Patterning self-assembled monolayers using microcontact printing: A new technology for biosensors?

Shape memory cycle conditions impact human bone marrow stromal cell binding to RGD- and YIGSR-conjugated poly (glycerol dodecanedioate)

Bioresorbable shape memory polymers (SMP) are an emerging class of polymers that can help address several challenges associated with minimally invasive surgery by providing a solution for structural tissue repair. Like most synthetic polymer networks, SMPs require additional biorelevance and modification for biomedical applications. Methodologies used to incorporate bioactive ligands must preserve SMP thermomechanics and ensure biofunctionality following in vivo delivery. We have previously described the development of a novel thermoresponsive bioresorbable SMP, poly (glycerol dodecanedioate) (PGD). In this study, cell-adhesive peptide sequences RGD and YIGSR were conjugated with PGD. We investigated 1) the impact of conjugated peptides on the fixity (Rf), recovery (Rr), and recovery rate (dRr/dT), 2) the impact of conjugated peptides on cell binding, and 3) the impact of the shape memory cycle (Tprog) on conjugated peptide functionality towards binding human bone marrow stromal cells (BMSC). Peptide conjugation conditions impact fixity but not the recovery or recovery rate (p < 0.01). Peptide-conjugated substrates increased cell attachment and proliferation compared with controls (p < 0.001). Using complementary integrin binding cell-adhesive peptides increased proliferation compared with using single peptides (p < 0.05). Peptides bound to PGD substrates exhibited specificity to their respective integrin targets. Following the shape memory cycle, peptides maintained functionality and specificity depending on the shape memory cycle conditions (p < 0.001). The dissipation of strain energy during recovery can drive differential arrangement of conjugated sequences impacting functionality, an important design consideration for functionalized SMPs. STATEMENT OF SIGNIFICANCE: Shape memory elastomers are an emerging class of polymers that are well-suited for minimally invasive repair of soft tissues. Tissue engineering approaches commonly utilize biodegradable scaffolds to deliver instructive cues, including cells and bioactive signals. Delivering these instructive cues on biodegradable shape memory elastomers requires modification with bioactive ligands. Furthermore, it is necessary to ensure the specificity of the ligands to their biological targets when conjugated to the polymer. Moreover, the bioactive ligand functionality must be conserved after completing the shape memory cycle, for applications in tissue engineering.

Toward the Development of Rapid, Specific, and Sensitive Microfluidic Sensors: A Comprehensive Device Blueprint

Recent advances in nano/microfluidics have led to the miniaturization of surface-based chemical and biochemical sensors, with applications ranging from environmental monitoring to disease diagnostics. These systems rely on the detection of analytes flowing in a liquid sample, by exploiting their innate nature to react with specific receptors immobilized on the microchannel walls. The efficiency of these systems is defined by the cumulative effect of analyte detection speed, sensitivity, and specificity. In this perspective, we provide a fresh outlook on the use of important parameters obtained from well-characterized analytical models, by connecting the mass transport and reaction limits with the experimentally attainable limits of analyte detection efficiency. Specifically, we breakdown when and how the operational (e.g., flow rates, channel geometries, mode of detection, etc.) and molecular (e.g., receptor affinity and functionality) variables can be tailored to enhance the analyte detection time, analytical specificity, and sensitivity of the system (i.e., limit of detection). Finally, we present a simple yet cohesive blueprint for the development of high-efficiency surface-based microfluidic sensors for rapid, sensitive, and specific detection of chemical and biochemical analytes, pertinent to a variety of applications.

Solid-Phase Microcontact Printing for Precise Patterning of Rough Surfaces: Using Polymer-Tethered Elastomeric Stamps for the Transfer of Reactive Silanes

We present a microcontact printing (μCP) routine suitable to introduce defined (sub-) microscale patterns on surface substrates exhibiting a high capillary activity and receptive to a silane-based chemistry. This is achieved by transferring functional trivalent alkoxysilanes, such as (3-aminopropyl)-triethoxysilane (APTES) as a low-molecular weight ink via reversible covalent attachment to polymer brushes grafted from elastomeric polydimethylsiloxane (PDMS) stamps. The brushes consist of poly{N-[tris(hydroxymethyl)-methyl]acrylamide} (PTrisAAm) synthesized by reversible addition-fragmentation chain-transfer (RAFT)-polymerization and used for immobilization of the alkoxysilane-based ink by substituting the alkoxy moieties with polymer-bound hydroxyl groups. Upon physical contact of the silane-carrying polymers with surfaces, the conjugated silane transfers to the substrate, thus completely suppressing ink-flow and, in turn, maximizing printing accuracy even for otherwise not addressable substrate topographies. We provide a concisely conducted investigation on polymer brush formation using atomic force microscopy (AFM) and ellipsometry as well as ink immobilization utilizing two-dimensional proton nuclear Overhauser enhancement spectroscopy (¹H-¹H-NOESY-NMR). We analyze the μCP process by printing onto Si-wafers and show how even distinctively rough surfaces can be addressed, which otherwise represent particularly challenging substrates.

The impact of antifouling layers in fabricating bioactive surfaces

Bioactive surfaces modified with functional peptides are critical for both fundamental research and practical application of implant materials and tissue repair. However, when bioactive molecules are tethered on biomaterial surfaces, their functions can be compromised due to unwanted fouling (mainly nonspecific protein adsorption and cell adhesion). In recent years, researchers have continuously studied antifouling strategies to obtain low background noise and effectively present the function of bioactive molecules. In this review, we describe several commonly used antifouling strategies and analyzed their advantages and drawbacks. Among these strategies, antifouling molecules are widely used to construct the antifouling layer of various bioactive surfaces. Subsequently, we summarize various structures of antifouling molecules and their surface grafting methods and characteristics. Application of these functionalized surfaces in microarray, biosensors, and implants are also introduced. Finally, we discuss the primary challenges associated with antifouling layers in fabricating bioactive surfaces and provide prospects for the future development of this field. STATEMENT OF SIGNIFICANCE: The nonspecific protein adsorption and cell adhesion will cause unwanted background "noise" on the surface of biological materials and detecting devices and compromise the performance of functional molecules and, therefore, impair the performance of materials and the sensitivity of devices. In addition, the selection of antifouling surfaces with proper chain length and high grafting density is also of great importance and requires further studies. Otherwise, the surface-tethered bioactive molecules may not function in their optimal status or even fail to display their functions. Based on these two critical issues, we summarize antifouling molecules with different structures, variable grafting methods, and diverse applications in biomaterials and biomedical devices reported in literature. Overall, we expect to shed some light on choosing the appropriate antifouling molecules in fabricating bioactive surfaces.

