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1. Nested non-covalent interactions expand the functions of supramolecular polymer networks

   https://doi.org/10.1038/s41467-024-47666-x  

   Lundberg, David J.; Brown, Christopher M.; Bobylev, Eduard O.; Oldenhuis, Nathan J.; Alfaraj, Yasmeen S.; Zhao, Julia; Kevlishvili, Ilia; Kulik, Heather J.; Johnson, Jeremiah A. (May 2024, Nature Communications)

   Abstract Supramolecular polymer networks contain non-covalent cross-links that enable access to broadly tunable mechanical properties and stimuli-responsive behaviors; the incorporation of multiple unique non-covalent cross-links within such materials further expands their mechanical responses and functionality. To date, however, the design of such materials has been accomplished through discrete combinations of distinct interaction types in series, limiting materials design logic. Here we introduce the concept of leveraging “nested” supramolecular crosslinks, wherein two distinct types of non-covalent interactions exist in parallel, to control bulk material functions. To demonstrate this concept, we use polymer-linked Pd₂L₄metal–organic cage (polyMOC) gels that form hollow metal–organic cage junctions through metal–ligand coordination and can exhibit well-defined host-guest binding within their cavity. In these “nested” supramolecular network junctions, the thermodynamics of host-guest interactions within the junctions affect the metal–ligand interactions that form those junctions, ultimately translating to substantial guest-dependent changes in bulk material properties that could not be achieved in traditional supramolecular networks with multiple interactions in series. 

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2. Rationally Designing the Supramolecular Interfaces of Nanoparticle Superlattices with Multivalent Polymers

   https://doi.org/10.1021/jacs.4c02617  

   Thrasher, Carl J; Jia, Fei; Yee, Daryl W; Kubiak, Joshua M; Wang, Yuping; Lee, Margaret S; Onoda, Michika; Hart, A John; Macfarlane, Robert J (April 2024, Journal of the American Chemical Society)

   In supramolecular materials, multiple weak binding groups can act as a single collective unit when confined to a localized volume, thereby producing strong but dynamic bonds between material building blocks. This principle of multivalency provides a versatile means of controlling material assembly, as both the number and the type of supramolecular moieties become design handles to modulate the strength of intermolecular interactions. However, in materials with building blocks significantly larger than individual supramolecular moieties (e.g., polymer or nanoparticle scaffolds), the degree of multivalency is difficult to predict or control, as sufficiently large scaffolds inherently preclude separated supramolecular moieties from interacting. Because molecular models commonly used to examine supramolecular interactions are intrinsically unable to examine any trends or emergent behaviors that arise due to nanoscale scaffold geometry, our understanding of the thermodynamics of these massively multivalent systems remains limited. Here we address this challenge via the coassembly of polymer-grafted nanoparticles and multivalent polymers, systematically examining how multivalent scaffold size, shape, and spacing affect their collective thermodynamics. Investigating the interplay of polymer structure and supramolecular group stoichiometry reveals complicated but rationally describable trends that demonstrate how the supramolecular scaffold design can modulate the strength of multivalent interactions. This approach to self-assembled supramolecular materials thus allows for the manipulation of polymer−nanoparticle composites with controlled thermal stability, nanoparticle organization, and tailored meso- to microscopic structures. The sophisticated control of multivalent thermodynamics through precise modulation of the nanoscale scaffold geometry represents a significant advance in the ability to rationally design complex hierarchically structured materials via self-assembly. 

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3. Order–Disorder Transition of Supramolecular Liquid Crystalline Elastomers

   https://doi.org/10.1021/acs.chemmater.4c02271  

   Lewis, Kristin L; Hoang, Jonathan D; Toney, Michael F; White, Timothy J (January 2025, Chemistry of Materials)

   Liquid crystalline elastomers (LCEs) are soft materials which disorder upon heating through the isotropic transition temperature. The order-disorder phase transition of LCEs results in a contraction of up to ∼50% along the aligned axis. Motivated by this distinctive stimuli-response, LCEs are increasingly considered as low-density actuators. Generally, LCEs are composed entirely of covalent bonds. Recently, we have prepared LCEs with intramesogenic supramolecular bonds from dimerized oxybenzoic acid derivatives and documented distinctive thermomechanical response in these supramolecular LCEs. Here, we report a detailed investigation of phase transitions in supramolecular LCEs by systematically varying the composition to affect the strength of the intermolecular interactions in the polymer network. The order-disorder phase transition is shown to be influenced by the conformation and dissociation of supramolecular dimers. Distinctly, this report isolates and details an LCE composition which undergoes an intermediate transition to an incommensurate phase at lower temperatures than the order-disorder transition. 

