Enhanced accessibility of peptide substrate toward membrane-bound metalloexopeptidase by supramolecular structure of polyrotaxane

Enzyme-Responsive Aqueous Two-Phase Systems in a Cationic-Anionic Surfactant Mixture

Enzyme-instructed self-assembly is an increasingly attractive topic owing to its broad applications in biomaterials and biomedicine. In this work, we report an approach to construct enzyme-responsive aqueous surfactant two-phase (ASTP) systems serving as enzyme substrates by using a cationic surfactant (myristoylcholine chloride) and a series of anionic surfactants. Driven by the hydrophobic interaction and electrostatic attraction, self-assemblies of cationic-anionic surfactant mixtures result in biphasic systems containing condensed lamellar structures and coexisting dilute solutions, which turn into homogeneous aqueous phases in the presence of hydrolase (cholinesterase). The enzyme-sensitive ASTP systems reported in this work highlight potential applications in the active control of biomolecular enrichment/release and visual detection of cholinesterase.

Soft Materials by Design: Unconventional Polymer Networks Give Extreme Properties

Hydrogels are polymer networks infiltrated with water. Many biological hydrogels in animal bodies such as muscles, heart valves, cartilages, and tendons possess extreme mechanical properties including being extremely tough, strong, resilient, adhesive, and fatigue-resistant. These mechanical properties are also critical for hydrogels' diverse applications ranging from drug delivery, tissue engineering, medical implants, wound dressings, and contact lenses to sensors, actuators, electronic devices, optical devices, batteries, water harvesters, and soft robots. Whereas numerous hydrogels have been developed over the last few decades, a set of general principles that can rationally guide the design of hydrogels using different materials and fabrication methods for various applications remain a central need in the field of soft materials. This review is aimed at synergistically reporting: (i) general design principles for hydrogels to achieve extreme mechanical and physical properties, (ii) implementation strategies for the design principles using unconventional polymer networks, and (iii) future directions for the orthogonal design of hydrogels to achieve multiple combined mechanical, physical, chemical, and biological properties. Because these design principles and implementation strategies are based on generic polymer networks, they are also applicable to other soft materials including elastomers and organogels. Overall, the review will not only provide comprehensive and systematic guidelines on the rational design of soft materials, but also provoke interdisciplinary discussions on a fundamental question: why does nature select soft materials with unconventional polymer networks to constitute the major parts of animal bodies?

Acid-labile polyrotaxane exerting endolysosomal pH-sensitive supramolecular dissociation for therapeutic applications

For achieving pH-sensitive dissociation and the subsequent release of threaded cyclic molecules from polyrotaxanes (PRXs) in weakly acidic environments, a novel acid-labile Pluronic/β-cyclodextrin-based PRX bearing ketal linkages was designed and its potential biomedical application was demonstrated.

Supramolecular polymers based on cyclodextrins for drug and gene delivery

Supramolecular polymers based on cyclodextrins (CDs) have inspired interesting and rapid developments as novel biomaterials in a broad range of drug and gene delivery applications, due to their low cytotoxicity, controllable size, and unique architecture. This review will summarize the potential applications of polyrotaxanes in the field of drug delivery and gene delivery. Generally, cyclodextrin-based biodegradable polypseudorotaxane hydrogels could be used as a promising injectable drug delivery system for sustained and controlled drug release. Temperature-responsive, pH-sensitive, and controllable hydrolyzable polyrotaxane hydrogels have attracted much attention because of their controllable properties, and the self-assembly micelles formed by amphiphilic copolymer threaded with CDs could be used as a carrier for controlled and sustained drug release. Polyrotaxanes with drug or ligand conjugated CDs threaded on a polymer chain with a biodegradable end group could be useful for controlled and multivalent targeted delivery. In the field of gene delivery, cationic polyrotaxanes consisting of multiple OEI-grafted CDs threaded on a block copolymer chain are attractive non-viral gene carries due to the strong DNA-binding ability, low cytotoxicity, and high gene delivery capability. Furthermore, cytocleavable end-caps were introduced in the polyrotaxane systems in order to ensure efficient endosomal escape for intracellular trafficking of DNA. The development of the supramolecular approach using CD-containing polyrotaxanes is expected to provide a new paradigm for biomaterials.

Formation of a “pseudosuitane”-type complex between a triptycene-derived bis(crown ether) host and 1,1′-(anthracene-9,10-diyl)bis(N-benzylmethanaminium): a new method for the synthesis of linear polyrotaxanes

Formation of a “pseudosuitane”-type complex based on triptycene-derived bis(crown ether) provides a new method for the synthesis of linear polyrotaxanes.

