Gradient Cues Research Articles

Gradient Nanofiber Scaffolds for Tissue Engineering

Scaffolds are one of the key factors for the success of tissue engineering, in particular when dealing with anchorage-dependent cells. The concept of using scaffolds in tissue engineering lies in mimicking the physical, chemical and biological features of native extracellular matrix (ECM) in order to support cell function, which in turn regulates cellular microenvironment that directs cell growth and subsequent tissue formation. Nanofibers fabricated from both synthetic and natural polymers are being used as scaffolds in many tissue engineering applications. At the molecular level, native ECM is made up of a gradient of fibrous proteins and polysaccharides that are nanoscale structures. The gradient cues of ECM, directs critical cell behaviors such as alignment, motility and differentiation, particularly in the region between soft and hard tissues called interfacial tissue. Therefore, it is essential to develop gradient nanofiber scaffolds particularly for interfacial tissue engineering applications. Keeping these points in view, in this article, we review the recent developments of gradient nanofiber scaffolds, their design strategies, and their applications in tissue engineering.

Directional Migration of Vascular Smooth Muscle Cells Guided by a Molecule Weight Gradient of Poly(2-hydroxyethyl methacrylate) Brushes

Directional migration of cells mediated by gradient cues in vitro can mimic the corresponding biological events in vivo and thereby provides a way to disclose the cascade responses in tissue regeneration processes and to develop novel criteria for design of tissue-inductive biomaterials. In this work, a molecular weight gradient of poly(2-hydroxyethyl methacrylate) (PHEMA) brushes with a thickness ranging from 3 to 30 nm and slopes of 0.8-3.2 nm/mm were fabricated by using surface-initiated atom transfer radical polymerization (ATRP) and a dynamically controlled reaction process. The PHEMA gradients were characterized by X-ray photoelectron spectrometry (XPS) and ellipsometry. The adhesion number, spreading area, adhesion force, and expression of focal adhesion and actin fibers of vascular smooth muscle cells (VSMCs) decreased along with the increase of the PHEMA brushes length. The VSMCs exhibited preferential orientation and enhanced directional migration toward the direction of reduced PHEMA thickness, whose extent was dependent on the gradient slope and polymer thickness. Most of the cells were oriented, and 87% of the cells moved directionally at the optimal conditions.

Directional cell migration through cell–cell interaction on polyelectrolyte multilayers with swelling gradients

The directional cell migration plays a crucial role in a variety of physiological and pathological processes. It can be controlled by the gradient cues immobilized on the substrate. The poly(sodium 4-styrenesulfonate) (PSS)/poly(diallyldimethylammonium) chloride (PDADMAC) multilayers were post-treated in a gradient NaCl solution with a concentration ranging from 3 m to 5 m, yielding the gradient multilayers with a similar chemistry composition (PSS domination) but gradually changed swelling ratio. The gradient nature and physicochemical properties were characterized by X-ray photoelectron spectroscopy and ellipsometry. Compared to the random migration with a lower rate at a smaller cell-seeding density, the vascular smooth muscle cells migrated directionally to the low hydration side at an appropriate cell-seeding density (1.5 × 104/cm2) under the assistance of cell–cell interactions. The cell migration rates on the gradient surface were significantly larger than those on the corresponding uniform surfaces etched by salt solutions of the same concentrations. Relative cell adherent strength and focal adhesion formation were studied to unveil the intrinsic mechanism of the gradient multilayers on the cell migration. It was found that both the gradient cues and cell–cell contact have major influences on the directional cell migration.

