Three-dimensionally ordered array of air bubbles in a polymer film

Biomimetic Hierarchies for Universal Surface Enhancement and Applications in Water Treatment

Hierarchical superstructures, ubiquitously found in nature, offer enhanced efficiency in both substance reaction and mass transport owing to their unique multiscale features. Inspired by these natural systems, this research reports a general and scalable electrochemical scheme for creating highly branched, multilevel porous superstructures on various electrically conductive substrates. These structures exhibit cascading features from centimeters, submillimeters, micrometers, down to sub-100 nm, significantly increasing the surface area of substrates, such as foams, foils, and carbon cloth by 2 orders of magnitude─among the highest reported enhancements. This versatile and low-cost method, applicable to a range of electrically conductive substrates, enables innovative flow-assisted water purification with enhanced energy efficiency. The performance, successfully removing 99% of mercury within 0.5 h at 540 rpm and meeting the U.S. Environmental Protection Agency (EPA) safety standards for drinking water, further validates the advantages of these unique structures. Overall, the reported general, economical, and versatile scheme could broadly impact energy and environmental remediation.

Durotaxis and Antidurotaxis Droplet Motion onto Gradient Gel-Substrates

The self-sustained motion of fluids on gradient substrates is a spectacular phenomenon, which can be employed and controlled in applications by carefully engineering the substrate properties. Here, we report on a design of a gel substrate with stiffness gradient, which can cause the spontaneous motion of a droplet along (durotaxis) or to the opposite (antidurotaxis) direction of the gradient, depending on the droplet affinity to the substrate. By using extensive molecular dynamics simulations of a coarse-grained model, we find that the mechanisms of the durotaxis and antidurotaxis droplet motion are distinct, require the minimization of the interfacial energy between the droplet and the substrate, and share similarities with those mechanisms previously observed for brush substrates with stiffness gradient. Moreover, durotaxis motion takes place over a wider range of affinities and is generally more efficient (faster motion) than antidurotaxis. Thus, our study points to further possibilities and guidelines for realizing both antidurotaxis and durotaxis motion on the same gradient substrate for applications in microfluidics, energy conservation, and biology.

Quantifying order in breath figure patterns through Voronoi entropy

In this study, we simulate breath figures that are evolving two-dimensional assemblies of droplets on a substrate. We focus on the Voronoi/Shannon entropy of these figures, which quantifies the order related to the coordination number of droplets. We show that the Voronoi entropy of the complete breath figure pattern converges to a value that is the one of a randomly distributed point system. Conversely, the subset containing exclusively large droplets of the breath figure exhibits significantly lower entropy than that obtained for all droplets. Using molecular dynamics simulations, we show that coalescence events in breath figures induce the same Voronoi entropy as that caused by repulsive interactions in a bidimensional atomic system.

Bilayer Scaffolds of PLLA/PCL/CAB Ternary Blend Films and Curcumin-Incorporated PLGA Electrospun Nanofibers: The Effects of Polymer Compositions and Solvents on Morphology and Molecular Interactions

Tissue engineering scaffolds have been dedicated to regenerating damaged tissue by serving as host biomaterials for cell adhesion, growth, differentiation, and proliferation to develop new tissue. In this work, the design and fabrication of a biodegradable bilayer scaffold consisting of a ternary PLLA/PCL/CAB blend film layer and a PLGA/curcumin (CC) electrospun fiber layer were studied and discussed in terms of surface morphology, tensile mechanical properties, and molecular interactions. Three different compositions of PLLA/PCL/CAB-60/15/25 (TBF1), 75/10/15 (TBF2), and 85/5/10 (TBF3)-were fabricated using the solvent casting method. The electrospun fibers of PLGA/CC were fabricated using chloroform (CF) and dimethylformamide (DMF) co-solvents in 50:50 and 60:40 volume ratios. Spherical patterns of varying sizes were observed on the surfaces of all blend films-TBF1 (17-21 µm) > TBF2 (5-9 µm) > TBF3 (1-5 µm)-caused by heterogeneous surfaces inducing bubble nucleation. The TBF1, TBF2, and TBF3 films showed tensile elongation at break values of approximately 170%, 94%, and 43%, respectively. The PLGA/CC electrospun fibers fabricated using 50:50 CF:DMF had diameters ranging from 100 to 400 nm, which were larger than those of the PLGA fibers (50-200 nm). In contrast, the PLGA/CC electrospun fibers fabricated using 60:40 CF:DMF had diameters mostly ranging from 200 to 700 nm, which were larger than those of PLGA fibers (200-500 nm). Molecular interactions via hydrogen bonding were observed between PLGA and CC. The surface morphology of the bilayer scaffold demonstrated adhesion between these two solid surfaces resembling "thread stitches" promoted by hydrophobic interactions, hydrogen bonding, and surface roughness.

