Deterministic Reshaping of Breath Figure Arrays by Directional Photomanipulation

High-throughput fabrication of antimicrobial phage microgels and example applications in food decontamination

Engineered by nature, biological entities are exceptional building blocks for biomaterials. These entities can impart enhanced functionalities on the final material that are otherwise unattainable. However, preserving the bioactive functionalities of these building blocks during the material fabrication process remains a challenge. We describe a high-throughput protocol for the bottom-up self-assembly of highly concentrated phages into microgels while preserving and amplifying their inherent antimicrobial activity and biofunctionality. Each microgel is comprised of half a million cross-linked phages as the sole structural component, self-organized in aligned bundles. We discuss common pitfalls in the preparation procedure and describe optimization processes to ensure the preservation of the biofunctionality of the phage building blocks. This protocol enables the production of an antimicrobial spray containing the manufactured phage microgels, loaded with potent virulent phages that effectively reduced high loads of multidrug-resistant Escherichia coli O157:H7 on red meat and fresh produce. Compared with other microgel preparation methods, our protocol is particularly well suited to biological materials because it is free of organic solvents and heat. Bench-scale preparation of base materials, namely microporous films (the template for casting microgels) and pure concentrated phage suspension, requires 3.5 h and 5 d, respectively. A single production run, that yields over 1,750,000 microgels, ranges from 2 h to 2 d depending on the rate of cross-linking chemistry. We expect that this platform will address bottlenecks associated with shelf-stability, preservation and delivery of phage for antimicrobial applications, expanding the use of phage for prevention and control of bacterial infections and contaminants.

Polarization-driven reversible actuation in a photo-responsive polymer composite

Light-responsive polymers and especially amorphous azopolymers with intrinsic anisotropic and polarization-dependent deformation photo-response hold great promises for remotely controlled, tunable devices. However, dynamic control requires reversibility characteristics far beyond what is currently obtainable via plastic deformation of such polymers. Here, we embed azopolymer microparticles in a rubbery elastic matrix at high density. In the resulting composite, cumulative deformations are replaced by reversible shape switching - with two reversible degrees of freedom defined uniquely by the writing beam polarization. We quantify the locally induced strains, including small creeping losses, directly by means of a deformation tracking algorithm acting on microscope images of planar substrates. Further, we introduce free-standing 3D actuators able to smoothly undergo multiple configurational changes, including twisting, roll-in, grabbing-like actuation, and even continuous, pivot-less shape rotation, all dictated by a single wavelength laser beam with controlled polarization.

Wavelength-Dependent Shaping of Azopolymer Micropillars for Three-Dimensional Structure Control

Surfaces endowed with three-dimensional (3D) mesostructures, showing features in the nanometer to micrometer range, are critical for applications in several fields of science and technology. Finding a fabrication method that is simultaneously inexpensive, simple, fast, versatile, highly scalable, and capable of producing complex 3D shapes is still a challenge. Herein, we characterize the photoreconfiguration of a micropillar array of an azobenzene-containing polymer at different light wavelengths and demonstrate the tailoring of the surface geometry and its related functionality only using light. By changing the irradiated light wavelength and its polarization, we demonstrate the fabrication of various complex isotropic and anisotropic 3D mesostructures from a single original pristine geometry. Quantitative morphological analyses revealed an interplay between the decay rate of absorbed light intensity, micropillar volume preservation, and the cohesive forces between the azopolymer chains as the origin of distinctive wavelength-dependent 3D structural remorphing. Finally, we show the potentialities of this method in surface engineering by photoreshaping a single original micropillar surface into two sets of different mesostructured surfaces exhibiting tunable hydrophobicity in a wide water contact angle range. Our study opens up a new paradigm for fabricating functional 3D mesostructures in a simple, low-cost, fast, and scalable manner.

