Preorganized Hydrogel: Self-Healing Properties of Supramolecular Hydrogels Formed by Polymerization of Host–Guest-Monomers that Contain Cyclodextrins and Hydrophobic Guest Groups

Takahiro Kakuta¹, Yoshinori Takashima¹, Masaki Nakahata¹, Miyuki Otsubo¹, Hiroyasu Yamaguchi¹, Akira Harada^1,2,

Supramolecular hydrogels formed by a host-guest interaction show self-healing properties. The cube-shaped hydrogels with β-cyclodextrin and adamantane guest molecules mends after being broken. The hydrogels sufficiently heal to form a single gel, and the initial strength is restored. Although contact between a freshly cut and uncut surface does not mend the gels, two freshly cut surfaces selectively mend.

Multichannel and Repeatable Self-Healing of Mechanical Enhanced Graphene-Thermoplastic Polyurethane Composites

Lu Huang, Ningbo Yi, Yingpeng Wu, Yi Zhang, Qian Zhang, Yi Huang^*, Yanfeng Ma, Yongsheng Chen^*

A novel self-healing material, which was fabricated using few-layered graphene (FG) and thermoplastic polyurethane (TPU) via a facile method, not only exhibits a mechanical enhanced property, but also can be repeatedly healed by various methods including infrared (IR) light, electricity and electromagnetic wave with healing efficiencies higher than 98%.

Microfluidic Mixing Triggered by an External LED Illumination

Anna Venancio-Marques †‡§, Fanny Barbaud †‡§, and Damien Baigl *†‡§

The mixing of confined liquids is a central yet challenging operation in miniaturized devices. Microfluidic mixing is usually achieved with passive mixers that are robust but poorly flexible, or active mixers that offer dynamic control but mainly rely on electrical or mechanical transducers, which increase the fragility, cost, and complexity of the device. Here, we describe the first remote and reversible control of microfluidic mixing triggered by a light illumination simply provided by an external LED illumination device. The approach is based on the light-induced generation of water microdroplets acting as reversible stirrers of two continuous oil phase flows containing samples to be mixed. We demonstrate many cycles of reversible photoinduced transitions between a nonmixing behavior and full homogenization of the two oil phases. The method is cheap, portable, and adaptable to many device configurations, thus constituting an essential brick for the generation of future all-optofluidic chip.

An Interface-Driven Stiffening Mechanism in Polymer Nanocomposites

Erkan Senses and Pinar Akcora *

Dynamic mechanical response in responsive and adaptive composites can be achieved either through the responsive polymer; with the chemical regulators affecting the bonding between fillers or through reversible covalent bonding. Tuning the interfaces between fillers and polymer matrix potentially plays a critical role in all these systems to enhance their adaptive responses. Here, we present that the bonding–debonding of chains on nanoparticles can be modulated under extensive periodic strains. Mechanical response of an attractive model polymer composite, poly(methyl methacrylate) filled with silica nanoparticles, is monitored in a series of deformation–resting experiments allowing us to tune the interfacial strength of polymer. Chains that are desorbed from the surface with the oscillatory shear entangle with the free chains during the rest time. We show that periodic deformation process results in unusual stiffening of composites. Mechanical response during the recovery reveals this behavior arising from the enhancement in the entanglement of chains at interfaces. The interfacial hardening can be used in designing polymer composites with stress-sensitive interfaces to achieve new repair mechanisms for biomedical applications, and also in energy absorbing reinforced systems.

Interesting paper on the stiffening of composites based on periodic input stress.

Nano-Encrypted Morse Code: A Versatile Approach to Programmable and Reversible Nanoscale Assembly and Disassembly

Ngo Yin Wong †, Hang Xing ‡, Li Huey Tan ‡, and Yi Lu *†‡

^†Department of Materials Science and Engineering, ^‡Department of Chemistry, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States

While much work has been devoted to nanoscale assembly of functional materials, selective reversible assembly of components in the nanoscale pattern at selective sites has received much less attention. Exerting such a reversible control of the assembly process will make it possible to fine-tune the functional properties of the assembly and to realize more complex designs. Herein, by taking advantage of different binding affinities of biotin and desthiobiotin toward streptavidin, we demonstrate selective and reversible decoration of DNA origami tiles with streptavidin, including revealing an encrypted Morse code “NANO” and reversible exchange of uppercase letter “I” with lowercase “i”. The yields of the conjugations are high (>90%), and the process is reversible. We expect this versatile conjugation technique to be widely applicable with different nanomaterials and templates.