Investigation of Orderliness of Breath Figures on Polydimethylsiloxane

Breath figures, the self-assembled water droplet patterns formed on cold surfaces, are ideally hexagonal. A deviation from the ideal honeycomb pattern can occur due to variation of roughness of the substrate, change in vapor from water to other liquids, etc. The thermodynamics of breath figure formation is complex, and any deviation from ideality is even more difficult to understand. In the absence of a unified theory to understand such patterns and experimental difficulties in monitoring all aspects of formation of breath figures, the patterns formed are studied in terms of their orderliness by determining their Voronoi entropy. We report here the Voronoi entropy calculations of the breath figure fabricated over the smooth and constrained surfaces using polydimethylsiloxane (PDMS) of molecular weight 235 g/mol in two different environments: (a) water and (b) binary mixture of ethanol-propanol over the entire concentration range. Ordered honeycomb patterns are seen on the smooth surfaces, and disordered patterns are seen on constrained surfaces when imaged using confocal microscopy. The latter is attributed to the depinning of the triple-phase contact line, implying that the underlying constraints influence the pore morphology. Contact angle studies of water over the breath figure patterned surfaces indicate the hydrophobic nature of the patterned surfaces.

Antidurotaxis Droplet Motion onto Gradient Brush Substrates

Durotaxis motion is a spectacular phenomenon manifesting itself by the autonomous motion of a nano-object between parts of a substrate with different stiffness. This motion usually takes place along a stiffness gradient from softer to stiffer parts of the substrate. Here, we propose a new design of a polymer brush substrate that demonstrates antidurotaxis droplet motion, that is, droplet motion from stiffer to softer parts of the substrate. By carrying out extensive molecular dynamics simulation of a coarse-grained model, we find that antidurotaxis is solely controlled by the gradient in the grafting density of the brush and is favorable for fluids with a strong attraction to the substrate (low surface energy). The driving force of the antidurotaxial motion is the minimization of the droplet-substrate interfacial energy, which is attributed to the penetration of the droplet into the brush. Thus, we anticipate that the proposed substrate design offers a new understanding and possibilities in the area of autonomous motion of droplets for applications in microfluidics, energy conservation, and biology.

PCL/PEO Polymer Membrane Prevents Biofouling in Wearable Detection Sensors

Technological advances in biosensing offer extraordinary opportunities to transfer technologies from a laboratory setting to clinical point-of-care applications. Recent developments in the field have focused on electrochemical and optical biosensing platforms. Unfortunately, these platforms offer relatively poor sensitivity for most of the clinically relevant targets that can be measured on the skin. In addition, the non-specific adsorption of biomolecules (biofouling) has proven to be a limiting factor compromising the longevity and performance of these detection systems. Research from our laboratory seeks to capitalize on analyte selective properties of biomaterials to achieve enhanced analyte adsorption, enrichment, and detection. Our goal is to develop a functional membrane integrated into a microfluidic sampling interface and an electrochemical sensing unit. The membrane was manufactured from a blend of Polycaprolactone (PCL) and Polyethylene oxide (PEO) through a solvent casting evaporation method. A microfluidic flow cell was developed with a micropore array that allows liquid to exit from all pores simultaneously, thereby imitating human perspiration. The electrochemical sensing unit consisted of planar gold electrodes for the monitoring of nonspecific adsorption of proteins utilizing Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The solvent casting evaporation technique proved to be an effective method to produce membranes with the desired physical properties (surface properties and wettability profile) and a highly porous and interconnected structure. Permeability data from the membrane sandwiched in the flow cell showed excellent permeation and media transfer efficiency with uniform pore activation for both active and passive sweat rates. Biofouling experiments exhibited a decrease in the extent of biofouling of electrodes protected with the PCL/PEO membrane, corroborating the capacity of our material to mitigate the effects of biofouling.

Influence of phase-separated structural morphologies on the piezo and triboelectric properties of polymer composites

Simplified and flexible fabrication methods, high output performance, and extreme flexibility of polymer-based nanocomposites represent versatile designs in self-powering devices for wearable electronics, sensors, and smart societies. Examples include polyvinylidene fluoride and its copolymers-based piezoelectric nanogenerators, green and recyclable triboelectric nanogenerators, etc. Advanced functionalities, multi-functional properties, and the extensive lifetime required for nanogenerators inspire researchers to focus on structural modifications of the polymeric materials, to fully exploit their performances. Phase separation is a physicochemical process in which polymeric phases rearrange, resulting in specific structures and properties, that ultimately influence mechanical, electronic, and other functional properties. This article will study the phase separation strategies used to modify the polymeric base, both physically and chemically, to generate the maximum electric power upon mechanical and frictional deformation. The effect of interfacial modification on the efficiency of the nanogenerators, chemical and mechanical stability, structural integrity, durable performance, and morphological appearance will be extensively covered in this review. Moreover, piezo- and triboelectric power generation have numerous challenges, such as poor resistance to mechanical deformation, reduced cyclic performance stability, and a high cost of production. These often depend on the method of developing the nanogenerators, and phase separation provides a unique advantage in reducing them. The current review provides a one-stop solution to understand and disseminate the phase separation process, types and mechanisms, advantages, and role in improving the piezoelectric and triboelectric performances of the nanogenerators.

