NIR-Cleavable and pH-Responsive Polymeric Yolk-Shell Nanoparticles for Controlled Drug Release.

Responsive drug release and low toxicity of drug carriers are important for designing controlled release systems. Here, a double functional diffractive o-nitrobenzyl, containing multiple electron-donating groups as a crosslinker and methacrylic acid (MAA) as a monomer, was used to decorate upconversion nanoparticles (UCNPs) to produce robust poly o-nitrobenzyl@UCNP nanocapsules using the distillation-precipitation polymerization and templating method. Poly o-nitrobenzyl@UCNP nanocapsules with a robust yolk-shell structure exhibited near-infrared (NIR) light-/pH-responsive properties. When the nanocapsules were exposed to 980 nm NIR irradiation, the loaded drug was efficiently released by altering the shell of the nanocapsules. The photodegradation kinetics of the poly o-nitrobenzyl@UCNP nanocapsules were studied. The anticancer drug, doxorubicin hydrochloride (DOX), was loaded at pH 8.0 with a loading efficiency of 13.2 wt %. The Baker-Lonsdale model was used to determine the diffusion coefficients under different release conditions to facilitate the design of dual-responsive drug release devices or systems. Additionally, cytotoxicity studies showed that the drug release of DOX could be efficiently triggered by NIR to kill cancer cells in a controlled manner.

Injectable Thermosensitive Iodine-Loaded Starch-g-poly(N-isopropylacrylamide) Hydrogel for Cancer Photothermal Therapy and Anti-Infection.

Although photothermal therapy (PTT) can effectively eliminate tumors, the normal tissues near tumors are inevitably damaged by heat and infected by bacteria, which greatly limits the therapeutic effect. In this work, an injectable thermosensitive hydrogel based on iodine-loaded starch-g-poly(N-isopropylacrylamide) (PNSI) is developed to overcome this problem. FTIR, 1 H NMR, and UV-vis spectra confirm the graft copolymerization of poly(N-isopropylacrylamide) with starch and the formation of "iodine-starch" complex. Transmission electron microscope images show PNSI polymer self-assembles into regular spherical nanogel with a size of ≈50 nm. The concentrated nanogel dispersion is a sol at room temperature and transforms to hydrogel at body temperature. Under NIR laser irradiation for 10 min, the ΔT of the nanogel dispersion approachs about 20 °C with excellent thermal stability and high cytotoxicity due to the photothermal effect of the "iodine-starch" complex. After intratumor injection, this injectable hydrogel efficiently inhibites the tumor growth under 808 nm laser irradiation. Furthermore, it can also suppress Staphylococcus aureus infection in the wound post-PTT due to the release of iodine, which promotes wound healing. Therefore, this injectable thermosensitive "iodine-starch" composite hydrogel with advantages of good biocompatible and easy preparation possesses potential application for tumor photothermal therapy and antibacterial infection.

Helix Induction and Inversion of Polymeric Foldamer Regulated by the Single Enantiomers.

Generally, a single enantiomer can induce a foldamer into a preferred-handed helix, while another condition is required for the helical inversion. Herein, it is found that the helix induction and subsequent inversion of poly(m-phenylene diethynylene)-based foldamer bearing aza-18-crown-6 pendants (Poly-1) can be realized by increasing the concentration of sterically hindered l-amino acid perchlorate salts. When the amount of chiral enantiomers is small, one enantiomer tends to complex with two non-adjacent aza-18-crown-6 rings via three N+ H···O hydrogen bonds in a sandwich mode. Notably, the transition dipole moment is perpendicular to the aza-18-crown-6 ring, so that the induced helical chirality in Poly-1 backbone is opposite to the chirality of enantiomers. When the amount of chiral enantiomers is large enough, each aza-18-crown-6 is occupied by one enantiomer, which causes the transition dipole moment in a parallel direction to aza-18-crown-6 ring. In this case, the increased steric hindrance can facilitate the inversion of screw sense of Poly-1 backbone, which is directed by chiral center of enantiomers. As a result, a helix inversion has been achieved successfully. This work not only provides a novel strategy for regulating the two-stage folded helical conformations by the single enantiomers, but opens a window to develop chiral recognition materials.

