Self-assembling, peptide-based scaffolds are frontrunners in the search for biomaterials with widespread impact in regenerative medicine. The inherent biocompatibility and cell signaling capabilities of peptides, in combination with control of secondary structure, has led to the development of a broad range of functional materials with potential for many novel therapies. More recently, membranes formed through complexation of peptide nanostructures with natural biopolymers have led to the development of hierarchically-structured constructs with potentially far-reaching applications in biology and medicine. In this review, we highlight recent advances in peptide-based gels and membranes, including work from our group and others. Specifically, we discuss the application of peptide-based materials in the regeneration of bone and enamel, cartilage, and the central nervous system, as well as the transplantation of islets, wound-healing, cardiovascular therapies, and treatment of erectile dysfunction after prostatectomy

Functional supramolecular systems like carbonyl-bridged triarylamine (CBT) trisamides are known for their long-range energy transport at room temperature. Understanding the complex self-assembly processes of this system allows for control over generated structures using controlled supramolecular polymerization. Here, we present two novel CBT trisamides with (S)- or (R)-chiral side chains which show a two-pathway self-assembly behavior in solution. Depending on the thermal profile during the self-assembly process, two different stable states are obtained under otherwise identical conditions. A kinetically trapped state A is reached upon cooling to 7 °C, via a proposed isodesmic process. In addition, there is a thermodynamically stable state B at 7 °C that is induced by first undercooling to -5 °C, via a nucleation-elongation mechanism. In both cases, helical supramolecular aggregates comprising H-aggregated CBTs are formed. Additionally, controlled supramolecular polymerization was achieved by mixing the two different states (A and B) from the same enantiomer, leading to a conversion of the kinetically trapped state to the thermodynamically stable state. This process is highly enantioselective, as no conversion is observed if the two states consist of opposite enantiomers. We thus show the importance and opportunities emerging from understanding the pathway complexity of functional supramolecular systems.

Water directs the self-assembly of both natural and synthetic molecules to form precise yet dynamic structures. Nevertheless, our molecular understanding of the role of water in such systems is incomplete, which represents a fundamental constraint in the development of supramolecular materials for use in biomaterials, nanoelectronics and catalysis . In particular, despite the widespread use of alkanes as solvents in supramolecular chemistry, the role of water in the formation of aggregates in oils is not clear, probably because water is only sparingly miscible in these solvents-typical alkanes contain less than 0.01 per cent water by weight at room temperature . A notable and unused feature of this water is that it is essentially monomeric . It has been determined previously that the free energy cost of forming a cavity in alkanes that is large enough for a water molecule is only just compensated by its interaction with the interior of the cavity; this cost is therefore too high to accommodate clusters of water. As such, water molecules in alkanes possess potential enthalpic energy in the form of unrealized hydrogen bonds. Here we report that this energy is a thermodynamic driving force for water molecules to interact with co-dissolved hydrogen-bond-based aggregates in oils. By using a combination of spectroscopic, calorimetric, light-scattering and theoretical techniques, we demonstrate that this interaction can be exploited to modulate the structure of one-dimensional supramolecular polymers.

Monodisperse oligodimethylsiloxanes end-functionalized with the hydrogen-bonding ureidopyrimidinone (UPy) motif undergo phase separation between their aromatic end groups and dimethylsiloxane midblocks to form ordered nanostructures with domain spacings of <5 nm. The self-assembly behavior of these well-defined oligomers resembles that of high degree of polymerization (N)–high block interaction parameter (χ) linear diblock copolymers despite their small size. Specifically, the phase morphology varies from lamellar to hexagonal to body-centered cubic with increasing asymmetry in molecular volume fraction. Mixing molecules with different molecular weights to give dispersity >1.13 results in disorder, showing importance of molecular monodispersity for ultrasmall ordered phase separation. In contrast, oligodimethylsiloxanes end-functionalized with an O-benzylated UPy derivative self-assemble into lamellar nanostructures regardless of volume fraction because of the strong preference of the end groups to aggregate in a planar geometry. Thus, these molecules display more classically liquid-crystalline self-assembly behavior where the lamellar bilayer thickness is determined by the siloxane midblock. Here the lamellar nanostructure is tolerant to molecular polydispersity. We show the importance of end groups in high χ–low N block molecules, where block-copolymer-like self-assembly in our UPy-functionalized oligodimethylsiloxanes relies upon the dominance of phase separation effects over directional end group aggregation.

