Seed-Induced Living Two-Dimensional (2D) Supramolecular Polymerization in Water: Implications on Protein Adsorption and Enzyme Inhibition

In biological systems, programmable supramolecular frameworks characterized by coordinated directional non-covalent interactions are widespread. However, only a small number of reports involve pure water-based dynamic supramolecular assembly of artificial π-amphiphiles, primarily due to the formidable challenge of counteracting the strong hydrophobic dominance of the π-surface in water, leading to undesired kinetic traps. This study reveals the pathway complexity in hydrogen-bonding-mediated supramolecular polymerization of an amide-functionalized naphthalene monoimide (NMI) building block with a hydrophilic oligo-oxyethylene (OE) wedge. O-NMI-2 initially produced entropically driven, collapsed spherical particles in water (Agg-1); however, over a span of 72 h, these metastable Agg-1 gradually transformed into two-dimensional (2D) nanosheets (Agg-2), favoured by both entropy and enthalpy contributions. The intricate self-assembly pathways in O-NMI-2 enable us to explore seed-induced living supramolecular polymerization (LSP) in water for controlled synthesis of monolayered 2D assemblies. Furthermore, we demonstrated the nonspecific surface adsorption of a model enzyme, serine protease α-Chymotrypsin (α-ChT), and consequently the enzyme activity, which could be regulated by controlling the morphological transformation of O-NMI-2 from Agg-1 to Agg-2. We delve into the thermodynamic aspects of such shape-dependent protein-surface interactions and unravel the impact of seed-induced LSP on temporally controlling the catalytic activity of α-ChT.

Therapeutic Supramolecular Polymers: Designs and Applications

The self-assembly of low-molecular-weight building motifs into supramolecular polymers has unlocked a new realm of materials with distinct properties and tremendous potential for advancing medical practices. Leveraging the reversible and dynamic nature of non-covalent interactions, these supramolecular polymers exhibit inherent responsiveness to their microenvironment, physiological cues, and biomolecular signals, making them uniquely suited for diverse biomedical applications. In this review, we intend to explore the principles of design, synthesis methodologies, and strategic developments that underlie the creation of supramolecular polymers as carriers for therapeutics, contributing to the treatment and prevention of a spectrum of human diseases. We delve into the principles underlying monomer design, emphasizing the pivotal role of non-covalent interactions, directionality, and reversibility. Moreover, we explore the intricate balance between thermodynamics and kinetics in supramolecular polymerization, illuminating strategies for achieving controlled sizes and distributions. Categorically, we examine their exciting biomedical applications: individual polymers as discrete carriers for therapeutics, delving into their interactions with cells, and in vivo dynamics; and supramolecular polymeric hydrogels as injectable depots, with a focus on their roles in cancer immunotherapy, sustained drug release, and regenerative medicine. As the field continues to burgeon, harnessing the unique attributes of therapeutic supramolecular polymers holds the promise of transformative impacts across the biomedical landscape.

Design of supramolecular nanosheets for drug delivery applications

Two specific concepts have emerged in the field of materials science over the last several decades: nanosheets and supramolecular polymers. More recently, supramolecular nanosheets, in which these two concepts are integrated, have attracted particular attention, and they exhibit many fascinating characteristics. This review focuses on the design and applications of supramolecular nanosheets consisting of tubulin proteins and phospholipid membranes.

Light-adjusted supramolecular host-guest interfacial recognition for reconfiguring soft colloidal aggregates

The soft interfacial template-assisted confined self-assembly of block copolymers (BCPs) guiding colloidal aggregates has been extensively investigated by interfacial instability. Whether the macromolecular polymer architectonics possessed stimulus-responsive self-regulated structural controllability more readily implement the morphological diversity of colloidal aggregates. Herein, we in-situ constructed the alginate-modified β-cyclodextrin/azobenzene-functionalized alkyl chains (Alg-β-CD/AzoC12) system by supramolecular host-guest interfacial recognition-engineered strategy, in which possessed photo-stimulated responsive structural reconfigurability by modulating assembly/disassembly behaviors between CD and Azo at oil/water interface. The host-guest droplet interfaces acted as soft templates managing interfacial instability by synergistically integrating supra-amphiphilic host-guest polymers with cosurfactants, further constructing various soft supracolloidal aggregates, including soft nanoaggregates, microspheres with tunable degrees of surface roughness. Additionally, the stimuli-altering structural reconfigurability of supramolecular host-guest polymers was regulated by ultraviolet/visible irradiation, endowing soft aggregates with structural diversity. It's highly anticipated that the supramolecular host-guest interfacial recognition self-assembly establishes great bridge between supramolecular host-guest chemistry and colloid interface science.

