Preparation and Characterization of Inclusion Complexes of Poly(propylene glycol) with Methylated Cyclodextrins

Engineered cyclodextrin-based supramolecular hydrogels for biomedical applications

Cyclodextrin (CD)-based supramolecular hydrogels are polymer network systems with the ability to rapidly form reversible three-dimensional porous structures through multiple cross-linking methods, offering potential applications in drug delivery. Although CD-based supramolecular hydrogels have been increasingly used in a wide range of applications in recent years, a comprehensive description of their structure, mechanical property modulation, drug loading, delivery, and applications in biomedical fields from a cross-linking perspective is lacking. To provide a comprehensive overview of CD-based supramolecular hydrogels, this review systematically describes their design, regulation of mechanical properties, modes of drug loading and release, and their roles in various biomedical fields, particularly oncology, wound dressing, bone repair, and myocardial tissue engineering. Additionally, this review provides a rational discussion on the current challenges and prospects of CD-based supramolecular hydrogels, which can provide ideas for the rapid development of CD-based hydrogels and foster their translation from the laboratory to clinical medicine.

Cyclodextrin-induced release of drug-entrapping liposomes associated with the solation of liposome gels

In this work, we demonstrate that liposome gels in which liposomes are connected by polyethylene glycol terminated by cholesterol groups at both ends can store hydrophilic and hydrophobic drugs in the gel interiors, inner aqueous phases, and lipid membranes. The addition of cyclodextrins (CDxs) as extrinsic stimuli led to the release of drug-entrapping liposomes due to the interactions between CDxs and cholesteryl groups and/or the alkyl chains of lipids. The addition of aqueous solutions of β-CDx, dimethyl-β-CDx, trimethyl-β-CDx, and γ-CDx (final concentration: 7.5 mM) induced the solation of liposome gels and the release of liposomes accompanying the solation. Furthermore, the addition of β-CDx led to the partial release of hydrophilic drugs encapsulated in the liposomes, although the drug release was scarcely observed in other CDxs. In particular, the addition of trimethyl-β-CDx, which has low cytotoxicity, accelerated solation, and cationic liposomes released from the gels were effectively taken up by murine colon cancer (Colon26) cells. Thus, we propose that liposomes released from liposome gels can function as drug carriers.

The solation of liposome gels owing to the addition of trimethyl-β-cyclodextrin (TMe-β-CDx) and the uptake of cationic liposomes released from liposome gels by Colon26 cells are demonstrated.

Supramolecular complex formation of polysulfide polymers and cyclodextrins

We report the first preparation of a supramolecular polysulfide polymer, which is a polyrotaxane containing sulfur-styrene copolymer and methylated α-cyclodextrins (TMαCDs) as linear and cyclic molecules, respectively (SPRx). Compared to the sulfur-styrene copolymer prepared by a copolymerization method typically used to synthesize polysulfide polymers, the environmental and thermal stabilities of SPRx are significantly improved because the polysulfide polymer is covered with TMαCD.

Thermoresponsive Formation of Dimethyl Cyclodextrin Polypseudorotaxanes and Subsequent One-Pot Synthesis of Polyrotaxanes

We demonstrated a new strategy for efficient preparation of polypseudorotaxanes (PpRXs) and polyrotaxanes (PRXs) with cyclodextrin derivatives, 2,6-di-O-methyl-cyclodextrins (DM-CyDs), by utilizing the cloud points of DM-CyDs. DM-α-CyD and DM-β-CyD formed PpRXs with polyethylene glycol (PEG) and polypropylene glycol (PPG) in water at >50 °C and >35 °C, respectively, but did not at room temperature. Meanwhile, randomly methylated β-CyD (RM-β-CyD) and 2,3,6-tri-O-methyl-β-CyD (TM-β-CyD) did not form PpRX with PPG at higher temperature. The driving force of thermoresponsive formation of DM-CyD PpRXs was derived from hydrophobic interaction of methyl groups and a hydrogen bond of hydroxyl groups formed by adjacent DM-CyD molecules. Furthermore, in one pot, DM-CyD PRXs were synthesized by capping the PpRXs with bulky ends in high yields.

