Nanopatterned polymer brushes: conformation, fabrication and applications

Advancing Glucose Sensing Through Auto-Fluorescent Polymer Brushes: From Surface Design to Nano-Arrays

Designing smart (bio)interfaces with the capability to sense and react to changes in local environments offers intriguing possibilities for new surface-based sensing devices and technologies. Polymer brushes make ideal materials to design such adaptive and responsive interfaces given their large variety of functional and structural possibilities as well as their outstanding abilities to respond to physical, chemical, and biological stimuli. Herein, a practical sensory interface for glucose detection based on auto-fluorescent polymer brushes decorated with phenylboronic acid (PBA) receptors is presented. The glucose-responsive luminescent surfaces, which are capable of translating conformational transitions triggered by pH variations and binding events into fluorescent readouts without the need for fluorescent dyes, are grown from both nanopatterned and non-patterned substrates. Two-photon laser scanning confocal microscopy and atomic force microscopy (AFM) analyses reveal the relationship between the brush conformation and glucose concentration and confirm that the phenylboronic acid functionalized brushes can bind glucose over a range of physiologically relevant concentrations in a reversible manner. The combination of auto-fluorescent polymer brushes with synthetic receptors presents a promising avenue for designing innovative and robust sensing systems, which are essential for various biomedical applications, among other uses.

Tip-Induced Nanopatterning of Ultrathin Polymer Brushes

Patterned, ultra-thin surface layers can serve as templates for positioning nanoparticlesor targeted self-assembly of molecular structures, for example, block-copolymers. This work investigates the high-resolution, atomic force microscopebased patterning of 2 nm thick vinyl-terminated polystyrene brush layers and evaluates the line broadening due to tip degradation. This work compares the patterning properties with those of a silane-based fluorinated self-assembled monolayer (SAM), using molecular heteropatterns generated by modified polymer blend lithography (brush/SAM-PBL). Stable line widths of 20 nm (FWHM) over lengths of over 20000 µm indicate greatly reduced tip wear, compared to expectations on uncoated SiO_x surfaces. The polymer brush acts as a molecularly thin lubricating layer, thus enabling a 5000 fold increase in tip lifetime, and the brush is bonded weakly enough that it can be removed with surgical accuracy. On traditionally used SAMs, either the tip wear is very high or the molecules are not completely removed. Polymer Phase Amplified Brush Editing is presented, which uses directed self-assembly to amplify the aspect ratio of the molecular structures by a factor of 4. The structures thus amplified allow transfer into silicon/metal heterostructures, fabricating 30 nm deep, all-silicon diffraction gratings that could withstand focused high-power 405 nm laser irradiation.

Theoretical analysis of the elastic free energy contributions to polymer brushes in poor solvent: A refined mean-field theory

We consider polymer brushes in poor solvent that are grafted onto planar substrates and onto the internal and external surfaces of a cylinder using molecular dynamics simulation, self-consistent field (SCF), and mean-field theory. We derive a unified expression for the mean field free energy for the three geometrical classes. While for low grafting densities, the effect of chain elasticity can be neglected in poor solvent conditions, it becomes relevant at higher grafting densities and, in particular, for concave geometries. Based on the analysis of the end monomer distribution, we introduce an analytical term that describes the elasticity as a function of grafting density. The accuracy of the model is validated with molecular dynamics simulations as well as SCF computations and shown to yield precise values for the layer thickness over a wide range of system parameters. We further apply this model to analyze the gating behavior of switchable brushes inside nanochannels.

Short vs. long chains competition during “grafting to” process from melt

A preferential grafting of short chains occurs during the “grafting to” reaction of hydroxy terminated P(S-st-MMA) blends consisting of short and long chains. The enrichment is enhanced when the chain length difference increases.

