Topological defect-mediated morphodynamics of active-active interfaces.

Physical interfaces widely exist in nature and engineering. Although the formation of passive interfaces is well elucidated, the physical principles governing active interfaces remain largely unknown. Here, we combine simulation, theory, and cell-based experiment to investigate the evolution of an active-active interface. We adopt a biphasic framework of active nematic liquid crystals. We find that long-lived topological defects mechanically energized by activity display unanticipated dynamics nearby the interface, where defects perform "U-turns" to keep away from the interface, push the interface to develop local fingers, or penetrate the interface to enter the opposite phase, driving interfacial morphogenesis and cross-interface defect transport. We identify that the emergent interfacial morphodynamics stems from the instability of the interface and is further driven by the activity-dependent defect-interface interactions. Experiments of interacting multicellular monolayers with extensile and contractile differences in cell activity have confirmed our predictions. These findings reveal a crucial role of topological defects in active-active interfaces during, for example, boundary formation and tissue competition that underlie organogenesis and clinically relevant disorders.

Spontaneous organization and phase separation of skyrmions in chiral active matter.

Skyrmions are topologically protected vortex-like excitations that hold promise for applications such as information processing and electron manipulation. Here we combine theoretical analysis and numerical simulations to show that skyrmions can spontaneously emerge in chiral active matter without external confinements or regulation. Strikingly, these activity-driven skyrmions can either self-organize into a periodic, stable square lattice consisting of half Néel skyrmions and antiskyrmions, where the in-plane flows display an antiferromagnetic vortex array, or undergo phase separation between skyrmions with different topological numbers. We identify that the emerging skyrmion dynamics stems from the competition between the chiral and polar coherence length scales dictated by the interplay of intrinsic chirality, polarity, and elasticity in the system. Our results reveal unanticipated topological excitations, self-organization, and phase separation in non-equilibrium systems and also suggest a potential way towards engineering complicated bespoke skyrmionic structures through manipulating active matter.

Pattern Formation and Defect Ordering in Active Chiral Nematics.

Many biological systems display intriguing chiral patterns and dynamics. Here, we present an active nematic theory accounting for individual spin to explore the collective handedness in chiral rod-shaped aggregations. We show that coordinated individual spin and motility can engender a vortex-array pattern with chirality and drive ordering of topological defects. During this chiral process, the stationary trefoil-like defects self-organize into a periodic, hexagon-dominated polygonal network, which segregates persistently rotating cometlike defects in pairs within each polygon, leading to a translation symmetry at the global scale while a broken reflection symmetry at the local scale. Such defect ordering agrees exactly with the Voronoi tiling of two-dimensional space and the emergence of the hexagonal symmetry is deciphered in analogy with topological charge neutralization. We calculate energy barriers to the topological transition of the defect ordering and explain the existing metastable states with nonhexagonal polygons. Our findings shed light on the chiral morphodynamics in life processes and also suggest a potential route towards tuning self-organization in active materials.

Arraying Octahedral {Cr2Dy4} Units into 3D Single-Molecule-Magnet-Like Inorganic Compounds with Sulfate Bridges.

Two novel 3D pure inorganic compounds based on [Cr2Dy4(µ4-O)2(µ3-OH)4]10+ cluster units and sulfate anions are presented. Both complexes exhibit single-molecule-magnet (SMM)-like behavior. Permutation of the magnetic moment direction among SMM-like cluster units has a significant effect on the performance of molecular nanomagnets, and directional consistency shows obvious advantages.

Single-Molecule Magnet Behavior of 1D Coordination Polymers Based on DyZn2(salen)2 Units and Pyridin- N-Oxide-4-Carboxylate: Structural Divergence and Magnetic Regulation.

Two 1D coordination polymers composed of DyZn2(salen)2 units and pyridin- N-oxide-4-carboxylate have been prepared by solvothermal reactions. Complex 1 with the formula {[DyZn2(La)2(POC)](OH)(ClO4)}·H2O·MeOH [H2La] = N, N'-bis(3-methoxysalicylidene)-1,3-diaminopropane, POC- = pyridin- N-oxide-4-carboxylate] is composed of a zigzag chain cation [DyZn2(La)2(POC)] n2 n+ as well as isolated hydroxide and perchlorate anions. Complex 2 with the formula {[Dy3Zn7(Lb)6(POC)6](OH)3(ClO4)2}·9H2O [H2Lb] = N, N'-bis(3-methoxysalicylidene)-1,2-diaminoethane] is also an ionic compound containing isolated hydroxide and perchlorate anions, but its cation shows a novel nanowire structure, in which six-coordinate zinc(II) ions with C3 symmetry act as the axis and [DyZn2(Lb)2(POC)]2+ structural units as spiral leaves. Complex 1 shows good single-molecule magnet performance with an Ueff/ k value of 235.3(3.1) K ( Hdc = 0 Oe), one of the largest values for coordination polymers. A butterfly-shaped magnetic hysteresis loop can be monitored at as high as 3.8 K for 1, while a dc field is necessary for complex 2 to display slow magnet relaxation owing to the quantum-tunneling effect, with a much smaller Ueff/ k value of 14.6(0.2) K ( Hdc = 1000 Oe). The difference of magnetic properties has been explained using detailed ab initio calculations.

