Polyrotaxanes for applications in life science and biotechnology

Recent advances in smart hydrogels derived from polysaccharides and their applications for wound dressing and healing

Owing to their inherent biocompatibility and biodegradability, hydrogels derived from polysaccharides have emerged as promising candidates for wound management. However, the complex nature of wound healing often requires the development of smart hydrogels---intelligent materials capable of responding dynamically to specific physical or chemical stimuli. Over the past decade, an increasing number of stimuli-responsive polysaccharide-based hydrogels have been developed to treat various types of wounds. While a range of hydrogel types and their versatile functions for wound management have been discussed in the literature, there is still a need for a review of the crosslinking strategies used to create smart hydrogels from polysaccharides. This review provides a comprehensive overview of how stimuli-responsive hydrogels can be designed and made using five key polysaccharides: chitosan, hyaluronic acid, alginate, dextran, and cellulose. Various methods, such as chemical crosslinking, dynamic crosslinking, and physical crosslinking, which are used to form networks within these hydrogels, ultimately determine their ability to respond to stimuli, have been explored. This article further looks at different polysaccharide-based hydrogel wound dressings that can respond to factors such as reactive oxygen species, temperature, pH, glucose, light, and ultrasound in the wound environment and discusses how these responses can enhance wound healing. Finally, this review provides insights into how stimuli-responsive polysaccharide-based hydrogels can be developed further as advanced wound dressings in the future.

Polycaprolactone/α-cyclodextrin polyrotaxanes with cellular uptake enhancing properties

Biodegradable poly(ε-caprolactone) (PCL) was rotaxanated with α-cyclodextrin (α-CD) and an α-CD/2-hydroxypropyl-α-CD (HP-α-CD) mixture. Stoppering was achieved using 2-mercaptosuccinic acid (MSA) via disulfide linkage. The structures of these polymeric supramolecular entities were confirmed by 1H NMR, with 75-80 wt% threaded CD, while the molar mass of the polyrotaxanes was around 18 kDa, determined by gel permeation chromatography. The aqueous solubility was as low as 20.2 ± 1.2 g L-1 for the α-CD-based polyrotaxane but considerably increased to 74.7 ± 6.0 g L-1 by the introduction of threaded HP-α-CD into the polymeric axis. Dethreading of the polyrotaxanes was triggered by the removal of the stopper molecules via disulfide-exchange reactions using glutathione. Additionally, the polyester axis proved to be fully degradable by lipase. Cellular uptake of these polyrotaxanes was investigated by flow cytometry and confocal microscopy. The results showed an almost up to 50-fold higher cellular uptake of polyrotaxanes than free CD. These disulfide end-stoppered polyrotaxanes of biodegradable PCL represent a promising tool for intracellular delivery of CDs and offer novel treatment possibilities for lysosomal storage dysfunctions.

Bridging host-guest chemistry with molecule chemistry-covalent organic polyrotaxanes (COPRs): from synthesis to inactivation of bacterial pathogens

As a thriving artificial material, covalent organic frameworks (COFs), boasting inherent structural designability and functional adaptability, and with compositions akin to biological macromolecules, have emerged as a rising star in the field of material science. However, the progression of COFs is significantly impeded by the arduous and intricate preparation procedures of novel building blocks, as well as the inefficient development process of new reactions. An efficient, uncomplicated, and versatile functionalization approach, which has the potential to not only facilitate customized preparation of COFs based on application demands but also enable precise performance control, has become a focal point of research. The formulation of multi-functional COFs through efficient and cost-effective methods poses a critical challenge for the practical application of COFs. This review aims to present the preparation of COFs by amalgamating rigid molecular chemistry with flexible supramolecular host-guest chemistry, adopting a "couple hardness with softness" strategy to meticulously construct intelligent covalent organic polyrotaxanes (COPRs) using conventional reactions. Herein, novel building blocks can be acquired by amalgamating existing macrocycle complexes with framework blocks. The amalgamation of supramolecular chemistry bolsters the capabilities to generate, sense, respond, and amplify distinctive signals, thereby expediting the advancement of multifaceted materials with sophisticated structures. Concurrently, the infusion of supramolecular force endows COPRs with exceptional performance, facilitating multi-mode collaborative antibacterial therapy. This comprehensive review not only promotes the efficient utilization of resources but also stimulates the rapid advancement of framework materials.