Preparation of Homopolymer, Block Copolymer, and Patterned Brushes Bearing Thiophene and Acetylene Groups Using Microliter Volumes of Reaction Mixtures

The synthesis of surface-grafted polymers with variable functionality requires the careful selection of polymerization methods that also enable spatially controlled grafting, which is crucial for the fabrication of, e.g., nano (micro) sensor or nanoelectronic devices. The development of versatile, simple, economical, and eco-friendly synthetic strategies is important for scaling up the production of such polymer brushes. We have recently shown that poly (3-methylthienyl methacrylate) (PMTM) and poly (3-trimethylsilyl-2-propynyl methacrylate) (PTPM) brushes with pendant thiophene and acetylene groups, respectively, could be used for the production of ladder-like conjugated brushes that are potentially useful in the mentioned applications. However, the previously developed syntheses of such brushes required the use of high volumes of reagents, elevated temperature, or high energy UV-B light. Therefore, we present here visible light-promoted metal-free surface-initiated ATRP (metal-free SI-ATRP) that allows the economical synthesis of PMTM and PTPM brushes utilizing only microliter volumes of reaction mixtures. The versatility of this approach was shown by the formation of homopolymers but also the block copolymer conjugated brushes (PMTM and PTPM blocks in both sequences) and patterned films using TEM grids serving as photomasks. A simple reaction setup with only a monomer, solvent, commercially available organic photocatalyst, and initiator decorated substrate makes the synthesis of these complex polymer structures achievable for non-experts and ready for scaling up.

High-Resolution Nanopatterning of Free-Standing, Self-Supported Helical Polypeptide Rod Brushes via Electron Beam Lithography

In this study of nanopatterned helical poly(benzyl-l-glutamate) (PBLG) brushes, rod-type brush arrays were fabricated via an integrated process of high-resolution lithography and surface-initiated vapor deposition polymerization (SI-VDP). "Nanospikes" of polymer brushes with spacings of less than 100 nm were produced. The topology and areal behavior of the resulting patterned rod-like brushes were analyzed and compared with patterned coil-type brushes. A geometric study of these self-assembled "nanospikes" was carried out, and their cross sections were investigated via focused ion beam (FIB) and scanning electron microscopy (SEM). Furthermore, the presence of poly(N-isopropylacrylamide) (PNIPAM) brushes in unpatterned regions was shown to inhibit undesired "inter-spike" bridging of the PBLG brushes, resulting in more well-defined nanostructures. It was shown that rod-like polypeptide brushes are capable of self-segregation and become arranged vertically without any external support from their surroundings, to form a rod bundle end-point functional topography that could provide possible pathways for studies of model biological surfaces, directed assembly of nanoparticles, or binary mixed brush surfaces with dual properties.

UV-Laser Interference Lithography for Local Functionalization of Plasmonic Nanostructures with Responsive Hydrogel

A novel approach to local functionalization of plasmonic hotspots at gold nanoparticles with biofunctional moieties is reported. It relies on photocrosslinking and attachment of a responsive hydrogel binding matrix by the use of a UV interference field. A thermoresponsive poly(N-isopropylacrylamide)-based (pNIPAAm) hydrogel with photocrosslinkable benzophenone groups and carboxylic groups for its postmodification was employed. UV-laser interference lithography with a phase mask configuration allowed for the generation of a high-contrast interference field that was used for the recording of periodic arrays of pNIPAAm-based hydrogel features with the size as small as 170 nm. These hydrogel arrays were overlaid and attached on the top of periodic arrays of gold nanoparticles, exhibiting a diameter of 130 nm and employed as a three-dimensional binding matrix in a plasmonic biosensor. Such a hybrid material was postmodified with ligand biomolecules and utilized for plasmon-enhanced fluorescence readout of an immunoassay. Additional enhancement of the fluorescence sensor signal by the collapse of the responsive hydrogel binding matrix that compacts the target analyte at the plasmonic hotspot is demonstrated.

Tuning the Properties of Nanogel Surfaces by Grafting Charged Alkylamine Brushes

Nanogels are chemically crosslinked polymeric nanoparticles endowed with high encapsulation ability, tunable size, ease of preparation, and responsiveness to external stimuli. The presence of specific functional groups on their surfaces provides an opportunity to tune their surface properties and direct their behavior. In this work, we used mesoscale modeling to describe conformational and mechanical properties of nanogel surfaces formed by crosslinked polyethylene glycol and polyethyleneimine, and grafted by charged alkylamine brushes of different lengths. Simulations show that both number of chains per area and chain length can be used to tune the properties of the coating. Properly selecting these two parameters allows switching from a hydrated, responsive coating to a dried, highly charged layer. The results also suggest that the scaling behavior of alkylamine brushes, e.g., the transition from a mushroom to semi-dilute brush, is only weakly coupled with the shielding ability of the coating and much more with its compressibility.