[In Situ Research on Ginger Oil Cell with Raman].

This article presents a novel and original approach to analyze the main components of the essential oils in ginger oil cell by means of Raman spectroscopy. Fresh ginger sample was prepareed with free-hand section. Under the DXR Laser confocal micro Raman spectrometer, the oil cell has 20 objective lens. As to the ginger oil cell, the Raman spectrum, all together 21 spectroscopic bands, was obtained. It has been found that the obtained Raman spectrums at different oil cells are very similar. The Raman spectrum of the commercial essential oils of ginger, together 37 spectroscopic bands, was obtained. It has been found that the 19 presented spectroscopic bands of ginger oil cell correlate very well with those obtained by the commercial essential oils. Density Functional Theory (DFT) of zingiberene calculations were performed in order to interpret the spectra of the essential oils of the ginger oil cell and essential oils of ginger. There are 31 spectroscopic bands of the essential oils of ginger, and 19 spectroscopic bands of ginger oil cell correlate very well with calculations. All these investigations are helpful tools to generate a fast and easy method to control the quality of the essential oils with Raman spectroscopic techniques in combination with DFT calculations.

[NIR-SERS Spectra Detection of Cytidine on Nano-Silver Films].

The polyvinyl alcohol (PVA) protected silver glass-like nanostructure (PVA-Ag-GNS) with high surface-enhanced Raman scattering (SERS) activity was prepared and employed to detect the near-infrared surface enhanced Raman scattering (NIR-SERS) spectra of cytidine aqueous solution (10(-2)-10(-8) mol x L(-1)). In the work, the near-infrared laser beam (785 nm) was used as the excitation light source. The experiment results show that high-quality NIR-SERS spectra were obtained in the ranges of 300 to 2 000 cm(-1) and the detection limit of cytidine aqueous solution was down to 10(-7) mol x L(-1). Meanwhile, the PVA-Ag-GNS shows a high enhancement factor (EF) of -10(8). In order to test the optical reproducibility of PVA-Ag-GNS, ten samples of cytidine aqueous solution (10(-2)-10(-5) mol x L(-1)) had been dropped onto the surface of PVA-Ag-GNS respectively. Meanwhile, these samples were measured by the portable Raman spectrometer. As a result, the PVA-Ag-GNS demonstrated good optical reproducibility in the detection of cytidine aqueous solution. In addition, to explain the reason of enhancement effect, the ultraviolet-visible (UV-Vis) extinction spectrum and scanning electron microscope (SEM) of cytidine molecules adsorbed on the surface of PVA-Ag-GNS were measured. There is plasmon resonance band at 800 nm in the UV-Vis extinction Spectrum of the compound system. Therefore, when the near-infrared laser beam (785 nm) was used as excitation light source, the compound system may produce strongly surface plasmon resonance (SPR). According to the SEM of PVA-Ag-GNS, there are much interstitial between the silver nanoparticles. So NIR-SERS is mainly attributed to electromagnetic (EM) fields associated with strong surface plasmon resonance. At last, the geometry optimization and pre-Raman spectrum of cytidine for the ground states were performed with DFT, B3LYP functional and the 6-311G basis set, and the near-infrared laser with wavelength of 785 nm was employed in the pre-Raman spectrum calculation process. The calculation results without imaginary frequency and the results match pretty well with the experimental Raman spectrum. At the same time, the assignations of Raman bands and adsorption behaviors of cytidine molecules on the surface of PVA-Ag-GNS are also discussed. According to our experiment and calculations, cytidine molecules mainly adsorbed on silver nanoparticles via the ribose moiety and amino group may get close to the local electromagnetic field.

Mixed behavior of p-phenylenediaminium guest binding with the inverted cucurbit[6]uril host.

