Sweet Janus Particles: Multifunctional Inhibitors of Carbohydrate-Based Bacterial Adhesion.

Escherichia coli and other bacteria use adhesion receptors, such as FimH, to attach to carbohydrates on the cell surface as the first step of colonization and infection. Efficient inhibitors that block these interactions for infection treatment are multivalent carbohydrate-functionalized scaffolds. However, these multivalent systems often lead to the formation of large clusters of bacteria, which may pose problems for clearing bacteria from the infected site. Here, we present Man-containing Janus particles (JPs) decorated on one side with glycomacromolecules to target Man-specific adhesion receptors of E. coli. On the other side, poly(N-isopropylacrylamide) is attached to the particle hemisphere, providing temperature-dependent sterical shielding against binding and cluster formation. While homogeneously functionalized particles cluster with multiple bacteria to form large aggregates, glycofunctionalized JPs are able to form aggregates only with individual bacteria. The formation of large aggregates from the JP-decorated single bacteria can still be induced in a second step by increasing the temperature and making use of the collapse of the PNIPAM hemisphere. This is the first time that carbohydrate-functionalized JPs have been derived and used as inhibitors of bacterial adhesion. Furthermore, the developed JPs offer well-controlled single bacterial inhibition in combination with cluster formation upon an external stimulus, which is not achievable with conventional carbohydrate-functionalized particles.

Donor:Acceptor Janus Nanoparticle-Based Films as Photoactive Layers: Control of Assembly and Impact on Performance of Devices.

Water-processable organic semiconductor nanoparticles (NPs) are considered promising materials for the next-generation of optoelectronic applications due to their controlled size, internal structure, and environmentally friendly processing. Reasonably, the controllable assembly of donor:acceptor (D:A) NPs on large areas, quality, and packing density of deposited films, as well as layer morphology, will influence the effectiveness of charge transfer at an interface and the final performance of designed optoelectronic devices.This work represents an easy and effective approach for designing self-assembled monolayers of D:A NPs. In this self-assembly procedure, the NP arrays are prepared on a large scale (2 × 2 cm2 ) at the air/water interface with controlled packing density and morphology. Due to the unique structure of individual D:A Janus particles and their assembled arrays, the Janus nanoparticle (JNP)-based device exhibits an 80% improvement of electron mobility and more balanced charge extraction compared to the conventional core-shell NP-based device. An outstanding performance of polymer solar cells with over 5% efficiency is achieved after post-annealing treatment of assembled arrays, representing one of the best results for NP-based organic photovoltaics. Ultimately, this work provides a new protocol for processing water-processable organic semiconductor colloids and future optoelectronic fabrication.

Impact of surface charge on the motion of light-activated Janus micromotors.

Control over micromotors' motion is of high relevance for lab-on-a-chip and biomedical engineering, wherein such particles encounter complex microenvironments. Here, we introduce an efficient way to influence Janus micromotors' direction of motion and speed by modifying their surface properties and those of their immediate surroundings. We fabricated light-responsive Janus micromotors with positive and negative surface charge, both driven by ionic self-diffusiophoresis. These were used to observe direction-of-motion reversal in proximity to glass substrates for which we varied the surface charge. Quantitative analysis allowed us to extract the dependence of the particle velocity on the surface charge density of the substrate. This constitutes the first quantitative demonstration of the substrate's surface charge on the motility of the light-activated diffusiophoretic motors in water. We provide qualitative understanding of these observations in terms of osmotic flow along the substrate generated through the ions released by the propulsion mechanism. Our results constitute a crucial step in moving toward practical application of self-phoretic artificial micromotors.

Thermo-Responsive Polymer Brushes with Side Graft Chains: Relationship Between Molecular Architecture and Underwater Adherence.

