Development of Smart Optical Gels with Highly Magnetically Responsive Bicelles

Bioinspired Supramolecular Hydrogel from Design to Applications

Nature offers a wealth of opportunities to solve scientific and technological issues based on its unique structures and function. The dynamic non-covalent interaction is considered to be the main base of living functions of creatures including humans, animals, and plants. Supramolecular hydrogels formed by non-covalent bonding interactions has become a unique platform for constructing promising materials for medicine, energy, electronic, and biological substitute. In this review, the self-assemble principle of supramolecular hydrogels is summarized. Next, the stimulation of external environment that triggers the assembly or disassembly of supramolecular hydrogels are recapitulated, including temperature, mechanics, light, pH, ions, etc. The main applications of bioinspired supramolecular hydrogels in terms of bionic objects including humans, animals, and plants are also described. Although so many efforts are done for revealing the synergized mechanism of the function and non-covalent interactions on the supramolecular hydrogel, the complexity and variability between stimulus and non-covalent bonding in the supramolecular system still require impeccable theories. As an outlook, the bioinspired supramolecular hydrogel is just beginning to exhibit its great potential in human life, offering significant opportunities in drug delivery and screening, implantable devices and substitutions, tissue engineering, micro-fluidic devices, and biosensors.

Fabrication method for a magnetically induced highly oriented nanohydroxyapatite/collagen composite

Both collagen fibres and nanohydroxyapatite crystals have anisotropic magnetisation, which allows them to be oriented by a high magnetic field. Highly oriented nanohydroxyapatite/collagen composites were prepared using a high magnetic field combined with in situ synthesis. These highly oriented composites were investigated and compared with conventional composites. The results showed that the collagen fibres in the magnetically induced highly oriented nanohydroxyapatite/collagen composites had a preferred orientation and smaller molecular spacing, while the nanohydroxyapatite crystals were tightly adhered along the collagen fibre surface. The magnetically induced composites exhibited superior resistance to swelling and degradation along with high compressive strength. This artificial composite, with a structure and composition similar to natural bone, represents a new idea for improving materials for vertical or horizontal bone augmentation.

Engineering Hydrogel-Based Biomedical Photonics: Design, Fabrication, and Applications

Light guiding and manipulation in photonics have become ubiquitous in events ranging from everyday communications to complex robotics and nanomedicine. The speed and sensitivity of light-matter interactions offer unprecedented advantages in biomedical optics, data transmission, photomedicine, and detection of multi-scale phenomena. Recently, hydrogels have emerged as a promising candidate for interfacing photonics and bioengineering by combining their light-guiding properties with live tissue compatibility in optical, chemical, physiological, and mechanical dimensions. Herein, the latest progress over hydrogel photonics and its applications in guidance and manipulation of light is reviewed. Physics of guiding light through hydrogels and living tissues, and existing technical challenges in translating these tools into biomedical settings are discussed. A comprehensive and thorough overview of materials, fabrication protocols, and design architectures used in hydrogel photonics is provided. Finally, recent examples of applying structures such as hydrogel optical fibers, living photonic constructs, and their use as light-driven hydrogel robots, photomedicine tools, and organ-on-a-chip models are described. By providing a critical and selective evaluation of the field's status, this work sets a foundation for the next generation of hydrogel photonic research.

Exploring Reversible Thermochromic Behavior in a Rare Ni(II)-MOF System

Thermochromic metal-organic frameworks (MOFs) are promising functional materials for a wide range of applications due to their ability to exhibit color variation under external temperature stimuli, yet the development of them with high cyclability and efficient regeneration processes remains challenging. Here, presented is a rare example of an ultrastable Ni(II)-MOF exhibiting an unprecedented reversible four-step color change between two complementary colors in a wide temperature range, which could be repeated for at least 500 cycles without losing crystallinity and thermochromic performance. Notably, the regeneration can be achieved within 1 min by simply letting the crystals cool naturally in the air, facilitated by the unique nature of the channels' inner surface. The reversible thermochromic behavior is owing to a series of reversible crystal structure changes with temperature, including the stepwise dehydration/rehydration process, and structural changes. This work facilitates the future development of more MOF-based reversible thermochromic materials with excellent performance and improved practical applicability.

Single network double cross-linker (SNDCL) hydrogels with excellent stretchability, self-recovery, adhesion strength, and conductivity for human motion monitoring

Hydrogels, as a kind of soft materials, are good candidates for smart skin-like materials. A double network is usually fabricated to improve the mechanical properties of hydrogels, and involves two different kinds of networks. In this work, a novel strategy for preparing single network double cross-linker (SNDCL) hydrogels was proposed and the prepared hydrogels exhibited excellent mechanical properties, including stretchability, compressibility, self-recovery, adhesion, shape memory and mechanical strength. N,N'-Methylenebisacrylamide forms covalent bonds with the network, while citric acid can form multiple weak interactions due to the polycarboxylic structure. This improves the tensile properties (6564%) and compressive properties of the hydrogel, and the hydrogels also exhibit long-lasting self-adhesion ability on various substrates. In addition, the hydrogels with multiple properties can be used as flexible strain sensors, allowing the monitoring of body movements. The hydrogels can hopefully be used in wearable electronic sensor devices and for healthcare monitoring.

