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Pathways in supramolecular polymerization traverse different regions of the system's energy landscape, affecting not only their architectures and internal structure but also their functions. We report here on the effects of pathway selection on polymerization for two isomeric peptide amphiphile monomers with amino acid sequences AAEE and AEAE. We subjected the monomers to five different pathways that varied in the order they were exposed to electrostatic screening by electrolytes and thermal annealing. We found that introducing electrostatic screening of E residues before annealing led to crystalline packing of AAEE monomers. Electrostatic screening decreased intermolecular repulsion among AAEE monomers thus promoting internal order within the supramolecular polymers, while subsequent annealing brought them closer to thermodynamic equilibrium with enhanced β-sheet secondary structure. In contrast, supramolecular polymerization of AEAE monomers was less pathway dependent, which we attribute to side-chain dimerization. Regardless of the pathway, the internal structure of AEAE nanostructures had limited internal order and moderate β-sheet structure. These supramolecular polymers generated hydrogels with lower porosity and greater bulk mechanical strength than those formed by the more cohesive AAEE polymers. The combination of dynamic, less ordered internal structure and bulk strength of AEAE networks promoted strong cell-material interactions in adherent epithelial-like cells, evidenced by increased cytoskeletal remodeling and cell spreading. The highly ordered AAEE nanostructures formed porous hydrogels with inferior bulk mechanical properties and weaker cell-material interactions. We conclude that pathway sensitivity in supramolecular synthesis, and therefore structure and function, is highly dependent on the nature of dominant interactions driving polymerization.

Supramolecular peptide chemistry offers a versatile strategy to create chemical systems useful as new biomaterials with potential to deliver nearly 1000 known candidate peptide therapeutics or integrate other types of bioactivity. We report here on the co-assembly of lipidated β-sheet-forming peptides with soluble short peptides, yielding supramolecular copolymers with various degrees of internal order. At low peptide concentrations, the co-monomer is protected by lodging within internal aqueous compartments and stabilizing internal β-sheets formed by the lipidated peptides. At higher concentrations, the peptide copolymerizes with the lipidated peptide and disrupts the β-sheet secondary structure. The thermodynamic metastability of the co-assembly in turn leads to the spontaneous release of peptide monomers and thus serves as a potential mechanism for drug delivery. We demonstrated the function of these supramolecular systems using a drug candidate for Alzheimer's disease and found that the copolymers enhance neuronal cell viability when the soluble peptide is released from the assemblies.

The concept of origami has influenced the development of responsive materials that can mimic complex functions performed by living organisms. An ultimate goal is to discover and design soft materials that can be remotely actuated into diverse structures. To achieve this goal, we design and synthesize here a light-responsive spiropyran hydrogel system that can display dynamic shape changes upon irradiation with local light. We use a continuum polymer model to analyze the behavior of the constructed photoactive hydrogel, which is in good agreement with the experimental results. We explore different buckling modalities and patterns in a different range of parameters. The synthesis and fabrication of these materials demonstrate that the theoretical model can be used to drive the development of responsive photoactive systems.

Herein, we report the photoinitiated polymerization-induced self-assembly (photo-PISA) of spherical micelles consisting of proapoptotic peptide-polymer amphiphiles. The one-pot synthetic approach yielded micellar nanoparticles at high concentrations and at scale (150 mg mL -1 ) with tunable peptide loadings up to 48 wt. %. The size of the micellar nanoparticles was tuned by varying the lengths of hydrophobic and hydrophilic building blocks. Critically, the peptide-functionalized nanoparticles imbued the proapoptotic "KLA" peptides (amino acid sequence: KLAKLAKKLAKLAK) with two key properties otherwise not inherent to the sequence: 1) proteolytic resistance compared to the oligopeptide alone; 2) significantly enhanced cell uptake by multivalent display of KLA peptide brushes. The result was demonstrated improved apoptosis efficiency in HeLa cells. These results highlight the potential of photo-PISA in the large-scale synthesis of functional, proteolytically resistant peptide-polymer conjugates for intracellular delivery., (© 2020 Wiley-VCH GmbH.)