Photochemically Induced Marangoni Patterning of Polymer Bilayers

Surface-tension gradients created along a polymer film by patterned photochemical reactions are a powerful tool for creating surface topography. Here, we use mathematical modeling to explore a strategy for patterning photochemically inactive polymers by coupling a light-sensitive and light-insensitive polymer to form a polymer bilayer. The light-sensitive polymer forms the top layer, and the most dominant surface-tension gradients are introduced at the interface between this layer and air. Lubrication theory is used to derive nonlinear partial differential equations describing the heights of each layer, and linear analysis and nonlinear simulations are performed to characterize interface dynamics. Patterns form at both the polymer-air and polymer-polymer interfaces at early thermal annealing times as a result of Marangoni stresses but decay on prolonged thermal annealing as a result of the dissipative mechanisms of capillary leveling and photoproduct diffusion, thus setting a limit to the maximum individual layer deformation. Simulations also show that the bottom-layer features can remain "trapped", i.e., exhibit no significant decay, even while the top layer topography has dissipated. We study the effects of two key parameters, the initial thickness ratio and the viscosity ratio of the two polymers, on the maximum deformation attained in the bottom layer and the time taken to attain this deformation. We identify regions of parameter space where the maximum bottom-layer deformation is enhanced and the attainment time is reduced. Overall, our study provides guidelines for designing processes to pattern photochemically inactive polymers and create interfacial topography in polymer bilayers.

Exploiting breath figure reversibility for in situ pattern modulation and hierarchical design

The breath figure (BF) method employs condensation droplets as dynamic templates for patterning polymer films. In the classical approach, dropwise condensation and film solidification are simultaneously induced through solvent evaporation, leading to empirically derived patterns with limited predictability of the final design. Here we use the temporally arrested BF methodology, controlling condensation and polymerisation independently to create diverse BF patterns with varied pore size, arrangement and distribution. External temperature control enables us to further investigate and exploit the inherent reversibility of the phase change process that governs the pattern formation. We modulate the level of subcooling and superheating to achieve subsequent regimes of condensation and evaporation, permitting in situ regulation of the droplet growth and shrinkage kinetics. The full reversibility of the phase change processes joined with active photopolymerisation in the current approach thus allows arresting of predictable BF kinetics at intermediate stages, thereby accessing patterns with varied pore size and spacing for unchanged material properties and environmental conditions. This simultaneous active control over both the kinetics of phase change and polymer solidification offers affordable routes for the fabrication of diverse predictable porous surfaces; manufacture of monolithic hierarchical BF patterns are ultimately facilitated through the advanced control of the BF assembly using the method presented here.

Porous polymer film formation by water droplet templating using polystyrene

Studies show that the formation of breath figures over polystyrene is not clearly understood-sometimes the patterns are regular and sometimes they are barely formed. In an attempt to understand this process a little more, breath figures over polystyrene of three molecular weights and on the smooth and grooved DVD surfaces are prepared and studied. The microporous films are prepared by the evaporation of the chloroform solution of the polymers in a humid environment. The thus formed breath figure patterns are studied under a confocal laser scanning microscope and the images are analyzed. Breath figures were formed for (a) three molecular weights of the polymer (b) two casting techniques, and (c) on smooth and grooved surfaces (of a commercial DVD). The wetting of the breath figures formed by water is also reported here. The pore diameters were found to increase with increase in molecular weight and also with concentration of the polymer used. Only drop-casting method yield breath figures. Voronoi entropy, calculated from the images, indicates ordered pores on the grooved surface compared to smooth surfaces. Contact angle studies indicate a hydrophobic nature of the polymer, with the hydrophobicity increasing by the patterning.