Tailored Nanopatterning by Controlled Continuous Nanoinscribing with Tunable Shape, Depth, and Dimension

We present that the tailored nanopatterning with tunable shape, depth, and dimension for diverse application-specific designs can be realized by utilizing controlled dynamic nanoinscribing (DNI), which can generate bur-free plastic deformation on various flexible substrates via continuous mechanical inscription of a small sliced edge of a nanopatterned mold in a compact and vacuum-free system. Systematic controlling of prime DNI processing parameters including inscribing force, temperature, and substrate feed rate can determine the nanopattern depths and their specific profiles from rounded to angular shapes as a summation of the force-driven plastic deformation and heat-driven thermal deformation. More complex nanopatterns with gradient depths and/or multidimensional profiles can also be readily created by modulating the horizontal mold edge alignment and/or combining sequential DNI strokes, which otherwise demand laborious and costly procedures. Many practical user-specific applications may benefit from this study by tailor-making the desired nanopattern structures within desired areas, including precision machine and optics components, transparent electronics and photonics, flexible sensors, and reattachable and wearable devices. We demonstrate one vivid example in which the light diffusion direction of a light-emitting diode can be tuned by application of specifically designed DNI nanopatterns.

Functionalization and Patterning of Self-Assembled Monolayers and Polymer Brushes Using Microcontact Chemistry

Because the surface connects a material to its environment, the functionalization, modification, and patterning of surfaces is key to a wide range of materials applied in microelectronics, displays, sensing, microarrays, photovoltaics, catalysis, and other fields. Self-assembled monolayers (SAMs), which can be deposited on a wide range of inorganic materials, are only a few nanometers thick, yet they can radically change the properties of the resulting interface. Alternatively, thin polymer films composed of polymer brushes grown from the surface provide a more robust molecular modification of inorganic materials. For many applications, patterned SAMs or polymer brushes are desired. Over the past decade, our group has shown that both SAMs as well as polymer brushes can be patterned very efficiently using microcontact printing. In microcontact printing, a molecular "ink" is deposited on a suitable substrate using a microstructured elastomer stamp, which delivers the ink exclusively in the area of contact between stamp and substrate. In contrast to most types of lithography, microcontact printing does not require expensive equipment. Our work has shown that "microcontact chemistry" is a powerful additive surface patterning method, in which molecular inks react with a precursor SAM during printing so that surfaces can be modified with various orthogonal functional groups or molecular recognition sites in microscale patterns. Functional groups include reactive groups for click chemistry or photochemistry and initiators for radical polymerization. Molecular recognition sites include host-guest chemistry as well as biochemical ligands such as carbohydrates and biotin. In this Account, we present an overview of our research in this area including selected examples of work by other groups. In the first part, we review our work on the patterning of SAMs using microcontact chemistry, with a focus on click chemistry and photochemistry. We will show how cycloadditions, thiol-ene reactions, and tetrazole chemistry can be used to obtain versatile surface patterns. In the second part, we demonstrate that microcontact chemistry can be used to pattern polymer brushes. Among others, initiators for surface-induced nitroxide-mediated polymerization and atom transfer polymerization were printed and used to grow patterned polymer brushes with molecular recognition groups suitable for responsive surface adhesion. In the third part, we describe how SAMs and polymer brushes can be printed on microparticles instead of flat substrates so that Janus particles with functional patches can be obtained. Finally, we present a brief outlook on further developments expected in this field.

