[Show abstract][Hide abstract] ABSTRACT: In response to external stimuli, cells polarize morphologically into teardrop shapes prior to moving in the direction of their blunt leading edge through lamellipodia extension and retraction of the rear tip. This textbook description of cell migration implies that the initial polarization sets the direction of cell migration. Using microfabrication techniques to control cell morphologies and the direction of migration without gradients, we demonstrate that after polarization, lamelipodia extension and attachment can feedback to change and even reverse the initial morphological polarization. Cells do indeed migrate faster in the direction of their morphologically polarization. However, feedback from subsequent lamellipodia extension and attachment can be so powerful as to induce cells to reverse and migrate against their initial polarization, albeit at a slower speed. Constitutively active mutants of RhoA show that RhoA stimulates cell motility when cells are guided either along or against their initial polarization. Cdc42 activation and inhibition, which results in loss of directional motility during chemotaxis, only reduces the speed of migration without altering the directionality of migration on the micropatterns. These results reveal significant differences between substrate directed cell migration and that induced by chemotactic gradients.
PLoS ONE 07/2015; 10(7):e0133117. DOI:10.1371/journal.pone.0133117 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Disparities in cellular behaviour between cultures of a single cell type and heterogeneous co-cultures require constructing spatially-defined arrays of multiple cell types. Such arrays are critical for investigating cellular properties as they exist in vivo. Current methods rely upon covalent surface modification or external physical micromanipulation to control cellular organization on a limited range of substrates. Here, we report a direct approach for creating co-cultures of different cell types by microcontact printing a photosensitive cell resist. The cell-resistant polymer converts to cell adhesive 0 with light exposure, thus the initial copolymer pattern dictates the position of both cell types. This strategy enables straightforward preparation of tailored heterotypic cell-cell contacts on materials ranging from polymers to metallic substrates.
Journal of Materials Chemistry B 11/2013; 1(42):5773-5777. DOI:10.1039/C3TB21038C · 4.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Morphological polarization involving changes in cell shape and redistribution of cellular signaling machinery, initiate the migration of mammalian cells. Golgi complex typically localizes in front of the nucleus, and this frontwards polarization has been proposed to be involved in directional migration. However, the sequence of events remains unresolved. Does Golgi polarization precede directional migration or vice-versa? We address this question by constraining cells to specific areas and shapes then tracking their motile behavior and the spatio-temporal distribution of Golgi apparatus upon release. Results show that while the position of the Golgi complex depends on the cell geometry, the subcellular localization of the Golgi complex does not define the cell's leading edge. Cells constrained within elongated geometries exhibit polarized extension of lamellipodia and upon release, migrate preferentially along the long axis of the cell. Minimally constrained cells released from larger areas however, exhibit retarded migration regardless of lamellipodia protrusion activity.
[Show abstract][Hide abstract] ABSTRACT: Directing cell movements within 3D channels is a key challenge in biomedical devices and tissue engineering. In two dimensions, closely spaced arrays of asymmetric teardrop islands can intermittently polarize cells and sustain their autonomous directional migration with no gradients. However, in 3D microchannels composed of linearly connected teardrop segments, negligibly low directional bias is observed. Rather than adopt teardrop shapes, cells evade morphological polarization by spreading across multiple teardrop segments, only partly filling each. We demonstrate here that cells can be forced to adopt the shape of individual segments by connecting the segments at an angle to minimize cell spreading across multiple segments. The resulting rhythmic polarization leads to significant directional bias for NIH3T3 fibroblasts, epithelial cells, and even cells whose intracellular signalling have been purposely altered to affect lamellipodia extension (Rac1) and cell polarity (Cdc42). This gradient-free appro
[Show abstract][Hide abstract] ABSTRACT: In vivo, different cell types assemble in specific patterns to form functional tissues. Reproducing this process in vitro by designing scaffold materials to direct cells precisely to the right locations at the right time is important for the next generation of biomaterials. Here, using microarray amplification of natural directional persistence (MANDIP), simultaneous assembly of fibroblasts and endothelial cells is demonstrated by directing their long-range migration. Amplification of the directional persistence occurs through morphology-induced polarity and the asymmetric positioning of individual microsized adhesive islands that restrict lamellipodia attachment, and thus migration, to one preset direction. Quantitative analysis of cell migration on different MANDIP designs yields insight to the relative importance of the asymmetric island shapes and their arrangement. The approach enables spatial patterning of different cell types with micrometer-scale precision over large areas for investigation of cell-cell interactions within complex tissue architectures.
