Photoreactive silver-containing supramolecular polymers that form self-assembled nanogels for efficient antibacterial treatment

In this study, an efficient synthetic strategy and potential route to obtain a photo-reactive silver-containing cytosine-functionalized polypropylene glycol polymer (Ag-Cy-PPG) was developed by combining a hydrophilic oligomeric polypropylene glycol (PPG) backbone with dual pH-sensitive/photo-reactive cytosine-silver-cytosine (Cy-Ag-Cy) linkages. The resulting photo-responsive Ag-Cy-PPG holds great promise as a multifunctional biomedical material that generates spherical-like nanogels in water; the nanogels exhibit high antibacterial activity and thus may significantly enhance the efficacy of antibacterial treatment. Due to the formation of photo-dimerized Cy-Ag-Cy cross-linkages after UV irradiation, Ag-Cy-PPG converts into water-soluble cross-linked nanogels that possess a series of interesting chemical and physical properties, such as intense and stable fluorescence behavior, highly sensitive pH-responsive characteristics, on/off switchable phase transition behavior, and well-controlled release of silver ions (Ag+) in mildly acidic aqueous solution. Importantly, antibacterial tests clearly demonstrated that irradiated Ag-Cy-PPG nanogels exhibited strong antibacterial activity at low doses (MIC values of < 50 μg/mL) against gram-positive and gram-negative bacterial pathogens, whereas non-irradiated Ag-Cy-PPG nanogels did not inhibit the viability of bacterial pathogens. These results indicate that irradiated Ag-Cy-PPG nanogels undergo a highly sensitive structural change in the bacterial microenvironment due to their relatively unstable π-conjugated structures (compared to non-irradiated nanogels); this change results in a rapid structural response that promotes intracellular release of Ag+ and induces potent antibacterial ability. Overall, this newly created metallo-supramolecular system may potentially provide an efficient route to dramatically enhance the therapeutic effectiveness of antibacterial treatments.

Photoreactive Cytosine-Functionalized Self-Assembled Micelles with Enhanced Cellular Uptake Capability for Efficient Cancer Chemotherapy

Design, fabrication, and control of photoreactive supramolecular macromers─which are composed of a thermoresponsive polymer backbone and photoreactive nucleobase end-groups─to achieve the desired physical-chemical performance and provide the high efficiency required for chemotherapy drug delivery purposes still present challenges. Herein, a difunctional cytosine-terminated supramolecular macromer was successfully obtained at high yield. UV-irradiation induces the formation of cytosine photodimers within the structure. The irradiated macromer can self-assemble into nanosized spherical micelles in water that possess a number of interesting and unique features, such as desired micellar size and morphology, tunable drug-loading capacity, and excellent structural stability in serum-containing medium, in addition to well-controlled drug-release behaviors in response to changes in environmental temperature and pH; these extremely desirable, rare features are required to augment the functions of polymeric nanocarriers for drug delivery. Importantly, a series of in vitro studies demonstrated that photodimerized cytosine moieties within the drug-loaded micelles substantially enhance their internalization and accumulation inside cells via endocytosis and subsequently lead to induction of massive apoptotic cell death compared with the corresponding nonirradiated micelles. Thus, this newly developed "photomodified" nanocarrier system could provide a potentially fruitful route to enhance the drug delivery performance of nanocages without the need to introduce targeting moieties or additional components.

Hydrogen Bond Strength-Mediated Self-Assembly of Supramolecular Nanogels for Selective and Effective Cancer Treatment

This study provides a significant contribution to the development of multiple hydrogen-bonded supramolecular nanocarrier systems by demonstrating that controlling the hydrogen bond strength within supramolecular polymers represents a crucial factor to tailor the drug delivery performance and enhance the effectiveness of cancer therapy. Herein, we successfully developed two kinds of poly(ethylene glycol)-based telechelic polymers Cy-PEG and UrCy-PEG having self-constituted double and quadruple hydrogen-bonding cytosine (Cy) and ureido-cytosine (UrCy) end-capped groups, respectively, which directly assemble into spherical nanogels with a number of interesting physical characteristics in aqueous solutions. The UrCy-PEG nanogels containing quadruple hydrogen-bonded UrCy dimers exhibited excellent long-term structural stability in a serum-containing biological medium, whereas the double hydrogen-bonded Cy moieties could not maintain the structural integrity of the Cy-PEG nanogels. More importantly, after the drug encapsulation process, a series of in vitro experiments clearly confirmed that drug-loaded UrCy-PEG nanogels induced selective apoptotic cell death in cancer cells without causing significant cytotoxicity to healthy cells, while drug-loaded Cy-PEG nanogels exerted nonselective cytotoxicity toward both cancer and normal cells, indicating that increasing the strength of hydrogen bonds in nanogels plays a key role in enhancing the selective cellular uptake and cytotoxicity of drugs and the subsequent induction of apoptosis in cancer cells.

