Reactive surface coatings based on polysilsesquioxanes: universal method toward light-responsive surfaces

A spiropyran-decorated nanocoating for dynamically regulating bacteria/cell adhesion and detachment

Microorganism adhesion and the resulting contamination of the biomaterial is one of the major causes of biomedical device failure. Stimuli-responsive materials based on dynamically regulating interactions with reversible characteristics of on-off states have attracted increasing attention. Here, a facile self-assembled biomaterial nanocoating constructed using acidity- and photoregulated spiropyran-modified nanoparticles was developed for reversibly regulating bacteria or mammalian cell adhesion-and-detachment. The coating was formed by coating a solution of spiropyran-conjugated nanoparticles around the surface of a silica gel followed by curing and drying at 60 °C for 30 min. Importantly, efficient adhesion-and-detachment of bacteria or cells could be controlled even after 8 cycles owing to the excellent acidity- and light-switched ability. Collectively, this well-defined self-assembled nanocoating as a dynamical and reversible agent provides promising insight for the development of biomedical devices, especially for biomaterial medical coatings.

Localization of Spiropyran Activation

Functionalization of planar and curved glass surfaces with spiropyran (SP) molecules and localized UV-induced activation of the mechanophore are demonstrated. Fluorescence spectra of UV-irradiated SP-functionalized surfaces reveal that increases in surface roughness or curvature produce more efficient conversion of the mechanophore to the open merocyanine (MC) form. Further, force-induced activation of the mechanophore is achieved at curved glass-polymer interfaces and not planar interfaces. Minimal fluorescence signal from UV-irradiated SP-functionalized planar glass surfaces precluded mechanical activation testing. Curved glass-polymer interfaces are prepared by SP functionalization of E-glass fibers, which are subsequently embedded in a poly(methyl methacrylate) (PMMA) matrix. Mechanical activation is induced through shear loading by a single fiber microbond testing protocol. In situ detection of SP activation at the interface is monitored by fluorescence spectroscopy. The fluorescence increase during interfacial testing suggests that attachment of the interfacial SP molecule to both fiber surface and polymer matrix is present and able to achieve significant activation of SP at the fiber-polymer matrix interface. Unlike previous studies for bulk polymers, SP activation is detected at relatively low levels of applied shear stress. By linking SP at the glass-polymer interface and transferring load directly to that interface, a more efficient mechanism for eliciting the SP response is achieved.

Design of Active Interfaces Using Responsive Molecular Components

Responsive interfaces are interfaces that show a defined and reversible change in physical properties in response to external stimuli. Typically, responsive interfaces result from the immobilization of responsive molecular components at the interface that translate a nanoscale signal into a macroscopic effect. Responsive interfaces can also be obtained if the topology of the interface can be reversibly changed using an external stimulus. As the surface of any material is its connection to the environment, responsive interfaces provide opportunities for interactive materials which are not only able to change properties upon demand, but also sense their environment and act autonomously. The application of responsive molecular components at interfaces, however, requires chemical and physical compatibility with the material surface of interest, posing a challenge not least in the retention of the responsive functionality. The state of the art in "active" interfaces which display responsive wettability, permeability, or adhesion is discussed, with a particular emphasis on microscale and nanoscale patterning since patterned interfaces can give rise to unique material properties. Finally, perspectives in the development of responsive interfaces, as well as promising approaches for bypassing the most prominent challenges are discussed.

Reactive Polymer Targeting dsRNA as Universal Virus Detection Platform with Enhanced Sensitivity

Reactive poly(pentafluorophenyl acrylate) (PPFPA)-grafted surfaces offer a versatile platform to immobilize biomolecules. Here, we utilize PPFPA-grafted surface and double-stranded RNA (dsRNA) recognizing J2 antibody to construct a universal virus detection platform with enhanced sensitivity. PPFPA on silicon substrates is prepared, and surface hydrophilicity is modulated by partial substitution of the pentafluorophenyl units with poly(ethylene glycol). Following dsRNA antibody immobilization, the prepared surfaces can distinguish long dsRNAs from single-stranded RNAs of the same length and short dsRNAs. As long dsRNAs are common byproducts of viral transcription/replication, these surfaces can detect the presence of different kinds of viruses without prior knowledge of their genomic sequences. To increase dsRNA detection sensitivity, a two-step method is devised where the captured dsRNAs are visualized with multiple fluorophore-tagged J2 antibodies. We show that the developed platform can differentiate foreign long dsRNAs from cellular dsRNAs and other biomolecules present in the cell lysate. Moreover, when tested against cells infected with hepatitis A or C viruses, both viruses are successfully detected using a single platform. Our study shows that the developed PPFPA platform immobilized with J2 antibody can serve as a primary diagnostic tool to determine the infection status for a wide range of viruses.

