Self-healing chemistry enables the stable operation of silicon microparticle anodes for high-energy lithium-ion batteries

• Chao Wang,
• Hui Wu,
• Zheng Chen,
• Matthew T. McDowell,
• Yi Cui
• & Zhenan Bao

The ability to repair damage spontaneously, which is termed self-healing, is an important survival feature in nature because it increases the lifetime of most living creatures. This feature is highly desirable for rechargeable batteries because the lifetime of high-capacity electrodes, such as silicon anodes, is shortened by mechanical fractures generated during the cycling process. Here, inspired by nature, we apply self-healing chemistry to silicon microparticle (SiMP) anodes to overcome their short cycle-life. We show that anodes made from low-cost SiMPs (~3–8 µm), for which stable deep galvanostatic cycling was previously impossible, can now have an excellent cycle life when coated with a self-healing polymer. We attain a cycle life ten times longer than state-of-art anodes made from SiMPs and still retain a high capacity (up to ~3,000 mA h g⁻¹). Cracks and damage in the coating during cycling can be healed spontaneously by the randomly branched hydrogen-bonding polymer used.

Interfacial assembly of protein–polymer nano-conjugates into stimulus-responsive biomimetic protocells

Xin Huang, Mei Li, David C. Green, David S. Williams, Avinash J. Patil & Stephen Mann

The mechanism of spontaneous assembly of microscale compartments is a central question for the origin of life, and has technological repercussions in diverse areas such as materials science, catalysis, biotechnology and biomedicine. Such compartments need to be semi-permeable, structurally robust and capable of housing assemblages of functional components for internalized chemical transformations. In principle, proteins should be ideal building blocks for the construction of membrane-bound compartments but protein vesicles with cell-like properties are extremely rare. Here we present an approach to the interfacial assembly of protein-based micro-compartments (proteinosomes) that are delineated by a semi-permeable, stimulus-responsive, enzymatically active, elastic membrane consisting of a closely packed monolayer of conjugated protein–polymer building blocks. The proteinosomes can be dispersed in oil or water, thermally cycled to temperatures of 70 °C, and partially dried and re-inflated without loss of structural integrity. As a consequence, they exhibit protocellular properties such as guest molecule encapsulation, selective permeability, gene-directed protein synthesis and membrane-gated internalized enzyme catalysis.

Stress-Responsive Polymers Containing Cyclobutane Core Mechanophores: Reactivity and Mechanistic Insights

Zachary S. Kean †, Zhenbin Niu †, Gihan B. Hewage †, Arnold L. Rheingold ‡, and Stephen L. Craig *†

A primary goal of covalent mechanochemistry is to develop polymer bound mechanophores that undergo constructive transformations in response to otherwise destructive forces. The [2 + 2] cycloreversion of cyclobutane mechanophores has emerged as a versatile framework to develop a wide range of stress-activated functionality. Herein, we report the development of a class of cyclobutane bearing bicyclo[4.2.0]octane mechanophores. Using carbodiimide polyesterification, these stress-responsive units were incorporated into high molecular weight polymers containing up to 700 mechanophores per polymer chain. Under exposure to the otherwise destructive elongational forces of pulsed ultrasound, these mechanophores unravel by 7 Å per monomer unit to form α,β-unsaturated esters that react constructively via thiol–ene conjugate addition to form sulfide functionalized copolymers and cross-linked polymer networks. To probe the dynamics of the mechanochemical ring opening, a series of bicyclo[4.2.0]octane derivatives that varied in stereochemistry, substitution, and symmetry were synthesized and activated. Reactivity and product stereochemistry was analyzed by 1H NMR, which allowed us to interrogate the mechanism of the mechanochemical [2 + 2] cycloreversion. These results support that the ring opening is not concerted but proceeds via a 1,4 diradical intermediate. The bicyclo[4.2.0]octanes hold promise as active functional groups in new classes of stress-responsive polymeric materials.