Bispillar[5]arene-Based Slide-Ring Polyrotaxanation Enables Enhanced Toughness, Recyclability, Impact, and Puncture Resistance of Polyisoprene Elastomers

A series of slide-ring polyrotaxanes (SRPs) have been constructed by the solvent-free blending of a ditopic pillar[5]arene (DP5A) and polyisoprene (PIP) after thermal annealing. Solid-state 13C NMR experiments supported the fact that the pillar[5]arene rings of DP5A were threaded by PIP chains to afford physically interlocked networks. Tensile tests revealed that 1% of DP5A can improve the elongation at break from 50 to 239%, the tensile modulus from 2.1 to 3.9 MPa, and the toughness from 0.35 to 4.5 MJ/m3. Impact and puncture resistance experiments show that the DP5A-doped materials exhibit remarkable enhancement of protective and impalement-resistant performance. The samples can be also recycled repeatedly due to their physical crosslinking nature. The important stress delocalization effects have been attributed to the pulley effect of DP5A in the SRP materials, which represents a supramolecular approach for improving the performance of PIP elastomers.

Cyclodextrin in drug delivery: Exploring scaffolds, properties, and cutting-edge applications

Cyclodextrins (CDs) are unique cyclic compounds that can form inclusion complexes via host-guest complexation with a wide range of molecules, thereby altering their physicochemical properties. These molecules offer the formation of inclusion complexes without the formation of covalent bonds, making them suitable for a variety of applications in pharmaceutical and biomedical fields. Due to their supramolecular host-guest properties, CDs are being utilized in the fabrication of biomaterials, metal-organic frameworks, and nano-drug carriers. Additionally, CDs in combination with biomolecules are biocompatible and can deliver nano to macromolecules at the site of drug actions. However, the availability of free hydroxyl groups and a simple crosslinking process for supramolecular fabrication show immense opportunities for researchers in the field of tissue engineering and biomedical applications. In this review article, we have covered the historical development, various types of chemical frameworks, unique chemical and physical properties, and important applications of CDs in drug delivery and biomedical sciences.

Synthesis of cyclodextrin-based polyrotaxanes and polycatenanes for supramolecular pharmaceutical sciences

Cyclodextrins (CDs) are essential in the pharmaceutical industry and have long been used as food and pharmaceutical additives. CD-based interlocked molecules, such as rotaxanes, polyrotaxanes, catenanes, and polycatenanes, have been synthesized and have attracted considerable attention in supramolecular chemistry. Among them, CD polyrotaxanes have been employed as slide-ring materials and biomaterials. CD polycatenanes are new materials; therefore, to date, no examples of applied research on CD polycatenanes have been reported. Consequently, we expect that applied research on CD polycatenanes will accelerate in the future. This review article summarizes the syntheses and structural analyses of CD polyrotaxanes and polycatenanes to facilitate their applications in the pharmaceutical industry. We believe that this review will promote further research on CD-based interlocked molecules.

Controlled Sublimation Rate of Guest Drug from Polymorphic Forms of a Cyclodextrin-Based Polypseudorotaxane Complex and Its Correlation with Molecular Dynamics as Probed by Solid-State NMR

