Strategy based on multiplexed brush architectures for regulating the spatiotemporal immobilization of biomolecules

Functional surfaces that enable both spatial and temporal control of biomolecules immobilization have attracted enormous attention for various fields including smart biointerface materials, high-throughput bioarrays, and fundamental research in the biosciences. Here, a flexible and promising method was presented for regulating the spatiotemporal arrangement of multiple biomolecules by constructing the topographically and chemically diverse polymer brushes patterned surfaces. A series of polymer brushes patterned surfaces, including antifouling brushes patterned surface, epoxy-presenting brushes patterned surface without and with antifouling background layer, were fabricated to control the spatial distribution of protein and cell adhesion through specific and nonspecific means. The fluorescence measurements demonstrated the effectiveness of spatially regulating the density of surface-immobilized protein through controlling the areal thickness of the poly (glycidyl methacrylate) (PGMA) brush patterns, leading to various complex patterns featuring well-defined biomolecule concentration gradients. Furthermore, a multiplexed surface bearing epoxy groups and azido groups with various areal densities was fabricated for regulating the spatiotemporal arrangement of different proteins, enabling binary biomolecules patterns with higher degrees of functionality and complexity. The presented strategy for the spatiotemporal control of biomolecules immobilization would boost the development of dynamic and multifunctional biosystems.

Symbiotic assembly of peptide nano-mosaics at solid interfaces

The spontaneous co-organization of distinct biomolecules at interfaces enables many of Nature's hierarchical organizations involving both hard and soft materials. Engineering efforts to mimic such hybrid complexes rely on our ability to rationally structure biomolecules at inorganic interfaces. Control over the nanoscale structure of patterned biomolecules remains challenging due to difficulties in controlling the multifarious interactions involved. This work discusses binary peptide assembly as a means to fabricate biomolecular nano-mosaics at graphite surfaces with predictable structures. Distinct peptide-substrate interactions lead to divergent crystallographic growth directions, molecular scale immiscibility, and a symbiotic assembly phenomenon. We present a symbiotic assembly model that accurately predicts the binary assembly structure relying solely on the constituent peptide nucleation kinetics and molar fractions. The ability to tune such biomolecular nano-mosaic structures facilitates the bottom up fabrication of high-density, multifunctional interfaces for nanotechnology.

Effects of Nano-Protein Complexes on Apoptosis of Myocardial Infarction Cells Based on Complex Curve Analysis

Myocardial infarction is one of the common types of coronary heart disease in the clinic. Its morbidity, lethality and disability are high, and it has become a serious threat to human health. At present, it is shown that in the early stage of acute myocardial infarction, myocardial cells are mainly apoptotic, suggesting that effectively blocking myocardial apoptosis in the early stage of myocardial infarction is of great significance for reducing tissue necrosis in the infarcted area. Recent studies have shown that NG nano-protein complexes have a better therapeutic effect on acute myocardial infarction and can inhibit left ventricular remodeling in patients with acute myocardial infarction. However, there are few studies on the effect of NG nano-protein complexes on myocardial cell apoptosis after ischemia. This study used a rat model of acute myocardial infarction to analyze its effect on apoptotic proteins of myocardial cells in rats with acute myocardial infarction in order to provide a certain theoretical basis for its clinical application. In this study, 45 SD rats were randomly divided into a sham operation group, a myocardial infarction group, and a NG nano-protein complex group, with 15 in each group. The sham operation group only underwent thoracotomy, and received normal saline gavage postoperatively; the myocardial infarction group and the NG nano-protein complex group were ligated to the left anterior descending coronary artery of the rat to establish an acute myocardial infarction model, and were performed separately treatment with saline and NG nanoprotein complexes. Finally, we conclude that this nano-protein complex can significantly reduce the expression level of myocardial apoptosis-related proteins in rats with acute myocardial infarction, and is of great significance in inhibiting the apoptosis of acute myocardial infarction cells.

