Modular design of micropattern geometry achieves combinatorial enhancements in cell motility

Shape of scaffold controlling the direction of cell migration

Cell migration plays an important role in the development and maintenance of multicellular organisms. Factors that induce cell migration and mechanisms controlling their expression are important for determining the mechanisms of factor-induced cell migration. Despite progress in the study of factor-induced cytotaxis, including chemotaxis and haptotaxis, precise control of the direction of cell migration over a wide area has not yet been achieved. Success in this area would update the cell migration assays, superior cell separation technologies, and artificial organs with high biocompatibility. The present study therefore sought to control the direction of cell migration over a wide area by adjusting the three-dimensional shape of the cell scaffold. The direction of cell migration was influenced by the shape of the cell scaffold, thereby optimizing cell adhesion and protrusion. Anisotropic arrangement of these three-dimensional shapes into a periodic structure induced unidirectional cell migration. Three factors were required for unidirectional cell migration: 1) the sizes of the anisotropic periodic structures had to be equal to or lower than the size of the spreading cells, 2) cell migration was restricted to a runway approximately the width of the cell, and 3) cells had to be prone to extension of long protrusions in one direction. Because the first two factors had been identified previously in studies of cell migration in one direction using two-dimensional shaped patterns, these three factors are likely important for the mechanism by which cell scaffold shapes regulate cell migration.

Advances in Regulating Cellular Behavior Using Micropatterns

Micropatterns, characterized as distinct physical microstructures or chemical adhesion matrices on substance surfaces, have emerged as a powerful tool for manipulating cellular activity. By creating specific extracellular matrix microenvironments, micropatterns can influence various cell behaviors, including orientation, proliferation, migration, and differentiation. This review provides a comprehensive overview of the latest advancements in the use of micropatterns for cell behavior regulation. It discusses the influence of micropattern morphology and coating on cell behavior and the underlying mechanisms. It also highlights future research directions in this field, aiming to inspire new investigations in materials medicine, regenerative medicine, and tissue engineering. The review underscores the potential of micropatterns as a novel approach for controlling cell behavior, which could pave the way for breakthroughs in various biomedical applications.

Guiding cell adhesion and motility by modulating cross-linking and topographic properties of microgel arrays

Biomaterial-driven modulation of cell adhesion and migration is a challenging aspect of tissue engineering. Here, we investigated the impact of surface-bound microgel arrays with variable geometry and adjustable cross-linking properties on cell adhesion and migration. We show that cell migration is inversely correlated with microgel array spacing, whereas directionality increases as array spacing increases. Focal adhesion dynamics is also modulated by microgel topography resulting in less dynamic focal adhesions on surface-bound microgels. Microgels also modulate the motility and adhesion of Sertoli cells used as a model for cell migration and adhesion. Both focal adhesion dynamics and speed are reduced on microgels. Interestingly, Gas2L1, a component of the cytoskeleton that mediates the interaction between microtubules and microfilaments, is dispensable for the regulation of cell adhesion and migration on microgels. Finally, increasing microgel cross-linking causes a clear reduction of focal adhesion turnover in Sertoli cells. These findings not only show that spacing and rigidity of surface-grafted microgels arrays can be effectively used to modulate cell adhesion and motility of diverse cellular systems, but they also form the basis for future developments in the fields of medicine and tissue engineering.

Multivariate relationships among nucleus and Golgi properties during fibrillar migration are robust to and unchanged by epithelial-to-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT) and maturation of a fibrillar tumor microenvironment play important roles in breast cancer progression. A better understanding of how these events promote cancer cell migration and invasion could help identify new strategies to curb metastasis. The nucleus and Golgi affect migration in a microenvironment-dependent manner. Nucleus size and mechanics influence the ability of a cell to squeeze through confined tumor microenvironments. Golgi positioning determines front-rear polarity necessary for migration. While the roles of individual attributes of nucleus and Golgi in migration are being clarified, how their manifold features are inter-related and work together remains to be understood at a systems level. Here, to elucidate relationships among nucleus and Golgi properties, we quantified twelve morphological and positional properties of these organelles during fibrillar migration of human mammary epithelial cells. Principal component analysis (PCA) reduced the twelve-dimensional space of measured properties to three principal components that capture 75% of the variations in organelle features. Unexpectedly, nucleus and Golgi properties that co-varied in a PCA model built with data from untreated cells were largely similar to co-variations identified using data from TGFβ-treated cells. Thus, while TGFβ-mediated EMT significantly alters gene expression and motile phenotype, it did not significantly affect the relationships among nucleus size, aspect ratio and orientation with migration direction and among Golgi size and nucleus-Golgi separation distance. Indeed, in a combined PCA model incorporating data from untreated and TGFβ-treated cells, scores of individual cells occupy overlapping regions in principal component space, indicating that TGFβ-mediated EMT does not promote a unique “Golgi-nucleus phenotype” during fibrillar migration. These results suggest that migration along spatially-confined fiber-like tracks employs a conserved nucleus-Golgi arrangement that is independent of EMT state.