Mechanochemical strengthening of a synthetic polymer in response to typically destructive shear forces

• Ashley L. Black Ramirez,
• Zachary S. Kean,
• Joshua A. Orlicki,
• Mangesh Champhekar,
• Sarah M. Elsakr,
• Wendy E. Krause
• & Stephen L. Craig

Abstract: High shear stresses are known to trigger destructive bond-scission reactions in polymers. Recent work has shown that the same shear forces can be used to accelerate non-destructive reactions in mechanophores along polymer backbones, and it is demonstrated here that such mechanochemical reactions can be used to strengthen a polymer subjected to otherwise destructive shear forces. Polybutadiene was functionalized with dibromocyclopropane mechanophores, whose mechanical activation generates allylic bromides that are crosslinked in situ by nucleophilic substitution reactions with carboxylates. The crosslinking is activated efficiently by shear forces both in solvated systems and in bulk materials, and the resulting covalent polymer networks possess moduli that are orders-of-magnitude greater than those of the unactivated polymers. These molecular-level responses and their impact on polymer properties have implications for the design of materials that, like biological materials, actively remodel locally as a function of their physical environment.

A general approach to DNA-programmable atom equivalents

Chuan Zhang,Robert J. Macfarlane,Kaylie L. Young,Chung Hang J. Choi,Liangliang Hao,Evelyn Auyeung,Guoliang Liu,Xiaozhu Zhou& Chad A. Mirkin

Nanoparticles can be combined with nucleic acids to programme the formation of three-dimensional colloidal crystals where the particles’ size, shape, composition and position can be independently controlled1, 2, 3, 4, 5, 6, 7. However, the diversity of the types of material that can be used is limited by the lack of a general method for preparing the basic DNA-functionalized building blocks needed to bond nanoparticles of different chemical compositions into lattices in a controllable manner. Here we show that by coating nanoparticles protected with aliphatic ligands with an azide-bearing amphiphilic polymer, followed by the coupling of DNA to the polymer using strain-promoted azide–alkyne cycloaddition⁸ (also known as copper-free azide–alkyne click chemistry), nanoparticles bearing a high-density shell of nucleic acids can be created regardless of nanoparticle composition. This method provides a route to a virtually endless class of programmable atom equivalents for DNA-based colloidal crystallization.

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 mend 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.
 

“Flex-Activated” Mechanophores: Using Polymer Mechanochemistry To Direct Bond Bending Activation

Michael B. Larsen and Andrew J. Boydston *

We describe studies in mechanochemical transduction that probe the activation of bonds orthogonal to an elongated polymer main chain. Compression of mechanophore-cross-linked materials resulted in the release of small molecules via cleavage of covalent bonds that were not integral components of the elongated polymer segments. The reactivity is proposed to arise from the distribution of force through the cross-linking units of the polymer network and subsequent bond bending motions that are consistent with the geometric changes in the overall reaction. This departure from contemporary polymer mechanochemistry, in which activation is achieved primarily by force-induced bond elongation, is a first step toward mechanophores capable of releasing side-chain functionalities without inherently compromising the overall macromolecular architecture.

In Situ Modification of Plain Liposomes with Lipidated Coiled Coil Forming Peptides Induces Membrane Fusion

 

Frank Versluis , Jens Voskuhl , Bartjan van Kolck , Harshal Zope , Marien Bremmer , Tjerk Albregtse , and Alexander Kros *

Complementary coiled coil forming lipidated peptides embedded in liposomal membranes are able to induce rapid, controlled, and targeted membrane fusion. Traditionally, such fusogenic liposomes are prepared by mixing lipids and lipidated peptides in organic solvent (e.g., chloroform). Here we prepared fusogenic liposomes in situ, i.e., by addition of a lipidated peptide solution to plain liposomes. As the lipid anchor is vital for the correct insertion of lipidated peptides into liposomal membranes, a small library of lipidated coiled coil forming peptides was designed in which the lipid structure was varied. The fusogenicity was screened using lipid and content mixing assays showing that cholesterol modified coiled coil peptides induced the most efficient fusion of membranes. Importantly, both lipid and content mixing experiments demonstrated that the in situ modification of plain liposomes with the cholesterol modified peptides yielded highly fusogenic liposomes. This work shows that existing membranes can be activated with lipidated coiled coil forming peptides, which might lead to highly potent applications such as the fusion of liposomes with cells.

