Formation and mechanics of fire ant rafts as an active self-healing membrane.

The unique ability of fire ants to form a raft to survive flooding rain has enchanted biologists as well as researchers in other disciplines. It was established during the last decade that a three-dimensional aggregation of fire ants exhibits viscoelasticity with respect to external compression and shearing among numerous unusual mechanical properties. Continuing these works, we will study the ant raft in its natural form, i.e., composing no more than two layers. This allowed us to focus on the cracks that are unique to membranes and see how their patterns are influenced by the fact that these ants are mobile and can self-repair the damage to keep their raft from disintegration. In the beginning, we show that vertical and horizontal shaking can also prompt fire ants to aggregate. The canonical view that the stability of ant raft relies on the Cheerios effect and a combination of other parameters is tested. The force-displacement experiment is performed to show that two distinct mechanical responses and fracture patterns, characteristic of ductile and brittle materials, can be elicited, depending on the magnitude of the pull speed. During the process, we counted the number of ants that actively participated in the stress-strain relation and used this information to roughly sketch out the force chain. The latter information reveals that the pull force expedites the alignment of fire ants, in analogy to the effect of an electric field on liquid crystal polymers. To highlight the self-healing nature, we employ the creep experiment to study how the length and Young's modulus of the raft change or relax with time. One major finding is that the raft can exhibit zero Poisson's ratio without resorting to specific geometry structures. This is enabled by the active recruitment of ants from the top layer to the bottom layer to keep the raft from disintegrating.

Metal-Organic Framework as a New Type of Magnetothermally-Triggered On-Demand Release Carrier.

The development of external stimuli-controlled payload systems has been sought after with increasing interest toward magnetothermally-triggered drug release (MTDR) carriers due to their non-invasive features. However, current MTDR carriers present several limitations, such as poor heating efficiency caused by the aggregation of iron oxide nanoparticles (IONPs) or the presence of antiferromagnetic phases which affect their efficiency. Herein, a novel MTDR carrier is developed using a controlled encapsulation method that fully fixes and confines IONPs of various sizes within the metal-organic frameworks (MOFs). This novel carrier preserves the MOF's morphology, porosity, and IONP segregation, while enhances heating efficiency through the oxidation of antiferromagnetic phases in IONPs during encapsulation. It also features a magnetothermally-responsive nanobrush that is stimulated by an alternating magnetic field to enable on-demand drug release. The novel carrier shows improved heating, which has potential applications as contrast agents and for combined chemo and magnetic hyperthermia therapy. It holds a great promise for magneto-thermally modulated drug dosing at tumor sites, making it an exciting avenue for cancer treatment.

From materials to clinical use: advances in 3D-printed scaffolds for cartilage tissue engineering.

Osteoarthritis caused by articular cartilage defects is a particularly common orthopedic disease that can involve the entire joint, causing great pain to its sufferers. A global patient population of approximately 250 million people has an increasing demand for new therapies with excellent results, and tissue engineering scaffolds have been proposed as a potential strategy for the repair and reconstruction of cartilage defects. The precise control and high flexibility of 3D printing provide a platform for subversive innovation. In this perspective, cartilage tissue engineering (CTE) scaffolds manufactured using different biomaterials are summarized from the perspective of 3D printing strategies, the bionic structure strategies and special functional designs are classified and discussed, and the advantages and limitations of these CTE scaffold preparation strategies are analyzed in detail. Finally, the application prospect and challenges of 3D printed CTE scaffolds are discussed, providing enlightening insights for their current research.

Recent Progress of Droplet Microfluidic Emulsification Based Synthesis of Functional Microparticles.

The remarkable control function over the functional material formation process enabled by droplet microfluidic emulsification approaches can lead to the efficient and one-step encapsulation of active substances in microparticles, with the microparticle characteristics well regulated. In comparison to the conventional fabrication methods, droplet microfluidic technology can not only construct microparticles with various shapes, but also provide excellent templates, which enrich and expand the application fields of microparticles. For instance, intersection with disciplines in pharmacy, life sciences, and others, modifying the structure of microspheres and appending functional materials can be completed in the preparation of microparticles. The as-prepared polymer particles have great potential in a wide range of applications for chemical analysis, heavy metal adsorption, and detection. This review systematically introduces the devices and basic principles of particle preparation using droplet microfluidic technology and discusses the research of functional microparticle formation with high monodispersity, involving a plethora of types including spherical, nonspherical, and Janus type, as well as core-shell, hole-shell, and controllable multicompartment particles. Moreover, this review paper also exhibits a critical analysis of the current status and existing challenges, and outlook of the future development in the emerging fields has been discussed.