The binding interaction between inverted cucurbit[6]uril (iQ[6]) and p-phenylenediaminium both in the solid state and in aqueous solution has been investigated by X-ray crystallography, (1)H NMR spectroscopy and isothermal titration calorimetry (ITC). The experimental results suggest that the binding interaction between iQ[6] and p-phenylenediaminium may generate two different types of complexes in the solid state: one is an inclusion structure and the other is a sandwich structure. In aqueous solution, the iQ[6] host has an ability to accommodate the p-phenylenediaminium guest and in-out guest exchange is fast on the NMR time scale. ITC data indicate that the complexation of iQ[6] with p-phenylenediaminium is entropy driven.

[Research on volatiles of rakkyo (Allium Chinense G. Don) and Chinese chive (Allium Tuberosum Rottl. ex Sprengel) based on headspace and the molecular recognition of SERS].

The head space and the molecular recognition of surface enhanced Raman scattering (SERS) were used to research volatiles of rakkyo and Chinese chive. Their volatiles SERS spectra were obtained using nano-silver colloid as the substrate. Then, volatiles SERS spectra of rakkyo and Chinese Chive were compared respectively with the volatiles SERS spectra of liquid allyl methyl sulfide, 1-propanethiol, diallyl disulfide and all possible pairings of the three compounds. The results showed that the repeatability of volatiles SERS spectra of rakkyo and Chinese Chive were all good. The volatiles SERS spectrum of rakkyo was basically consistent with the volatiles SERS spectrum of the mixture of liquid allyl methyl sulfide and 1-propanethiol. The volatiles SERS spectrum of rakkyo included both characteristic peaks at 626 and 674 cm(-1) in volatiles SERS spectrum of allyl methyl sulfide and characteristic peaks at 702, 893, 1024,1085, 1215 and 1320 cm(-1) in volatiles SERS spectrum of 1-Propanethiol. The volatiles SERS spectrum of Chinese chive was basically consistent with the volatiles SERS spectrum of the mixture of liquid allyl methyl sulfide and diallyl disulfide. The volatiles SERS spectrum of Chinese chive included both characteristic peak at 674 cm(-1) in volatiles SERS spectrum of allyl methyl sulfide and characteristic peaks at 407, 577, 716, 1189, 1291 and 1401 cm(-1) in volatiles SERS spectrum of diallyl disulfide. These illustrated that volatiles of rakkyo contained allyl methyl sulfide and 1-Propanethiol and volatiles of Chinese chive contained allyl methyl sulfide and diallyl disulfide. The volatiles of rakkyo and Chinese chive were different, but they all contained allyl methyl sulfide. All of the above have revealed that the headspace combined with molecular recognition of SERS can be directly used to study volatiles of rakkyo and Chinese chive. The technology under room temperature, can guarantee the volatiles obtained were the primitive constituents in plant volatiles. By comparison with the standard sample, the constituents in plant volatiles can be determined.

[Study of volatile organic compounds of fresh allium species using headspace combined with surface-enhanced Raman scattering].

In order to identify volatile organic compounds of fresh plants at room temperature and avoid sample pretreatment and extractions which can be labor intensive, garlic, Chinese chives and scallion were chopped into pieces. Then some of them were placed in the headspace vial and sealed. The gases were drawn from the vial with a syringe and were injected very slowly into Ag colloids for test using R-3000 portable Raman spectrometer. The spectra of volatile organic compounds of allium species, fresh garlic, Chinese chive and shallot plants were successfully.recorded for the first time. For garlic high intensity bands are present at 307, 399, 569, 711, 1,182, 1,287, 1,397 and 1,622 cm(-1). For Chinese chives the high intensity band is present at 672 cm(-1). Low intensity bands are present at 274, 412, 575, 1,185, 1,289, 1,396, 1,618 cm(-1). For shallot high intensity bands are present at 693 cm(-1). Lower intensity bands are present at 372, 888, 1,023 cm(-1). Low intensity bands are present at 1,088, 1,211 and 1,322 cm(-1). The SERS of diallyl disulfide, allyl methyl sulfide and 1-propanethiol in liquid state and gas state were also obtained. The main volatile organic compound of fresh garlic, Chinese chive and shallot are diallyl disulfide, allyl methyl sulfide and 1-propanethiol respectively, and the volatile organic compound of fresh onion, scallion, shallot and chive are all 1-propanethiol. The presented results illustrate that combining headspace and SERS is a powerful tool for volatile organic compound analysis in fresh plants. The volatile organic compound can be detected in fresh plant samples directly and quickly without extraction.