Self-assembling nanofibrous bacteriophage microgels as sprayable antimicrobials targeting multidrug-resistant bacteria

Nanofilamentous bacteriophages (bacterial viruses) are biofunctional, self-propagating, and monodisperse natural building blocks for virus-built materials. Minifying phage-built materials to microscale offers the promise of expanding the range function for these biomaterials to sprays and colloidal bioassays/biosensors. Here, we crosslink half a million self-organized phages as the sole structural component to construct each soft microgel. Through an in-house developed, biologics-friendly, high-throughput template method, over 35,000 phage-built microgels are produced from every square centimetre of a peelable microporous film template, constituting a 13-billion phage community. The phage-exclusive microgels exhibit a self-organized, highly-aligned nanofibrous texture and tunable auto-fluorescence. Further preservation of antimicrobial activity was achieved by making hybrid protein-phage microgels. When loaded with potent virulent phages, these microgels effectively reduce heavy loads of multidrug-resistant Escherichia coli O157:H7 on food products, leading to up to 6 logs reduction in 9 hours and rendering food contaminant free.

Fabrication of Adsorption-Type Hierarchical Functional Films by Using a Facile Swollen Based Breath Figure Method

The morphology transition from primary to hierarchical adsorption-type microporous domains of amphiphilic block copolymer (BCP) honeycomb-structured films is demonstrated by a facile swollen based breath figure (BF) method. The characteristic parameters of poly(4-vinylpyridine)-block-polystyrene (P4VP-b-PS) hierarchical micro- and submicro-porous films can be controlled by changing the length of segments or subsequent swelling conditions. A plausible mechanism is demonstrated in this research. A typical amphiphilic BCP with very low volume content of hydrophilic blocks (f_P4VP ≤ 0.050) can efficiently stabilize water droplets and inherently assist in the formation of morphology transition. This BCP film can be used for Cr(VI) removal from wastewater, which additionally has enormous potential application in the field of novel optical devices, soft lithography, size-selective separation, etc. This article is protected by copyright. All rights reserved.

Temporally Arrested Breath Figure

Since its original conception as a tool for manufacturing porous materials, the breath figure method (BF) and its variations have been frequently used for the fabrication of numerous micro- and nanopatterned functional surfaces. In classical BF, reliable design of the final pattern has been hindered by the dual role of solvent evaporation to initiate/control the dropwise condensation and induce polymerization, alongside the complex effects of local humidity and temperature influence. Herein, we provide a deterministic method for reliable control of BF pore diameters over a wide range of length scales and environmental conditions. To this end, we employ an adapted methodology that decouples cooling from polymerization by using a combination of initiative cooling and quasi-instantaneous UV curing to deliberately arrest the desired BF patterns in time. Through in situ real-time optical microscopy analysis of the condensation kinetics, we demonstrate that an analytically predictable self-similar regime is the predominant arrangement from early to late times O(10-100 s), when high-density condensation nucleation is initially achieved on the polymer films. In this regime, the temporal growth of condensation droplets follows a unified power law of D ∝ t. Identification and quantitative characterization of the scale-invariant self-similar BF regime allow fabrication of programmed pore size, ranging from hundreds of nanometers to tens of micrometers, at high surface coverage of around 40%. Finally, we show that temporal arresting of BF patterns can be further extended for selective surface patterning and/or pore size modulation by spatially masking the UV curing illumination source. Our findings bridge the gap between fundamental knowledge of dropwise condensation and applied breath figure patterning techniques, thus enabling mechanistic design and fabrication of porous materials and interfaces.

Reversible Photo-Induced Reshaping of Imprinted Microstructures Using a Low Molecular Azo Dye

A blend of low molecular azo glass (AZOPD) and polystyrene (PS) were used for the systematic investigation of photo-induced stretching and recovery of nanoimprinted structures. For this purpose, light and heat was used as recovery stimuli. The AZOPD/PS microstructures, fabricated with thermal nanoimprint lithography (tNIL), comprises three different shapes (circles, crosses and squares) and various concentrations of AZOPD fractions. The results show a concentration-dependent reshaping. Particularly the sample with 43 w-% of the AZOPD fraction have shown the best controllable recovery for the used parameters. A possible explanation for shape recovery might be the stabilizing effect of the PS-matrix.