Self-Healing and Thermoresponsive Dual-Cross-Linked Alginate Hydrogels Based on Supramolecular Inclusion Complexes

β-Cyclodextrin (β-CD), with a lipophilic inner cavity and hydrophilic outer surface, interacts with a large variety of nonpolar guest molecules to form noncovalent inclusion complexes. Conjugation of β-CD onto biomacromolecules can form physically cross-linked hydrogel networks upon mixing with a guest molecule. Herein, the development and characterization of self-healing, thermoresponsive hydrogels, based on host-guest inclusion complexes between alginate-graft-β-CD and Pluronic F108 (poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol)), are described. The mechanics, flow characteristics, and thermal response were contingent on the polymer concentration and the host-guest molar ratio. Transient and reversible physical cross-linking between host and guest polymers governed self-assembly, allowing flow to occur under shear stress and facilitating complete recovery of the material's properties within a few seconds of unloading. The mechanical properties of the dual-cross-linked, multi-stimuli-responsive hydrogels were tuned as high as 30 kPa at body temperature and are advantageous for biomedical applications such as drug delivery and cell transplantation.

Selective tuning of the self-assembly and gelation of a hydrophilic poloxamine by cyclodextrins

Complexes formed between cyclodextrins (CDs) and polymers - pseudopolyrotaxanes (PPRs) - are the starting point of a multitude of supramolecular structures, which are proposed for a wide range of biomedical and technological applications. In this work, we investigate the complexation of a range of cyclodextrins with Tetronic T1307, a four-arm block copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) with a pH-responsive central ethylene diamine spacer, and its impact on micellization and the sol-gel transition. At low concentrations, small-angle neutron scattering (SANS) combined with dynamic light scattering (DLS) measurements show the presence of spherical micelles with a highly hydrated shell and a dehydrated core. Increasing the temperature leads to more compact micelles and larger aggregation numbers, whereas acidic conditions induce a shrinking of the micelles, with fewer unimers per micelle and a more hydrated corona. At high concentrations, T1307 undergoes a sol-gel transition, which is suppressed at pH below the pKa,1 (4.6). SANS data analysis reveals that the gels result from a random packing of the micelles, which have an increasing aggregation number and increasingly dehydrated shell and hydrated core with the temperature. Native CDs (α, β, γ-CD) can complex T1307, resulting in the precipitation of a PPR. Instead, modified CDs compete with micellization to an extent that is critically dependent on the nature of the substitution. (1)H and ROESY NMR combined with SANS demonstrate that dimethylated β-CD can thread onto the polymer, preferentially binding to the PO units, thus hindering self-aggregation by solubilizing the hydrophobic block. The various CDs are able to modulate the onset of gelation and the extent of the gel phase, and the effect correlates with the ability of the CDs to disrupt the micelles, with the exception of a sulfated sodium salt of β-CD, which, while not affecting the CMT, is able to fully suppress the gel phase.

Water-soluble porphyrin nanospheres: enhanced photo-physical properties achieved via cyclodextrin driven double self-inclusion

We describe a method to construct water-soluble porphyrinic nanospheres with enhanced photo-physical properties as a result of precluding (via intra-molecular host-guest interactions) the individual porphyrins units from aromatic-aromatic stacking.

Modulating the self-assembly of amphiphilic X-shaped block copolymers with cyclodextrins: structure and mechanisms

Inclusion complexes between cyclodextrins and polymers-so-called pseudopolyrotaxanes (PPR)-are at the origin of fascinating supramolecular structures, which are finding increasing uses in biomedical and technological fields. Here we explore the impact of both native and a range of modified cyclodextrins (CD) on the self-assembly of X-shaped poly(ethylene oxide)-poly(propylene oxide) block copolymers, so-called Tetronics or poloxamines, by focusing on Tetronic 904 (T904, Mw 6700). The effects are markedly dependent on the type and arrangement of the substituents on the macrocycle. While native CDs drive the formation of a solid PPR, most substituted CDs induce micellar breakup, with dimethylated β-CD (DIMEB) having the strongest impact and randomly substituted CDs a much weaker disruptive effect. Using native α-CD as a "molecular trap", we perform competitive binding experiments-where two types of CDs thread together onto the polymer chains-to establish that DIMEB indeed has the highest propensity to form an inclusion complex with the polymer, while hydroxypropylated CDs do not thread. 1D (1)H NMR and ROESY experiments confirm the formation of a soluble PPR with DIMEB in which the CD binds preferentially to the PO units, thus providing the drive for the observed demicellization. A combination of dynamic light scattering (DLS) and small-angle neutron scattering (SANS) is used to extract detailed structural parameters on the micelles. A binding model is proposed, which exploits the chemical shifts of selected protons from the CD in conjunction with the Hill equation, to prove that the formation of the PPR is a negatively cooperative process, in which threaded DIMEBs hamper the entrance of subsequent macrocycles.