A 3D Microfabricated Scaffold System for Unidirectional Cell Migration

The present study demonstrates unidirectional cell migration using a novel 3D microfabricated scaffold, as revealed by the uneven sorting of cells into an area of 1 mm × 1 mm. To induce unidirectional cell migration, it is important to determine the optimal arrangement of 3D edges, and thus, the anisotropic periodic structures of micropatterns are adjusted appropriately. The cells put forth protrusions directionally along the sharp edges of these micropatterns, and migrated in the protruding direction. There are three advantages to this novel system. First, the range of applications is wide, because this system effectively induces unidirectional migration as long as 3D shapes of the scaffolds are maintained. Second, this system can contribute to the field of cell biology as a novel taxis assay. Third, this system is highly applicable to the development of medical devices. In the present report, unique 3D microfabricated scaffolds that provoked unidirectional migration of NIH3T3 cells are described. The 3D scaffolds could provoke cells to accumulate in a single target location, or could provoke a dissipated cell distribution. Because the shapes are very simple, they could be applied to the surfaces of various medical devices. Their utilization as a cell separation technology is also anticipated.

Area and Geometry Dependence of Cell Migration in Asymmetric Two-State Micropatterns

Microstructured surfaces provide a unique framework to probe cell migration and cytoskeletal dynamics in a standardized manner. Here, we report on the steady-state occupancy probability of cells in asymmetric two-state microstructures that consist of two fibronectin-coated adhesion sites connected by a thin guidance cue. In these dumbbell-like structures, cells transition between the two sites in a repeated and stochastic manner, and average dwell times in the respective microenvironments are determined from the cell trajectories. We study the dynamics of human breast carcinoma cells (MDA-MB-231) in these microstructures as a function of area, shape, and orientation of the adhesion sites. On square adhesive sites with different areas, we find that the occupancy probability ratio is directly proportional to the ratio of corresponding adhesion site areas. These asymmetries are well captured by a simple model for the stochastic nonlinear dynamics of the cells, which reveals generic features of the motion. Sites of equal area but different shape lead to equal occupancy if shapes are isotropic (e.g., squared or circular). In contrast, an asymmetry in the occupancy is induced by anisotropic shapes like rhombi, triangles, or rectangles that enable motion in the direction perpendicular to the transition axis. Analysis of the two-dimensional motion of cells between two rectangles with orthogonal orientation suggests that cellular transition rates depend on the cell polarization induced by anisotropic micropatterns. Taken together, our results illustrate how two-state micropatterns provide a dynamic migration assay with distinct dwell times and relative cell occupancy as readouts, which may be useful to probe cell-microenvironment interactions.

Golgi Stabilization, Not Its Front-Rear Bias, Is Associated with EMT-Enhanced Fibrillar Migration

Epithelial-to-mesenchymal transition (EMT) and maturation of collagen fibrils in the tumor microenvironment play a significant role in cancer cell invasion and metastasis. Confinement along fiber-like tracks enhances cell migration. To what extent and in what manner EMT further promotes migration in a microenvironment already conducive to migration is poorly understood. Here, we show that TGFβ-mediated EMT significantly enhances migration on fiber-like micropatterned tracks of collagen, doubling migration speed and tripling persistence relative to untreated mammary epithelial cells. Thus, cell-intrinsic EMT and extrinsic fibrillar tracks have nonredundant effects on motility. To better understand EMT-enhanced fibrillar migration, we investigated the regulation of Golgi positioning, which is involved in front-rear polarization and persistent cell migration. Confinement along fiber-like tracks has been reported to favor posterior Golgi positioning, whereas anterior positioning is observed during 2-day wound healing. Although EMT also regulates cell polarity, little is known about its effect on Golgi positioning. Here, we show that EMT induces a 2:1 rearward bias in Golgi positioning; however, positional bias explains less than 2% of single-cell variability in migration speed and persistence. Meanwhile, EMT significantly stabilizes Golgi positioning. Cells that enhance migration in response to TGFβ maintain Golgi position for 2- to 4-fold longer than nonresponsive counterparts irrespective of whether the Golgi is ahead or behind the nucleus. In fact, 28% of TGFβ-responsive cells exhibit a fully committed Golgi phenotype with the organelle either in the anterior or posterior position for over 90% of the time. Furthermore, single-cell differences in Golgi stability capture up to 18% of variations in migration speed. These results suggest a hypothesis that the Golgi may be part of a core physical scaffold that affects how cell-generated forces are distributed during migration. A stable scaffold would be expected to more consistently and therefore more productively distribute forces over time, leading to efficient migration.