Substrate-enzyme affinity-based surface modification strategy for endothelial cell-specific binding under shear stress

Establishing an endothelial cell (EC) monolayer on top of the blood contacting surface of grafts is considered to be a promising approach for creating a hemocompatible surface. Here we utilized the high affinity interactions between the EC plasma membrane expressed enzyme called endothelin converting enzyme-1 (ECE-1) and its corresponding substrate big Endothelin-1 (bigET-1) to engineer an EC-specific binding surface. Since enzymatic cleavage of substrates require physical interaction between the enzyme and its corresponding substrate, it was hypothesized that a surface with chemically immobilized synthetic bigET-1 will preferentially attract ECs over other types of cells found in vascular system such as vascular smooth muscle cells (VSMCs). First, the expression of ECE-1 was significantly higher in ECs, and ECs processed synthetic bigET-1 to produce ET-1 in a cell number-dependent manner. Such interaction between ECs and synthetic bigET-1 was also detectible in blood. Next, vinyl-terminated self-assembled monolayers (SAMs) were established, oxidized and activated on a glass substrate as a model to immobilize synthetic bigET-1 via amide bonds. The ECs cultured on the synthetic bigET-1-immobilized surface processed larger amount of synthetic bigET-1 to produce ET-1 compared to VSMCs (102.9±5.13 vs. 9.75±0.74 pg/ml). The number of ECs bound to the synthetic bigET-1-immobilized surface during 1 h of shearing (5dyne/cm2) was approximately 3-fold higher than that of VSMCs (46.25±12.61 vs. 15.25±3.69 cells/100×HPF). EC-specific binding of synthetic bigET-1-immobilized surface over a surface modified with collagen, a common substance for cell adhesion, was also observed. The present study demonstrated that using the substrate-enzyme affinity (SEA) of cell type-specific enzyme and its corresponding substrate can be an effective method to engineer a surface preferentially binds specific type of cells. This novel strategy might open a new route toward rapid endothelialization under dynamic conditions supporting the long-term patency of cardiovascular implants.

Patterning Nanoparticles with DNA Molds

We report a nanopatterning strategy in which self-assembled DNA nanostructures serve as structural templates. In previous work, ordering of NPs primarily relied on specific recognition, e.g., DNA-DNA hybridization. Only a few cases have been reported on nonspecific adsorption. Unfortunately, these studies were limited by the integrity and homogeneity of templates and the variety of patterned nanoparticles (NPs). Herein, we have developed a general method to pattern various NPs. The NPs adsorb onto substrate via NP-substrate direct interactions and the substrates are patterned into large arrays (>4 × 4 μm) of tiny, accessible cavities by self-assembled DNA arrays. As a demonstration, DNA templates include tetragonal and hexagonal arrays and the NPs include individual DNA nanomotifs, gold nanoparticles (AuNPs), and proteins. All nanostructures have been confirmed by atomic force microscopy and corresponding fast Fourier transform (FFT) analysis.

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.

Modulation of the mesenchymal stem cell migration capacity via preconditioning with topographic microstructure

Controlling mesenchymal stem cells (MSCs) behavior is necessary to fully exploit their therapeutic potential. Various approaches are employed to effectively influence the migration capacity of MSCs. Here, topographic microstructures with different microscale roughness were created on polystyrene (PS) culture vessel surfaces as a feasible physical preconditioning strategy to modulate MSC migration. By analyzing trajectories of cells migrating after reseeding, we demonstrated that the mobilization velocity of human adipose derived mesenchymal stem cells (hADSCs) could be promoted by and persisted after brief preconditioning with the appropriate microtopography. Moreover, the elevated activation levels of focal adhesion kinase (FAK) and mitogen-activated protein kinase (MAPK) in hADSCs were also observed during and after the preconditioning process. These findings underline the potential enhancement of in vivo therapeutic efficacy in regenerative medicine via transplantation of topographic microstructure preconditioned stem cells.