[Show abstract][Hide abstract] ABSTRACT: We report here a new methodology for sorting mammalian cells based on their intrinsic motility on planar substrates, independent of chemoattractants and external fields. This biological analogue of thin layer chromatography consists of arrays of asymmetric adhesive islands on tissue culture dishes that rectify the random movement of cells and direct their migration in a specific direction. We demonstrated the use of planar cell chromatography in the separation of mixtures of 3T3 fibroblasts that express constitutively active Rac1 or RhoA and mixtures of 3T3 fibroblasts and SH-SY5Y neuroblastoma cells.
[Show abstract][Hide abstract] ABSTRACT: Discrete micropatterns on biomaterial surfaces can be used to guide the direction of mammalian cell movement by orienting cell morphology. However, guiding cell assembly in three-dimensional scaffolds remains a challenge. Here we demonstrate that the random motions of motile cells can be rectified within continuous microchannels without chemotactic gradients or fluid flow. Our results show that uniform width microchannels with an overhanging zigzag design can induce polarization of NIH3T3 fibroblasts and human umbilical vein endothelial cells by expanding the cell front at each turn. These continuous zigzag microchannels can guide the direction of cell movement even for cells with altered intracellular signals that promote random movement. This approach for directing cell migration within microchannels has important potential implications in the design of scaffolds for tissue engineering.
[Show abstract][Hide abstract] ABSTRACT: In vivo, neurons form neurites, one of which develops into the axon while others become dendrites. While this neuritogenesis process is well programmed in vivo, there are limited methods to control the number and location of neurite extension in vitro. Here we report a method to control neuritogenesis by confining neurons in specific regions using cell resistant poly(oligoethyleneglycol methacrylate-co-methacrylic acid (OEGMA-co-MA)) or poly(ethyleneglycol-block-lactic acid) PEG-PLA. Line patterned substrates reduce multiple extension of neurites and stimulate bi-directional neurite budding for PC12 and cortical neurons. PC12 cells on 20 and 30 μm line patterns extended one neurite in each direction along the line pattern while cortical neuron on 20 and 30 μm line patterns extended one or two neurites in each direction along the line pattern. Statistical analysis of neurite lengths revealed that PC12 cells and cortical neurons on line patterns extend longer neurites. The ability to guide formation of neurites on patterned substrates is useful for generating neural networks and promoting neurite elongation.
Journal of Biomedical Materials Research Part A 06/2011; 97(4):451-6. DOI:10.1002/jbm.a.33082 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cell locomotion plays a key role in embryonic morphogenesis, wound healing, and cancer metastasis. Here we show that intermittent control of cell shape using microarrays can be used to amplify the natural directional persistence of cells and guide their continuous migration along preset paths and directions. The key to this geometry-based, gradient-free approach for directing cell migration is the finding that cell polarization, induced by the asymmetric shape of individual microarray islands, is retained as cells traverse between islands. Altering the intracellular signals involved in lamellipodia extension (Rac1), contractility (RhoA), and cell polarity (Cdc42) alters the speed of fibroblast migration on these micropatterns but does not affect their directional bias significantly. These results provide insights into the role of cell morphology in directional movement and the design of micropatterned materials for steering cellular traffic.
[Show abstract][Hide abstract] ABSTRACT: Differential cell migration and growth drives the organization of specific tissue forms and plays a critical role in embryonic development, tissue morphogenesis, and tumor invasion. Localized gradients of soluble factors and extracellular matrix have been shown to modulate cell migration and proliferation. Here we show that in addition to these factors, initial tissue geometry can feedback to generate differential proliferation, cell polarity, and migration patterns. We apply layer by layer polyelectrolyte assembly to confine multicellular organization and subsequently release cells to demonstrate the spatial patterns of cell migration and growth. The cell shapes, spreading areas, and cell-cell contacts are influenced strongly by the confining geometry. Cells within geometric ensembles are morphologically polarized. Symmetry breaking was observed for cells on the circular pattern and cells migrate toward the corners and in the direction parallel to the longest dimension of the geometric shapes. This migration pattern is disrupted when actomyosin based tension was inhibited. Cells near the edge or corner of geometric shapes proliferate while cells within do not. Regions of higher rate of cell migration corresponded to regions of concentrated growth. These findings demonstrate that multicellular organization can result in spatial patterns of migration and proliferation.
