Visible-light controlled supramolecular transformations of donor-acceptor Stenhouse adducts amphiphiles at multiple length-scale

Supramolecular assemblies of amphiphilic donor-acceptor Stenhouse adducts as macroscopic soft scaffolds

In the design of photoharvesting and photoresponsive supramolecular systems in aqueous medium, the fabrication of amphiphilic photoswitches enables a noninvasive functional response through photoirradiation. Although most aqueous supramolecular assemblies are driven by high-energy and biodamaging UV light, we have previously reported a design of amphiphilic donor-acceptor Stenhouse adducts (DASAs) controlled by white light. Herein, we present a series of DASA amphiphiles (DAs) with minor structural modifications on the alkyl linker chain length connecting the DASA motif with the hydrophilic moiety. The excellent photoswitchability in organic medium and the photoresponsiveness in aqueous medium, driven by visible light, were investigated by UV-vis absorption spectroscopy. The assembled supramolecular nanostructures were confirmed by electron microscopy, while the supramolecular packing was revealed by X-ray diffraction analysis. Upon visible-light irradiation, significant transformations of the DA geometry enabled transformations of the supramolecular assemblies on a microscopic scale, subsequently disassembling macroscopic soft scaffolds of DAs. The current work shows promising use for the fabrication of visible-light-controlled macroscopic scaffolds, offering the next generation of biomedical materials with visible-light-controlled microenvironments and future soft-robotic systems.

Aqueous Supramolecular Transformations of Motor Bola-Amphiphiles at Multiple Length-Scale

Molecular motor amphiphiles have already been widely attempted for dynamic nanosystems across multiple length-scale for developments of small functional materials, including controlling macroscopic foam properties, amplifying motion as artificial molecular muscles, and serving as extracellular matrix mimicking cell scaffolds. However, limiting examples of bola-type molecular motor amphiphiles are considered for constructing macroscopic biomaterials. Herein, this work presents the designed two second generation molecular motor amphiphiles, motor bola-amphiphiles (MBAs). Aside from the photoinduced motor rotation of MBAs achieved in both organic and aqueous media, the rate of recovering thermal helix inversion step can be controlled by the rotor part with different steric hindrances. Dynamic assembled structures of MBAs are observed under (cryo)-transmission electron microscopy (TEM). This dynamicity assists MBAs in further assembling as macroscopic soft scaffolds by applying a shear-flow method. Upon photoirradiation, the phototropic bending function of MBA scaffolds is observed, demonstrating the amplification of molecular motion into macroscopic phototropic bending functions at the macroscopic length-scale. Since MBAs are confirmed with low cytotoxicity, human bone marrow-derived mesenchymal stem cells (hBM-MSCs) can grow on the surface of MBA scaffolds. These results clearly demonstrate the concept of designing MBAs for developing photoresponsive dynamic functional materials to create new-generation soft robotic systems and cell-material interfaces.

Red-light-controlled supramolecular assemblies of indigo amphiphiles at multiple length scales

Amphiphilic molecules functionalized with photoresponsive motifs have attractive prospects for applications in smart functional bio-material ranging from cell-material interfaces to drug delivery systems owing to the precisely controllable functionality of self-assembled hierarchical supramolecular structures in aqueous media by a non-invasive light stimulation with high temporal- and spatial-resolution. However, most of reported photoresponsive amphiphiles are triggered by bio-damaging UV-light, which greatly limits the potential in bio-related applications. Herein, we present newly designed red-light controlled N,N'-diaryl-substituted indigo amphiphiles (IA), exhibiting excellent photoswitchablity and photostability with dual red-/green-light in organic media. Meanwhile, aqueous solutions of IA assembled into supramolecular structures in both microscopic and macroscopic length-scale, though the photoresponsiveness of IA is slightly compromised in aqueous media. At macroscopic length-scale, morphological changes of IA macroscopic scaffold prepared by a shear-flow method can be fine adjusted upon red-light irradiation. Moreover, the preferential attachment of live h-MSCs to IA macroscopic scaffold surface also indicates a good biocompatibility of IA macroscopic scaffold. These results provide the potential for developing the next generation of red-light controlled soft functional materials with good biocompatibility.

Responsive Supramolecular Polymers for Diagnosis and Treatment

Stimuli-responsive supramolecular polymers are ordered nanosized materials that are held together by non-covalent interactions (hydrogen-bonding, metal-ligand coordination, π-stacking and, host-guest interactions) and can reversibly undergo self-assembly. Their non-covalent nature endows supramolecular polymers with the ability to respond to external stimuli (temperature, light, ultrasound, electric/magnetic field) or environmental changes (temperature, pH, redox potential, enzyme activity), making them attractive candidates for a variety of biomedical applications. To date, supramolecular research has largely evolved in the development of smart water-soluble self-assemblies with the aim of mimicking the biological function of natural supramolecular systems. Indeed, there is a wide variety of synthetic biomaterials formulated with responsiveness to control and trigger, or not to trigger, aqueous self-assembly. The design of responsive supramolecular polymers ranges from the use of hydrophobic cores (i.e., benzene-1,3,5-tricarboxamide) to the introduction of macrocyclic hosts (i.e., cyclodextrins). In this review, we summarize the most relevant advances achieved in the design of stimuli-responsive supramolecular systems used to control transport and release of both diagnosis agents and therapeutic drugs in order to prevent, diagnose, and treat human diseases.