Encapsulation of active pharmaceutical ingredients (APIs) in confined spaces has been extensively explored as it dramatically alters the molecular dynamics and physical properties of the API. Herein, we explored the effect of encapsulation on the molecular dynamics and physical stability of a guest drug, salicylic acid (SA), confined in the intermolecular spaces of γ-cyclodextrin (γ-CD) and poly(ethylene glycol) (PEG)-based polypseudorotaxane (PPRX) structure. The sublimation tendency of SA encapsulated in three polymorphic forms of the γ-CD/PEG-based PPRX complex, monoclinic columnar (MC), hexagonal columnar (HC), and tetragonal columnar (TC), was investigated. The SA sublimation rate was decreased by 3.0-6.6-fold and varied in the order of MC form > HC form > TC form complex. The 13C and 1H magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) spectra and 13C spin-lattice relaxation time (T1) indicated that the encapsulated SA molecules existed as the monomeric form, and its molecular mobility increased in the order of MC form > HC form > TC form complex. In the complexes, a rapid chemical exchange between two dynamic states of SA (free and bound) was suggested, with varying adsorption/desorption rates accounting for its distinct molecular mobility. This adsorption/desorption process was influenced by proton exchange at the interaction site and interaction strength of SA in the complexes, as evidenced by 1H MAS spectra and temperature dependency of the 13C carbonyl chemical shift. A positive correlation between the molecular mobility of SA and its sublimation rate was established. Moreover, the molecular mobility of γ-CD and PEG in the complexes coincided with that of SA, which can be explained by fast guest-driven dynamics. This is the first report on the stability improvement of an API through complexation in polymorphic supramolecular host structures. The relationship between the molecular dynamics and physical properties of encapsulated API will aid in the rational design of drug delivery systems.

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.

Pillar[5]arene-based supramolecular pseudorotaxane polymer material for ultra-sensitive detection of Fe3+ and F. RSC Adv 2023;13:12270-12275. [PMID: 37091614 PMCID: PMC10113919 DOI: 10.1039/d3ra00997a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Recent advancements in ultra-sensitive detection, particularly the Aggregation Induced Emission (AIE) materials, have demonstrated a promising detection method due to their low cost, real-time detection, and simplicity of operation. Here, coumarin functionalized pillar[5]arene (P5C) and bis-bromohexyl pillar[5]arene (DP5) were successfully combined to create a linear AIE supramolecular pseudorotaxane polymer (PCDP-G). The use of PCDP-G as a supramolecular AIE polymer material for recyclable ultra-sensitive Fe³⁺ and F^- detection is an interesting application of the materials. According to measurements, the low detection limits of PCDP-G for Fe³⁺ and F^- are 4.16 × 10^-10 M and 6.8 × 10^-10 M, respectively. The PCDP-G is also a very effective logic gate and a material for luminous displays.

Cyclodextrin-Based Polymeric Drug Delivery Systems for Cancer Therapy

Cyclodextrins (CDs) are one of the most extensively studied cyclic-oligosaccharides due to their low toxicity, good biodegradability and biocompatibility, facile chemical modification, and unique inclusion capacity. However, problems such as poor pharmacokinetics, plasma membrane disruption, hemolytic effects and a lack of target specificity still exist for their applications as drug carriers. Recently, polymers have been introduced into CDs to combine the advantages of both biomaterials for the superior delivery of anticancer agents in cancer treatment. In this review, we summarize four types of CD-based polymeric carriers for the delivery of chemotherapeutics or gene agents for cancer therapy. These CD-based polymers were classified based on their structural properties. Most of the CD-based polymers were amphiphilic with the introduction of hydrophobic/hydrophilic segments and were able to form nanoassemblies. Anticancer drugs could be included in the cavity of CDs, encapsulated in the nanoparticles or conjugated on the CD-based polymers. In addition, the unique structures of CDs enable the functionalization of targeting agents and stimuli-responsive materials to realize the targeting and precise release of anticancer agents. In summary, CD-based polymers are attractive carriers for anticancer agents.

Mechanically interlocked polymers based on rotaxanes

The nature of mechanically interlocked molecules (MIMs) has continued to encourage researchers to design and construct a variety of high-performance materials. Introducing mechanically interlocked structures into polymers has led to novel polymeric materials, called mechanically interlocked polymers (MIPs). Rotaxane-based MIPs are an important class, where the mechanically interlocked characteristic retains a high degree of structural freedom and mobility of their components, such as the rotation and sliding motions of rotaxane units. Therefore, these MIP materials are known to possess a unique set of properties, including mechanical robustness, adaptability and responsiveness, which endow them with potential applications in many emerging fields, such as protective materials, intelligent actuators, and mechanisorption. In this review, we outline the synthetic strategies, structure-property relationships, and application explorations of various polyrotaxanes, including linear polyrotaxanes, polyrotaxane networks, and rotaxane dendrimers.

