Formation of well-defined supramolecular microstructures consisting of γ-cyclodextrin and polyether —rods, cubes, plates, and nanosheets—guided by guest polymer structure

Supramolecular Modular Assembly of Imaging-Trackable Enzymatic Nanomotors

Self-propelled micro/nanomotors (MNMs) have shown great application potential in biomedicine, sensing, environmental remediation, etc. In the past decade, various strategies or technologies have been used to prepare and functionalize MNMs. However, the current preparation strategies of the MNMs were mainly following the pre-designed methods based on specific tasks to introduce expected functional parts on the various micro/nanocarriers, which lacks a universal platform and common features, making it difficult to apply to different application scenarios. Here, we have developed a modular assembly strategy based on host-guest chemistry, which enables the on-demand construction of imaging-trackable nanomotors mounted with suitable driving and imaging modules using a universal assembly platform, according to different application scenarios. These assembled nanomotors exhibited enhanced diffusion behavior driven by enzymatic reactions. The loaded imaging functions were used to dynamically trace the swarm motion behavior of assembled nanomotors with corresponding fuel conditions both in vitro and in vivo. The modular assembly strategy endowed with host-guest interaction provides a universal approach to producing multifunctional MNMs in a facile and controllable manner, which paves the way for the future development of MNMs systems with programmable functions.

Drug-Loaded Nanocarriers Composed of Cholesteryl Oleate Crystal Cores and Multiple-Nanosheet Shells of γ-Cyclodextrin Inclusion Complex Crystals

In this study, we prepared drug-loaded nanocarriers made of cholesteryl oleate (ChO) and γ-cyclodextrin (γ-CD). A nanosuspension (nanosuspension-I, NS-I) containing nanoparticles with a mean size of approximately 170 nm was obtained through the solvent-diffusion method using ethanol. A second nanosuspension (nanosuspension-II, NS-II), which was prepared by freeze-drying and redispersion of NS-I, exhibited an increased particle size of approximately 210 nm. Cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM) force-distance curves indicated that the nanoparticles in NS-I were oblong and soft. However, those in NS-II were angular and stiff, and, interestingly, multiple nanosheets covered the solid-liquid interface. Synchrotron wide-angle X-ray diffraction (WAXD) analysis of NS-II indicated that the nanoparticles in it had a core-shell structure, where the ChO crystal in the inner core was covered by multiple nanosheets of ChO/γ-CD inclusion complex crystals. The X-ray peak analysis suggested that the γ-CD columns of the nanosheets were vertically stacked onto the ChO crystal interface. It was found that the nanosheets on the nanoparticle interface were formed during the freezing process. A model drug carbamazepine (CBZ) was loaded into the ChO/γ-CD nanoparticles by pre-dissolving CBZ in ethanol during the solvent-diffusion process. Cryo-TEM, ¹H NMR, ζ-potentials, and synchrotron WAXD indicated that CBZ was unexpectedly loaded into the shell as a CBZ/γ-CD inclusion complex crystalline nanosheet. The specific nanosheet structure, where ChO and CBZ coexisted in the same crystal of γ-CD, could achieve CBZ loading in the nanoparticles. ChO/γ-CD nanoparticles with the unique core-shell structure are expected to perform as practical carriers for drug delivery.

Thermally induced disassembly mechanism of pseudo-polyrotaxane nanosheets consisting of β-CD and a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymer

PPRNSs dissolved in two steps during heating owing to the anisotropy of the topological constraint of β-CD by axis polymers.

Molecular Recognition of Fluorescent Probe Molecules with a Pseudopolyrotaxane Nanosheet

Pseudopolyrotaxane nanosheets (PPRNS) are ultrathin two-dimensional (2D) materials fabricated via supramolecular self-assembly of β-cyclodextrin (β-CD) and poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymers. In this study, the molecular loading of various fluorescent probe molecules onto PPRNS was systematically investigated. ¹H NMR study for R6G absorption to PPRNS indicated that the small hydrophobic groups, such as the methyl group, of R6G were absorbed by PPRNS. Consistently, the fluorescent probes without methyl groups were not absorbed. These results indicate that PPRNS has a molecular recognition absorption property based on the host-guest interaction of the functional groups on probe molecules and molecular-sized spaces of PPRNS surfaces, which may be vacant β-CDs and voids between β-CD columns. The absorbed amount of the molecular probes onto PPRNS was investigated by UV-vis spectra, and the absorption behavior could be described well by the Langmuir absorption isotherm. This is consistent with the suggested model that the probes are absorbed onto the PPRNS surfaces. This study demonstrates that PPRNSs can be applied as adsorbents for toxic compounds, drug delivery systems, and 2D sensors.

Precise control of cyclodextrin-based pseudo-polyrotaxane lamellar structure via axis polymer composition

Self-assembly of cyclodextrin (CD) with guest polymers has attracted much attention owing to its biocompatibility and accessibility. In this study, we investigate the composition effect of poly(ethylene oxide)m-b-poly(propylene oxide)n-b-poly(ethylene oxide)m (EOmPOnEOm) triblock copolymers on lamellar or plate structures formed by complexation with β-CD. EO5PO29EO5, EO14PO29EO14, and EO75PO29EO75 show periodic lamellar morphology consisting of single-crystalline pseudo-polyrotaxane (PPR) nanosheets with a thickness equal to the central PO length. This is because β-CDs selectively cover the PO component and cause the microphase separation between β-CD and EO layers. The thickness of the EO layers increases linearly with increasing number of EO units, which suggests that the EO chains are constrained into virtual cylinders with the diameter of the β-CD. This means that we can precisely control the thickness of both the crystal (β-CD and PO) and the amorphous (EO) layers in the lamellar structure. In contrast, EO2PO29EO2 forms a thin plate structure, where not only PO but also EO chains are covered with β-CD. Furthermore, the length of the central PO component is necessary to form the lamellar structure with the phase separation between the β-CD and EO layers. These findings provide a more fundamental understanding to enhance the variety and applicability of CD-based self-assembled materials.