Surface-Patterned DNA Origami Rulers Reveal Nanoscale Distance Dependency of the Epidermal Growth Factor Receptor Activation

The nanoscale arrangement of ligands can have a major effect on the activation of membrane receptor proteins and thus cellular communication mechanisms. Here we report on the technological development and use of tailored DNA origami-based molecular rulers to fabricate "Multiscale Origami Structures As Interface for Cells" (MOSAIC), to enable the systematic investigation of the effect of the nanoscale spacing of epidermal growth factor (EGF) ligands on the activation of the EGF receptor (EGFR). MOSAIC-based analyses revealed that EGF distances of about 30-40 nm led to the highest response in EGFR activation of adherent MCF7 and Hela cells. Our study emphasizes the significance of DNA-based platforms for the detailed investigation of the molecular mechanisms of cellular signaling cascades.

Biofunctional Nanodot Arrays in Living Cells Uncover Synergistic Co-Condensation of Wnt Signalodroplets

Qualitative and quantitative analysis of transient signaling platforms in the plasma membrane has remained a key experimental challenge. Here, biofunctional nanodot arrays (bNDAs) are developed to spatially control dimerization and clustering of cell surface receptors at the nanoscale. High-contrast bNDAs with spot diameters of ≈300 nm are obtained by capillary nanostamping of bovine serum albumin bioconjugates, which are subsequently biofunctionalized by reaction with tandem anti-green fluorescence protein (GFP) clamp fusions. Spatially controlled assembly of active Wnt signalosomes is achieved at the nanoscale in the plasma membrane of live cells by capturing the co-receptor Lrp6 into bNDAs via an extracellular GFP tag. Strikingly, co-recruitment is observed of co-receptor Frizzled-8 as well as the cytosolic scaffold proteins Axin-1 and Disheveled-2 into Lrp6 nanodots in the absence of ligand. Density variation and the high dynamics of effector proteins uncover highly cooperative liquid-liquid phase separation (LLPS)-driven assembly of Wnt "signalodroplets" at the plasma membrane, pinpointing the synergistic effects of LLPS for Wnt signaling amplification. These insights highlight the potential of bNDAs for systematically interrogating nanoscale signaling platforms and condensation at the plasma membrane of live cells.

Dynamic in Situ Confinement Triggers Ligand-Free Neuropeptide Receptor Signaling

Membrane receptor clustering is fundamental to cell-cell communication; however, the physiological function of receptor clustering in cell signaling remains enigmatic. Here, we developed a dynamic platform to induce cluster formation of neuropeptide Y₂ hormone receptors (Y₂R) in situ by a chelator nanotool. The multivalent interaction enabled a dynamic exchange of histidine-tagged Y₂R within the clusters. Fast Y₂R enrichment in clustered areas triggered ligand-independent signaling as determined by an increase in cytosolic calcium and cell migration. Notably, the calcium and motility response to ligand-induced activation was amplified in preclustered cells, suggesting a key role of receptor clustering in sensitizing the dose response to lower ligand concentrations. Ligand-independent versus ligand-induced signaling differed in the binding of arrestin-3 as a downstream effector, which was recruited to the clusters only in the presence of the ligand. This approach allows in situ receptor clustering, raising the possibility to explore different receptor activation modalities.

Synthesis of Silver Nano Particles Using Myricetin and the In-Vitro Assessment of Anti-Colorectal Cancer Activity: In-Silico Integration

The creation of novel anticancer treatments for a variety of human illnesses, including different malignancies and dangerous microbes, also potentially depends on nanoparticles including silver. Recently, it has been successful to biologically synthesize metal nanoparticles using plant extracts. The natural flavonoid 3,3′, 4′, 5,5′, and 7 hexahydroxyflavon (myricetin) has anticancer properties. There is not much known about the regulatory effects of myricetin on the possible cell fate-determination mechanisms (such as apoptosis/proliferation) in colorectal cancer. Because the majority of investigations related to the anticancer activity of myricetin have dominantly focused on the enhancement of tumor cell uncontrolled growth (i.e., apoptosis). Thus, we have decided to explore the potential myricetin interactors and the associated biological functions by using an in-silico approach. Then, we focused on the main goal of the work which involved the synthesis of silver nanoparticles and the labeling of myricetin with it. The synthesized silver nanoparticles were examined using UV-visible spectroscopy, dynamic light scattering spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. In this study, we have investigated the effects of myricetin on colorectal cancer where numerous techniques were used to show myricetin’s effect on colon cancer cells. Transmission Electron Microscopy was employed to monitor morphological changes. Furthermore, we have combined the results of the colorectal cancer gene expression dataset with those of the myricetin interactors and pathways. Based on the results, we conclude that myricetin is able to efficiently kill human colorectal cancer cell lines. Since, it shares important biological roles and possible route components and this myricetin may be a promising herbal treatment for colorectal cancer as per an in-silico analysis of the TCGA dataset.