Genetically engineered fusion of allergen and viral-like particle induces a more effective allergen-specific immune response than a combination of them

Chimeric virus-like particles (VLPs) were developed as a candidate for allergen-specific immunotherapy. In this study, hepatitis B core antigen (HBcAg) that genetically fused to Chenopodium album polcalcin (Che a 3)-derived peptide was expressed in E. coli BL21, purified, and VLP formation was evaluated using native agarose gel electrophoresis (NAGE) and transmission electron microscopy (TEM). Chimeric HBc VLPs were characterized in terms of their reactivity to IgE, the induction of blocking IgG and allergen-specific IgE, basophil-activating capacity, and Th1-type immune responses. Results from IgE reactivity and basophil activation test showed that chimeric HBc VLPs lack IgE-binding capacity and basophil degranulation activity. Although chimeric HBc VLPs induced the highest level of efficient polcalcin-specific IgG antibody in comparison to those induced by recombinant Che a 3 (rChe a 3) mixed either with HBc VLPs or alum, they triggered the lowest level of polcalcin-specific IgE in mice following immunization. Furthermore, in comparison to the other antigens, chimeric HBc VLPs produced a polcalcin-specific Th1 cell response. Taken together, genetically fusion of allergen derivatives to HBc VLPs, in comparison to a mix of them, may be a more effective way to induce appropriate immune responses in allergen-specific immunotherapy. KEY POINTS: • The insertion of allergen-derived peptide into major insertion region (MIR) of hepatitis B virus core (HBc) antigen resulted in nanoparticles displaying allergen-derived peptide upon its expression in prokaryotic host. • The resultant VLPs (chimeric HBc VLPs) did not exhibit IgE reactivity with allergic patients' sera and were not able to degranulate basophils. • Chimeric HBc VLPs dramatically improved protective IgG antibody response compared with those induced by allergen mixed either with HBc VLPs or alum. • Chimeric HBc VLPs induced Th1 responses that were counterparts of Th2 responses (allergic). • Chimeric HBc VLPs increased IgG2a/ IgG1 ratio and the level of IFN-γ compared to those induced by allergen mixed with either HBc VLPs or alum. Graphical Abstract.

Polyrotaxanes as emerging biomaterials for tissue engineering applications: a brief review

The field of tissue engineering and regeneration constantly explores the possibility of utilizing various biomaterials' properties to achieve effective and uneventful tissue repairs. Polyrotaxanes (PRXs) are supramolecular assemblies, which possess interesting mechanical property at a molecular scale termed as molecular mobility. This molecular mobility could be utilized to stimulate various cellular mechanosignaling elements, thereby altering the cellular functions. Apart from this, the versatile nature of PRXs such as the ability to form complex with growth factors and peptides, numerous sites for chemical modifications, and processability into different forms makes them interesting candidates for applications towards tissue engineering. This literature briefly reviews the concepts of PRXs and molecular mobility, the versatile nature of PRXs, and its emerging utility towards certain tissue engineering applications.

Biodegradable Polyester of Poly (Ethylene glycol)-sebacic Acid as a Backbone for β -Cyclodextrin-polyrotaxane: A Promising Gene Silencing Vector

BACKGROUND

Polyrotaxane, a macromolecular interlocked assembly, consisting of cyclodextrin has excellent inclusion capabilities and functionalization capacity, which makes it a versatile material as a vector for gene delivery applications.

OBJECTIVE

A biodegradable linear aliphatic polyester axle composed of Polyethylene Glycol (PEG) and Sebacic Acid (SA) was used to fabricate the β-Cyclodextrin (β-CD) based polyrotaxane as a cationic polymeric vector and evaluated for its potential gene silencing efficiency.

METHODS

The water-soluble aliphatic polyester was synthesized by the solvent esterification process and characterized using viscometry, GPC, FT-IR and 1H NMR spectroscopy. The synthesized polyester was further evaluated for its biodegradability and cellular cytotoxicity. Hence, this water-soluble polyester was used for the step-wise synthesis of polyrotaxane, via threading and blocking reactions. Threading of β-CD over PEG-SA polyester axle was conducted in water, followed by end-capping of polypseudorotaxane using 2,4,6-trinitrobenzenesulfonic acid to yield polyester-based polyrotaxane. For gene delivery application, cationic polyrotaxane (PRTx⁺) was synthesized and evaluated for its gene loading and gene silencing efficiency.