MWCNTs-GNPs Reinforced TPU Composites with Thermal and Electrical Conductivity: Low-Temperature Controlled DIW Forming.

As an effective technique for fabricating conductive and thermally conductive polymer composites, a multi-filler system incorporates different types and sizes of multiple fillers to form interconnected networks with improved electrical, thermal, and processing properties. In this study, DIW forming of bifunctional composites was achieved by controlling the temperature of the printing platform. The study was based on enhancing the thermal and electrical transport properties of hybrid ternary polymer nanocomposites with multi-walled carbon nanotubes (MWCNTs) and graphene nanoplates (GNPs). With thermoplastic polyurethane (TPU) used as the matrix, the addition of MWCNTs, GNPs and both mixtures further improved the thermal conductivity of the elastomers. By adjusting the weight fraction of the functional fillers (MWCNTs and GNPs), the thermal and electrical properties were gradually explored. Here, the thermal conductivity of the polymer composites increased nearly sevenfold (from 0.36 W·m-1·k-1 to 2.87 W·m-1·k-1) and the electrical conductivity increased up to 5.49 × 10-2 S·m-1. It is expected to be used in the field of electronic packaging and environmental thermal dissipation, especially for modern electronic industrial equipment.

Core-Shell-Structured Electrorheological Fluid with a Polarizability-Tunable Nanocarbon Shell for Enhanced Stimuli-Responsive Activity.

The incorporation of nanocarbon-based materials into electrorheological fluids has been shown to be an effective means of improving the electrorheological (ER) response. However, the mechanism of the sp2/sp3-hybridized carbon structure and high ER response is still under investigation. Herein, barium titanate@nanocarbon shell (BTO@NCs) composites are proposed and prepared by introducing carbonized polydopamine (C-PDA) into a shell. When the polymerization time of dopamine is tuned, the shell thickness, surface polar functional groups, and sp2/sp3-hybridized carbon can be effectively controlled. The maximum yield stress of the BTO@NCs-24 h ER fluid reaches 2.5 kPa under an electric field of 4 kV mm-1, which is attributed to the increased content of sp3 C-OH and oxygenous functional groups within the shell, resulting in a rapidly achievable polarization. Furthermore, the SiO2@NCs and TiO2@NCs ER fluids are also prepared with enhanced ER behavior in these phenomena, confirming an approach to high-performance ER fluids based on nanocarbon composites.

Variable Stiffness Conductive Composites by 4D Printing Dual Materials Alternately.

Materials that can be designed with programmable properties and which change in response to external stimuli are of great importance in numerous fields of soft actuators, involving robotics, drug delivery and aerospace applications. In order to improve the interaction of human and robots, materials with variable stiffness are introduced to develop their compliance. A variable stiffness composite has been investigated in this paper, which is composed of liquid metals (LMs) and silicone elastomers. The phase changing materials (LMs) have been encapsulated into silicone elastomer by printing the dual materials alternately with three-dimensional direct ink writing. Such composites enable the control over their own stiffness between soft and rigid states through LM effective phase transition. The tested splines demonstrated that the stiffness changes approximately exceeded 1900%, and the storage modulus is 4.75 MPa and 0.2 MPa when LM is rigid and soft, respectively. In the process of heating up, the stretching strain can be enlarged by at least three times, but the load capacity is weakened. At a high temperature, the resistance of the conductive composites changes with the deformation degree, which is expected to be applied in the field of soft sensing actuators.

Aging-induced dynamics for statically indeterminate systems.

Statically indeterminate systems are experimentally demonstrated to be in fact dynamical. Take the classic problems of a beam with three supporting points, granules in a silo, and a ladder leaning against a wall, for instance; their reaction forces are found to vary logarithmically for over 10^{4}s with an increment or decrement of more than 10%. This seemingly contradictory mixture of dynamics for a static system is shown to derive from the evolution of microcontact area with the ground and/or wall due to the aging effect.

Phase diagram and snap-off transition for twisted party balloons.