Hypo-attenuating Berry Sign as a Novel Imaging Marker of Ruptured Aneurysm in Patients with Subarachnoid Hemorrhage; a Diagnostic Accuracy Study.

Introduction: Aneurysmal subarachnoid hemorrhage (SAH) constitutes a life-threatening condition, and identifying the ruptured aneurysm is essential for further therapy. This study aimed to evaluate the diagnostic accuracy of hypo-attenuating berry sign (HBS) observed on computed tomography (CT) scan in distinguishing ruptured aneurysms. Methods: In this diagnostic accuracy study, patients who had SAH and underwent non-enhanced brain CT scan were recruited. The HBS was defined as a hypo-attenuating area with an identifiable border in the blood-filled hyper-dense subarachnoid space. The screening performance characteristics of HBS in identifying ruptured aneurysms were calculated considering the digital subtraction angiography (DSA) as the gold standard. Results: A total of 129 aneurysms in 131 patients were analyzed. The overall sensitivity and specificity of HBS in the diagnosis of aneurysms were determined to be 78.7% (95%CI: 73.1% - 83.4%) and 70.7% (95%CI: 54.3% - 83.4%), respectively. Notably, the sensitivity increased to 90.9% (95%CI: 84.3% - 95.0%) for aneurysms larger than 5mm. The level of inter-observer agreement for assessing the presence of HBS was found to be substantial (kappa=0.734). The diagnostic accuracy of HBS in individuals exhibited enhanced specificity, sensitivity, and reliability when evaluating patients with a solitary aneurysm or assessing ruptured aneurysms. The multivariate logistic regression analysis revealed a statistically significant relationship between aneurysm size and the presence of HBS (odds ratios of 1.667 (95%CI: 1.238 - 2.244; p < 0.001) and 1.696 (95%CI: 1.231 - 2.335; p = 0.001) for reader 1 and reader 2, respectively). Conclusions: The HBS can serve as a simple and easy-to-use indicator for identifying a ruptured aneurysm and estimating its size in SAH patients.  .

Field-induced single-ion magnets based on enantiopure chiral ß-diketonate ligands.

A pair of homochiral ß-diketonate ligands (+)-3-trifluoroacetyl)camphor (d-Htfc) and (-)-3-trifluoroacetyl)camphor (l-Htfc) were used to construct two enantiomeric pairs of Dy(III) single-ion magnets [Dy(d-tfc)3(bpy)]2 (d-1)/[Dy(l-tfc)3(bpy)]2 (l-1) (bpy = 2,2'-bipyridine) and [Dy(d-tfc)3(phen)]·2H2O (d-2)/[Dy(l-tfc)3(phen)] (l-2) (phen = 1,10-phenanthroline). The capping aromatic N,N'-donors have a dramatic influence on the structural and magnetic characteristics of the Dy(III) ß-diketonate enantiomeric pairs: the cocrystal of two homochiral Dy(III) ß-diketonate stereoisomers with the 2,2'-bipyridine ligand was formed, showing field-induced single-ion magnet behaviors with a two-step relaxation process, while no stereoisomerization happened for the homochiral Dy(III) ß-diketonate with the 1,10-phenanthroline coligand, exhibiting a single relaxation process of the magnetization only. The anisotropy barriers of d-1 (36.5 and 46.1 K) are slightly smaller than those of l-1 (37.0 and 49.3 K), while d-2 has a larger energy barrier (30.5 K) with respect to l-2 (25.1 K).

Evaluation of early precut with needle-knife in difficult biliary cannulation during ERCP.

BACKGROUND: There is scarce information on whether performing the precut procedure early rather than after several cannulation attempts is associated with different success and complication rates. OBJECTIVE: The aim of this retrospective study was is to compare the early precut technique with the standard one in terms of the results and complications. METHODS: The contemporary success rate and postoperative complications in 792 endoscopic retrograde cholangiopancreatography cases were frequently observed during the period from June 2007 to May 2011, and 56 of these cases were carried out with precut biliary sphincterotomy after the standard sphincterotomy had failed. RESULTS: The success rate for standard sphincterotomy was 89.8%: 51 out of 56 cases were carried out with precut biliary sphincterotomy and succeeded. The total success rate was 96.3%. The difference was significant (χ2=25.62, p<0.01) compared to the success rate of first cannulation, while the difference in complication rates between precut and standard sphincterotomy was minor (9.9 vs. 12.5%, p>0.05). CONCLUSION: Early precut with a needle-knife in a difficult biliary cannulation was safe and effective if performed by experienced endoscopists.