RESULTS AND DISCUSSION

The resulting novel macromolecular assembly was found to be safe for use in biomedical applications. Further, characterization by GPC and ¹H NMR techniques revealed successful formation of PE-β-CD-PRTx with a threading efficiency of 16%. Additionally, the cellular cytotoxicity assay indicated biosafety of the synthesized polyrotaxane, exploring its potential for gene delivery and other biomedical applications. Further, the biological profile of PRTx⁺: siRNA complexes was evaluated by measuring their zeta potential and gene silencing efficiency, which were found to be comparable to Lipofectamine 3000, the commercial transfecting agent.

CONCLUSION

The combinatory effect of various factors such as biodegradability, favourable complexation ability, near zero zeta potentials, good cytotoxicity properties of poly (ethylene glycol)-sebacic acid based β-Cyclodextrin-polyrotaxane makes it a promising gene delivery vector for therapeutic applications.

A precise polyrotaxane synthesizer

Mechanically interlocked molecules are likely candidates for the design and synthesis of artificial molecular machines. Although polyrotaxanes have already found niche applications in exotic materials with specialized mechanical properties, efficient synthetic protocols to produce them with precise numbers of rings encircling their polymer dumbbells are still lacking. We report the assembly line-like emergence of poly[n]rotaxanes with increasingly higher energies by harnessing artificial molecular pumps to deliver rings in pairs by cyclical redox-driven processes. This programmable strategy leads to the precise incorporation of two, four, six, eight, and 10 rings carrying 8+, 16+, 24+, 32+, and 40+ charges, respectively, onto hexacationic polymer dumbbells. This strategy depends precisely on the number of redox cycles applied chemically or electrochemically, in both stepwise and one-pot manners.

Suspending Polyrotaxane Dissociation via Photo-Reversible Capping of Terminals

Reversible covalent bonds yield polymeric materials with functional characteristics such as self-healing, shape memory, stress relaxation, and stimuli-responsiveness. Here, photo-reversibly cappable polyrotaxanes are designed and the on-off controlled dissociation of their supramolecular architectures is demonstrated. The polyrotaxanes are synthesized by capping dithiobenzoates at both terminals of polyethylene glycol threaded through multiple α-cyclodextrins. Since dethreading of the α-cyclodextrins is prevented by the dithiobenzoate stoppers, the supramolecular dissociation is induced by their photo-cleavage. Subsequently, the cleaved dithiobenzoates spontaneously re-cap the polyrotaxane terminals in darkness. Thus, the supramolecular dissociation can be modulated by photo-reversible capping of the dithiobenzoate stoppers. These polyrotaxanes with dithiobenzoate stoppers are promising functional materials for photo-controlling physical properties and structures.

Polyrotaxane-based biointerfaces with dynamic biomaterial functions

The molecular mobility of cyclic molecules (e.g.α-cyclodextrins) threaded along a linear polymer chain (e.g. poly(ethylene glycol)) in polyrotaxanes is a unique feature for biomaterials with dynamic functionality. Surfaces with molecular mobility can be obtained by introducing polyrotaxanes. The molecular mobility of polyrotaxane-based surfaces can be modulated by changing the number of threaded cyclic molecules and modifying their functional groups. Biological ligands modified with α-cyclodextrins exhibit increased multivalent interactions with their receptors due to the molecular mobility of the latter. Furthermore, polyrotaxane-based surfaces not only improve the initial response of cells via multivalent interactions, but also affect cytoskeleton formation and the inherent quality of cells, including differentiation. Such polyrotaxane surfaces can emerge as new biointerfaces that can adapt to the dynamic biological nature.