Polymer Microcapsules with Programmable Active Release

Alireza Abbaspourrad †, Nick J. Carroll †, Shin-Hyun Kim †‡, and David A. Weitz *†

We present a new type of microcapsule programmed with a tunable active release mechanism. The capsules are triggered by a plasticizing stimulus that induces a phase change transition of the polymeric membrane from a solid to a fluidized form; thereafter, the cargo is actively driven out of the capsule through a defect at the capsule wall with controllable release kinetics. Tuning the degree of membrane fluidity by tailoring the amount of plasticizing stimulus present allows us to obtain temporal variation of the release kinetics from a subsecond abrupt burst release to a slow sustained release of encapsulant over many minutes. Moreover, we demonstrate tuning of the collective capsule triggering response by adjusting stimulus content, polymer molecular weight, and capsule membrane thickness. For this model system, we use a microfluidic approach to fabricate polystyrene capsules triggered by a toluene stimulus. However, this active release approach is general and is applicable to diverse polymeric capsule systems; this versatility is demonstrated by extension of our trigger-release scheme to capsules fabricated from a rubberlike block copolymer. The utility of our technique further enhances the potential of these active release capsules for practical application.

Metastable Liquid Crystal as Time-Responsive Reaction Medium: Aging-Induced Dual Enantioselective Control

Yasuhiro Ishida *†‡, Yuki Matsuoka ‡, Yukiko Kai §, Kuniyo Yamada †, Kenta Nakagawa , Toru Asahi , and Kazuhiko Saigo #

A metastable liquid crystal (LC) was found to serve as a time-responsive reaction medium, in which the enantioselectivity of a photoreaction was perfectly switched through isothermal annealing of the reaction system. When the LC salt of an enantiopure amine with a photoreactive acid was irradiated with UV/vis light, in situ photodimerization of the acid moiety proceeded smoothly to afford the (+)-isomer of the photodimer with high enantioselectivity (+86% ee). In contrast, photoirradiation of an aged sample, isothermally annealed for 20 h, gave predominantly the (−)-isomer (−94% ee). Systematic studies revealed that the reversal in selectivity originated from metastability of the LC system, which gradually transformed into a crystalline phase during annealing. This finding demonstrates the potential use of metastable aggregates as dynamic time-responsive media, reminiscent of biological systems.

Defined Polymer–Peptide Conjugates to Form Cell-Instructive starPEG–Heparin Matrices In Situ

Mikhail V. Tsurkan^†, Karolina Chwalek^†, Silvana Prokoph, Andrea Zieris, Kandice R. Levental^‡*, Uwe Freudenberg^*, Carsten Werner

 Poly(ethylene glycol)-peptide- and glycosaminoglycan-peptide conjugates obtained by a regio-selective amino acid protection strategy are converted into cell-instructive hydrogel matrices capable of inducing morphogenesis in embedded human vascular endothelial cells and dorsal root ganglia.

A molecular design principle of lyotropic liquid-crystalline conjugated polymers with directed alignment capability for plastic electronics

Bong-Gi Kim,Eun Jeong Jeong,Jong Won Chung,Sungbaek Seo,Bonwon Koo & Jinsang Kim

Conjugated polymers with a one-dimensional p-orbital overlap exhibit optoelectronic anisotropy. Their unique anisotropic properties can be fully realized in device applications only when the conjugated chains are aligned. Here, we report a molecular design principle of conjugated polymers to achieve concentration-regulated chain planarization, self-assembly, liquid-crystal-like good mobility and non-interdigitated side chains. As a consequence of these intra- and intermolecular attributes, chain alignment along an applied flow field occurs. This liquid-crystalline conjugated polymer was realized by incorporating intramolecular sulphur–fluorine interactions and bulky side chains linked to a tetrahedral carbon having a large form factor. By optimizing the polymer concentration and the flow field, we could achieve a high dichroic ratio of 16.67 in emission from conducting conjugated polymer films. Two-dimensional grazing-incidence X-ray diffraction was performed to analyse a well-defined conjugated polymer alignment. Thin-film transistors built on highly aligned conjugated polymer films showed more than three orders of magnitude faster carrier mobility along the conjugated polymer alignment direction than the perpendicular direction.

