Nanofiber curvature with Rho GTPase activity increases mouse embryonic fibroblast random migration velocity

Mechanotransduction arises from information encoded in the shape of materials such as curvature. It induces activation of small GTPase signaling affecting cell phenotypes including differentiation. We carried out a set of preliminary experiments to test the hypothesis that curvature (1/radius) would also affect cell motility due to signal pathway crosstalk. High molecular weight poly (methyl methacrylate) straight nanofibers were electrospun with curvature ranging from 41 to 1 μm−1 and collected on a passivated glass substrate. The fiber curvature increased mouse mesenchymal stem cell aspect ratio (P < 0.02) and decreased cell area (P < 0.01). Despite little effect on some motility patterns such as polarity and persistence, we found selected fiber curvatures can increase normalized random fibroblastic mouse embryonic cell (MEF) migration velocity close to 2.5 times compared with a flat surface (P < 0.001). A maximum in the velocity curve occurred near 2.5 μm−1 and may vary with the time since initiation of attachment to the surface (range of 0–20 h). In the middle range of fiber curvatures, the relative relationship to curvature was similar regardless of treatment with Rho-kinase inhibitor (Y27632) or cdc42 inhibitor (ML141), although it was decreased on most curvatures (P < 0.05). However, below a critical curvature threshold MEFs may not be able to distinguish shallow curvature from a flat surface, while still being affected by contact guidance. The preliminary data in this manuscript suggested the large low curvature fibers were interpreted in a manner similar to a non-curved surface. Thus, curvature is a biomaterial construct design parameter that should be considered when specific biological responses are desired. Statement of integration, innovation, and insight Replacement of damaged or diseased tissues that cannot otherwise regenerate is transforming modern medicine. However, the extent to which we can rationally design materials to affect cellular outcomes remains low. Knowing the effect of material stiffness and diameter on stem cell differentiation, we investigated cell migration and signaling on fibrous scaffolds. By investigating diameters across orders of magnitude (50–2000 nm), we identified a velocity maximum of ~800 nm. Furthermore, the results suggest large fibers may not be interpreted by single cells as a curved surface. This work presents insight into the design of constructs for engineering tissues.

Migration velocity analysis based on focusing diffractions generated using the CRS wavefront attributes: Application to real land data

In land seismic data processing, the prestack time migration (PSTM) image remains the standard imaging output, but a reliable migrated image of the subsurface depends on the accuracy of the migration velocity model. We have adopted two new algorithms for time-domain migration velocity analysis based on wavefield attributes of the common-reflection-surface (CRS) stack method. These attributes, extracted from multicoverage data, were successfully applied to build the velocity model in the depth domain through tomographic inversion of the normal-incidence-point (NIP) wave. However, there is no practical and reliable method for determining an accurate and geologically consistent time-migration velocity model from these CRS attributes. We introduce an interactive method to determine the migration velocity model in the time domain based on the application of NIP wave attributes and the CRS stacking operator for diffractions, to generate synthetic diffractions on the reflection events of the zero-offset (ZO) CRS stacked section. In the ZO data with diffractions, the poststack time migration (post-STM) is applied with a set of constant velocities, and the migration velocities are then selected through a focusing analysis of the simulated diffractions. We also introduce an algorithm to automatically calculate the migration velocity model from the CRS attributes picked for the main reflection events in the ZO data. We determine the precision of our diffraction focusing velocity analysis and the automatic velocity calculation algorithms using two synthetic models. We also applied them to real 2D land data with low quality and low fold to estimate the time-domain migration velocity model. The velocity models obtained through our methods were validated by applying them in the Kirchhoff PSTM of real data, in which the velocity model from the diffraction focusing analysis provided significant improvements in the quality of the migrated image compared to the legacy image and to the migrated image obtained using the automatically calculated velocity model.