Positive Quantitative Relationship between EMT and Contact-Initiated Sliding on Fiber-like Tracks

Epithelial-mesenchymal transition (EMT) is a complex process by which cells acquire invasive properties that enable escape from the primary tumor. Complete EMT, however, is not required for metastasis: circulating tumor cells exhibit hybrid epithelial-mesenchymal states, and genetic perturbations promoting partial EMT induce metastasis in vivo. An open question is whether and to what extent intermediate stages of EMT promote invasiveness. Here, we investigate this question, building on recent observation of a new invasive property. Migrating cancer cell lines and cells transduced with prometastatic genes slide around other cells on spatially confined, fiberlike micropatterns. We show here that low-dosage/short-duration exposure to transforming growth factor beta (TGFβ) induces partial EMT and enables sliding on narrower (26 μm) micropatterns than untreated counterparts (41 μm). High-dosage/long-duration exposure induces more complete EMT, including disrupted cell-cell contacts and reduced E-cadherin expression, and promotes sliding on the narrowest (15 μm) micropatterns. These results identify a direct and quantitative relationship between EMT and cell sliding and show that EMT-associated invasive sliding is progressive, with cells that undergo partial EMT exhibiting intermediate sliding behavior and cells that transition more completely through EMT displaying maximal sliding. Our findings suggest a model in which fiber maturation and EMT work synergistically to promote invasiveness during cancer progression.

Label-Free Automated Cell Tracking: Analysis of the Role of E-cadherin Expression in Collective Electrotaxis

Collective cell migration plays an important role in wound healing, organogenesis, and the progression of metastatic disease. Analysis of collective migration typically involves laborious and time-consuming manual tracking of individual cells within cell clusters over several dozen or hundreds of frames. Herein, we develop a label-free, automated algorithm to identify and track individual epithelial cells within a free-moving cluster. We use this algorithm to analyze the effects of partial E-cadherin knockdown on collective migration of MCF-10A breast epithelial cells directed by an electric field. Our data show that E-cadherin knockdown in free-moving cell clusters diminishes electrotactic potential, with empty vector MCF-10A cells showing 16% higher directedness than cells with E-cadherin knockdown. Decreased electrotaxis is also observed in isolated cells at intermediate electric fields, suggesting an adhesion-independent role of E-cadherin in regulating electrotaxis. In additional support of an adhesion-independent role of E-cadherin, isolated cells with reduced E-cadherin expression reoriented within an applied electric field 60% more quickly than control. These results have implications for the role of E-cadherin expression in electrotaxis and demonstrate proof-of-concept of an automated algorithm that is broadly applicable to the analysis of collective migration in a wide range of physiological and pathophysiological contexts.

Modeling cell shape and dynamics on micropatterns

Adhesive micropatterns have become a standard tool to study cells under defined conditions. Applications range from controlling the differentiation and fate of single cells to guiding the collective migration of cell sheets. In long-term experiments, single cell normalization is challenged by cell division. For all of these setups, mathematical models predicting cell shape and dynamics can guide pattern design. Here we review recent advances in predicting and explaining cell shape, traction forces and dynamics on micropatterns. Starting with contour models as the simplest approach to explain concave cell shapes, we move on to network and continuum descriptions as examples for static models. To describe dynamic processes, cellular Potts, vertex and phase field models can be used. Different types of model are appropriate to address different biological questions and together, they provide a versatile tool box to predict cell behavior on micropatterns.

Ring-Shaped Microlanes and Chemical Barriers as a Platform for Probing Single-Cell Migration

Quantification and discrimination of pharmaceutical and disease-related effects on cell migration requires detailed characterization of single-cell motility. In this context, micropatterned substrates that constrain cells within defined geometries facilitate quantitative readout of locomotion. Here, we study quasi-one-dimensional cell migration in ring-shaped microlanes. We observe bimodal behavior in form of alternating states of directional migration (run state) and reorientation (rest state). Both states show exponential lifetime distributions with characteristic persistence times, which, together with the cell velocity in the run state, provide a set of parameters that succinctly describe cell motion. By introducing PEGylated barriers of different widths into the lane, we extend this description by quantifying the effects of abrupt changes in substrate chemistry on migrating cells. The transit probability decreases exponentially as a function of barrier width, thus specifying a characteristic penetration depth of the leading lamellipodia. Applying this fingerprint-like characterization of cell motion, we compare different cell lines, and demonstrate that the cancer drug candidate salinomycin affects transit probability and resting time, but not run time or run velocity. Hence, the presented assay allows to assess multiple migration-related parameters, permits detailed characterization of cell motility, and has potential applications in cell biology and advanced drug screening.

Optimizing micropattern geometries for cell shape and migration with genetic algorithms

Adhesive micropatterns have become a standard tool to control cell shape and function in cell culture.