Controlled Supramolecular Assemblies of Chiral Cyclometalated Gold (III) Amphiphiles in Aqueous Media

Gold (III) cyclometalated based amphiphiles in aqueous media have been revealed with excellent supramolecular transformations to external stimuli to open new pathways for soft functional material fabrications. Herein, we report a new chiral cyclometalated gold (III) amphiphile (GA) assembling into lamellar nanostructures in aqueous media confirmed with transmission electron microscopy (TEM). Counterion exchange with D-, L-, or racemic-camphorsulfonates features the significant supramolecular helicity enhancements, enabling transformations of GA from lamellar structure to vesicles and to nanotubes with multi-equivalents of counterion. The limited cytotoxicity of GA in aqueous media exhibits good biocompatibility.

Tailoring Multicontrolled Supramolecular Assemblies of Stiff-Stilbene Amphiphiles into Macroscopic Soft Scaffolds as Cell-Material Interfaces

Biocompatible synthetic supramolecular systems have shed light on biomedical and tissue-regenerative material applications. The intrinsic functional applicability, tunability, and stimuli-responsiveness of synthetic supramolecular systems allow one to develop various multicontrolled supramolecular assemblies in aqueous media. However, it remains highly challenging to use state-of-the-art supramolecular assemblies of photoresponsive amphiphiles controlled by multiple stimulations in fabricating macroscopic materials. Herein, we demonstrate a stiff-stilbene amphiphile (SA) multicontrolled supramolecular assembling system that comprises two different charged end groups. The excellent photoswitchabilities of SA in both organic and aqueous media are demonstrated. Furthermore, multiple stimuli, i.e., light, pH, and counterions, are applied to control the supramolecular assembling behaviors, which are monitored by circular dichroism spectroscopy and electron microscopies. This multicontrolled supramolecular system can be systematically assembled into macroscopic soft functional scaffolds, whose structural parameters are investigated by electron microscopies and X-ray diffraction techniques, suggesting the large aspect ratio of SA nanostructures assembled into macroscopic soft scaffolds. The fabricated soft functional scaffold is highly biocompatible for photocontrolled biotarget encapsulation/release selectively, as well as a cell-material interface for diverse cells' attachment. This new synthetic multicontrolled soft functional material provides a new strategy toward the development of next-generation controllable and biocompatible soft functional materials.

Visible light-responsive materials: the (photo)chemistry and applications of donor-acceptor Stenhouse adducts in polymer science

Donor-acceptor Stenhouse adduct (DASA) photoswitches have gained a lot of attention since their discovery in 2014. Their negative photochromism, visible light absorbance, synthetic tunability, and the large property changes between their photoisomers make them attractive candidates over other commonly used photoswitches for use in materials with responsive or adaptive properties. The development of such materials and their translation into advanced technologies continues to widely impact forefront materials research, and DASAs have thus attracted considerable interest in the field of visible-light responsive molecular switches and dynamic materials. Despite this interest, there have been challenges in understanding their complex behavior in the context of both small molecule studies and materials. Moreover, incorporation of DASAs into polymers can be challenging due to their incompatibility with the conditions for most common polymerization techniques. In this review, therefore, we examine and critically discuss the recent developments and challenges in the field of DASA-containing polymers, aiming at providing a better understanding of the interplay between the properties of both constituents (matrix and photoswitch). The first part summarizes current understanding of DASA design and switching properties. The second section discusses strategies of incorporation of DASAs into polymers, properties of DASA-containing materials, and methods for studying switching of DASAs in materials. We also discuss emerging applications for DASA photoswitches in polymeric materials, ranging from light-responsive drug delivery systems, to photothermal actuators, sensors and photoswitchable surfaces. Last, we summarize the current challenges in the field and venture on the steps required to explore novel systems and expand both the functional properties and the application opportunities of DASA-containing polymers.

Exploration of molecular machines in supramolecular soft robotic systems

Soft robotic system, a new era of material science, is rapidly developing with advanced processing technology in soft matters, featured with biomimetic nature. An important bottom-up approach is through the implementation of molecular machines into polymeric materials, however, the synchronized molecular motions, acumination of strain across multiple length-scales, and amplification into macroscopic actuations remained highly challenging. This review presents the significances, key design strategies, and outlook of the hierarchical supramolecular systems of molecular machines to develop novel types of supramolecular-based soft robotic systems.