Positioning multiple proteins at the nanoscale with electron beam cross-linked functional polymers

Controlling the roll-to-helix transformation in electron-beam-patterned gel-based micro-ribbons

Helix formation has been of ongoing interest because of its role in both natural and synthetic materials systems. It has been extensively studied in gel-based ribbons where swelling anisotropies drive out-of-plane bending. In contrast to approaches based on photolithography or mechanical bilayer construction, we use electron-beam patterning to create microscale ribbons at ∼1-100 μm length scales in pure homopolymer precursor films of poly(acrylic acid) (PAA). The radiation chemistry creates a ribbon comprising a crosslinked hydrophobic top layer and a hydrophilic gel bottom layer with a continuous through-thickness variation in between. The classic roll-to-helix transition occurs as the ribbon aspect ratio increases. Notably, we see examples of single-loop rolls, multi-loop rolls, minimal-pitch helices, plus a transition structure comprising both helical and roll-like features. Finite-element modelling recapitulates key aspects of these conformations. Increasing the pH from below to above the PAA pKa increases the out-of-plane bending to the extent that the ribbons plastically deform and nonminimal-pitch helices form across a wide range of aspect ratios and irradiation conditions. The nonminimal pitch is caused by an in-plane anisotropy associated with the plastic deformation. We mimic this anisotropy by patterning ribbons comprising micro-tiles separated by gaps which receive electron exposure due to proximity effects. We observe a transition from roll to helix to tube with increasing gap angle. The chirality is completely determined by the gap orientation (±θ). However, in contrast to established approaches to generate in-plane anisotropies based on mechanical properties, finite-element modelling indicates that anisotropic through-thickness swelling of the gap material plays a dominant role in helix formation and suggests that this micro-composite ribbon behaves like a rigid origami metamaterial where deformation at the creases (the gaps) between structural elements controls the shape shifting.

Elasto-plastic effects on shape-shifting electron-beam-patterned gel-based micro-helices

Shape-shifting helical gels have been created by various routes, notably by photolithography. We explore electron-beam lithography as an alternative to prescribe microhelix formation in tethered patterns of pure poly(acrylic acid). Simulations indicate the nanoscale spatial distribution of deposited energy that drives the loss of acid groups and crosslinking. Upon exposure to buffer, a patterned line converts to a 3D helix whose cross section comprises a crosslinked and hydrophobic core surrounded by a high-swelling pH-responsive corona. Through-thickness asymmetries generate out-of-plane bending to drive helix formation. The relative core and corona fractions are determined by the electron dose which in turn controls the helical radius and pitch. Increasing pH substantially raises the swelling stress and the rod elongates plastically. The pitch concurrently changes from minimal to non-minimal. The in-plane asymmetry driving this change can be attributed to shear-band formation in the hydrophobic core. Subsequent pH cycling drives elastic cycling of the helical properties. These findings illustrate the effects of elastoplastic deformation on helical properties and elaborate unique attributes of electron lithography as an alternate means to create shape-shifting structures.

Protein-based bioactive coatings: from nanoarchitectonics to applications

Protein-based bioactive coatings have emerged as a versatile and promising strategy for enhancing the performance and biocompatibility of diverse biomedical materials and devices. Through surface modification, these coatings confer novel biofunctional attributes, rendering the material highly bioactive. Their widespread adoption across various domains in recent years underscores their importance. This review systematically elucidates the behavior of protein-based bioactive coatings in organisms and expounds on their underlying mechanisms. Furthermore, it highlights notable advancements in artificial synthesis methodologies and their functional applications in vitro. A focal point is the delineation of assembly strategies employed in crafting protein-based bioactive coatings, which provides a guide for their expansion and sustained implementation. Finally, the current trends, challenges, and future directions of protein-based bioactive coatings are discussed.

Maskless, Reusable Visible-Light Direct-Write Stamp for Microscale Surface Patterning

We report a straightforward method for creating large-area, microscale resolution patterns of functional amines on self-assembled monolayers by the photoinduced local acidification of a flat elastomeric stamp enriched with photoacid. The limited diffusivity of the photoactivated merocyanine acid in poly(dimethylsiloxane) (PDMS) enabled to confine efficient deprotection of N-tert-butyloxycarbonyl amino group (N-Boc) to line widths below 10 μm. The experimental setup is very simple and is built around the conventional HD-DVD optical pickup. The method allows cost-efficient, maskless, large-area chemical patterning while avoiding potentially cytotoxic photochemical reaction products. The activation of the embedded photoacid occurs within the stamp upon illumination with the laser beam and the process is fully reversible. Preliminary positive results highlight the possibility of repeatable use of the same stamp for the creation of different patterns.