Neuron-fibrous scaffold interfaces in the peripheral nervous system: a perspective on the structural requirements

The nerves of the peripheral nervous system are not able to effectively regenerate in cases of severe neural injury. This can result in debilitating consequences, including morbidity and lifelong impairments affecting the quality of the patient’s life. Recent findings in neural tissue engineering have opened promising avenues to apply fibrous tissue-engineered scaffolds to promote tissue regeneration and functional recovery. These scaffolds, known as neural scaffolds, are able to improve neural regeneration by playing two major roles, namely, by being a carrier for transplanted peripheral nervous system cells or biological cues and by providing structural support to direct growing nerve fibers towards the target area. However, successful implementation of scaffold-based therapeutic approaches calls for an appropriate design of the neural scaffold structure that is capable of up- and down-regulation of neuron-scaffold interactions in the extracellular matrix environment. This review discusses the main challenges that need to be addressed to develop and apply fibrous tissue-engineered scaffolds in clinical practice. It describes some promising solutions that, so far, have shown to promote neural cell adhesion and growth and a potential to repair peripheral nervous system injuries.

Micropatterned Ligand Arrays to Investigate Spatial Regulation of Cellular Signaling Initiated by Clustered Fc Receptors

Cell surface receptors that bind the Fc segment of antibodies to initiate signaling play fundamental roles in immune responses. Multiple, diverse Fc receptors (e.g., Fc gamma, Fc-alpha, and Fc-epsilon) are expressed on different immune cells, including natural killer cells, macrophages, mast cells, and neutrophils. Fc receptors bind particular antibody isotypes (e.g., IgG, IgA, IgE, respectively) thereby sensitizing the cells to their specific antigens. Receptor clustering by antigen or other multivalent ligands induces a signaling cascade that leads to targeted secretion of chemical mediators (e.g., histamine, cytokines, and chemokines) and other cell-specific responses. Spatial targeting and compartmentalization are common mechanisms for regulating Fc receptor signaling. However, the tools for studying these dynamic interactions at cellular levels have been limited due to the nanoscale dimensions of the signaling complexes and their dispersal across the cell surface. To overcome these limitations in our model system, we use microfabricated surfaces containing spatially defined ligands to cluster and activate IgE receptors (FcεRI), which initiate allergic responses by mast cells. Micron-scale control of receptor assemblies allows investigation with conventional fluorescence microscopy of spatially regulated redistributions of intracellular signaling components. This approach in conjunction with biochemical techniques has proven valuable for investigating immune receptor signaling.

Photoinduced receptor confinement drives ligand-independent GPCR signaling

Cell-cell communication relies on the assembly of receptor-ligand complexes at the plasma membrane. The spatiotemporal receptor organization has a pivotal role in evoking cellular responses. We studied the clustering of heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) and established a photoinstructive matrix with ultrasmall lock-and-key interaction pairs to control lateral membrane organization of hormone neuropeptide Y₂ receptors in living cells by light. Within seconds, receptor clustering was modulated in size, location, and density. After in situ confinement, changes in cellular morphology, motility, and calcium signaling revealed ligand-independent receptor activation. This approach may enhance the exploration of mechanisms in cell signaling and mechanotransduction.

New perspectives on the roles of nanoscale surface topography in modulating intracellular signaling

The physical properties of biomaterials, such as elasticity, stiffness, and surface nanotopography, are mechanical cues that regulate a broad spectrum of cell behaviors, including migration, differentiation, proliferation, and reprogramming. Among them, nanoscale surface topography, i.e. nanotopography, defines the nanoscale shape and spatial arrangement of surface elements, which directly interact with the cell membranes and stimulate changes in the cell signaling pathways. In biological systems, the effects of nanotopography are often entangled with those of other mechanical and biochemical factors. Precise engineering of 2D nanopatterns and 3D nanostructures with well-defined features has provided a powerful means to study the cellular responses to specific topographic features. In this Review, we discuss efforts in the last three years to understand how nanotopography affects membrane receptor activation, curvature-induced cell signaling, and stem cell differentiation.

Geometrical reorganization of Dectin-1 and TLR2 on single phagosomes alters their synergistic immune signaling

Receptors of innate immune cells function synergistically to detect pathogens and elicit appropriate immune responses. Many receptor pairs also appear "colocalized" on the membranes of phagosomes, the intracellular compartments for pathogen ingestion. However, the nature of the seemingly receptor colocalization and the role it plays in immune regulation are unclear, due to the inaccessibility of intracellular phagocytic receptors. Here, we report a geometric manipulation technique to directly probe the role of phagocytic receptor "colocalization" in innate immune regulation. Using particles with spatially patterned ligands as phagocytic targets, we can decouple the receptor pair, Dectin-1 and Toll-like receptor (TLR)2, to opposite sides on a single phagosome or bring them into nanoscale proximity without changing the overall membrane composition. We show that Dectin-1 enhances immune responses triggered predominantly by TLR2 when their centroid-to-centroid proximity is <500 nm, but this signaling synergy diminishes upon receptor segregation beyond this threshold distance. Our results demonstrate that nanoscale proximity, not necessarily colocalization, between Dectin-1 and TLR2 is required for their synergistic regulation of macrophage immune responses. This study elucidates the relationship between the spatial organization of phagocytic receptors and innate immune responses. It showcases a technique that allows spatial manipulation of receptors and their signal cross-talk on phagosomes inside living cells.

Recent Advances in ROS-Responsive Cell Sheet Techniques for Tissue Engineering

Cell sheet engineering has evolved rapidly in recent years as a new approach for cell-based therapy. Cell sheet harvest technology is important for producing viable, transplantable cell sheets and applying them to tissue engineering. To date, most cell sheet studies use thermo-responsive systems to detach cell sheets. However, other approaches have been reported. This review provides the progress in cell sheet detachment techniques, particularly reactive oxygen species (ROS)-responsive strategies. Therefore, we present a comprehensive introduction to ROS, their application in regenerative medicine, and considerations on how to use ROS in cell detachment. The review also discusses current limitations and challenges for clarifying the mechanism of the ROS-responsive cell sheet detachment.