Many of us have the experience of inflating balloons and twisting them into different shapes and animals. Snapping the balloon into two separate compartments is a necessary step that bears resemblance to the pinch-off phenomenon when a water droplet detaches from the faucet. In addition to testing whether balloons exhibit the properties of self-similarity and memory effect that are often associated with the latter event, we determine their phase diagram by experiments. It turns out that a common party balloon does not just snap, but can assume five more shapes, i.e., straight, necking, wrinkled, helix, and supercoil, depending on the twist angle and ratio of its length and diameter. Moreover, history also matters due to their prominent hysteresis. One may shift the phase boundary and/or reshuffle the phases by untwisting or lengthening the balloon at different twist angle and initial length. A heuristic minimal model is provided to obtain analytic expressions for the phase boundaries.

Role of the crown in tree resistance against high winds.

Rather than using wooden sticks to simulate the breakage of trees in high winds as in most research, we employ fresh samples from camphor and Formosa gum with branches and leaves to certify the crucial role of the tree crown. By using a blowdown wind tunnel with a maximum wind speed of 50 m/s, we purposely reduce the number of leaves and show that the drag force will drop by as much as two thirds when half pruned. Based on real observations, we model the leaf by an open and full cone in the presence of light and strong winds, and calculate how their corresponding cross-sectional area A and drag force F vary with wind speed v. Different slopes before and after the formation of a full cone are predicted and confirmed when these two quantities are plotted in full-log scale. Compared to the empirical value, our simple model gave α=2/5 and 2/3 for A∝v^{-α} and ß=4/5 and 2/3 for F∝v^{ß} at low and high winds. Discrepancies can be accounted for by including further details, such as the reorientation of open cones and the movement of branches.

Electrorheological Fluids with High Shear Stress Based on Wrinkly Tin Titanyl Oxalate.

Electrorheological (ER) fluids are considered as a type of smart fluids because their rheological characteristics can be altered through an electric field. The discovery of giant ER effect revived the researchers' interest in the ER technological area. However, the poor stability including the insufficient dynamic shear stress, the large leakage current density, and the sedimentation tendency still hinders their practical applications. Herein, we report a facile and scalable coprecipitation method for synthesizing surfactant-free tin titanyl oxalate (TTO) particles with tremella-like wrinkly microstructure (W-TTO). The W-TTO-based ER fluids exhibit enhanced ER activity compared to that of the pristine TTO because of the improved wettability between W-TTO and the silicone oil. In addition, the static yield stress and leakage current of W-TTO ER fluids also show a fine time stability during the 30 day tests. More importantly, the dynamic shear stress of W-TTO ER fluids can remain stable throughout the shear rate range, which is valuable for their use in engineering applications. The results in this work provided a promising strategy to solving the long-standing problem of ER fluid stability. Moreover, this convenient route of synthesis may be considered a green approach for the mass production of giant ER materials.

An Optimized and Feasible Preparation Technique for the Industrial Production of Hydrogel Patches.

For hydrogel patches, the laboratory tests could not fully reveal the existing problems of full scale of industrial production, and there are few studies about the preparation technique for the industrial manufacturing process of hydrogel patches. So, the purpose of this work was to elucidate the effects of mainly technological operation and its parameters on the performance of hydrogel patches at the industrial-scale production. The results revealed the following: (1) the aqueous phase was obtained by polyvinylpyrrolidone (PVP) along with tartaric acid dissolved in purified water, then feeding this into a vacuum mixer as a whole in one batch, thus extended the crosslinking reaction time of hydrogel paste (matrix) and allowed the operation of coating/cutting-off to be carried out easily, and there was no permeation of backing layer; (2) the gel strength of the hydrogel patches increased with the increase of working temperature, however, once the temperature exceeded 35 ± 2 °C, the hydrogel paste would lose water severely and the resultant physical crosslinking structure which has lower gel/cohesive strength would easily bring gelatinization/residues during application; (3) the relative humidity (RH) of the standing-workshop was dynamically controlled (namely at 35 ± 2 °C, keeping the RH at 55 ± 5% for 4 days, then 65 ± 5% for 2 days), which would make patches with satisfactory characteristics such as better flexibility, higher adhesive force, smooth flat matrix surface, and without gelatinization/residues and warped edge during the using process; (4) the aging of the packaged hydrogel patches was very sensitive to storage temperature, higher temperature, higher gel strength and lower adhesiveness. The storage temperature of 10 ± 2 °C could effectively prevent matrix aging and adhesion losing, which would also facilitate the expiration date of patches extended obviously. In conclusion, this work provides an optimized and feasible preparation technique for the industrial production of the hydrogel patches and establishes the hydrogel patches as a novel carrier for transdermal drug delivery.