Single molecule DNA origami nanoarrays with controlled protein orientation

The nanoscale organization of functional (bio)molecules on solid substrates with nanoscale spatial resolution and single-molecule control-in both position and orientation-is of great interest for the development of next-generation (bio)molecular devices and assays. Herein, we report the fabrication of nanoarrays of individual proteins (and dyes) via the selective organization of DNA origami on nanopatterned surfaces and with controlled protein orientation. Nanoapertures in metal-coated glass substrates were patterned using focused ion beam lithography; 88% of the nanoapertures allowed immobilization of functionalized DNA origami structures. Photobleaching experiments of dye-functionalized DNA nanostructures indicated that 85% of the nanoapertures contain a single origami unit, with only 3% exhibiting double occupancy. Using a reprogrammed genetic code to engineer into a protein new chemistry to allow residue-specific linkage to an addressable ssDNA unit, we assembled orientation-controlled proteins functionalized to DNA origami structures; these were then organized in the arrays and exhibited single molecule traces. This strategy is of general applicability for the investigation of biomolecular events with single-molecule resolution in defined nanoarrays configurations and with orientational control of the (bio)molecule of interest.

Catalyst-Free Click Chemistry for Engineering Chondroitin Sulfate-Multiarmed PEG Hydrogels for Skin Tissue Engineering

The quest for an ideal biomaterial perfectly matching the microenvironment of the surrounding tissues and cells is an endless challenge within biomedical research, in addition to integrating this with a facile and sustainable technology for its preparation. Engineering hydrogels through click chemistry would promote the sustainable invention of tailor-made hydrogels. Herein, we disclose a versatile and facile catalyst-free click chemistry for the generation of an innovative hydrogel by combining chondroitin sulfate (CS) and polyethylene glycol (PEG). Various multi-armed PEG-Norbornene (A-PEG-N) with different molecular sizes were investigated to generate crosslinked copolymers with tunable rheological and mechanical properties. The crosslinked and mechanically stable porous hydrogels could be generated by simply mixing the two clickable Tetrazine-CS (TCS) and A-PEG-N components, generating a self-standing hydrogel within minutes. The leading candidate (TCS-8A-PEG-N (40 kD)), based on the mechanical and biocompatibility results, was further employed as a scaffold to improve wound closure and blood flow in vivo. The hydrogel demonstrated not only enhanced blood perfusion and an increased number of blood vessels, but also desirable fibrous matrix orientation and normal collagen deposition. Taken together, these results demonstrate the potential of the hydrogel to improve wound repair and hold promise for in situ skin tissue engineering applications.

Nanometer-scale patterning of hard and soft interfaces: from photolithography to molecular-scale design

Many areas of modern materials chemistry, from nanoscale electronics to regenerative medicine, require design of precisely-controlled chemical environments at near-molecular scales on both hard and soft surfaces.

Chemical Orthogonality in Surface-Patterned Poly(ethylene glycol) Microgels

Because of its widely known antifouling properties, a variety of lithographic approaches has been used to pattern surfaces with poly(ethylene glycol) (PEG) to control surface interactions with biomolecules and cells over micro- and nanolength scales. Often, however, particular applications need additional functions within PEG-patterned surfaces. Monofunctional films can be generated using PEG modified to include a chemically functional group. We show that patterning with focused electron beams, in addition to cross-linking a monofunctional PEG homopolymer thin-film precursor and grafting the resulting patterned microgels to an underlying substrate, induces additional chemical functionality by radiation chemistry along the polymer main chain and that this second functionality can be orthogonal to the initial one. Specifically, we explore the reactivity of biotin-terminated PEG (PEG-B) as a function of electron dose using 2 keV electrons. At low doses (∼4-10 μC/cm²), the patterned PEG-B microgels are reactive with streptavidin (SA). As dose increases, the SA reactivity decays as biotin is damaged by the incident electrons. Independently, amine reactivity appears at higher doses (∼150-500 μC/cm²). At both extremes, the patterned PEG microgels retain their ability to resist fibronectin adsorption. We confirm that the amine reactivity derives from the PEG main chain by demonstrating similar dose response in hydroxy-terminated PEG (PEG-OH), and we attribute this behavior to the formation of ketones, aldehydes, and/or carboxylic acids during and after electron-beam (e-beam) patterning. Based on relative fluorescent intensities, we estimate that the functional contrast between the differentially patterned areas is about a factor of six or more. This approach provides the ability to easily pattern biospecific functionality while preserving the ability to resist nonspecific adsorption at length scales relevant to controlling protein and cell interactions.

