Preorganized Hydrogel: Self-Healing Properties of Supramolecular Hydrogels Formed by Polymerization of Host–Guest-Monomers that Contain Cyclodextrins and Hydrophobic Guest Groups

Takahiro Kakuta¹, Yoshinori Takashima¹, Masaki Nakahata¹, Miyuki Otsubo¹, Hiroyasu  Yamaguchi¹, Akira Harada^1,2,*

 

Supramolecular hydrogels formed by a host-guest interaction show self-healing properties. The cube-shaped hydrogels with β-cyclodextrin and adamantane guest molecules mend after being broken. The hydrogels sufficiently heal to form a single gel, and the initial strength is restored. Although contact between a freshly cut and uncut surface does not mend the gels, two freshly cut surfaces selectively mend.
 

“Flex-Activated” Mechanophores: Using Polymer Mechanochemistry To Direct Bond Bending Activation

Michael B. Larsen and Andrew J. Boydston *

We describe studies in mechanochemical transduction that probe the activation of bonds orthogonal to an elongated polymer main chain. Compression of mechanophore-cross-linked materials resulted in the release of small molecules via cleavage of covalent bonds that were not integral components of the elongated polymer segments. The reactivity is proposed to arise from the distribution of force through the cross-linking units of the polymer network and subsequent bond bending motions that are consistent with the geometric changes in the overall reaction. This departure from contemporary polymer mechanochemistry, in which activation is achieved primarily by force-induced bond elongation, is a first step toward mechanophores capable of releasing side-chain functionalities without inherently compromising the overall macromolecular architecture.

In Situ Modification of Plain Liposomes with Lipidated Coiled Coil Forming Peptides Induces Membrane Fusion

 

Frank Versluis , Jens Voskuhl , Bartjan van Kolck , Harshal Zope , Marien Bremmer , Tjerk Albregtse , and Alexander Kros *

Complementary coiled coil forming lipidated peptides embedded in liposomal membranes are able to induce rapid, controlled, and targeted membrane fusion. Traditionally, such fusogenic liposomes are prepared by mixing lipids and lipidated peptides in organic solvent (e.g., chloroform). Here we prepared fusogenic liposomes in situ, i.e., by addition of a lipidated peptide solution to plain liposomes. As the lipid anchor is vital for the correct insertion of lipidated peptides into liposomal membranes, a small library of lipidated coiled coil forming peptides was designed in which the lipid structure was varied. The fusogenicity was screened using lipid and content mixing assays showing that cholesterol modified coiled coil peptides induced the most efficient fusion of membranes. Importantly, both lipid and content mixing experiments demonstrated that the in situ modification of plain liposomes with the cholesterol modified peptides yielded highly fusogenic liposomes. This work shows that existing membranes can be activated with lipidated coiled coil forming peptides, which might lead to highly potent applications such as the fusion of liposomes with cells.

Polymer Microcapsules with Programmable Active Release

Alireza Abbaspourrad †, Nick J. Carroll †, Shin-Hyun Kim †‡, and David A. Weitz *†

We present a new type of microcapsule programmed with a tunable active release mechanism. The capsules are triggered by a plasticizing stimulus that induces a phase change transition of the polymeric membrane from a solid to a fluidized form; thereafter, the cargo is actively driven out of the capsule through a defect at the capsule wall with controllable release kinetics. Tuning the degree of membrane fluidity by tailoring the amount of plasticizing stimulus present allows us to obtain temporal variation of the release kinetics from a subsecond abrupt burst release to a slow sustained release of encapsulant over many minutes. Moreover, we demonstrate tuning of the collective capsule triggering response by adjusting stimulus content, polymer molecular weight, and capsule membrane thickness. For this model system, we use a microfluidic approach to fabricate polystyrene capsules triggered by a toluene stimulus. However, this active release approach is general and is applicable to diverse polymeric capsule systems; this versatility is demonstrated by extension of our trigger-release scheme to capsules fabricated from a rubberlike block copolymer. The utility of our technique further enhances the potential of these active release capsules for practical application.

Metastable Liquid Crystal as Time-Responsive Reaction Medium: Aging-Induced Dual Enantioselective Control

Yasuhiro Ishida *†‡, Yuki Matsuoka ‡, Yukiko Kai §, Kuniyo Yamada †, Kenta Nakagawa , Toru Asahi , and Kazuhiko Saigo #

A metastable liquid crystal (LC) was found to serve as a time-responsive reaction medium, in which the enantioselectivity of a photoreaction was perfectly switched through isothermal annealing of the reaction system. When the LC salt of an enantiopure amine with a photoreactive acid was irradiated with UV/vis light, in situ photodimerization of the acid moiety proceeded smoothly to afford the (+)-isomer of the photodimer with high enantioselectivity (+86% ee). In contrast, photoirradiation of an aged sample, isothermally annealed for 20 h, gave predominantly the (−)-isomer (−94% ee). Systematic studies revealed that the reversal in selectivity originated from metastability of the LC system, which gradually transformed into a crystalline phase during annealing. This finding demonstrates the potential use of metastable aggregates as dynamic time-responsive media, reminiscent of biological systems.

Defined Polymer–Peptide Conjugates to Form Cell-Instructive starPEG–Heparin Matrices In Situ

Mikhail V. Tsurkan^†, Karolina Chwalek^†, Silvana Prokoph, Andrea Zieris, Kandice R. Levental^‡*, Uwe Freudenberg^*, Carsten Werner

 Poly(ethylene glycol)-peptide- and glycosaminoglycan-peptide conjugates obtained by a regio-selective amino acid protection strategy are converted into cell-instructive hydrogel matrices capable of inducing morphogenesis in embedded human vascular endothelial cells and dorsal root ganglia.

A molecular design principle of lyotropic liquid-crystalline conjugated polymers with directed alignment capability for plastic electronics

Bong-Gi Kim,Eun Jeong Jeong,Jong Won Chung,Sungbaek Seo,Bonwon Koo & Jinsang Kim

Conjugated polymers with a one-dimensional p-orbital overlap exhibit optoelectronic anisotropy. Their unique anisotropic properties can be fully realized in device applications only when the conjugated chains are aligned. Here, we report a molecular design principle of conjugated polymers to achieve concentration-regulated chain planarization, self-assembly, liquid-crystal-like good mobility and non-interdigitated side chains. As a consequence of these intra- and intermolecular attributes, chain alignment along an applied flow field occurs. This liquid-crystalline conjugated polymer was realized by incorporating intramolecular sulphur–fluorine interactions and bulky side chains linked to a tetrahedral carbon having a large form factor. By optimizing the polymer concentration and the flow field, we could achieve a high dichroic ratio of 16.67 in emission from conducting conjugated polymer films. Two-dimensional grazing-incidence X-ray diffraction was performed to analyse a well-defined conjugated polymer alignment. Thin-film transistors built on highly aligned conjugated polymer films showed more than three orders of magnitude faster carrier mobility along the conjugated polymer alignment direction than the perpendicular direction.