X-ray analysis on the nanogram to microgram scale using porous complexes

• Yasuhide Inokuma,
• Shota Yoshioka,
• Junko Ariyoshi,
• Tatsuhiko Arai,
• Yuki Hitora,
• Kentaro Takada,
• Shigeki Matsunaga,
• Kari Rissanen
• & Makoto Fujita

X-ray single-crystal diffraction (SCD) analysis has the intrinsic limitation that the target molecules must be obtained as single crystals. Here we report a protocol for SCD analysis that does not require the crystallization of the sample. In our method, tiny crystals of porous complexes are soaked in a solution of the target, such that the complexes can absorb the target molecules. Crystallographic analysis clearly determines the absorbed guest structures along with the host frameworks. Because the SCD analysis is carried out on only one tiny crystal of the complex, the required sample mass is of the nanogram–microgram order. We demonstrate that as little as about 80 nanograms of a sample is enough for the SCD analysis. In combination with high-performance liquid chromatography, our protocol allows the direct characterization of multiple fractions, establishing a prototypical means of liquid chromatography SCD analysis. Furthermore, we unambiguously determined the structure of a scarce marine natural product using only 5 micrograms of the compound.

Not something related to our work, but still a super cool analysis technique. I look forward to seeing what can be done with this idea.

Force Sensors: Hybrid Mechanoresponsive Polymer Wires Under Force Activation (Adv. Mater. 12/2013)

 Hongbin Feng¹,Jin Lu¹,Jinghong Li^1,*,Francis Tsow²,Erica Forzani²,Nongjian Tao^2,*

Force activation is triggered in a stretched polymer wire with color changes produced as the molecules undergo structural and conformational changes. Nongjian Tao, Jinghong Li, and co-workers show on page 1729 that the hybrid mechanosensitive polymer wire can function as a micro- and nanoscale force sensor.

Biocompatible, Functional Spheres Based on Oxidative Coupling Assembly of Green Tea Polyphenols

Zhenhua Chen †‡, Caihong Wang †, Junze Chen †, and Xudong Li *†

Green luminescent, monodisperse, smooth, porous and hollow spheres were simply prepared by Cu2+ and temperature mediated oxidative coupling assembly of green tea polyphenols in water. These polymeric tea polyphenol spheres are GSH responsive, acid resistant but alkali-responsive, ideally used as platform for controlled delivery of functional guests.

Nanocontainer-Based Anticorrosive Coatings: Effect of the Container Size on the Self-Healing Performance

1. Dimitriya Borisova^1,*, 
2. Dilek Akçakayıran¹,
3. Matthias Schenderlein¹, 
4. Helmuth Möhwald¹,
5. Dmitry G. Shchukin^1,2

Organic coatings based on inhibitor loaded inorganic containers for smart corrosion inhibition are presented. The overall coating performance is strongly influenced by the containers as well as their inhibitor capacity, compatibility with the coating matrix, and size. The important effect of container size is described for the first time in this work by investigating two types of mesoporous silica containers of different diameters: 80 and 700 nm. The coating physical properties (thickness and adhesion) are comparable for both container types. In contrast, the coating barrier properties are strongly influenced by the container size as assessed with electrochemical impedance spectroscopy (EIS). The incorporation of bigger containers reduces the coating resistance by a factor of two. Surprisingly, despite the similar amounts (20 wt%) of loaded inhibitor (2-mercaptobenzothiazole), different active inhibition ability is detected with the scanning vibrating electrode technique (SVET). Therefore, it is found that coatings with smaller containers exhibit better self-healing performance.

Interesting article for anyone working on nanocontainers and self-healing.

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.