Integration of FISH and Microfluidics

Suitable molecular methods for a faster microbial identification in food and clinical samples have been explored and optimized during the last decades. However, most molecular methods still rely on time-consuming enrichment steps prior to detection, so that the microbial load can be increased and reach the detection limit of the techniques.In this chapter, we describe an integrated methodology that combines a microfluidic (lab-on-a-chip) platform, designed to concentrate cell suspensions and speed up the identification process in Saccharomyces cerevisiae , and a peptide nucleic acid fluorescence in situ hybridization (PNA-FISH) protocol optimized and adapted to microfluidics. Microfluidic devices with different geometries were designed, based on computational fluid dynamics simulations, and subsequently fabricated in polydimethylsiloxane by soft lithography. The microfluidic designs and PNA-FISH procedure described here are easily adaptable for the detection of other microorganisms of similar size.

Fabrication of Tapered 3D Microstructure Arrays Using Dual-Exposure Lithography (DEL)

Three-dimensional (3D) microstructure arrays (MSAs) have been widely used in material science and biomedical applications by providing superhydrophobic surfaces, cell-interactive topography, and optical diffraction. These properties are tunable through the engineering of microstructure shapes, dimensions, tapering, and aspect ratios. However, the current fabrication methods are often too complex, expensive, or low-throughput. Here, we present a cost-effective approach to fabricating tapered 3D MSAs using dual-exposure lithography (DEL) and soft lithography. DEL used a strip-patterned film mask to expose the SU-8 photoresist twice. The mask was re-oriented between exposures (90° or 45°), forming an array of dual-exposed areas. The intensity distribution from both exposures overlapped and created an array of 3D overcut micro-pockets in the unexposed regions. These micro-pockets were replicated to DEL-MSAs in polydimethylsiloxane (PDMS). The shape and dimension of DEL-MSAs were tuned by varying the DEL parameters (e.g., exposure energy, inter-exposure wait time, and the photomask re-orientation angle). Further, we characterized various properties of our DEL-MSAs and studied the impact of their shape and dimension. All DEL-MSAs showed optical diffraction capability and increased hydrophobicity compared to plain PDMS surface. The hydrophobicity and diffraction angles were tunable based on the MSA shape and aspect ratio. Among the five MSAs fabricated, the two tallest DEL-MSAs demonstrated superhydrophobicity (contact angles >150°). Further, these tallest structures also demonstrated patterning proteins (with ~6–7 μm resolution), and mammalian cells, through microcontact printing and direct culturing, respectively. Our DEL method is simple, scalable, and cost-effective to fabricate structure-tunable microstructures for anti-wetting, optical-, and bio-applications.

Wetting-Controlled Localized Placement of Surface Functionalities within Nanopores

In the context of sensing and transport control, nanopores play an essential role. Designing multifunctional nanopores and placing multiple surface functionalities with nanoscale precision remains challenging. Interface effects together with a combination of different materials are used to obtain local multifunctionalization of nanoscale pores within a model pore system prepared by colloidal templating. Silica inverse colloidal monolayers are first functionalized with a gold layer to create a hybrid porous architecture with two distinct gold nanostructures on the top surface as well as at the pore bottom. Using orthogonal silane- and thiol-based chemistry together with a control of the wetting state allows individual addressing of the different locations within each pore resulting in nanoscale localized functional placement of three different functional units. Ring-opening metathesis polymerization is used for inner silica-pore wall functionalization. The hydrophobized pores create a Cassie-Baxter wetting state with aqueous solutions of thiols, which enables an exclusive functionalization of the outer gold structures. In a third step, an ethanolic solution able to wet the pores is used to self-assemble a thiol-containing initiator at the pore bottom. Subsequent controlled radical polymerization provides functionalization of the pore bottom. It is demonstrated that the combination of orthogonal surface chemistry and controlled wetting states can be used for the localized functionalization of porous materials.

Chemical Lift-Off Lithography of Metal and Semiconductor Surfaces

Chemical lift-off lithography (CLL) is a subtractive soft-lithographic technique that uses polydimethylsiloxane (PDMS) stamps to pattern self-assembled monolayers of functional molecules for applications ranging from biomolecule patterning to transistor fabrication. A hallmark of CLL is preferential cleavage of Au-Au bonds, as opposed to bonds connecting the molecular layer to the substrate, i.e., Au-S bonds. Herein, we show that CLL can be used more broadly as a technique to pattern a variety of substrates composed of coinage metals (Pt, Pd, Ag, Cu), transition and reactive metals (Ni, Ti, Al), and a semiconductor (Ge) using straightforward alkanethiolate self-assembly chemistry. We demonstrate high-fidelity patterning in terms of precise features over large areas on all surfaces investigated. We use patterned monolayers as chemical resists for wet etching to generate metal microstructures. Substrate atoms, along with alkanethiolates, were removed as a result of lift-off, as previously observed for Au. We demonstrate the formation of PDMS-stamp-supported bimetallic monolayers by performing CLL on two different metal surfaces using the same PDMS stamp. By expanding the scope of the surfaces compatible with CLL, we advance and generalize CLL as a method to pattern a wide range of substrates, as well as to produce supported metal monolayers, both with broad applications in surface and materials science.