During the last few decades, wet adhesives have been developed for applications in various fields. Nonetheless, key questions such as the most suitable polymer architecture as well as the most suitable chemical composition remain open. In this article, we investigate the underwater adhesion properties of novel responsive polymer brushes with side graft chain architecture prepared using "grafting through" approach on flat surfaces. The incorporation in the backbone of thermo-responsive poly(N-isopropylacrylamide) (PNIPAm) allowed us to obtain LCST behavior in the final layers. PNIPAm is co-polymerized with poly(methyl ethylene phosphate) (PMEP), a poloyphosphoester. The final materials are characterized studying the surface-grafted polymer as well as the polymer from the bulk solution, and pure PNIPAm brush is used as reference. PNIPAm-g-PMEP copolymers retain the responsive behavior of PNIPAm: when T > LCST, a clear switching of properties is observed. More specifically, all layers above the critical temperature show collapse of the chains, increased hydrophobicity and variation of the surface charge even if no ionizable groups are present. Secondly, effect of adhesion parameters such as debonding rate and contact time is studied. Thirdly, the reversibility of the adhesive properties is confirmed by performing adhesion cycles. Finally, the adhesive properties of the layers are studied below and above the LCST against hydrophilic and hydrophobic substrates.

Tuning the Interactions in Multiresponsive Complex Coacervate-Based Underwater Adhesives.

In this work, we report the systematic investigation of a multiresponsive complex coacervate-based underwater adhesive, obtained by combining polyelectrolyte domains and thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) units. This material exhibits a transition from liquid to solid but, differently from most reactive glues, is completely held together by non-covalent interactions, i.e., electrostatic and hydrophobic. Because the solidification results in a kinetically trapped morphology, the final mechanical properties strongly depend on the preparation conditions and on the surrounding environment. A systematic study is performed to assess the effect of ionic strength and of PNIPAM content on the thermal, rheological and adhesive properties. This study enables the optimization of polymer composition and environmental conditions for this underwater adhesive system. The best performance with a work of adhesion of 6.5 J/m2 was found for the complex coacervates prepared at high ionic strength (0.75 M NaCl) and at an optimal PNIPAM content around 30% mol/mol. The high ionic strength enables injectability, while the hydrated PNIPAM domains provide additional dissipation, without softening the material so much that it becomes too weak to resist detaching stress.

Detachment of Rough Colloids from Liquid-Liquid Interfaces.

Particle surface roughness and chemistry play a pivotal role in the design of new particle-based materials. Although the adsorption of rough particles has been studied in the literature, desorption of such particles remains poorly understood. In this work, we specifically focus on the detachment of rough and chemically modified raspberry-like microparticles from water/oil interfaces using colloidal-probe atomic force microscopy. We observe different contact-line dynamics occurring upon particle detachment (pinning vs sliding), depending on both the particle roughness and surface modification. In general, surface roughness leads to a reduction of the desorption force of hydrophobic particles into the oil and provides a multitude of pinning points that can be accessed by applying different loads. Our results hence suggest future strategies for stabilization and destabilization of Pickering emulsions and foams.

Controlled and tunable design of polymer interface for immobilization of enzymes: does curvature matter?

Control and tuning of surface properties is indispensable for the programmed and rational design of materials. Particularly, polymeric brush-modified colloids can be used as carrier materials for enzyme immobilization. Although it is of prime importance to control the brush architecture, there is still a lack of systematic investigations concerning the impact of grafting density on the properties of the designed interface, as well as on the immobilization of biomolecules. In this work, we investigate the surface properties of polymer brushes with different grafting densities prepared using a "grafting from" approach on flat and on colloidal particle substrates by varying the density of initiator groups. In this way, we control and tune interfacial properties of the carrier material such as swelling, charge, adhesion as well as adsorption of laccase from Trametes versicolor on the grafted polyelectrolyte layer. We show that there is no direct transferability of the results received from planar to curved substrates regarding the swelling behavior in dependence on the grafting density. The maximum of swelling degree of PDMAEMA layers is achieved at 0.34 nm-2 and at 0.1 nm-2 grafting density for planar and curved particle substrates, respectively. The adhesion properties of the polymeric layer on both substrates are also strongly influenced by the grafting density, i.e. a decrease of the grafting density causes a transition from the adhesive to non-adhesive state. As proven by the cryo-TEM and AFM force distance measurements, an immobilization of laccase from Trametes versicolor causes a decrease of the polymer swelling and therefore leads to the changes in the surface morphology, charge and adhesion performance of final polymer-enzyme layer. Moreover, the higher effectiveness and activity of laccase were observed for the intermediate grafting densities which seem to be preferable over the maximum brush densities.