Underwater Superoleophobic Surface Based on Silica Hierarchical Cylinder Arrays with a Low Aspect Ratio

A superantiwetting surface based on low-aspect-ratio hierarchical cylinder arrays (HCAs) was successfully obtained on a silica substrate by colloidal lithography with photolithography. Colloidal lithography is a technique involving transfer of a pattern to a substrate by etching or exposure to a radiation source through a mask composed of a packed colloidal crystal, while photolithography is utilized by which a pattern is transferred photographically to a photoresist-coated substrate, and the substrate is subsequently etched. The surface provides an alternative approach to apply aligned micro-nano integrated structures with a relatively low aspect ratio in superantiwetting. The obtained HCAs successfully integrated micro- and nanoscale structures into one system, and the physical structure of the HCAs can be tuned by modulating the fabrication approach. Using a postmodification process, the underwater-oil wetting behavior of cylinder-array based surfaces can be easily modulated from the superoleophobic state (an oil contact angle (OCA) of 161°) to oleophilic state (an OCA of 19°). Moreover, the underwater-oil wettability can be reversibly transformed from the superoleophobic state (an OCA of approximately 153°) into the oleophilic state (an OCA of approximately 31°) by grafting stimuli-responsive polymer (PNIPAAm) brushes onto this specific hierarchical structure. Due to the temperature-responsive property, modifying the surface with PNIPAAm provides a possibility to control the oil wettability (repellent or sticky) by temperature, which will benefit the use of HCAs in oil-water separation and other application fields.

Modular Fabrication of Intelligent Material-Tissue Interfaces for Bioinspired and Biomimetic Devices

One of the goals of biomaterials science is to reverse engineer aspects of human and nonhuman physiology. Similar to the body's regulatory mechanisms, such devices must transduce changes in the physiological environment or the presence of an external stimulus into a detectable or therapeutic response. This review is a comprehensive evaluation and critical analysis of the design and fabrication of environmentally responsive cell-material constructs for bioinspired machinery and biomimetic devices. In a bottom-up analysis, we begin by reviewing fundamental principles that explain materials' responses to chemical gradients, biomarkers, electromagnetic fields, light, and temperature. Strategies for fabricating highly ordered assemblies of material components at the nano to macro-scales via directed assembly, lithography, 3D printing and 4D printing are also presented. We conclude with an account of contemporary material-tissue interfaces within bioinspired and biomimetic devices for peptide delivery, cancer theranostics, biomonitoring, neuroprosthetics, soft robotics, and biological machines.

Functional Changes during Electron-Beam Lithography of Biotinylated Poly(ethylene glycol) Thin Films

In contrast to photolithography where particular wavelengths of light can couple to specific photochemistries, electron-beam lithography can drive competing chemistries. To separate surface-grafting, cross-linking, and chemical functionality, we studied the effects of 2 keV electrons on thin films of poly(ethylene glycol) end-functionalized with hydroxyls (PEG-OH) or biotins (PEG-B). Similarities in the dose-dependent thickness changes of the patterned PEGs indicate that surface grafting and cross-linking primarily involve the ethylene oxide main chain. While higher doses create thicker patterns with more biotin, the concurrent increase in thiol reactivity indicates that cross-linking competes with biotin degradation. The dose window for optimal e-beam patterning of biotinylated PEG is very narrow. Biotin is entirely consumed at higher doses. Its modified functionality is reactive with 5-((2-(and-3)-S-(acetylmercapto) succinoyl) amino) (SAMSA). This effect creates a dose-dependent orthogonal functionality that can be patterned from a single precursor thin film.

Tools for Low-Dimensional Chemistry

Many biological mechanisms can be considered to be low-dimensional systems: their function is determined by molecular objects of reduced dimensionality. Bacterial photosynthesis is a very good example: the photosynthetic pathway is contained within nano-objects (vesicles) whose function is determined by the numbers and nanoscale organization of membrane proteins and by the ratios of the different types of protein that they contain. Systems biology has provided computational models for studying these processes, but there is a need for experimental platforms with which to test their predictions. This Invited Feature Article reviews recent work on the development of tools for the reconstruction of membrane processes on solid surfaces. Photochemical methods provide a powerful, versatile means for the organization of molecules and membranes across length scales from the molecular to the macroscopic. Polymer brushes are highly effective supports for model membranes and versatile functional and structural components in low-dimensional systems. The incorporation of plasmonic elements facilitates enhanced measurement of spectroscopic properties and provides an additional design strategy via the exploitation of quantum optical phenomena. A low-dimensional system that incorporates functional transmembrane proteins and a mechanism for the in situ measurement of proton transport is described.

Topology effects on protein–polymer block copolymer self-assembly

Bioconjugates made of the model red fluorescent protein mCherry and synthetic polymer blocks show that topology, i.e. the BA, BA₂, ABA and ABC chain structure of the block copolymers, where B represents the protein and A and C represent polymers, has a significant effect on ordering transitions and the type and size of nanostructures formed during microphase separation.