Nanotechnology with S-layer Proteins

Nanosciences are distinguished by the cross-fertilization of biology, chemistry, material sciences, and solid-state physics and, hence, open up a great variety of new opportunities for innovation. The technological utilization of self-assembly systems, wherein molecules spontaneously associate under equilibrium conditions into reproducible supramolecular structures, is one key challenge in nanosciences for life and non-life science applications. The attractiveness of such processes is due to their ability to build uniform, ultra-small functional units with predictable properties down to the nanometer scale. Moreover, newly developed techniques and methods open up the possibility to exploit these structures at meso- and macroscopic scale. An immense significance at innovative approaches for the self-assembly of supramolecular structures and devices with dimensions of a few to tens of nanometers constitutes the utilization of crystalline bacterial cell surface proteins. The latter have proven to be particularly suited as building blocks in a molecular construction kit comprising of all major classes of biological molecules. The controlled immobilization of biomolecules in an ordered fashion on solid substrates and their directed confinement in definite areas of nanometer dimensions are key requirements for many applications including the development of bioanalytical sensors, biochips, molecular electronics, biocompatible surfaces, and signal processing between functional membranes, cells, and integrated circuits.

Quantifying the effects of engineered nanomaterials on endothelial cell architecture and vascular barrier integrity using a cell pair model

Engineered nanomaterials (ENMs) are increasingly used in consumer products due to their unique physicochemical properties, but the specific hazards they pose to the structural and functional integrity of endothelial barriers remain elusive. When assessing the effects of ENMs on vascular barrier function, endothelial cell monolayers are commonly used as in vitro models. Monolayer models, however, do not offer a granular understanding of how the structure-function relationships between endothelial cells and tissues are disrupted due to ENM exposure. To address this issue, we developed a micropatterned endothelial cell pair model to quantitatively evaluate the effects of 10 ENMs (8 metal/metal oxides and 2 organic ENMs) on multiple cellular parameters and determine how these parameters correlate to changes in vascular barrier function. This minimalistic approach showed concerted changes in endothelial cell morphology, intercellular junction formation, and cytoskeletal organization due to ENM exposure, which were then quantified and compared to unexposed pairs using a "similarity scoring" method. Using the cell pair model, this study revealed dose-dependent changes in actin organization and adherens junction formation following exposure to representative ENMs (Ag, TiO2 and cellulose nanocrystals), which exhibited trends that correlate with changes in tissue permeability measured using an endothelial monolayer assay. Together, these results demonstrate that we can quantitatively evaluate changes in endothelial architecture emergent from nucleo-cytoskeletal network remodeling using micropatterned cell pairs. The endothelial pair model therefore presents potential applicability as a standardized assay for systematically screening ENMs and other test agents for their cellular-level structural effects on vascular barriers.

Single molecule protein patterning using hole mask colloidal lithography

The ability to manipulate single protein molecules on a surface is useful for interfacing biology with many types of devices in optics, catalysis, bioengineering, and biosensing. Control of distance, orientation, and activity at the single molecule level will allow for the production of on-chip devices with increased biological activity. Cost effective methodologies for single molecule protein patterning with tunable pattern density and scalable coverage area remain a challenge. Herein, Hole Mask Colloidal Lithography is presented as a bench-top colloidal lithography technique that enables a glass coverslip to be patterned with functional streptavidin protein onto patches from 15-200 nm in diameter with variable pitch. Atomic force microscopy (AFM) was used to characterize the size of the patterned features on the glass surface. Additionally, single-molecule fluorescence microscopy was used to demonstrate the tunable pattern density, measure binding controls, and confirm patterned single molecules of functional streptavidin.

Bio-orthogonal fluorinated resist for biomolecules patterning applications

The patterning of organic materials on solid substrate surfaces has been demonstrated by several methods, such as photolithography, soft lithography, imprint lithography and ink-jet printing. Fluorinated polymers and solvents provide attractive material systems to develop new patterning approaches, as they are chemically orthogonal to non-fluorinated organic molecules, allowing their efficient incorporation in different devices and systems. Moreover, fluorinated polymers are soluble in hydrofluoroether solvents, benign to biomolecules, and can be properly engineered to enable efficient photolithographic patterning. In this work, we report the development of a new photolithographic process for patterning biomolecules on any kind of surfaces either by physical adsorption or covalent bonding. The photoresist is based on a fluorinated material and hydrofluoroether solvents that have minimum interactions with biomolecules and thus they can be characterized as orthogonal to the biomolecules (bio-orthogonal). In both cases, the creation of patterns with dimensions down to 2 μm was achieved. The implementation of the developed photolithographic procedure for the creation of a multi-protein microarray is demonstrated.

Bifunctionalized Redox-Responsive Layers Prepared from a Thiolactone Copolymer

The development of multifunctional surfaces is of general interest for the fabrication of biomedical, catalytic, microfluidic or biosensing devices. Herein, we report on the preparation of copolymer layers immobilized on gold surface and showing both free thiol and amino groups. These layers are produced by aminolysis of a thiolactone-based copolymer in the presence of a diamine, according to a one-step procedure. The free thiol and amino groups present in the modified copolymer layers can be successfully functionalized with respectively thiolated and carboxylic derivatives, in order to produce bifunctionalized surfaces. In addition, we show that the grafted thiolated derivative can be released by cleavage of the disulfide bond under mild reducing conditions. On the other hand, a side cross-linking reaction occurring during the grafting process and resulting in the formation of copolymer aggregates on the metal surface is evidenced. The methodology developed for the preparation of these bifunctionalized redox-responsive layers should be advantageously used to produce bioactive surfaces with drug loading/release properties.

Impact of surface adhesion and sample heterogeneity on the multiscale mechanical characterisation of soft biomaterials

The mechanical properties of soft materials used in the biomedical field play an important role on their performance. In the field of tissue engineering, it is known that cells sense the mechanical properties of their environment, however some materials, such as Sylard 184 PDMS (poly(dimethylsiloxane)), have failed to elicit such response. It was proposed that differences in the mechanical properties of such soft materials, at different scales, could account for these discrepancies. Indeed, the variation in the elastic moduli obtained for soft materials characterised at different scales can span several orders of magnitude. This called for a side-by-side comparison of the mechanical behaviour of soft materials at different scales. Here we use indentation, rheology and atomic force microscopy nanoidentation (using different tip geometries) to characterise the mechanical properties of PDMS, poly(acrylamide) (PAAm) and carboxymethyl cellulose (CMC) hydrogels at different length scales. Our results highlight the importance of surface adhesion and the resulting changes in contact area, and sample microstructural heterogeneity, in particular for the mechanical characterisation of ultra-soft substrates at the nano- to micro-scale.

