Complementary Gradient Research Articles

Axial gradient excitation accelerates volumetric imaging of two-photon microscopy

Two-photon excitation fluorescence microscopy (TPM), owing to its capacity for subcellular resolution, intrinsic optical sectioning, and superior penetration depth in turbid samples, has revolutionized biomedical research. However, its layer-by-layer scanning to form a three-dimensional image inherently limits the volumetric imaging speed and increases phototoxicity significantly. In this study, we develop a gradient excitation technique to accelerate TPM volumetric imaging. The axial positions of the fluorophores can be decoded from the intensity ratio of the paired images obtained by sequentially exciting the specimen with two axially elongated two-photon beams of complementary gradient intensities. We achieved a 0.63 μm axial localization precision and demonstrate the flexibility of the gradient TPM on various sparsely labeled samples, including bead phantoms, mouse brain tissues, and live macrophages. Compared with traditional TPM, our technique improves volumetric imaging speed (by at least sixfold), decreases photobleaching (i.e., less than 2.07 ± 2.89 % in 25 min), and minimizes photodamages.

Alleviating Class-Wise Gradient Imbalance for Pulmonary Airway Segmentation.

Automated airway segmentation is a prerequisite for pre-operative diagnosis and intra-operative navigation for pulmonary intervention. Due to the small size and scattered spatial distribution of peripheral bronchi, this is hampered by a severe class imbalance between foreground and background regions, which makes it challenging for CNN-based methods to parse distal small airways. In this paper, we demonstrate that this problem is arisen by gradient erosion and dilation of the neighborhood voxels. During back-propagation, if the ratio of the foreground gradient to background gradient is small while the class imbalance is local, the foreground gradients can be eroded by their neighborhoods. This process cumulatively increases the noise information included in the gradient flow from top layers to the bottom ones, limiting the learning of small structures in CNNs. To alleviate this problem, we use group supervision and the corresponding WingsNet to provide complementary gradient flows to enhance the training of shallow layers. To further address the intra-class imbalance between large and small airways, we design a General Union loss function that obviates the impact of airway size by distance-based weights and adaptively tunes the gradient ratio based on the learning process. Extensive experiments on public datasets demonstrate that the proposed method can predict the airway structures with higher accuracy and better morphological completeness than the baselines.

Multi-Scale Continuous Gradient Local Binary Pattern for Leaky Cable Fixture Detection in High-Speed Railway Tunnel

The feature of leaky cable fixture extracted by Local Binary Pattern (LBP) and its variants in high-speed railway tunnel has the defects of lacking description and high dimension. This paper proposes a new operator named Multi-scale Continuous Gradient Local Binary Pattern (MCG-LBP), which can realize the scale transformation of feature maps and ensure the low dimensionality of descriptors. For MCG-LBP, firstly a bi-directional triplet around the central pixel is presented to indicate the specific direction of gradient in circle neighborhood. Then, an effective dimensionality reduction strategy is introduced to perform successive down-sampling iterations. Finally, the multi-scale joint descriptors are encoded by continuous gradient sequences from different down-sampling maps, and Support Vector Machines is used to classify faulty cable fixtures. The proposed MCG-LBP can elicit a discriminative description through complementary gradient information generated by the combination of different single-scale features. While the low dimensionality of descriptor and no complex parameter to deal with both make it has higher computational efficiency. Experimental results show that the Recall and Precision of MCG-LBP reach 92.6% and 83.5% respectively on cable fixture data set, which is superior to the state-of-the-art methods.

Selective Adhesion and Directional Migration of Endothelial Cells Guided by Cys-Ala-Gly Peptide Density Gradient on Antifouling Polymer Brushes.

Selective adhesion and directional migration of endothelial cells (ECs) on biomaterials is critical to realize the rapid endothelialization. In this study, a Cys-Ala-Gly (CAG) peptide density gradient is generated on homogeneous cell-resisting poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate) brushes by immersing the brushes in a complementary gradient solution of CAG and competitive mercapto-terminated methoxyl poly(ethylene glycol). The adhesion and spreading of smooth muscle cells (SMCs) is impaired effectively on the gradient surface. About six folds of adherent ECs over SMCs are achieved at the position (10 mm) of highest CAG density on the gradient surface in a co-culture condition. Due to the gradient cues, ECs migrate fastest with the best directionality of 86.7% at the middle of the gradient, leading to the maximum net displacement as well.

Drosophila Peptide Hormones Allatostatin A and Diuretic Hormone 31 Exhibiting Complementary Gradient Distribution in Posterior Midgut Antagonistically Regulate Midgut Senescence and Adult Lifespan.