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4. Iterative Design Reveals Molecular Domain Relationships in Supramolecular Peptide–Drug Conjugates

   https://doi.org/10.1021/acs.biomac.4c00519  

   Sis, Matthew J; Liu, Dongping; Allen, Isabella; Webber, Matthew J (July 2024, Biomacromolecules)

   Supramolecular peptide-drug conjugates (sPDCs) are prepared by covalent attachment of a drug moiety to a peptide motif programmed for one-dimensional self-assembly, with subsequent physical entanglement of these fibrillar structures enabling formation of nanofibrous hydrogels. This class of prodrug materials presents an attractive platform for mass-efficient and site-specific delivery of therapeutic agents using a discrete single-component molecular design. However, a continued challenge in sPDC development is elucidating relationships between supramolecular interactions in their drug and peptide domains and the resultant impact of these domains on assembly outcomes and material properties. Inclusion of a saturated alkyl segment alongside the prodrug in the hydrophobic domain of sPDCs could relieve some of the necessity for ordered, prodrug-produg interactions. Accordingly, nine sPDCs are prepared here to iterate the design variables of amino acid sequence and hydrophobic prodrug/alkyl block design. All molecules spontaneously formed hydrogels under physiological conditions, indicating a less hindered thermodynamic path to self-assembly relative to previous prodrug-only designs. However, material studies on the supramolecular arrangement, formation, and mechanical properties of the resultant sPDC hydrogels, as well as their drug release profiles, showed complex relationships between the hydrophobic and peptide domains in the formation and function of the resulting assemblies. Together, these results indicate that sPDC material properties are intrinsically linked to holistic molecular design, with coupled contributions from their prodrug and peptide domains in directing properties of the emergent materials. 

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5. Advanced supramolecular design for direct ink writing of soft materials

   https://doi.org/10.1039/D2CS01011A  

   Tang, Miao; Zhong, Zhuoran; Ke, Chenfeng (February 2023, Chemical Society Reviews)

   The exciting advancements in 3D-printing of soft materials are changing the landscape of materials development and fabrication. Among various 3D-printers that are designed for soft materials fabrication, the direct ink writing (DIW) system is particularly attractive for chemists and materials scientists due to the mild fabrication conditions, compatibility with a wide range of organic and inorganic materials, and the ease of multi-materials 3D-printing. Inks for DIW need to possess suitable viscoelastic properties to allow for smooth extrusion and be self-supportive after printing, but molecularly facilitating 3D printability to functional materials remains nontrivial. While supramolecular binding motifs have been increasingly used for 3D-printing, these inks are largely optimized empirically for DIW. Hence, this review aims to establish a clear connection between the molecular understanding of the supramolecularly bound motifs and their viscoelastic properties at bulk. Herein, extrudable (but not self-supportive) and 3D-printable (self-supportive) polymeric materials that utilize noncovalent interactions, including hydrogen bonding, host–guest inclusion, metal–ligand coordination, micro-crystallization, and van der Waals interaction, have been discussed in detail. In particular, the rheological distinctions between extrudable and 3D-printable inks have been discussed from a supramolecular design perspective. Examples shown in this review also highlight the exciting macroscale functions amplified from the molecular design. Challenges associated with the hierarchical control and characterization of supramolecularly designed DIW inks are also outlined. The perspective of utilizing supramolecular binding motifs in soft materials DIW printing has been discussed. This review serves to connect researchers across disciplines to develop innovative solutions that connect top-down 3D-printing and bottom-up supramolecular design to accelerate the development of 3D-print soft materials for a sustainable future. 

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