Nanodroplet Depinning from Nanoparticles

by Qi Liu, Fong Yew Leong, Zainul Aabdin, Utkarsh Anand, Tran Si Bui Quang, and Utkur Mirsaidov

ACS Nano, Article ASAP DOI: 10.1021/acsnano.5b03078
Publication Date (Web): August 18, 2015

Nanoscale defects on a substrate affect the sliding motion of water droplets. Using in situ transmission electron microscopy imaging, we visualized the depinning dynamics of water nanodroplets from gold nanoparticles on a flat SiNx surface. Our observations showed that nanoscale pinning effects of the gold nanoparticle oppose the lateral forces, resulting in stretching, even breakup, of the water nanodroplet. Using continuum long wave theory, we modeled the dynamics of a nanodroplet depinning from a nanoparticle of comparable length scales, and the model results are consistent with experimental findings and show formation of a capillary bridge prior to nanodroplet depinning. Our findings have important implications on surface cleaning at the nanoscale.

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Cryo-EM structure of an antibody that neutralizes dengue virus type 2 by locking E protein dimers

by Guntur Fibriansah, Kristie D Ibarra, Thiam-Seng Ng, Scott A Smith,  Joanne L Tan, Xin-Ni Lim, Justin S G Ooi, Victor A Kostyuchenko, Jiaqi Wang, Aravinda M de Silva, Eva Harris, James E Crowe Jr, Shee-Mei Lok

Science 3 July 2015: Vol. 349 no. 6243 pp. 88-91. DOI: 10.1126/science.aaa8651

There are four closely-related dengue virus (DENV) serotypes. Infection with one serotype generates antibodies that may cross-react and enhance infection with other serotypes in a secondary infection. We demonstrated that DENV serotype 2 (DENV2)–specific human monoclonal antibody (HMAb) 2D22 is therapeutic in a mouse model of antibody-enhanced severe dengue disease. We determined the cryo–electron microscopy (cryo-EM) structures of HMAb 2D22 complexed with two different DENV2 strains. HMAb 2D22 binds across viral envelope (E) proteins in the dimeric structure, which probably blocks the E protein reorganization required for virus fusion. HMAb 2D22 “locks” two-thirds of or all dimers on the virus surface, depending on the strain, but neutralizes these DENV2 strains with equal potency. The epitope defined by HMAb 2D22 is a potential target for vaccines and therapeutics.

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Traction stress analysis and modeling reveal amoeboid migration in confined spaces is accompanied by expansive forces and requires the structural integrity of the  membrane-cortex interactions

by Ai Kia Yip, Keng-Hwee Chiam and Paul Matsudaira

Integrative Biology, 2015, DOI: 10.1039/C4IB00245H. First published online 27 May 2015

Cell migration is crucial in many biological processes such as embryonic development, wound closure, as part of the body’s inflammatory response, as well as during cancer cell metastasis. A cell can translocate across a surface by either a mesenchymal or amoeboid cell migration mechanism. While cells are known to adhere to the extracellular matrix and generate contractile cell traction forces during integrin-dependent mesenchymal migration, little is known about the nature of the traction forces required for amoeboid migration in the absence of cell-matrix adhesions.

In this paper, we have combined 3-dimensional traction force microscopy with a confinement assay, where neutrophil-like cells are confined between two pieces of polyacrylamide gels. In the absence of cell-matrix adhesions, confined cells migrate by amoeboid “chimneying”, that is, generate traction by applying expansive and divergent forces against opposing surfaces. This chimneying speed was shown, both experimentally and computationally, to depend on both the magnitude of the intracellular pressure and the location where blebs are formed as determined by the membrane-cortex adhesion strength.


Picture caption: A cell confined between two pieces of non-adhesive polyacrylamide gels. 3D traction forces can be calculated based on gel deformations detected by the displacements of the embedded beads (orange).

Movie caption: An amoeboid neutrophil-like, differentiated HL60 cell migrating in between two pieces of non-adhesive polyacrylamide gels (DIC image, far left). Cell nuclei were stained with Hoechst (middle left panel, blue) and cells were transfected with Lifeact-GFP (middle right panel, green), which labels the F-actin. The three channels are overlaid in the far right panel. The number on the top of the images indicates the time in hour: minute: second.

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