Programmed assembly of oppositely charged homogeneously decorated and Janus particles.

The exploitation of colloidal building blocks with morphological and functional anisotropy facilitates the generation of complex structures with unique properties, which are not exhibited by isotropic particle assemblies. Herein, we demonstrate an easy and scalable bottom-up approach for the programmed assembly of hairy oppositely charged homogeneously decorated and Janus particles based on electrostatic interactions mediated by polyelectrolytes grafted onto their surface. Two different assembly routes are proposed depending on the target structures: raspberry-like/half-raspberry-like or dumbbell-like micro-clusters. Ultimately, stable symmetric and asymmetric micro-structures could be obtained in a well-controlled manner for the homogeneous-homogeneous and homogeneous-Janus particle assemblies, respectively. The spatially separated functionalities of the asymmetric Janus particle-based micro-clusters allow their further assembly into complex hierarchical constructs, which may potentially lead to the design of materials with tailored plasmonics and optical properties.

Postsynthetic Inner-Surface Functionalization of the Highly Stable Zirconium-Based Metal-Organic Framework DUT-67.

A postsynthetic functionalization approach was used to tailor the hydrophobicity of DUT-67, a metal-organic framework (MOF) consisting of 8-connected Zr6O6(OH)2 clusters and 2,5-thiophenedicarboxylate as the ligand, using postsynthetic exchange of the modulator by fluorinated monocarboxylates. Water adsorption isotherms demonstrated that, by the incorporation of such hydrophobic molecules, the hydrophobicity of the inner surface of the network can be tuned. Furthermore, tolerance of the material toward the removal of adsorbed water can be significantly enhanced compared to the parent DUT-67 MOF.

New insight into icing and de-icing properties of hydrophobic and hydrophilic structured surfaces based on core-shell particles.

Icing is an important problem, which often leads to emergency situations in northern countries. The reduction of icing requires a detailed understanding of this process. In this work, we report on a systematic investigation of the effects of geometry and chemical properties of surfaces on the formation of an ice layer, its properties, and thawing. We compare in detail icing and ice thawing on flat and rough hydrophilic and hydrophobic surfaces. We also show advantages and disadvantages of the surfaces of each kind. We demonstrate that water condenses in a liquid form, leading to the formation of a thin continuous water layer on a hydrophilic surface. Meanwhile, separated rounded water droplets are formed on hydrophobic surfaces. As a result of slower heat exchange, the freezing of rounded water droplets on a hydrophobic surface occurs later than the freezing of the continuous water layer on a hydrophilic one. Moreover, growth of ice on hydrophobic surfaces is slower than on the hydrophilic ones, because ice grows due to the condensation of water vapor on already formed ice crystals, and not due to the condensation on the polymer surface. Rough hydrophobic surfaces also demonstrate a very low ice adhesion value, which is because of the reduced contact area with ice. The main disadvantage of hydrophobic and superhydrophobic surfaces is the pinning of water droplets on them after thawing. Flat hydrophilic poly(ethylene glycol)-modified surfaces also exhibit very low ice adhesion, which is due to the very low freezing point of the water-poly(ethylene glycol) mixtures. Water easily leaves from flat hydrophilic poly(ethylene glycol)-modified surfaces, and they quickly become dry. However, the ice growth rate on poly(ethylene glycol)-modified hydrophilic surfaces is the highest. These results indicate that neither purely (super)hydrophobic polymeric surfaces, nor "antifreeze" hydrophilic ones provide an ideal solution to the problem of icing.

