Rapid casting of patterned vascular networks for perfusable engineered three-dimensional tissues

 

In the absence of perfusable vascular networks, three-dimensional (3D) engineered tissues densely populated with cells quickly develop a necrotic core¹. Yet the lack of a general approach to rapidly construct such networks remains a major challenge for 3D tissue culture^{2, 3, 4}. Here, we printed rigid 3D filament networks of carbohydrate glass, and used them as a cytocompatible sacrificial template in engineered tissues containing living cells to generate cylindrical networks that could be lined with endothelial cells and perfused with blood under high-pressure pulsatile flow. Because this simple vascular casting approach allows independent control of network geometry, endothelialization and extravascular tissue, it is compatible with a wide variety of cell types, synthetic and natural extracellular matrices, and crosslinking strategies. We also demonstrated that the perfused vascular channels sustained the metabolic function of primary rat hepatocytes in engineered tissue constructs that otherwise exhibited suppressed function in their core.

 

Autonomous Motion of Metallic Microrods Propelled by Ultrasound

Autonomously moving micro-objects, or micromotors, have attracted the attention of the scientific community over the past decade, but the incompatibility of phoretic motors with solutions of high ionic strength and the use of toxic fuels have limited their applications in biologically relevant media. In this letter we demonstrate that ultrasonic standing waves in the MHz frequency range can levitate, propel, rotate, align, and assemble metallic microrods (2 μm long and 330 nm diameter) in water as well as in solutions of high ionic strength. Metallic rods levitated to the midpoint plane of a cylindrical cell when the ultrasonic frequency was tuned to create a vertical standing wave. Fast axial motion of metallic microrods at 200 μm/s was observed at the resonant frequency using continuous or pulsed ultrasound. Segmented metal rods (AuRu or AuPt) were propelled unidirectionally with one end (Ru or Pt, respectively) consistently forward. A self-acoustophoresis mechanism based on the shape asymmetry of the metallic rods is proposed to explain this axial propulsion. Metallic rods also aligned and self-assembled into long spinning chains, which in the case of bimetallic rods had a head-to-tail alternating structure. These chains formed ring or streak patterns in the levitation plane. The diameter or distance between streaks was roughly half the wavelength of the ultrasonic excitation. The ultrasonically driven movement of metallic rods was insensitive to the addition of salt to the solution, opening the possibility of driving and controlling metallic micromotors in biologically relevant media using ultrasound.

Controlled Orientation and Alignment in Films of Single-Walled Carbon Nanotubes Using Inkjet Printing

An inkjet printing procedure for depositing films of carbon nanotubes (CNTs) that exhibit a very high degree of long-range mutual alignment as well as a controlled orientation with respect to the printed geometry is presented. CNT self-assembly was induced by the intrinsic lyotropic liquid crystallinity of CNT suspensions. Sufficient concentrations are reached by matching the inkjet deposition rate to the numerically modeled local evaporation rate of the printed feature and enable the CNT suspension to be printed using standard inkjet printing. Surface alignment was verified using scanning electron microscopy (SEM) and polarized light microscopy. In addition, the bulk morphology was investigated and found to be composed of stacked planar layers that did not necessarily have the same long-range orientation found on the surface. The bulk morphology was characterized by removing layers through an elastomeric peeling process and by observing cross sections of the films using SEM. CNT concentration and length were spanned experimentally, and it was found that very short and very long CNTs as well as low concentration suspensions did not yield long-range alignment.

In silico screening of carbon-capture materials

One of the main bottlenecks to deploying large-scale carbon dioxide capture and storage (CCS) in power plants is the energy required to separate the CO₂ from flue gas. For example, near-term CCS technology applied to coal-fired power plants is projected to reduce the net output of the plant by some 30% and to increase the cost of electricity by 60–80%. Developing capture materials and processes that reduce the parasitic energy imposed by CCS is therefore an important area of research. We have developed a computational approach to rank adsorbents for their performance in CCS. Using this analysis, we have screened hundreds of thousands of zeolite and zeolitic imidazolate framework structures and identified many different structures that have the potential to reduce the parasitic energy of CCS by 30–40% compared with near-term technologies.

Gel-Based Self-Propelling Particles Get Programmed to Dance

We present a class of gel-based self-propelling particles moving by the Marangoni effect in an oscillatory mode. The particles are made of an ethanol-infused polyacrylamide hydrogel contained in plastic tubing. These gel boats floating on the water surface exhibit periodic propulsion for several hours. The release of ethanol from the hydrogel takes place beneath the liquid surface. The released ethanol rises to the air-water interface by buoyancy, and generates a self-sustained cycle of surface tension gradient driven motion. The disruption of the ethanol flux to the surface by the bulk flows around the moving particle results in their pulsating motion. The pulse interval and the distance propelled in a pulse by these gel floaters were measured and approximated by simple expressions based on the rate of ethanol mass-transfer through and out of the hydrogel. This allowed us to design a multitude of particles performing periodic steps in different directions or at different angles of rotation, travelling in complex preprogrammed trajectories on the surface of the liquid. Similar gel-based self-propelling floaters can find applications as mixers and cargo carriers in lab-on-a-chip devices, and in various platforms for sensing and processing at the microscale.