Controlling Protein Adsorption through Nanostructured Polymeric Surfaces

The initial host response to healthcare materials' surfaces after implantation is the adsorption of proteins from blood and interstitial fluids. This adsorbed protein layer modulates the biological/cellular responses to healthcare materials. This stresses the significance of the surface protein assembly for the biocompatibility and functionality of biomaterials and necessitates a profound fundamental understanding of the capability to control protein-surface interactions. This review, therefore, addresses this by systematically analyzing and discussing strategies to control protein adsorption on polymeric healthcare materials through the introduction of specific surface nanostructures. Relevant proteins, healthcare materials' surface properties, clinical applications of polymer healthcare materials, fabrication methods for nanostructured polymer surfaces, amorphous, semicrystalline and block copolymers are considered with a special emphasis on the topographical control of protein adsorption. The review shows that nanostructured polymer surfaces are powerful tools to control the amount, orientation, and order of adsorbed protein layers. It also shows that the understanding of the biological responses to such ordered protein adsorption is still in its infancy, yet it has immense potential for future healthcare materials. The review, which is-as far as it is known-the first one discussing protein adsorption on nanostructured polymer surfaces, concludes with highlighting important current research questions.

Orthogonal supramolecular protein assembly on patterned bifunctional surfaces

Selective dual protein assembly achieved using metal–ion and host–guest interactions with fluorescent proteins, modified with binding tags, by controlling opposing supramolecular interactions.

Fabrication of carbon quantum dots with nano-defined position and pattern in one step via sugar-electron-beam writing

Quantum dots (QDs) are promising materials in nanophotonics, biological imaging, and even quantum computing. Precise positioning and patterning of QDs is a prerequisite for realizing their actual applications. Contrary to the traditional two discrete steps of fabricating and positioning QDs, herein, a novel sugar-electron-beam writing (SEW) method is reported for producing QDs via electron-beam lithography (EBL) that uses a carefully chosen synthetic resist, poly(2-(methacrylamido)glucopyranose) (PMAG). Carbon QDs (CQDs) could be fabricated in situ through electron beam exposure, and the nanoscale position and luminescence intensity of the produced CQDs could be precisely controlled without the assistance of any other fluorescent matter. We have demonstrated that upon combining an electron beam with a glycopolymer, in situ production of CQDs occurs at the electron beam spot center with nanoscale precision at any place and with any patterns, an advancement that we believe will stimulate innovations in future applications.

Bio-mimicking nano and micro-structured surface fabrication for antibacterial properties in medical implants

Orthopaedic and dental implants have become a staple of the medical industry and with an ageing population and growing culture for active lifestyles, this trend is forecast to continue. In accordance with the increased demand for implants, failure rates, particularly those caused by bacterial infection, need to be reduced. The past two decades have led to developments in antibiotics and antibacterial coatings to reduce revision surgery and death rates caused by infection. The limited effectiveness of these approaches has spurred research into nano-textured surfaces, designed to mimic the bactericidal properties of some animal, plant and insect species, and their topographical features. This review discusses the surface structures of cicada, dragonfly and butterfly wings, shark skin, gecko feet, taro and lotus leaves, emphasising the relationship between nano-structures and high surface contact angles on self-cleaning and bactericidal properties. Comparison of these surfaces shows large variations in structure dimension and configuration, indicating that there is no one particular surface structure that exhibits bactericidal behaviour against all types of microorganisms. Recent bio-mimicking fabrication methods are explored, finding hydrothermal synthesis to be the most commonly used technique, due to its environmentally friendly nature and relative simplicity compared to other methods. In addition, current proposed bactericidal mechanisms between bacteria cells and nano-textured surfaces are presented and discussed. These models could be improved by including additional parameters such as biological cell membrane properties, adhesion forces, bacteria dynamics and nano-structure mechanical properties. This paper lastly reviews the mechanical stability and cytotoxicity of micro and nano-structures and materials. While the future of nano-biomaterials is promising, long-term effects of micro and nano-structures in the body must be established before nano-textures can be used on orthopaedic implant surfaces as way of inhibiting bacterial adhesion.