Tailoring a Tyrosine-Rich Peptide into Size- and Thickness-Controllable Nanofilms

Self-assembled nanostructures of tyrosine-rich peptides have a number of potential applications such as biocatalysts, organic conducting films, and ion-selective membranes. In modulating a self-assembly process of peptides, the interfacial force is an important factor for kinetic control. Here, we present the formation of large-sized and thickness-controllable nanofilms from the YYACAYY peptide sequence (Tyr-C7mer peptide) using Langmuir-Blodgett and Langmuir-Schaefer deposition methods. The Tyr-C7mer peptide showed typical surfactant-like properties, which were demonstrated via the isotherm test (surface pressure-area) by spreading the Tyr-C7mer peptide solution onto an air/water interface. Uniform and flat peptide nanofilms were successfully fabricated and characterized. The redox activity of densely packed tyrosine moieties on the peptide nanofilm was also evaluated by assembling silver nanoparticles on the nanofilm without requiring any additives.

Self-assembled monolayers in organic electronics

Self-assembly is possibly the most effective and versatile strategy for surface functionalization. Self-assembled monolayers (SAMs) can be formed on (semi-)conductor and dielectric surfaces, and have been used in a variety of technological applications. This work aims to review the strategy behind the design and use of self-assembled monolayers in organic electronics, discuss the mechanism of interaction of SAMs in a microscopic device, and highlight the applications emerging from the integration of SAMs in an organic device. The possibility of performing surface chemistry tailoring with SAMs constitutes a versatile approach towards the tuning of the electronic and morphological properties of the interfaces relevant to the response of an organic electronic device. Functionalisation with SAMs is important not only for imparting stability to the device or enhancing its performance, as sought at the early stages of development of this field. SAM-functionalised organic devices give rise to completely new types of behavior that open unprecedented applications, such as ultra-sensitive label-free biosensors and SAM/organic transistors that can be used as robust experimental gauges for studying charge tunneling across SAMs.

Surface-Anchored Thiol-Reactive Soft Interfaces: Engineering Effective Platforms for Biomolecular Immobilization and Sensing

Fabrication of antibiofouling, specifically reactive polymeric coatings that undergo facile functionalization with thiol-bearing small molecules and ligands, yields effective platforms for biomolecular immobilization and sensing. Poly(ethylene glycol) (PEG)-based copolymers containing alkoxysilyl groups to enable surface-anchoring and furan-protected maleimide groups as latent thiol-reactive moieties as side-chains were synthesized. Reactive interfaces were obtained by coating these copolymers onto Si/SiO₂ or glass surfaces and activating the maleimide groups to their thiol-reactive forms via thermal treatment. A series of surfaces modified with copolymers containing varying amounts of maleimide groups were synthesized. Effectiveness of surface modification was probed using Fourier transform infrared spectroscopy, contact angle goniometry, ellipsometry and X-ray photoelectron spectroscopy. Facile surface modification through thiol-maleimide conjugation was established by attachment of a thiol-containing fluorescent dye, namely BODIPY-SH. It was demonstrated that these surfaces allow spatially localized modification through microcontact printing. Importantly, the extent of surface modification could be tuned by varying the initial composition of the copolymer used for coating. Using fluorescence microscopy, it was observed that increasing amount of fluorescent dye was attached onto surfaces fabricated with copolymers with increasing amount of masked maleimide groups. Thereafter, the thiol-maleimide conjugation was utilized to decorate these surfaces with biotin, a protein-binding ligand. It was observed that though these biotinylated surfaces were able to bind Streptavidin effectively, some nonspecific binding was observed on places that were not in conformal contact with the stamp during microcontact printing. This nonspecific binding was eliminated upon neutralizing the residual maleimide units on the printed surface using thiol-containing PEG. Notably, fluorescence analysis of Streptavidin immobilized onto biotinylated surfaces fabricated using varying amounts of maleimide demonstrated that the amount of immobilized protein could be tuned by varying surface composition. It can be envisioned that facile fabrication of these maleimide-containing polymeric surfaces, their effective functionalization in a tunable manner to engineer interfaces for effective immobilization or sensing of biomolecules in a spatially controlled manner would make them attractive candidates for various biotechnological applications.

Printing Functional Protein Nanodots on Soft Elastomers: From Transfer Mechanism to Cell Mechanosensing

Living cells sense the physical and chemical nature of their micro/nano environment with exquisite sensitivity. In this context, there is a growing need to functionalize soft materials with micro/nanoscale biochemical patterns for applications in mechanobiology. This, however, is still an engineering challenge. Here a new method is proposed, where submicronic protein-patterns are first formed on glass and are then printed on to an elastomer. The degree of transfer is shown to be governed mainly by hydrophobic interactions and to be influenced by grafting an appropriate fluorophore onto the core protein of interest. The transfer mechanism is probed by measuring the forces of adhesion/cohesion using atomic force microscopy. The transfer of functional arrays of dots with size down to about 400 nm, on elastomers with stiffness ranging from 3 kPa to 7 MPa, is demonstrated. Pilot studies on adhesion of T lymphocytes on such soft patterned substrates are reported.

Copper Contamination of Self-Assembled Organic Monolayer Modified Silicon Surfaces Following a "Click" Reaction Characterized with LAPS and SPIM

A copper(I)-catalyzed azide alkyne cycloaddition (CuAAC) reaction combined with microcontact printing was used successfully to pattern alkyne-terminated self-assembled organic monolayer-modified silicon surfaces. Despite the absence of a copper peak in X-ray photoelectron spectra, copper contamination was found and visualized using light-addressable potentiometric sensors (LAPS) and scanning photo-induced impedance microscopy (SPIM) after the "click"-modified silicon surfaces were rinsed with hydrochloric acid (HCl) solution, which was frequently used to remove copper residues in the past. Even cleaning with an ethylenediaminetetraacetic acid (EDTA) solution did not remove the copper residue completely. Different strategies for avoiding copper contamination, including the use of bulky chelators for the copper(I) catalyst and rinsing with different reagents, were tested. Only cleaning of the silicon surfaces with an EDTA solution containing trifluoroacetic acid (TFA) after the click modification proved to be an effective method as confirmed by LAPS and SPIM results, which showed the expected potential shift due to the surface charge introduced by functional groups in the monolayer and allowed, for the first time, imaging the impedance of an organic monolayer.

