No abstract

Due to their similarity to some bio-architectures, for example, extracellular matrix, hydrogels are considered as bio-inspired networks with bio-mimetic and bio-functional properties. With natural cytocompatibility and biocompatibility, hydrogels nowadays are more and more involved in various bioapplications including shape morphing, artificial muscles, soft robotics, regenerative medicine, and so on. As an important subclass, stimuli-responsive hydrogels have been attracting interest within decades. In response to single or multi-triggers in biological microenvironment, stimuli-responsive hydrogels can undergo phase transition, stiffness change, or biochemical properties activation, which make them intriguing biomaterials with broad applications including sensing, drug delivery, tissue engineering, and wound healing. This review presents typical synthetic and natural gelators comprising small molecules and polymers as building blocks of functional architectures. The fabrication strategies of hydrogels varied from supramolecular assembly to dynamic covalent binding are detailed. Various exogenous or endogenous, physical or chemical, and synthetic or natural stimuli together with response mechanism, design principle are demonstrated. Through recent examples from different perspectives, such as bionic devices, wound dressing, and cargo carrier, the benefits and opportunities of stimuli-responsive hydrogels for biological applications are highlighted. Finally, the current challenges and future prospects in view of translation from fundamental researches to clinical application are briefly discussed.

Metalens, a prominent application of two-dimensional metasurfaces, has demonstrated powerful abilities even beyond traditional optical lenses. By manipulating the phase distribution of metalens composed of appropriately arranged nanoscale building blocks, the wavefront of incident wave can be controlled based on Huygens principle, thus achieving the desired reflected and transmitted wave for many different purposes. Metalenses will lead a revolution in optical imaging due to its flat nature and compact size, multispectral acquisition and even off-axis focusing. Here, we review the recent progress of metalenses presenting excellent properties, with a focus on the imaging application using these metalenses. We firstly discuss the mechanism for achieving metalenses with high efficiency, large numerical aperture, controlling the chromatic dispersion or monochromatic aberrations and large area fabrication. Then, we review several important imaging applications including wide-band focusing imaging, polarization dependent imaging, light field imaging and some other significant imaging systems in different areas. Finally, we make a conclusion with an outlook on the future development and challenges of this developing research field.

Two organic-inorganic iodobismuthates, C 5 H 6 NBiI 4 ([py][BiI 4 ]) and C 6 H 8 NBiI 4 ([mepy][BiI 4 ]), have been prepared with their structures revealed by single-crystal X-ray diffraction. One-dimensional BiI 4 À anionic chains built by edge-sharing BiI 6 octahedra were found in both materials; short I/I, I/C contacts and hydrogen bonding give rise to three-dimensional intermolecular interactions. Both compounds are semiconductors, with band gaps of around 2.0 eV, and the contribution from the organic moieties to the conduction band minimum has been derived by density functional theory. Solid-state optical and electrochemical studies performed on powders and thin films were carried out, and their stabilities under an ambient environment have been demonstrated. Their use as the absorber layer in printable mesoscopic solar cells without any hole transport material has led to efficiencies up to 0.9%, showing a promising new approach towards the development of lead-free third-generation photovoltaic materials.