The confluence of dynamic and constitutional features related to supramolecular self-assemblies - when they occur within mixtures of competing molecular architectures - has recently opened a very intriguing branch of chemical science, the so-called dynamic combinatorial chemistry (DCC). Within this framework, emerging lines of investigations have been directed towards the development of dynamic combinatorial materials and devices. These ones can be defined as multi-component chemical systems which, thanks to the reversibility of their interconnections within networks of competing reactions, and thanks to their sensitivity to environmental parameters, aim at performing modular functional tasks by responding to external stimuli. The behaviour of such dynamic materials is by essence more complex than the one produced by their static or single-component counterparts and as such, they hold higher potentialities in terms of information processing and functionality tuning. Besides materials science, another recent approach in DCC consists in coupling networks of reversible reactions with autocatalytic loops, in order to combine their constitutional “plasticity” with a self-replicating process as an amplification tool. We will discuss some of our works concerning such responsive systems along these two different lines and, more particularly, we will focus on their merging to access self-constructing materials with advanced functional properties for electronic conduction. We will also outline the potential of such systems to act as vectors of information.

The dynamic control over materials shape plays a key role in the complex biological environment and has attracted considerable attention in science, engineering, and medicine. We report on a novel type of dynamic shape responses exhibited by cubical hydrogel microcapsules. The capsules are produced as poly(methacrylic acid)-based hydrogel (PMAA) hollow replicas of cubical sacrificial templates and obtained from chemically cross-linked multilayers of hydrogen-bonded precursor films. We found that while cubical (PMAA)20 capsules turned into spherical-like when transitioned from pH=3 to pH=8, cubical PMAA-poly(vinylpyrrolidone), (PMAA-PVPON)5, hydrogel cubical capsules retained their cubical shape and increased in size instead. The decrease in cross-link density in the (PMAA-PVPON)5 hydrogel hollow microcontainers resulted in the increase in their swelling ratio. The drastic difference in pH-triggered shape responses was rationalized through the difference in hydrogel rigidity expressed as the ratio of the polymer contour length between the neighboring cross-links to persistence polymer length. We believe that our findings provide new prospects for developing polymeric materials with predictable shape and size-changing properties for controlled drug delivery and cellular uptake.

The fabrication of functional supramolecular architectures that able to display good electrical conductivity is a major challenge in bio-nanoelectronics. The electronic communication between the components involved in the supramolecular self-assembly plays a key role to obtain high electrical conductivity. A simple, yet sophisticated, approach to improve the electronic communication would be the involvement of strong charge-transfer interactions between donor and acceptor components. Recent reports have demonstrated that the enzyme-driven dynamic peptide library (eDPL) can be used to identify the most stable self-assembling peptides from component mixtures through enzyme-assisted self-assembly of short aromatic peptides. The ultimate aim of this research is to exploit eDPL to achieve the most stable conductive nanomaterials from a library of several self-assembling precursor components based on the charge transfer interactions between donors and acceptors.

The molecular self-assembly of Fmoc containing aromatic short peptides by thermolysin-catalysed reversed hydrolysis was previously exploited to develop supramolecular hydrogels. According to our preliminary results, the replacement of these Fmoc groups with naphthalene and/or naphthalenediimide derivatives may have a pronounced effect on the resultant electronic properties of such supramolecular hydrogels. In particular, thermodynamically controlled thermolysin-assisted molecular self-assembly of aromatic Fmoc substituted short dipeptides has already been reported.
In this contribution, we show that the thermolsyin-assisted reversed hydrolysis can also be extended to the non-Fmoc containing aromatic short dipeptides Nap-xy-z that forms superfast supramolecular hydrogels. We have already observed unprecedented enzyme-assisted superfast gelation behaviour for the amide derivatives, Nap-YF-NH2, Nap-YL-NH2, Nap-FF-NH2 and Nap-FL-NH2 that form supramolecular hydrogels within couple of minutes after the addition of enzyme to the corresponding precursor components. These hydrogels were characterised by various techniques such as rheology, fluorescence spectroscopy, FT-IR spectroscopy, UV-vis spectroscopy, circular dichroism, transmission electron microscopy and atomic force microscopy.

Supra-amphiphiles refer to amphiphiles that are formed on the basis of non-covalent interactions, such as host-guest interactions, hydrogen bonding, and charge transfer interactions. In contrast with conventional amphiphiles, the functional building blocks can be incorporated to the supra-amphiphiles by non-covalent interactions, therefore reducing the needs of time-consuming chemical synthesis. Moreover, we are able to easily introduce stimuli moiety into the supra-amphiphiles for fabricating photo-responsive, pH responsive and enzyme responsive self-assembled nanostructures. For example, we have successfully fabricated a pH responsive supra-amphiphile, which can self-assemble in water to form nanofibers. The morphology of the nanofibers can be manipulated reversibly between random coils and straight rods by changing the pH of the aqueous medium. The concept of supra-amphiphiles can be extended to the fabrication of inexpensive and non-toxic enzyme-responsive polymeric self-assemblies, which have great potential in drug-delivery applications. Recently, we have provided a novel and noncovalent way to fabricate highly emissive assemblies based on a new kind of responsive “dumbbell-shape” supra-amphiphile. We have demonstrated that the “dumbbell-shape” supra-amphiphiles can be used as a supramolecular sensor for the rapid detection of spermine with high sensitivity and selectivity, which is crucial for the early cancer diagnosis.
References
[1] X. Zhang, C. Wang, Chem. Soc. Rev. 2011, 40, 94.
[2] C. Wang, Z. Q. Wang, X. Zhang, Small 2011, 7, 1379.
[3] C. Wang, Z. Q. Wang, X. Zhang, Acc. Chem. Res. 2012, 45, 608.
[4] C. Wang, Y. S. Guo, Y. P. Wang, H. P. Xu, R. J. Wang, X. Zhang, Angew. Chem. Int. Ed. 2009, 48, 8962.
[5] C. Wang, Q. S. Chen, Z. Q. Wang, X. Zhang, Angew. Chem. Int. Ed. 2010, 49, 8612.

The molecular architectures of polymer networks allow the variation of several structural parameters (e.g. netpoint functionality or chain segment length), so that their macroscopic properties can be adjusted in a wide range and tailored to the application specific requirements. In this presentation molecular processes are introduced, which result in changes of the netpoints or of the polymer chain segments. Mechanisms are explained for translating these molecular processes to macroscopic functions.
Examples are the formation reversible covalent netpoints on the basis of cin-nammic acid or the provision of physical netpoints in multiphase polymer net-works as well as chemical reactions occurring at the polymer chain segments such as their hydrolytic cleavage [1-4]. The resulting macroscopic functions are polymers whose elasticity is increased or which are capable to change their shape. The effect of macroscopic changes on variations on the molecular level will be discussed for macroscopic, mechanical deformations and the influence of the molecular polymer network architecture on this process is elucidated [5].
The understanding of such structure - function relationships provides the fundament for the creations of adaptive functions.
References
[1] A. Lendlein and S. Kelch, Angew. Chem. Int. Ed. 2002, 41, 2034-2057.
[2] A. Lendlein, H.Y. Jiang, O. Jünger, and R. Langer, Nature 2005, 434, 879-882.
[3] A.T. Neffe, G. Tronci, A. Alteheld, and A. Lendlein, Macromol. Chem. Phys.
2010, 211, 182-194.
[4] A.T. Neffe, B.D. Hanh, S. Steuer, and A. Lendlein, Adv. Mater. 2009, 21, 3394-
3398.
[5] Q. Zhao, M. Behl, A. Lendlein, Soft Matter, 2012, DOI: 10.1039/c2sm27077c.