Blends of nitrophenylmaleimide isomers with carboxymethylcellulose for the preparation of supramolecular polymers

Novel water-compatible supramolecular polymers (WCSP) based on the non-covalent interaction between carboxymethylcellulose (CMC) and o, m, and p-nitrophenylmaleimide isomers are proposed. The non-covalent supramolecular polymer was obtained from high viscosity CMC with a degree of substitution 1.03 with o, m, and p-nitrophenylmaleimide molecules that were synthesized from maleic anhydride and its corresponding nitroaniline. Subsequently, blends were made at different nitrophenylmaleimide concentrations, stirring rate, and temperatures, with 1.5% CMC, to select the best conditions for each case and to evaluate the rheological properties. The selected blends were used to form films and analyze spectroscopic, physicochemical, and biological properties. Then, the interaction between a CMC monomer and each isomer of nitrophenylmaleimide was investigated using quantum chemistry computational calculations with the B3LYP/6-311 + G (d,p) method, providing a detailed explanation of their intermolecular interactions. The supramolecular polymers obtained exhibit an increase in viscosity of blends between 20% and 30% compared to CMC, a shift in the wavenumber of the OH infrared band by approximately 66 cm^-1, and the first decomposition peak at the glass transition temperature occurring between 70 and 110 °C. These changes in properties are attributed to the formation of hydrogen bonds between the species. However, the degree of substitution and the viscosity of the CMC affects the physical, chemical, and biological properties of the polymer obtained. The supramolecular polymers are biodegradable regardless of the type of blends made and are easily obtainable. Notably, the CMC with m-nitrophenylmaleimide yields the polymer with the best properties.

GOx-assisted synthesis of pillar[5]arene based supramolecular polymeric nanoparticles for targeted/synergistic chemo-chemodynamic cancer therapy

Background

Cancer is the most serious world's health problems on the global level and various strategies have been developed for cancer therapy. Pillar[5]arene-based supramolecular therapeutic nano-platform (SP/GOx NPs) was constructed successfully via orthogonal dynamic covalent bonds and intermolecular H-bonds with the assistance of glucose oxidase (GOx) and exhibited efficient targeted/synergistic chemo-chemodynamic cancer therapy.

Methods

The morphology of SP/GOx NPs was characterized by DLS, TEM, SEM and EDS mapping. The cancer therapy efficinecy was investigated both in vivo and in vitro.

Results

SP/GOx NPs can load drug molecules (Dox) and modify target molecule (FA-Py) on its surface conveniently. When the resultant FA-Py/SP/GOx/Dox NPs enters blood circulation, FA-Py will target it to cancer cells efficiently, where GOx can catalyst the overexpressed glucose to generate H₂O₂. Subsequently, the generated H₂O₂ in cancer cells catalyzed by ferrocene unit to form •OH, which can kill cancer cells. Furthermore, the loaded Dox molecules released under acid microenvironment, which can further achieve chemo-therapy.

Conclusion

All the experiments showed that the excellent antitumor performance of FA-Py/SP/GOx/Dox NPs, which provided an new method for pillar[5]arene-based supramolecular polymer for biomedical applications.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01237-0.

On-Site Supramolecular Adhesion to Wet and Soft Surfaces via Solvent Exchange

A series of poly(thioctic acid-catechol)s was prepared by supramolecular copolymerization of two low-molecular-weight monomers, thioctic acid (TA) and catechol (CA). The addition of a small amount of CA molecules significantly improved the adhesion ability of poly(TA) and transformed it into an applicable supramolecular polymer adhesive material. The robust adhesion of poly(TA-CA)s to soft surfaces was achieved by employing a hot-melt method. However, the supramolecular adhesion via the hot-melt method failed to perform in the presence of water. On-site supramolecular adhesion to wet and soft substrates was successfully realized through the solvent exchange behavior between water and the poly(TA-CA)s ethanol solution. Compared to the hot-melt method, the solvent exchange method displays various fascinating advantages and is suitable for adhesion conditions normally under the presence of water.