Polyrotaxanes for applications in life science and biotechnology

Due to their low cytotoxicity, controllable size, and unique architecture, cyclodextrin (CD)-based polyrotaxanes and polypseudorotaxanes have inspired interesting exploitation as novel biomaterials. This review will update the recent progress in the studies on the structures of polyrotaxanes and polypseudorotaxanes based on different CDs and polymers, followed by summarizing their potential applications in life science and biotechnology, such as drug delivery, gene delivery, and tissue engineering. CD-based biodegradable polypseudorotaxane hydrogels could be used as promising injectable drug delivery systems for sustained and controlled drug release. Polyrotaxanes with drug or ligand-conjugated CDs threaded on polymer chain with biodegradable end group could be useful for controlled and multivalent targeting delivery. Cationic polyrotaxanes consisting of multiple oligoethylenimine-grafted CDs threaded on a block copolymer chain were attractive non-viral gene carries due to the strong DNA-binding ability, low cytotoxicity, and high gene transfection efficiency. Cytocleavable end caps were also introduced in the polyrotaxane systems in order to ensure efficient endosomal escape for intracellular trafficking of DNA. Finally, hydrolyzable polyrotaxane hydrogels with cross-linked α-CDs could be a desirable scaffold for cartilage and bone tissue engineering.

Cyclodextrin-based polymeric materials: synthesis, properties, and pharmaceutical/biomedical applications

This review describes the synthesis, properties, and, in particular, biomedical and pharmaceutical applications of an upcoming class of polymeric networks and assemblies based on cyclodextrins (CDs). CDs are cyclic oligosaccharides composed of alpha-1,4-coupled d-glucose units, which contain a hydrophobic internal cavity that can act as a host for various, generally lipophilic, guest molecules. Because of this unique physicochemical property, commonly referred to as inclusion complex formation, CDs have often been used to design polymeric materials, such as hydrogels and nanoparticles. Polymeric systems based on CDs exhibit unique characteristics in terms of mechanical properties, stimuli-responsiveness, and drug release characteristics. In this contribution, first, an outline is given of covalently cross-linked polymeric networks in which CD moieties were structurally incorporated to modulate the network strength as well as the complexation and release of low molecular weight drugs. Second, physically assembled polymeric systems are discussed, of which the formation is accomplished by inclusion complexes between polymer-conjugated CDs and various guest molecule-derivatized polymers. Due to their physical nature, these polymeric systems are sensitive to external stimuli, such as temperature changes, shear forces and the presence of competing CD-binding molecules, which can be exploited to use these systems as injectable, in situ gelling devices. In recent years, many interesting CD-containing polymeric systems have been described in literature. These systems have to be optimized and extensively evaluated in preclinical studies concerning their safety and efficacy, making future clinical applications of these materials in the biomedical and pharmaceutical field feasible.

Cyclodextrin-based supramolecular architectures: syntheses, structures, and applications for drug and gene delivery

The supramolecular structures formed between cyclodextrins (CDs) and polymers have inspired interesting developments of novel supramolecular biomaterials. This review will update the recent progress in studies on supramolecular structures based on CDs and block copolymers, followed by the design and synthesis of CD-based supramolecular hydrogels and biodegradable polyrotaxanes for potential controlled drug delivery, and CD-containing cationic polymers and cationic polyrotaxanes for gene delivery. Supramolecular hydrogels based on the self-assembly of the inclusion complexes between CDs with biodegradable block copolymers could be used as promising injectable drug delivery systems for sustained controlled release of macromolecular drugs. Biodegradable polyrotaxanes with drug-conjugated CDs threaded on a polymer chain with degradable end-caps could be interesting supramolecular prodrugs for controlled and targeting delivery of drugs. CD-containing cationic polymers as gene carriers showed reduced cytotoxicity than non-CD-containing polymer counterparts. More importantly, the polyplexes of CD-containing cationic polymers with DNA could be pegylated through a supramolecular process using inclusion complexation between the CD moieties and a modified PEO. Finally, new cationic polyrotaxanes composed of multiple oligoethylenimine-grafted CDs threaded and end-capped on a block copolymer chain were designed and synthesized as a new class of polymeric gene delivery vectors, where the chain-interlocked cationic cyclic units formed an integrated supramolecular entity to function as a macromolecular gene vector. The development of the supramolecular biomaterials through inclusion complexation has opened up a new approach for designing novel drug and gene delivery systems, which may have many advantages over the systems based on the conventional polymeric materials.