Self-folding is a deterministic assembly approach that generates desired 3D structures from pre-defined 2D templates with high fidelity. Self-folding has a number of applications, including, reconfigurable devices, sensors, and packaging. Conventional approaches achieve folding by defining ‘hinges&’ (i.e., regions that fold) that physically connect and actuate rigid ‘panels&’. These methods require complex lithography and multiple fabrication steps.
We have demonstrated and modeled a simple approach for folding using pre-strained polymer sheets and inkjet printing. The pre-strained sheets shrink in-plane if heated uniformly. Here, we pattern ink to define ‘hinges&’ via a desktop printer. The ink absorbs light, which heats locally the polymer underneath the ink. The temperature gradients through the depth of the sheet induce localized shrinkage and the sheet folds within seconds. The polymer sheets are a polymer network that acts as a shape memory material that can be programmed into arbitrary shapes based on the patterns of ink.
Sequential folding is the ability to control the order and timing of the folding of the hinges. It is attractive for fabricating more complex geometries. Our approach utilizes assorted colors of inks as ‘hinges&’ absorbing light in different wavelengths, while the polymer sheet transmits those wavelengths. By selectively choosing light sources with different emission wavelengths, folding is triggered in a sequential manner. Moreover, we study the effect of key variables (e.g., hinge width, optical absorption of color inks, etc.) to realize sequential folding. In summary, we pattern polymer sheets by inkjet printing to realize self-folding in a simple manner.

Recently, there has been much interest in photorheological (PR) fluids, i.e., fluids whose rheological properties can be tuned by light. A “holy grail” in this field has been the search for simple, low-cost PR fluids that can be easily created using inexpensive, commercially available ingredients and that show substantial, reversible changes in rheology upon exposure to different wavelengths of light. Towards this end, we report a class of photoreversible PR fluids prepared by combining the azobenzene derivative 4-azobenzene carboxylic acid (ACA) with the cationic surfactant erucyl bis(2-hydroxyethyl)methyl ammonium chloride (EHAC). We show that certain aqueous mixtures of EHAC and ACA, which are low-viscosity solutions at the outset, undergo nearly a million-fold increase in viscosity when irradiated with UV light. The same solutions revert to their initial viscosity when subsequently exposed to visible light. Using an array of techniques including UV-Vis and NMR spectroscopies, small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM), we have comprehensively characterized our PR fluids at the molecular, nanostructural, and macroscopic scales. Initially, EHAC/ACA are self-assembled into unilamellar vesicles, which are discrete container structures and give the sample a low viscosity. Upon exposure to UV light, ACA undergoes a trans to cis photoisomerization, which alters the geometry of the EHAC/ACA complex. In turn, the molecules self-assemble into a different structure, viz. wormlike micelles, which are long, entangled chains and impart a high viscosity to the sample. The above changes in viscosity are repeatable, and the sample can be reversibly cycled back and forth between low and high viscosity states. Our photoreversible PR fluids can be easily replicated in any industrial or academic lab, and it is hoped that these “smart” fluids will eventually find a host of applications.

In Nature, nanomaterials are often assembled and organized with nanoscale precision across multiple length scale using dynamic, programmable supramolecular filaments. For example microtubules, assembled from dimeric building blocks of tubulin protein, facilitate a multitude of complex biological processes ranging from chromosome separation during cell division to regulating cellular morphology and the trafficking of motile intracellular cargo. The dynamic supramolecular assembly processes that enable these diverse functions rely on collaborative and precisely regulated protein conformation, electrostatic interactions, intra- and intermolecular hydrogen bonding, and even the involvement of secondary biomolecules. Developing synthetic analogs, inspired by such biological materials and processes, opens the door to the advanced and programmable assembly of nanomaterials. Here, we explore peptides as synthetic nanofiber building blocks, focusing in particular on how peptide structure (e.g., linear, ringed, or wedged) and chemistry (e.g., charge distribution, amphiphilicity, or hydrogen bonding) affect the assembly of peptide nanofibers. In addition, we introduce programmable elements to these peptides, such that exposure to light, heat, or even active biomolecules such as enzymes, can be used to regulate peptide nanofiber assembly. With biology as inspiration, tailoring the chemistry of peptide building blocks and controlling their supramolecular assembly promise new opportunities for advanced nanoscale materials development.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Spherical nucleic acids (SNAs) are often comprised of an inorganic nanoparticle core functionalized with a densely-organized and highly-oriented nucleic acid shell. Aside from their uses in biomedicine, these unique materials can be utilized to generate nanoparticle superlattice assemblies with crystal structures never before seen in nature. SNAs are new types of programmable atom equivalents that are generally comprised of both hard and soft matter. The strength and length of the DNA “bonds” can be adjusted by varying sequence and length; the properties of the nanoparticle “atom” equivalents can be adjusted by varying size, shape, and composition. Since DNA binding dictates assembly, it follows that any monodisperse nanoparticle that can be functionalized with a densely layer of DNA can be used as a building block. New developments towards creating a universal strategy to position any type of SNA into a wide variety of crystalline architectures will be discussed. Also, work focused on incorporating dynamic elements into such structures that allow them to sense, respond, and adapt to external stimuli will be highlighted. This work has important implications in materials, optics, plasmonics, biology, catalysis, and energy.

Physical hydrogels are water-swollen networks made from either the self-assembly of small molecules or through the non-covalent crosslinking of polymer chains. The great advantage of small molecule gelators is the possibility for precisely tuning the gel&’s properties through the synthetic power of organic chemistry. However, to date it has not been possible to achieve periodic nanoscale ordering from small molecule gelators; a property that is readily accessible in bulk block co-polymer materials through nanoscale phase separation of the polymer blocks.
Here we introduce a novel hydrogel material formed by the supramolecular interaction between a water-soluble triblock co-polymer and a wide variety of water-soluble, amphiphilic small molecules. The polymer acts as a template to arrange the small molecules in various nanostructures, such as a body centered cubic lattice or hexagonally packed cylinders. Besides structural features, we will discuss the mechanical properties of the gels, detail the nature of the non-covalent interactions and demonstrate responsiveness to external stimuli such as reversible redox-controlled transitions between solution and gel states. Robust nanostructured gels can be formed from small molecules with great variety in function (catalysts, drug molecules, dyes) and structural features (organometallic, π-conjugated, aliphatic), creating a versatile platform technology for functional hydrogels.

The morphology of nanoscale particles can strongly influence their physical and functional properties. Of great interest in our research is how morphology may be utilized to influence, switch and optimize the in vivo properties of nanoscale delivery vehicles for imaging and therapeutics applications. Therefore, we have set about developing a range of soft materials capable of switching morphology in response to specific biochemical stimuli in biological environments. Herein, we present an approach that blends synthetic polymers with biopolymers to construct materials that respond selectively to particular enzymes including nucleases, proteases, kinases and phosphatases. We will describe this approach to programmable and adaptive materials in the context of their applications and potential in tumor targeting.