Postsynthetically Modified Covalent Organic Frameworks for Efficient and Effective Mercury Removal.

A key challenge in environmental remediation is the design of adsorbents bearing an abundance of accessible chelating sites with high affinity, to achieve both rapid uptake and high capacity for the contaminants. Herein, we demonstrate how two-dimensional covalent organic frameworks (COFs) with well-defined mesopore structures display the right combination of properties to serve as a scaffold for decorating coordination sites to create ideal adsorbents. The proof-of-concept design is illustrated by modifying sulfur derivatives on a newly designed vinyl-functionalized mesoporous COF (COF-V) via thiol-ene "click" reaction. Representatively, the material (COF-S-SH) synthesized by treating COF-V with 1,2-ethanedithiol exhibits high efficiency in removing mercury from aqueous solutions and the air, affording Hg2+ and Hg0 capacities of 1350 and 863 mg g-1, respectively, surpassing all those of thiol and thioether functionalized materials reported thus far. More significantly, COF-S-SH demonstrates an ultrahigh distribution coefficient value (Kd) of 2.3 × 109 mL g-1, which allows it to rapidly reduce the Hg2+ concentration from 5 ppm to less than 0.1 ppb, well below the acceptable limit in drinking water (2 ppb). We attribute the impressive performance to the synergistic effects arising from densely populated chelating groups with a strong binding ability within ordered mesopores that allow rapid diffusion of mercury species throughout the material. X-ray absorption fine structure (XAFS) spectroscopic studies revealed that each Hg is bound exclusively by two S via intramolecular cooperativity in COF-S-SH, further interpreting its excellent affinity. The results presented here thus reveal the exceptional potential of COFs for high-performance environmental remediation.

Propylene glycol-embodying deformable liposomes as a novel drug delivery carrier for vaginal fibrauretine delivery applications.

The purpose of this work was to develop and characterize the fibrauretine (FN) loaded propylene glycol-embodying deformable liposomes (FDL), and evaluate the pharmacokinetic behavior and safety of FDL for vaginal drug delivery applications. FDL was characterized for structure, particle size, zeta potential, deformability and encapsulation efficiency; the ability of FDL to deliver FN across vagina tissue in vitro and the distribution behavior of FN in rat by vaginal drug delivery were investigated, the safety of FDL to the vagina of rabbits and rats as well as human vaginal epithelial cells (VK2/E6E7) were also evaluated. Results revealed that: (i) the FDL have a closed spherical shape and lamellar structure with a homogeneous size of 185±19nm, and exhibited a negative charge of -53±2.7mV, FDL also have a good flexibility with a deformability of 92±5.6 (%phospholipids/min); (ii) the dissolving capacity of inner water phase and hydrophilicity of phospholipid bilayers of deformable liposomes were increased by the presence of propylene glycol, this may be elucidated by the fluorescent probes both lipophilic Nile red and hydrophilic calcein that were filled up the entire volume of the FDL uniformly, so the FDL with a high entrapment capacity (were calculated as percentages of total drug) for FN was 78±2.14%; (iii) the permeability of FN through vaginal mucosa was obviously improved by propylene glycol-embodying deformable liposomes, no matter whether the FN loaded in liposomes or not, although FN loaded in liposomes caused the highest permeability and drug reservoir in vagina; (iv) the FN mainly aggregated in the vagina and uterus, then the blood, spleen, liver, kidney, heart and lungs for vaginal drug delivery, this indicating vaginal delivery of FDL have a better 'vaginal local targeting effect'; and (v) the results of safety evaluation illustrate that the FDL is non-irritant and well tolerated in vivo, thereby establishing its vaginal drug delivery potential. These results indicate that the propylene glycol-embodying deformable liposomes may be a promising drug delivery carrier for vaginal delivery of fibrauretine.

