Multifunctional Stimuli-Responsive Supramolecular Materials with Stretching, Coloring, and Self-Healing Properties Functionalized via Host–Guest Interactions

Encapsulated di-chloro-ethane-mediated inter-locked supra-molecular polymeric assembly of A1/A2-dihydroxy-oct-yloxy pillar[5]arene 1,2-di-chloro-ethane monosolvate

Crystals of 1-(1,4-dihy-droxy)-2,3,4,5-(1,4-dioct-yloxy)-pillar[5]arene, C99H158O10·C2H4Cl2, were grown from a 1,2-dicholoro-ethane/n-hexane solvent system. In the crystal, the encapsulated 1,2-di-chloro-ethane solvent is stabilized by C-H⋯π inter-actions and mediates the formation of an inter-locked supra-molecular polymer via C-H⋯Cl inter-actions.

Sonochemistry-Assembled Stimuli-Responsive Polymer Microcapsules for Drug Delivery

Stimuli-responsive polymer microcapsules (PMs) fabricated by the sonochemical method have emerged for developing useful drug delivery systems, and the latest developments are mainly focusing on the synthetic strategies and properties such as structure, size, stability, loading capacity, drug delivery, and release. There, the primary attribution of sonochemistry is to offer a simple and practical approach for the preparation of PMs. Structure, size, stability, and properties of PMs are designed mainly according to synthetic materials, implementation schemes, or specific demands. Numerous functionalities of PMs based on different stimuli are demonstrated: targeting motion in a magnetic field or adhering to the living cells with sensitive sites through molecular recognition, and stimuli-triggered release including enzymatic catalysis, chemical reaction as well as physical or mechanical process. The current review discusses the basic principles and mechanisms of stimuli effects, and describes the progress in the application such as targeted drug systems and controlled drug systems, and also gives an outlook on the future challenges and opportunities for drug delivery and theranostics.

A Recent Perspective on Noncovalently Formed Polymeric Hydrogels

Chemically crosslinked covalent hydrogels form a permanent and often strong network, and have been extensively used so far in drug delivery and tissue engineering. However, it is more difficult to induce dynamic and highly tunable changes in these hydrogels. Noncovalently formed hydrogels show promise as inherently reversible systems with an ability to change in response to dynamic environments, and have garnered strong interest recently. In this Personal Account, we elucidate a few key attractive properties of noncovalent hydrogels and describe recent developments in hydrogels crosslinked using various different noncovalent interactions. These hydrogels offer huge control for modulating material properties and could be more relevant mimics for biological systems.

Photoregulating of Stretchability and Toughness of a Self-Healable Polymer Hydrogel

Supramolecular hydrogels that are assembled through dynamic host-guest interactions have presented apparent potential in the construction of materials with promising performance. Herein, a photoregulated hydrogel cross-linked by host-guest interactions with multifunctions of high stretchability, strong toughness, and rapid self-healing property is reported. The hydrogel exhibits unique light-responsive property due to the introduction of two photoisomerized groups. For example, the stress-strain curve of the original hydrogel indicates 1020% rupture strain with the maximum tensile strain value of 214 kPa. Upon 365 nm light irradiation for an hour, its tensile strain increases to 15 times with lower tensile stress indicating a better stretchability. Moreover, the hydrogel is photochromic and surface patternable, where it can reversibly switch color between luminous yellow and brown while exposed to 365 and 440 nm light irradiation. It holds great promise for applying in self-recovering optically controlled and labeled elastic mechanical materials.

Aqueous Phase Exfoliation of Two-Dimensional Materials Assisted by Thermoresponsive Polymeric Ionic Liquid and Their Applications in Stimuli-Responsive Hydrogels and Highly Thermally Conductive Films

With the increasing attention for various two-dimensional (2D) materials in recent years, developing a universal, facile, and eco-friendly method to exfoliate them into single- and few-layered nanosheets is becoming more and more urgent. Herein, we use a thermoresponsive polymeric ionic liquid (TRPIL) as a universal polymer surfactant to assist the high-efficiency exfoliation of molybdenum disulfide (MoS₂), graphite, and hexagonal boron nitride in an aqueous medium through consecutive sonication. In this case, the reliable interaction between 2D materials and the TRPIL would facilitate the exfoliation and simultaneously achieve a noncovalent functionalization of the exfoliated nanosheets. Interestingly, the dispersion stability of exfoliated nanosheet suspensions can be reversibly tuned by temperature because of the thermoresponsive phase transition behavior of the TRPIL. As a proof of potential applications, a temperature and photo-dual-responsive TRPIL/MoS₂ coloring hydrogel with robust mechanical property and an artificial nacre-like BN nanosheet film with high thermal conductivity were fabricated.

Cyclodextrins as versatile building blocks for regenerative medicine

Cyclodextrins (CDs) are one of the most versatile substances produced by nature, and it is in the aqueous biological environment where the multifaceted potential of CDs can be completely unveiled. CDs form inclusion complexes with a variety of guest molecules, including polymers, producing very diverse biocompatible supramolecular structures. Additionally, CDs themselves can trigger cell differentiation to distinct lineages depending on the substituent groups and also promote salt nucleation. These features together with the affinity-driven regulated release of therapeutic molecules, growth factors and gene vectors explain the rising interest for CDs as building blocks in regenerative medicine. Supramolecular poly(pseudo)rotaxane structures and zipper-like assemblies exhibit outstanding viscoelastic properties, performing as syringeable implants. The sharp shear-responsiveness of the supramolecular assemblies is opening new avenues for the design of bioinks for 3D printing and also of electrospun fibers. CDs can also be transformed into polymerizable monomers to prepare alternative nanostructured materials. The aim of this review is to analyze the role that CDs may play in regenerative medicine through the analysis of the last decade research. Most applications of CD-based scaffolds are focussed on non-healing bone fractures, cartilage reparation and skin recovery, but also on even more challenging demands such as neural grafts. For the sake of clarity, main sections of this review are organized according to the architecture of the CD-based scaffolds, mainly syringeable supramolecular hydrogels, 3D printed scaffolds, electrospun fibers, and composites, since the same scaffold type may find application in different tissues.

Photosensitive poly(o-nitrobenzyloxycarbonyl-l-lysine)-b-PEO polypeptide copolymers: synthesis, multiple self-assembly behaviors, and the photo/pH-thermo-sensitive hydrogels

We synthesize a photosensitive poly(o-nitrobenzyloxycarbonyl-l-lysine)-b-poly(ethylene glycol) block copolymer and fabricate three kinds of dual-sensitive (i.e., photo/pH-thermo) polypeptide normal and reverse micellar hydrogels.