Proteins represent the functionally and structurally most sophisticated building blocks for creating ordered yet dynamic and chemically responsive nanoscale architectures. Such protein arrays have been exploited as templates for inorganic materials and found numerous applications in nanotechnology thanks to their ease of chemical/genetic manipulation. Nevertheless, the chemical complexity of proteins also translates into a dearth of approaches for controlling their self-assembly into periodic structures in a predictable manner. We developed an easily accessible approach for protein self-assembly based on directional metal coordination. Using this approach, we show how monomeric protein building blocks can be arranged into 0-, 1-, 2- and 3D assemblies with crystalline order in a chemically controllable fashion.

The fusion of lipid membranes is essential for the delivery of chemicals across biological barriers to specific cellular locations. Intracellular membrane fusion is particularly precise, and is critically mediated by SNARE proteins. To allow membrane fusion to be better understood and harnessed we have mimicked this important process with a simple bottom-up model in which synthetic fusogens replicate the essential features of SNARE proteins. In our fusogens, the coiled-coil molecular recognition motif of SNARE proteins is replaced by the coiled-coil E/K peptide complex, which is one ninth the size. The peptides are anchored in liposome membranes via pegylated lipids. Here we discuss how the liposome fusion process is controlled by different parameters and examples of controlled content mixing between complementary liposomal nanoreactors will be discussed.

The organization of matter across length scales, starting from well defined building blocks, is a key challenge in the design of advanced functional materials and devices. Patterned, or highly structured, assemblies can be formed spontaneously in systems which are exposed to fluxes of matter and energy. These assemblies can sustain themselves far from equilibrium whilst the fluxes are maintained, leading to the emergence of temporal and spatial structures, and we are interested in using these structures to direct the assembly of nanoscale clusters, atom by atom from the bottom up. In our work we have been using polyoxometalate clusters as they are built from an extraordinary library of metal oxide building blocks which bridge multiple length scales. Classically these systems are constructed in ‘one-pot&’ reactions, but these mask a vast and complex range of intricate self-assembly processes that must invariably occur in solution. In our work we have designed a ‘networked&’ approach to explore self-assembly at the nanoscale using a 'Networked Reactor System', and was able to discovery and assemble a new range of complex metastable molecules and materials.

Species ranging from single-cell organisms to social insects can undergo auto-chemotaxis, where the entities move towards a chemo-attractant that they themselves emit. This mode of signaling allows the organisms to form large-scale structures, with amoebas and E coli self-organizing into extensive multi-cellular clusters and termites constructing macroscopic mounds. Notably there are few examples of synthetic materials that display auto-chemotactic self-organization. The latter materials would open new routes for dynamic, reconfigurable self-assembly, where self-propelled elements communicate with neighboring units and thereby actively participate in constructing the final structure. We use computational modeling to show that millimeter-sized polymer gels can display such self-sustained, auto-chemotatic behavior. In particular, we demonstrate that gels undergoing the self-oscillating Belousov-Zhabotinsky (BZ) reaction not only respond to a chemical signal from the surrounding solution, but also emit this signal and thus, multiple neighboring gel pieces can spontaneously self-aggregate into macroscopic objects. These findings indicate that the BZ gels can undergo a type of self-recombining: if a BZ gel is cut into distinct pieces and the pieces are moved relatively far apart, then their auto-chemotactic behavior drives the parts to move autonomously and recombine into a structure resembling the original, uncut sample. We also show that the gels&’ coordinated motion can be regulated by light, allowing us to achieve selective self-aggregation and control over the shape of the gel aggregates, as well as reconfiguration of the entire structure. Finally, we show that the aggregated gel pieces can rotate as a unit. For example, four millimeter-sized gels can associate into a structure that resembles a pinwheel and then undergo spontaneous, autonomous rotation. With eight gel pieces, the system can form two pinwheels, which communicate and coordinate their motion. Notably, this communication can be controlled with light. In particular, light can be used to not only translate the pinwheels, but also control the relative rotation of two such clusters. Overall, these findings reveal that the BZ gels resemble pieces of a construction toy that can be reused to build multiple structures and thus, provide a new route for creating dynamically reconfigurable materials.

We will discuss the systematic study of the use of molecular self-assembly to generate hydrogels that oscillating during chemical oscillation, such as the Belousov-Zhabotinsky (BZ) reaction. Two types of hydrogels will be discussed: without and with post self-assembly crosslinking. While the first case provides the insights on the molecular self-assembly during energy dissipation, the second case offers a new way to combine molecular nanofibers with copolymer for generating a chemical oscillatory system. Particularly, the formation of the nanofibers from the designed hydrogelators provides multiple polymerizable sites for copolymerizing with N-isopropylacrylamide and for attaching a ruthenium bipyridine complex on the copolymer as the catalysts for BZ reaction. Our results indicates that the combination of supramolecular self-assembly with copolymerization offers a versatile and facile approach for generating soft materials that have larger pores in the matrices of the network of the gels for the diffusion of the reactants, thus resulting in relatively fast chemical oscillation. We will also discuss the use of microfluidic device for maximizing the chemomechanical transduction of the gel materials during the BZ reaction.

Belousov-Zhabotinsky (BZ) hydrogels are unique mechano-chemical coupled materials that autonomously swell and de-swell in response to an oscillating chemical environment. By spatially patterning BZ active material in a non-active polymer matrix, we can design composite BZ hydrogels with specific swell motions and functionality. The power of this approach is highlighted through the design of in-phase and out-of-phase synching between the active BZ patches, which selectively amplifies or mitigates the swelling response. However, design criteria to control the synch behavior of BZ composites are needed. Previous works have demonstrated that the interspacing distance between active patches affects their synchronization. The hydrogels in that study were not chemically cross-linked composites, but instead were active patches separated by non-active hydrogel spacers. In comparison, composite hydrogels retain the mechanical communication between BZ active patches through the elastic deformation of the matrix, which will further influence their synchronization. We used the Fab@Home robotic printer to systematically vary BZ active patch size, patch to gel edge distance, ruthenium (Ru) catalyst concentration, and patch interspacing. We printed active patches of Ru bonded gelatin in pairs of variable size (0.2 - 1.5 mm) and interspace distance (0.1 - 1.5 mm) in 2D. Patches were then covered in a thin layer (200 - 400 mu;m) of non-active gelatin and chemically cross-linked with glutaraldehyde. The relative frequency and phase angle of the oscillating patches in BZ solution were compared. Our results indicate that synchrony increases as interspace distance decreases and that swelling increases with Ru concentration. Large patches oscillate slower than small patches, which reduces the synch frequency of unequally sized pairs. With these design criteria, we can now propose the construction of novel structures to exploit the dynamic BZ behavior, such as the buckling a polymer beam or wrinkling of a thin film. These design rules provide an important framework for efficient design of BZ structures and a means in which to integrate other BZ sensitive stimuli, such as temperature, pressure, and light.