Fluctuation-induced dynamics of multiphase liquid jets with ultra-low interfacial tension

Control of fluid dynamics at micrometer scale is essential to emulsion science and materials design, which is ubiquitous in everyday life and frequently encountered in industrial applications. Most studies on multiphase flow focus on oil-water systems with substantial interfacial tension. Advances in microfluidics have enabled the study of multiphase flow with more complex dynamics. Here, we show that the evolution of the interface in a jet surrounded by a co-flowing continuous phase with an ultra-low interfacial tension presents new opportunities to the control of flow morphologies. The introduction of a harmonic perturbation to the dispersed phase leads to the formation of interfaces with unique shapes. The periodic structures can be tuned by controlling the fluid flow rates and the input perturbation; this demonstrates the importance of the inertial effects in flow control at ultra-low interfacial tension. Our works provide new insight into microfluidic flows at ultra-low interfacial tension and their potential applications.

Interfacial viscoelasticity controls buckling, wrinkling and arrest in emulsion drops undergoing mass transfer

Contrary to the notion that ‘oil and water do not mix’, many oils possess a residual diffusive mobility through water, causing the drop sizes in oil-in-water emulsions to slowly evolve with time. Liquid interfaces are therefore typically stabilized with polymeric or particulate emulsifiers. Upon adsorption, these may induce strong, localized viscoelasticity in the interfacial region. Here, we show that shrinkage of oil drops due to bulk mass transfer may render such adsorption layers mechanically unstable, causing them to buckle, crumple and, finally, to attain a stationary shape and size. We demonstrate using two types of model interfaces that this only occurs if the adsorption layer has a high interfacial shear elasticity. This is typically the case for adsorbed layers that are cross-linked or ‘jammed’. Conversely, interfacial compression elasticity alone is a poor predictor of interface buckling or arrest. These results provide a new perspective on the role of interfacial rheology for compositional ripening in emulsions. Moreover, they directly affect a variety of applications, including the rapid screening of amphiphilic biopolymers such as the Acacia gum or the octenyl succinic anhydride modified starch used here, the interpretation of light scattering data for size measurements of emulsion drops, or the formulation of delivery systems for encapsulation and release of drugs and volatiles.

Towards Textile Energy Storage from Cotton T-Shirts

A simple chemical activation route is developed to convert insulating cotton T-shirt textiles into highly conductive and flexible activated carbon textiles (ACTs) for energy-storage applications. Such conversion gives these ACTs an ideal electrical double-layer capacitive behavior. The constructed asymmetric supercapacitors based on the ACTs and MnO2/ACT composite show superior electrochemical performances.

State-of-the-Art Graphene High-Frequency Electronics

High-performance graphene transistors for radio frequency applications have received much attention and significant progress has been achieved. However, devices based on large-area synthetic graphene, which have direct technological relevance, are still typically outperformed by those based on mechanically exfoliated graphene. Here, we report devices with intrinsic cutoff frequency above 300 GHz, based on both wafer-scale CVD grown graphene and epitaxial graphene on SiC, thus surpassing previous records on any graphene material. We also demonstrate devices with optimized architecture exhibiting voltage and power gains reaching 20 dB and a wafer-scale integrated graphene amplifier circuit with voltage amplification.

Printable Superhydrophilic-Superhydrophobic Micropatterns Based on Supported Lipid Layers

The ability to create superhydrophilic-superhydrophobic micropatterns and arrays is essential for a variety of applications ranging from microfluidics to cell microarrays and high-throughput screenings. Here we report a novel facile method for printing superhydrophilic patterns on a superhydrophobic surface using a simple microcontact printer. The formation of superhydrophilic areas is based on printing an ethanol solution containing a phospholipid onto a superhydrophobic porous polymer surface. This creates a supported lipid layer on the polymer surface, thereby switching from superhydrophobicity to superhydrophilicity. Therefore, the amphiphilic lipid functions as an ink that can be printed to create superhydrophilic patterns on the superhydrophobic surface.

Hydrodynamically directed multiscale assembly of shaped polymer fibers

A long-sought goal of material science is the development of fabrication processes by which synthetic materials can be made to mimic the multiscale organization many natural materials utilize to achieve unique functional and material properties. Here we demonstrate how the microfluidic fabrication of polymer fibers can take advantage of hydrodynamic forces to simultaneously direct assembly at the molecular and micron scales. The microfluidic device generates long fibers by initiating polymerization of a continuously flowing fluid via UV irradiation within the microfluidic channel. Prior to polymerization, hydrodynamic shear forces direct molecular scale assembly and a combination of hydrodynamic focusing and advection driven by grooves in the channel walls manipulate the cross-sectional shape of the pre-polymer stream. Polymerization subsequently locks in both molecular scale alignment and micron-scale fiber shape. This simple method for generating structures with multiscale organization could be useful for fabricating materials with multifunctionality or enhanced mechanical properties.