Photocatalytic Lithography

Patterning, the controlled formation of ordered surface features with different physico-chemical properties, is a cornerstone of contemporary micro- and nanofabrication. In this context, lithographic approaches owe their wide success to their versatility and their relative ease of implementation and scalability. Conventional photolithographic methods require several steps and the use of polymeric photoresists for the development of the desired pattern, all factors which can be deleterious, especially for sensitive substrates. Efficient patterning of surfaces, with resolution down to the nanometer scale, can be achieved by means of photocatalytic lithography. This approach is based on the use of photocatalysts to achieve the selective chemical modification or degradation of self-assembled monolayers, polymers, and metals. A wide range of photoactive compounds, from semiconducting oxides to porphyrins, have been demonstrated to be suitable photocatalysts. The goal of the present review is to provide a comprehensive state-of-the-art photocatalytic lithography, ranging from approaches based on semiconducting oxides to singlet oxygen-based lithography. Special attention will be dedicated to the results obtained for the patterning of polymer brushes, the sculpturing of metal nanoparticle arrays, and the patterning of graphene-based structures.

Practical use of polymer brushes in sustainable energy applications: interfacial nanoarchitectonics for high-efficiency devices

The discovery and development of novel approaches, materials and manufacturing processes in the field of energy are compelling increasing recognition as a major challenge for contemporary societies. The performance and lifetime of energy devices are critically dependent on nanoscale interfacial phenomena. From the viewpoint of materials design, the improvement of current technologies inevitably relies on gaining control over the complex interface between dissimilar materials. In this sense, interfacial nanoarchitectonics with polymer brushes has seen growing interest due to its potential to overcome many of the limitations of energy storage and conversion devices. Polymer brushes offer a broad variety of resources to manipulate interfacial properties and gain molecular control over the synergistic combination of materials. Many recent examples show that the rational integration of polymer brushes in hybrid nanoarchitectures greatly improves the performance of energy devices in terms of power density, lifetime and stability. Seen in this light, polymer brushes provide a new perspective from which to consider the development of hybrid materials and devices with improved functionalities. The aim of this review is therefore to focus on what polymer brush-based solutions can offer and to show how the practical use of surface-grafted polymer layers can improve the performance and efficiency of fuel cells, lithium-ion batteries, organic radical batteries, supercapacitors, photoelectrochemical cells and photovoltaic devices.

Responsive and Synergistic Antibacterial Coatings: Fighting against Bacteria in a Smart and Effective Way

Antibacterial coatings that eliminate initial bacterial attachment and prevent subsequent biofilm formation are essential in a number of applications, especially implanted medical devices. Although various approaches, including bacteria-repelling and bacteria-killing mechanisms, have been developed, none of them have been entirely successful due to their inherent drawbacks. In recent years, antibacterial coatings that are responsive to the bacterial microenvironment, that possess two or more killing mechanisms, or that have triggered-cleaning capability have emerged as promising solutions for bacterial infection and contamination problems. This review focuses on recent progress on three types of such responsive and synergistic antibacterial coatings, including i) self-defensive antibacterial coatings, which can "turn on" biocidal activity in response to a bacteria-containing microenvironment; ii) synergistic antibacterial coatings, which possess two or more killing mechanisms that interact synergistically to reinforce each other; and iii) smart "kill-and-release" antibacterial coatings, which can switch functionality between bacteria killing and bacteria releasing under a proper stimulus. The design principles and potential applications of these coatings are discussed and a brief perspective on remaining challenges and future research directions is presented.

A photo-selective chain-end modification of polyacrylate-iodide and its application in patterned polymer brush synthesis

A photo-selective chain-end modification of polyacrylate-iodide (polymer-I) was developed. The method was used to generate chain-end patterned polymer brushes.

Stimuli-responsive bio-based polymeric systems and their applications

This article highlights the properties of stimuli-responsive bio-based polymeric systems and their main intelligent applications.

Close-packed silane nanodot arrays by capillary nanostamping coupled with heterocyclic silane ring opening

We report the parallel generation of close-packed ordered silane nanodot arrays with nanodot diameters of few 100 nm and nearest-neighbor distances in the one-micron range.

Hierarchical structures on nickel-titanium fabricated by ultrasonic nanocrystal surface modification

Hierarchical structures on metallic implants can enhance the interaction between cells and implants and thus increase their biocompatibility. However, it is difficult to directly fabricate hierarchical structures on metallic implants. In this study, we used a simple one-step method, ultrasonic nanocrystal surface modification (UNSM), to fabricate hierarchical surface structures on a nickel-titanium (NiTi) alloy. During UNSM, a tungsten carbide ball hits metal surfaces at ultrasonic frequency. The overlapping of the ultrasonic strikes generates hierarchical structures with microscale grooves and embedded nanoscale wrinkles. Cell culture experiments showed that cells adhere better and grow more prolifically on the UNSM-treated samples. Compared with the untreated samples, the UNSM-treated samples have higher corrosion resistance. In addition, the surface hardness increased from 243 Hv to 296 Hv and the scratch hardness increased by 22%. Overall, the improved biocompatibility, higher corrosion resistance, and enhanced mechanical properties demonstrate that UNSM is a simple and effective method to process metallic implant materials.