Multiplex Photoluminescent Silicon Nanoprobe for Diagnostic Bioimaging and Intracellular Analysis

Herein, a label-free multiplex photoluminescent silicon nanoprobe (PLSN-probe) is introduced as a potential substitute for quantum dots (QDs) in bioimaging. An inherently non-photoluminescent silicon substrate is altered to create the PLSN-probe, to overcome the major drawbacks of presently available QDs. Additionally, crystallinity alterations of the multiplane crystalline PLSN-probes lead to broad absorption and multiplex fluorescence emissions, which are attributed to the simultaneous existence of multiple crystal planes. The PLSN-probe not only demonstrates unique optical properties that can be exploited for bioimaging but also exhibits cell-selective uptake that allows the differentiation and diagnosis of HeLa and fibroblast cells. Moreover, multiplex emissions of the PLSN-probe illuminate different organelles such as the nucleus, nucleolemma, and cytoskeleton, depending on size-based preferential uptake by the cell organs. This in vitro study reveals that cancerous HeLa cells have a higher propensity for taking up the PLSN-probe compared to fibroblast cells, allowing the diagnosis of cancerous HeLa cells. Additionally, the fluorescence intensity per unit area of the cell is found to be a reliable means for distinguishing between dead and healthy cells. It is anticipated that the multifunctionality of the PLSN-probes will lead to better insight into the use of such probes for bioimaging and diagnosis applications.

Spatial Control of Biological Ligands on Surfaces Applied to T Cell Activation

In this chapter, we present techniques, based on molecular-scale nanofabrication and selective self-assembly, for the presentation of biomolecules of interest (ligands, receptors, etc.) on a surface with precise spatial control and arbitrary geometry at the single-molecule level. Metallic nanodot arrays are created on glass coverslips and are then used as anchors for the immobilization of biological ligands via thiol linking chemistry. The nanodot size is controlled by both lithography and metallization. The reagent concentration in self-assembly can be adjusted to ensure single-molecule occupancy for a given dot size. The surrounding glass is backfilled by a protein-repellent layer to prevent nonspecific adsorption. Moreover, bifunctional surfaces are created, whereby a second ligand is presented on the background, which is frequently a requirement for simulating complex cellular functions involving more than one key ligand. This platform serves as a novel and powerful tool for molecular and cellular biology, e.g., to study the fundamental mechanisms of receptor-mediated signaling.

Applying Pattern Recognition to High-Resolution Images to Determine Cellular Signaling Status

Two frequently used tools to acquire high- resolution images of cells are scanning electron microscopy (SEM) and atomic force microscopy (AFM). The former provides a nanometer resolution view of cellular features rapidly and with high throughput, while the latter enables visualizing hydrated and living cells. In current practice, these images are viewed by eye to determine cellular status, e.g., activated versus resting. Automatic and quantitative data analysis is lacking. This paper develops an algorithm of pattern recognition that works very effectively for AFM and SEM images. Using rat basophilic leukemia cells, our approach creates a support vector machine to automatically classify resting and activated cells. Ten-fold cross-validation with cells that are known to be activated or resting gives a good estimate of the generalized classification results. The pattern recognition of AFM images achieves 100% accuracy, while SEM reaches 95.4% for our images as well as images published in prior literature. This outcome suggests that our methodology could become an important and frequently used tool for researchers utilizing AFM and SEM for structural characterization as well as determining cellular signaling status and function.

Functional nanoscale coupling of Lyn kinase with IgE-FcεRI is restricted by the actin cytoskeleton in early antigen-stimulated signaling

Spatial targeting of signaling components to activated receptors on the plasma membrane is key for initiating signal transduction. The actin cytoskeleton restricts antigen-stimulated colocalization of IgE-FcεRI with membrane-anchored signaling partner Lyn kinase, and this regulation is mediated by organization of plasma membrane lipids.

The allergic response is initiated on the plasma membrane of mast cells by phosphorylation of the receptor for immunoglobulin E (IgE), FcεRI, by Lyn kinase after IgE-FcεRI complexes are cross-linked by multivalent antigen. Signal transduction requires reorganization of receptors and membrane signaling proteins, but this spatial regulation is not well defined. We used fluorescence localization microscopy (FLM) and pair-correlation analysis to measure the codistribution of IgE-FcεRI and Lyn on the plasma membrane of fixed cells with 20- to 25-nm resolution. We directly visualized Lyn recruitment to IgE-FcεRI within 1 min of antigen stimulation. Parallel FLM experiments captured stimulation-induced FcεRI phosphorylation and colocalization of a saturated lipid-anchor probe derived from Lyn’s membrane anchorage. We used cytochalasin and latrunculin to investigate participation of the actin cytoskeleton in regulating functional interactions of FcεRI. Inhibition of actin polymerization by these agents enhanced colocalization of IgE-FcεRI with Lyn and its saturated lipid anchor at early stimulation times, accompanied by augmented phosphorylation within FcεRI clusters. Ising model simulations provide a simplified model consistent with our results. These findings extend previous evidence that IgE-FcεRI signaling is initiated by colocalization with Lyn in ordered lipid regions and that the actin cytoskeleton regulates this functional interaction by influencing the organization of membrane lipids.