Non enzymatic replication has been the subject of intense research, related to plausible scenarios in early molecular evolution and the origins of life. Several different synthetic replication systems have been prepared and analyzed, including nucleic acids, fatty acids, peptides, and organic molecules. We have been interested recently in the analysis of replication networks[1] operating far from equilibrium as better models for selection and adaptation in response to the ever-changing chemical environment. In this talk we will present the following two new systems emphasizing the effects of transient supramolecular structures on the mechanism and dynamics of peptide self organization and replication. (i) Light-dependent replication of α-helix proteins[2] and its utility for manipulating dynamic combinatorial libraries[3] and chemical logic operations[2,4], and (ii) one-dimensional assemblies as active traps facilitating β-sheet peptides replication[5,6].
[1] Dadon, Wagner, Ashkenasy Angew. Chem. Int. Ed. 2008, 47, 6128.
[2] Dadon, Samiappan, Yishay, Ashkenasy Chem. Eur. J. 2010 16, 12096.
[3] Dadon, Samiappan, Wagner, Ashkenasy Chem. Commun. 2012, 48, 1419.
[4] Samiappan, Dadon, Ashkenasy Chem. Commun. 2011, 47, 710.
[5] Rubinov, Wagner, Rapaport, Ashkenasy Angew. Chem. Int. Ed. 2009, 48, 6683.
[6] Rubinov, Wagner, Matmor, Regev, N. Ashkenasy, G. Ashkenasy ACS nano 2012, 6, 7893.

Functionalized dipeptides self-assemble in solution to form gels. This assembly can be triggered by lowering the pH of the solution below the pKa of the gelator. Gelation of the bulk solution occurs. Hydrogels can be produced electrochemically via the use of a readily oxidisable material, which can generate protons to lower the pH of the gelator solution. Such control can be of interest for electrochemical biosensors.
We demonstrate a method which electrochemically lowers the pH at an electrode surface from which the gel grows. Gelation is controlled at the surface of the electrode rather than bulk gelation. We use this technique to demonstrate multiple layers of gel and selective gelation when multiple gelator molecules are in the bulk solution, with gel growth being monitored in real-time.

Catalytic control over self-assembly is widespread in nature, directing vital processes such as cell motility, intracellular transport and muscle contraction, and resulting in rapid turnover of self-assembled structures. In artificial systems, only a few specific examples of catalysis exist, most notably in enzyme controlled peptide assembly. Here, I will show how the rate of formation of supramolecular materials, and the resulting mechanical properties, can be drastically enhanced by catalytically controlling the rate of formation of their molecular building blocks. Using simple acid or nucleophilic aniline catalysis, we found it possible to make hydrazone based hydrogels in a matter of minutes instead of hours, under ambient conditions (room temperature, mild pH, aqueous media) starting from simple, soluble building blocks. Notably, by changing the rate of formation of the gelator molecules by means of the catalyst, the overall rate of gelation and the resulting gel morphology are affected, providing access to metastable gel states with improved mechanical strength and appearance despite identical molecular composition.[1] In the future, catalysis could provide dynamic and spatial control of material formation and properties using for instance switchable catalysts, or catalytically active, patterned surfaces.
[1] J. Boekhoven, J. M. Poolman, C. Maity, F. Li, L. van der Mee, C. B. Minkenberg, J. H. van Esch, R. Eelkema, submitted for publication.

We describe the creation of soft microscale assemblies that can propel themselves in the presence of a chemical fuel or can be actuated by an external magnetic field. These assemblies are created in situ within a microfluidic platform using the biopolymer chitosan as precursor. Our approach generates individual microscale droplets bearing chitosan, which are then made to undergo controlled cross-linking and coalescence into higher-order structures such as dimers or trimers. The size, shape, and functionality of each individual capsule within the dimer or trimer can be precisely controlled. For example, we have prepared dimers wherein one lobe contains nanoparticles of platinum (Pt). Such capsule dimers undergo self-propelled motion in water upon the introduction of hydrogen peroxide (H2O 2) to the solution. In this case, the catalytic reaction of H2O 2 with the encapsulated Pt produces oxygen gas, and the expulsion of this gas from the capsule in the form of bubbles propels the dimer forward in a direction away from the Pt-containing lobe. Similarly, magnetically responsive dimers can be created by substituting the Pt with paramagnetic Fe2O 3 nanoparticles. The resulting dimers undergo controlled rotation in an external magnetic field, much like a magnetic stir bar. The overall approach described here is simple and versatile: it can be easily adapted in a multitude of ways to produce soft structures with designed functions and properties.

This talk will provide an overview of our recent developments in the design of nanomaterials for ultrasensitive biosensing. Bio-responsive nanomaterials are of growing importance with potential applications including drug delivery, diagnostics and tissue engineering (1). DNA-, protein- or peptide-functionalised nanoparticle aggregates are particularly useful systems since triggered changes in their aggregation states may be readily monitored. Our recent simple conceptually novel approaches to real-time monitoring of protease, lipase and kinase enzyme action using modular peptide functionalized gold nanoparticles and quantum dots will be presented (2). Furthermore we have recently developed a new approach to ultrasensitive biosensing through plasmonic nanosensors with inverse sensitivity by means of enzyme-guided crystal growth (3) as well as a “Plasmonic ELISA” for the ultrasensitive detection of disease biomarkers with the naked eye (4). We are applying these biosensing approaches both in high throughput drug screening and to diagnose diseases ranging from cancer to global health applications.
References
[1] Stevens MM, George JH, Exploring and engineering the cell surface interface., Science, 2005, Vol:310, Pages:1135-1138. [2] Aili D, Mager M, Roche D, Stevens MM, Hybrid Nanoparticle-Liposome Detection of Phospholipase Activity., Nano Lett, Vol:11, Pages:1401-1405. [3] Rodriguez-Lorenzo L, de la Rica R, Alvarez-Puebla RA, Liz-Marzan LM, Stevens MM, Plasmonic nanosensors with inverse sensitivity by means of enzyme-guided crystal growth, Nature Materials, 2012, Vol:11, Pages:604-607. [4] De la Rica R, Stevens MM, Plasmonic ELISA for the ultrasensitive detection of disease biomarkers with the naked eye., Nature Nanotechnology, 2012 online. doi:10.1038/nnano.2012.186.

The immobilisation of vesicles and liposomes via recognition units such as complementary DNA strands, electrostatic interactions
and protein-ligand pairs has attracted increasing attention in recent years. By using these recognition units, it was possible to attach liposomes and vesicles to a variety of substrates, to prepare microarrays of liposomes, to construct sensing platforms and to investigate reactions in immobilized liposomes, including single molecules reactions. Coiled-coil motifs are abundant in proteins where they exhibit an array of functions like gene regulation, cell signalling, transport of small molecules and membrane fusion. Native SNARE proteins control fusion processes between and within cells (e.g. exocytosis). The common feature of all these coiled-coils is that at least two α-helical peptide strands bind, thereby acting as molecular Velcro. The specific molecular recognition between helices has enabled scientists to develop self-assembled, highly structured materials based on the coiled-coil motif. Here we describe a completely new function for the coiled-coil peptide binding units - their application in material science and surface modification. In this communication we report that an α-helical coiled-coil pair shown to exclusively form parallel heterodimers, denoted “peptide E” (EIAALEK)3 and “peptide K” (KIAALKE)3, act as selective recognition units through which liposomes and vesicles can be selectively immobilized in surface patterns obtained using microcontact printing. In summary we described a novel system for the immobilization of liposomes and the formation of supported bilayers by using a coiled-coil binding motif which was printed using microcontact printing-induced click chemistry. It was possible to obtain well defined structures of liposomes and supported bilayers. This technique shows great potential to study fluidity and recognition processes of supported lipid bilayers. Further experiments will be conducted in the future to investigate orthogonality of the coiled-coil binding motifs as well as the