Experimental Cell Research 02/2011; 317(10):1340-52. DOI:10.1016/j.yexcr.2011.02.009 · 3.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fouling is one of the key factors limiting the application of membrane processes. Recent studies have demonstrated that membrane fouling can be reduced by various surface modification techniques. However, the surface modification methods currently available often result in simultaneous changes in other membrane properties (e.g. reduction in pore size, damage to the base membrane, spatial non-uniformity in the degree of modification). These complications pose a challenge to quantitatively identify the key features in the surface modification that are needed to reduce fouling.Here a controlled surface modification technique without altering other membrane properties was applied to identify the surface chemistry required for developing fouling resistant membranes. We use self-assembled monolayers with various terminal functional groups including acid, alcohol, alkane, and tri(ethylene glycol) on silver membranes to investigate the effects of membrane surface chemistry on protein fouling. This method allows uniform coating of the internal pore structure with a monolayer of the modifier.The flux decline of the tri(ethylene glycol) terminated SAMs modified membrane is significantly reduced compared to the native membrane during bovine serum albumin (BSA) filtration. Other SAMs modified membranes also showed some minor effects on reducing the rate of flux decline. These results demonstrate a new approach to modify membrane surface chemistry for fouling investigation.
Fuel and Energy Abstracts 01/2011; 366(1):342-348. DOI:10.1016/j.memsci.2010.10.021
[Show abstract][Hide abstract] ABSTRACT: We will present here recent developments on alternating copolymers of alkylmaleimides and vinyl gluconamide that spontaneously form ultra-small (10-20 nm) and medium (50-300 nm) size vesicles (Macromolecules 2009, 42, 2702-2707). The size and shape of these vesicles have been characterized by cryogenic-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and small angle neutron scattering (SANS). These alternating copolymer vesicles exhibit alkyl chain length dependent release characteristics and bilayer thickness (1.7, 2.0, and 2.6 nm for alkyl chains of 10, 12, and 14 carbons, respectively).
Recent unpublished results on the unique pH reversible self-assembly of these polymers in solution will also be presented here. Carrying no charged, acid, or base groups, these alternating polymers are insensitive to ionic strength, yet respond strongly to small changes in acidity/basicity near pH ~6, by reversibly precipitating and reassembling. DLS measurements show no change in size distribution of the vesicles before and after the acid or base additions to effect pH change. We attribute this unique behavior to hydrogen bonding interactions as observed by FTIR.
[Show abstract][Hide abstract] ABSTRACT: Alternating copolymers of N-n-alkylmaleimides and vinyl gluconamide spontaneously form ultrasmall- and medium-sized (10−20 and 50−300 nm, respectively) vesicles when dissolved in water at room temperature. These materials have molecular weights that are approximately 100 times higher than those of previously reported alternating oligomers of alkylmaleate and vinyl ether monomers and conclusively demonstrate that alternating copolymers can form vesicles. The size and shape of the vesicles are thoroughly characterized by cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The copolymer vesicles exhibit alkyl-chain-length-dependent release characteristics and bilayer thickness (1.7, 2.0, and 2.6 nm for alkyl chains of 10, 12, and 14 carbons, respectively).
[Show abstract][Hide abstract] ABSTRACT: Amphiphilic self-assembly has become the basis for a wide gamut of materials and commercial product applications. In many situations however, the best use of self-assembling complex fluids comes when their microstructures can be made permanent. The impetus for a static microstructure can often be such that an alternative non-aqueous media is preferable. Highlighted here is a new approach to capturing self-assembly through replacement of water in traditional complex fluids with sugars to form room temperature complex glasses. Combining solid and liquid properties at the nanoscale, complex glasses have broad potential applications in encapsulation and materials template synthesis.