A new azobenzene-based design strategy for detergents in membrane protein research

Mass spectrometry enables the in-depth structural elucidation of membrane protein complexes, which is of great interest in structural biology and drug discovery. Recent breakthroughs in this field revealed the need for design rules that allow fine-tuning the properties of detergents in solution and gas phase. Desirable features include protein charge reduction, because it helps to preserve native features of protein complexes during transfer from solution into the vacuum of a mass spectrometer. Addressing this challenge, we here present the first systematic gas-phase study of azobenzene detergents. The utility of gas-phase techniques for monitoring light-driven changes of isomer ratios and molecular properties are investigated in detail. This leads to the first azobenzene detergent that enables the native mass spectrometry analysis of membrane proteins and whose charge-reducing properties can be tuned by irradiation with light. More broadly, the presented work outlines new avenues for the high-throughput characterization of supramolecular systems and opens a new design strategy for detergents in membrane protein research.

Programmable hydraulic resistor for microfluidic chips using electrogate arrays

Flow rates play an important role in microfluidic devices because they affect the transport of chemicals and determine where and when (bio)chemical reactions occur in these devices. Flow rates can conveniently be determined using external peripherals in active microfluidics. However, setting specific flow rates in passive microfluidics is a significant challenge because they are encoded on a design and fabrication level, leaving little freedom to users for adjusting flow rates for specific applications. Here, we present a programmable hydraulic resistor where an array of "electrogates" routes an incoming liquid through a set of resistors to modulate flow rates in microfluidic chips post-fabrication. This approach combines a battery-powered peripheral device with passive capillary-driven microfluidic chips for advanced flow rate control and measurement. We specifically show a programmable hydraulic resistor composed of 7 parallel resistors and 14 electrogates. A peripheral and smartphone application allow a user to activate selected electrogates and resistors, providing 127 (27-1) flow resistance combinations with values spanning on a 500 fold range. The electrogates feature a capillary pinning site (i.e. trench across the flow path) to stop a solution and an electrode, which can be activated in a few ms using a 3 V bias to resume flow based on electrowetting. The hydraulic resistor and microfluidic chip shown here enable flow rates from ~0.09 nL.s-1 up to ~5.66 nL.s-1 with the resistor occupying a footprint of only 15.8 mm2 on a 1 × 2 cm2 microfluidic chip fabricated in silicon. We illustrate how a programmable hydraulic resistor can be used to set flow rate conditions for laminar co-flow of 2 liquids and the enzymatic conversion of a substrate by stationary enzymes (alkaline phosphatase) downstream of the programmable hydraulic resistor.

Smart Copolymer-Functionalized Flexible Surfaces with Photoswitchable Wettability: From Superhydrophobicity with "Rose Petal" Effect to Superhydrophilicity

Realizing smart surfaces with switchable wettability inspired by nature continues to be fascinating as well as challenging. Herein, we present a versatile dip-coating approach to fabricate smart polymer-functionalized flexible surfaces with photoswitchable superwettability. Decorated with novel acrylate copolymers bearing a trifluoromethyl side chain and fluorine-containing azobenzene derivative moieties, the modified cotton fabric possesses a rose petal-like superhydrophobicity with contact angles larger than 150° and high water adhesion. This smart surface exhibits rapid phototriggered wettability transformation between superhydrophobicity and superhydrophilicity via alternate irradiation with ultraviolet and visible light, respectively. Meanwhile, the as-prepared flexible smart surfaces have excellent chemical and physical stabilities, which could tolerate harsh environmental conditions and repetitive mechanical deformation (e.g., stretching, curling, folding, and twisting) as well as multiple washing. More importantly, based on the excellent photocontrollability, various erasable and rewritable patterns with distinct wetting properties upon selective photoirradiation can be obtained. This simple strategy and the developed smart surface may find more advanced potential applications in controllable liquid transport, patterning droplet microarrays, and microfluidic devices.

Development of Multimodal Antibacterial Surfaces Using Porous Amine-Reactive Films Incorporating Lubricant and Silver Nanoparticles

Anti-biofouling has been improved by passive or active ways. Passive antifouling strategies aim to prevent the initial adsorption of foulants, while active strategies aim to eliminate proliferative fouling by destruction of the chemical structure and inactivation of the cells. However, neither passive antifouling strategies nor active antifouling strategies can solely resist biofouling due to their inherent limitations. Herein, we successfully developed multimodal antibacterial surfaces for waterborne and airborne bacteria with the benefit of a combination of antiadhesion (passive) and bactericidal (active) properties of the surfaces. We elaborated multifunctionalizable porous amine-reactive (PAR) polymer films from poly(pentafluorophenyl acrylate) (PPFPA). Pentafluorophenyl ester groups in the PAR films facilitate creation of multiple functionalities through a simple postmodification under mild condition, based on their high reactivity toward various primary amines. We introduced amine-containing poly(dimethylsiloxane) (amine-PDMS) and dopamine into the PAR films, resulting in infusion of antifouling silicone oil lubricants and formation of bactericidal silver nanoparticles (AgNPs), respectively. As a result, the PAR film-based lubricant-infused AgNPs-incorporated surfaces demonstrate outstanding antibacterial effects toward both waterborne and airborne Escherichia coli, suggesting a new door for development of an effective multimodal anti-biofouling surface.