Surfaces with self-repairable ultrahydrophobicity based on self-organizing freely floating colloidal particles.

We report an approach for the design of materials with self-repairable ultrahydrophobic properties. The materials are based on highly fluorinated crystalline fusible wax with incorporated colloidal particles. Due to the highly pronounced tendency of the wax to crystallize, the formation of blends with rough fractal surfaces was observed. In order to prove their self-repairing ability, we mechanically damaged them by scratching, which removed most of the particles from the surface. Melting of the damaged blend resulted in reorganization of the particles at the wax-air interface, restoring the initial structure and thus the ultrahydrophobic behavior.

Tuning the adhesion of silica microparticles to a poly(2-vinyl pyridine) brush: an AFM force measurement study.

AFM force measurements have been performed to study the influence of the pH value and salt concentration on the interactions between poly(2-vinyl pyridine) brushes and microsized silica spheres, focusing on attractive and adhesion forces. It was found that the interaction was composed of a repulsive component reflecting the conformation of the brush and an additional attractive force. It can therefore be switched reversibly between purely repulsive at pH 2.5 to strong and medium adhesion by changing the pH value to pH 4 and 6, respectively. Addition of KCl showed different effects: at pH 2.5 high salt concentrations induced an attractive force; at pH 4 the interaction changed from strong attraction in the osmotic brush regime to repulsion and weaker adhesion in the salted brush regime; at pH 6 increase of the KCl concentration weakened the attractive force. These effects could partly be explained by the theory of polyelectrolyte brushes; under some conditions the mechanism of the attractive force is still unclear.

Self-healing superhydrophobic materials.

Development of materials with self-healing properties is highly important task. This review covers recent development in the design of materials with durable, easy repairable and self-healing superhydrophobic properties.

Fibrous Scaffolds for Muscle Tissue Engineering Based on Touch-Spun Poly(Ester-Urethane) Elastomer.

Development of fiber-spinning technologies and materials with proper mechanical properties is highly important for the manufacturing of aligned fibrous scaffolds mimicking structure of the muscle tissues. Here, the authors report touch spinning of a thermoplastic poly(1,4-butylene adipate)-based polyurethane elastomer, obtained via solvent-free polymerization. This polymer possesses a combination of important advantages such as 1) low elastic modulus in the range of a few MPa, 2) good recovery ratio and 3) resilience, 4) processability, 5) nontoxicity, 6) biocompatibility, and 7) biodegradability that makes it suitable for fabrication of structures mimicking extracellular matrix of muscle tissue. Touch spinning allows fast and precise deposition of highly aligned micro- and nano-fibers without use of high voltage. C2C12 myoblasts readily align along soft polymer fibers and demonstrate high viability as well as proliferation that make proposed combination of polymer and fabrication method highly suitable for engineering skeletal muscles.

4D Biofabrication Using a Combination of 3D Printing and Melt-Electrowriting of Shape-Morphing Polymers.

We report the fabrication of scroll-like scaffolds with anisotropic topography using 4D printing based on a combination of 3D extrusion printing of methacrylated alginate, melt-electrowriting of polycaprolactone fibers, and shape-morphing of the fabricated object. A combination of 3D extrusion printing and melt-electrowriting allows programmed deposition of different materials and fabrication of structures with high resolution. Shape-morphing allows the transformation of a patterned surface of a printed structure in a pattern on inner surface of a folded object that is used to align cells. We demonstrate that the concentration of calcium ions, the environment media, and the geometrical shape of the scaffold influences shape-morphing that allows it to be efficiently programmed. Myoblasts cultured inside a scrolled bilayer scaffold demonstrate excellent viability and proliferation. Moreover, the patterned surface generated by PCL fibers allow a very high degree of orientation of cells, which cannot be achieved on the alginate layer without fibers.