Unidirectional Droplet Propulsion onto Gradient Brushes without External Energy Supply

Using extensive molecular dynamics simulation of a coarse-grained model, we demonstrate the possibility of sustained unidirectional motion (durotaxis) of droplets without external energy supply when placed on a polymer brush substrate with stiffness gradient in a certain direction. The governing key parameters for the specific substrate design studied, which determine the durotaxis efficiency, are found to be the grafting density of the brush and the droplet adhesion to the brush surface, whereas the strength of the stiffness gradient, the viscosity of the droplet, or the length of the polymer chains of the brush have only a minor effect on the process. It is shown that this durotaxial motion is driven by the steady increase of the interfacial energy between droplet and brush as the droplet moves from softer to stiffer parts of the substrate whereby the mean driving force gradually declines with decreasing roughness of the brush surface. We anticipate that our findings indicate further possibilities in the area of nanoscale motion without external energy supply.

Controlling Surface Deformation and Feature Aspect Ratio in Photochemically Induced Marangoni Patterning of Polymer Films

Thin liquid polymer films can be topographically patterned when polymer/air interfaces are deformed by surface-tension gradients. Toward this end, a recently developed method first photochemically patterns surface-tension gradients along a solid, flat polymer film. On heating to the liquid state, the film initially develops topography reflecting the patterned surface-tension gradients. But capillary leveling and diffusion of the photoproduct oppose this causing the features to eventually decay back to a flat film upon extended thermal annealing. Intuitively, this interplay between competing mechanisms sets a limit on the maximum film deformation during the process. Prior studies show that the initial film thickness, photomask periodicity, and amount of photochemical conversion significantly affect the maximum film deformation. Here, we use a model based on lubrication theory to develop additional insights into this observation. We identify two regimes, capillary-leveling-dominated and photoproduct-diffusion-dominated, wherein the respective dominant mechanism determines the maximum film deformation that can be additionally related to various experimental parameters. Scaling laws for the variation of maximum film deformation and aspect ratio with film thickness and surface-tension pattern periodicity are also developed. Complementary experiments show good agreement with model predictions. Insights into the effect of surface-tension pattern asymmetry on the maximum film deformation are also provided. These findings reveal mechanistic detail and fundamental principles that are useful for controlling the process to form target patterns of interest.

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.

Modified Breath Figure Methods for the Pore-Selective Functionalization of Honeycomb-Patterned Porous Polymer Films

Recent developments in the field of the breath figure (BF) method have led to renewed interest from researchers in the pore-selective functionalization of honeycomb-patterned (HCP) films. The pore-selective functionalization of the HCP film gives unique properties to the film which can be used for specific applications such as protein recognition, catalysis, selective cell culturing, and drug delivery. There are several comprehensive reviews available for the pore-selective functionalization by the self-assembly process. However, considerable progress in preparation technologies and incorporation of new materials inside the pore surface for exact applications have emerged, thus warranting a review. In this review, we have focused on the pore-selective functionalization of the HCP films by the modified BF method, in which the self-assembly process is accompanied by an interfacial reaction. We review the importance of pore-selective functionalization, its applications, present limitations, and future perspectives.

Aggregation-Induced Emission Boosting the Study of Polymer Science

The past one hundred years witness the great development of polymer science. The advancement of polymer science is closely related with the developing of characterization techniques and methods, from viscometry in molecular weight determination to advanced techniques including differential scanning calorimetry, nuclear magnetic resonance and scanning electron microscopy. However, these techniques are normally constrained to tedious sample preparation, high cost, harsh experimental condition, or ex-situ characterization. Fluorescence technology has the merits of high sensitivity and direct visualization. Contrary to conventional aggregation-causing quenching fluorophores, those dyes with aggregation-induced emission characteristic show high emission efficiency in aggregate states. Based on the restriction of intramolecular motions for AIE properties, the AIE materials are very sensitive to the surrounding microenvironments owing to the twisted propeller-like structures and therefore reveal great potentials in polymer's study. The AIE concept has been successfully used in polymer's study and provides us a deeper understanding on polymer structure and properties. In this review, the applications of AIEgens in polymer science for visualizing polymerization, glass transition, dissolution, crystallization, gelation, self-assembly, phase separation, cracking and self-healing were exemplified and summarized. Lastly, the challenges and perspectives in the study of polymer science using AIEgens are addressed. This article is protected by copyright. All rights reserved.

Smart surfaces with reversibly switchable wettability: Concepts, synthesis and applications

As a growing hot research topic, manufacturing smart switchable surfaces has attracted much attention in the past a few years. The state-of-the-art study on reversibly switchable wettability of smart surfaces has been presented in this systematic review. External stimuli are brought about to render the alteration in chemical conformation and surface morphology to drive the wettability switch. Here, starting from the fundamental theories related to the surfaces wetting principles, highlights on different triggers for switchable wettability, such as pH, light, ions, temperature, electric field, gas, mechanical force, and multi-stimuli are discussed. Different applications that have various wettability requirement are targeted, including oil-water separation, droplets manipulation, patterning, liquid transport, and so on. This review aims to provide a deep insight into responsive interfacial science and offer guidance for smart surface engineering. It ends with a summary of current challenges, future opportunities, and potential solutions on smart switch of wettability on superwetting surfaces.