From Monochrome to Technicolor: Simple Generic Approaches to Multicomponent Protein Nanopatterning Using Siloxanes with Photoremovable Protein-Resistant Protecting Groups

We show that sequential protein deposition is possible by photodeprotection of films formed from a tetraethylene-glycol functionalized nitrophenylethoxycarbonyl-protected aminopropyltriethoxysilane (NPEOC-APTES). Exposure to near-UV irradiation removes the protein-resistant protecting group, and allows protein adsorption onto the resulting aminated surface. The protein resistance was tested using proteins with fluorescent labels and microspectroscopy of two-component structures formed by micro- and nanopatterning and deposition of yellow and green fluorescent proteins (YFP/GFP). Nonspecific adsorption onto regions where the protecting group remained intact was negligible. Multiple component patterns were also formed by near-field methods. Because reading and writing can be decoupled in a near-field microscope, it is possible to carry out sequential patterning steps at a single location involving different proteins. Up to four different proteins were formed into geometric patterns using near-field lithography. Interferometric lithography facilitates the organization of proteins over square cm areas. Two-component patterns consisting of 150 nm streptavidin dots formed within an orthogonal grid of bars of GFP at a period of ca. 500 nm could just be resolved by fluorescence microscopy.

Designing Peptide and Protein Modified Hydrogels: Selecting the Optimal Conjugation Strategy

Hydrogels are used in a wide variety of biomedical applications including tissue engineering, biomolecule delivery, cell delivery, and cell culture. These hydrogels are often designed with a specific biological function in mind, requiring the chemical incorporation of bioactive factors to either mimic extracellular matrix or to deliver a payload to diseased tissue. Appropriate synthetic techniques to ligate bioactive factors, such as peptides and proteins, onto hydrogels are critical in designing materials with biological function. Here, we outline strategies for peptide and protein immobilization. We specifically focus on click chemistry, enzymatic ligation, and affinity binding for transient immobilization. Protein modification strategies have shifted toward site-specific modification using unnatural amino acids and engineered site-selective amino acid sequences to preserve both activity and structure. The selection of appropriate protein immobilization strategies is vital to engineering functional hydrogels. We provide insight into chemistry that balances the need for facile reactions while maintaining protein bioactivity or desired release.

A NASBA on microgel-tethered molecular-beacon microarray for real-time microbial molecular diagnostics

Gel-tethered molecular beacons coupled with NASBA RNA amplification enable real-time microbial detection and differentiation in a bloodstream infection model.

Molecular Crowding Effects on Microgel-Tethered Oligonucleotide Probes

Microgel tethering is a nontraditional method with which to bind oligonucleotide hybridization probes to a solid surface. Microgel-tethering physically positions the probes away from the underlying hard substrate and maintains them in a highly waterlike environment. This paper addresses the question of whether molecular crowding affects the performance of microgel-tethered molecular beacon probes. The density of probe-tethering sites is controlled experimentally using thin-film blends of biotin-terminated [PEG-B] and hydroxyl-terminated [PEG-OH] poly(ethylene glycol) from which microgels are synthesized and patterned by electron beam lithography. Fluorescence measurements indicate that the number of streptavidins, linear DNA probes, hairpin probes, and molecular beacon probes bound to the microgels increases linearly with increasing PEG-B/PEG-OH ratio. For a given tethering-site concentration, more linear probes can bind than structured probes. Crowding effects emerge during the hybridization of microgel-tethered molecular beacons but not during the hybridization of linear probes, as the tethering density increases. Crowding during hybridization is associated with conformational constraints imposed by the close proximity of closed and hybridized structured probes. The signal-to-background ratio (SBR) of hybridized beacons is highest and roughly constant for low tethering densities and decreases at the highest tethering densities. Despite differences between microgel tethering and traditional oligonucleotide surface-immobilization approaches, these results show that crowding defines an optimum tethering density for molecular beacon probes that is less than the maximum possible, which is consistent with previous studies involving various linear and structured oligonucleotide probes.

Direct Write Protein Patterns for Multiplexed Cytokine Detection from Live Cells Using Electron Beam Lithography

Simultaneous detection of multiple biomarkers, such as extracellular signaling molecules, is a critical aspect in disease profiling and diagnostics. Precise positioning of antibodies on surfaces, especially at the micro- and nanoscale, is important for the improvement of assays, biosensors, and diagnostics on the molecular level, and therefore, the pursuit of device miniaturization for parallel, fast, low-volume assays is a continuing challenge. Here, we describe a multiplexed cytokine immunoassay utilizing electron beam lithography and a trehalose glycopolymer as a resist for the direct writing of antibodies on silicon substrates, allowing for micro- and nanoscale precision of protein immobilization. Specifically, anti-interleukin 6 (IL-6) and antitumor necrosis factor alpha (TNFα) antibodies were directly patterned. Retention of the specific binding properties of the patterned antibodies was shown by the capture of secreted cytokines from stimulated RAW 264.7 macrophages. A sandwich immunoassay was employed using gold nanoparticles and enhancement with silver for the detection and visualization of bound cytokines to the patterns by localized surface plasmon resonance detected with dark-field microscopy. Multiplexing with both IL-6 and TNFα on a single chip was also successfully demonstrated with high specificity and in relevant cell culture conditions and at different times after cell stimulation. The direct fabrication of capture antibody patterns for cytokine detection described here could be useful for biosensing applications.