Heparin micropatterning onto fouling-release perfluoropolyether-based polymers via photobiotin activation

A simple method for constructing versatile ordered biotin/avidin arrays on UV-curable perfluoropolyethers (PFPEs) is presented. The goal is the realization of a versatile platform where any biotinylated biological ligands can be further linked to the underlying biotin/avidin array. To this end, microcontact arrayer and microcontact printing technologies were developed for photobiotin direct printing on PFPEs. As attested by fluorescence images, we demonstrate that this photoactive form of biotin is capable of grafting onto PFPEs surfaces during irradiation. Bioaffinity conjugation of the biotin/avidin system was subsequently exploited for further self-assembly avidin family proteins onto photobiotin arrays. The excellent fouling release PFPEs surface properties enable performing avidin assembly step simply by arrays incubation without PFPEs surface passivation or chemical modification to avoid unspecific biomolecule adsorption. Finally, as a proof of principle biotinylated heparin was successfully grafted onto photobiotin/avidin arrays.

Direct and reversible immobilization and microcontact printing of functional proteins on glass using a genetically appended silica-binding tag

Fusion of disulfide-constrained or linear versions of the Car9 dodecapeptide to model fluorescent proteins support their on-contact and oriented immobilization onto unmodified glass. Bound proteins can be released and the surface regenerated by incubation with l-lysine. This noncovalent chemistry enables rapid and reversibe microcontact printing of tagged proteins and speeds up the production of bicontinuous protein patterns.

Suspended Planar-Array Chips for Molecular Multiplexing at the Microscale

A novel suspended planar-array chips technology is described, which effectively allows molecular multiplexing using a single suspended chip to analyze extraordinarily small volumes. The suspended chips are fabricated by combining silicon-based technology and polymer-pen lithography, obtaining increased molecular pattern flexibility, and improving miniaturization and parallel production. The chip miniaturization is so dramatic that it permits the intracellular analysis of living cells.

A supramolecular two-photon-active hydrogel platform for direct bioconjugation under near-infrared radiation

A novel hydrogel self-assembled from partially methacrylated polyethyleneimine shows photo-activity at near-infrared wavelengths and offers a selective platform for the rapid and direct conjugation of biomolecules by two-photon laser irradiation without additional initiators.

Reversible switching between nonquenched and quenched states in nanoscale linear arrays of plant light-harvesting antenna complexes

A simple and robust nanolithographic method that allows sub-100 nm chemical patterning on a range of oxide surfaces was developed in order to fabricate nanoarrays of plant light-harvesting LHCII complexes. The site-specific immobilization and the preserved functionality of the LHCII complexes were confirmed by fluorescence emission spectroscopy. Nanopatterned LHCII trimers could be reversibly switched between fluorescent and quenched states by controlling the detergent concentration in the imaging buffer. A 3-fold quenching of the average fluorescence intensity was accompanied by a decrease in the average (amplitude-weighted) fluorescence lifetime from approximately 2.24 ns to approximately 0.4 ns, attributed to the intrinsic ability of LHCII to switch between fluorescent and quenched states upon changes in its conformational state. The nanopatterning methodology was extended by immobilizing a second protein, the enhanced green fluorescent protein (EGFP), onto LHCII-free areas of the chemically patterned surfaces. This very simple surface chemistry, which allows simultaneous selective immobilization and therefore sorting of the two types of protein molecules on the surface, is a key underpinning step toward the integration of LHCII into switchable biohybrid antenna constructs.

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.

Adhesion behaviors on superhydrophobic surfaces

The adhesion behaviors of superhydrophobic surfaces have become an emerging topic to researchers in various fields as a vital step in the interactions between materials and organisms/materials. Controlling the chemical compositions and topological structures via various methods or technologies is essential to fabricate and modulate different adhesion properties, such as low-adhesion, high-adhesion and anisotropic adhesion on superhydrophobic surfaces. We summarize the recent developments in both natural superhydrophobic surfaces and artificial superhydrophobic surfaces with various adhesions and also pay attention to superhydrophobic surfaces switching between low- and high-adhesion. The methods to regulate or translate the adhesion of superhydrophobic surfaces can be considered from two perspectives. One is to control the chemical composition and change the surface geometric structure on the surfaces, respectively or simultaneously. The other is to provide external stimulations to induce transitions, which is the most common method for obtaining switchable adhesions. Additionally, adhesion behaviors on solid-solid interfaces, such as the behaviors of cells, bacteria, biomolecules and icing on superhydrophobic surfaces are also noticeable and controversial. This review is aimed at giving a brief and crucial overview of adhesion behaviors on superhydrophobic surfaces.