Slope-Dependent Cell Motility Enhancements at the Walls of PEG-Hydrogel Microgroove Structures

In recent years, research utilizing micro- and nanoscale geometries and structures on biomaterials to manipulate cellular behaviors, such as differentiation, proliferation, survival, and motility, have gained much popularity; however, how the surface microtopography of 3D objects, such as implantable devices, can affect these various cell behaviors still remains largely unknown. In this study, we discuss how the walls of microgroove topography can influence the morphology and the motility of unrestrained cells, in a different fashion from 2D line micropatterns. Here adhesive substrates made of tetra(polyethylene glycol) (tetra-PEG) hydrogels with microgroove structures or 2D line micropatterns were fabricated, and cell motility on these substrates was evaluated. Interestingly, despite being unconstrained, the cells exhibited drastically different migration behaviors at the edges of the 2D micropatterns and the walls of microgroove structures. In addition to acquiring a unilamellar morphology, the cells increased their motility by roughly 3-fold on the microgroove structures, compared with the 2D counterpart or the nonpatterned surface. Immunostaining revealed that this behavior was dependent on the alignment and the aggregation of the actin filaments, and by varying the slope of the microgroove walls, it was found that relatively upright walls are necessary for this cell morphology alterations. Further progress in this research will not only deepen our understanding of topography-assisted biological phenomena like cancer metastasis but also enable precise, topography-guided manipulation of cell motility for applications such as cancer diagnosis and cell sorting.

Collective migration exhibits greater sensitivity but slower dynamics of alignment to applied electric fields

During development and disease, cells migrate collectively in response to gradients in physical, chemical and electrical cues. Despite its physiological significance and potential therapeutic applications, electrotactic collective cell movement is relatively less well understood. Here, we analyze the combined effect of intercellular interactions and electric fields on the directional migration of non-transformed mammary epithelial cells, MCF-10A. Our data show that clustered cells exhibit greater sensitivity to applied electric fields but align more slowly than isolated cells. Clustered cells achieve half-maximal directedness with an electric field that is 50% weaker than that required by isolated cells; however, clustered cells take ∼2-4 fold longer to align. This trade-off in greater sensitivity and slower dynamics correlates with the slower speed and intrinsic directedness of collective movement even in the absence of an electric field. Whereas isolated cells exhibit a persistent random walk, the trajectories of clustered cells are more ballistic as evidenced by the superlinear dependence of their mean square displacement on time. Thus, intrinsically-directed, slower clustered cells take longer to redirect and align with an electric field. These findings help to define the operating space and the engineering trade-offs for using electric fields to affect cell movement in biomedical applications.

Microfabricated Systems and Assays for Studying the Cytoskeletal Organization, Micromechanics, and Motility Patterns of Cancerous Cells

Cell motions are driven by coordinated actions of the intracellular cytoskeleton - actin, microtubules (MTs) and substrate/focal adhesions (FAs). This coordination is altered in metastatic cancer cells resulting in deregulated and increased cellular motility. Microfabrication tools, including photolithography, micromolding, microcontact printing, wet stamping and microfluidic devices have emerged as a powerful set of experimental tools with which to probe and define the differences in cytoskeleton organization/dynamics and cell motility patterns in non-metastatic and metastatic cancer cells. In this review, we discuss four categories of microfabricated systems: (i) micropatterned substrates for studying of cell motility sub-processes (for example, MT targeting of FAs or cell polarization); (ii) systems for studying cell mechanical properties, (iii) systems for probing overall cell motility patterns within challenging geometric confines relevant to metastasis (for example, linear and ratchet geometries), and (iv) microfluidic devices that incorporate co-cultures of multiple cells types and chemical gradients to mimic in vivo intravasation/extravasation steps of metastasis. Together, these systems allow for creating controlled microenvironments that not only mimic complex soft tissues, but are also compatible with live cell high-resolution imaging and quantitative analysis of single cell behavior.

Directed cytoskeleton self-organization

The cytoskeleton architecture supports many cellular functions. Cytoskeleton networks form complex intracellular structures that vary during the cell cycle and between different cell types according to their physiological role. These structures do not emerge spontaneously. They result from the interplay between intrinsic self-organization properties and the conditions imposed by spatial boundaries. Along these boundaries, cytoskeleton filaments are anchored, repulsed, aligned, or reoriented. Such local effects can propagate alterations throughout the network and guide cytoskeleton assembly over relatively large distances. The experimental manipulation of spatial boundaries using microfabrication methods has revealed the underlying physical processes directing cytoskeleton self-organization. Here we review, step-by-step, from molecules to tissues, how the rules that govern assembly have been identified. We describe how complementary approaches, all based on controlling geometric conditions, from in vitro reconstruction to in vivo observation, shed new light on these fundamental organizing principles.