Molecular dynamics study of the influence of uniaxial deformation on the migration velocity of tilt boundaries in nickel

The molecular dynamics method was used to study the influence of elastic uniaxial deformation on the migration velocity of tilt boundaries with misorientation axes [100] and [111] in nickel. The dependences of the migration velocity at a temperature of 1600 K on the misorientation angle were obtained. It is shown that the high-angle [100] and [111] tilt boundaries migrate at approximately the same velocity, while the low-angle [111] boundaries migrate approximately twice as fast as the [100] boundaries. The obtained dependences of the migration velocity of the boundaries on the value of uniaxial deformation in almost all cases turned out to be nonmonotonic and had a maximum at a tension value of about 1%. With a further increase in tension, migration slowed down, which is most likely explained by a decrease in the surface tension of the boundaries and, accordingly, in the driving force due to the finite sorption capacity of grain boundaries with respect to the free volume. Under elastic compression, in most cases, a monotonic decrease in the migration velocity was observed, which is due to a decrease in free space during compression and a decrease in the mobility of atoms at the boundary.

Joint inversion of the reflectivity and the velocity model

During linearized waveform inversion, the presence of small inaccuracies in the background subsurface model can lead to unfocused seismic events in the final image. The effect on the amplitude can mislead the interpretation. We present a joint inversion scheme in the model domain of the reflectivity and the background velocity model. The idea is to unify the inversion of the background and the reflectivity model into a single framework instead of treating them as decoupled problems. We show that with this method, we can obtain a better estimate of the reflectivity than that obtained with conventional linearized waveform inversion. Conversely, the background model is improved by the joint inversion with the reflectivity in comparison with wave-equation migration velocity analysis. We perform tests on 2D synthetics and 3D field data that demonstrate both benefits.

Angle-domain common-image gathers from plane-wave least-squares reverse time migration

Angle-domain common-image gathers (ADCIGs) that can be used for migration velocity analysis and amplitude versus angle analysis are important for seismic exploration. However, because of limited acquisition geometry and seismic frequency band, the ADCIGs extracted by reverse time migration (RTM) suffer from illumination gaps, migration artifacts, and low resolution. We have developed a reflection angle-domain pseudo-extended plane-wave least-squares RTM method for obtaining high-quality ADCIGs. We build the mapping relations between the ADCIGs and the plane-wave sections using an angle-domain pseudo-extended Born modeling operator and an adjoint operator, based on which we formulate the extraction of ADCIGs as an inverse problem. The inverse problem is iteratively solved by a preconditioned stochastic conjugate gradient method, allowing for reduction in computational cost by migrating only a subset instead of the whole dataset and improving image quality thanks to preconditioners. Numerical tests on synthetic and field data verify that the proposed method can compensate for illumination gaps, suppress migration artifacts, and improve resolution of the ADCIGs and the stacked images. Therefore, compared with RTM, the proposed method provides a more reliable input for migration velocity analysis and amplitude versus angle analysis. Moreover, it also provides much better stacked images for seismic interpretation.

Development of Gelatin-Based Flexible Three-Dimensional Capillary Pattern Microfabrication Technology for Analysis of Collective Cell Migration

Collective cell migration is thought to be a dynamic and interactive behavior of cell cohorts that is essential for diverse physiological developments in living organisms. Recent studies revealed that the topographical properties of the environment regulate the migration modes of cell cohorts, such as diffusion versus contraction relaxation transport and the appearance of vortices in larger available space. However, conventional in vitro assays fail to observe changes in cell behavior in response to the structural changes. In this study, we developed a method to fabricate the flexible three-dimensional structures of capillary microtunnels to examine the behavior of vascular endothelial cells (ECs). Microtunnels with altering diameters were formed inside gelatin gel through spot heating a portion of gelatin by irradiating the µm-sized absorption at the tip of the microneedle with a focused permeable 1064 nm infrared laser. The ECs moved and spread two-dimensionally on the inner surface of the capillary microtunnels as a monolayer instead of filling the capillary. In contrast to the 3D straight topographical constraint, which exhibited width-dependent migration velocity, the leading ECs altered its migration velocity according to the change in the supply of cells behind the leading ECs, caused by their progression through the diameter-altering structure. Our findings provide insights into the collective migration modes inside 3D confinement structures, including their fluid-like behavior and the conservation of cell numbers.