Photo-switchable smart superhydrophobic surface with controllable superwettability

An azobenzene-based smart superhydrophobic surface undergoes reversible transformations among multiple bioinspired superwetting states through photo-manipulation, demonstrating promising potential on a rewritable platform for droplet transportation.

Dynamic azopolymeric interfaces for photoactive cell instruction

The ability to affect a wide range of biophysical properties through the use of light has led to the development of dynamic cell instructive materials. Using photoresponsive materials such as azopolymers, smart systems that use external, minimally damaging, light irradiation can be used to trigger specific surface morpho-physical properties in the presence of living cells. The interaction of light with an azopolymer film induces a mass migration phenomenon, allowing a variety of topographic patterns to be embossed on the polymeric film. Photoisomerization induces conformational changes at the molecular and macroscopic scale, resulting in light-induced variations of substrate morphological, physical, and mechanical properties. In this review, we discuss the photoactuation of azopolymeric interfaces to provide guidelines for the engineering and design of azopolymer films. Laser micropatterning for the modulation of azopolymer surfaces is examined as a way to diversify the capabilities of these polymers in cellular systems. Mass migration effects induced by azopolymer switching provides a foundation for performing a broad range of cellular manipulation techniques. Applications of azopolymers are explored in the context of dynamic culture systems, gaining insight into the complex processes involved in dynamic cell-material interactions. The review highlights azopolymers as a candidate for various applications in cellular control, including cell alignment, migration, gene expression, and others. Recent advances have underlined the importance of these systems in applications regarding three-dimensional cell culture and stem cell morphology. Azopolymers can be used not only to manipulate cells but also to probe for mechanistic studies of cellular crosstalk in response to chemical and mechanical stimuli.

Dynamic Manipulation of Cell Membrane Curvature by Light-Driven Reshaping of Azopolymer

Local curvatures on the cell membrane serve as signaling hubs that promote curvature-dependent protein interactions and modulate a variety of cellular processes including endocytosis, exocytosis, and the actin cytoskeleton. However, precisely controlling the location and the degree of membrane curvature in live cells has not been possible until recently, where studies show that nanofabricated vertical structures on a substrate can imprint their shapes on the cell membrane to induce well-defined curvatures in adherent cells. Nevertheless, the intrinsic static nature of these engineered nanostructures prevents dynamic modulation of membrane curvatures. In this work, we engineer light-responsive polymer structures whose shape can be dynamically modulated by light and thus change the induced-membrane curvatures on-demand. Specifically, we fabricate three-dimensional azobenzene-based polymer structures that change from a vertical pillar to an elongated vertical bar shape upon green light illumination. We observe that U2OS cells cultured on azopolymer nanostructures rapidly respond to the topographical change of the substrate underneath. The dynamically induced high membrane curvatures at bar ends promote local accumulation of actin fibers and actin nucleator Arp2/3 complex. The ability to dynamically manipulate the membrane curvature and analyze protein response in real-time provides a new way to study curvature-dependent processes in live cells.

Design of Collective Motions from Synthetic Molecular Switches, Rotors, and Motors

Precise control over molecular movement is of fundamental and practical importance in physics, biology, and chemistry. At nanoscale, the peculiar functioning principles and the synthesis of individual molecular actuators and machines has been the subject of intense investigations and debates over the past 60 years. In this review, we focus on the design of collective motions that are achieved by integrating, in space and time, several or many of these individual mechanical units together. In particular, we provide an in-depth look at the intermolecular couplings used to physically connect a number of artificial mechanically active molecular units such as photochromic molecular switches, nanomachines based on mechanical bonds, molecular rotors, and light-powered rotary motors. We highlight the various functioning principles that can lead to their collective motion at various length scales. We also emphasize how their synchronized, or desynchronized, mechanical behavior can lead to emerging functional properties and to their implementation into new active devices and materials.