Using porous magnetic iron oxide nanomaterials as a facile photoporation nanoplatform for macromolecular delivery

The intracellular delivery of exogenous macromolecules such as functional proteins, antibodies, polysaccharides and nucleic acids into living cells for biomedical applications is of great interest. Even though great efforts have been devoted to this task, universal delivery systems that provide excellent intracellular delivery performance combined with easy cell recovery are urgently needed. Magnetic iron oxide nanoparticles show promising potential for various biomedical applications because of their advantages such as high biocompatibility and cost-effectiveness. Herein, a new facile platform for macromolecular delivery was developed based on the photothermal properties of porous magnetic iron oxide nanoparticles (P-MNPs). The near-infrared radiation (NIR) absorption behavior of P-MNPs remarkably facilitates the delivery of macromolecules into cells while maintaining high cell viability. Furthermore, the assistance of polycationic polyethylenimine improves the efficiency of DNA delivery. Most importantly, the cells could be easily recovered after macromolecular delivery by trypsinization, which is of great significance for further practical application of the delivery system. The facile and cost-effective platform proposed in this work provides a new avenue for the utilization of P-MNPs in macromolecular delivery.

Sweet Switch: Sugar-Responsive Bioactive Surfaces Based on Dynamic Covalent Bonding

Smart bioactive surfaces that can modulate interactions with biological systems are of great interest. In this work, a surface with switchable bioactivity in response to sugars has been developed. It is based on dynamic covalent bonding between phenylboronic acid (PBA) and secondary hydroxyls on the "wide" rim of β-cyclodextrin (β-CD). The system reported consists of gold surface modified with PBA-containing polymer brushes and a series of functional β-CD derivatives conjugated to diverse bioactive ligands (CD-X). CD-X molecules are attached to the surface to give specified bioactivity such as capture of a specific protein or killing of attached bacteria. Subsequent treatment with cis-diol containing biomolecules having high affinity for PBA (e.g. fructose) leads to the release of CD-X together with the captured proteins, killed bacteria, and so forth from the surface. The surface bioactivity is thereby "turned off". Effectively, this constitutes an on-off bioactivity switch in a mild and noninvasive way, which has the potential in the design of dynamic bioactive surfaces for biomedical applications.

Nanoplasmonic sensors for biointerfacial science

In recent years, nanoplasmonic sensors have become widely used for the label-free detection of biomolecules across medical, biotechnology, and environmental science applications. To date, many nanoplasmonic sensing strategies have been developed with outstanding measurement capabilities, enabling detection down to the single-molecule level. One of the most promising directions has been surface-based nanoplasmonic sensors, and the potential of such technologies is still emerging. Going beyond detection, surface-based nanoplasmonic sensors open the door to enhanced, quantitative measurement capabilities across the biointerfacial sciences by taking advantage of high surface sensitivity that pairs well with the size of medically important biomacromolecules and biological particulates such as viruses and exosomes. The goal of this review is to introduce the latest advances in nanoplasmonic sensors for the biointerfacial sciences, including ongoing development of nanoparticle and nanohole arrays for exploring different classes of biomacromolecules interacting at solid-liquid interfaces. The measurement principles for nanoplasmonic sensors based on utilizing the localized surface plasmon resonance (LSPR) and extraordinary optical transmission (EOT) phenomena are first introduced. The following sections are then categorized around different themes within the biointerfacial sciences, specifically protein binding and conformational changes, lipid membrane fabrication, membrane-protein interactions, exosome and virus detection and analysis, and probing nucleic acid conformations and binding interactions. Across these themes, we discuss the growing trend to utilize nanoplasmonic sensors for advanced measurement capabilities, including positional sensing, biomacromolecular conformation analysis, and real-time kinetic monitoring of complex biological interactions. Altogether, these advances highlight the rich potential of nanoplasmonic sensors and the future growth prospects of the community as a whole. With ongoing development of commercial nanoplasmonic sensors and analytical models to interpret corresponding measurement data in the context of biologically relevant interactions, there is significant opportunity to utilize nanoplasmonic sensing strategies for not only fundamental biointerfacial science, but also translational science applications related to clinical medicine and pharmaceutical drug development among countless possibilities.