Temperature Sculpting in Yoctoliter Volumes

Joseph E. Reiner *†, Joseph W. F. Robertson *‡, Daniel L. Burden §, Lisa K. Burden , Arvind Balijepalli ‡, and John J. Kasianowicz *‡

The ability to perturb large ensembles of molecules from equilibrium led to major advances in understanding reaction mechanisms in chemistry and biology. Here, we demonstrate the ability to control, measure, and make use of rapid temperature changes in fluid volumes that are commensurate with the size of single molecules. The method is based on attaching gold nanoparticles to a single nanometer-scale pore formed by a protein ion channel. Visible laser light incident on the nanoparticles causes a rapid and large increase of the adjacent solution temperature, which is estimated from the change in the nanopore ionic conductance. The temperature shift also affects the ability of individual molecules to enter into and interact with the nanopore. This technique could significantly improve sensor systems and force measurements based on single nanopores, thereby enabling a method for single molecule thermodynamics and kinetics.

Advances in Microfluidic Materials, Functions, Integration, andApplications

Pamela N. Nge, Chad I. Rogers, and Adam T. Woolley

Introduction:Microfluidics consist of microfabricated structures for liquid
handling, with cross sections in the 1−500 μm range and small
volume capacity (femtoliter to nanoliter). Capillary tubes
connected with fittings,1 although utilizing small volumes, are
not considered microfluidics for the purposes of this paper
since they are not microfabricated. Likewise, millifluidic systems
made by conventional machining tools are excluded due to
their larger feature sizes (>500 μm).

A nice review of Microfluidics just got ASAP.

Ultralight, Flexible, and Fire-Resistant Carbon Nanofiber Aerogels from Bacterial Cellulose^†

Zhen-Yu Wu, Chao Li, Dr. Hai-Wei Liang, Prof. Dr. Jia-Fu Chen, Prof. Dr. Shu-Hong Yu^*

Thirsty fibers: The aerogels described in the title can be fabricated in large scale by using a low-cost biomass, bacterial cellulose, as a precursor, which can be produced at industrial level in a microbial fermentation process. The carbon nanofiber aerogels (black pieces in picture) exhibit superior absorption capacity for organic solvents (red solution) and high potential for pressure sensing.

Fabrication of three-dimensional electrical connections by means of directed actin self-organization

Rémi Galland,Patrick Leduc,Christophe Guérin,David Peyrade,Laurent Blanchoin & Manuel Théry

A promising approach to improve the performance of microelectronic devices is to build three-dimensional (3D) chips made of stacked circuits. However, a major hurdle lies in the fabrication of dense arrays of electrical interconnections between these layers, where accessibility is limited1, 2. Here we show that the directed growth and self-organization of actin filaments can offer a solution to this problem. We defined the shape and orientation of 3D actin networks through both micropatterning of actin nucleation factors and biochemical control of actin filament polymerization. Networks growing from two opposing layers were able to interpenetrate and form mechanically stable connections, which were then coated with gold using a selective metallization process. The electrical conductivity, robustness and modularity of the metallized self-organized connections make this approach potentially attractive for 3D chip manufacturing.

Enzymatically Active Self-Standing Protein-Polymer Surfactant Films Prepared by Hierarchical Self-Assembly

Kamendra P. Sharma, Andrew M. Collins, Adam W. Perriman, Stephen Mann

Cross-linked protein-polymer surfactant films consisting of enzymatically active hybrid nanoclusters are prepared using a novel approach based on electrostatically mediated hierarchical self-assembly. The free-standing films are structurally robust, highly hydrophilic, and exhibit sustained fluorescence or recyclable enzymatic phosphatase or oxido-reductase behavior.

Solid-State NMR on Bacterial Cells: Selective Cell Wall Signal Enhancement and Resolution Improvement using Dynamic Nuclear Polarization

Hiroki Takahashi †, Isabel Ayala ‡, Michel Bardet †, Gaël De Paëpe †, Jean-Pierre Simorre ‡, and Sabine Hediger *†

 

Dynamic nuclear polarization (DNP) enhanced solid-state nuclear magnetic resonance (NMR) has recently emerged as a powerful technique for the study of material surfaces. In this study, we demonstrate its potential to investigate cell surface in intact cells. Using Bacillus subtilis bacterial cells as an example, it is shown that the polarizing agent 1-(TEMPO-4-oxy)-3-(TEMPO-4-amino)propan-2-ol (TOTAPOL) has a strong binding affinity to cell wall polymers (peptidoglycan). This particular interaction is thoroughly investigated with a systematic study on extracted cell wall materials, disrupted cells, and entire cells, which proved that TOTAPOL is mainly accumulating in the cell wall. This property is used on one hand to selectively enhance or suppress cell wall signals by controlling radical concentrations and on the other hand to improve spectral resolution by means of a difference spectrum. Comparing DNP-enhanced and conventional solid-state NMR, an absolute sensitivity ratio of 24 was obtained on the entire cell sample. This important increase in sensitivity together with the possibility of enhancing specifically cell wall signals and improving resolution really opens new avenues for the use of DNP-enhanced solid-state NMR as an on-cell investigation tool.