Functional protein micropatterning for drug design and discovery

INTRODUCTION

The past decade has witnessed tremendous progress in surface micropatterning techniques for generating arrays of various types of biomolecules. Multiplexed protein micropatterning has tremendous potential for drug discovery providing versatile means for high throughput assays required for target and lead identification as well as diagnostics and functional screening for personalized medicine. However, ensuring the functional integrity of proteins on surfaces has remained challenging, in particular in the case of membrane proteins, the most important class of drug targets. Yet, generic strategies to control functional organization of proteins into micropatterns are emerging.

AREAS COVERED

This review includes an overview introducing the most common approaches for surface modification and functional protein immobilization. The authors present the key photo and soft lithography techniques with respect to compatibility with functional protein micropatterning and multiplexing capabilities. In the second part, the authors present the key applications of protein micropatterning techniques in drug discovery with a focus on membrane protein interactions and cellular signaling.

EXPERT OPINION

With the growing importance of target discovery as well as protein-based therapeutics and personalized medicine, the application of protein arrays can play a fundamental role in drug discovery. Yet, important technical breakthroughs are still required for broad application of these approaches, which will include in vitro "copying" of proteins from cDNA arrays into micropatterns, direct protein capturing from single cells as well as protein microarrays in living cells.

Trehalose glycopolymer resists allow direct writing of protein patterns by electron-beam lithography

Direct-write patterning of multiple proteins on surfaces is of tremendous interest for a myriad of applications. Precise arrangement of different proteins at increasingly smaller dimensions is a fundamental challenge to apply the materials in tissue engineering, diagnostics, proteomics and biosensors. Herein, we present a new resist that protects proteins during electron-beam exposure and its application in direct-write patterning of multiple proteins. Polymers with pendant trehalose units are shown to effectively crosslink to surfaces as negative resists, while at the same time providing stabilization to proteins during the vacuum and electron-beam irradiation steps. In this manner, arbitrary patterns of several different classes of proteins such as enzymes, growth factors and immunoglobulins are realized. Utilizing the high-precision alignment capability of electron-beam lithography, surfaces with complex patterns of multiple proteins are successfully generated at the micrometre and nanometre scale without requiring cleanroom conditions.

Post-Electrospinning "Triclick" Functionalization of Degradable Polymer Nanofibers

4-Dibenzocyclooctynol (DIBO) was used as an initiator for the ring-opening copolymerization of ε-caprolactone and 1,4,8-trioxaspiro[4.6]-9-undecanone (TOSUO) resulting in a series of DIBO end-functionalized copolymers. Following deprotection of the ketone group, the polymers were derivatized with aminooxyl-containing compounds by oxime ligation. Mixtures of keto- and alkyne-derivatized polymers were co-electrospun into well-defined nanofibers containing three separate chemical handles. Strain-promoted azide alkyne cycloaddition (SPAAC), oxime ligation, and copper-catalyzed azide alkyne cycloaddition (CuAAC) were used to sequentially functionalize the nanofibers first with fluorescent reporters and then separately with bioactive Gly-Arg-Gly-Asp-Ser (GRGDS), BMP-2 peptide, and dopamine. This translationally relevant approach facilitates the straightforward derivatization of diverse bioactive molecules that can be controllably tethered to the surface of nanofibers.

Hierarchically ordered nanopatterns for spatial control of biomolecules

The development and study of a benchtop, high-throughput, and inexpensive fabrication strategy to obtain hierarchical patterns of biomolecules with sub-50 nm resolution is presented. A diblock copolymer of polystyrene-b-poly(ethylene oxide), PS-b-PEO, is synthesized with biotin capping the PEO block and 4-bromostyrene copolymerized within the polystyrene block at 5 wt %. These two handles allow thin films of the block copolymer to be postfunctionalized with biotinylated biomolecules of interest and to obtain micropatterns of nanoscale-ordered films via photolithography. The design of this single polymer further allows access to two distinct superficial nanopatterns (lines and dots), where the PEO cylinders are oriented parallel or perpendicular to the substrate. Moreover, we present a strategy to obtain hierarchical mixed morphologies: a thin-film coating of cylinders both parallel and perpendicular to the substrate can be obtained by tuning the solvent annealing and irradiation conditions.