Microcontact printing with aminosilanes: creating biomolecule micro- and nanoarrays for multiplexed microfluidic bioassays

Aqueous based microcontact printing (μCP) to create micro- and nanoarrays of (3-aminopropyl)triethoxysilane (APTES) on glass substrates of microfluidic devices for covalent immobilization of DNA aptamers and antibodies.

A Microfluidic Chip for Cell Patterning Utilizing Paired Microwells and Protein Patterns

Cell patterning has been widely used in research on fundamental cell biology and in applications such as tissue engineering, neuron network formation, cell based biosensor and drug screening. Although various methods have been developed, cell patterning in an enclosed microfluidic device at single cell level remains challenging. This paper describes a microfluidic device with microwells and protein patterns paired together in a single microchannel for an easy cell patterning. Cells captured in the microwells were positioned directly onto the protein patterns within 5 min and the patterning performance was successfully demonstrated using HeLa cells and human gallbladder carcinoma cells (SGC-996). Cells survived for 6 days in the microchannel. Cell attachment, migration, proliferation and cell colony formation were observed. Our device is free of topographic constraint for the patterned cells and no complex chemical modification to the substrate is needed, offering a simple, fast, and easy-to-operate way of patterning cells at single cell level in an enclosed microfluidic channel.

Effect of Substrate Morphology on the Odd-Even Effect in Hydrophobicity of Self-Assembled Monolayers

Surface roughness, often captured through root-mean-square roughness (R_rms), has been shown to impact the quality of self-assembled monolayers (SAMs) formed on coinage metals. Understanding the effect of roughness on hydrophobicity of SAMs, however, is complicated by the odd-even effect-a zigzag oscillation in contact angles with changes in molecular length. We recently showed that for surfaces with R_rms > 1 nm, the odd-even effect in hydrophobicity cannot be empirically observed. In this report, we compare wetting properties of SAMs on Ag and Au surfaces of different morphologies across the R_rms ∼ 1 nm limit. We prepared surfaces with comparable properties (grain sizes and R_rms) and assessed the wetting properties of resultant SAMs. Substrates with R_rms either below or above the odd-even limit were investigated. With smoother surfaces (lower R_rms), an inverted asymmetric odd-even zigzag oscillation in static contact angles (θ_s) was observed with change from Au to Ag. Asymmetry in odd-even oscillation in Au was attributed to a larger change in θ_s from odd to even number of carbons in the n-alkanethiol and vice versa for Ag. For rougher surfaces, no odd-even effect was observed; however, a gradual increase in the static contact angle was observed. Increase in the average grain sizes (>3 times larger) on rough surfaces did not lead to significant difference in the wetting properties, suggesting that surface roughness significantly dominated the nature of the SAMs. We therefore infer that the predicted roughness-dependent limit to the observation of the odd-even effect in wetting properties of n-alkanethiols cannot be overcome by creating surfaces with large grain sizes for surfaces with R_rms > 1 nm. We also observed that the differences between Au and Ag surfaces are dominated by differences in the even-numbered SAMs, but this difference vanishes with shorter molecular chain length (≤C₃).

DNA self-assembly-driven positioning of molecular components on nanopatterned surfaces

We present a method for the specific, spatially targeted attachment of DNA molecules to lithographically patterned gold surfaces-demonstrated by bridging DNA strands across nanogap electrode structures. An alkanethiol self-assembled monolayer was employed as a molecular resist, which could be selectively removed via electrochemical desorption, allowing the binding of thiolated DNA anchoring oligonucleotides to each electrode. After introducing a bridging DNA molecule with single-stranded ends complementary to the electrode-tethered anchoring oligonucleotides, the positioning of the DNA molecule across the electrode gap, driven by self-assembly, occurred autonomously. This demonstrates control of molecule positioning with resolution limited only by the underlying patterned structure, does not require any alignment, is carried out entirely under biologically compatible conditions, and is scalable.

Nano- and micro-patterning biotemplated magnetic CoPt arrays

Patterned thin-films of magnetic nanoparticles (MNPs) can be used to make: surfaces for manipulating and sorting cells, sensors, 2D spin-ices and high-density data storage devices. Conventional manufacture of patterned magnetic thin-films is not environmentally friendly because it uses high temperatures (hundreds of degrees Celsius) and high vacuum, which requires expensive specialised equipment. To tackle these issues, we have taken inspiration from nature to create environmentally friendly patterns of ferromagnetic CoPt using a biotemplating peptide under mild conditions and simple apparatus. Nano-patterning via interference lithography (IL) and micro-patterning using micro-contact printing (μCP) were used to create a peptide resistant mask onto a gold surface under ambient conditions. We redesigned a biotemplating peptide (CGSGKTHEIHSPLLHK) to self-assemble onto gold surfaces, and mineralised the patterns with CoPt at 18 °C in water. Ferromagnetic CoPt is biotemplated by the immobilised peptides, and the patterned MNPs maintain stable magnetic domains. This bioinspired study offers an ecological route towards developing biotemplated magnetic thin-films for use in applications such as sensing, cell manipulation and data storage.

Micropatterning control of tubular commitment in human adult renal stem cells

The treatment of renal injury by autologous, patient-specific adult stem cells is still an unmet need. Unsolved issues remain the spatial integration of stem cells into damaged areas of the organ, the commitment in the required cell type and the development of improved bioengineered devices. In this respect, biomaterials and architectures have to be specialized to control stem cell differentiation. Here, we perform an extensive study on micropatterned extracellular matrix proteins, which constitute a simple and non-invasive approach to drive the differentiation of adult renal progenitor/stem cells (ARPCs) from human donors. ARPCs are interfaced with fibronectin (FN) micropatterns, in the absence of exogenous chemicals or cellular reprogramming. We obtain the differentiation towards tubular cells of ARPCs cultured in basal medium conditions, the tubular commitment thus being specifically induced by micropatterned substrates. We characterize the stability of the tubular differentiation as well as the induction of a polarized phenotype in micropatterned ARPCs. Thus, the developed cues, driving the functional commitment of ARPCs, offer a route to recreate the microenvironment of the stem cell niche in vitro, that may serve, in perspective, for the development of ARPC-based bioengineered devices.