Spatiotemporally Controlled Reorganization of Signaling Complexes in the Plasma Membrane of Living Cells

Triggered immobilization of proteins in the plasma membrane of living cells into functional micropatterns is established by using an adaptor protein, which is comprised of an antiGFP nanobody fused to the HaloTag protein. Efficient in situ reorganization of the type I interferon receptor subunits as well as intact, fully functional signaling complexes in living cells are achieved by this method.

One-Photon Lithography for High-Quality Lipid Bilayer Micropatterns

A relevant question in cell biology with broad implications in biomedicine is how the organization and dynamics of interacting membranes modulate signaling cascades that involve cell-cell contact. The functionalization of surfaces with supported lipid bilayers containing tethered proteins is a particularly useful method to present ligands with membrane-like mobility to cells. Here, we present a method to generate micrometer-sized patches of lipid bilayers decorated with proteins. The method uses an economic microcontact printing technique based on one-photon lithography that can be easily implemented in a commercial laser scanning microscope. We verified that both proteins and lipids freely diffuse within the patterned bilayer, as assessed by z-scan fluorescence correlation spectroscopy and fluorescence recovery after photobleaching. These results suggest that the supported lipid bilayer patterns constitute an optimal system to explore processes involving direct interactions between cells. We also illustrate possible applications of this method by exploring the interaction of cells expressing the Fas receptor and patterns of lipid bilayers containing an agonist antibody against Fas.

Engineered Nanostructures of Haptens Lead to Unexpected Formation of Membrane Nanotubes Connecting Rat Basophilic Leukemia Cells

A recent finding reports that co-stimulation of the high-affinity immunoglobulin E (IgE) receptor (FcεRI) and the chemokine receptor 1 (CCR1) triggered formation of membrane nanotubes among bone-marrow-derived mast cells. The co-stimulation was attained using corresponding ligands: IgE binding antigen and macrophage inflammatory protein 1α (MIP1 α), respectively. However, this approach failed to trigger formation of nanotubes among rat basophilic leukemia (RBL) cells due to the lack of CCR1 on the cell surface (Int. Immunol. 2010, 22 (2), 113-128). RBL cells are frequently used as a model for mast cells and are best known for antibody-mediated activation via FcεRI. This work reports the successful formation of membrane nanotubes among RBLs using only one stimulus, a hapten of 2,4-dinitrophenyl (DNP) molecules, which are presented as nanostructures with our designed spatial arrangements. This observation underlines the significance of the local presentation of ligands in the context of impacting the cellular signaling cascades. In the case of RBL, certain DNP nanostructures suppress antigen-induced degranulation and facilitate the rearrangement of the cytoskeleton to form nanotubes. These results demonstrate an important scientific concept; engineered nanostructures enable cellular signaling cascades, where current technologies encounter great difficulties. More importantly, nanotechnology offers a new platform to selectively activate and/or inhibit desired cellular signaling cascades.

Modern fluorescent techniques to investigate the mechanisms of lymphocyte activation

Fluorescent proteins are promising toolsfor studying intracellular signaling processes in lymphocytes. This brief review summarizes fluorescence-based imaging techniques developed in recent years and discusses new methodological advances, such as fluorescent photoswitches, fluorescence recovery after photobleaching (FRAP), fluorescent resonance energy transfer (FRET), fluorescence lifetime imaging microscopy (FLIM), photoactivated localization microscopy (PALM), stochastic optical reconstruction microscopy (STORM), stimulated emission depletion (STED), total internal reflection fluorescence (TIRF) and other techiques. This survey also highlights recent advances in vitro imaging of live tissues, novel applications of flow cytometry with genetically modifed fluorescent proteins, and future prospects for the development of new immunological test systems based on fluorescent protein technology.

Streptavidin functionalized polymer nanodots fabricated by visible light lithography

Background

Two-photon polymerization, optionally combined with stimulated emission depletion (STED) lithography, allows two and three dimensional polymer fabrication with structure sizes and resolution below the diffraction limit. Structuring of polymers with photons, whose wavelength is within the visible range of the electromagnetic spectrum, gives new opportunities to a large field of applications e.g. in the field of biotechnology and tissue engineering. In order to create new biotechnological applications, versatile methods are needed to functionalize the polymeric structures.

Results

Here we report the creation of polymer-nanodots with high streptavidin (SA) affinity via two-photon polymerization (TPP). Controlling the size of the polymer dots allows for limiting the number of the SA molecules. TPP dots with a diameter of a few 100 nm show up to 100% streptavidin loading. We can show that most of the dots are loaded by one to two streptavidins on average. Attached streptavidin molecules remain functional and are capable to bind 0.7 biotin molecules on average.

Conclusion

The presented functionalized nanostructures may be used as platforms for a multitude of biological experimental setups. Nanoscopic well defined structures, capable of selective binding of streptavin proteins, used as linkers for other biotinylated biomolecules, may also find application in in-vitro sensing, like for example lab on chip devices with limited surface area.

Complex micropatterning of proteins within microfluidic channels

Microfluidic channels containing protein micropatterned surfaces are useful in many bioanalytical and biological applications. In this study, we developed a new method to integrate microfluidics and protein micropatterning by attaching poly(dimethylsiloxane) (PDMS) microfluidic channels to bio-friendly photoresist films via poly(dopamine) (PDA) adhesive. A bio-friendly photoresist poly(2,2-dimethoxy nitrobenzyl methacrylate-r-methyl methacrylate-r-poly(ethylene glycol) methacrylate) (PDMP) was synthesized and used. By performing microscope projection photolithography (MPP) to the PDMP thin films within PDMS microchannels, complex micropatterns of proteins were successfully generated within microfluidic channels.