Advances in the surface modification techniques of bone-related implants for last 10 years

At the time of implanting bone-related implants into human body, a variety of biological responses to the material surface occur with respect to surface chemistry and physical state. The commonly used biomaterials (e.g. titanium and its alloy, Co-Cr alloy, stainless steel, polyetheretherketone, ultra-high molecular weight polyethylene and various calcium phosphates) have many drawbacks such as lack of biocompatibility and improper mechanical properties. As surface modification is very promising technology to overcome such problems, a variety of surface modification techniques have been being investigated. This review paper covers recent advances in surface modification techniques of bone-related materials including physicochemical coating, radiation grafting, plasma surface engineering, ion beam processing and surface patterning techniques. The contents are organized with different types of techniques to applicable materials, and typical examples are also described.

Development of functional biomaterials with micro- and nanoscale technologies for tissue engineering and drug delivery applications

Micro- and nanotechnologies have emerged as potentially effective fabrication tools for addressing the challenges faced in tissue engineering and drug delivery. The ability to control and manipulate polymeric biomaterials at the micron and nanometre scale with these fabrication techniques has allowed for the creation of controlled cellular environments, engineering of functional tissues and development of better drug delivery systems. In tissue engineering, micro- and nanotechnologies have enabled the recapitulation of the micro- and nanoscale detail of the cell's environment through controlling the surface chemistry and topography of materials, generating 3D cellular scaffolds and regulating cell-cell interactions. Furthermore, these technologies have led to advances in high-throughput screening (HTS), enabling rapid and efficient discovery of a library of materials and screening of drugs that induce cell-specific responses. In drug delivery, controlling the size and geometry of drug carriers with micro- and nanotechnologies have allowed for the modulation of parametres such as bioavailability, pharmacodynamics and cell-specific targeting. In this review, we introduce recent developments in micro- and nanoscale engineering of polymeric biomaterials, with an emphasis on lithographic techniques, and present an overview of their applications in tissue engineering, HTS and drug delivery.

Chemoselective immobilization of proteins by microcontact printing and bio-orthogonal click reactions

Herein, a combination of microcontact printing of functionalized alkanethiols and site-specific modification of proteins is utilized to chemoselectively immobilize proteins onto gold surfaces, either by oxime- or copper-catalyzed alkyne-azide click chemistry. Two molecules capable of click reactions were synthesized, an aminooxy-functionalized alkanethiol and an azide-functionalized alkanethiol, and self-assembled monolayer (SAM) formation on gold was confirmed by IR spectroscopy. The alkanethiols were then individually patterned onto gold surfaces by microcontact printing. Site-specifically modified proteins-horse heart myoglobin (HHMb) containing an N-terminal α-oxoamide and a red fluorescent protein (mCherry-CVIA) with a C-terminal alkyne-were immobilized by incubation onto respective stamped functionalized alkanethiol patterns. Pattern formation was confirmed by fluorescence microscopy.

Local pH-responsive diazoketo-functionalized photoresist for multicomponent protein patterning

Selective surface immobilization of multiple biomolecule components, under mild conditions where they do not denature, is attractive for applications in biosensors and biotechnology. Here, we report on a biocompatible and pH-responsive photoresist containing diazoketo-functionalized methacrylate, methacrylic acid, and poly(ethylene glycol) methacrylate monomers, where the photolithographic process may be carried out in a local pH range to minimize biomolecular denaturation. The polymer is insoluble or sparsely soluble in pH 6.4 or more acidic solution or deionized water, but soluble in a basic solution, pH 7.9 or more. After UV exposure, however, carboxylic acid groups are generated by Wolff rearrangement and photodissociation of the diazoketo groups in the polymer chain, leading to dissolution of UV-exposed polymer at pH 6.4. Using the property of the pH-solubility switching, we demonstrate dual streptavidin patterning using only biological buffers, pH 6.4 and 7.9 solutions, and double exposure patterning to confirm the sustainability of the diazoketo groups in unexposed regions despite carrying out several wet processes.

Orthogonality in organic, polymer, and supramolecular chemistry: from Merrifield to click chemistry

The concept of orthogonality has been applied to many areas of chemistry, ranging from wave functions to chromatography. But it was Barany and Merrifield's orthogonal protecting group strategy that paved the way for solid phase peptide syntheses, other important classes of biomaterials such as oligosaccharides and oligonucleotides, and ultimately to a term in widespread usage that is focused on chemical reactivity and binding selectivity. The orthogonal protection strategy has been extended to the development of orthogonal activation, and recently the click reaction, for streamlining organic synthesis. The click reaction and its variants are considered orthogonal as the components react together in high yield and in the presence of many other functional groups. Likewise, supramolecular building blocks can also be orthogonal, thereby enabling programmed self-assembly, a superb strategy to create complex architectures. Overall, orthogonal reactions and supramolecular interactions have dramatically improved the syntheses, the preparation of functional materials, and the self-assembly of nanoscale structures.