Walking with coffee: Why does it spill?

 

In our busy lives, almost all of us have to walk with a cup of coffee. While often we spill the drink, this familiar phenomenon has never been explored systematically. Here we report on the results of an experimental study of the conditions under which coffee spills for various walking speeds and initial liquid levels in the cup. These observations are analyzed from the dynamical systems and fluid mechanics viewpoints as well as with the help of a model developed here. Particularities of the common cup sizes, the coffee properties, and the biomechanics of walking proved to be responsible for the spilling phenomenon. The studied problem represents an example of the interplay between the complex motion of a cup, due to the biomechanics of a walking individual, and the low-viscosity-liquid dynamics in it.

Effects of chemical bonding on heat transport across interfaces

Interfaces often dictate heat flow in micro- and nanostructured systems^{1, 2, 3}. However, despite the growing importance of thermal management in micro- and nanoscale devices^{4, 5, 6}, a unified understanding of the atomic-scale structural features contributing to interfacial heat transport does not exist. Herein, we experimentally demonstrate a link between interfacial bonding character and thermal conductance at the atomic level. Our experimental system consists of a gold film transfer-printed to a self-assembled monolayer (SAM) with systematically varied termination chemistries. Using a combination of ultrafast pump–probe techniques (time-domain thermoreflectance, TDTR, and picosecond acoustics) and laser spallation experiments, we independently measure and correlate changes in bonding strength and heat flow at the gold–SAM interface. For example, we experimentally demonstrate that varying the density of covalent bonds within this single bonding layer modulates both interfacial stiffness and interfacial thermal conductance. We believe that this experimental system will enable future quantification of other interfacial phenomena and will be a critical tool to stimulate and validate new theories describing the mechanisms of interfacial heat transport. Ultimately, these findings will impact applications, including thermoelectric energy harvesting, microelectronics cooling, and spatial targeting for hyperthermal therapeutics.

Spatial-temporal dynamics of collective chemosensing

Although the process of chemosensing by individual cells is intrisically stochastic, multicellular organisms exhibit highly regulated responses to external stimulations. Two key elements to understand the deterministic features of chemosensing are intercellular communications and the role of pacemaker cells. To characterize the collective behavior induced by these two factors, we study the spatial-temporal calcium dynamics of fibroblast cells in response to ATP stimulation. We find that closely packed cell colonies exhibit faster, more synchronized, and highly correlated responses compared to isolated cells. In addition, we demonstrate for chemosensing the existence of pacemaker cells and how the presence of gap junctions impact the first step of the collective response. By further comparing these results with the calcium dynamics of cells embedded in thin hydrogel films, where intercellular communication is only possible via diffusing molecules, we conclude that gap junctions are required for synchronized and highly correlated responses among cells in high density colonies. In addition, in high density cell colonies, both communication channels lead to calcium oscillations following the stimulation by external ATP. While the calcium oscillations associated with cells directly exposed to external flows were transient, the oscillations of hydrogel trapped cells can persist with a fundamental frequency and higher harmonics. Our observations and measurements highlight the crucial role of intercellular signaling for generating regulated spatial and temporal dynamics in cell colonies and tissues.

Microfluidic synthesis of monodisperse porous microspheres with size-tunable pores

We use a perfluorinated-dendrimer–dye complex that stabilizes microbubbles as a novel pore-forming agent. We use microfluidics to produce monodisperse emulsions containing a polymer matrix material, a model active, and the perfluorinated complex; upon drying, the emulsions form porous microspheres. This porosity causes the encapsulated model active to be released faster than from non-porous microspheres. Moreover, because of the fluorous features of the pores, we can also attach an additional guest molecule to the pores which is released with a profile that is distinct from that of the encapsulated active. These porous microspheres can encapsulate and controllably release multiple actives; this makes them valuable for applications such as drug delivery and imaging.

Self-Assembly of Colloidal Cubes via Vertical Deposition

The vertical deposition technique for creating crystalline microstructures is applied for the first time to nonspherical colloids in the form of hollow silica cubes. Controlled deposition of the cubes results in large crystalline films with variable symmetry. The microstructures are characterized in detail with scanning electron microscopy and small-angle X-ray scattering. In single layers of cubes, distorted square to hexagonal ordered arrays are formed. For multilayered crystals, the intralayer ordering is predominantly hexagonal with a hollow site stacking, similar to that of the face centered cubic lattice for spheres. Additionally, a distorted square arrangement in the layers is also found to form under certain conditions. These crystalline films are promising for various applications such as photonic materials.