Representation of 3-D surface orientation by velocity and disparity gradient cues in area MT

Neural coding of the three-dimensional (3-D) orientation of planar surface patches may be an important intermediate step in constructing representations of complex 3-D surface structure. Spatial gradients of binocular disparity, image velocity, and texture provide potent cues to the 3-D orientation (tilt and slant) of planar surfaces. Previous studies have described neurons in both dorsal and ventral stream areas that are selective for surface tilt based on one or more of these gradient cues. However, relatively little is known about whether single neurons provide consistent information about surface orientation from multiple gradient cues. Moreover, it is unclear how neural responses to combinations of surface orientation cues are related to responses to the individual cues. We measured responses of middle temporal (MT) neurons to random dot stimuli that simulated planar surfaces at a variety of tilts and slants. Four cue conditions were tested: disparity, velocity, and texture gradients alone, as well as all three gradient cues combined. Many neurons showed robust tuning for surface tilt based on disparity and velocity gradients, with relatively little selectivity for texture gradients. Some neurons showed consistent tilt preferences for disparity and velocity cues, whereas others showed large discrepancies. Responses to the combined stimulus were generally well described as a weighted linear sum of responses to the individual cues, even when disparity and velocity preferences were discrepant. These findings suggest that area MT contains a rudimentary representation of 3-D surface orientation based on multiple cues, with single neurons implementing a simple cue integration rule.

Edge Point Grouping for Line Detection

SUMMARY This paper proposes a method of accurately detecting the boundary of narrow stripes, such as lane markings, by employing gradient cues of edge points. Using gradient direction cues, the edge points at the two sides of the boundary of stripes are classified into two groups before the Hough transform is applied to extract the boundary lines. The experiments show that the proposed method improves significantly the performance in terms of the accuracy of boundary detection of narrow stripes over the con

The Selectivity of Neurons in the Macaque Fundus of the Superior Temporal Area for Three-Dimensional Structure from Motion

Motion is a potent cue for the perception of three-dimensional (3D) shape in primates, but little is known about its underlying neural mechanisms. Guided by recent functional magnetic resonance imaging results, we tested neurons in the fundus of the superior temporal sulcus (FST) area of two macaque monkeys (Macaca mulatta, one male) using motion-defined surface patches with various 3D shapes such as slanted planes, saddles, or cylinders. The majority of the FST neurons (>80%) were selective for stimuli depicting specific shapes, and all the surfaces tested were represented among the selective FST neurons. Importantly, this selectivity tolerated changes in speed, position, size, or between binocular and monocular presentations. This tolerance demonstrates that the 3D structure-from-motion (3D-SFM) selectivity of FST neurons is a higher-order selectivity, which cannot be reduced to a lower-order speed selectivity. The 3D-SFM selectivity of FST neurons was unaffected by removal of the opposed-motion cue that supplemented the speed gradient cue in the standard stimuli. When tested with the same standard stimuli, fewer neurons in the middle temporal/visual 5 (MT/V5) area were selective than FST neurons. In addition, selective MT/V5 neurons represented fewer types of surfaces and were less tolerant of stimulus changes than FST neurons. Overall, these results indicate that FST neurons code motion-defined 3D shape fragments, underscoring the central role of FST in processing 3D-SFM.

Gender Differences in the Effects of Acute Stress on Spatial Ability

Although reports that men and women differ in spatial ability are common, recent research examining stress effects on spatial navigation have not included analyses of gender differences. The current study investigated cue perception and mental rotation after an acute cold-water hand immersion stress in 156 undergraduates from the western United States. Gender differences were observed in spatial performance and spatial anxiety. Discriminant analysis revealed that distal gradient cue identification and mental rotation reaction times as well as spatial anxiety differed among men and women exposed to the acute stress and their warm-water hand immersion controls. These results indicate that stress differentially alters spatial performance in men and women, and underscores the importance of assessing gender differences when examining spatial ability.