Oxime cross-linked injectable hydrogels for catheter delivery

Catheter delivery of therapeutic materials is important for developing minimally invasive treatment approaches. However, the majority of injectable materials gel rapidly upon mixing and/or heating to body temperature. The application of an oxime cross-linked hydrogel system is demonstrated. The system has a broad range of tunable gelation rates, is capable of injection through a catheter, and exhibits rapid gelation upon injection into tissue.

High-resolution, high-throughput, positive-tone patterning of poly(ethylene glycol) by helium beam exposure through stencil masks

In this work, a collimated helium beam was used to activate a thiol-poly(ethylene glycol) (SH-PEG) monolayer on gold to selectively capture proteins in the exposed regions. Protein patterns were formed at high throughput by exposing a stencil mask placed in proximity to the PEG-coated surface to a broad beam of helium particles, followed by incubation in a protein solution. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) spectra showed that SH-PEG molecules remain attached to gold after exposure to beam doses of 1.5-60 µC/cm(2) and incubation in PBS buffer for one hour, as evidenced by the presence of characteristic ether and methoxy peaks at 1120 cm(-1) and 2870 cm(-1), respectively. X-ray Photoelectron Spectroscopy (XPS) spectra showed that increasing beam doses destroy ether (C-O) bonds in PEG molecules as evidenced by the decrease in carbon C1s peak at 286.6 eV and increased alkyl (C-C) signal at 284.6 eV. XPS spectra also demonstrated protein capture on beam-exposed PEG regions through the appearance of a nitrogen N1s peak at 400 eV and carbon C1s peak at 288 eV binding energies, while the unexposed PEG areas remained protein-free. The characteristic activities of avidin and horseradish peroxidase were preserved after attachment on beam-exposed regions. Protein patterns created using a 35 µm mesh mask were visualized by localized formation of insoluble diformazan precipitates by alkaline phosphatase conversion of its substrate bromochloroindoyl phosphate-nitroblue tetrazolium (BCIP-NBT) and by avidin binding of biotinylated antibodies conjugated on 100 nm gold nanoparticles (AuNP). Patterns created using a mask with smaller 300 nm openings were detected by specific binding of 40 nm AuNP probes and by localized HRP-mediated deposition of silver nanoparticles. Corresponding BSA-passivated negative controls showed very few bound AuNP probes and little to no enzymatic formation of diformazan precipitates or silver nanoparticles.

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.

Large-Scale Fabrication of Three-Dimensional Surface Patterns Using Template-Defined Electrochemical Deposition

A new strategy to achieve large-scale, three-dimensional (3D) micro- and nanostructured surface patterns through selective electrochemical growth on monolayer colloidal crystal (MCC) templates is reported. This method can effectively create large-area (>1 cm2), 3D surface patterns with well-defined structures in a cost-effective and time-saving manner (<30 min). A variety of 3D surface patterns, including semishells, Janus particles, microcups, and mushroom-like clusters, is generated. Most importantly, our method can be used to prepare surface patterns with prescribed compositions, such as metals, metal oxides, organic materials, or composites (e.g., metal/metal oxide, metal/polymer). The 3D surface patterns produced by our method can be valuable in a wide range of applications, such as biosensing, data storage, and plasmonics. In a proof-of-concept study, we investigated, both experimentally and theoretically, the surface-enhanced Raman scattering (SERS) performance of the fabricated silver 3D semishell arrays.

Nano-anchors with single protein capacity produced with STED lithography

Acrylate nanoanchors of subdiffraction-limited diameter are written with optical stimulated emission depletion (STED) lithography. After incubation, 98% of all nanoanchors are loaded quickly with fluorescently labeled antibodies. Controlling the size of the nanoanchors allows for limiting the number of the antibodies. Direct stochastic optical reconstruction microscopy (dSTORM) imaging, statistical distribution of fluorescence, quantitative fluorescence readout, and single molecule blinking consistently prove that 80% of the nanoanchors with a 65 nm diameter are carrying only one antibody each, which are functional as confirmed with live erythrocytes.

The influence of nanostructured materials on biointerfacial interactions

Control over biointerfacial interactions in vitro and in vivo is the key to many biomedical applications: from cell culture and diagnostic tools to drug delivery, biomaterials and regenerative medicine. The increasing use of nanostructured materials is placing a greater demand on improving our understanding of how these new materials influence biointerfacial interactions, including protein adsorption and subsequent cellular responses. A range of nanoscale material properties influence these interactions, and material toxicity. The ability to manipulate both material nanochemistry and nanotopography remains challenging in its own right, however, a more in-depth knowledge of the subsequent biological responses to these new materials must occur simultaneously if they are ever to be affective in the clinic. We highlight some of the key technologies used for fabrication of nanostructured materials, examine how nanostructured materials influence the behavior of proteins and cells at surfaces and provide details of important analytical techniques used in this context.