Biorecognition by DNA oligonucleotides after exposure to photoresists and resist removers

Combining biological molecules with integrated circuit technology is of considerable interest for next generation sensors and biomedical devices. Current lithographic microfabrication methods, however, were developed for compatibility with silicon technology rather than bioorganic molecules, and consequently it cannot be assumed that biomolecules will remain attached and intact during on-chip processing. Here, we evaluate the effects of three common photoresists (Microposit S1800 series, PMGI SF6, and Megaposit SPR 3012) and two photoresist removers (acetone and 1165 remover) on the ability of surface-immobilized DNA oligonucleotides to selectively recognize their reverse-complementary sequence. Two common DNA immobilization methods were compared: adsorption of 5'-thiolated sequences directly to gold nanowires and covalent attachment of 5'-thiolated sequences to surface amines on silica coated nanowires. We found that acetone had deleterious effects on selective hybridization as compared to 1165 remover, presumably due to incomplete resist removal. Use of the PMGI photoresist, which involves a high temperature bake step, was detrimental to the later performance of nanowire-bound DNA in hybridization assays, especially for DNA attached via thiol adsorption. The other three photoresists did not substantially degrade DNA binding capacity or selectivity for complementary DNA sequences. To determine whether the lithographic steps caused more subtle damage, we also tested oligonucleotides containing a single base mismatch. Finally, a two-step photolithographic process was developed and used in combination with dielectrophoretic nanowire assembly to produce an array of doubly contacted, electrically isolated individual nanowire components on a chip. Postfabrication fluorescence imaging indicated that nanowire-bound DNA was present and able to selectively bind complementary strands.

Specific immobilization of biotinylated fusion proteins NGF and Sema3A utilizing a photo-cross-linkable diazirine compound for controlling neurite extension

In this study we report the successful synthesis of N-(2-mercaptoethyl)-3-(3-methyl-3H-diazirine-3-yl) propanamide (N-MCEP-diazirine), with sulfhydryl and amine photoreactive ends to allow recombinant protein tethering to chitosan films. This regimen allows mimicry of the physiological endeavor of axon pathfinding in the nervous system where neurons rely on cues for guidance during development and regeneration. Our strategy incorporates strong covalent and noncovalent interactions, utilizing N-MCEP-diazirine, maleimide-streptavidin complex, and two custom biotinylated-fusion proteins, nerve growth factor (bNGF), and semaphorin3A (bSema3A). Synthetic yield of N-MCEP-diazirine was 87.3 ± 1.9%. Characteristic absorbance decrease at 348 nm after N-MCEP-diazirine exposure to UV validated the photochemical properties of the diazirine moiety, and the attachment of cross-linker to chitosan films was verified with Fourier transform infrared spectroscopy (FTIR). Fluorescence techniques showed no significant difference in the detection of immobilized proteins compared to absorbing the proteins to films (p < 0.05); however, in vitro outgrowth of dorsal root ganglia (DRG) was more responsive to immobilized bNGF and bSema3A compared to adsorbed bNGF and bSema3A over a 5 day period. Immobilized bNGF significantly increased DRG length over time (p < 0.0001), but adsorbed bNGF did not increase in axon extension from day 1 to day 5 (p = 0.4476). Immobilized bSema3A showed a significant decrease in neurite length (524.42 ± 57.31 μm) at day 5 compared to adsorbed bSema3A (969.13 ± 57.31 μm). These results demonstrate the superiority of our immobilization approach to protein adsorption because biotinylated-fusion proteins maintain their active confirmation and their tethering can be spatially controlled via a UV activated N-MCEP-diazirine cross-linker.