Enteroendocrine cells (EEs) are evolutionarily conserved gastrointestinal secretory cells that show scattered distribution in the intestinal epithelium. These cells classified into several subtypes based on the hormones they produce in both mammals and insects. In the fruit fly Drosophila, it has been suggested that nearly equal numbers of two subtypes of EEs (Allatostatin A: AstA and Diuretic hormone 31 : Dh31) are alternately produced from the intestinal stem cells in the posterior midgut. However, we found that these two subtypes are not always present in this manner, but are rather distributed in a complementary frequency gradient along the posterior midgut. We show that midgut-preferential RNA knockdown of the peptide hormones AstA or Dh31 respectively results in decreased or increased adult lifespan. This effect on longevity is apparently correlated with the midgut senescence phenotypes as a result of direct hormone action through both hormone receptors expressed in the enteroblasts or other midgut cell types. However, gut senescence does not appear to be the direct cause for longevity regulation, as knockdown of both hormone receptors did not affect adult lifespan. Furthermore, these senescence phenotypes appear to be independent of insulin signaling and manifest in an organ-specific manner. These results indicate that the two intestinal secretory peptides antagonistically regulate adult lifespan and intestinal senescence through multiple pathways, irrespective of insulin, which implicates a complementary gradient distribution of each of the hormone-producing EEs, consistent with local requirements for cell activity along the posterior midgut.

Controlling the selective and directional migration of hepatocytes by a complementary density gradient of glycosylated hyperbranched polymers and poly(ethylene glycol) molecules.

Repair and regeneration of defected tissues and organs depends strongly on the directional migration of targeted cells, for example, the enhancement of directional migration of hepatocytes could be helpful in liver regeneration and transplantation. Herein a complementary gradient of galactose-modified hyperbranched polymers (LA-HPMA) and poly(ethylene glycol) (PEG) molecules was designed and prepared on a same substrate. Characterizations of X-ray photoelectron spectrometry and quartz crystal microbalance with dissipation (QCM-d) demonstrated the unidirectional change in grafting density of LA-HPMA and PEG molecules, respectively. On the LA-HPMA/PEG complementary gradient surface, the human hepatoma (HepG2) cells showed preferential orientation and enhanced directional migration toward the region of lower PEG density and higher LA-HPMA density. By contrast, the mouse embryonic fibroblasts (NIH3T3) showed random migration irrelevant to the gradient. The success of the complementary gradient relies on the specific interaction between galactose and asialoglycoprotein receptor (ASGPR) expressed on HepG2 cells. STATEMENT OF SIGNIFICANCE.

HPLC-UV Method for the Identification and Screening of Hydroquinone, Ethers of Hydroquinone and Corticosteroids Possibly Used as Skin-Whitening Agents in Illicit Cosmetic Products.

Corticosteroids, hydroquinone and its ethers are regulated in cosmetics by the Regulation 1223/2009. As corticosteroids are forbidden to be used in cosmetics and cannot be present as contaminants or impurities, an identification of one of these illicit compounds deliberately introduced in these types of cosmetics is enough for market survey control. In order to quickly identify skin-whitening agents present in illegal cosmetics, this article proposes an HPLC-UV method for the identification and screening of hydroquinone, 3 ethers of hydroquinone and 39 corticosteroids that may be found in skin-whitening products. Two elution gradients were developed to separate all compounds. The main solvent gradient (A) allows the separation of 39 compounds among the 43 compounds considered in 50 min. Limits of detection on skin-whitening cosmetics are given. For compounds not separated, a complementary gradient elution (B) using the same solvents is proposed. Between 2004 and 2009, a market survey on "skin-whitening cosmetic" was performed on 150 samples and highlights that more than half of the products tested do not comply with the Cosmetic Regulation 1223/2009 (amending the Council Directive 76/768/EEC).

A complementary density gradient of zwitterionic polymer brushes and NCAM peptides for selectively controlling directional migration of Schwann cells

Selective enhancement of directional migration of Schwann cells (SCs) over fibroblasts (FIBs) plays a significant role in peripheral nerve regeneration, because this behavior facilitates neuron repair and avoids fibrosis. Herein a complementary density gradient of poly(3-dimethyl-methacryloyloxyethyl ammonium propane sulfonate) (PDMAPS, a zwitterionic polymer with antifouling property) and KHIFSDDSSE peptide (KHI, derived from neural cell adhesion molecule NCAM which mediates cell–cell adhesion) was fabricated. The gradient was visualized by fluorescent labeling, and further characterized by X-ray photoelectron spectrometry (XPS) and quartz crystal microbalance with dissipation (QCM-d). The SCs exhibited preferential orientation and enhanced directional migration on the gradient surface toward the region of lower PDMAPS density and higher KHI peptide density, while FIBs showed random migration. Moreover, the migration rate of the SCs was significantly enhanced to 2 folds, whereas that of the FIBs was reduced to 60% compared to their natural state on glass, leading to a faster migration rate of SCs than FIBs. The success of the complementary gradient relies on the appropriate interplay between the PDMAPS brushes and the cell-specific ligands, enabling the selective guidance of SCs migration.

