Bioprocess‐Inspired Microscale Additive Manufacturing of Multilayered TiO2/Polymer Composites with Enamel‐Like Structures and High Mechanical Properties

Natural structure‐forming processes found in biological systems are fantastic and perform at ambient temperatures, in contrast with anthropogenic technologies that commonly require harsh conditions. A new research direction “bioprocess‐inspired fabrication” is proposed to develop novel fabrication techniques for advanced materials. Enamel, an organic–inorganic composite biomaterial with outstanding mechanical performance and durability, is formed by repeating the basic blocks consisting of columnar hydroxyapatite or fluorapatite and an organic matrix. Inspired by the enamel formation process, a microscale additive manufacturing method is proposed for achieving a multilayered organic–inorganic columnar structure. In this approach, rutile titanium dioxide (TiO₂) nanorods, polymers, and graphene oxide (GO) are sequentially assembled in a layer‐by‐layer fashion to form an organic–inorganic structure. In particular, GO serves as a substrate for TiO₂ nanorods and interacts with polymers, jointly leading to the strength of the composites. Impressively, this enamel‐like structure material has hardness (1.56 ± 0.05 GPa) and ultrahigh Young's modulus (81.0 ± 2.7 GPa) comparable to natural enamel, and viscoelastic property (0.76 ± 0.12 GPa) superior to most solid materials. Consequently, this biomimetic synthetic approach provides an in‐depth understanding for the formation process of biomaterials and also enables the exploration of a new avenue for the preparation of organic–inorganic composite materials.     

Organic–Inorganic Hierarchical Self‐Assembly into Robust Luminescent Supramolecular Hydrogel

Luminescent hydrogels are of great potential for many fields, particularly serving as biomaterials ranging from fluorescent sensors to bioimaging agents. Here, robust luminescent hydrogels are reported using lanthanide complexes as emitting sources via a hierarchical organic–inorganic self‐assembling strategy. A new organic ligand is synthesized, consisting of a terpyridine unit and two flexibly linked methylimidazole moieties to coordinate with europium(III) (Eu³⁺) tri‐thenoyltrifluoroacetone (Eu(TTA)₃), leading to a stable amphiphilic Eu³⁺‐containing monomer. Synergistic coordination of TTA and terpyridine units allows the monomer to self‐assemble into spherical micelles in water, thus maintaining the luminescence of Ln complexes in water. The micelles further coassemble with exfoliated Laponite nanosheets coated with sodium polyacrylate into networks based on the electrostatic interactions, resulting in the supramolecular hydrogel possessing strong luminescence, extraordinary mechanical property, as well as self‐healing ability. The results demonstrate that hierarchical organic–inorganic self‐assembly is a versatile and effective strategy to create luminescent hydrogels containing lanthanide complexes, giving rise to great potential applications as a soft material.     

Citrate‐Based Tannin‐Bridged Bone Composites for Lumbar Fusion

Conventional bone composites consistently fail to mimic the chemical composition and integrated organic/inorganic structure of natural bone, lacking sufficient mechanics as well as inherent osteoconductivity and osteoinductivity. Through a facile surface coating process, the strong adhesive, tannic acid (TA), is adhered to the surface of the natural bone component, hydroxyapatite (HA), with and without the immobilization of in situ formed silver nanoparticles. Residual functional groups available on the immobilized TA substituents are subsequently covalently linked to the citrate‐based biodegradable polymer, poly(octamethylene citrate) (POC), effectively bridging the organic and inorganic phases. Due to the synergistic effects of the tannin and citrate components, the obtained citrate‐based tannin‐bridged bone composites (CTBCs) exhibit vastly improved compression strengths up to 323.0 ± 21.3 MPa compared to 229.9 ± 15.6 MPa for POC‐HA, and possess tunable degradation profiles, enhanced biomineralization performance, favorable biocompatibility, increased cell adhesion and proliferation, as well as considerable antimicrobial activity. In vivo study of porous CTBCs using a lumbar fusion model further confirms CTBCs' osteoconductivity and osteoinductivity, promoting bone regeneration. CTBCs possess great potential for bone regeneration applications while the immobilized TA additionally preserves surface bioconjugation sites to further tailor the bioactivity of CTBCs.     