CTAB micelles assisted rGO-AgNP hybrids for SERS detection of polycyclic aromatic hydrocarbons.

A structure of hexadecyl trimethyl ammonium bromide (CTAB) micelle-assisted reduced graphene oxide-Ag nanoparticle (rGO-AgNP) hybrids is designed and fabricated for SERS detection of nonpolar polycyclic aromatic hydrocarbons (PAHs), in which CTAB micelles act as the host material to capture PAH molecules. This method provides stable aqueous suspensions of functionalized graphene with an alkyl chain, since the rGO-AgNP hybrids do not need to be pre-modified by CTAB. The result shows that the CTAB-assisted rGO-AgNP substrate has excellent SERS performance toward PAHs and ideal stability under continuous laser radiation. With further optimization, the detection limits of pyrene and perylene were 10(-6) M and 10(-7) M, respectively. Two different PAH molecules could be detected simultaneously by their characteristic peaks.

Fabrication of graphene oxide/Ag hybrids and their surface-enhanced Raman scattering characteristics.

A kind of surface-enhanced Raman scattering (SERS) substrate with high sensitivity was prepared via covalent assembly between silver nanoparticles (AgNPs) and graphene oxide (GO) sheets. With the high specific surface area, GO sheets can adsorb plenty of AgNPs; moreover, these adsorbed AgNPs formed some gathered state which can generate more hot spots of SERS. 4-Mercaptopyridine (4-MPY) was used to evaluate the SERS performance of the as-prepared substrate. The Raman enhancement factor (EF) of 4-MPY on the GO/AgNPs hybrids was up to 5.04×10(7), and the detection limit was estimated to be as low as 1 nM. The result showed that GO/AgNPs hybrids can produce stronger signals compared to silver colloids.

The influence of high dielectric constant core on the activity of core-shell structure electrorheological fluid.

The core-shell structural dielectric particles are applied widely in the electrorheological (ER) fluids. The properties of the dielectric core are critical factors influencing their ER activity. In this paper, we successfully synthesized two kinds of core-shell hydroxyl titanium oxalate (TOC) particles with SiO(2) and TiO(2) as core, respectively. The obtained core-shell structural SiO(2)-TOC and TiO(2)-TOC particles were well-dispersed spherical nanoparticles with ideal morphology and a narrow size distribution. Under DC electric fields, the TiO(2)-TOC ER fluid showed notable ER activity with a yield stress of about 96 kPa (at 4 kV/mm), which is 3 times of that SiO(2)-TOC ER fluid and outclassed the yield stress of the TOC ER fluid. The dielectric spectra indicated that the higher dielectric constant of TiO(2) core induces the stronger interaction between the neighboring particles, which contribute to the enhancement of ER activity.

Fabrication of uniform core-shell structural calcium and titanium precipitation particles and enhanced electrorheological activities.

A simple co-precipitation route was developed to synthesize uniform core-shell structured calcium and titanium precipitation (CTP) particles with ideal morphology and no aggregation. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), and interface tension/contact angle (CA) measurement were utilized to characterize the components, structure, morphology, and wettability of the SiO(2)-CTP materials. The obtained core-shell structural SiO(2)-CTP particles were well dispersed spherical nanoparticles with a narrow size distribution. The electrorheological (ER) properties were studied by the shear stress under various electric fields. The SiO(2) (2.3 wt%)-CTP ER fluid showed notable ER activity with a shear stress of about 109 kPa (at 5 kV mm(-1)), which outclassed the shear stress (65 kPa) of the CTP ER fluid. The ER properties of samples can be tuned by a few factors in the experimental process, such as the concentration of SiO(2) particles and citric acid, pointing out the great potential for application of this route in bulk synthesis of many other types of ER materials.

Size-controllable synthesis of monodispersed colloidal silica nanoparticles via hydrolysis of elemental silicon.

A new method is presented for preparing monodisperse and uniform-size silica nanoparticles using a two-stage hydrolysis of silicon powder in aqueous medium. The influence of synthesis conditions including solution composition and temperature on the formation of silica nanoparticles were systematically investigated. The structure and morphology of the silica particles were characterized via transmission electron microscopy (TEM) and dynamic light scattering (DLS). Various-sized particles in the range 10-100 nm were synthesized. The size of the nanoparticles can be precisely controlled by using a facile regrowth procedure in the same reaction media.