Ground-plane influences on size estimation in early visual processing

Ground-planes have an important influence on the perception of 3D space ( Gibson, 1950) and it has been shown that the assumption that a ground-plane is present in the scene plays a role in the perception of object distance ( Bruno & Cutting, 1988). Here, we investigate whether this influence is exerted at an early stage of processing, to affect the rapid estimation of 3D size. Participants performed a visual search task in which they searched for a target object that was larger or smaller than distracter objects. Objects were presented against a background that contained either a frontoparallel or slanted 3D surface, defined by texture gradient cues. We measured the effect on search performance of target location within the scene (near vs. far) and how this was influenced by scene orientation (which, e.g., might be consistent with a ground or ceiling plane, etc.). In addition, we investigated how scene orientation interacted with texture gradient information (indicating surface slant), to determine how these separate cues to scene layout were combined. We found that the difference in target detection performance between targets at the front and rear of the simulated scene was maximal when the scene was consistent with a ground-plane – consistent with the use of an elevation cue to object distance. In addition, we found a significant increase in the size of this effect when texture gradient information (indicating surface slant) was present, but no interaction between texture gradient and scene orientation information. We conclude that scene orientation plays an important role in the estimation of 3D size at an early stage of processing, and suggest that elevation information is linearly combined with texture gradient information for the rapid estimation of 3D size.

Mechanical Gradient Cues for Guided Cell Motility and Control of Cell Behavior on Uniform Substrates

AbstractA novel method for the fabrication and the use of simple uniform poly(dimethylsiloxane) PDMS substrates for controlling cell motility by a mechanical gradient is reported. The substrate is fabricated in PDMS using soft lithography and consists of a soft membrane suspended on top of a patterned PDMS substrate. The difference in the gradient stiffness is related to the underlying pattern. It is shown experimentally that these uniform substrates can modulate the response of cell motility, thus enabling patterning on the surfaces with precise cell motility. Because of the uniformity of the substrate, cells can spread equally and a directional movement to stiffer regions is clearly observed. Varying the geometry underlying the membrane, cell patterning and movement can be quantitatively characterized. This procedure is capable of controlling cell motility with high fidelity over large substrate areas. The most significant advance embodied in this method is that it offers the use of mechanical features to control cell adhesion and not topographical or chemical variations, which has not been reported so far. This modulation of the response of cell motility will be useful for the design and fabrication of advanced planar and 3D biological assemblies suitable for applications in the field of biotechnology and for tissue‐engineering purposes.

Sex differences in cue perception in a visual scene: Investigation of cue type.

Sex differences in spatial navigation indicate that women may focus on positional, landmark cues whereas men favor Euclidean, directional cues. Some studies have investigated sex differences in proximal and distal cue use; however, sex differences in gradient (i.e., graded features) and pinpoint (i.e., single, defined) cue perception remain unexamined. In the current experiments, paired photographs were presented in which the 2nd photograph showed the same scene with cues removed (Experiment 1) or isolated (Experiment 2) from the 1st photograph. In Experiment 1, women showed less disruption of task performance than men showed following cue removal but were slowest after proximal pinpoint cue removal. Male performance was slowed by distal gradient and proximal pinpoint cue removal. In Experiment 2, women were faster than men at identifying isolated proximal and distal pinpoint cues and were more accurate at identifying isolated distal gradient and distal pinpoint cues. Better pinpoint cue perception and memory in women indicates one possible mechanism underlying female preference for landmark-based navigation strategies. Findings also show that whereas men may preferentially rely on distal gradient cues they are not better at perceiving those cues than are women.

A hybrid 3D watershed algorithm incorporating gradient cues and object models for automatic segmentation of nuclei in confocal image stacks.

Automated segmentation of fluorescently-labeled cell nuclei in 3D confocal microscope images is essential to many studies involving morphological and functional analysis. A common source of segmentation error is tight clustering of nuclei. There is a compelling need to minimize these errors for constructing highly automated scoring systems. A combination of two approaches is presented. First, an improved distance transform combining intensity gradients and geometric distance is used for the watershed step. Second, an explicit mathematical model for the anatomic characteristics of cell nuclei such as size and shape measures is incorporated. This model is constructed automatically from the data. Deliberate initial over-segmentation of the image data is performed, followed by statistical model-based merging. A confidence score is computed for each detected nucleus, measuring how well the nucleus fits the model. This is used in combination with the intensity gradient to control the merge decisions. Experimental validation on a set of rodent brain cell images showed 97% concordance with the human observer and significant improvement over prior methods. Combining a gradient-weighted distance transform with a richer morphometric model significantly improves the accuracy of automated segmentation and FISH analysis.