Increase of cyclooxygenase-2 inhibition with celecoxib combined with 5-FU enhances tumor cell apoptosis and antitumor efficacy in a subcutaneous implantation tumor model of human colon cancer.

BACKGROUND: The purpose of this study was to investigate the anti-tumor effect and explore the mechanisms of celecoxib (a selective cyclooxygenase-2 inhibitor) combined with 5-fluorouracil (5-FU) on the treatment of human colorectal cancer in a BALB/C nude mouse subcutaneous xenograft model. METHODS: Effects of celecoxib combined with 5-FU on the proliferation of xenograft carcinoma induced by HT-29 were investigated. The apoptotic cells were detected by electron microscope and TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) assay. Immunohistochemistry and Western blot were used to estimate the expression of cytochrome C, caspase-3 and caspase-9. RESULTS: Compared with the control group, treatment groups showed significant inhibition of tumor growth. More apoptotic cells existed after treatment with celecoxib combined with 5-FU. Cytochrome C, caspase-3 and caspase-9 were increased in treated groups, and more obviously in the drug combination group. Cyclooxygenase-2 (COX-2) were decreased after treatment with celecoxib only or combined with 5-FU. And the combined group showed a greater decrease. CONCLUSIONS: Celecoxib combined with 5-FU could inhibit the growth of tumors in vivo by inducing apoptosis and activation of the cytochrome C dependency apoptosis signal pathway. A decrease of COX-2 and an increase of cytochrome C, caspase-3 and caspase-9 may be involved in this process.

[Elementary SERS spectroscopy studies of three kinds of pathogens in Ag colloids prepared by microwave method].

The normal Raman (NR) and surface enhanced Raman spectroscopy (SERS) for Alternaria alternate, Colletotrichum musae, and fusarium suspensions were measured by a portable Raman spectrometer (785 nm). The result indicates that the silver colloid prepared by microwave method shows high enhancement of Raman scattering for the three kinds of pathogens. Comparing SERS spectrums of the three kinds of pathogens, there are some similarities. In these SERS spectrums, the peaks in the range of 500-1 000 cm(-1) are very weak. Additionally, the peaks in the range of 1 000-1 600 cm(-1) are strong. Meanwhile, the peak at 481 cm(-1) is the strongest. Although these spectrums are similar, there are some differences such as the distribution and shape of peaks. Therefore, the three kinds of pathogens can be discriminated quickly.

[Experimental studies of effects of hydrogen-rich saline in rats with severe acute pancreatitis].

OBJECTIVE: To explore the mechanism and effectiveness of inducing severe acute pancreatitis (SAP) with saline saturated hydrogen in rats. METHODS: Based on a random number table, 54 Sprague-Dawley rats were divided into 3 groups: control, SAP and treatment (n = 18 each). The model of SAP was established by a retrograde injection of 5% sodium taurocholate into biliary-pancreatic duct. The treatment group received an injection of 5 ml/kg hydrogen-rich saline into tail vein at 1 h post-modeling. The control group underwent only pancreatic tipping. All rats were exsanguinated under anesthesia by aortal puncture after 24 hours. The serum levels of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and interleukin-18 (IL-18) in 3 groups were measured by enzyme-linked immunosorbent assay (ELISA). The expression of TNF-αmRNA in pancreatic tissue was measured by reverse transcription (RT)-PCR. And intercellular adhesion molecule-1 (ICAM-1) in pancreatic tissue was measured by immunohistochemistry. The pancreatic tissues were harvested to examine the microscopic changes. The levels of malonic aldehyde (MDA), myeloperoxidase (MPO), superoxide dismutase (SOD) and glutathione (GSH) in pancreatic tissue was measured by specific kits. RESULTS: The pathological scores of pancreatic tissue were significantly lower in the treatment group than those in the SAP group (9.7 ± 2.0 vs 13.2 ± 2.5, P < 0.05). The serum level of TNF-αwas significantly lower in the treatment group than that in the SAP group ((88 ± 17) vs (1171 ± 18) pg/ml, P < 0.05). And the serum levels of IL-6 and IL-18 were lower in the treatment group than those in the SAP group ((25.2 ± 5.9) vs (37.3 ± 4.6) ng/L, (401 ± 100) vs (439 ± 103) ng/L, both P < 0.05). As compared with the SAP group, the levels of MDA and MPO decreased significantly in the treatment group ((8.2 ± 2.8) vs (14.7 ± 2.7) nmol/mg, (0.040 ± 0.011) vs (0.170 ± 0.071) U/g, both P < 0.05). However, the levels of SOD and GSH significantly higher than those of the treatment group ((22.1 ± 1.3) vs (15.1 ± 1.7) U/mg, (4.8 ± 0.4) vs (2.5 ± 0.3) U/mg, both P < 0.05). The expressions of TNF-α mRNA and ICAM-1 in pancreatic tissues were lower than those of the treatment group (0.33 ± 0.17 vs 0.94 ± 0.31, 2.0 ± 0.4 vs 2.8 ± 0.8, both P < 0.05). CONCLUSION: Hydrogen-rich saline can decrease the levels of inflammatory mediators and reduce the pathological damage of pancreas through the inhibition of oxidative stress.