The development of synthetic structures that mimic mechanical actuation in living matter such as autonomous translation and shape changes remains a grand challenge for materials science. In living systems the integration of supramolecular structures and covalent polymers contributes to the responsive behaviour of membranes, muscles and tendons, among others. Here we describe hybrid light-responsive soft materials composed of peptide amphiphile supramolecular polymers chemically bonded to spiropyran-based networks that expel water in response to visible light. The supramolecular polymers form a reversibly deformable and water-draining skeleton that mechanically reinforces the hybrid and can also be aligned by printing methods. The noncovalent skeleton embedded in the network thus enables faster bending and flattening actuation of objects, as well as longer steps during the light-driven crawling motion of macroscopic films. Our work suggests that hybrid bonding polymers, which integrate supramolecular assemblies and covalent networks, offer strategies for the bottom-up design of soft matter that mimics living organisms.

Skeletal muscle provides inspiration on how to achieve reversible, macroscopic, anisotropic motion in soft materials. Here we report on the bottom-up design of macroscopic tubes that exhibit anisotropic actuation driven by a thermal stimulus. The tube is built from a hydrogel in which extremely long supramolecular nanofibers are aligned using weak shear forces, followed by radial growth of thermoresponsive polymers from their surfaces. The hierarchically ordered tube exhibits reversible anisotropic actuation with changes in temperature, with much greater contraction perpendicular to the direction of nanofiber alignment. We identify two critical factors for the anisotropic actuation, macroscopic alignment of the supramolecular scaffold and its covalent bonding to polymer chains. Using finite element analysis and molecular calculations, we conclude polymer chain confinement and mechanical reinforcement by rigid supramolecular nanofibers are responsible for the anisotropic actuation. The work reported suggests strategies to create soft active matter with molecularly encoded capacity to perform complex tasks.

Electrospinning is a high-throughput, low-cost technique for manufacturing long fibers from solution. Conventionally, this technique is used with covalent polymers with large molecular weights. We report here the electrospinning of functional peptide-based supramolecular polymers from water at very low concentrations (<4 wt %). Molecules with low molecular weights (<1 kDa) could be electrospun because they self-assembled into one-dimensional supramolecular polymers upon solvation and the critical parameters of viscosity, solution conductivity, and surface tension were optimized for this technique. The supramolecular structure of the electrospun fibers could ensure that certain residues, like bioepitopes, are displayed on the surface even after processing. This system provides an opportunity to electrospin bioactive supramolecular materials from water for biomedical applications.

One of the challenges in organic systems with semiconducting function is the achievement of molecular orientation over large scales. We report here on the use of self-assembly kinetics to control long-range orientation of a quarterthiophene derivative designed to combine intermolecular π-π stacking and hydrogen bonding among amide groups. Assembly of these molecules in the solution phase is prevented by the hydrogen-bond-accepting solvent tetrahydrofuran, whereas formation of H-aggregates is facilitated in toluene. Rapid evaporation of solvent in a solution of the quarterthiophene in a 2:1:1 mixture of 1,4-dioxane/tetrahydrofuran/toluene leads to self-assembly of kinetically trapped mats of bundled fibers. In great contrast, slow drying in a toluene atmosphere leads to the homogeneous nucleation and growth of ordered structures shaped as rhombohedra or hexagonal prisms depending on concentration. Furthermore, exceedingly slow delivery of toluene from a high molecular weight polymer solution into the system through a porous aluminum oxide membrane results in the growth of highly oriented hexagonal prisms perpendicular to the interface. The amide groups of the compound likely adsorb onto the polar aluminum oxide surface and direct the self-assembly pathway toward heterogeneous nucleation and growth to form hexagonal prisms. We propose that the oriented prismatic polymorph results from the synergy of surface interactions rooted in hydrogen bonding on the solid membrane and the slow kinetics of self-assembly. These observations demonstrate how self-assembly conditions can be used to guide the supramolecular energy landscape to generate vastly different structures. These fundamental principles allowed us to grow oriented prismatic assemblies on transparent indium-doped tin oxide electrodes, which are of interest in organic electronics.