Control of Cell Attachment and Spreading on Poly(acrylamide) Brushes with Varied Grafting Density

To achieve spatial control of fibroblast cell attachment and spreading on a biocompatible polymer coating, the effect of poly(acrylamide) (PAAm) brushes with varied grafting density was investigated. The synthesis of the brushes was performed by surface-initiated atom transfer radical polymerization (SI-ATRP). Gold substrates were modified with binary self-assembled monolayers (SAMs) of an initiator and 16-mercaptohexadecanoic acid (MHDA) as an "inert" thiol to initiate the ATRP of AAm. By using different mixtures for the binary SAMs, a series of polymer brushes with varied grafting densities were prepared. The fractional coverage of surface bound initiator was determined by grazing incidence Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and contact angle measurements. A linear relationship between the Br/S ratio determined by XPS and ToF-SIMS versus the fraction of initiator on the surface determined by water contact angle measurements was observed. The varied initiation concentration on the gold substrates yielded PAAm brushes with different thicknesses, indicating a transition from mushroom to brush regimes with increasing grafting density. Thereby we achieved exquisite control of the degree of cell adhesion. Cell attachment experiments with NIH 3T3 fibroblast cells revealed cell spreading on PAAm brushes with low grafting densities (initiator fractional coverage <0.2) as well as a complete passivation by polymer brushes with higher grafting densities.

Supported lipid bilayer membrane arrays on micro-patterned ITO electrodes

Lipid bilayer arrays were formed on micropatterned ITO electrodes. With this bilayer array platform both the fluorescence microscopy and electrochemical detection can be realized to explore the biophysical properties of cell membrane.

Recent Advances in Genetic Technique of Microbial Report Cells and Their Applications in Cell Arrays

Microbial cell arrays have attracted consistent attention for their ability to provide unique global data on target analytes at low cost, their capacity for readily detectable and robust cell growth in diverse environments, their high degree of convenience, and their capacity for multiplexing via incorporation of molecularly tailored reporter cells. To highlight recent progress in the field of microbial cell arrays, this review discusses research on genetic engineering of reporter cells, technologies for patterning live cells on solid surfaces, cellular immobilization in different polymers, and studies on their application in environmental monitoring, disease diagnostics, and other related fields. On the basis of these results, we discuss current challenges and future prospects for novel microbial cell arrays, which show promise for use as potent tools for unraveling complex biological processes.

"Click" Patterning of Self-Assembled Monolayers on Hydrogen-Terminated Silicon Surfaces and Their Characterization Using Light-Addressable Potentiometric Sensors

Two potential strategies for chemically patterning alkyne-terminated self-assembled monolayers (SAMs) on oxide-free silicon or silicon-on-sapphire (SOS) substrates were investigated and compared. The patterned surfaces were validated using a light-addressable potentiometric sensor (LAPS) for the first time. The first strategy involved an integration of photolithography with "click" chemistry. Detailed surface characterization (i.e. water contact angle, ellipsometry, AFM, and XPS) and LAPS measurements showed that photoresist processing not only decreases the coverage of organic monolayers but also introduces chemically bonded contaminants on the surfaces, thus significantly reducing the quality of the SAMs and the utility of "click" surface modification. The formation of chemical contaminants in photolithography was also observed on carboxylic acid- and alkyl-terminated monolayers using LAPS. In contrast, a second approach combined microcontact printing (μCP) with "click" chemistry; that is azide (azido-oligo(ethylene glycol) (OEG)-NH2) inks were printed on alkyne-terminated SAMs on silicon or SOS through PDMS stamps. The surface characterization results for the sample printed with a flat featureless PDMS stamp demonstrated a nondestructive and efficient method of μCP to perform "click" reactions on alkyne-terminated, oxide-free silicon surfaces for the first time. For the sample printed with a featured PDMS stamp, LAPS imaging showed a good agreement with the pattern of the PDMS stamp, indicating the successful chemical patterning on non-oxidized silicon and SOS substrates and the capability of LAPS to image the molecular patterns with high sensitivity.

Revealing the dependence of cell spreading kinetics on its spreading morphology using microcontact printed fibronectin patterns

Since the dawn of in vitro cell cultures, how cells interact and proliferate within a given external environment has always been an important issue in the study of cell biology. It is now well known that mammalian cells typically exhibit a three-phase sigmoid spreading on encountering a substrate. To further this understanding, we examined the influence of cell shape towards the second rapid expansion phase of spreading. Specifically, 3T3 fibroblasts were seeded onto silicon elastomer films made from polydimethylsiloxane (PDMS), and micro-contact printed with fibronectin stripes of various dimensions. PDMS is adopted in our study for its biocompatibility, its ease in producing very smooth surfaces, and in the fabrication of micro-contact printing stamps. The substrate patterns are compared with respect to their influence on cell spreading over time. Our studies reveal, during the early rapid expansion phase, 3T3 fibroblasts are found to spread radially following a t≃¹·⁸ law; meanwhile, they proliferated in a lengthwise fashion on the striped patterns, following a t≃¹ law. We account for the observed differences in kinetics through a simple geometric analysis which predicted similar trends. In particular, a t² law for radial spreading cells, and a t¹ law for lengthwise spreading cells.

Bio-inspired direct patterning functional nanothin microlines: controllable liquid transfer

Developing a general and low-cost strategy that enables direct patterning of microlines with nanometer thickness from versatile liquid-phase functional materials and precise positioning of them on various substrates remains a challenge. Herein, with inspiration from the oriental wisdom to control ink transfer by Chinese brushes, we developed a facile and general writing strategy to directly pattern various functional microlines with homogeneous distribution and nanometer-scale thickness. It is demonstrated that the width and thickness of the microlines could be well-controlled by tuning the writing method, providing guidance for the adaptation of this technique to various systems. It is also shown that various functional liquid-phase materials, such as quantum dots, small molecules, polymers, and suspensions of nanoparticles, could directly write on the substrates with intrinsic physicochemical properties well-preserved. Moreover, this technique enabled direct patterning of liquid-phase materials on certain microdomains, even in multiple layered style, thus a microdomain localized chemical reaction and the patterned surface chemical modification were enabled. This bio-inspired direct writing device will shed light on the template-free printing of various functional micropatterns, as well as the integrated functional microdevices.