Self-Healing Polymer Coatings Based on Crosslinked Metallosupramolecular Copolymers

Stefan Bode^1,2, Linda Zedler^2,3,4, Felix H. Schacher^1,2, Benjamin Dietzek^2,3,4, Michael Schmitt^2,3, Jürgen Popp^2,3,4, Martin D. Hager^1,2,*, Ulrich S. Schubert^1,2,5,*

Self-healing coating based on metallopolymers are prepared and fully characterized. Iron bisterpyridine complexes are incorporated into a polymer network based on methacrylates, resulting in self-healing properties of these materials. Moreover, the influence of the comonomers on the thermal properties is studied in detail.

Responsive biomimetic networks from polyisocyanopeptide hydrogels

Paul H. J. Kouwer,

Matthieu Koepf,

Vincent A. A. Le Sage,

Maarten Jaspers,

Arend M. van Buul,

Zaskia H. Eksteen-Akeroyd,

Tim Woltinge,

Erik Schwartz,

Heather J. Kitto,

Richard Hoogenboom,

Stephen J. Picken,

Roeland J. M. Nolte,

Eduardo Mendes

& Alan E. Rowan

Mechanical responsiveness is essential to all biological systems down to the level of tissues and cells1, 2. The intra- and extracellular mechanics of such systems are governed by a series of proteins, such as microtubules, actin, intermediate filaments and collagen3, 4. As a general design motif, these proteins self-assemble into helical structures and superstructures that differ in diameter and persistence length to cover the full mechanical spectrum1. Gels of cytoskeletal proteins display particular mechanical responses (stress stiffening) that until now have been absent in synthetic polymeric and low-molar-mass gels. Here we present synthetic gels that mimic in nearly all aspects gels prepared from intermediate filaments. They are prepared from polyisocyanopeptides5, 6, 7 grafted with oligo(ethylene glycol) side chains. These responsive polymers possess a stiff and helical architecture, and show a tunable thermal transition where the chains bundle together to generate transparent gels at extremely low concentrations. Using characterization techniques operating at different length scales (for example, macroscopic rheology, atomic force microscopy and molecular force spectroscopy) combined with an appropriate theoretical network model8, 9, 10, we establish the hierarchical relationship between the bulk mechanical properties and the single-molecule parameters. Our results show that to develop artificial cytoskeletal or extracellular matrix mimics, the essential design parameters are not only the molecular stiffness, but also the extent of bundling. In contrast to the peptidic materials, our polyisocyanide polymers are readily modified, giving a starting point for functional biomimetic hydrogels with potentially a wide variety of applications11, 12, 13, 14, in particular in the biomedical field.

Nature 493 651 doi: 10.1038/nature11839

This is a pretty cool polymer system in terms of supramolecular structure and mechanical properties.

MRI-detectable pH nanosensors incorporated into hydrogels for in vivo sensing of transplanted-cell viability

Kannie W. Y. Chan,Guanshu Liu,Xiaolei Song,Heechul Kim,Tao Yu,Dian R. Arifin,Assaf A. Gilad,Justin Hanes,Piotr Walczak,Peter C. M. van Zijl,Jeff W. M. Bulte & Michael T. McMahon

Biocompatible nanomaterials and hydrogels have become an important tool for improving cell-based therapies by promoting cell survival and protecting cell transplants from immune rejection. Although their potential benefit has been widely evaluated, at present it is not possible to determine, in vivo, if and how long cells remain viable following their administration without the use of a reporter gene. Here, we report a pH-nanosensor-based magnetic resonance imaging (MRI) technique that can monitor cell death in vivo non-invasively. We demonstrate that specific MRI parameters that change on cell death of microencapsulated hepatocytes are associated with the measured bioluminescence imaging radiance. Moreover, the readout from this pH-sensitive nanosensor can be directly co-registered with high-resolution anatomical images. All of the components of these nanosensors are clinical grade and hence this approach should be a translatable and universal modification of hydrogels.

Revisiting the Hammett ρ Parameter for the Determination of Philicity: Nucleophilic Substitution with Inverse Charge Interaction

Recent work identified a fascinating charge/FMO control dichotomy in oxidations of substituted phenyl sulfoxides. A great read for those interested in FMO theory, the role of partial charges in controlling reaction pathways, and/or linear free energy relationships.

Abstract

Too OT to handle? In oxygen transfer (OT) reactions the inversion of the ρ value is not representative of a change in mechanism. Substituents bonded to aromatic sulfoxides have the opposite effect on the rates of oxidation depending on whether the reaction is dominated by electrostatic or orbital-overlap effects (see picture).

DOI Link