Presenter: Jeff Bates
Seung Hei Cho, Jules Magda, Prashant Tahireddy, Loren Rieth, Swomitra Mohanty
University of Utah: Departments of Materials Science and Engineering and Chemical Engineering
Hydrogels are considered smart materials because they respond to environmental stimuli. pH responsive hydrogels swell at lower pH levels and deswell as the pH increases. Sensors that monitor the body&’s pH levels would be helpful for doctors to determine the severity of a patient&’s condition, especially if they exhibit signs of shock. The motivation of this project is to create a biomedical device that can be worn sublingually or implanted into the body to help doctors in their diagnoses. The magnitude of the swelling/deswelling behavior can be measured by placing a sample of the hydrogel in a piezoresistive sensor. The degree of swelling/deswelling is directly proportional to the change in pH of the aqueous solution it is placed in. In this study, a variety of compositions of pH responsive hydrogels were designed and tested to determine the response magnitudes and rates in both a macro and micro sensor array. A new micro sensor will be used to characterize the gels. This pressure sensor has been designed for use with much thinner gels than have been used in the past. The swelling rate and magnitude results were compared to determine the effect of the thickness of the hydrogel samples on the swelling/deswelling kinetics of the material in order to find the appropriate composition, thickness and device that will yield the desired response rate and sensitivity.
Contact Information:
Jeff Bates
[email protected]

Amphiphilic block copolymers capable of self-assembly into various nanoscale structures are attractive candidates for applications in sensing, controlled delivery and as nanoreactors. We report on synthesis of novel temperature responsive copolymers of water-soluble poly(vinylcaprolactam) (PVCL) and poly(vinylpyrrolidone) (PVPON) blocks and their assembly into temperature-responsive nanostructures in aqueous solutions. The PVCL-block-PVON copolymers were synthesized by RAFT polymerization. The copolymers became amphiphilic upon increase in solution temperature due to the reversible coil-to-globule transition of PVCL blocks. The LCST of the diblock copolymers ranged from 35 to 43°C depending on PVCL molecular weight and the ratio of PVCL to PVPON lengths. Remarkably, the PVCL-block-PVPON copolymers underwent temperature-induced self-assembly into nanostructures of 70 nm to 200 nm in size with hydrophobic PVCL blocks shielded by hydrophilic PVPON. The effects of the block lengths ratio, PVCL molecular weight, and the copolymer concentration on the temperature-triggered formation and disassembly of the nanostructures were examined by NMR, light scattering, TEM and SEM.

Polymeric carriers with finely controlled and responsive properties have been receiving great interest in therapeutic delivery systems for biomedical applications [1]. Mesoporous silica (MS) particles are attractive candidates as templates for preparation of such polymeric carriers, due to their facile preparation method, high loading capacity, and tunable template properties including surface area, controllable pore size, and tunable diameter. The polymeric particles can be easily prepared by infiltrating the polymer into MS particles, followed by crosslinking and subsequent removal of the template. Recently, we have developed a new technique to make polymeric carriers with customised material properties including controlled particle stiffness, loading of a range of therapeutics and tunable release of cargo with biological stimuli (e.g., enzyme, pH, reduction) using MS particles as templates [2-4]. Both hydrophilic (e.g., doxorubicin) and hydrophobic (e.g., paclitaxel and thiocoraline) anticancer drugs have been encapsulated in the MS-mediated polymer particles. These durg-loaded materials demonstrated cytotoxicity in cancer cells. In addition, vaccine particles with effective dendritic cell stimulation are also prepared using this general method, which highlights the potential of nanoengineered polymer particles for vaccine delivery. The reported technique is facile and versatile method to prepare cargo-loaded polymeric carriers, which represents a novel paradigm in the delivery of drugs and vaccines.
References
[1] G. K. Such, A. P. R. Johnston, F. Caruso Chem. Soc. Rev. 2011, 40, 19.
[2] J. Cui, Y. Yan, Y. Wang, F. Caruso Adv. Funct. Mater. 2012, DOI: 10.1002/adfm.201201191.
[3] Y. Wang, V. Bansal, A. N. Zelikin, F. Caruso Nano Lett. 2008, 8, 1741.
[4] Y. Wang, Y. Yan, J. Cui, L. Hosta-Rigau, J. K. Heath, E. C. Nice, F. Caruso Adv. Mater. 2010, 22, 4293.

We determine the time- and force-dependent viscoelastic responses of reconstituted networks of microtubules that have been strongly bonded by labile crosslinkers. To measure the microscale viscoelasticity of such networks, we use a magnetic tweezers device to apply localized forces. At short time scales, the networks respond nonlinearly to applied force, with stiffening at small forces, followed by a reduction in the stiffening response at high forces, which we attribute to the force-induced unbinding of crosslinks. At long time scales, force-induced bond unbinding leads to local network rearrangement and significant bead creep. Interestingly, for rigidly crosslinked networks, the material retains its elastic modulus even under conditions of significant plastic flow, suggesting that crosslinker breakage is balanced by the formation of new bonds. To
better understand this effect, we developed a finite element model of such a stiff filament network with crosslinkers obeying force-dependent Bell model unbinding dynamics. The coexistence of dissipation, due to bond breakage, and the elastic recovery of the network is possible because each filament has many crosslinkers. Recovery can occur as long as a sufficient number of the original crosslinkers are preserved under the loading period. When these
remaining original crosslinkers are broken, plastic flow results. We will discuss both passive crosslinkers (for example, biotin-streptavidin bonds) as well as ATP-dependent motor proteins that are capable of dynamic network reorganization, and can generate force.

We report on synthesis of a new type of highly swellable ultrathin cationic hydrogel with pH-triggered swelling behaviour and surface wettability. The single-component poly(4-vinyl pyridine) (P4VP) hydrogel films are produced by selective cross-linking of P4VP copolymers in layer-by-layer (LbL) films assembled via spin-assisted deposition. These multilayer hydrogels exhibit drastic and reversible 10-fold swelling when the pH is changed from neutral to acidic. The swelling amplitude of the hydrogels is controlled by varying cross-link densities within the films. These densities are varied by the number of cross-linkable amino-containing units in P4VP copolymer chains. We have found surface morphology of the hydrogels to be significantly affected by fabrication conditions. Contact angles vary from 70° to less than 10° for the films prepared from neutral and acidic solutions, respectively. Our work opens new prospects for developing highly swellable stimuli-responsive nanothin hydrogels for sensing and transport regulation in microfluidic devices.

The controlled assembly of peptides and polypeptides into a variety of structures continues to attract significant research interest. The choice of peptide sequence predetermines the higher order structure, improves desired properties, and adds functionality to the assembly. Previously, many of these structures have been confined to a range of less than half a micron. In our lab, we discovered the formation of a unique tubular hollow assembly from the FITC-modified non-helical collagen mimetic peptide Gly-Gly-(Pro-Hyp-Gly)₄. These structures are up to 2 mu;m in diameter and retain many of the appealing properties of other well-studied structures such as thermal and pH stability and ease of fabrication. Our goal for this project has been to characterize the structural features of these assemblies and discover their mechanism of formation. To that end, various visualization methods including confocal microscopy and transmission electron microscopy, as well as ATR-FTIR and TGA are employed.