Biomimetic delivery with micro- and nanoparticles

The nascent field of biomimetic delivery with micro- and nanoparticles (MNP) has advanced considerably in recent years. Drawing inspiration from the ways that cells communicate in the body, several different modes of "delivery" (i.e., temporospatial presentation of biological signals) have been investigated in a number of therapeutic contexts. In particular, this review focuses on (1) controlled release formulations that deliver natural soluble factors with physiologically relevant temporal context, (2) presentation of surface-bound ligands to cells, with spatial organization of ligands ranging from isotropic to dynamically anisotropic, and (3) physical properties of particles, including size, shape and mechanical stiffness, which mimic those of natural cells. Importantly, the context provided by multimodal, or multifactor delivery represents a key element of most biomimetic MNP systems, a concept illustrated by an analogy to human interpersonal communication. Regulatory implications of increasingly sophisticated and "cell-like" biomimetic MNP systems are also discussed.

Quantitative photochemical immobilization of biomolecules on planar and corrugated substrates: a versatile strategy for creating functional biointerfaces

Methods for the generation of substratespresenting biomolecules in a spatially controlled manner are enabling tools for applications in biosensor systems, microarray technologies, fundamental biological studies and biointerface science. We have implemented a method to create biomolecular patterns by using light to control the direct covalent immobilization of biomolecules onto benzophenone-modified glass substrates. We have generated substrates presenting up to three different biomolecules patterned in sequence, and demonstrate biomolecular photopatterning on corrugated substrates. The chemistry of the underlying monolayer was optimized to incorporate poly(ethylene glycol) to enable adhesive cell adhesion onto patterned extracellular matrix proteins. Substrates were characterized with contact angle goniometry, AFM, and immunofluorescence microscopy. Importantly, radioimmunoassays were performed to quantify the site density of immobilized biomolecules on photopatterned substrates. Retained function of photopatterned proteins was demonstrated both by native ligand recognition and cell adhesion to photopatterned substrates, revealing that substrates generated with this method are suitable for probing specific cell receptor-ligand interactions. This molecularly general photochemical patterning method is an enabling tool for the creation of substrates presenting both biochemical and topographical variation, which is an important feature of many native biointerfaces.

Etched glass microarrays with differential resonance for enhanced contrast and sensitivity of surface plasmon resonance imaging analysis

We report the fabrication and characterization of gold-coated etched glass array substrates for surface plasmon resonance imaging (SPRi) analysis with significantly enhanced performance, in particular image contrast and sensitivity. The etching of the glass substrate induces a variation in the resonance condition and thus in the resonance angle between the etched wells and the surrounding area, leading to the isolation of the array spot resonance with a significant reduction of the background signal. FDTD simulations show arrays with large spots and minimal spot-to-spot spacing yield ideal differential resonance conditions, which are verified by experimental results. Simulations also indicate the etched well structure exhibits enhanced SPR electric field intensity by 3-fold as compared to standard planar gold chips. Changes in the bulk sensitivity of the etched arrays have been obtained at the 10(-4) RIU level based on image intensity difference. The strong image contrast allows for improved microarray imaging analysis with easily distinguished signals from background resonance. The etched array chips are demonstrated for SPRi detection of bacterial toxins through the coating of an ultrathin SiO(2) film for direct vesicle fusion that establishes a supported membrane-based biosensing interface. Protein detection with cholera toxin (CT) at 5 nM is obtained, making this chip one of the most sensitive SPR imaging substrates ever reported without a postbinding amplification scheme. Furthermore, the surface can be regenerated by Triton X-100 for repeated cycles of membrane formation, protein binding, and biomolecular removal. The reusability and enhanced performance of the etched glass array chips should find a broad range of applications, opening up new avenues for high-throughput SPR imaging detection with convenience and marked surface sensitivity.