Acid-Sensitive Polypseudorotaxanes Based on Ortho Ester-Modified Cyclodextrin and Pluronic F-127

We demonstrate a new type of acid-sensitive amphiphilic polypseudorotaxanes (PPRs) formed via inclusion complexation between Pluronic F127 and the hydrophobic β-cyclodextrin (CD) derivative in alcoholic solvents. The 6-OH ortho ester-substituted hydrophobic β-CD derivative (EMD-CD) was prepared by "click" reaction of β-CD with 2-ethylidene-4-methyl-1,3-dioxalane under mild conditions. The water-insoluble EMD-CD (host) is capable of forming PPRs with F127 (guest) in ethanol or methanol but not in water, which is confirmed by ¹H NMR, wide-angle X-ray diffraction, small-angle X-ray scattering, and the time-dependent threading kinetics. Depending on the host/guest ratio, the PPRs self-assembled into sheet-like structure or vesicular nanoparticles with different sizes in water. These PPR assemblies were stable at pH 8.4 but quickly dissociated into biocompatible products in neutral or in acidic buffers due to the hydrolysis of the ortho ester groups. Good biocompatibility, ease of fabrication, and extremely pH-sensitive character make the PPRs promising carriers for anticancer drug delivery. Moreover, the present work provides an alternative method for the preparation of PPRs composed of water-insoluble CD derivatives.

The effect of ring size on the mechanical relaxation dynamics of polyrotaxane gels

A simple molecular design based on the size of the cyclic components of polyrotaxanes achieved a significant variation of mechanical relaxation dynamics of polyrotaxane gels.

β-Cyclodextrin polyrotaxane monoaldehyde: a novel bio-crosslinker with high biocompatibility

We synthesized CD-capped polyrotaxanes monoaldehydes with appropriate weights which was used as bio-crosslinker with better crosslinking efficiency and lower cytotoxicity.

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.

Electrochemical Deposition of Mesoporous Nickel Hydroxide Films from Dilute Surfactant Solutions

A series of micelle-templated mesoporous nickel hydroxide films were prepared by electrochemical deposition from dilute surfactant solutions by using different types of template and by varying plating solvent composition. Lamellar mesostructured Ni(OH)2 films are obtained with only anionic surfactant sodium dodecyl sulfate (SDS) as the template. In particular, a unique cooperative assembly fashion, that is, the combination between Ni2+ and a complex composed of the primary template SDS and a cosurfactant, such as triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) copolymers and poly(ethylene glycol), was explored, by which two-dimensional hexagonal mesoporous Ni(OH)2 films were electrodeposited. Meanwhile, the deposition medium also plays a crucial role in determining the mesostructure of Ni(OH)2 films. For the composite nickel hydroxide films deposited from aqueous solution or dilute aqueous solution of ethylene glycol (<20 wt %) in the presence of SDS or the SDS-poly(alkylene oxide) polymer complexes, a mixed lamellar phase with d(001) = 37.4 A and d(001) = 28.5 A was obtained. However, single lamellar phase with d(001) = 37.4 A was electrodeposited from concentrated aqueous solutions of ethylene glycol (> or = 20 wt %). Furthermore, such deposition baths have access to hexagonal mesoporous nickel hydroxide films with d(100) = 37.4 A at 70 degrees C with the SDS-poly(alkylene oxide) polymer complexes as the templates. Within the potential window for Ni(OH)2, the morphology and quality of mesostructured films are significantly dependent on the deposition potential, while the mesostructures of the composite films always remain unchanged.