Shape-Morphing Fibrous Hydrogel/Elastomer Bilayers Fabricated by a Combination of 3D Printing and Melt Electrowriting for Muscle Tissue Regeneration.

This paper reports an approach for the fabrication of shape-changing bilayered scaffolds, which allow the growth of aligned skeletal muscle cells, using a combination of 3D printing of hyaluronic acid hydrogel, melt electrowriting of thermoplastic polycaprolactone-polyurethane elastomer, and shape transformation. The combination of the selected materials and fabrication methods allows a number of important advantages such as biocompatibility, biodegradability, and suitable mechanical properties (elasticity and softness of the fibers) similar to those of important components of extracellular matrix (ECM), which allow proper cell alignment and shape transformation. Myoblasts demonstrate excellent viability on the surface of the shape-changing bilayer, where they occupy space between fibers and align along them, allowing efficient cell patterning inside folded structures. The bilayer scaffold is able to undergo a controlled shape transformation and form multilayer scroll-like structures with cells encapsulated inside. Overall, the importance of this approach is the fabrication of tubular constructs with a patterned interior that can support the proliferation and alignment of muscle cells for muscle tissue regeneration.

Interaction forces between microsized silica particles and weak polyelectrolyte brushes at varying pH and salt concentration.

The AFM colloidal probe technique was used to measure the interaction between microsized silica spheres and annealed polyelectrolyte brushes made of poly(acrylic acid) (PAA) and poly(2-vinyl pyridine) (P2VP) in KCl solutions of various pH values and salt concentrations. The interaction energy showed a distance dependence that was affected strongly by the swelling and the electric properties of the brushes. Between PAA brushes and silica particles, a repulsive interaction has been observed for all pH values and salt concentrations reflecting the swelling of the brush with varying pH value and the transition from osmotic to salted brush regime with increasing KCl concentration. Force measurements between P2VP brushes and silica particles revealed a much more complex behavior: a steric repulsion by the swollen brush at low pH values, a complex interplay of attractive and repulsive forces at intermediate pH values and a short-ranged attraction between the collapsed brush and the silica particle at basic pH values and high salt concentrations. The results are interpreted in comparison with the Alexander de Gennes model and zeta potential and ellipsometric measurements.

Protein-resistant polymer coatings based on surface-adsorbed poly(aminoethyl methacrylate)/poly(ethylene glycol) copolymers.

We report on the protein-resistant properties of glass substrates coated with novel copolymers of 2-aminoethyl methacrylate hydrochloride and poly(ethylene glycol) methyl ether methacrylate (AEM-PEG). In comparison to currently available protein-blocking polymer systems, such as poly-l-lysine-poly(ethylene glycol), silane-based poly(ethylene glycol), and poly(ethylene glycol) brushes prepared by surface-initiated polymerization, the proposed AEM-PEG offers the combined advantages of low cost, simplicity of use, and applicability in aqueous solutions. We demonstrate the capability of AEM-PEG to block the surface binding of globular proteins (tubulin), their assemblies (microtubules), and functional motor proteins (kinesin-1). Moreover, we demonstrate the applicability of AEM-PEG for surface patterning of proteins in microfluidic devices.

Microparticle-supported conjugated polyelectrolyte brushes prepared by surface-initiated kumada catalyst transfer polycondensation for sensor applications.

A 'grafting-from' approach to synthesize microparticle-supported conjugated polyelectrolyte brushes is presented. Poly(3-bromohexylthiophene) is selectively grown from monodisperse organosilica microparticles by surface-initiated Kumada catalyst-transfer polycondensation (SI-KCTP) and then ionizable amino groups are introduced by a two-step polymer analogous transformation. Optical properties of the resulting microparticle-supported conjugated polyelectrolyte brushes were found to be dependent on the surrounding chemical environment and thus the particles are promising materials for sensor applications.