Self-healing is a vital function of the human skin. However, the human skin&’s repeatable self-healing ability has never been successfully realized on electronic sensor skins until now. Here, we demonstrated the first example of a repeatable self-healing electronic sensor skin by using a composite of a self-healing supramolecular polymer and nano-structured metal particles. By rationally varying the composition of the electrically conductive inorganic fillers, we can obtain both electrodes and piezo-resistive sensor materials. The composite exhibits excellent mechanical flexibility and its electrical conductivity can reach as high as 40 S cm-1. Remarkably, both conductors and sensors display repeatable high electrical and mechanical healing capability at room temperature. We further integrated our self-healing electronic composite into an electronic sensor skin capable of detecting touch and flexion. We anticipate that our strategy of using supramolecular organic-inorganic composites will push forward the exciting application frontier of self-healing, multi-functional electronic composites.
References:
1 C. Wang*, B. Tee*, Z. Bao et al. Nat. Nanotechnol. accepted.

Materials with tunable morphology and mechanical properties show great promise for a wide range of applications in energy, biotechnology, and medicine. Assemblies that rely on highly specific biomolecular interactions are an attractive approach for the bottom-up design of materials with sophisticated properties. Here, we use the intrinsic self-assembling properties of the designed, rod shaped, superhelical consensus sequence tetratricopeptide repeat protein, CTPR, to generate such protein-polymers hybrid materials.
CTPR arrays comprised of 20 tandem repeats self-assemble into uniformly birefringent, transparent films upon solvent casting. X-ray scattering experiments confirm macroscopic alignment of the CTPR molecules within the film and CD and FTIR measurements show that the CTPR protein retains α-helical secondary structure. Individual CTPR arrays in the film are further covalently cross-linked using linear bi-functional photoactive polyethylene glycol. Here we will discuss rheological and thermal properties of resulting networks as a function of polyethylene glycol concentration and length.

Hydrogels are broadly used in bioengineering, but the scope of their applications is often severely limited by the mechanical behavior of hydrogels. Here we report exceptionally stretchable and tough hydrogels made of polymers forming networks via ionic and covalent crosslinks. Although such a gel contains ~ 90% water, it can be stretched beyond 20 times its initial length, and has fracture energy of ~9000 J/m2. Even for samples containing notches, a stretch of 17 is demonstrated. The high fracture energy is attributed to the synergy of two toughening mechanisms: crack bringing by the network of covalent crosslinks, and hysteresis by unzipping the network of ionic crosslinks over a large region of the gel. Furthermore, the network of covalent crosslinks preserves the memory of the initial state, so that much of the large deformation is removed when the load is removed. The unzipped ionic crosslinks cause internal damage, which heals as ionic crosslinks re-zip. We envision that these hydrogels will serve as model systems to explore mechanisms of deformation and energy dissipation, and that hydrogels with enhanced mechanical properties will considerably expand the scope of their applications. This talk draws upon Jeong-Yun Sun, Xuanhe Zhao, Widusha R.K. Illeperuma, Kyu Hwan Oh, David J. Mooney, Joost J. Vlassak, Zhigang Suo. Highly stretchable and tough hydrogels. Nature 489, 133-136 (2012).

Reconfigurable covalent networks confer many unique capabilities in smart materials including shape-memory properties and the capacity for self-healing. In this work, we describe the application of general strategies for reconfigurable polymers for use in medical devices and materials. These efforts utilize concepts of reconfigurable polymer networks across multiple length scales and utilize several exogenous stimuli such as light and heat. The results of these efforts are a new class of stimuli-responsive biodegradable elastomers and gels that will be illustrated in two examples. The first case describes the design and synthesis of elastomeric polyesters with reconfigurable covalent crosslinking. These biodegradable materials can be processed into structures with complex geometries and linear degradation kinetics. The properties of these materials render them ideal for applications in endovascular devices. The second example describes the use of crosslinked networks that are can reconfigured using exogenous light. Photolabile block copolymers are assembled into physically crosslinked networks that can be tuned to form either solid films or hydrogels. The morphological and physical properties of these networks were characterized using several techniques including atomic force microscopy, tensile testing, and rheology. The rapid disintegration of these networks can be triggered through reconfiguration of the physical crosslinks. Taken together, these results suggest that reconfigurable biodegradable polymeric networks have the potential for substantial utility as smart medical materials.

Hydrogels have been long used as cell-entrapping carriers for applications ranging from injectable biomaterials to in vitro cell culture studies. In such scenarios, the cells are passively entrapped in a polymer gel matrix. We demonstrate an alternate scenario where cells serve as active structural elements (crosslinks) in a polymer gel network. The polymers used in this context are hydrophobically modified (hm) derivatives of common polysaccharides such as alginate and chitosan. These polymers are able to rapidly transform a liquid suspension of cells into an elastic gel. In contrast, the native biopolymer (without hydrophobes) does not cause such gelation. Gelation occurs because the hydrophobes extending from the polymer chains get inserted into cell membranes due to hydrophobic interactions. The polymer chains thus bridge the cells, which act as crosslink points (junctions) in a 3-D network. We will show that a variety of cell types, including blood cells and endothelial cells, can be gelled by this approach, and we will discuss the fate of the cells in the network after gelation. Finally, as the crosslinking mechanism is based on hydrophobic interactions, we will show that addition of supramolecules with strong hydrophobic binding pockets can reverse the crosslinking and release the cells.

Self-assembly of nanoscopic components into higher-order architectures defines the forefront of fundamental nanoscience research and is important for the development of new materials with potential applications in optoelectronics, high-density data storage, catalysis, and biological sensing. In my talk, I will discuss how the peculiar nature of electrostatic, photoinduced dipole-dipole, and other forces acting between nanoscale components can mediate their self-assembly into various superstructures and materials. I will show how the interactions underlying self-assembly can be studied and understood in quantitative detail, and how they can be tailored to synthesize unusual higher-order architectures: ionic-like crystals of nanoparticles, crystalline aggregates that can be assembled and disassembled by light, as well as extremely durable and yet very flexible metallic structures. Since these materials display a range of novel optical, electrical and mechanical properties, the discussion of experimental results will be accompanied by theoretical analyses combining elements of thermodynamics, statistical mechanics, electrodynamics and elasticity.

We develop a computational model to simulate the behavior of photo-responsive polymer gels that contain spirobenzopyran (SP) chromophores. Using this model, we design three-dimensional samples with dynamically reconfigurable morphologies and photo-induced motility. In the dark, the SP moieties assume an open ring conformation and are hydrophilic; under illumination with blue light, the chromophores assume a closed ring conformation and are hydrophobic. This collapse of the gels is caused by the decrease in hydration due to conformational changes and not by a light-induced heating of the polymer network. We demonstrate that these gels can be effectively patterned remotely and reversibly with light by illuminating the sample through photomasks. We also show that by introducing variations in crosslink density within the gels during their preparation, as well as introducing temperature gradients, we have additional means of guiding the dynamic behavior of these versatile, responsive systems. Furthermore, we demonstrate that one can use a mobile light source to move multiple gel pieces to a specific location. The results point to a novel method for controlling the self-organization of soft, reconfigurable materials.