Direct quantitative imaging of the writing stage in a photosensitive azopolymer by digital holography

In this paper, we demonstrated that the gradual formation of a surface relief grating (SRG) in azopolymer thin films under continuous light exposure could be directly observed in situ and in real-time, allowing full-field characterization with high spatial resolution. We reported here for the first time, to the best of our knowledge, that digital holography (DH) can be adopted for investigating and monitoring an inscribed holographic surface relief grating (SRG) of azopolymers by two-beam laser interference lithography over a wide area. The writing process could be assessed through quantitative phase imaging (QPI). The reported results show that the proposed method is a truly valuable diagnostic tool that can be useful for investigating the spatial distribution of the writing process, which can eventually contribute to shedding light on the still unclear origin and related mechanism of SRG formation in azopolymers.

Controlling the pore size in conjugated polymer films via crystallization-driven phase separation

A wide range of possible applications in sensors and optoelectronic devices have focused considerable attention on porous membranes made of semi-conducting polymers. In this study, porous films of poly(3-hexylthiophene) (P3HT) were conveniently constructed through spin-coating of solutions of a blend of P3HT and polyethylene glycol (PEG). Pores were formed by phase separation driven simultaneously by incompatibility and crystallization. The influence of the polymer concentration (c), molecular weight (Mn) and spin-coating temperature (Tsp) on the pore size and structure was investigated. With increasing c from 0.5 to 5.0 wt%, the pore diameter (d) varied from ≈1.3 μm to ≈38 μm. Similarly, we observed a substantial increase of d with increasing Mn of PEG, while changing Mn of P3HT did not affect d. Micron- and nano-scale pores coexisted in porous P3HT films. While incompatibility of P3HT and PEG caused the formation of nano-pores, micron-scale pores resulted from crystallization in the PEG-rich domains by forcing PEG molecules to diffuse from the surrounding PEG-P3HT blend region to the crystal growth front.

Photo-Reconfigurable Azopolymer Etch Mask: Photofluidization-Driven Reconfiguration and Edge Rectangularization

Directional photofluidization of azobenzene materials has provided unprecedented opportunities for the structural reconfiguration of circular holes, line gaps, ellipsoidal holes, and nanofunnel-shaped micro/nanoarchitectures. However, all the reconfigured structures have a parabolic or round wall due to the tendency of the photofluidized azobenezene materials to minimize the surface area, which limits their use as a reconfigurable etch-mask for the lithography process. In this work, a simple method is presented that can change the round walls of azopolymer architectures into rectangular walls, which is named rectangularization. By irradiating far-field light on reconfigured azopolymer in a conformal contact with a flat polydimethylsiloxane (PDMS) film, the round wall transforms to a rectangular one because the azopolymer adheres along the PDMS surface while being photofluidized. As a result, the rectangularization process creates a variety of structural features and sizes ranging from a few micrometers to 150 nm having a rectangular wall. By exploiting the rectangularization process, the concept of a photo-reconfigurable etch mask is achieved, which transfers the mask patterns to a silicon pattern with a high structural fidelity and imparts a considerable flexibility to the lithography process.

Rationally designed hyperbranched azopolymer with temperature, photo and pH responsive behavior

A novel hyperbranched azopolymer, HPAzoAMAM-star-EG₃, was synthesized and it could self-assemble into uniform large compound micelles with multi-stimuli responsive behavior.