Mussel‐Inspired Polydopamine Coating as a Universal Route to Hydroxyapatite Crystallization

Bone tissue is a complex biocomposite material with a variety of organic (e.g., proteins, cells) and inorganic (e.g., hydroxyapatite crystals) components hierarchically organized with nano/microscale precision. Based on the understanding of such hierarchical organization of bone tissue and its unique mechanical properties, efforts are being made to mimic these organic–inorganic hybrid biocomposites. A key factor for the successful designing of complex, hybrid biomaterials is the facilitation and control of adhesion at the interfaces, as many current synthetic biomaterials are inert, lacking interfacial bioactivity. In this regard, researchers have focused on controlling the interface by surface modifications, but the development of a simple, unified way to biofunctionalize diverse organic and inorganic materials remains a critical challenge. Here, a universal biomineralization route, called polydopamine‐assisted hydroxyapatite formation (pHAF), that can be applied to virtually any type and morphology of scaffold materials is demonstrated. Inspired by the adhesion mechanism of mussels, the pHAF method can readily integrate hydroxyapatites on ceramics, noble metals, semiconductors, and synthetic polymers, irrespective of their size and morphology (e.g., porosity and shape). Surface‐anchored catecholamine moieties in polydopamine enriches the interface with calcium ions, facilitating the formation of hydroxyapatite crystals that are aligned to the c‐axes, parallel to the polydopamine layer as observed in natural hydroxyapatites in mineralized tissues. This universal surface biomineralization can be an innovative foundation for future tissue engineering.     

Imidazole‐Grafted Nanogels for the Fabrication of Organic–Inorganic Protein Hybrids

Here, a platform for the development of highly responsive organic–inorganic enzyme hybrids is provided. The approach entails a first step of protein engineering, in which individual enzymes are armored with a porous nanogel decorated with imidazole motifs. In a second step, by mimicking the biomineralization mechanism, the assembly of the imidazole nanogels with CuSO₄ and phosphate salts is triggered. A full characterization of the new composites reveals the first reported example in which the assembly mechanism is triggered by the sum of Cu(II)–imidazole interaction and Cu₃(PO₄)₂ inorganic salt formation. It is demonstrated that the organic component of the hybrids, namely the imidazole‐modified polyacrylamide hydrogel, provides a favorable spatial distribution for the enzyme. This results in enhanced conversion rates, robustness of the composite at low pH values, and a remarkable thermal stability at 65 °C, exhibiting 400% of the activity of the mineralized enzyme lacking the organic constituent. Importantly, unlike in previous works, the protocol applies to the use of a broad range of transition metal cations (including mono‐, di‐, and trivalent cations) to trigger the mineralization mechanism, which eventually broadens the chemical and structural diversity of organic–inorganic protein hybrids.     

Macroscopic Properties of Biomimetic Ceramics Are Governed by the Molecular Recognition at the Bioorganic–Inorganic Interface

Bioinspired materials design aims for high‐performing composite materials based on natural biomineralization processes and biomineral architectures. A key component to the research is the bioorganic–inorganic interface, one of the most crucial parameters for controlling the material properties. In this study, genetically engineered phages expressing an inorganic‐binding peptide for the molecular recognition of a ceramic material is exploited to generate thin film multilayer assemblies, with the phage template as minority component. The bioorganic–inorganic interface in the ceramic (zinc oxide, ZnO) multilayer systems is strengthened by the ZnO‐binding motif HSSHH of a peptide to increase Young's modulus and hardness. Applying a point‐mutated version of the peptide, DSSHH, which modulates the interface forces, shows an increased fracture toughness without deteriorating the Young's modulus and the hardness. Molecular matching of the organic phase and its modulation in order to form a specific interface is shown to be important in controlling material properties like in natural biominerals. With this tool in hand, it is not only possible to imitate the structure of biominerals but also to genetically control the molecular recognition of bioorganic molecules to induce macroscopic effects in synthetic composite materials.     

A 0D Lead‐Free Hybrid Crystal with Ultralow Thermal Conductivity

Organic–inorganic hybrid materials are of significant interest owing to their diverse applications ranging from photovoltaics and electronics to catalysis. Control over the organic and inorganic components offers flexibility through tuning their chemical and physical properties. Herein, it is reported that a new organic–inorganic hybrid, [Mn(C₂H₆OS)₆]I₄, with linear tetraiodide anions exhibit an ultralow thermal conductivity of 0.15 ± 0.01 W m^?1 K^?1 at room temperature, which is among the lowest values reported for organic–inorganic hybrid materials. Interestingly, the hybrid compound has a unique 0D structure, which extends into 3D supramolecular frameworks through nonclassical hydrogen bonding. Phonon band structure calculations reveal that low group velocities and localization of vibrational energy underlie the observed ultralow thermal conductivity, which could serve as a general principle to design novel thermal management materials.     