We report here the self-assembly of macroscopic sacs and membranes at the interface between two aqueous solutions, one containing a megadalton polymer and the other, small self-assembling molecules bearing opposite charge. The resulting structures have a highly ordered architecture in which nanofiber bundles align and reorient by nearly 90 degrees as the membrane grows. The formation of a diffusion barrier upon contact between the two liquids prevents their chaotic mixing. We hypothesize that growth of the membrane is then driven by a dynamic synergy between osmotic pressure of ions and static self-assembly. These robust, self-sealing macroscopic structures offer opportunities in many areas, including the formation of privileged environments for cells, immune barriers, new biological assays, and self-assembly of ordered thick membranes for diverse applications.

The coupling of electronic and biological functionality through self-assembly is an interesting target in supramolecular chemistry. We report here on a set of diacetylene-derivatized peptide amphiphiles (PAs) that react to form conjugated polydiacetylene backbones following self-assembly into cylindrical nanofibers. The polymerization reaction yields highly conjugated backbones when the peptidic segment of the PAs has a linear, as opposed to a branched, architecture. Given the topotactic nature of the polymerization, these results suggest that a high degree of internal order exists in the supramolecular nanofibers formed by the linear PA. On the basis of microscopy, the formation of a polydiacetylene backbone to covalently connect the beta-sheets that help form the fibers does not disrupt the fiber shape. Interestingly, we observe the appearance of a polydiacetylene (PDA) circular dichroism band at 547 nm in linear PA nanofibers suggesting the conjugated backbone in the core of the nanostructures is twisted. We believe this CD signal is due to chiral induction by the beta-sheets, which are normally twisted in helical fashion. Heating and cooling shows simultaneous changes in beta-sheet and conjugated backbone structure, indicating they are both correlated. At the same time, poor polymerization in nanofibers formed by branched PAs indicates that less internal order exists in these nanostructures and, as expected, then a circular dichroism signal is not observed for the conjugated backbone. The general variety of materials investigated here has the obvious potential to couple electronic properties and in vitro bioactivity. Furthermore, the polymerization of monomers in peptide amphiphile assemblies by a rigid conjugated backbone also leads to mechanical robustness and insolubility, two properties that may be important for the patterning of these materials at the cellular scale.

The precise structural control is known for self-assembly into closed spherical structures (e.g., micelles), but similar control of open structures is much more challenging. Inspired by natural tobacco mosaic virus, we present the use of a rigid-rod template to control the size of a one-dimensional self-assembly. We believe that this strategy is novel for organic self-assembly and should provide a general approach to controlling size and dimension.

Molecular self-assembly offers an effective method to modify the surface properties of common biomaterials by presenting biologically relevant chemistry in a controlled, ordered fashion. This work reports on self-assembling triblock molecules containing rigid cholesteryl segments followed by flexible oligomers of L-(lactic acid) and second generation L-lysine dendrons. Second harmonic generation and small angle X-ray scattering indicate these molecules self-assemble into multilayer polar structures when cast from ethyl acetate solutions and segregate into polar polydomains when annealed. These self-assembled layers significantly improve water wettability when coated onto poly(L-lactic acid) fibers. Scaffolds formed from fibers modified by self-assembly enhance adhesion of 3T3 mouse calvaria cells and produce greater population growth rates. These results demonstrate the use of self-assembly to present biologically relevant chemistry on surfaces of biomaterials. Applications of this technology include the modification of substrates for cell culture, tissue engineering, and cell transplantation.

The combination of bottom-up and top-down processes to organize nanophases in hybrid materials is a key strategy to create functional materials. We found that oxide and sulphide nanocrystals become spontaneously dispersed in organic media during the self-assembly of nanoribbon supramolecular polymers. These nanoribbon polymers form by self-assembly of dendron rodcoil molecules, which contain three molecular blocks with dendritic, rod-like, and coil-like architectures. In an electric field these supramolecular assemblies carrying bound nanocrystals migrate to the positive electrode in an etched channel and align in the field. In the system containing ZnO nanocrystals as the inorganic component, both phases are oriented in the hybrid material forming an ultraviolet lasing medium with a lower threshold relative to pure ZnO nanocrystals.