Live cell micropatterning reveals the dynamics of signaling complexes at the plasma membrane

The use of micropatterned surfaces that bind HaloTag fusion proteins allows spatial organization of plasma membrane proteins for efficient visualization and quantification of protein–protein interactions in live cells.

Interactions of proteins in the plasma membrane are notoriously challenging to study under physiological conditions. We report in this paper a generic approach for spatial organization of plasma membrane proteins into micropatterns as a tool for visualizing and quantifying interactions with extracellular, intracellular, and transmembrane proteins in live cells. Based on a protein-repellent poly(ethylene glycol) polymer brush, micropatterned surface functionalization with the HaloTag ligand for capturing HaloTag fusion proteins and RGD peptides promoting cell adhesion was devised. Efficient micropatterning of the type I interferon (IFN) receptor subunit IFNAR2 fused to the HaloTag was achieved, and highly specific IFN binding to the receptor was detected. The dynamics of this interaction could be quantified on the single molecule level, and IFN-induced receptor dimerization in micropatterns could be monitored. Assembly of active signaling complexes was confirmed by immunostaining of phosphorylated Janus family kinases, and the interaction dynamics of cytosolic effector proteins recruited to the receptor complex were unambiguously quantified by fluorescence recovery after photobleaching.

Biofunctional surface patterns retaining activity after exposure to whole blood

Biofunctional surface patterns capable of resisting nonspecific bioadsorption while retaining bioactivity play crucial roles in the advancement of life science and biomedical technologies. The currently available functional surface coatings suffer from a high level of nonspecific surface adsorption of proteins under biologically challenging conditions, leading to a loss of activity in functional moieties over time. In this study, the recently discovered facile method of temperature-induced polyelectrolyte (TIP) grafting has been used to graft two biofunctional variants (biotin and nitrilotriacetic acid, NTA) of poly(l-lysine)-grafted PEG (PLL-g-PEG) onto a titanium surface. A significant increase in the polymer adsorption was observed from the TIP-grafted surfaces assembled at 80 °C, compared to the polymer surfaces assembled at ambient temperature (20 °C). These functional PLL-g-PEG surfaces were subsequently incubated in whole human blood continuously for up to 7 days, and the TIP-grafted surfaces achieved close-to-zero nonspecific protein adsorption, as confirmed by ultrasensitive time-of-flight secondary ion mass spectrometry (ToF-SIMS). To test the maintenance of the bioactivity of the biotin and NTA moieties, submicrometer-scale mono- (biotin) and bi- (biotin/NTA) functional surface chemical patterns were fabricated via two-step TIP grafting using colloidal lithography (CL), preincubated in blood for up to 7 days and sequentially exposed to streptavidin and Ni(2+)-histidine-tagged calmodulin. The fluorescence microscopy studies revealed that the PLL-g-PEG-NTA and -biotin surfaces grafted from the TIP method were still capable of recognizing the corresponding affinity proteins for up to 1 and 7 days of preincubation in blood, respectively. These results highlight the bioresistant robustness realized by the facile TIP grafting method, which in turn preserves the activities of biofunctional moieties over a prolonged period in whole blood.

Chemically orthogonal three-patch microparticles

Compared to two-dimensional substrates, only a few methodologies exist for the spatially controlled decoration of three-dimensional objects, such as microparticles. Combining electrohydrodynamic co-jetting with synthetic polymer chemistry, we were able to create two- and three-patch microparticles displaying chemically orthogonal anchor groups on three distinct surface patches of the same particle. This approach takes advantage of a combination of novel chemically orthogonal polylactide-based polymers and their processing by electrohydrodynamic co-jetting to yield unprecedented multifunctional microparticles. Several micropatterned particles were fabricated displaying orthogonal click functionalities. Specifically, we demonstrate novel two- and three-patch particles. Multi-patch particles are highly sought after for their potential to present multiple distinct ligands in a directional manner. This work clearly establishes a viable route towards orthogonal reaction strategies on multivalent micropatterned particles.

Elliptical polymer brush ring array mediated protein patterning and cell adhesion on patterned protein surfaces

This paper presents a novel method to fabricate elliptical ring arrays of proteins. The protein arrays are prepared by covalently grafting proteins to the polymer brush ring arrays which are prepared by the techniques combining colloidal lithography dewetting and surface initiated atom-transfer radical polymerization (SI-ATRP). Through this method, the parameters of protein patterns, such as height, wall thickness, periods, and distances between two elliptical rings, can be finely regulated. In addition, the sample which contains the elliptical protein ring arrays can be prepared over a large area up to 1 cm(2), and the protein on the ring maintains its biological activity. The as-prepared ring and elliptical ring arrays (ERAs) of fibronectin can promote cell adhesion and may have an active effect on the formation of the actin cytoskeleton.