Harnessing Polyhydroxyalkanoates and Pressurized Gyration for Hard and Soft Tissue Engineering

Organ dysfunction is a major cause of morbidity and mortality. Transplantation is typically the only definitive cure, challenged by the lack of sufficient donor organs. Tissue engineering encompasses the development of biomaterial scaffolds to support cell attachment, proliferation, and differentiation, leading to tissue regeneration. For efficient clinical translation, the forming technology utilized must be suitable for mass production. Herein, uniaxial polyhydroxyalkanoate scaffolds manufactured by pressurized gyration, a hybrid scalable spinning technique, are successfully used in bone, nerve, and cardiovascular applications. Chorioallantoic membrane and in vivo studies provided evidence of vascularization, collagen deposition, and cellular invasion for bone tissue engineering. Highly efficient axonal outgrowth was observed in dorsal root ganglion-based 3D ex vivo models. Human induced pluripotent stem cell derived cardiomyocytes exhibited a mature cardiomyocyte phenotype with optimal calcium handling. This study confirms that engineered polyhydroxyalkanoate-based gyrospun fibers provide an exciting and unique toolbox for the development of scalable scaffolds for both hard and soft tissue regeneration.

N-acylhydrazone Derivative-Loaded Cellulose Acetate Films: Thermoanalytical, Spectroscopic, Mechanical and Morphological Characterization

Cellulose acetate (ACT) is one of the most important cellulose derivatives due to its biodegradability and low toxicity, presenting itself as one of the main substitutes for synthetic materials in the development of wound dressing films. The incorporation of a N-acylhydrazonic derivative (JR19), with its promising anti-inflammatory activity, may represent an alternative for the treatment of skin wounds. This work aims to develop and to physicochemically and mechanically characterize ACT films containing JR19. The films were prepared using the ‘casting’ method and further characterized by thermoanalytical and spectroscopic techniques. In addition, mechanical tests and morphological analysis were performed. Thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses showed that the thermal events attributed to excipients and films were similar, indicating the absence of physical incompatibilities between ACT and JR19. Infrared spectroscopy showed that JR19 was incorporated into ACT films. The characteristic band attributed to C≡N (2279 to 2264 cm⁻¹) was observed in the spectra of JR19, in that of the physical mixture of JR19/ACT, and, to a lesser extent, in the spectra of JR19 incorporated into the ACT film, suggesting some interaction between JR19 and ACT. X-ray diffraction (XRD) evidenced the suppression of the crystallinity of JR19 (diffraction peaks at 8.54°, 12.80°, 14.09°, 16.08°, 18.19°, 22.65°, 23.59°, 24.53°, 25.70°, 28.16° and 30.27°2θ) after incorporation into ACT films. The mechanical tests indicated the adequate integrity of the films and their resistance to bending. The morphological characterization showed JR19 crystals along with a homogeneously distributed porous structure throughout the surface of the films with an average diameter of 21.34 µm and 22.65 µm of the films alone and of those incorporating JR19F, respectively. This study was able to characterize the ACT films incorporating JR19, showing their potential to be further developed as wound healing dressings.

Achieving Stable Patterns in Multicomponent Polymer Thin Films Using Marangoni and van der Waals Forces

Liquid-air interfaces can be deformed by surface-tension gradients to create topography, a phenomenon useful for polymer film patterning. A recently developed method creates these gradients by photochemically patterning a solid polymer film. Heating the film to the liquid state leads to flow driven by the patterned surface-tension gradients, but capillary leveling and diffusion of surface-active species facilitate eventual dissipation of the topography. However, experiments demonstrate that using blends of high- and low-molar-mass polymers can considerably delay the decay in topography. To gain insight into this observation, we develop a model based on lubrication theory that yields coupled nonlinear partial differential equations describing how the film height and species concentrations evolve with time and space. Incorporation of a nonmonotonic disjoining pressure is found to significantly increase the lifetime of topographical features, making the model predictions qualitatively consistent with experiments. A parametric study reveals the key variables controlling the kinetics of film deformation and provides guidelines for photochemically induced Marangoni patterning of polymer films.