Herein, we report the photoinitiated polymerization‐induced self‐assembly (photo‐PISA) of spherical micelles consisting of proapoptotic peptide–polymer amphiphiles. The one‐pot synthetic approach yielded micellar nanoparticles at high concentrations and at scale (150 mg mL−1) with tunable peptide loadings up to 48 wt. %. The size of the micellar nanoparticles was tuned by varying the lengths of hydrophobic and hydrophilic building blocks. Critically, the peptide‐functionalized nanoparticles imbued the proapoptotic "KLA" peptides (amino acid sequence: KLAKLAKKLAKLAK) with two key properties otherwise not inherent to the sequence: 1) proteolytic resistance compared to the oligopeptide alone; 2) significantly enhanced cell uptake by multivalent display of KLA peptide brushes. The result was demonstrated improved apoptosis efficiency in HeLa cells. These results highlight the potential of photo‐PISA in the large‐scale synthesis of functional, proteolytically resistant peptide–polymer conjugates for intracellular delivery. [ABSTRACT FROM AUTHOR]

Staudinger established a century ago the existence of covalent macromolecules, work that led to the development of transformative materials of great benefit to society and a "quantum leap" in our understanding of biological systems. Over the past few decades the concept of supramolecular polymers has emerged–chemical systems in which structural units bond strongly to each other non‐covalently. These dynamic systems actually exist in the natural world and can create soft materials with structures, properties, and functions beyond the ones we know in Staudinger polymers. We reflect here on the potential of novel systems in which covalent and supramolecular polymers are chemically integrated and describe them as hybrid bonding polymers. This paper describes the concept with recent examples from the Stupp laboratory, and discusses their potential functions as robotic materials that mimic living matter and structures that offer new ideas on how to recycle and reuse soft materials. [ABSTRACT FROM AUTHOR]

There are three general methods for preparing graft copolymers: grafting onto, grafting through, and grafting from. Grafting onto requires the presence of complimentary functionalities on the graft unit and the backbone. Grafting through utilizes macromonomers, which are polymer chains that contain a copolymerizable moiety at the chain end. Homoor copolymerization with another monomer produces the graft copolymer. The grafting from technique employs a backbone containing reactive sites that are capable of initiating a polymerization. Each method suffers from its own particular disadvantages, but steric hindrance of the reactive center is common to all the graft copolymer routes, affecting the grafting efficiency. Figure 38 illustrates the three approaches. The least utilized in CRP is perhaps the grafting onto approach, while grafting through and grafting from are common. These will be detailed below. [ABSTRACT FROM AUTHOR]

This review has summarized the information available in the literature regarding various copolymers that involved some aspect of controlled/living radical polymerization (CRP) for their synthesis. The topics addressed included the formation of statistical, periodic and gradient copolymers, block and graft copolymers, including tethered copolymers, and segmented polymers with star-type chain architectures. There are numerous examples of the synthesis of all of these types of copolymers using only CRP techniques, whether it is the use of nitroxide-mediated systems, ATRP, or the degenerative transfer approach. In addition, other polymerization methods have been combined with CRP to afford segmented copolymers whose compositional combinations were never before possible. Living carbocationic, carbanionic, various types of ring-opening polymerization, coordination polymerization, and even step-growth processes have all been used in conjunction with CRP methods to produce polymers with novel structures. Finally, one of the most unique approaches to the preparation of segmented copolymers has been the development of initiators and monomers that can be used for two types of polymerization processes, whether it be in a stepwise or concurrent manner. These types of advances lend themselves to the development of routes for the preparation of materials with properties that can be specifically tuned for particular applications. [ABSTRACT FROM AUTHOR]