Biocompatible fluorescent silicon nanocrystals for single-molecule tracking and fluorescence imaging

Fluorescence microscopy is used extensively in cell-biological and biomedical research, but it is often plagued by three major problems with the presently available fluorescent probes: photobleaching, blinking, and large size. We have addressed these problems, with special attention to single-molecule imaging, by developing biocompatible, red-emitting silicon nanocrystals (SiNCs) with a 4.1-nm hydrodynamic diameter. Methods for producing SiNCs by simple chemical etching, for hydrophilically coating them, and for conjugating them to biomolecules precisely at a 1:1 ratio have been developed. Single SiNCs neither blinked nor photobleached during a 300-min overall period observed at video rate. Single receptor molecules in the plasma membrane of living cells (using transferrin receptor) were imaged for ≥10 times longer than with other probes, making it possible for the first time to observe the internalization process of receptor molecules at the single-molecule level. Spatial variations of molecular diffusivity in the scale of 1-2 µm, i.e., a higher level of domain mosaicism in the plasma membrane, were revealed.

Triggering cell adhesion, migration or shape change with a dynamic surface coating

There's an APP for that: cell-repellent APP (azido-[polylysine-g-PEG]) is used to create substrates for spatially controlled dynamic cell adhesion. The simple addition of a functional peptide to the culture medium rapidly triggers cell adhesion. This highly accessible yet powerful technique allows diverse applications, demonstrated through tissue motility assays, patterned coculturing and triggered cell shape change.

Hierarchical polymer brush nanoarrays: a versatile way to prepare multiscale patterns of proteins

This paper presents a versatile way to prepare multiscale and gradient patterns of proteins. The protein patterns are fabricated by conjugating proteins covalently on patterns of polymer brush that are prepared by techniques combining colloidal lithography with photolithography, and two-step colloidal lithography. Taking advantages of this technique, the parameters of protein patterns, such as height, diameters, periods, and distances between two dots, can be arbitrarily tuned. In addition, the protein patterns with varies of architectures, such as microdiscs, microstripes, microrings, microtriangles, microgrids, etc., consisting of protein nanodots, are prepared and the sample size is up to 4 cm(2). The as-prepared patterns of fibronectin can promote the cell adhesion and cell location.

Functional single-cell analysis of T-cell activation by supported lipid bilayer-tethered ligands on arrays of nanowells

Supported lipid bilayers are an important biomolecular tool for characterizing immunological synapses. Immobilized bilayers presenting tethered ligands on planar substrates have yielded both spatio-temporal and structural insights into how T cell receptors (TCRs) reorganize during the initial formation of synapses upon recognition of peptide antigens bound to major histocompatibility complex (MHC) molecules. The prototypical configuration of these assays, however, limits the extent to which the kinetics and structure of the supramolecular activation clusters of the synapse (that occur in seconds or minutes) can be related to subsequent complex cellular responses, such as cytokine secretion and proliferation, occurring over hours to days. Here we describe a new method that allows correlative measures of both attributes with single-cell resolution by using immobilized lipid bilayers and tethered ligands on the surface of dense arrays of subnanoliter wells. This modification allows each nanowell to function as an artificial antigen-presenting cell (APC), and the synapses formed upon contact can be imaged by fluorescence microscopy. We show that the lipid bilayers remain stable and mobile on the surface of the PDMS, and that modifying the ligands tethered to the bilayer alters the structure of the resulting synapses in expected ways. Finally, we demonstrate that this approach allows the subsequent characterization of secreted cytokines from the activated human T cell clones by microengraving in both antigen- and pan-specific manners. This new technique should allow detailed investigations on how biophysical and structural aspects of the synapse influence the activation of individual T cells and their complex functional responses.

Laser-induced cell detachment, patterning, and regrowth on gold nanoparticle functionalized surfaces

We report on the selective cell detachment from nanoengineered gold nanoparticle (AuNP) surfaces triggered by laser irradiation, which occurs in a nonthermal manner. The gold nanoparticle-based surfaces reveal good adhesion of NIH3T3 fibroblast cells. Patterning is achieved by lithographic microcontact printing, selective gold nanoparticle deposition, and by laser beam profiling. It is shown that the effectiveness of fibroblast cell detachment depends on the cell age, laser power, and AuNP patterning profile. Heat distribution and temperature rise around gold nanoparticle functionalized surfaces is modeled, revealing low heating of nanoparticles by laser illumination. The nonthermal photochemical mechanism of cell detachment due to production of reactive oxygen species under illumination of gold nanoparticles by green laser light is studied. We also demonstrate that cells migrate from unirradiated areas leading to their reattachment and surface recovery which is important for controlled spatial organization of cells in wound healing and tissue engineering. Research presented in this work is targeted at designing biointerfaces for cell cultures.

Nanostructures of designed geometry and functionality enable regulation of cellular signaling processes

Extracellular matrices (ECM) triggered cellular signaling processes often begin with the clustering of the cellular receptors such as integrin and FcεRI. The sizes of these initial protein complexes or clusters are tens to 100 nm in dimension; therefore, engineered nanostructures could provide effective mimics of ECM for investigation and control of the initial and downstream specific signaling processes. This current topic discusses recent advances in nanotechnology in the context of design and production of matching chemical functionality and geometry for control of specific cellular signaling processes. Two investigations are reported to demonstrate this concept: (a) how the presentation of antigen at the nanometer scale would influence the aggregation of FcεRI, which would impact the formation of activation complexes, leading to the rearrangement of actin in cytoskeleton and degranulation or activation of mast cells; (b) how the engineered nanostructure could guide the initial integrin clustering, which would impact the formation of focal adhesion and downstream cell signaling cascades, leading to polarization, migration, and morphological changes. Complementary to engineered ECMs using synthetic ligands or peptides, or topographic control at the micrometer scale, nanostructures of designed geometry and chemical functionality provide new and effective biochemical cues for regulation of cellular signaling processes and downstream behaviors.