Capturing the value in printed pharmaceuticals - A study of inkjet droplets released from a polymer matrix

The future of personalised combination dosages will rely on the programming and delivery of multiple, separate APIs, their carrier fluids and excipients to a stable matrix, where each will remain separate until it is needed to be released. A recent technique has demonstrated how to print, capture and release materials from a polymer matrix using inkjet printing, a low cost and customisable technique. Droplets of a formulation are delivered to a fluid polymer matrix, where they are imbibed and remain pinned just under the upper surface, held in place by a balance of interfacial energies. Once the surrounding matrix cures and solidifies, the coating or matrix has trapped the formulation, but each drop has a small opening or pore to the outside that will allow delivery through diffusion. However, while the trapping mechanism has been explored in detail, to-date the release involved in this delivery has never been studied or quantified to the same level. Here we show a first study to quantify the release of a model system from a polymer matrix. An aqueous fluorescein solution is delivered and trapped, with release demonstrated to an agarose gel and aqueous environments. The work reveals that the balance of interfacial tensions prevents a reliable release until low concentrations of surfactant are included. This provides a route forward to further explore stabilising combinations of drugs within one material using a digitally controlled and affordable technique.

Surfactant location and internal phase volume fraction dictate emulsion electrospun fiber morphology and modulate drug release and cell response

Emulsion electrospinning is a versatile technique used to create fibrous meshes for applications in drug delivery and tissue engineering. In this study, the effects of surfactant and increasing internal phase volume fraction on emulsion electrospun fiber morphology were investigated. The fiber diameter, surface topography, internal architecture, mesh hydrophobicity, and fiber volume fraction were all characterized and the resulting effects on model drug release and cell response were determined. Surfactant relocation to the fiber surface resulted in alterations to fiber surface topography and internal morphology, increased rate of water adsorption into the mesh, and reduced burst effects of drug release. Increasing the internal phase volume fraction within the emulsion resulted in minimal change to fiber diameter, surface morphology, fiber volume fraction, and rate of water adsorption illustrating the ability to increase drug loading without affecting fiber properties. Lastly, all meshes promoted cell adhesion and good viability with a trend of increased MTT absorbance from cells on the surfactant and emulsion fibers possibly suggesting that an increase in surface area via smaller fiber diameter and fiber volume fraction increases metabolic activity. Overall, these studies indicate that fiber morphology and mesh hydrophobicity can be tuned by controlling surfactant location within fibers and internal phase volume fraction. Modulating fiber properties within the emulsion electrospun mesh is important to achieve controlled drug release and cell response for tissue engineering applications.

Projectile Impact Shock-Induced Deformation of One-Component Polymer Nanocomposite Thin Films

Matrix-free assemblies of polymer-grafted nanoparticles (PGNs) enable mechanically robust materials for a variety of structural, electronic, and optical applications. Recent quasi-static mechanical studies have identified the key parameters that enhance canopy entanglement and promote plasticity of the PGNs below T_g. Here we experimentally explore the high-strain-rate shock impact behavior of polystyrene grafted NPs and compare their energy absorption capabilities to that of homopolystyrene for film thicknesses ranging from 75 to 550 nm and for impact velocities from 350 to 800 m/s. Modeling reveals that the initial shock compression results in a rapid temperature increase at the impact site. The uniformity of this heating is consistent with observations of greater kinetic energy absorption per mass (E_p^*) of thinner films due to extensive visco-plastic deformation of molten film around the penetration site. Adiabatic heating is insufficient to raise the temperature at the exit surface of the thickest films resulting in increased strain localization at the impact periphery with less melt elongation. The extent and distribution of entanglements also influence E_p^*. Structurally, each NP acts as a giant cross-link node, coupling surrounding nodes via the number of canopy chains per NP and the nature and number of entanglements between canopies anchored to different NPs. Load sharing via this dual network, along with geometrical factors such as film thickness, lead to extreme E_p^* arising from the sequence of instantaneous adiabatic shock heating followed by visco-plastic drawing of the film by the projectile. These observations elucidate the critical factors necessary to create robust polymer-nanocomposite multifunctional films.

Direct-writing microporous polymer architectures - print, capture and release

In the nature-inspired breath figure method, rafts of condensed water droplets self-organise and imprint into a permanent microporous polymer structure. This could have exciting applications in drug delivery, tissue engineering and sensors but it is extremely difficult to control or functionalise the final structure. Here, we show direct-writing of droplets onto fluid surfaces by inkjet printing as a breakthrough to dial-in a required pattern, structure and function into the polymer film.

Novel Drug Delivery Systems Fighting Glaucoma: Formulation Obstacles and Solutions

Glaucoma is considered to be one of the biggest health problems in the world. It is the main cause of preventable blindness due to its asymptomatic nature in the early stages on the one hand and patients' non-adherence on the other. There are several approaches in glaucoma treatment, whereby this has to be individually designed for each patient. The first-line treatment is medication therapy. However, taking into account numerous disadvantages of conventional ophthalmic dosage forms, intensive work has been carried out on the development of novel drug delivery systems for glaucoma. This review aims to provide an overview of formulation solutions and strategies in the development of in situ gel systems, nanosystems, ocular inserts, contact lenses, collagen corneal shields, ocular implants, microneedles, and iontophoretic devices. The results of studies confirming the effectiveness of the aforementioned drug delivery systems were also briefly presented.