Complementary density gradient of Poly(hydroxyethyl methacrylate) and YIGSR selectively guides migration of endotheliocytes.

Selective enhancement of directional migration of endotheliocytes (ECs) over vascular smooth muscle cells (SMCs) plays a significant role for the fast endothelialization of blood-contacting implants, in particular for the antirestenosis of vascular stents. Herein, a complementary density gradient of poly(2-hydroxyethyl methacrylate) (PHEMA) brushes and YIGSR peptide, a sequence specifically improving the mobility of ECs, was fabricated using a dynamically controlled reaction process. The gradients were visualized by fluorescent labeling and further quantified by X-ray photoelectron spectrometry (XPS) and quartz crystal microbalance with dissipation (QCM-d). The ECs exhibited preferential orientation and enhanced directional migration behavior on the gradient surface toward the region of lower PHEMA density and higher YIGSR density. The migration rate of the ECs was significantly enhanced to 5-fold, whereas the mobility of SMCs was not significantly influenced, leading to faster migration of ECs than SMCs. Therefore, the success of the complementary gradient relies on the appropriate interplay between the PHEMA brushes and the cell-specific ligands, enabling the selective guidance of EC migration.

Complementary modes of impulse generation for flow past a three-dimensional obstacle

A Lagrangian model for viscous incompressible flow past a stationary solid obstacle is developed in terms of the creation over successive instants of time of fluid impulse at the obstacle’s bounding surface. Upon creation this compactly supported vector field actively evolves into the flow interior according to its equation of motion. At the wall, distinct creation modes can be identified by specifying two exterior Poisson problems, distinguished from each other by complementary gradient boundary conditions. We demonstrate how in each case the relevant Poisson problem is to be solved numerically. Impulse generation is modeled in Lagrangian terms for each mode in turn for the case of flow past a sphere. (In the spherical geometry we exploit image theory to simplify some aspects of the computation.) We argue that the concurrent existence of these two distinct modes provides an insight into the complex phenomenology of turbulent wake formation.

A General Method for Patterning Gradients of Biomolecules on Surfaces Using Microfluidic Networks

This report outlines a general method for the fabrication of immobilized gradients of biomolecules on surfaces. This method utilizes a microfluidic network that generates a gradient of avidin in solution and immobilizes this protein on the surface of glass or poly(dimethylsiloxane) by physical adsorption. The immobilized gradient of avidin is then translated into gradients of biotinylated ligands (e.g., small molecules, oligomers of DNA, polysaccharides) using the specific interaction between biotin and avidin. This method can also generate immobilized gradients of certain proteins and artificial polymers by a direct transfer of gradients from solution onto the surface. The major advantage of this method is that almost any type of molecule can, in principle, be immobilized in a well-defined surface gradient of arbitrary shape with dimensions of a few micrometers to a few centimeters. It is possible to tailor the precise shapes of gradients on surfaces from gradients in solution, either kinetically or competitively. Kinetic methods rely on controlling the time that the surface is exposed to the gradient in solution: when a single protein adsorbs from solution, the amount that adsorbs depends both on its concentration in solution and on the time allowed for adsorption. Competitive methods rely on exposure of the surface to a complementary gradient of two proteins in solution (In these experiments, the sum of the concentrations of the proteins in solution is independent of positions although the concentration of each, individually, depends on the position. In this procedure, the relative amount of each protein, at saturation on the surface, depends only on its concentration.).

Interfacial transition zone in concrete

In fresh concrete a watercement (W:C) ratio gradient develops around the aggregate particles during casting, resulting in a different microstructure of the surrounding hydrated cement paste. This zone around the aggregate is called the interfacial transition zone (ITZ). This review describes the formation mechanisms and the microstructure of the ITZ. The higher W:C implies a diffusion process during hydration, and this zone may be consequently described as a heterogeneous area with a porosity gradient and a complementary gradient of anhydrous and hydrated phases. By using very fine and well-dispersed mineral additions, the initial W:C gradient around the aggregates is lowered and the ITZ is densified. The microstructure of the ITZ may be improved in the vacinity of calcereous aggregate, which reacts with calcium aluminates of Portland cement paste, forming calcium carboaluminates. The overall engineering properties of concrete in relation to the ITZ are beyond the scope of this review. Nevertheless, the local properties of the interfacial zone are reviewed: the mechanical and the transport characteristics of the ITZ are discussed in relation to the porosity and connectivity of pores.