[Show abstract][Hide abstract] ABSTRACT: The survival of three-dimensional tissue requires a vascular network to provide transport of oxygen and metabolic byproduct. Here, we report a new approach to create capillary blood vessels in vitro on biomaterials suitable for use as scaffolds in engineering tissues. Endothelial cells were cultured on chemical and topographical patterns of micro-sized grooves on gelatin. Selective attachment and spreading of cells within the grooves was ensured by microcontact printing the plateau regions with cell resistant PEG/PLA (polyethyleneglycol-L-polylacticacid). Human microvascular endothelial cells plated on these patterned biomaterials attached and spread exclusively within the grooves. These topographical features promote endothelial cells to form capillary tube-like structures. The results demonstrated that capillary structures formed on biomaterials are useful for engineering vascularized tissues.
Advances in Experimental Medicine and Biology 02/2008; 614:199-205. DOI:10.1007/978-0-387-74911-2_23 · 1.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We demonstrate here that the formation of polymervesicles is not the exclusive realm of amphiphilic block copolymers. The natural alternating conjugation of hydrophobic alkyl maleates and hydrophilic polyhydroxy vinyl ethers under free-radical polymerization conditions also yields polymers with sufficient backbone amphiphilicity to form vesicles. In contrast to conventional polymersomes, these polymervesicles have thin flexible shells capable of forming ultra-small unilamellar vesicles in water as confirmed by cryogenic-transmission electron microscopy (cryo-TEM), small-angle neutron scattering (SANS), and dynamic light scattering (DLS). The encapsulation and release characteristics of these alternating polymervesicles are, however, similar to their surfactant counterparts.
[Show abstract][Hide abstract] ABSTRACT: In aqueous systems, the hydrophobic effect drives the self-assembly of amphiphiles into a broad range of micellar, rod-like, bicontinuous and liquid-crystalline complex fluids. Many of these are relevant to biological matter or technological applications. However, amphiphilic self-assembly is not limited to aqueous systems. Replacement of water with supercritical carbon dioxide, for example, results in complex fluids that combine the properties of gases and liquids. Along this vein, we explore the self-assembly of surfactants in anhydrous sugars. Our study reveals that anhydrous powders of sugars and surfactants suspended in oil spontaneously form molten glasses with nanometre-size domains of sugar and liquid oil without mixing. The low cost, water solubility, low toxicity and stabilizing properties of glassy sugars make them ideal water replacements for many pharmaceutical, food and materials synthesis applications. The optical clarity and solid appearance of these glasses at room temperature belie their inclusion of more than 50% (vol.) oil, which confers liquid-like diffusivity. The unique combination of solid- and liquid-like properties may lead to applications in sensors and optical devices.
Nature Material 05/2007; 6(4):287-90. DOI:10.1038/nmat1864 · 36.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Micropattern arrays can be effectively used to guide the long-range directional migration of attached mammalian cells. These microarrays impose directionality with strong compliance and simultaneously guide the migration of an arbitrary number of cells independently over arbitrary paths without chemoattractants, external fields, or mechanical manipulation. Cells migrate directionally in response to gradients in chemoattractants and shear stress through complex signaling pathways that lead to coordinated local actin polymerization and depolymerization. One-way microarrays can be used to control continuously and simultaneously the migratory direction and speed of an arbitrary number of cells over long distances without external fields or stimulus gradients. The technique can also be used in several applications that include drug screening, wound healing, assembly of three dimensional tissues through cell-sheet engineering approaches, and motility-based sorting of cell mixtures.
[Show abstract][Hide abstract] ABSTRACT: We have studied the phase behavior and microstructure of edible microemulsions of d-limonene with concentrated aqueous sugar solutions (>65 wt%) using sucrose laurate and sucrose oleate as surfactants. The phase behavior of these mixtures was systematically studied as a function of temperature and surfactant composition, identifying the specific effects of sugar concentration, surfactant chain length, and oil loading on the formation of microemulsion and lamellar phases. Small-angle neutron scattering experiments confirm the presence of well-structured microemulsions with domain sizes ranging from ∼35 to 60 nm. With few exceptions, the patterns of microemulsion phase behavior with concentrated sugar solutions are very similar to that of aqueous systems.
Colloids and Surfaces A Physicochemical and Engineering Aspects 03/2007; 296(1-3):45-50. DOI:10.1016/j.colsurfa.2006.09.020 · 2.75 Impact Factor