Development of Porous and Flexible PTMC Membranes for In Vitro Organ Models Fabricated by Evaporation-Induced Phase Separation

Polymeric membranes are widely applied in biomedical applications, including in vitro organ models. In such models, they are mostly used as supports on which cells are cultured to create functional tissue units of the desired organ. To this end, the membrane properties, e.g., morphology and porosity, should match the tissue properties. Organ models of dynamic (barrier) tissues, e.g., lung, require flexible, elastic and porous membranes. Thus, membranes based on poly (dimethyl siloxane) (PDMS) are often applied, which are flexible and elastic. However, PDMS has low cell adhesive properties and displays small molecule ad- and absorption. Furthermore, the introduction of porosity in these membranes requires elaborate methods. In this work, we aim to develop porous membranes for organ models based on poly(trimethylene carbonate) (PTMC): a flexible polymer with good cell adhesive properties which has been used for tissue engineering scaffolds, but not in in vitro organ models. For developing these membranes, we applied evaporation-induced phase separation (EIPS), a new method in this field based on solvent evaporation initiating phase separation, followed by membrane photo-crosslinking. We optimised various processing variables for obtaining form-stable PTMC membranes with average pore sizes between 5 to 8 µm and water permeance in the microfiltration range (17,000-41,000 L/m2/h/bar). Importantly, the membranes are flexible and are suitable for implementation in in vitro organ models.

Hierarchically structured porous materials: synthesis strategies and applications in energy storage

To address the growing energy demands of sustainable development, it is crucial to develop new materials that can improve the efficiency of energy storage systems. Hierarchically structured porous materials have shown their great potential for energy storage applications owing to their large accessible space, high surface area, low density, excellent accommodation capability with volume and thermal variation, variable chemical compositions and well controlled and interconnected hierarchical porosity at different length scales. Porous hierarchy benefits electron and ion transport, and mass diffusion and exchange. The electrochemical behavior of hierarchically structured porous materials varies with different pore parameters. Understanding their relationship can lead to the defined and accurate design of highly efficient hierarchically structured porous materials to enhance further their energy storage performance. In this review, we take the characteristic parameters of the hierarchical pores as the survey object to summarize the recent progress on hierarchically structured porous materials for energy storage. This is the first of this kind exclusively to survey the performance of hierarchically structured porous materials from different porous characteristics. For those who are not familiar with hierarchically structured porous materials, a series of very significant synthesis strategies of hierarchically structured porous materials are firstly and briefly reviewed. This will be beneficial for those who want to quickly obtain useful reference information about the synthesis strategies of new hierarchically structured porous materials to improve their performance in energy storage. The effect of different organizational, structural and geometric parameters of porous hierarchy on their electrochemical behavior is then deeply discussed. We outline the existing problems and development challenges of hierarchically structured porous materials that need to be addressed in renewable energy applications. We hope that this review can stimulate strong intuition into the design and application of new hierarchically structured porous materials in energy storage and other fields.

Nanoparticle-Induced Self-Assembly of Block Copolymers into Nanoporous Films at the Air-Water Interface

Herein, we report the cooperative self-assembly of nanoparticles and block copolymers at the air-water interface, which can generate highly uniform and readily transferable composite films with tunable nanoscale architecture and functionalities. Interestingly, the incorporation of nanoparticles significantly affects the self-assembly of block copolymers at the interface. The nanoparticle-induced morphology change occurs through distinct mechanisms depending on the volume fraction of the hydrophobic block. For block copolymers with a relatively small hydrophobic volume fraction, the morphology transition occurs through the nanoparticle-induced swelling of a selective block. When the hydrophobic volume fraction is large enough, added nanoparticles promote the breath figure assembly, which generates uniform honeycomb-like porous structures with unusual nanoscale periodicity. This approach is generally applicable to various types of nanoparticles, constituting a simple one-step method to porous thin films with various functionalities.

Recent advances on porous interfaces for biomedical applications

Porous structures on solid surfaces prepared artificially through the water droplet template method have the features of easy operation, low cost and self-removal of templates, and thus are widely applied in the fields of medicine, biomedicine, adsorption, catalysis, and separation, optical and electronic materials. Due to their tunable dimensions, abundant selection of materials, mechanical stability, high porosity, and enlarged pore surface, the formed porous interfaces show specific significance in bio-related systems. In this study, recent achievements related to applications of porous interfaces and a focus into biological and medical-related systems are summarized. The discussion involves the preparation of porous interfaces, and porous interface-induced cell behaviors including culture, growth, proliferation, adhesion, and differentiation of cells. The inhibitory effect of bacteria and separated features of microorganisms supported by porous interfaces, the immobilization of biomolecules related to proteins, DNA and enzymes, and the controllable drug delivery are also discussed. The summary of recent advances pointed out in the study, are suggestive of insights for motivating unique potential applications including their extension to porous interfaces in biomedical materials.