The light-controlling of temperature-responsivity in stimuli-responsive polymers

Light-controlling of phase separation in temperature-responsive polymer solutions by using light-responsive materials for reversible controlling physical and chemical properties of the media with an out-of-system stimulus with tunable intensity.

Preparation of reversible photoresponsive N-hydroxyethyl spiropyran/polyacrylonitrile fiber materials with mechanical stability by electrospinning for regulating wettability and humidity automatically

Novel photoresponsive N-hydroxyethyl spiropyran (SP-OH)/polyacrylonitrile (PAN) fiber materials with reversible changes in wettability and humidity were prepared by electrospinning in this work. SP-OH and PAN were mixed through a physical doping method. The wettability and humidity regulation of the electrospun films can be reversibly manipulated by the simple change of ultraviolet (UV)-visible (UV-Vis) light irradiation due to the photoisomerization mechanism of the spiropyran chromophore. Under UV light irradiation, SP-OH molecules exhibit a colored polar open-ring status, resulting in electrostatic attraction with water. However, under visible light irradiation, they are colorless and nonpolar and lose the attraction effect. Wettability and ambient humidity were regulated by this repeated transformation between polar surface and nonpolar surface. The tensile strength and the reversible change ranges of wettability and humidity under UV-Vis irradiation are all closely related to the doping amount of SP-OH. Electrospinning is a promising method to achieve large-scale production that can put such a material into practical application.

Visible Light-Responsive DASA-Polymer Conjugates

A modular synthesis of Donor-Acceptor Stenhouse Adduct (DASA) polymer conjugates is described. Pentafluorophenyl-ester chemistry is employed to incorporate aromatic amines into acrylate and methacrylate copolymers, which are subsequently coupled with activated furans to generate polymers bearing a range of DASA units in a modular manner. The effect of polymer glass transition temperature on switching kinetics is studied, showing dramatic rate enhancements in going from a glassy to a rubbery matrix. Moreover, tuning the DASA absorption profile allows for selective switching, as demonstrated by ternary photopatterning, with potential applications in rewriteable data storage.

Synthesis of thermo- and photo-responsive polysiloxanes with tunable phase separationviaaza-Michael addition

Two kinds of thermo- and photo-dual-responsive polysiloxanes were synthesized through a facile, effective, and catalyst-free aza-Michael addition.

The effect of high-current pulsed electron beam modification on the surface wetting property of polyamide 6

This study demonstrates that different modification pulse voltages affect the wetting property of the surface of polyamide 6 (PA6) with a certain regularity. Broadly, the hydrophilic property of PA6’s surface increases with increasing pulsed voltage. Based on scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis, this paper discusses the mechanism by which high current pulsed electron beam (HCPEB) etching modification influences the surface wettability of PA6. Within a certain range below 28 kV, this effect is caused by an increase of in surface roughness due to HCPEB bombardment of the surface. Within a certain range above 28 kV, HCPEB changes the surface morphology, resulting in changes to the wetting property. Furthermore, by using various pulsed voltages to modify the PA6 surface, this study investigated the ability of the Wenzel model to explain changes in the water contact angle and wetting property of PA6’s surface.

Fabrication of Chemically Tunable, Hierarchically Branched Polymeric Nanostructures by Multi-branched Anodic Aluminum Oxide Templates

In this paper, a template-assisted replication method is demonstrated for the fabrication of hierarchically branched polymeric nanostructures composed of post-modifiable poly(pentafluorophenyl acrylate). Anodic aluminum oxide templates with various shapes of hierarchically branched pores are fabricated by an asymmetric two-step anodization process. The hierarchical polymeric nanostructures are obtained by infiltration of pentafluorophenyl acrylate with a cross-linker and photoinitiator, followed by polymerization and selective removal of the template. Furthermore, the nanostructures containing reactive pentafluorophenyl ester are modified with spiropyran amine via post-polymerization modification to fabricate ultraviolet-responsive nanostructures. This method can be readily extended to other amines and offers a generalized strategy for controlling functionality and wettability of surfaces.

Preparation of photochromic paper, using fibre-attached spiropyran polymer networks

Spiropyran-based photochromic paper was prepared by covalent immobilisation of functional polymer networks. The sensitivity of the UV-induced colour change was dynamically adjusted by a damping method. Thereby, a colourimetric UV sensor was designed.