Controlled synthesis of diverse single-chain polymeric nanoparticles using polymers bearing furan-protected maleimide moieties

This study is devoted to the control fabrication of SCNPs from the same precursor and exploring the surface properties of SCNP-made films.

Smart Antibacterial Surfaces with Switchable Bacteria-Killing and Bacteria-Releasing Capabilities

The attachment and subsequent colonization of bacteria on the surfaces of synthetic materials and devices lead to serious problems in both human healthcare and industrial applications. Therefore, antibacterial surfaces that can prevent bacterial attachment and biofilm formation have been a long-standing focus of considerable interest and research efforts. Recently, a promising "kill-release" strategy has been proposed and applied to construct so-called smart antibacterial surfaces, which can kill bacteria attached to their surface and then undergo on-demand release of the dead bacteria and other debris to reveal a clean surface under an appropriate stimulus, thereby maintaining effective long-term antibacterial activity. This Review focuses on the recent progress (particularly over the past 5 years) on such smart antibacterial surfaces. According to the different design strategies, these surfaces can be divided into three categories: (i) "K + R"-type surfaces, which have both a killing unit and a releasing unit; (ii) "K → R"-type surfaces, which have a surface-immobilized killing unit that can be switched to perform a releasing function; and (iii) "K + (R)"-type surfaces, which have only a killing unit but can release dead bacteria upon the addition of a release solution. In the end, a brief perspective on future research directions and the major challenges in this promising field is also presented.

Construction of Functional Coatings with Durable and Broad-Spectrum Antibacterial Potential Based on Mussel-Inspired Dendritic Polyglycerol and in Situ-Formed Copper Nanoparticles

A novel surface coating with durable broad-spectrum antibacterial ability was prepared based on mussel-inspired dendritic polyglycerol (MI-dPG) embedded with copper nanoparticles (Cu NPs). The functional surface coating is fabricated via a facile dip-coating process followed by in situ reduction of copper ions with a MI-dPG coating to introduce Cu NPs into the coating matrix. This coating has been demonstrated to possess efficient long-term antibacterial properties against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and kanamycin-resistant E. coli through an "attract-kill-release" strategy. The synergistic antibacterial activity of the coating was shown by the combination of two functions of the contact killing, reactive oxygen species production and Cu ions released from the coating. Furthermore, this coating inhibited biofilm formation and showed good compatibility to eukaryotic cells. Thus, this newly developed Cu NP-incorporated MI-dPG surface coating may find potential application in the design of antimicrobial coating, such as implantable devices.

Homopolymer Nanolithography

Future progress in nanoscience and nanotechnology necessitates further development of versatile, labor-, and cost-efficient surface patterning strategies. A new approach to nanopatterning is reported, which utilizes surface segregation of a smooth layer of an end-grafted homopolymer in a poor solvent. The variation in polymer grafting density yields a range of surface nanostructures, including randomly organized pinned spherical micelles, worm-like structures, networks, and porous films. The capability to use the polymer patterns for site-specific deposition of small molecules, polymers, or nanoparticles is shown. This versatile strategy enables patterning of curved surfaces with direct access to the substrate and no need in changing polymer composition to realize different surface patterns.