Recent advances in the preparation of cyclodextrin-based polyrotaxanes and their applications to soft materials

The present review article deals with recent novel studies on the preparation and application of polyrotaxanes comprised of cyclodextrins (CDs) and various linear polymers, especially poly(ethylene glycol) (PEG). First, a brief introduction of the historical background of the pioneering work on the preparation of an inclusion complex and polyrotaxane is provided. Subsequently, the authors have focused on the recently developed solvent systems for the polyrotaxane. These new solvents are interesting from two fundamental viewpoints: (1) from the perspective of the clarification of the hydrogen-bonding-based dissolution mechanism of polyrotaxanes; and (2) from the practical viewpoint of the preparation of modified polyrotaxanes or slide-ring gels containing ionic liquids. A wide variety of polyrotaxane derivatives, whose cyclodextrin moiety was modified to carry various functional groups, and their intriguing characteristics are introduced in this article. Finally, many instances of the application of the PEG-CD polyrotaxane to soft materials, such as gels, molecular tubes and multivalent ligand systems, are summarized.

Synthesis, Characterization, and pH-Triggered Dethreading of α-Cyclodextrin-Poly(ethylene glycol) Polyrotaxanes Bearing Cleavable Endcaps

The synthesis, characterization, and degradation kinetics of three alpha-cyclodextrin (alpha-CD)-poly(ethylene glycol) (PEG) polyrotaxanes with endcaps that were installed using Cu(I)-catalyzed Huisgen cyclization is reported. PEG1500, azidated with azidoacetic acid, was threaded with alpha-CD to form a pseudopolyrotaxane that was then capped in up to 82% yield with three different substituents to provide polyrotaxanes that were either acid-, base-, or fluoride-sensitive. NMR, GPC, XRD, and AFM methods were used to characterize the polyrotaxanes. Dethreading rates upon exposure to mild deprotection conditions were monitored by turbidity analysis. The vinyl ether-endcapped polyrotaxane is stable at pH 7 for 16 h but is solubilized at approximately 0.0211 min(-1) at pH 4. The ester-endcapped polyrotaxane is solubilized at 0.0122 min(-1) at pH 12.1. Our results show that pH-triggerable polyrotaxanes can be readily and efficiently prepared from pseudopolyrotaxanes in high yield by Huisgen cyclization of azido- and alkynyl-modified precursors in the presence of Cu(I).

Biocleavable polyrotaxane-plasmid DNA polyplex for enhanced gene delivery

A biocleavable polyrotaxane, having a necklace-like structure consisting of many cationic alpha-cyclodextrins (alpha-CDs) and a disulfide-introduced poly(ethylene glycol) (PEG), was synthesized and examined as a nonviral gene carrier. The polyrotaxane formed a stable polyplex having positively charged surface even at low charge ratio. This is likely to be due to structural factors of the polyrotaxane, such as the mobile motion of alpha-CDs in the necklace-like structure. Rapid endosomal escape was observed 90 min after transfection. The positively charged surface and the good buffering capacity are advantageous to show the proton sponge effect. The pDNA decondensation occurred through disulfide cleavage of the polyrotaxane and subsequent supramolecular dissociation of the noncovalent linkages between alpha-CDs and PEG. Transfection of the DMAE-SS-PRX polyplex is independent of the amount of free polycation. Those properties played a key role for delivery of pDNA clusters to the nucleus. Therefore, the polyplex nature and the supramolecular dissociation of the polyrotaxane contributed to the enhanced gene delivery.

Formation of Pseudorotaxane Induced by Electrochemical Oxidation of Ferrocene-Containing Axis Molecule in the Presence of Crown Ether

The electrochemical oxidation of aminomethylferrocenes in the presence of dibenzo[24]crown-8 affords pseudorotaxanes containing a ferrocenyl group in its axis moiety. The formation of the pseudorotaxanes results from formation of secondary ammonium ions by rapid electron transfer from the N atom to the initially formed Fe(III) state, followed by hydrogen atom transfer from TEMPOH to the N+*.

In vitro biocompatibility assessment of sulfonated polyrotaxane-immobilized polyurethane surfaces

Sulfonated polyrotaxanes (PRx-SO(3)'s), in which sulfonated alpha-cyclodextrins (alpha-CDs) were threaded onto the poly(ethylene glycol) (PEG) segments in a PEG-b-poly(propylene glycol) (PPG)-b-PEG triblock copolymer (Pluronic) capped with benzyloxycarbonyl (Z)-L-phenylalanine (Z-L-Phe), were prepared as a novel surface-modifying biomaterial. Surface modification of the polyurethane (PU) was carried out by blending the PRx-SO(3)'s with a PU solution, followed by solution casting. The incorporated PRx-SO(3)'s led to the enhanced hydrophilicity by changing the surface properties of the PU matrix. Modified PUs showed the stable entrapment of the PRx-SO(3)'s with little extraction into water and enhanced mechanical properties after exposure to water compared to the PU control. The incorporated PRx-SO(3)'s repelled the proteins and kept them from closely approaching the surface areas, prevented platelet activation by thrombin, and effectively repelled bacteria. These results suggest that both the supramolecular structure of the polyrotaxanes and exposure of the sulfonated groups onto the surfaces contribute to these phenomena. Thus, surface modification with PRx-SO(3)'s is suggested to be useful for the fabrication of biocompatible medical devices.