Supramolecular Depolymerization in the Mixture of Two Poor Solvents: Mechanistic Insights and Modulation of Supramolecular Polymerization of Ionic π-Systems

Solvents are fundamentally essential for the synthesis and processing of soft materials. Supramolecular polymers (SPs), an emerging class of soft materials, are usually stable in single and mixtures of poor solvents. In contrast to these preconceived notions, here we report the depolymerization of SPs in the mixture of two poor solvents. This surprising behavior was observed for well-known cationic perylene diimides (cPDIs) in the mixtures of water and amphiphilic organic solvents such as isopropanol (IPA). cPDIs form stable SPs in water and IPA but readily depolymerize into monomers in 50-70 vol% IPA containing water. This is due to the selective solvation of the π-surface of cPDIs by alkyl chains of IPA and ionic side chains by water, as evidenced by molecular dynamic simulations. Moreover, by systematically changing the ratio between water and amphiphilic organic solvent, we could achieve an unprecedented supramolecular polymerization both by increasing and decreasing the solvent polarity.

Design of materials with supramolecular polymers

One hundred years ago Hermann Staudinger was strongly criticized by his scientific peers for his macromolecular hypothesis, but today it is hard to imagine a world without polymers. His hypothesis described polymers as macromolecules composed of large numbers of structural units connected by covalent bonds. In the 1990s the concept of supramolecular polymers emerged in the scientific literature as discrete entities of large molar mass comparable to that of classical polymers but built through non-covalent bonds among monomers. Supramolecular polymers exist in biological systems, and potentially blend the physical properties of covalent polymers with unique features such as high degrees of internal order within the polymeric structure, defined shapes, and novel dynamics. This trend article provides a summary of seminal contributions in supramolecular polymerization and provides recent examples from the Stupp laboratory to demonstrate the potential applications of an exciting class of materials composed fully or partially of supramolecular polymers. In closing, we provide our perspective on future opportunities provided by this field at the onset of a second century of polymers. It is our objective here to demonstrate that this second century could be as prosperous, if not more so, than the preceding one.

Meglumine-based supra-amphiphile self-assembled in water as a skin drug delivery system: Influence of unfrozen bound water in the system bioadhesiveness

Hexagonal liquid crystals and supramolecular polymers from meglumine-based supra-amphiphiles were developed as drug delivery systems to be applied on the skin. The influence of fatty acid unsaturation on the structure and mechanical properties was evaluated. Moreover, we have investigated the system biocompatibility and how the type of water could influence its bioadhesive properties. Meglumine-oleic acid (MEG-OA) was arranged as hexagonal liquid crystals at 30-70 wt% water content, probably due to its curvature and increased water solubility. Meglumine-stearic acid (MEG-SA) at 10-80 wt% water content self-assembled as a lamellar polymeric network, which can be explained by the low mobility of MEG-SA in water due to hydrophobic interactions between fatty acid chains and H-bonds between meglumine and water molecules. Both systems have shown suitable mechanical parameters and biocompatibility, making them potential candidates to encapsulate therapeutic molecules for skin delivery. Moreover, a strong positive correlation between the amount of unfrozen bound water in meglumine-based systems and the bioadhesion properties was observed. This work shows that a better understanding of the physicochemical properties of a drug delivery system is extremely important for the correlation with the desired biological response and, thus, improve the product performance for biomedical applications.

Entrapment of an adenine derivative by a photo-irradiated uracil-functionalized micelle confers controlled self-assembly behavior

HYPOTHESIS

Invoking cooperative assembly of the uracil-functionalized supramolecular polymer BU-PPG [uracil end-capped poly(propylene glycol)] upon association with the nucleobase adenine derivative A-MA [methyl 3-(6-amino-9H-purin-9-yl)propanoate] as a model drug provides a new concept to control and tune the properties of supramolecular complexes and holds significant potential for the development of safer, more effective drug delivery systems.