Transparent Conducting Silver Nanowire Networks

We present a transparent conducting electrode composed of a periodic two-dimensional network of silver nanowires. Networks of Ag nanowires are made with wire diameters of 45–110 nm and a pitch of 500, 700, and 1000 nm. Anomalous optical transmission is observed, with an averaged transmission up to 91% for the best transmitting network and sheet resistances as low as 6.5 Ω/sq for the best conducting network. Our most dilute networks show lower sheet resistance and higher optical transmittance than an 80 nm thick layer of ITO sputtered on glass. By comparing measurements and simulations, we identify four distinct physical phenomena that govern the transmission of light through the networks: all related to the excitation of localized surface plasmons and surface plasmon polaritons on the wires. The insights given in this paper provide the key guidelines for designing high-transmittance and low-resistance nanowire electrodes for optoelectronic devices, including thin-film solar cells. For the latter, we discuss the general design principles to use the nanowire electrodes also as a light trapping scheme.

Tunable metallic-like conductivity in microbial nanowire networks

Electronic nanostructures made from natural amino acids are attractive because of their relatively low cost, facile processing and absence of toxicity(1-3). However, most materials derived from natural amino acids are electronically insulating(1-6). Here, we report metallic-like conductivity in films of the bacterium Geobacter sulfurreducens(7) and also in pilin nanofilaments (known as microbial nanowires(8,9)) extracted from these bacteria. These materials have electronic conductivities of similar to 5 mS cm(-1), which are comparable to those of synthetic metallic nanostructures(2). They can also conduct over distances on the centimetre scale, which is thousands of times the size of a bacterium. Moreover, the conductivity of the biofilm can be tuned by regulating gene expression, and also by varying the gate voltage in a transistor configuration. The conductivity of the nanofilaments has a temperature dependence similar to that of a disordered metal, and the conductivity could be increased by processing.
 

Control of the length of microfibers

Uniform polymeric microfibers of prescribed lengths were synthesized in microfluidic devices using two different approaches—valve actuation and pulses of ultraviolet (UV) light. The more versatile valve approach was employed to demonstrate control of the length of the microfiber as a function of the frequency of valve actuation.

Magnetic field responsive silicone elastomer loaded with short steel wires having orientation distribution

We fabricated a magnetic field responsive silicone rubber–steel wire composite that exhibits large bending deformation under a magnetic field as weak as 0.2 T. The starting materials are commonly available, and the fabrication method is simple. The deformation is the result of the magnetic torque produced by the chosen orientation of short steel wires embedded in the elastomer matrix. This mechanism is confirmed by theoretical modelling. A strip of the composite exhibits a flexible motion of inchworm-like walking when it is subjected to repeated increases and decreases in the applied magnetic field.

Unexpected β-sheets and molecular orientation in flagelliform spider silk as revealed by Raman spectromicroscopy

Silk Materials – A Road to Sustainable High Technology

This review addresses the use of silk protein as a sustainable material in optics and photonics, electronics and optoelectronic applications. These options represent additional developments for this technology platform that compound the broad utility and impact of this material for medical needs that have been recently described in the literature. The favorable properties of the material certainly make a favorable case for the use of silk, yet serve as a broad inspiration to further develop biological foundries for both the synthesis and processing of Nature's materials for technological applications.

Molecular Logic with a Saccharide Probe on the Few-Molecules Level

In this Communication we describe a two-component saccharide probe with logic capability. The combination of a boronic acid-appended viologen and perylene diimide was able to perform a complementary implication/not implication logic function. Fluorescence quenching and recovery with fructose was analyzed with fluorescence correlation spectroscopy on the level of a few molecules of the reporting dye.

Nanotextured Silica Surfaces with Robust Superhydrophobicity and Omnidirectional Broadband Supertransmissivity

Designing multifunctional surfaces that have user-specified interactions with impacting liquids and with incident light is a topic of both fundamental and practical significance. Taking cues from nature, we use tapered conical nanotextures to fabricate the multifunctional surfaces; the slender conical features result in large topographic roughness, while the axial gradient in the effective refractive index minimizes reflection through adiabatic index-matching between air and the substrate. Precise geometric control of the conical shape and slenderness of the features as well as periodicity at the nanoscale are all keys to optimizing the multifunctionality of the textured surface, but at the same time, these demands pose the toughest fabrication challenges. Here we report a systematic approach to concurrent design of optimal structures in the fluidic and optical domains and a fabrication procedure that achieves the desired aspect ratios and periodicities with few defects and large pattern area. Our fabricated nanostructures demonstrate structural superhydrophilicity or, in combination with a suitable chemical coating, robust superhydrophobicity. Enhanced polarization-independent optical transmission exceeding 98% has also been achieved over a broad range of bandwidth and incident angles. These nanotextured surfaces are also robustly antifogging or self-cleaning, offering potential benefits for applications such as photovoltaic solar cells.