Materials with highly ordered molecular arrangements have the capacity to display unique properties derived from their nanoscale structure. Here, the synthesis and characterization of azobenzene (AZO)-functionalized siloxane oligomers of discrete length that form photoswitchable supramolecular materials are described. Specifically, synergy between phase segregation and azobenzene crystallization leads to the self-assembly of an exfoliated 2D crystal that becomes isotropic upon photoisomerization with UV light. Consequently, the material undergoes a rapid athermal solid-to-liquid transition which can be reversed using blue light due to the unexpectedly fast 2D crystallization that is facilitated by phase segregation. In contrast, enabling telechelic supramolecular polymerization through hydrogen bonding inhibits azobenzene crystallization, and nanostructured pastes with well-ordered morphologies are obtained based on phase segregation alone, thus demonstrating block copolymer-like behavior. Therefore, by tailoring the balance of self-assembly forces in the azobenzene-functionalized siloxane oligomers, fast and reversible phase-changing materials can be engineered with various mechanical properties for applications in photolithography or switchable adhesion to lubricant properties. In these materials, contraction along the LC director occurs with isomerization of the planar trans-azobenzenes to the bent cis-azobenzenes. By limiting the depth of photoactivity, generally through utilizing the inherently high absorption coefficient of the azobenzenes, this contraction can give rise to anisotropic bending in poly mer films, [7,8] gels, [9] fibers, [10][11][12] and even crystals. [13] Different modes of motion arise with more complex molecular arrangements. For example, expansion of chiral nematic LCs along the helical axis has been utilized to create polymer coatings with photoswitchable topologies [14][15][16][17] and polymer films with macroscopic helical motion. [18] Additionally, polymer films with splay-bend configuration, in which LC-mesogens gradually change orientation throughout the film cross-section, have shown to exhibit inherently anisotropic bending as well as achieve significantly faster and larger bending when compared to uniaxially aligned films. [19][20][21] The ability of azobenzene photoisomerization to generate anisotropic dimension change and motion in LC networks typically results from increased molecular disorder caused by bent cis-azobenzene relative to networks with rod-like transazobenzene. Such photocontrol of order/disorder has been used to induce rapid nematic-to-isotropic phase transitions in LC films for applications in optical image storage [22] and holography. [23] The reversibility of azobenzene photoisomerization is beneficial for such applications, and the ability of azobenzene materials to undergo many trans-cis photoisomerization cycles without noticeable degradation in performance has been demonstrated. [24,25] Furthermore, few examples have demonstrated the photocontrolled swit...

Inspired by the catechol and amine-rich adhesive proteins of mussels, polydopamine (pDA) has become one of the most widely employed methods for functionalizing material surfaces, powered in part by the versatility and simplicity of pDA film deposition that takes place spontaneously on objects immersed in an alkaline aqueous solution of dopamine monomer. Despite the widespread adoption of pDA as a multifunctional coating for surface modification, it exhibits poor mechanical performance. Attempts to modify the physical properties of pDA by incorporation of oxidizing agents, cross-linkers, or carbonization of the films at ultrahigh temperatures have been reported; however, improving mechanical properties with mild post-treatments without sacrificing the functionality and versatility of pDA remains a challenge. Here, we demonstrate thermal annealing at a moderate temperature (130 °C) as a facile route to enhance mechanical robustness of pDA coatings. Chemical spectroscopy, X-ray scattering, molecular force spectroscopy, and bulk mechanical analyses indicate that monomeric and oligomeric species undergo further polymerization during thermal annealing, leading to fundamental changes in molecular and bulk mechanical behavior of pDA. Considerable improvements in scratch resistance were noted in terms of both penetration depth (32% decrease) and residual depth (74% decrease) for the annealed pDA coating, indicating the enhanced ability of the annealed coating to resist mechanical deformations. Thermal annealing resulted in significant enhancement in the intermolecular and cohesive interactions between the chains in the pDA structure, attributed to cross-linking and increased entanglements, preventing desorption and detachment of the chains from the coating. Importantly, improvements in pDA mechanical performance through thermal annealing did not compromise the ability of pDA to support secondary coating reactions as evidenced by electroless deposition of a metal film adlayer on annealed pDA.

Self-assembly programmed by molecular structure and guided dynamically by energy dissipation is a ubiquitous phenomenon in biological systems that build functional structures from the nanoscale to macroscopic dimensions. This paper describes examples of one-dimensional self-assembly of peptide amphiphiles and the consequent biological functions that emerge in these systems. We also discuss here hierarchical self-assembly of supramolecular peptide nanostructures and polysaccharides, and some new results are reported on supramolecular crystals formed by highly charged peptide amphiphiles. Reflecting on presentations at this Faraday Discussion, the paper ends with a discussion of some of the future opportunities and challenges of the field.

Silk is a source of marvel for centuries as one of nature's high-performance materials. More recently, chemical and structural analysis techniques have helped explore the relationship between silk's properties and its hierarchical structure. Furthermore, recombinant protein engineering as well as polymer and organic synthesis techniques have enabled the production of silk-like materials. It has become apparent that silk is a supramolecular polymer with many of the properties exhibited by well-known synthetic supramolecular materials, such as block copolymers, liquid crystals, thermoplastic elastomers, and self-assembling peptides. In this review, the hierarchical structure and supramolecular assembly of silk are discussed in comparison to these synthetic supramolecular systems. By focusing on the connections between chemical structure, nanoscale molecular organization, and material properties, the aim is to provide perspectives on the rational design of advanced soft matter to supramolecular chemists and molecular engineers who look to nature for inspiration.