Fabrication of biocompatible and efficient antimicrobial porous polymer surfaces by the Breath Figures approach

We designed and fabricated highly efficient and selective antibacterial substrates, i.e. surface non-cytotoxic against mammalian cells but exhibiting strong antibacterial activity. For that purpose, microporous substrates (pore sizes in the range of 3-5 μm) were fabricated using the Breath Figures approach (BFs). These substrates have additionally a defined chemical composition in the pore cavity (herein either a poly(acrylic acid) or the antimicrobial peptide Nisin) while the composition of the rest of the surface is identical to the polymer matrix. As a result, considering the differences in size of bacteria (1-4 μm) in comparison to mammalian cells (above 10 µm) the bacteria were able to enter in contact with the inner part of the pores where the antimicrobial functionality has been placed. On the opposite, mammalian cells remain in contact with the top surface thus preventing cytotoxic effects and enhancing the biocompatibility of the substrates. The resulting antimicrobial surfaces were exposed to Staphylococcus aureus as a model bacteria and murine endothelial C166-GFP cells. Superior antibacterial performance while maintaining an excellent biocompatibility was obtained by those surfaces prepared using PAA while no evidence of significant antibacterial activity was observed at those surfaces prepared using Nisin.

Poly (ionic liquid)-Based Breath Figure Films: A New Kind of Honeycomb Porous Films with Great Extendable Capability

In this work, we reported a new method for the convenient fabrication of various functional porous films, which cannot be directly generated using breath figures (BFs). A series of polystyrene-b-poly (ionic liquid) (PS-b-PIL) block copolymers were employed for BFs process for the first time. It was found that PS-b-PIL could form well-defined BFs porous structure. Remarkably, the described PS-b-PIL copolymers are prone to form hierarchical structure, and the formed pore structure is strongly dependent on the used experimental parameters. Importantly, we found that the anion exchange could provide as an effective means, by which the porous films could be further and facilely converted into other functional films. As a demonstration, in our case, porous films with different surface (hydrophilic and hydrophobic) property, porous polydopamine films decorated with Au nanoparticles or glutathione and porous SiO2 films were prepared by using different counteranions as well as further conversion. Due to the unlimited combination of cation and anion in ionic liquid moiety, all the results indicate that the BFs films generated by using PS-PIL could serve as a platform to access various functional porous films by a simple counteranion exchange, showing a great extendable capability.

Light-Driven Wettability Tailoring of Azopolymer Surfaces with Reconfigured Three-Dimensional Posts

The directional light-induced mass migration phenomenon arising in the photoresponsive azobenzene-containing materials has become an increasingly used approach for the fabrication of controlled tridimensional superficial textures. In the present work we demonstrate the tailoring of the superficial wettability of an azopolymer by means of the light-driven reconfiguration of an array of imprinted micropillars. Few simple illumination parameters are controlled to induce nontrivial wetting effects. Wetting anisotropy with controlled directionality, unidirectional spreading, and even polarization-intensity driven two-dimensional paths for wetting anisotropy are obtained starting from a single pristine pillar geometry. The obtained results prove that the versatility of the light-reconfiguration process, together with the possibility of reversible reshaping at reduced costs, represents a valid approach for both applications and fundamental studies in the field of geometry-based wettability of solid surfaces.

Photomanipulated Architecture and Patterning of Azopolymer Array

Here reported is the approach to prepare the tunable 3D architecture and patterning through photoinduced orientation of azopolymer. The hemispherical PAzoMA array can be transformed into spindlelike, flat ellipsoidlike, thick spindlelike, near-hexagon, near-quadrangle, and near-rhombus arrays while being exposed to linearly polarized light (LPL). The size and alignment of the arrays can be precisely controlled by manipulating the irradiation time. Furthermore, complex 3D architectures of the PAzoMA array are readily fabricated through secondary irradiation along different direction. This technique is promising for functionalized surfaces and photonic devices.

Self-assembly and multi-stimuli responsive behavior of PAA-b-PAzoMA-b-PNIPAM triblock copolymers

A PAA-b-PAzoMA-b-PNIPAM triblock copolymer containing pH, photo and temperature sensitive groups could self-assemble into spherical micelles or vesicles with multi-stimuli responsiveness.