Crystallization Mechanisms in Convective Particle Assembly

Colloidal particles are continuously assembled into crystalline particle coatings using convective fluid flows. Assembly takes place inside a meniscus on a wetting reservoir. The shape of the meniscus defines the profile of the convective flow and the motion of the particles. We use optical interference microscopy, particle image velocimetry and particle tracking to analyze the particles’ trajectory from the liquid reservoir to the film growth front and inside the deposited film as a function of temperature. Our results indicate a transition from assembly at a static film growth front at high deposition temperatures to assembly in a precursor film with high particle mobility at low deposition temperatures. A simple model that compares the convective drag on the particles to the thermal agitation explains this behavior. Convective assembly mechanisms exhibit a pronounced temperature dependency and require a temperature that provides sufficient evaporation. Capillary mechanisms are nearly temperature independent and govern assembly at lower temperatures. The model fits the experimental data with temperature and particle size as variable parameters and allows prediction of the transition temperatures. While the two mechanisms are markedly different, dried particle films from both assembly regimes exhibit hexagonal particle packings. We show that films assembled by convective mechanisms exhibit greater regularity than those assembled by capillary mechanisms.

Novel 3D Wollastonite-Based Scaffolds from Preceramic Polymers Containing Micro- and Nano-Sized Reactive Particles

Wollastonite (CaSiO3) ceramics are well known biomaterials which can be produced using many different techniques. The present paper illustrates an innovative processing method employing preceramic polymers (silicone resins) containing CaCO3 micro- and nano-sized particles, which act as reactive fillers. Silica from the decomposition of the silicone resins reacts at low temperature with the CaO deriving from the fillers, yielding wollastonite ceramics. Hydroxyapatite powders can also be added, to modify the biological response of the material. This approach enables the fabrication of 3D scaffolds via fused deposition or via conventional hot extrusion.

Photoinduced Deformation of Crosslinked Liquid-Crystalline Polymer Film Oriented by a Highly Aligned Carbon Nanotube Sheet

Bending over backwards: A highly aligned carbon nanotube sheet orients crosslinked liquid-crystalline polymer through a simple melting process (see picture). The resulting composite film can be rapidly bent and unbent by alternate irradiation with UV and visible light. The film also exhibits excellent mechanical and electrical properties due to the incorporation of aligned CNTs.

A Strong Bio-Inspired Layered PNIPAM–Clay Nanocomposite Hydrogel

Inspired by nacre, a layered poly(N-isopropylacrylamide)–clay nanocomposite hydrogel was successfully fabricated by combination of vacuum-filtration self-assembly and photo-initiated in situ polymerization. This bio-inspired layered nanocomposite hydrogel shows excellent mechanical properties, which can rival some biological soft tissues (see picture).

Force–Reactivity Property of a Single Monomer Is Sufficient To Predict the Micromechanical Behavior of Its Polymer

We demonstrate an accurate prediction of the micromechanical behavior of a single chain of cyclopropanated polybutadiene, which is governed by rapid isomerization of the cyclopropane moieties at 1.2 nN, from the force–rate correlation of this reaction measured in a small series of increasingly strained macrocycles. The data demonstrate that a single physical quantity, force, uniquely defines the dynamics across length scales from >100 to <1 nm and that strain imposed through molecular design and that imposed by micromanipulation techniques have equivalent effects on the kinetics of a chemical reaction. This represents a new method of screening potential monomers for applications in stress-responsive materials that could also facilitate atomistic interpretations of single-molecule force experiments.

Carbon Nanotubes in the Liquid Phase: Addressing the Issue of Dispersion

The inherent size and hollow geometry with extraordinary electronic and optical properties make carbon nanotubes (CNTs) promising building blocks for molecular or nanoscale devices. Unfortunately, their hydrophobic nature and their existence in the form of agglomerated and parallel bundles make this interesting material inadequately soluble or dispersible in most of the common solvents, which is crucial to their processing. Therefore, various ingenious techniques have been reported to disperse the CNTs in various solvents with different experimental conditions. However, by analyzing the published scientific research articles, it is evident that there is an important issue or misunderstanding between the term “dispersion” and “solubilization”. As a result many researchers use the terms interchangeably, particularly when stating the interaction of CNTs with liquids, which causes confusion among the readers, students, and researchers. In this article, this fundamental issue is addressed in order to give basic insight to the researchers who are working with CNTs, as well as to the scientists who deal with nano-related research domains.

Stoichiometric Self-Assembly of Isomeric, Shape-Persistent, Supramacromolecular Bowtie and Butterfly Structures

 Two novel macromolecular constitutional isomers have been self-assembled from previously unreported terpyridine ligands in a three-component system. The terpyridine ligands were synthesized in high yields via a key Suzuki coupling. Restrictions of the possible outcomes for self-assembly ultimately provided optimum conditions for isolation of either a molecular bowtie or its isomeric butterfly motif. These isomers have been characterized by ESI-MS, TWIM-MS, ¹H NMR, and ¹³C NMR. Notably, these structural isomers have remarkably different drift times in ion mobility separation, corresponding to different sizes and shapes at high charge states.