Dynamic Hydrogels from Host-Guest Supramolecular Interactions

Hydrogel biomaterials are pervasive in biomedical use. Applications of these soft materials range from contact lenses to drug depots to scaffolds for transplanted cells. A subset of hydrogels is prepared from physical cross-linking mediated by host-guest interactions. Host macrocycles, the most recognizable supramolecular motif, facilitate complex formation with an array of guests by inclusion in their portal. Commonly, an appended macrocycle forms a complex with appended guests on another polymer chain. The formation of poly(pseudo)rotaxanes is also demonstrated, wherein macrocycles are threaded by a polymer chain to give rise to physical cross-linking by secondary non-covalent interactions or polymer jamming. Host-guest supramolecular hydrogels lend themselves to a variety of applications resulting from their dynamic properties that arise from non-covalent supramolecular interactions, as well as engineered responsiveness to external stimuli. These are thus an exciting new class of materials.

Multivalent polyrotaxane vectors as adaptive cargo complexes for gene therapy

The philosophy to design and construct polyrotaxane carriers, as efficient gene delivery systems.

Polypseudorotaxane Constructed from Cationic Polymer with Cucurbit[7]uril for Controlled Antibacterial Activity

This letter is aimed to develop a general strategy to fabricate polypseudorotaxanes with controlled antibacterial activity based on cationic polymers. As a proof of concept, the commercially available antibacterial cationic polymer, ε-poly-l-lysine hydrochloride, was chosen for the demonstration. Using host-guest chemistry, cucurbit[7]uril (CB[7]), a water-soluble macrocyclic host, was employed to bind with the positive charge and hydrophobic component on ε-poly-l-lysine hydrochlorides for antibacterial regulation. In this way, by tuning the ratio of CB[7] to the cationic polymer, the antibacterial polypseudorotaxane can be obtained, and the antibacterial efficiency can be well tuned from 5% to 100%. This line of research will enrich the field of cationic polymers and polypseudorotaxanes with important functions on precise control over antibacterial activity.

Iterative Synthesis of Oligo[n]rotaxanes in Excellent Yield

We present an operationally simple iterative coupling strategy for the synthesis of oligomeric homo- and hetero[n]rotaxanes with precise control over the position of each macrocycle. The exceptional yield of the AT-CuAAC reaction, combined with optimized conditions that allow the rapid synthesis of the target oligomers, opens the door to the study of precision-engineered oligomeric interlocked molecules.

Efficient pDNA Delivery Using Cationic 2-Hydroxypropyl-β-Cyclodextrin Pluronic-Based Polyrotaxanes

A family of cationic Pluronic-based polyrotaxanes (PR(+)), threaded with 2-hydroxypropyl-β-cyclodextrin (HPCD), was synthesized for pDNA delivery into multiple cell lines. All PR(+) formed highly stable, positively charged pDNA complexes that were < 250 nm in diameter. The cellular uptake and pDNA transfection efficiencies of the PR(+):pDNA complexes was enhanced relative to the commercial transfection standards L2K and bPEI, while displaying similar or lower toxicity profiles. Charge density and threading efficiency of the PR(+) agent significantly influenced the colloidal stability and physical properties of the complexes, which impacted their intracellular transfection efficiencies. Taken together, our results suggest that HPCD: Pluronic PR(+) can be used as potent vectors for pDNA-based therapeutics.

Design and Evaluation of the Highly Concentrated Human IgG Formulation Using Cyclodextrin Polypseudorotaxane Hydrogels

To achieve the potent therapeutic effects of human immunoglobulin G (IgG), highly concentrated formulations are required. However, the stabilization for highly concentrated human IgG is laborious work. In the present study, to investigate the potentials of polypseudorotaxane (PPRX) hydrogels consisting of polyethylene glycol (PEG) and α- or γ-cyclodextrin (α- or γ-CyD) as pharmaceutical materials for highly concentrated human IgG, we designed the PPRX hydrogels including human IgG and evaluated their pharmaceutical properties. The α- and γ-CyDs formed PPRX hydrogels with PEG (M.W. 20,000) even in the presence of highly concentrated human IgG (>100 mg/mL). According to the results of (1)H-NMR, powder X-ray diffraction, and Raman microscopy, the formation of human IgG/CyD PPRX hydrogels was based on physical cross-linking arising from their columnar structures. The release profiles of human IgG from the hydrogels were in accordance with the non-Fickian diffusion model. Importantly, the stabilities of human IgG included into the hydrogels against thermal and shaking stresses were markedly improved. These findings suggest that PEG/CyD PPRX hydrogels are useful to prepare the formulation for highly concentrated human IgG.