Liquid crystalline side-chain triblock copolymers consisting of a nematic central subblock edged by photochromic azobenzene-containing fragments: their synthesis, structure and photooptical behaviour

Synthesis, phase and photooptical properties of new symmetrical fully liquid crystalline triblock copolymers.

Light-responsive polymer surfaces via postpolymerization modification of grafted polymer-brush structures

Light-induced, spatially well-defined, reversible switching of surface properties enables the creation of remote-controlled smart surfaces. We have taken advantage of the unique high-resolution structuring capabilities of extreme ultraviolet (EUV) interference lithography to produce nanostructured photoresponsive polymer brushes. Patterns of poly(glycidyl methacrylate) (PGMA) and poly(methacrylic acid) (PMAA) were grafted from two different 100 μm thick fluoropolymer substrates by means of a radiation-initiated, grafting-from approach based on free-radical polymerization (FRP). Photochromic properties were introduced via novel one- or two-step postpolymerization modifications with spiropyran (SP) derivatives, which allowed us to control the number of photochromic groups on the polymer brushes. Depending on the degree of functionalization and the local chemical environment, the SP moieties can open upon UV-light exposure to form zwitterionic, deeply colored, and fluorescent merocyanines (MCs) and reclose to the colorless SP configuration via thermal or visible light-induced relaxation. Switching kinetics were studied by means of time-resolved fluorescence microscopy and compared with kinetic measurements of the SP moiety in solution. The results indicated the importance, for the intensity of the switching, of the local chemical environment provided by both the polymer brush and added solvents, and showed the predominant influence on the ring-closing kinetics of polar solvents, which stabilize the MC form. To allow further characterization of the polymer-brush arrangements on a macroscopic scale, similar, but unstructured brush systems were grafted from fluoropolymers after large-area activation using EUV radiation or argon plasma. All steps of the postpolymerization modification were characterized in detail using attenuated total reflection infrared (ATR-IR) spectroscopy. Furthermore, a light-induced reversible static-contact-angle switch with a range of up to 15° for PGMA-SP brushes and up to 30° for PMA-SP brushes was demonstrated upon alternating UV- and visible-light irradiation.

Reconfigurable and actuating structures from soft materials

The recent interest in reconfigurable soft materials may lead to the next paradigm in the development of adaptive and actuating materials and structures. Actuating soft materials eventually can be precisely designed to show stimuli-sensing, multi-length scale actuation, tunable transport, programmed shape control and multifunctional orthogonal responses. Herein, we discuss the various advances in the emerging field of reconfigurable soft materials with a focus on the various parameters that can be modulated to control a complex system behavior. In particular, we detail approaches that use either long-range fields (i.e. electrical, magnetic) or changes in local thermodynamic parameters (e.g., solvent quality) in order to elicit a precise dimensional and controlled response. The theoretical underpinnings and practical considerations for different approaches are briefly presented alongside several illustrative examples from the recent studies. In the end, we summarize recent accomplishments, critical issues to consider, and give perspectives on the developments of this exciting research field.

Spiropyran-based dynamic materials

In the past few years, spiropyran has emerged as the molecule-of-choice for the construction of novel dynamic materials. This unique molecular switch undergoes structural isomerisation in response to a variety of orthogonal stimuli, e.g. light, temperature, metal ions, redox potential, and mechanical stress. Incorporation of this switch onto macromolecular supports or inorganic scaffolds allows for the creation of robust dynamic materials. This review discusses the synthesis, switching conditions, and use of dynamic materials in which spiropyran has been attached to the surfaces of polymers, biomacromolecules, inorganic nanoparticles, as well as solid surfaces. The resulting materials show fascinating properties whereby the state of the switch intimately affects a multitude of useful properties of the support. The utility of the spiropyran switch will undoubtedly endow these materials with far-reaching applications in the near future.

Redox active polymer brushes with phenothiazine moieties

We have investigated two different concepts to synthesize redox active polymer brushes using surface initiated atomic transfer radical polymerization (SI-ATRP). This polymerization technique allows the synthesis of well-defined grafted polymer brushes. In the initial step the surface was functionalized with a self-assembling monolayer of the SI-ATRP starter. Then, polymer brushes carrying phenothiazine moieties were grafted from the surface via SI-ATRP. The first concept consists of polymerizing monomers with phenothiazine pendant moieties to directly incorporate the redox functionality as side group in the growing polymer brush. The second concept consists of using grafted activated ester brushes which are functionalized with phenothiazine redox moieties in a successive reaction step. The electrochemical properties of the grafted redox active brushes were examined by cyclic voltammetry. Furthermore, the surface morphology and the chemical composition of the polymer brushes were characterized using scanning force microscopy (SFM), X-ray techniques, and UV/vis spectroscopy. Apart from their redox behavior, the synthesized brushes revealed increased mechanical stability on the nanoscale.