Colloidal crystallization in the quasi-two-dimensional induced by electrolyte gradients

We investigated driven crystal formation events in thin layers of sedimented colloidal particles under low salt conditions. Using optical microscopy, we observe particles in a thermodynamically stable colloidal fluid to move radially converging towards cation exchange resin fragments acting as seed particles. When the local particle concentration has become sufficiently large, subsequently crystallization occurs. Brownian dynamics simulations of a 2D system of purely repulsive point-like particles exposed to an attractive potential, yield strikingly similar scenarios, and kinetics of accumulation and micro-structure formation. This offers the possibility of flexibly designing and manufacturing thin colloidal crystals at controlled positions and thus to obtain specific micro-structures not accessible by conventional approaches. We further demonstrate that particle motion is correlated with the existence of a gradient in electrolyte concentration due to the release of electrolyte by the seeds.

Re-entrant melting as a design principle for DNA-coated colloids

Colloids functionalized with DNA hold great promise as building blocks for complex self-assembling structures. However, the practical use of DNA-coated colloids (DNACCs) has been limited by the narrowness of the temperature window where the target structures are both thermodynamically stable and kinetically accessible1, 2, 3, 4, 5. Here we propose a strategy to design DNACCs, whereby the colloidal suspensions crystallize on cooling and then melt on further cooling. In a phase diagram with such a re-entrant melting, kinetic trapping of the system in non-target structures should be strongly suppressed. We present model calculations and simulations that show that real DNA sequences exist that should bestow this unusual phase behaviour on suitably functionalized colloidal suspensions. We present our results for binary systems, but the concepts that we develop apply to multicomponent systems and should therefore open the way towards the design of truly complex self-assembling colloidal structures.

Paper-Based, Capacitive Touch Pads

Metallized paper is patterned to create touch pads of arrayed buttons that are sensitive to contact with both bare and gloved fingers. The paper-based keypad detects the change in capacitance associated with the touch of a finger to one of its buttons. Mounted on an alarmed cardboard box, the keypad requires the appropriate sequence of touches to disarm the system.

 

Rapidly in situ forming polyphosphoester-based hydrogels for injectable drug delivery carriers

In situ forming hydrogels allow the modulation of physicochemical properties and are providing new opportunities for biomedical applications. Here, the preparation and characterization of a series of rapidly in situ forming and pH-responsive hydrogels with different crosslinking degrees are reported, which were achieved by accelerated free radical copolymerization of polyphosphoester-based macrocrosslinker and 2-(dimethylamino)ethyl methacrylate (DMAEMA) monomer. The hydrogel formation can be completed very quickly under mild conditions, ranging from several to tens of minutes with varying concentrations of components. The polyphosphoester-based macrocrosslinker was synthesized via a combination of ring-opening polymerization and post-polymerization modification, and it was characterized by 1H NMR, 31P NMR, and GPC measurements. The sol–gel transition was monitored by dynamic time sweep rheological analysis. Moreover, the swelling kinetics, interior morphology, pH-responsive property, in vitro cytotoxicity and drug release of these hydrogels were characterized. The results indicate that these hydrogels show great potential as injectable drug delivery system.

Biotemplated Synthesis of Perovskite Nanomaterials for Solar Energy Conversion

 
A synthetic method of using genetically engineered M13 virus to mineralize perovskite nanomaterials, particularly strontium titanate (STO) and bismuth ferrite (BFO), is presented. Genetically engineered viruses provide effective templates for perovskite nanomaterials. The virus-templated nanocrystals are small in size, highly crystalline, and show photocatalytic and photovoltaic properties.

Pattern Formation in Nature: Physical Constraints and Self-Organising Characteristics

Pattern formations are apparent in natural systems ranging from clouds to animal markings, and from sand dunes to shells of microscopic marine organisms. Despite the astonishing range and variety of such structures, many have comparable features. In this article, Philip Ball reviews some of the common patterns found in nature. He explains how they are typically formed through simple, local interactions between many components of a system – a form of physical computation that gives rise to self-organisation and emergent structures and behaviours.

Design to Self-Assembly

The increasing power of design software, the widespread availability of digital fabrication and growing complexity of our built environment are in stark contrast to the inefficient techniques that currently plague the construction industry. Today's processes of assembly can be fundamentally re-imagined by looking at biological systems that are building structures with far more complexity, information capacity and assembly instructions than even the most advanced structures possible with current technologies. Skylar Tibbits explains that the key ingredient embedded within these natural systems is self-assembly. He outlines four principles for designing systems that build themselves, and shows a number of projects that demonstrate first steps towards this new mode of architectural production.

Programming Matter

A direct parallel can be made between the Modernist separation of form, structure and material and the more recent tripartite division in digital processes of modelling, analysis and fabrication, which has resulted in the predominance of geometric-driven form-generation. Today, though, design culture is experiencing a shift to a new level of material awareness. Inspired by nature's strategies where form-generation is driven by maximal performance with minimal resources through local material property variation, Neri Oxman investigates a novel design approach to digital fabrication that offers the potential to program physical matter.