[Preparation and SERS activity studies on substrate of nano-silver film with broad plasma absorption band].

A highly reproducible and broad plasma absorption band nano-silver film was prepared by electrostatic self-assembly technology. The size of nano-silver particles on the surface of silver film, in the scanning electron microscopy (SEM) micrograph, is in a wide distribution from 18 to 200 nm. At the same time, the ultraviolet-visible spectrophotometer was employed to detect the nano-silver film. There is a broad plasma absorption band in the UV-Vis spectrum. To test the SERS activity of the nano-silver film, crystal violet and serum of healthy person were used as probe molecules and the high quality SERS spectra were obtained.

[SERS spectroscopy study of three pathogenic bacteria].

The SERS spectra of staphylococcus aureus, proteus, and Escherichia coli was obtained on colloidal Ag nanoparticles prepared by the microwave method with the portable Raman spectrometer. Staphylococcus aureus have obvious Raman vibrating peak at 725, 1 330 and 1 450 cm(-1), proteus have obvious Raman vibrating peaks at 650,725,950, 1 325 and 1 463 cm(-1), while E. coli have obvious Raman vibrating peaks at 650, 950, 1 125, 1 242,1 320 and 1 457 cm(-1). Each peak was assigned preliminarily. Not only the position of Raman vibration peaks but also the intensity of the three bacteria is obviously different, so SERS can be used for identification and distinction of E. coli, staphylococcus aureus and proteus.

Self-rotation regulates interface evolution in biphasic active matter through taming defect dynamics.

Chirality can endow nonequilibrium active matter with unique features and functions. Here, we explore the chiral dynamics in biphasic active nematics composed of self-rotating units that continuously inject energy and angular momentum at the microscale. We show that the self-rotation of units can regularize the boundaries between two phases, rendering sinusoidal-like interfaces, which allow lateral wave propagation and are characterized by chains of ordered antiferromagnetic cross-interface flow vortices. Through the spontaneous coordination of counter-rotating units across the interfaces, topological defects excited by activity are sorted spatiotemporally, where positive defects are locally trapped at the interfaces but, unexpectedly, are transported laterally in a unidirectional rather than wavy mode, whereas inertial negative defects remain spinning in the bulks. Our findings reveal that individual chirality could be harnessed to modulate interfacial morphodynamics in active systems and suggest a potential approach toward controlling topological defects for programmable microfluidics and logic operations.

Collective Polarization of Cancer Cells at the Monolayer Boundary.

Cell polarization, a process depending on both intracellular and intercellular interactions, is crucial for collective cell migration that commonly emerges in embryonic development, tissue morphogenesis, wound healing and cancer metastasis. Although invasive cancer cells display weak cell-cell interactions, they can invade host tissues through a collective mode. Yet, how cancer cells without stable cell-cell junctions polarize collectively to migrate and invade is not fully understood. Here, using a wound-healing assay, we elucidate the polarization of carcinoma cells at the population level. We show that with loose intercellular connections, the highly polarized leader cells can induce the polarization of following cancer cells and subsequent transmission of polarity information by membrane protrusions, leading to gradient polarization at the monolayer boundary. Unlike the polarization of epithelial monolayer where Rac1/Cdc42 pathway functions primarily, our data show that collective polarization of carcinoma cells is predominantly controlled by Golgi apparatus, a disruption of which results in the destruction of collective polarization over a large scale. We reveal that the Golgi apparatus can sustain membrane protrusion formation, polarized secretion, intracellular trafficking, and F-actin polarization, which contribute to collective cancer cell polarization and its transmission between cells. These findings could advance our understanding of collective cancer invasion in tumors.