Quadruple Hydrogen Bonding Supramolecular Elastomers for Melt Extrusion Additive Manufacturing

This manuscript describes the versatility of highly directional, noncovalent interactions, i.e., quadruple hydrogen bonding (QHB), to afford novel polyurea segmented supramolecular polymers for melt extrusion three-dimensional (3D) printing processes. The molecular design of the polyurea elastomers features (1) flexible polyether segments and relatively weak urea hydrogen-bonding sites in the soft segments to provide elasticity and toughness, and (2) strong ureido-cytosine (UCyt) QHB in the hard segments to impart enhanced mechanical integrity. The resulting polyureas were readily compression-molded into mechanically-robust, transparent, and creasable films. Optimization of polyurea composition offered a rare combination of high tensile strength (95 MPa), tensile elongation (788% strain), and toughness (94 MJ/m³), which are superior to a commercially available Ninjaflex elastomer. The incorporation of QHB facilitated melt processability, where hydrogen bonding dissociation provided low viscosities at printing temperatures. During cooling, directional self-assembly of UCyt QHB facilitated the solidification process and contributed to part fidelity with the formation of a robust physical network. The printed objects displayed high layer fidelity, smooth surfaces, minimal warpage, and complex geometries. The presence of highly directional QHB effectively diminished mechanical anisotropy, and the printed samples exhibited comparable Young's moduli along (x-y direction, 0°) and perpendicular to (z-direction, 90°) the layer direction. Remarkably, the printed samples exhibited ultimate tensile strains approaching 500% in the z-direction prior to failure, which was indicative of improved interlayer adhesion. Thus, this design paradigm, which is demonstrated for novel polyurea copolymers, suggests the potential of supramolecular polymers with enhanced mechanical performance, melt processability, recyclability, and improved interlayer adhesion for melt extrusion additive manufacturing processes.

Order–disorder transition in supramolecular polymer combs/brushes with polymeric side chains

Three groups of supramolecular comb/brush polymers with polymeric side chains are developed, showing different mechanical properties and morphologies.

A Critical Approach to Polymer Dynamics in Supramolecular Polymers

Over the past few years, the concurrent (1) development of polymer synthesis and (2) introduction of new mathematical models for polymer dynamics have evolved the classical framework for polymer dynamics once established by Doi-Edwards/de Gennes. Although the analysis of supramolecular polymer dynamics based on linear rheology has improved a lot recently, there are a large number of insecurities behind the conclusions, which originate from the complexity of these novel systems. The interdependent effect of supramolecular entities (stickers) and chain dynamics can be overwhelming depending on the type and location of stickers as well as the architecture and chemistry of polymers. This Perspective illustrates these parameters and strives to determine what is still missing and has to be improved in the future works.

Self-assembling supramolecular polymer membranes for highly effective filtration of water-soluble fluorescent dyes

A new supramolecular membrane can effectively filter the water-soluble dye rhodamine 6G, resulting in high fluorescence performance and improved color stability.

Dynamic supramolecular self-assembly: hydrogen bonding-induced contraction and extension of functional polymers

A ureido-cytosine-functionalized supramolecular polymer can be manipulated to control nano-scale microstructures and its ability to form long-range order during self-assembly.

Evolution of hierarchical porous structures in supramolecular guest-host hydrogels

Macromolecular interactions are used to form supramolecular assemblies, including through the interaction of guest-host chemical pairs. Microstructural heterogeneity has been observed within such physical hydrogels; yet, systematic investigation of the microstructure and its determining inputs are lacking. Herein, we investigated the hierarchical self-assembly of hyaluronic acid (HA) modified by the guest-host pair adamantane (Ad-HA, guest) and β-cyclodextrin (CD-HA, host), as well as with methacrylate groups to both tether fluorescent agents and to covalently stabilize the material structure. We observed microporous materials in the hydrated state, which temporally arose from initially homogenous hydrogels composed of the two polymers. Independent fluorescent labeling of Ad-HA and CD-HA demonstrated spatiotemporal co-localization, indicative of guest-host polymer condensation on the microscale. The hydrogel void fractions and pore diameters were independently tuned through incubation time (0-7 days), polymer concentration (1.25-10 wt%), and polymer modification (25-50% Ad-HA modification). Void fractions as great as 93.3 ± 2.4% were achieved and pore diameters ranged from 2.1 ± 0.5 to 1025.4 ± 209.4 μm. The segregation of discrete solid and solute phases was measured with both atomic force microscopy and diffusive microparticle tracking analysis, where the solute phase contained only dilute polymer. The study represents a systematic investigation of hierarchical self-assembly in binary associating hydrogels, and provides insights on mechanisms that control microstructure within supramolecular hydrogels.

Functionalized graphene nanomaterials: new insight into direct exfoliation of graphite with supramolecular polymers

A novel urea-cytosine end-capped polypropylene glycol (UrCy-PPG) can self-assemble into a long-range ordered lamellar microstructure on the surface of graphene, due to the strong specific interactions between UrCy-PPG and graphene. In addition, the graphene composite produced exhibits a high conductivity (∼1093 S m(-1)) with a dramatic thermo-responsive ON/OFF resistance-switching behavior (10 consecutive cycles).

Ureido cytosine and cytosine-containing acrylic copolymers

Ureido-cytosine pendant groups contributed to random acrylic copolymers with enhanced thermomechanical performance, well-defined morphologies, and reduced water uptake.

Supramolecular assembly-mediated lithium ion transport in nanostructured solid electrolytes

Supramolecular solid polymer electrolytes provide mechanical integrity and well-defined ion-conducting paths for rapid ion transport that can be applied in high-performance lithium-ion batteries.

High-efficiency self-healing materials based on supramolecular polymer networks

A new urea–cytosine-functionalized supramolecular polymer can be rapidly reshaped and reprocessed under mild conditions via rearrangement of the hydrogen bonding network.