Monodisperse Gas-Filled Microparticles from Reactions in Double Emulsions

We present a strategy for preparing size-controlled gas-filled microparticles using two aqueous components that chemically react to produce the gas. We use a dual-bore microfluidic device to isolate the reactants of two gas-producing reactions until they are encapsulated in the outer droplet. The reactants in the monodisperse droplets merge and produce the gas bubbles, which are stabilized with a surfactant and form the core of the microparticles. The number and size of the generated gas bubbles are governed by the gas-forming reaction used. Our versatile strategy can be applied to a wide range of gas-producing reactions.

Zipping Effect on Omniphobic Surfaces for Controlled Deposition of Minute Amounts of Fluid or Colloids

When a drop sits on a highly liquid-repellent surface (super-hydrophobic or super-omniphobic) made of periodic micrometer-sized posts, its contact-line can recede with very weak mechanical retention providing that the liquid stays on top of the microsized posts. Occurring in both sliding and evaporation processes, the achievement of low-contact-angle hysteresis (low retention) is required for discrete microfluidic applications involving liquid motion or self-cleaning; however, careful examination shows that during receding, a minute amount of liquid is left on top of the posts lying at the receding edge of the drop. For the first time, the heterogeneities of these deposits along the drop-receding contact-line are underlined. Both nonvolatile liquid and particle-laden water are used to quantitatively characterize what rules the volume distribution of deposited liquid. The experiments suggest that the dynamics of the liquid de-pinning cascade is likely to select the volume left on a specific post, involving the pinch-off and detachment of a liquid bridge. In an applied prospective, this phenomenon dismisses such surfaces for self-cleaning purposes, but offers an original way to deposit controlled amounts of liquid and (bio)-particles at well-targeted locations.

Carbon Nanomaterials for Advanced Energy Conversion and Storage

It is estimated that the world will need to double its energy supply by 2050. Nanotechnology has opened up new frontiers in materials science and engineering to meet this challenge by creating new materials, particularly carbon nanomaterials, for efficient energy conversion and storage. Comparing to conventional energy materials, carbon nanomaterials possess unique size-/surface-dependent (e.g., morphological, electrical, optical, and mechanical) properties useful for enhancing the energy-conversion and storage performances. During the past 25 years or so, therefore, considerable efforts have been made to utilize the unique properties of carbon nanomaterials, including fullerenes, carbon nanotubes, and graphene, as energy materials, and tremendous progress has been achieved in developing high-performance energy conversion (e.g., solar cells and fuel cells) and storage (e.g., supercapacitors and batteries) devices. This article reviews progress in the research and development of carbon nanomaterials during the past twenty years or so for advanced energy conversion and storage, along with some discussions on challenges and perspectives in this exciting field.

Reductively Responsive siRNA-Conjugated Hydrogel Nanoparticles for Gene Silencing

 

A critical need still remains for effective delivery of RNA interference (RNAi) therapeutics to target tissues and cells. Self-assembled lipid- and polymer-based systems have been most extensively explored for transfection with small interfering RNA (siRNA) in liver and cancer therapies. Safety and compatibility of materials implemented in delivery systems must be ensured to maximize therapeutic indices. Hydrogel nanoparticles of defined dimensions and compositions, prepared via a particle molding process that is a unique off-shoot of soft lithography known as particle replication in nonwetting templates (PRINT), were explored in these studies as delivery vectors. Initially, siRNA was encapsulated in particles through electrostatic association and physical entrapment. Dose-dependent gene silencing was elicited by PEGylated hydrogels at low siRNA doses without cytotoxicity. To prevent disassociation of cargo from particles after systemic administration or during postfabrication processing for surface functionalization, a polymerizable siRNA pro-drug conjugate with a degradable, disulfide linkage was prepared. Triggered release of siRNA from the pro-drug hydrogels was observed under a reducing environment while cargo retention and integrity were maintained under physiological conditions. Gene silencing efficiency and cytocompatibility were optimized by screening the amine content of the particles. When appropriate control siRNA cargos were loaded into hydrogels, gene knockdown was only encountered for hydrogels containing releasable, target-specific siRNAs, accompanied by minimal cell death. Further investigation into shape, size, and surface decoration of siRNA-conjugated hydrogels should enable efficacious targeted in vivo RNAi therapies.

Multifunctional Nanoparticle-Loaded Spherical and Wormlike Micelles Formed by Interfacial Instabilities

Hybrid spherical and wormlike amphiphilic block copolymer micelles are formed through evaporation-induced interfacial instabilities of emulsion droplets, allowing for incorporation of pre-synthesized hydrophobic inorganic nanoparticles within the micelle cores, as well as co-encapsulation of different nanoparticles. This encapsulation behavior is largely insensitive to particle surface chemistry, shape, and size, thus providing a versatile route to fabricate multifunctional micelles.