Neural correlates for perception of 3D surface orientation from texture gradient.

A goal in visual neuroscience is to reveal how the visual system reconstructs the three-dimensional (3D) representation of the world from two-dimensional retinal images. Although the importance of texture gradient cues in the process of 3D vision has been pointed out, most studies concentrate on the neural process based on binocular disparity. We report the neural correlates of depth perception from texture gradient in the cortex. In the caudal part of the lateral bank of intraparietal sulcus, many neurons were selective to 3D surface orientation defined by texture gradient, and their response was invariant over different types of texture pattern. Most of these neurons were also sensitive to a disparity gradient, suggesting that they integrate texture and disparity gradient signals to construct a generalized representation of 3D surface orientation.

Object tracking using deformable templates

We propose a method for object tracking using prototype-based deformable template models. To track an object in an image sequence, we use a criterion which combines two terms: the frame-to-frame deviations of the object shape and the fidelity of the modeled shape to the input image. The deformable template model utilizes the prior shape information which is extracted from the previous frames along with a systematic shape deformation scheme to model the object shape in a new frame. The following image information is used in the tracking process: 1) edge and gradient information: the object boundary consists of pixels with large image gradient, 2) region consistency: the same object region possesses consistent color and texture throughout the sequence, and 3) interframe motion: the boundary of a moving object is characterized by large interframe motion. The tracking proceeds by optimizing an objective function which combines both the shape deformation and the fidelity of the modeled shape to the current image (in terms of gradient, texture, and interframe motion). The inherent structure in the deformable template, together with region, motion, and image gradient cues, makes the proposed algorithm relatively insensitive to the adverse effects of weak image features and moderate amounts of occlusion.

Hand Action in a Radial Direction Captures Visual Motion in Depth

Transversal hand action in the frontoparallel plane biases the perception of bistable visual motion. This has been called action capture. In daily behaviour, however, hand action in a ‘radial’ direction from the head might be more important, because we frequently reach our hand for an object in front of us while guiding the action with vision. The purpose of this study was to measure the strength of action capture in the radial direction. Horizontal luminance gratings were placed above and below the fixation point. Binocular disparity, perspective contour, and spatial frequency gradient cues were attached to the gratings so that they simulated the ‘ceiling’ and the ‘floor’ of a long corridor. The display was reflected on a tilted mirror to face upward. The subject looked into the display and moved his/her dominant hand toward, or away from, the face behind the mirror. Just after the action onset, detected by the computer, one of the two gratings (the ceiling or the floor) flickered in short period to simulate bistable visual motion in depth (approaching or departing). The subject indicated the perceived motion direction in the frontoparallel plane using a 2AFC (upward or downward) method. The results showed that perceived motion was significantly biased to the ‘departing’ direction when the hand moved ‘away from’ the face, and it was biased to the ‘approaching’ direction when the hand moved ‘toward’ it. It is concluded that action capture occurs not only in transversal but also in radial movements.

UNDERWATER ORIENTATION IN THE SAND FIDDLER CRAB,UCA PUGILATOR

The semi-terrestrial sand fiddler crab, Uca pugilator, occasionally is forced by avian and mammalian predators to go into the water where it becomes vulnerable to aquatic predators. Therefore, it would be adaptive for Uca to possess some means of detecting the direction of the shore and its burrow while submerged. Using crabs from Florida and Long Island, New York, the identity of the cues used in underwater orientation and the possible hierarchial arrangement of these cues were ascertained.Under various cue regimes, the crabs were individually observed in a long narrow tank that allowed the crabs to proceed either toward shore or away from it. The potential cues for shoreward orientation which were available to the submerged crab were celestial cues, landmarks, and gradient cues (hydrostatic pressure, light wavelength, light intensity and substrate slope). Each cue was isolated and then tested for its effectiveness in orientation. It was next presented to the crabs in a conflicting configuration with oth...