Tuning ratios, densities, and supramolecular spacing in bifunctional DNA-modified gold nanoparticles

Methods for combining multiple functions into well-defined nanomaterials are still lacking, despite their need in nanomedicine and within the broader field of nanotechnology. Here several strategies for controlling the amount and the ratio of combinations of labeled DNA on 13-nm gold nanoparticles using self-assembly of thiolated DNA and/or DNA-directed assembly are explored. It is found that the self-assembly of mixtures of fluorescently labeled DNA can lead to a higher amount of labeled DNA per particle; however, the ratio of fluorophores on the nanoparticles differs greatly from that in the self-assembly solution. In contrast, when fluorescently labeled DNA are hybridized to DNA-modified gold nanoparticles, the fluorophore ratio on the nanoparticles is much closer to their ratio in solution. The use of bifunctional DNA-doublers in self-assembly and DNA-directed assembly is also explored to increase the complexity of these materials and control their composition. Finally, tuning the distance between the labels from 2.9 to 5.4 nm was achieved using different hybridized DNA clamp complexes. Fluorescent results suggest that assembling these clamps on nanoparticle surfaces may be possible, although the resulting label spacing could not be quantified.

Nanofabrication for the analysis and manipulation of membranes

Recent advancements and applications of nanofabrication have enabled the characterization and control of biological membranes at submicron scales. This review focuses on the application of nanofabrication towards the nanoscale observing, patterning, sorting, and concentrating membrane components. Membranes on living cells are a necessary component of many fundamental cellular processes that naturally incorporate nanoscale rearrangement of the membrane lipids and proteins. Nanofabrication has advanced these understandings, for example, by providing 30 nm resolution of membrane proteins with metal-enhanced fluorescence at the tip of a scanning probe on fixed cells. Naturally diffusing single molecules at high concentrations on live cells have been observed at 60 nm resolution by confining the fluorescence excitation light through nanoscale metallic apertures. The lateral reorganization on the plasma membrane during membrane-mediated signaling processes has been examined in response to nanoscale variations in the patterning and mobility of the signal-triggering molecules. Further, membrane components have been separated, concentrated, and extracted through on-chip electrophoretic and microfluidic methods. Nanofabrication provides numerous methods for examining and manipulating membranes for both greater understandings of membrane processes as well as for the application of membranes to other biophysical methods.

Exploring the formation of focal adhesions on patterned surfaces using super-resolution imaging

The formation of focal adhesions on various sizes of fibronectin patterns, ranging from 200 μm to 250 nm, was systematically investigated by total internal reflection fluorescence microscopy and super-resolution imaging. It was found that cells adhered to and spread on these micro/nanopatterns, forming focal adhesions. On a micrometer scale the shape of the focal adhesions was elongated. However, on the nanometer scale, the shape of focal adhesions became dotlike. To further explore the distribution of focal adhesion proteins formed on surfaces, a localization-based super-resolution imaging technique was employed in order to determine the position and density of vinculin proteins. A characteristic distance of 50 nm was found between vinculin molecules in the focal adhesions, which did not depend on the size of the fibronectin nanopatterns. This distance was found to be crucial for the formation of focal adhesions. In addition, the density of vinculin at the focal adhesions formed on the nanopatterns increased as the pattern size decreased. The density of the protein was found to be 425 ± 247, 584 ± 302, and 703 ± 305 proteins μm(-2) on the 600, 400, and 250 nm fibronectin patterns respectively. Whereas 226 ± 77 proteins μm(-2) was measured for the matured focal adhesions on homogeneous fibronectin coated substrates. The increase in vinculin density implies that an increase in mechanical load was applied to the focal adhesions formed on the smaller nanopatterns.

Micropatterned ligand arrays to study spatial regulation in Fc receptor signaling

Fc receptor signaling plays a fundamental role in immune responses. A plethora of Fc -receptors (e.g., Fc gamma, Fc-alpha, and Fc-epsilon) are expressed on different immune cells, including natural killer cells, macrophages, mast cells, and neutrophils. Receptor clustering and activation by multivalent ligands or opsonized particles induce a signaling cascade that leads to targeted secretion of chemical mediators (i.e., histamine, cytokines, and chemokines) and phagocytosis, among other responses. Spatial targeting and compartmentalization are common mechanisms of regulation in Fc receptor signaling. However, the tools for studying these dynamic interactions have been limited. To overcome these limitations in our model system, microfabricated surfaces containing spatially defined ligands are used to cluster- and activate IgE receptors (FcεRI), involved in allergic responses by mast cells. Micron-scale control of cell activation allows investigation of spatially regulated mechanisms for intracellular signaling with -fluorescence microscopy. This approach in conjunction with biochemical techniques has proven to be valuable for investigating immune receptor signaling.

Nanofiber-modified surface directed cell migration and orientation in microsystem

Cell-microscale pattern surface interactions are crucial to understand many fundamental biological questions and develop regenerative medicine and tissue engineering approaches. In this work, we demonstrated a simple method to pattern PDMS surface by sacrificing poly vinyl pyrrolidone (PVP) electrospinning nanofibers and investigated the growth profile of cells on the modified patterned surfaces using stroma cells. The stromal cells were observed to exhibit good viability on this modified surface and the patterned surface with alignment nanofibers could promote cell migration. Furthermore, the modified PDMS surface was integrated with microfluidic channels to create the microscale spatial factor and was used to explore the cell migration and orientation under this microsystem. Both spatial factor and patterned surfaces were found to contribute to the complex cell orientation under the combined dual effects. This established method is simple, fast, and easy for use, demonstrating the potential of this microsystem for applications in addressing biological questions in complex environment.