High-Performance Photochromic Hydrogels for Rewritable Information Record.

Rewritable information record materials usually demand not only reversibly stimuli-responsive ability, but also strong mechanical properties. To achieve one photochromic hydrogel with super-strong mechanical strength, hydrophobic molecule spiropyran (SP) has been introduced into a copolymer based on ion-hybrid crosslink. The hydrogels exhibit both photoinduced reversible color changes and excellent mechanical properties, i.e., the tensile stress of 3.22 MPa, work of tension of 12.8 MJ m-3 , and modulus of elasticity of 8.6 MPa. Moreover, the SP-based Ca2+ crosslinked hydrogels can be enhanced further when exposed to UV-light via ionic interaction coordination between Ca2+ , merocyanine (MC) with polar copolymer chain. In particular, hydrogels have excellent reversible conversion behavior, which can be used to realize repeatable writing of optical information. Thus, the novel design is demonstrated to support future applications in writing repeatable optical information, optical displays, information storage, artificial intelligence systems, and flexible wearable devices.

Concurrent solution-like decoloration rate and high mechanical strength from polymer-dispersed photochromic organogel.

To achieve a fast photochromic response in solid matrix, photochromic molecules/segments have been either dispersed into elastomers via physical doping or linked to glassy polymers by soft units through covalent bonding. However, the former is lack of high mechanical strength and the latter owes the drawback of time-consumption of synthesis. Here, we propose a facile strategy of co-solvent evaporation to prepare polymer-dispersed photochromic organogel where both high mechanical strength of the glassy polymer matrix and solution-like fast photochromism of the photochromic molecule within organogel can be retained concurrently. Glassy PVA matrix and dispersed organogel of 1,3:2,4-di-O-benzylidene-d-sorbitol/poly(propylene glycol) (DBS/PPG) provide high mechanical strength and sufficient free volume for intramolecular rotation of photochromic spiropyran (SP), respectively. Interestingly, these thin films behave a solution-like decoloration the decay rate of which is 65-70 fold faster than that in the SP-directly doped PVA film and only slightly slower than those in their corresponding PPG solutions.

A Review on Low-Molecular-Weight Gels Driven by Halogen-Effect.

As a new type of non-covalent interaction similar to hydrogen bond, halogen bond has become an important supramolecular tool in crystal engineering, material chemistry, biological science, etc., due to its unique properties. In fact, halogen bond has been confirmed on the effect of molecular assemblies and soft materials, and widely used in various functional soft materials including liquid crystals, gels and polymers. In recent years, halogen bonding has aroused strong interest in inducing molecular assembly into low-molecular-weight gels (LMWGs). To the best of our knowledge, there is still a lack of in-depth review of this field. So, in this paper, the recent progress of LMWGs driven by halogen bonding is reviewed. According to the number of components forming halogen bonded gels, the structural characteristics of halogen bonded supramolecular gels, the relationship between halogen bonding and other non-covalent interactions, as well as the application fields of halogen bonded gels are introduced, respectively. In addition, the challenges faced by halogenated supramolecular gels at present and their development prospects in future have been proposed. We believe that the halogen bonded gel will have more impressive applications in the next few years, opening exciting new opportunities for the development of soft materials.

Mesoporous block copolymer nanoparticles with tailored structures by hydrogen-bonding-assisted self-assembly.

A simple, yet robust route to prepare polymer nanoparticles with tunable internal structures through supramolecular assembly within emulsion droplets is presented. Nanoparticles with various internal morphologies, including dispersed spheres, dispersed spirals, stacked toroids, and concentric lamellae, are obtained due to the 3D confinement and variation of hydrogen-bonding agent. This method also allows us to form mesoporous particles through further disassembly of the supramoleclar assemblies by rupturing the hydrogen bonding.