Diblock-Copolymer-Coated Water- and Oil-Repellent Cotton Fabrics

A diblock copolymer consisting of a sol–gel-forming block and a fluorinated block was used to coat cotton fabrics, yielding textiles that were highly oil- and water-repellent. The coating procedure was simple. At grafted polymer amounts of as low as 1.0 wt %, water, diodomethane, hexadecane, cooking oil, and pump oil all had contact angles surpassing 150° on the coated cotton fabrics and were readily rolled. The liquids were not drawn into the interfiber space by the coated fabrics. Rather, droplets of the nonvolatile liquids such as cooking oil retained their beaded shapes for months with minimal contact angle changes. When forced into water, the coated fabrics trapped an air or plastron layer and this plastron layer was stable for months. In addition, the coating had high stability against simulated washing, and the mechanical properties were essentially identical to those of uncoated cotton fabrics.

Directed Orientation of Asymmetric Composite Dumbbells by Electric Field Induced Assembly

Assembly and directed orientation of anisotropic particles with an external ac electric field in a range from 1 kHz to 2 MHz were studied for asymmetric composite dumbbells incorporating a silica, titania, or titania/silica (titania:silica = 75:25 vol %) sphere. The asymmetric composite dumbbells, which were composed of a polymethylmethacrylate (PMMA)-coated sphere (core–shell part) and a polystyrene (PSt) lobe, were synthesized with a soap-free emulsion polymerization to prepare PMMA-coated inorganic spheres and another soap-free emulsion polymerization to form a polystyrene (PSt) lobe from the PMMA-coated inorganic spheres. The composite dumbbells dispersed in water were directly observed with optical microscopy. The dumbbells incorporating a silica sphere oriented parallel to an electric field in the whole frequency range and they formed a pearl chain structure at a high frequency of 2 MHz. The titania-incorporated dumbbells formed chain structures, in which they contacted their core–shell parts and oriented perpendicularly to a low-frequency (kHz) field, whereas they oriented parallel to a high-frequency (MHz) field. Since the alignment of dumbbells in the chains depends not only on the interparticle forces but also on the torque that the induced dipoles in the dumbbells experience in the electric field, the orientation of dumbbells perpendicular to the electric field was the case dominated by the interparticle force, whereas the other orientation was the case dominated by the torque. The present experiments show that the incorporation of inorganic dumbbells is an effective way to control the assembled structure and orientation with an electric field.

Superparamagnetic cellulose fiber networks via nanocomposite functionalization

We present a simple and cost-effective method for rendering networks of cellulose fibers, such as paper, fabrics or membranes, superparamagnetic by impregnating the individual fibers with a reactive acrylic monomer. The cellulose fibers are wetted by a cyanoacrylate monomer solution containing superparamagnetic manganese ferrite colloidal nanoparticles. Upon moisture initiated polymerization of the monomer on the fiber surfaces, a thin nanocomposite shell forms around each fiber. The nanocomposite coating renders the cellulose fibers water repellent and magnetically responsive. Magnetic and microscopy studies prove that the amount of the entrapped nanoparticles in the nanocomposite shell is fully controllable, and that the magnetic response is directly proportional to this amount. A broad range of applications can be envisioned for waterproof magnetic cellulose materials (such as magnetic paper/tissues) obtained by such a simple yet highly efficient method.

Polymer/nucleotide droplets as bio-inspired functional micro-compartments

Using a range of physical methods, we describe the formation, structure, stability, physical properties and uptake behavior of condensed liquid micro-droplets prepared by electrostatically induced complexation of poly(diallyldimethylammonium) chloride (PDDA) and adenosine triphosphate (ATP) in water. Depending on the PDDA monomer: ATP molar ratio, positively charged or charge-neutral droplets are produced spontaneously by simple mixing. The former are typically 60–600 nm in mean size and stable with respect to sedimentation up to temperatures of 85 °C, whilst the latter grow into droplets several tens of micrometres in diameter that coalesce into a macroscopic coacervate phase. Coacervation is inhibited at pH values less than 3 and at high ionic strength, confirming the importance of charge interactions in droplet formation and stability. The droplet interior is structurally homogeneous with no surrounding membrane, comprises dynamically fluctuating domains of partially desolvated polymer/nucleotide complexes, and has a dielectric constant considerably lower than water. As a consequence, dye molecules, porphyrin macrocycles, inorganic nanoparticles or globular proteins can be sequestered from the external water phase into the droplets to produce PDDA/ATP droplets comprising supramolecular J-aggregate nanostructures, magnetically responsive deformable fluids, or soft compartments with potential storage and release properties.

Microrheology of biomaterial hydrogelators

Microrheology uses the motion of dispersed colloidal probe particles to measure the viscosity or viscoelastic moduli of soft materials. The distinct advantages of microrheology include small sample volume requirements, access to a large range of time scales for the dynamic response and short acquisition times. These advantages make microrheology important for studies of biomaterial hydrogelators. Recent advances have enabled the precise characterization of hydrogelator sol–gel transitions, measurements of rare and scarce materials and high-throughput screening of hydrogel rheology over a large composition space. In this review, we focus on multiple particle tracking microrheology, including the considerations that define its operating regimes and its recent applications. Those interested in biomaterial rheology will find these methods as accessible as bulk rheological measurements and straightforward to implement in their own work.