Materials that autonomously respond to environmental changes are a fundamentally unique class of adaptive materials that require no additional external stimulus or input (eg. an “on/off switch”), to change from one state to another. While such “autonomous materials” in general hold incredible potential for a wide range of uses, their implementation is currently limited by the small number of specific material systems that have been fully developed and studied. For example, one class of these materials that is gaining attention is self-oscillating hydrogels driven by the Belousovminus;Zhabotinsky (BZ) reaction. Here, chemical energy is converted to mechanical swellminus;deswell motion as the hydrophobicity of the gel oscillates between two states in response to the reduction and oxidation of a tethered transition metal catalyst. Using this scheme, we have developed a technique where a reactive Ru catalyst-containing ink is printed onto a nonreactive polymer substrate. This postfunctionalization technique substantially broadens the abilities of autonomous, self-oscillating polymer systems beyond what is currently available because the ink can be printed on any substrate polymer or biomacromolecule with a primary amine functionality, including those copolymerized with 1-20% amine-containing monomer such as N-(3-Aminopropyl)methacrylamide. The resultant digital fabrication via printing or stamping provides various patterns, including spots, lines, and geometric shapes, on multiple substrate materials (e.g. polyacrylamide (PAAm), poly-N-isopropylacrylamide (PNIPAAm), gelatin, and copolymers of these). Using this technique, we will discuss the complex interaction of various design variables, including reactant concentrations, catalyst loading, boundary conditions and choice of substrate material, on the oscillation period and mechanical strain behavior of the patterned gels. These performance bounds provide the foundation for the development of improved autonomic materials as well as routes to applications, such as encryption devices and photo-regulated micro transport vehicles.

We have recently developed a Systems Chemistry [1] approach to the development of new materials. Where molecular self-assembly is a well-established tool for preparing new materials, this approach still requires the design and synthesis of the self-assembling molecules. We have recently coined the term “self-synthesizing materials” to describe materials for which the assembly process also drives the selection and synthesis of the very molecules that assemble [2]. The starting point for such approach is an equilibrium mixture of interconverting compounds (a dynamic combinatorial library [3,4]) that is made by mixing simple building blocks together that connect to each other by forming reversible covalent bonds. The idea is that, when any of the resulting library members are capable of binding to other molecules in the system (identical to themselves or otherwise), the equilibrium will shift in favor of these assembling molecules. This process will result in materials that self-synthesize and that are based on molecular constituents that can be considered to self-replicate. I will show several systems that exhibit the emergence of self-synthesizing materials based on this principle, resulting in fibers, sheets, vesicles and hydrogels [4,5]. The generality of the approach is further demonstrated by the diversity of assembly motifs that may drive self-synthesis and self-replication and that include beta-sheet formation by peptides, hydrophobic interactions between amphiphiles and metal-ligand coordination.
Relevant publications:
1 R. F. Ludlow, S. Otto, Chem. Soc. Rev. 2008, 37, 101-108.
2 J. M. A. Carnall; C. A. Waudby; A. M. Belenguer; M. C. A. Stuart, J. J.-P. Peyralans, S. Otto Science 2010, 327, 1502-1506.
3 P. T. Corbett, J. Leclaire, L. Vial, K. R. West, J.-L. Wietor, J. K. M. Sanders, S. Otto Chem. Rev. 2006, 106, 3652-3711.
4 S. Otto Acc. Chem. Res. in press DOI: 10.1021/ar200246j
5 J. Li; J. M. A. Carnall; M. C. A. Stuart; S. Otto Angew. Chem. Int. Ed. 2011, 50, 8384-8386.

Magnetic resonance contrast agents were engineered by pure hierarchical self-assembly of micelles of the ligand 1,4,7,10-tetraza-1-(1-carboxymethylundecane)-4,7,10-triacetic acid cyclododecane (DOTAC10) inside protein cages of the cowpea chlorotic mottle virus (CCMV). The DOTAC10 ligand was used to either complex with Gd3+ in order to form paramagnetic micelles for MRI or to encapsulate amphiphilic Zn2+ phthalocyanine (ZnPc) dye molecules, which optically confirmed the encapsulation of the micelles. We report the successful encapsulation Gd-DOTAC10 micelles inside CCMV, to form stable assemblies. Subsequent incorporation of the ZnPc dye in these paramagnetic micelles led to noticeably higher capsid loadings and improved ionic and capsid relaxivities, which were confirmed by transmission electron microscopy, elemental analysis and size exclusion chromatography. These purely self-assembled protein cages containing paramagnetic micelles show enhanced capsid r1 relaxivities, highlighting the potential of these nanostructures as CAs for MRI. The enhanced relaxivity properties are attributed to aggregation and altered micelle association kinetics resulting from local confinement inside the protein cage and ZnPc dye encapsulation.

We build branched DNA species that can be joined using sticky ends to produce N-connected objects and lattices. We have used ligation to construct topological targets, such as DNA stick-polyhedra, Borromean rings and a Solomon's knot. Branched junctions with up to 12 arms have been assembled.
Nanorobotics is a key area of application. We have made robust 2-state and 3-state sequence-dependent devices that change structural states by varied hybridization topology. Bipedal walkers, both clocked and autonomous have been built. We have constructed a molecular assembly line by combining a DNA origami layer with three 2-state devices, so that there are eight different states represented by their arrangements. We have demonstrated that all eight products (including the null product) can be built from this system.
A central goal of DNA nanotechnology is the self-assembly of periodic and aperiodic matter. We have constructed 2-dimensional DNA arrays with designed patterns from many different motifs. We have used DNA scaffolding to organize active DNA components. Active DNA components include DNAzymes and DNA nanomechanical devices; both are active when incorporated in 2D DNA lattices. We have used pairs of 2-state devices to capture a variety of different targets. Multi-tile DNA arrays have been used to organize gold nanoparticles in specific arrangements. We have also used the principles of algorithmic assembly for the organization of nanoparticles.
We have self-assembled a 3D crystalline array and have solved its crystal structure to 4 Å resolution, using unbiased crystallographic methods. More than ten other crystals have been designed following the same principles of sticky-ended cohesion. We can use crystals with two molecules in the crystallographic repeat to control the color of the crystals. Thus, structural DNA nanotechnology has fulfilled its initial goal of controlling the structure of matter in three dimensions. A new era in nanoscale control awaits us.
This research has been supported by the NIGMS, NSF, ONR, ARO and DOE.

Highly reticulated, interconnected, and dynamic lipid organelles (e.g., endoplasmic reticulum) play important roles in physiological processes ranging from compartmentalization to higher-order functions such as vesicular trafficking. Foundational their functions, these organelles are capable of dynamically reorganizing their structure in response to intrinsic physiological signal based on energy-dissipative transport. Here, we report a dynamic, biomimetic assembly system in which millimeter-scale nanofluidic lipid networks are fabricated at synthetic interfaces through biomolecular motor-driven active transport. Introduction of multilamellar liposomes in gliding motility system, where surface-adsorbed kinesin motor propel the transport of microtubule filaments, results in a “tug-of-war” phenomenon in which lipid nanotubes are extracted from the larger vesicle and form highly bifurcated networks. The total size of these networks can exceed 10 mm in length, and is limited only by microtubule trajectories, microtubule surface density, kinesin fuel (ATP), and amount and properties of the source lipid. Similar to their cellular analogs, the lipid networks are highly dynamic in nature: they grow, shrink, move, and transform. The dynamic and highly-reticulated nature of these networks also provides a model for nanoscale materials transport where inherent redundancies built into the network enable high-fidelity transport. As an example, we characterized the diffusive transport of nanocrystals on the external leaflet of these lipid networks including transport through various types of junctions. Overall, this model system has broad applicability with respect to further understanding the dynamic assembly of adaptive soft matter, as well as how design fail-safe networks for nanoscale transport and communication processes.
* Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