Preparation of polypseudorotaxanes composed of cyclodextrin and polymers in microspheres

We prepared polypseudorotaxanes (PPRXs) composed of cyclodextrin (CyD) and polyethylene glycol (PEG) inside microspheres (MSs) by an emulsifying process using polypropylene glycol (PPG) that shows temperature-dependent hydrophilicity changes; PPG is hydrophobic at high temperatures but hydrophilic at low temperatures. An aqueous solution of CyD and PEG was dispersed as droplets in PPG at 60°C then cooled to 0°C to allow water of droplets to transfer into PPG. On removal of water in the droplets, CyD and PEG were left behind as a CyD/PEG PPRX inside the solid-state MSs. Examination of α-, β-, and γ-CyD revealed that α-CyD was suitable for the formation of PPRX containing PEG in this MS preparation procedure. Interestingly, a new PPRX composed of α-CyD and PPG was formed in the α-CyD MSs when they were prepared in the absence of PEG from the aqueous solution of α-CyD. This MS fabrication procedure can control the size and shape of PPRX particles, and will contribute to the production of new types of CyD inclusion complexes.

Supramolecular cyclodextrin-based drug nanocarriers

Supramolecular systems formed by the binding of several cyclodextrins (CDs) to polymers or lipids, either via non-covalent or covalent links, open a wide range of possibilities for the delivery of active substances. CDs can perform as multifunctionalizable cores to which very diverse (macro)molecules and drugs can be conjugated. Grafting with amphiphilic molecules can lead to nanoassemblies exhibiting a variety of architectures. CDs can also polymerize with other CDs or can be used to functionalize preexisting polymers to form polymers/networks with enhanced capability to form inclusion complexes. Alternatively, CDs can be exploited as transient cross-linkers to form poly(pseudo)rotaxane-based networks or zipper-like assemblies. Combination of mutifunctionality and complexation ability of CDs has been shown to be useful to develop depot-like formulations and colloidal nanocarriers with improved performances regarding easiness of administration, protection of the encapsulated substances, control of the delivery rate, and cell interactions. The aim of this review is to provide an overall view of the diversity of designs of CD-based supramolecular nanosystems with a special focus on the advances materialized in the last five years, including clinical trials.

Sugar-Responsive Pseudopolyrotaxane Composed of Phenylboronic Acid-Modified Polyethylene Glycol and γ-Cyclodextrin

We have designed a sugar-responsive pseudopolyrotaxane (PPRX) by combining phenylboronic acid-modified polyethylene glycol (PBA–PEG) and γ-cyclodextrin. Phenylboronic acid (PBA) was used as a sugar-recognition motif in the PPRX because PBA reacts with a diol portion of the sugar molecule and forms a cyclic ester. When D-fructose or D-glucose was added to a suspension of PPRX, PPRX disintegrated, depending on the concentration of the sugars. Interestingly, catechol does not show a response although catechol has a high affinity for PBA. We analyzed the response mechanism of PPRX by considering equilibria.

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.

Crosslinking of collagen using a controlled molecular weight bio-crosslinker: β-cyclodextrin polyrotaxane multi-aldehydes

A novel bio-crosslinker which can improve the properties of collagen effectively.

Fabrication of ultra-thin polyrotaxane-based films via solid-state continuous assembly of polymers

Surface-confined ultra-thin polyrotaxane (PRX)-based films with tunable composition, surface topology and swelling characteristics were prepared by solid-state continuous assembly of polymers (ssCAP).

Enhanced uptake and siRNA-mediated knockdown of a biologically relevant gene using cyclodextrin polyrotaxane

Cellular investigations confirm the ability of cyclodextrin polyrotaxane nanoplexes to deliver siRNA for down-regulating genes relevant to the pathogenesis of tuberculosis.