Nanoparticle-functionalized polymer platform for controlling metastatic cancer cell adhesion, shape, and motility

Controlling and understanding the changes in metastatic cancer cell adhesion, shape, and motility are of paramount importance in cancer research, diagnosis, and treatment. Here, we used gold nanoparticles (AuNPs) as nanotopological structures and protein nanocluster forming substrates. Cell adhesion controlling proteins [in this case, fibronection (Fn) and ephrinB3] were modified to AuNPs, and these particles were then modified to the layer-by-layer (LbL) polymer surface that offers a handle for tuning surface charge and mechanical property of a cell-interfacing substrate. We found that metastatic cancer cell adhesion is affected by nanoparticle density on a surface, and ∼140 particles per 400 μm(2) (∼1.7 μm spacing between AuNPs) is optimal for effective metastatic cell adhesion. It was also shown that the AuNP surface density and protein nanoclustering on a spherical AuNP are controlling factors for the efficient interfacing and signaling of metastatic cancer cells. Importantly, the existence of nanotopological features (AuNPs in this case) is much more critical in inducing more dramatic changes in metastatic cell adhesion, protrusion, polarity, and motility than the presence of a cell adhesion protein, Fn, on the surface. Moreover, cell focal adhesion and motility-related paxillin clusters were heavily formed in cell lamellipodia and filopodia and high expression of phospho-paxillins were observed when the cells were cultured on either an AuNP or Fn-modified AuNP polymer surface. The ephrin signaling that results in the decreased expression of paxillin was found to be more effective when ephrins were modified to the AuNP surface than when ephrinB3 was directly attached to the polymer film. The overall trend for cell motility change is such that a nanoparticle-modified LbL surface induces higher cell motility and the AuNP modification to the LbL surface results in more pronounced change in cell motility than Fn or ephrin modification to the LbL surface.

Cellular responses to patterned poly(acrylic acid) brushes

We use patterned poly(acrylic acid) (PAA) polymer brushes to explore the effects of surface chemistry and topography on cell-surface interactions. Most past studies of surface topography effects on cell adhesion have focused on patterned feature sizes that are larger than the dimensions of a cell, and PAA brushes have been characterized as cell repellent. Here we report cell adhesion studies for RBL mast cells incubated on PAA brush surfaces patterned with a variety of different feature sizes. We find that when patterned at subcellular dimensions on silicon surfaces, PAA brushes that are 30 or 15 nm thick facilitate cell adhesion. This appears to be mediated by fibronectin, which is secreted by the cells, adsorbing to the brushes and then engaging cell-surface integrins. The result is detectable accumulation of plasma membrane within the brushes, and this involves cytoskeletal remodeling at the cell-surface interface. By decreasing brush thickness, we find that PAA can be 'tuned' to promote cell adhesion with down-modulated membrane accumulation. We exemplify the utility of patterned PAA brush arrays for spatially controlling the activation of cells by modifying brushes with ligands that specifically engage IgE bound to high-affinity receptors on mast cells.

Large-area protein patterns generated by ordered binary colloidal assemblies as templates

We demonstrate the use of binary colloidal assemblies as lithographic masks to generate tunable Au patterns on SiO(2) substrates with dimensions ranging from micrometers to nanometers. Such patterns can be modified with different chemistries to create patterns with well-defined sites for selective adsorption of proteins, where the pattern size and spacing is adjustable depending on particle choice. In our system, the binary colloidal assemblies contain large and small particles of similar or different material and are self-assembled from dilute dispersions with particle size ratios ranging from 0.10 to 0.50. This allows masks with variable morphology and thus production of chemical patterns of tunable geometry. Finally, the Au or SiO(2) regions of the pattern are surface modified with protein resistant oligoethyleneglycol self-assembled molecules, which facilitates site selective adsorption of proteins into the unmodified regions of the pattern. This we show with fluorescently labeled bovine serum albumin.

Effect of fiber diameter on the spreading, proliferation and differentiation of chondrocytes on electrospun chitosan matrices

Tissue-engineered neocartilage with appropriate biomechanical properties holds promise not only for graft applications but also as a model system for controlled studies of chondrogenesis. Our objective in the present research study is to better understand the impact of fiber diameter on the cellular activity of chondrocytes cultured on nanofibrous matrices. By using the electrospinning process, fibrous scaffolds with fiber diameters ranging from 300 nm to 1 μm were prepared and the physicomechanical properties of the scaffolds were characterized. Bovine articular chondrocytes were then seeded and maintained on the scaffolds for 7 and 14 days in culture. An upregulation in the gene expression of collagen II was noted with decreasing fiber diameters. For cells that were cultured on scaffolds with a mean fiber diameter of 300 nm, a 2-fold higher ratio of collagen II/collagen I was noted when compared to cells cultured on sponge-like scaffolds prepared by freeze drying and lyophilization. Integrin (α(5), αv, β(1)) gene expression was also observed to be influenced by matrix morphology. Our combined results suggest that matrix geometry can regulate and promote the retention of the chondrocyte genotype.