Au@Phenyacetylene organogold clusters: direct spectroscopic evidence of gold-carbon covalent band

Surface-enhanced Raman Scattering (SERS) as a powerful vibrational spectroscope technique is used to investigate the existence of AuC band between gold nanoparticles (AuNPs) and phenylacetylene (PA) which is characterized by a new Raman-active peak at 405 cm(-1). The measurements with transmission electron microscopy (TEM) and extinction spectroscopy show an increasing in size and spectral redshift for AuNPs after the addition of the PA molecule demonstrating the production of gold-PA organogold cluster (Au:C₂Ph). Furthermore, a strong band characteristic of AuC stretch mode is observed in the SERS spectra of Au:C₂Ph and supported by the density functional theory (DFT) calculation. In addition, the optimal adsorption of PA on AuNPs' surface is also investigated theoretically. These findings show a direct spectroscopic sight into AuC band, and offer promising alternative to thiol compounds for anchoring organic molecules to gold surface to form self-assembled monolayers.

Challenges and developments of self-assembled monolayers and polymer brushes as a green lubrication solution for tribological applications

Surface initiated polymer brushes, grafted from self-assembled initiating monolayers on a contact surface, provide opportunities to develop innovative solutions for friction reduction in tribological systems.

Review of methods to probe single cell metabolism and bioenergetics

Single cell investigations have enabled unexpected discoveries, such as the existence of biological noise and phenotypic switching in infection, metabolism and treatment. Herein, we review methods that enable such single cell investigations specific to metabolism and bioenergetics. Firstly, we discuss how to isolate and immobilize individuals from a cell suspension, including both permanent and reversible approaches. We also highlight specific advances in microbiology for its implications in metabolic engineering. Methods for probing single cell physiology and metabolism are subsequently reviewed. The primary focus therein is on dynamic and high-content profiling strategies based on label-free and fluorescence microspectroscopy and microscopy. Non-dynamic approaches, such as mass spectrometry and nuclear magnetic resonance, are also briefly discussed.

Skeletal muscle tissue engineering: methods to form skeletal myotubes and their applications

Skeletal muscle tissue engineering (SMTE) aims to repair or regenerate defective skeletal muscle tissue lost by traumatic injury, tumor ablation, or muscular disease. However, two decades after the introduction of SMTE, the engineering of functional skeletal muscle in the laboratory still remains a great challenge, and numerous techniques for growing functional muscle tissues are constantly being developed. This article reviews the recent findings regarding the methodology and various technical aspects of SMTE, including cell alignment and differentiation. We describe the structure and organization of muscle and discuss the methods for myoblast alignment cultured in vitro. To better understand muscle formation and to enhance the engineering of skeletal muscle, we also address the molecular basics of myogenesis and discuss different methods to induce myoblast differentiation into myotubes. We then provide an overview of different coculture systems involving skeletal muscle cells, and highlight major applications of engineered skeletal muscle tissues. Finally, potential challenges and future research directions for SMTE are outlined.

Fundamentals of nanoscale polymer-protein interactions and potential contributions to solid-state nanobioarrays

Protein adsorption onto polymer surfaces is a very complex, ubiquitous, and integrated process, impacting essential areas of food processing and packaging, health devices, diagnostic tools, and medical products. The nature of protein-surface interactions is becoming much more complicated with continuous efforts toward miniaturization, especially for the development of highly compact protein detection and diagnostic devices. A large body of literature reports on protein adsorption from the perspective of ensemble-averaged behavior on macroscopic, chemically homogeneous, polymeric surfaces. However, protein-surface interactions governing the nanoscale size regime may not be effectively inferred from their macroscopic and microscopic characteristics. Recently, research efforts have been made to produce periodically arranged, nanoscopic protein patterns on diblock copolymer surfaces solely through self-assembly. Intriguing protein adsorption phenomena are directly probed on the individual biomolecule level for a fundamental understanding of protein adsorption on nanoscale surfaces exhibiting varying degrees of chemical heterogeneity. Insight gained from protein assembly on diblock copolymers can be effectively used to control the surface density, conformation, orientation, and biofunctionality of prebound proteins in highly miniaturized applications, now approaching the nanoscale. This feature article will highlight recent experimental and theoretical advances made on these fronts while focusing on single-biomolecule-level investigations of protein adsorption behavior combined with surface chemical heterogeneity on the length scale commensurate with a single protein. This article will also address advantages and challenges of the self-assembly-driven patterning technology used to produce protein nanoarrays and its implications for ultrahigh density, functional, and quantifiable protein detection in a highly miniaturized format.

Human pluripotent stem cells on artificial microenvironments: a high content perspective

Self-renewing stem cell populations are increasingly considered as resources for cell therapy and tools for drug discovery. Human pluripotent stem (hPS) cells in particular offer a virtually unlimited reservoir of homogeneous cells and can be differentiated toward diverse lineages. Many diseases show impairment in self-renewal or differentiation, abnormal lineage choice or other aberrant cell behavior in response to chemical or physical cues. To investigate these responses, there is a growing interest in the development of specific assays using hPS cells, artificial microenvironments and high content analysis. Several hurdles need to be overcome that can be grouped into three areas: (i) availability of robust, homogeneous, and consistent cell populations as a starting point; (ii) appropriate understanding and use of chemical and physical microenvironments; (iii) development of assays that dissect the complexity of cell populations in tissues while mirroring specific aspects of their behavior. Here we review recent progress in the culture of hPS cells and we detail the importance of the environment surrounding the cells with a focus on synthetic material and suitable high content analysis approaches. The technologies described, if properly combined, have the potential to create a paradigm shift in the way diseases are modeled and drug discovery is performed.