Hierarchically Structured Porous Piezoelectric Polymer Nanofibers for Energy Harvesting

Hierarchically porous piezoelectric polymer nanofibers are prepared through precise control over the thermodynamics and kinetics of liquid-liquid phase separation of nonsolvent (water) in poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) solution. Hierarchy is achieved by fabricating fibers with pores only on the surface of the fiber, or pores only inside the fiber with a closed surface, or pores that are homogeneously distributed in both the volume and surface of the nanofiber. For the fabrication of hierarchically porous nanofibers, guidelines are formulated. A detailed experimental and simulation study of the influence of different porosities on the electrical output of piezoelectric nanogenerators is presented. It is shown that bulk porosity significantly increases the power output of the comprising nanogenerator, whereas surface porosity deteriorates electrical performance. Finite element method simulations attribute the better performance to increased volumetric strain in bulk porous nanofibers.

Light-Driven Locomotion of Bubbles

Remotely controlling the movement of small objects is a challenging research topic, which can realize the transportation of materials. In this study, remote locomotion control of particle-stabilized bubbles on a planar water surface by near-infrared laser or sunlight irradiation is demonstrated. A light-induced Marangoni flow was utilized to induce the locomotion of the bubbles on water surface, and the timing and direction of the locomotion can be controlled by irradiation timing and direction on demand. The velocity, acceleration, and force of the bubbles were analyzed. It was also confirmed that the bubbles can work as light-driven towing engines to pull other objects. Furthermore, it was demonstrated that the bubbles can work as an adhesive to bond two solid substrates by application of compressive stress under water. Such remote transport of the materials, pulling of the objects by light, and controlling the release of gas on demand should open up a wide field of conceivable applications.

Mono-Dispersed Microspheres Locally Assembled on Porous Substrates Formed through a Microemulsion Approach

A cost-effective, simple, and time-saving method to fabricate mono-dispersed periodic microsphere structures on substrates with patterned sites is very meaningful due to their significance on various biological studies. Herein, a simple and facile method to fabricate mono-dispersed microsphere arrays on porous substrates was developed. The mixture of polystyrene and an organic stabilizer solution which contains aqueous solution, fabricated through shaking, was applied to prepare microemulsion solution. An ordered porous structure was produced by spreading and evaporating the solvent of microemulsion on a glass slide, accompanied by the enrichment of didodecylamine in the cavities. The porous cavities were further modified with polyacrylic acid and poly(diallyldimethylammonium chloride) which could immobilize the microspheres. The charged microspheres were incorporated into the cavities by an electrostatic interaction with the oppositely charged polyelectrolytes. The positive polyelectrolytes with abundant charges as well as a suitable content and dimension of microspheres, ensured the formation of mono-dispersed and ordered arrays. Considering that other charged particles were universally suitable for the present strategy, the reported approach opened an efficient way for the preparation of microsphere-based materials.

Optimising micro-hydroxyapatite reinforced poly(lactide acid) electrospun scaffolds for bone tissue engineering

HA-mineralised composite electrospun scaffolds have been introduced for bone regeneration due to their ability to mimic both morphological features and chemical composition of natural bone ECM. Micro-sized HA is generally avoided in electrospinning due to its reduced bioactivity compared to nano-sized HA due to the lower surface area. However, the high surface area of nanoparticles provides a very high surface energy, leading to agglomeration. Thus, the probability of nanoparticles clumping leading to premature mechanical failure is higher than for microparticles at higher filler content. In this study, two micron-sized hydroxyapatites were investigated for electrospinning with PLA at various contents, namely spray dried HA (HA1) and sintered HA (HA2) particles to examine the effect of polymer concentration, filler type and filler concentration on the morphology of the scaffolds, in addition to the mechanical properties and bioactivity. SEM results showed that fibre diameter and surface roughness of 15 and 20 wt% PLA fibres were significantly affected by incorporation of either HA. The apatite precipitation rates for HA1 and HA2-filled scaffolds immersed in simulated body fluid (SBF) were similar, however, it was affected by the fibre diameter and the presence of HA particles on the fibre surface. Degradation rates of HA2-filled scaffolds in vitro over 14 days was lower than for HA1-filled scaffolds due to enhanced dispersion of HA2 within PLA matrix and reduced cavities in PLA/HA2 interface. Finally, increasing filler surface area led to enhanced thermal stability as it reduced thermal degradation of the polymer.