Modulation of Surface-Initiated ATRP by Confinement: Mechanism and Applications

The mechanism of surface-initiated atom transfer polymerization (SI-ATRP) of methacrylates in confined volumes is systematically investigated by finely tuning the distance between a grafting surface and an inert plane by means of nanosized patterns and micrometer thick foils. The polymers were synthesized from monolayers of photocleavable initiators, which allow the analysis of detached brushes by size-exclusion chromatography (SEC). Compared to brushes synthesized under "open" polymerization mixtures, nearly a 4-fold increase in brush molar mass was recorded when SI-ATRP was performed within highly confined reaction volumes. Correlating the SI-ATRP of methyl methacrylate (MMA), with and without "sacrificial" initiator, to that of lauryl methacrylate (LMA) and analyzing the brush growth rates within differently confined volumes, we demonstrate faster grafting kinetics with increasing confinement due to the progressive hindering of CuII-based deactivators from the brush propagating front. This effect is especially noticeable when viscous polymerization mixtures are generated and enables the synthesis of several hundred nanometer thick brushes within relatively short polymerization times. The faster rates of confined SI-ATRP can be additionally used to fabricate, in one pot, precisely structured brush gradients, when volume confinement is continuously varied across a single substrate by spatially tuning the vertical distance between the grafting and the confining surfaces.

Salt-Induced Regenerative Surface for Bacteria Killing and Release

Antibacterial surfaces with both bacteria killing and release functions show great promise in biological and biomedical applications, in particular for reusable medical devices. However, these surfaces either require a sophisticated technique to create delicate structures or need rigorous stimuli to trigger the functions, greatly limiting their practical application. In this study, we made a step forward by developing a simple system based on a salt-responsive polyzwitterionic brush. Specifically, the salt-responsive brush of poly(3-(dimethyl (4-vinylbenzyl) ammonium) propyl sulfonate) (polyDVBAPS) was endowed with bactericidal function by grafting an effective bactericide, i.e., triclosan (TCS). This simple functionalization successfully integrated the bacteria attach/release function of polyDVBAPS and bactericidal function of TCS. As a result, the surface could kill more than 95% attached bacteria and, subsequently, could rapidly detach ∼97% bacteria after gently shaking in 1.0 M NaCl for 10 min. More importantly, such high killing efficiency and release rate could be well retained (unchanged effectiveness of both killing and release after four severe killing/release cycles), indicating the highly efficient regeneration and long-term reusability of this system. This study not only contributes zwitterionic polymers by conferring new functions but also provides a new, highly efficient and reliable surface for "killing-release" antibacterial strategy.

Supramolecular Platform with Switchable Multivalent Affinity: Photo-Reversible Capture and Release of Bacteria

Surfaces having dynamic control of interactions at the biological system-material interface are of great scientific and technological interest. In this work, a supramolecular platform with switchable multivalent affinity was developed to efficiently capture bacteria and on-demand release captured bacteria in response to irradiation with light of different wavelengths. The system consists of a photoresponsive self-assembled monolayer containing azobenzene (Azo) groups as guest and β-cyclodextrin (β-CD)-mannose (CD-M) conjugates as host with each CD-M containing seven mannose units to display localized multivalent carbohydrates. Taking the advantage of multivalent effect of CD-M, this system exhibited high capacity and specificity for the capture of mannose-specific type 1-fimbriated bacteria. Moreover, ultraviolet (UV) light irradiation caused isomerization of the Azo groups from trans-form to cis-form, resulting in the dissociation of the host-guest Azo/CD-M inclusion complexes and localized release of the captured bacteria. The capture and release process could be repeated for multiple cycles, suggesting good reproducibility. This platform provides the basis for development of reusable biosensors and diagnostic devices for the detection and measurement of bacteria and exhibits great potential for use as a standard protocol for the on-demand switching of surface functionalities.

Polymeric Biomaterials: Diverse Functions Enabled by Advances in Macromolecular Chemistry

Biomaterials have been extensively used to leverage beneficial outcomes in various therapeutic applications, such as providing spatial and temporal control over the release of therapeutic agents in drug delivery as well as engineering functional tissues and promoting the healing process in tissue engineering and regenerative medicine. This perspective presents important milestones in the development of polymeric biomaterials with defined structures and properties. Contemporary studies of biomaterial design have been reviewed with focus on constructing materials with controlled structure, dynamic functionality, and biological complexity. Examples of these polymeric biomaterials enabled by advanced synthetic methodologies, dynamic chemistry/assembly strategies, and modulated cell-material interactions have been highlighted. As the field of polymeric biomaterials continues to evolve with increased sophistication, current challenges and future directions for the design and translation of these materials are also summarized.