Evaluation of Molecular Ordering in Bicelle Bilayer Membranes Based on Induced Circular Dichroism Spectra

Bicelles are submicrometer-sized disc-shaped molecular self-assemblies that can be obtained in aqueous solution by dispersing mixtures of certain amphiphiles. Although phospholipid bicelle and phospholipid vesicle assemblies adopt similar lipid bilayer structures, the differences in bilayer characteristics, especially physicochemical properties such as bilayer fluidity, are not clearly understood. Herein, we report the lipid ordering properties of bicelle bilayer membranes based on induced circular dichroism (ICD) and fluorescence polarization analyses using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a probe. Bicelles were prepared by using 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC), while pure DMPC vesicles and pure DHPC micelles were used as references. At temperatures below the phase transition temperature of DMPC, the bicelles showed lower membrane fluidities, whereas DHPC micelles showed higher membrane fluidity, suggesting no significant differences in bilayer fluidity between the bicelle and vesicle assemblies. The ICD signals of DPH were induced only when the membrane was in ordered (solid-ordered or ripple-gel) phases. In the bicelle systems, the ICD of DPH was more significant than that of the DMPC vesicle. The induced chirality of DPH was dependent on the chirality of the bilayer lipid. Compared to that of the DMPC/DHPC bicelle, the ICD of the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/DHPC bicelle was higher, while that of the bovine sphingomyelin/DHPC bicelle was lower. Because the lipids are tightly packed in the ordered phase, the ICD intensity reflects the molecular ordering state of the lipids in the bicelle bilayer.

Reversible Nontoxic Thermochromic Microcapsules

Thermochromic materials exhibit a color change in response to a change in temperature. Creating nontoxic microcapsules containing thermochromic materials for applications in ink and film materials is historically challenging. In this study, we develop a nontoxic chlorophenol red (CPR)-water thermochromic system and its microcapsules with silicone shells via a reaction between water and octadecyltrichlorosilane (OTS) at the interface of a w/o emulsion. The obtained microcapsules exhibit a clear color change with full reversibility and are successfully used as inks by screen printing and as additives in films. Nontoxicity of both microcapsules and films is demonstrated through cell cytotoxicity assays. These features make these novel materials applicable to the next generation of intelligent sensors, coating, and food packaging materials.

Use of paramagnetic systems to speed-up NMR data acquisition and for structural and dynamic studies

NMR spectroscopy is a powerful experimental technique to study biological systems at the atomic resolution. However, its intrinsic low sensitivity results in long acquisition times that in extreme cases lasts for days (or even weeks) often exceeding the lifetime of the sample under investigation. Different paramagnetic agents have been used in an effort to decrease the spin-lattice (T1) relaxation times of the studied nuclei, which are the main cause for long acquisition times necessary for signal averaging to enhance the signal-to-noise ratio of NMR spectra. Consequently, most of the experimental time is "wasted" in waiting for the magnetization to recover between successive scans. In this review, we discuss how to set up an optimal paramagnetic relaxation enhancement (PRE) system to effectively reduce the T1 relaxation times avoiding significant broadening of NMR signals. Additionally, we describe how PRE-agents can be used to provide structural and dynamic information and can even be used to follow the intermediates of chemical reactions and to speed-up data acquisition. We also describe the unique challenges and benefits associated with the application of PRE to solid-state NMR spectroscopy, explaining how the use of PREs is more complex for membrane mimetic systems as PREs can also be exploited to change the alignment of oriented membrane systems. Functionalization of membrane mimetics, such as bicelles, can provide a controlled region of paramagnetic effect that has the potential, together with the desired alignment, to provide crucial biologically relevant structural information. And finally, we discuss how paramagnetic metals can be utilized to further increase the dynamic nuclear polarization (DNP) effects and how to preserve the enhancements when dissolution DNP is implemented.

A novel bis-component AIE smart gel with high selectivity and sensitivity to detect CN-, Fe3+ and H2PO4. SOFT MATTER 2019;15:6348-6352. [PMID: 31290897 DOI: 10.1039/c9sm01035a]

A novel bis-component AIE-gel TG was facilely constructed from two "easy-to-synthesize" tripodal gelators by a simple host-guest self-assembly process. Interestingly, the TG shows strong aggregation-induced emission (AIE) and could be used for highly efficient and sensitive detection and separation of ions (CN^-, Fe³⁺ and H₂PO₄^-). The LODs (limits of lowest detection) of TG for CN^-, Fe³⁺ and H₂PO₄^- are in the range of 4.93 × 10^-9-7.80 × 10^-8 M. Meanwhile, the xerogel of TG could adsorb and separate Fe³⁺ from aqueous solutions, and the adsorption rate is 96%. In addition, a thin film based on the TG could act as a convenient test kit for the detection of CN^- and Fe³⁺. What is more, the TG-Fe film could not only be used as an erasable secure fluorescent display material, but also as a convenient reversible H₂PO₄^- test kit.