Control of adhesion of human induced pluripotent stem cells to plasma-patterned polydimethylsiloxane coated with vitronectin and γ-globulin

Human induced pluripotent stem cells (hiPSCs) are a promising source of cells for medical applications. Recently, the development of polydimethylsiloxane (PDMS) microdevices to control the microenvironment of hiPSCs has been extensively studied. PDMS surfaces are often treated with low-pressure air plasma to facilitate protein adsorption and cell adhesion. However, undefined molecules present in the serum and extracellular matrix used to culture cells complicate the study of cell adhesion. Here, we studied the effects of vitronectin and γ-globulin on hiPSC adhesion to plasma-treated and untreated PDMS surfaces under defined culture conditions. We chose these proteins because they have opposite properties: vitronectin mediates hiPSC attachment to hydrophilic siliceous surfaces, whereas γ-globulin is adsorbed by hydrophobic surfaces and does not mediate cell adhesion. Immunostaining showed that, when applied separately, vitronectin and γ-globulin were adsorbed by both plasma-treated and untreated PDMS surfaces. In contrast, when PDMS surfaces were exposed to a mixture of the two proteins, vitronectin was preferentially adsorbed onto plasma-treated surfaces, whereas γ-globulin was adsorbed onto untreated surfaces. Human iPSCs adhered to the vitronectin-rich plasma-treated surfaces but not to the γ-globulin-rich untreated surfaces. On the basis of these results, we used perforated masks to prepare plasma-patterned PDMS substrates, which were then used to pattern hiPSCs. The patterned hiPSCs expressed undifferentiated-cell markers and did not escape from the patterned area for at least 7 days. The patterned PDMS could be stored for up to 6 days before hiPSCs were plated. We believe that our results will be useful for the development of hiPSC microdevices.

MOF positioning technology and device fabrication

Methods for permanent localisation, dynamic localisation and spatial control of functional materials within MOF crystals are critical for the development of miniaturised MOF-based devices for a number of technological applications.

Magnetic control of protein spatial patterning to direct microtubule self-assembly

Living systems offer attractive strategies to generate nanoscale structures because of their innate functional properties such as the dynamic assembly of ordered nanometer fibers, the generation of mechanical forces, or the directional transport mediated by molecular motors. The design of hybrid systems, capable of interfacing artificial building blocks with biomolecules, may be a key step toward the rational design of nanoscale devices and materials. Here, we have designed a bottom-up approach to organize cytoskeletal elements in space using the self-assembly properties of magnetic nanoparticles conjugated to signaling proteins involved in microtubule nucleation. We show that magnetic nanoparticles conjugated to signaling proteins involved in microtubule nucleation can control the positioning of microtubule assembly. Under a magnetic field, a self-organized pattern of biofunctionalized nanoparticles is formed and leads to the nucleation of a periodical network of microtubules in Xenopus laevis egg extract. Our method shows how bioactive nanoparticles can generate a biochemically active pattern upon magnetic actuation, which triggers the spatial organization of nonequilibrium biological structures.

Molecular flux dependence of chemical patterning by microcontact printing

We address the importance of the dynamic molecular ink concentration at a polymer stamp/substrate interface during microcontact displacement or insertion printing. We demonstrate that by controlling molecular flux, we can influence both the molecular-scale order and the rate of molecular exchange of self-assembled monolayers (SAMs) on gold surfaces. Surface depletion of molecular ink at a polymer stamp/substrate interface is driven predominantly by diffusion into the stamp interior; depletion occurs briefly at the substrate by SAM formation, but diffusion of molecules into the bulk of the stamp dominates over practical experimental time scales. As contact time is increased, the interface concentration varies significantly due to diffusion, affecting the quality and coverage of printed films. Controlling interfacial concentration improves printed film reproducibility and the fractional coverage of multicomponent films can be controlled to within a few percent. We first briefly review the important aspects of molecular ink diffusion at a stamp interface and how it relates to experimental duration. We then describe two examples that illustrate control over ink transfer during experiments: the role of contact time on monolayer reproducibility and molecular order, and the fine control of fractional monolayer coverage for the displacement printing of 1-adamantanethiolate SAMs by 1-dodecanethiol.

Microfluidic immunodetection of cancer cells via site-specific microcontact printing of antibodies on nanoporous surface

We demonstrate an efficient method for cancer cell capture via cell line-specific protein deposition on nanoporous surface in microfluidic channels. Specifically, anti-epithelial cell adhesion molecules (EpCAM) were microcontact printed onto nanoporous silica substrate with optimal pore size of 4 nm, porosity of 52.4 ± 0.2%, and thin film thickness of 130 ± 0.5 nm. SkBr3, Colo205, and MDA-MB-435 cancer cells suspended in buffer solution were captured on the stamped nanoporous silica substrate. The method demonstrated significantly higher numbers of captured EpCAM-positive cancer cells within anti-EpCAM stamped areas. For site-selective cell capture, grooved microfluidic channels were designed to investigate effects of local confinement due to the laminar flows. Both theoretical modeling and experiments show that the integration of the microfluidic channels greatly enhances cell capture. Patterning of anti-EpCAM in areas of downward flow (optimal regions for cell capture), generated by grooves of the microchannel, enables higher capture numbers than that of stamped areas of upward flow (non-optimal). Fluorescence microscopy images were acquired for captured SkBr3 and Colo205 cells using anti-EpCAM on the nanoporous silica substrate. It was shown that higher numbers of cells were captured across all EpCAM-positive cell lines in optimal areas versus non-optimal areas. Spatial control and large scale patterning of proteins enable novel designs and productions of cost effective, high throughput, and integrated detection and analysis systems. Site-selective detection provides the capability of defining optimal locations for cell capture based on various channel geometries and flow profile. The demonstrated method shows great potential for point-of-care cancer diagnostic tools to quantify the progression and status of the disease.

Microdevices for nanomedicine

This review surveys selected methods of manufacture and applications of microdevices-miniaturized functional devices capable of handling cell and tissue cultures or producing particles-and discusses their potential relevance to nanomedicine. Many characteristics of microdevices such as miniaturization, increased throughput, and the ability to mimic organ-specific microenvironments are promising for the rapid, low-cost evaluation of the efficacy and toxicity of nanomaterials. Their potential to accurately reproduce the physiological environments that occur in vivo could reduce dependence on animal models in pharmacological testing. Technologies in microfabrications and microfluidics are widely applicable for nanomaterial synthesis and for the development of diagnostic devices. Although the use of microdevices in nanomedicine is still in its infancy, these technologies show promise for enhancing fundamental and applied research in nanomedicine.