Hydrogel-colloid interfacial interactions: a study of tailored adhesion using optical tweezers

Dynamics of colloidal particles adhering to soft, deformable substrates, such as tissues, biofilms, and hydrogels play a key role in many biological and biomimetic processes. These processes, including, but not limited to colloid-based delivery, stitching, and sorting, involve microspheres exploring the vicinity of soft, sticky materials in which the colloidal dynamics are affected by the fluid environment (e.g., viscous coupling), inter-molecular interactions between the colloids and substrates (e.g., Derjaguin-Landau-Verwey-Overbeek (DLVO) theory), and the viscoelastic properties of contact region. To better understand colloidal dynamics at soft interfaces, an optical tweezers back-focal-plane interferometry apparatus was developed to register the transverse Brownian motion of a silica microsphere in the vicinity of polyacrylamide (PA) hydrogel films. The time-dependent mean-squared displacements are well described by a single exponential relaxation, furnishing measures of the transverse interfacial diffusion coefficient and binding stiffness. Substrates with different elasticities were prepared by changing the PA crosslinking density, and the inter-molecular interactions were adjusted by coating the microspheres with fluid membranes. Stiffer PA hydrogels (with bulk Young's moduli ≈1-10 kPa) immobilize the microspheres more firmly (lower diffusion coefficient and position variance), and coating the particles with zwitterionic lipid bilayers (DOPC) completely eliminates adhesion, possibly by repulsive dispersion forces. Remarkably, embedding polyethylene glycol-grafted lipid bilayers (DSPE-PEG2k-Amine) in the zwitterionic fluid membranes produces stronger adhesion, possibly because of polymer-hydrogel attraction and entanglement. This study provides new insights to guide the design of nanoparticles and substrates with tunable adhesion, leading to smarter delivery, sorting, and screening of micro- and nano-systems.

Self-Assembly into Strands in Amphiphilic Polymer Brushes

The self-assembly of amphiphilic macromolecules end-grafted to a plane surface is studied using mean-field theory and computer simulations. Chain backbones are built from hydrophobic groups, whereas side groups are hydrophilic. The brush is immersed in a solvent, which can be good or poor, but on average is not far from θ conditions. It is demonstrated that the strong amphiphilicity of macromolecules at a monomer unit level leads to their self-assembly into a system of strands with a 2D hexagonal order in a cross-section parallel to the grafting plane. The structure period is determined by the length of side groups. In theory, this effect is explained by the orientation of strongly amphiphilic monomer units at a strand/solvent boundary that leads to an effective negative contribution to the surface tension. Computer simulations with molecular dynamics (MD) are used for a detailed study of the local brush structure. The aggregation number of strands grows with the increase of the grafting density and side group length.

Nanopatterned polymer brushes by reactive writing

Polymer brush patterns were prepared by a combination of electron beam induced damage in self-assembled monolayers (SAMs), creating a stable carbonaceous deposit, and consecutive self-initiated photografting and photopolymerization (SIPGP). This newly applied technique, reactive writing (RW), is investigated with 1H,1H,2H,2H-perfluorooctyltriethoxysilane SAM (PF-SAM) on silicon oxide, which, when modified by RW, can be selectively functionalized by SIPGP. With the monomer N,N-dimethylaminoethyl methacrylate (DMAEMA), we demonstrate the straightforward formation of polymer brush gradients and single polymer lines of sub-100 nm lateral dimensions, with high contrast to the PF-SAM background. The lithography parameters acceleration voltage, irradiation dose, beam current and dwell time were systematically varied to identify the optimal conditions for the maximum conversion of the SAM into a carbonaceous deposit. The results of this approach were compared to patterns prepared by carbon templating (CT) under analogous conditions, revealing a dwell time dependency, which differs from earlier reports. This new technique expands the range of CT by giving the opportunity to not only vary the chemistry of the created polymer patterns with monomer choice but also vary the chemistry of the surrounding substrate.

Optimization of 4D polymer printing within a massively parallel flow-through photochemical microreactor

Brush polymer patterns, where the position (x,y), height (z), and chemical composition of each feature in an array were controlled independently, were prepared by combining massively parallel tip-based photolithography, microfluidics, and photochemical radical polymerizations.