There have been numerous literature reports on the preparation of block copolymers using CRP methods. These copolymers range from those synthesized wholly by CRP to those that involve either transformation from other living polymerization techniques (anionic, cationic, ring-opening, etc.) to CRP, or functionalization of a macromolecule that can then be used as a macroinitiator for CRP. Each of these methods will be addressed separately. Nitroxides were predominantly used for styrene containing copolymers, whereas ATRP was successful for the acrylates and methacrylates as well [42]. [ABSTRACT FROM AUTHOR]

The simplest type of copolymer is one where two or more comonomers are simultaneously copolymerized. This technique is commonly used to modify and/or improve the mechanical and physical properties of many polymers. The relative rates of incorporation of each monomer in a given set of comonomers will be dependent on their reactivity ratios. These have been determined for the radical polymerization of numerous monomer pairs [5]. Choosing comonomers that have reactivity ratios close to 1 produces statistical copolymers, where the radical chain ends react as often with their own monomer as they do with the others, assuming equal concentrations of both monomers. If both the reactivity ratios are significantly higher than 1, indicating that the radical would prefer to homopropagate rather than cross-propagate, the backbone copolymer exhibits a more blocky structure. If both are much lower than 1, indicating that both radicals would prefer to cross-propagate, the copolymer takes on an alternating structure. This is the most typical case for a radical polymerization. If the copolymerization obeys Bernoullian statistics, a random copolymer is formed. However, polymerization may follow other types of statistics (e.g., Markovian), resulting in a variety of statistical copolymers. [ABSTRACT FROM AUTHOR]

This review is focused on controlled/living radical polymerization methods for the preparation of various copolymers. A brief introduction to the subject of radical polymerization, and early attempts to control it, is followed by a detailed examination of the literature on controlled/living radical copolymerizations from the mid-1990s until 2001. The topics covered include statistical/gradient, block, graft, and star copolymers, and the polymerization methods used to produce them. These copolymers were prepared using three major controlled radical methods (either nitroxide mediated polymerization, atom transfer radical polymerization, or degenerative transfer) and a combination of polymerization techniques, including transformation chemistry or the simultaneous/dual living polymerizations, to achieve the desired chain architecture or topology. An evaluation of the current state of the field is also presented. [ABSTRACT FROM AUTHOR]

The article discusses the design of photo- and electroactivated hydrogels capable of autonomously capturing and delivering cargo, navigating obstacles, and returning without external control. Topics include the creation of chemically random networks for photoregulated charge reversal and autonomous behavior, as well as using electric field guidance to attract or bypass materials with different dielectric constants, showing potential for intelligent robotic materials.

The electrosynthesis of a low band-gap and neutral-state green linear polymer incorporating a BODIPY core as the acceptor and bis(3,4-ethylenedioxythiophene) (bis-EDOT) as the donor has been described. Resulted polymer exhibited two well-defined absorption bands at 430 and 690 nm allowing it to absorb light in the whole visible spectrum. The resulting highly conjugated polymer showed electrochromic behavior and the color changes from neutral-state green to oxidized-state dark blue. The electrogenerated thin film of the polymer displayed good hole mobility in solid state and registered a photo-electrochemical response when light was applied. [ABSTRACT FROM AUTHOR]

We report here the synthesis and self-assembly of a series of three molecules with dendron rodcoil architecture that contain conjugated segments of oligo(thiophene), oligo(phenylene-vinylene), and oligo(phenylene). Despite their structural differences, all three molecules yield similar self-assembled structures. Electron and atomic force microscopy reveals the self-assembly of the molecules into high aspect ratio ribbon-like nanostructures which at low concentrations induce gelation in nonpolar solvent. Self- assembly results in a blue-shifted absorption spectrum and a red-shifted, quenched fluorescence spectrum, indicating aggregation of the conjugated segments within the ribbon-like structures. The assembly of these molecules into one-dimensional nanostructures is a route to π-π stacked supramolecular polymers for organic electronic functions. in the oligo(thiophene) derivative, self-assembly leads to a 3 orders of magnitude increase in the conductivity of iodine-doped films due to self-assembly. We also found that electric field alignment of these supramolecular assemblies can be used to create arrays of self-assembled nanowires on a device substrate. [ABSTRACT FROM AUTHOR]