal axons, newly formed myelinated axons were irregular in shape and orientation. Results of the present study show that re-implantation of avulsed ventral root can greatly enhance long-term motoneuron survival and these surviving motoneurons can regrow their axons into the original ventral root and get remyelinated. Supported by RGC grants, Hong Kon

Cyanine 5.5 conjugated nanobubbles as a tumor selective contrast agent for dual ultrasound-fluorescence imaging in a mouse model.

Nanobubbles and microbubbles are non-invasive ultrasound imaging contrast agents that may potentially enhance diagnosis of tumors. However, to date, both nanobubbles and microbubbles display poor in vivo tumor-selectivity over non-targeted organs such as liver. We report here cyanine 5.5 conjugated nanobubbles (cy5.5-nanobubbles) of a biocompatible chitosan-vitamin C lipid system as a dual ultrasound-fluorescence contrast agent that achieved tumor-selective imaging in a mouse tumor model. Cy5.5-nanobubble suspension contained single bubble spheres and clusters of bubble spheres with the size ranging between 400-800 nm. In the in vivo mouse study, enhancement of ultrasound signals at tumor site was found to persist over 2 h while tumor-selective fluorescence emission was persistently observed over 24 h with intravenous injection of cy5.5-nanobubbles. In vitro cell study indicated that cy5.5-flurescence dye was able to accumulate in cancer cells due to the unique conjugated nanobubble structure. Further in vivo fluorescence study suggested that cy5.5-nanobubbles were mainly located at tumor site and in the bladder of mice. Subsequent analysis confirmed that accumulation of high fluorescence was present at the intact subcutaneous tumor site and in isolated tumor tissue but not in liver tissue post intravenous injection of cy5.5-nanobubbles. All these results led to the conclusion that cy5.5-nanobubbles with unique crosslinked chitosan-vitamin C lipid system have achieved tumor-selective imaging in vivo