EXPERIMENTS

BU-PPG and A-MA were successfully developed and exhibited specific recognition and high affinity, which enabled reversible complementary adenine-uracil (A-U) hydrogen bonding-induced formation of spherical micelles in aqueous solution. The self-assembly and controllable A-MA release behavior of BU-PPG/A-MA micelles were studied using morphological analysis and optical and light scattering techniques to investigate the effect of photoirradiation and temperature on the complementary hydrogen bond interactions between BU-PPG and A-MA.

FINDINGS

The resulting micelles possess unusual physical properties, including controlled photoreactivity kinetics, controllable self-assembled morphology and low cytotoxicity in vitro, as well as reversible temperature-responsive behavior. Importantly, irradiated micelles exhibited excellent long-term structural stability under normal physiological conditions and serum disturbance. Increasing the temperature triggered rapid release of A-MA by disrupting A-U complexes. These findings represent an entirely new, promising strategy for the development of multi-controlled release drug delivery nanocarriers based on complementary hydrogen bonding interactions.

Bio Mimicking of Extracellular Matrix

Biomaterials play a critical role in regenerative strategies such as stem cell-based therapies and tissue engineering, aiming to replace, remodel, regenerate, or support damaged tissues and organs. The design of appropriate three-dimensional (3D) scaffolds is crucial for generating bio-inspired replacement tissues. These scaffolds are primarily composed of degradable or non-degradable biomaterials and can be employed as cells, growth factors, or drug carriers. Naturally derived and synthetic biomaterials have been widely used for these purposes, but the ideal biomaterial remains to be found. Researchers from diversified fields have attempted to design and fabricate novel biomaterials, aiming to find novel theranostic approaches for tissue engineering and regenerative medicine. Since no single biomaterial has been found to possess all the necessary characteristics for an ideal performance, over the years scientists have tried to develop composite biomaterials that complement and combine the beneficial properties of multiple materials into a superior matrix. Herein, we highlight the structural features and performance of various biomaterials and their application in regenerative medicine and for enhanced tissue engineering approaches.

Two different pathways for assembling bis-urea in benzene and toluene

The thermodynamic stability of assemblies formed by a bis-urea-based supramolecular polymer, 2,4-bis(2-ethylhexylureido)toluene (EHUT), was investigated in solutions using either benzene or toluene as the solvent. Starting from a higher temperature in which EHUT was soluble in both solvents, molecules spontaneously self-organized into tubular assemblies upon cooling and these assemblies were stable in a wide range of temperatures. However, the systems followed different paths below a specific temperature: while the supramolecular polymer remained stable in toluene, EHUT molecules underwent precipitation in benzene. The causes for these different behaviors were explored by molecular dynamics simulations, which provided support for stronger enthalpic stabilization of the tubular assemblies in toluene as compared to benzene. This stabilization was due mainly to the better interaction energy of trapped toluene molecules instead of benzene ones. For both cases, lowering the temperature makes the solvent penetration inside the tubes less favorable, which reduces the stability of supramolecular structures upon cooling. Graphical abstract Different EHUT solubilities.

Drug delivery's quest for polymers: Where are the frontiers?

Since the legendary 1964 article of Folkman and Long entitled "The use of silicone rubber as a carrier for prolonged drug therapy" the role of polymers in controlled drug delivery has come a long way. Today it is evident that polymers play a crucial if not the prime role in this field. The latest boost owes to the interest in drug delivery for the purpose of tissue engineering in regenerative medicine. The focus of this commentary is on a selection of general and personal observations that are characteristic for the current state of polymer therapeutics and carriers. It briefly highlights selected examples for the long march of synthetic polymer-drug conjugates from bench to bedside, comments on the ambivalence of selected polymers as inert excipients versus biological response modifiers, and on the yet unsolved dilemma of cationic polymers for the delivery of nucleic acid therapeutics. Further subjects are the complex design of multifunctional polymeric carriers including recent concepts towards functional supramolecular polymers, as well as observations on stimuli-sensitive polymers and the currently ongoing trend towards natural and naturally-derived biopolymers. The final topic is the discovery and early development of a novel type of biodegradable polyesters for parenteral use. Altogether, it is not the basic and applied research in polymer therapeutics and carriers, but the translational process that is the key hurdle to proceed towards an authoritative approval of new polymer therapeutics and carriers.