There is great current interest in the synthesis of well-defined and functional polymers using controlled radical polymerization (CRP) techniques. The advances in the development of these techniques has enabled access to a wide range of functional and responsive materials for a diverse range of applications. Of the many CRP techniques that have been developed, reversible addition fragmentation chain transfer (RAFT) shows significant promise because of its ability to generate a large range of different architectures, and its tolerance to solvent and functionality within the chain transfer agent and the monomer. In the O&’Reilly group we use RAFT techniques to synthesize functional and responsive amphiphilic diblock copolymers from a range of monomers which have unique properties such as responsive capabilities, catalytic activity or selective recognition. We are interested in the solution self assembly and the characterization of the resultant aggregates along with their exploration in a range of applications. One interesting example is in the design of nanostructures which can exhibit fast and reversible transitions between different morphologies (and hence give rise to a change in physical properties) as a result of an alteration in the packing parameter of the constituent polymers in response to applied external stimuli. We have explored the application of these responsive materials in controlled release and also sensor applications.

Polyelectrolyte-based ionic hydrogels are three-dimensional networks which facilitate the transport of ions, particles and other molecules while maintaining their structure during swelling, shrinking and/or bending. Due to their biocompatibility and vigorous response to various external stimuli, hydrogels hold large promise as elements of stimuli-sensitive systems. Our research focuses on tuning the ionic equilibria of hydrogels to enable their application as soft matter components in robotics, drug delivery systems, actuation and sensing. We focus on mimicking the locomotion of miniature walking species, such as inchworms, by applying an electric field to manipulate gel ion distribution in solution. Prototype walkers with functionalized moving “legs” for an asymmetric response mechanism were developed. We also developed a method for patterning ions on hydrated gels utilizing metal ion complexation by an electric field. Termed ‘ionoprinting&’, this technique has the capability to topographically structure and actuate gels in 2D and 3D by patterning ions from electrodes in contact with hydrogels. These ionic patterns are stable for months and the ionoprinting process is fully reversible since patterns erase when immersed in a chelator. The ionic binding changes the local mechanical properties of the gel to induce 2D relief patterns and evokes localized stresses large enough to cause folding. These prepatterned hydrogels exhibit programmable temporal and spatial shape memory behavior and serve as basis of a new class of soft actuators able to gently manipulate objects both in air and in liquid.

Molecular designs that afford tunable supramolecular assemblies are of interest in a variety of applications, including catalysis and sensing. When these assemblies are nanoscopic in size and are responsive to specific stimulus, then the interests in these nanoscale scaffolds are even higher. We have developed macromolecule-based amphiphilic supramolecular assemblies, which not only exhibit these features, but also can bind guest molecules efficiently. We have also shown that these non-covalently bound guest molecules can be released in response to specific triggers. The molecular design principle is versatile enough to be adapted for physical, chemical, or biological stimuli.
From a fundamental perspective, we show the structural factors that underlie the stimuli-responsive behavior of supramolecular assemblies. From an application perspective, the implications are numerous. For example, non-covalent encapsulation of guest molecules and their triggered release is of paramount importance in the filed of drug delivery. Achieving such release characteristics using proteins as trigger would have significant implications in both drug delivery and bio-sensing, since protein imbalances are primary bases for the most of human diseases. Our molecular design not only allows for assembly and disassembly for more traditional stimuli, but also for protein-based stimuli.

Constitutional self-instructed membranes were developed and used for mimicking the adaptive structural functionality of natural ion-channel systems. These membranes are based on dynamic hybrid materials in which the functional self-organized macrocycles are reversibly connected with the inorganic silica through hydrophobic non-covalent interactions. Supramolecular columnar ion-channel architectures confined within scaffolding hydrophobic silica mesopores can be structurally determined and morphologically tuned by alkali salts templating. From the conceptual point of view these membranes express a synergistic adaptive behavior: the addition of the fittest alkali ion drives a constitutional evolution of the membrane toward the selection and amplification of the specific transporting superstructures within the membrane in the presence of the cation that promoted its generation in the first place. This is the nice example of dynamic self-instructed (“trained”) membranes where a solute induces the upregulation (prepare itself) of its own selective membrane.
1. A. Cazacu, Y.M. Legrand, A. Pasc, G. Nasr, A. van der Lee, E. Mahon, M. Barboiu, Proc. Natl. Acad. Sci., 2009, 106(20), 8117-8122.
2. M. Barboiu, Chem. Commun. 2010, 46, 7466-7476.S. Mihai, J. Dauthier, Y. Le Duc, A. El Mansouri, A. Mehdi, M. Barboiu, Eur. J. Inorg. Chem. 2012, DOI: 10.1002/ejic.201200754
3. M. Barboiu, A. Cazacu, S. Mihai, Y.-M. Legrand, G. Nasr, Y. Le Duc, E. Petit, A. van der Lee, Dynamic constitutional hybrid materials-toward adaptive self-organized devices, Microp. Mesop. Mat. 2011, 140, 51-57.

We explore various ways to control the structure of self-assembled tubules. We have previously developed a model wedge-shaped monomer that can self-assemble into tubule structures. We now add chirality and a lock-and-key mechanisms to the model to enhance structural control of the self-assembly. Previously, we found that helical tubes are frequently formed despite the fact that chiral symmetry is not present in the monomer. We now identify the physical origin of helicity as the large overlap in the energy distributions between nonhelical and helical tubes. The helical tubes typically undergo a twist deformation that lowers the energy substantially. We find that a modification of the location of binding sites on the bottom and top surfaces of the wedge into a lock-and-key configuration leads to a better control of the helicity and twist deformation of the assembled tubes. Better control occurs when the interaction strength between the vertical binding sites is stronger than that between the lateral ones. We can also control the pitch of the helicity by these additions to the monomer model. Our results shed new light on the structure of in vitro microtubules formed with various numbers of protofilaments of tubulins, which also exhibit twisted structures when the number is different from 13.

Atherosclerosis is a major cause of mortality worldwide. Consequently, there has been great interest in developing new therapeutic modalities, particularly involving the elevation or functional modulation of high-density lipoproteins (HDLs), to treat coronary heart disease and stroke. The antiatherogenic effects of HDL stems from its participation in reverse cholesterol transport (RCT), a process by which excess free cholesterol and other lipids are transported from peripheral tissues to the liver for elimination. I will present the design and discovery of designer peptides that functionally mimic apolipoprotein A-I (apoA-I), the key protein component of high-density lipoprotein (HDL). The apoA-I mimetic peptides can be fashioned into nanolipid particles of similar size and shape as native HDL that function in human or mouse plasma to remodel mature HDL into nascent, discoidal HDL, the key initial particles in RCT. Moreover, the apoA-I mimetic peptides are effective in promoting cholesterol efflux from human macrophage cells. These constructs were found to be remarkably stable to proteolysis, display a protracted half-life in mouse plasma in vivo, and highly efficacious in reducing plaque buildup in a 10-week in vivo study. Together our results provide a potential path toward developing novel therapeutic agents for the management of atherosclerosis.