Carboxyethylester-polyrotaxanes as a new calcium chelating polymer: synthesis, calcium binding and mechanism of trypsin inhibition

A carboxyethylester-polyrotaxane was synthesized as a novel calcium chelating polymer in the field of oral drug delivery and characterized in terms of mechanism of trypsin inhibition. Here, carboxyethylester (CEE) groups are introduced to all the primary hydroxyl groups in alpha-cyclodextrins (alpha-CDs), which are threaded onto a poly(ethylene glycol) chain capped with bulky end-groups (polyrotaxane). The solubility of the CEE-polyrotaxane in physiological conditions increased with pH, indicating ionization-related solubility similar to conventional polyacrylates. The ability of calcium (Ca2+) chelation was found to increase in the order of poly(acrylic acid) (PAA)>CEE-polyrotaxanez.Gt;CEE-alpha-CD, suggesting that the increased density of carboxyl groups enhances the Ca2+ chelating ability. The activity of trypsin was inhibited by these compounds in the same order of the calcium chelation. However, the inhibitory effect of CEE-polyrotaxane was reduced by adding excess Ca2+ without precipitation that was observed in the presence of PAA. Such the reduced inhibition and precipitation by CEE-alpha-CD was not observed. Therefore, the inhibitory effect of CEE-polyrotaxane is due to Ca2+ chelation from trypsin without non-specific interaction.

Multivalent interactions between biotin-polyrotaxane conjugates and streptavidin as a model of new targeting for transporters

Kinetic analysis of interactions between biotin-polyrotaxane or biotin-alpha-cyclodextrin (biotin-alpha-CD) conjugates and streptavidin was carried out as a model of new targeting to transporters using the surface plasmon resonance (SPR) technique. The biotin-polyrotaxane conjugates, in which biotin-introduced alpha-CDs are threaded onto a poly(ethylene oxide) chain capped with bulky end-groups, are expected to increase the valency of biotin from monovalent to multivalent binding. The number of biotins conjugated with one polyrotaxane molecule varied from 11 to 78, and apparently increased the association equilibrium constant (K(a)), assuming pseudo-first-order kinetics. A detailed dissociation kinetics was analyzed and the re-binding of the biotin-polyrotaxane conjugates was observed on the streptavidin-deposited SPR surface. The magnitude of the re-binding is likely to become larger with increasing the number of biotins, suggesting multivalent interaction on the SPR surface. To quantify the effect of valency, competitive inhibition assay was performed in terms of the supramolecular structure of the polyrotaxane. The inhibitory potency of the biotin-polyrotaxane conjugate was found to be 4-5 times greater than that of the biotin-alpha-CD conjugate. Therefore, the biotin-polyrotaxane conjugates by supramolecular formation of the biotin-alpha-CD conjugate significantly switches from monovalent to multivalent bindings to the model binding protein, streptavidin.

Anticoagulant activity of sulfonated polyrotaxanes as blood-compatible materials

Polyrotaxanes, in which alpha-cyclodextrins (alpha-CDs) are threaded onto poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) triblock copolymers (Pluronic) capped with benzyloxycarbonyl(Z)-L-phenylalanine (Z-L-Phe), were prepared, and sulfopropyl groups were introduced to hydroxyl groups of alpha-CDs in the polyrotaxanes. The supramolecular structure and the chemical composition of the polyrotaxanes after the sulfonation were confirmed by 1H-NMR, 13C-NMR, and elemental analysis. Anticoagulant activity of the polyrotaxanes and sulfonated polyrotaxanes was measured by activated partial thromboplastin time (APTT). It was found that the polyrotaxanes and the sulfonated polyrotaxanes showed greater anticoagulant activity than Pluronic itself, suggesting that both the supramolecular structure of the polyrotaxanes and the sulfonated groups contribute to the inhibition of intrinsic coagulation factors. Finally, our designed polyrotaxanes are suggested to be a promising candidate when fabricating blood-compatible medical devices by blending with or coating on clinically used polymers.