Highly Flexible and Stretchable Nanowire Superlattice Fibers Achieved by Spring‐Like Structure of Sub‐1 nm Nanowires

Conventional inorganic nanowire (NW) fibers are usually not stretchable and elastic, which may limit their practical applications. Inspired by the similarity between inorganic sub‐1 nm NWs and polymer chains in dimension, and helical spring‐like structure of cellulose in cherry bark, highly flexible and stretchable NW superlattice fibers composed of sub‐1 nm GdOOH NWs are fabricated. The NW fibers could be twined, bent, twisted, and tied without any damage. When the strain is less than 10%, the fibers present elastic deformation. The elongation at break of the fibers usually reaches ≈40–50% and the highest elongation could reach ≈86%. Excellent flexibility and stretchability of the NW fibers are attributed to the well‐aligned spring‐like NWs assembled superlattice, which are demonstrated by scanning electron microscopy tests, synchrotron small‐angle X‐ray scattering, and obvious birefringence. Moreover, NW‐nanoparticle (NP) fibers are fabricated, inspired by inorganic nanoparticle–reinforced polymers. The strength is improved compared with the NW fibers. Based on this work, it is possible to fabricate multifunctional, flexible, and stretchable inorganic NW materials composed of different inorganic sub‐1 nm NWs, which may be useful in practical applications.     

Multicomponent Hierarchical Cu‐Doped NiCo‐LDH/CuO Double Arrays for Ultralong‐Life Hybrid Fiber Supercapacitor

Fiber supercapacitors have aroused great interest in the field of portable and wearable electronic devices. However, the restrained surface area of fibers and limited reaction kinetics of active materials are unfavorable for performance enhancement. Herein, an efficient multicomponent hierarchical structure is constructed by integrating the Cu‐doped cobalt copper carbonate hydroxide@nickel cobalt layered double hydroxide (CCCH@NiCo‐LDH) core–shell nanowire arrays (NWAs) on Cu fibers with highly conductive Au‐modified CuO nanosheets (CCCH@NiCo‐LDH NWAs@Au–CuO/Cu) via a novel in situ corrosion growth method. This multicomponent hierarchical structure contributes to a large accessible surface area, which results in sufficient permeation of the electrolyte. The Cu dopant could reduce the work function and facilitate fast charge transfer kinetics. Therefore, the effective ion diffusion and electron conduction will facilitate the electrochemical reaction kinetics of the electrode. Benefiting from this unique structure, the electrode delivers a high specific capacitance (1.97 F cm^?2/1237 F g^?1/193.3 mAh g^?1) and cycling stability (90.8% after 30 000 cycles), exhibiting superb performance compared with most oxide‐based fiber electrodes. Furthermore, the hybrid fiber supercapacitor of CCCH@NiCo‐LDH NWAs@Au–CuO/Cu//VN/carbon fibers is fabricated, providing a remarkable maximal energy density of 34.97 Wh kg^?1 and a power density of 13.86 kW kg^?1, exhibiting a great potential in high‐performance fiber‐shape energy‐related systems.     

Cactus‐Like NiCoP/NiCo‐OH 3D Architecture with Tunable Composition for High‐Performance Electrochemical Capacitors

To effectively enhance the energy density and overall performance of electrochemical capacitors (ECs), a new strategy is demonstrated to increase both the intrinsic activity of the reaction sites and their density. Herein, nickel cobalt phosphides (NiCoP) with high activity and nickel cobalt hydroxides (NiCo‐OH) with good stability are purposely combined in a hierarchical cactus‐like structure. The hierarchical electrode integrates the advantages of 1D nanospines for effective charge transport, 2D nanoflakes for mechanical stability, and 3D carbon cloth substrate for flexibility. The NiCoP/NiCo‐OH 3D electrode delivers a high specific capacitance of ≈1100 F g^?1, which is around seven times higher than that of bare NiCo‐OH. It also possesses ≈90% capacitance retention after 1000 charge–discharge cycles. An asymmetric supercapacitor composed of NiCoP/NiCo‐OH cathode and metal–organic framework‐derived porous carbon anode achieves a specific capacitance of ≈100 F g^?1, high energy density of ≈34 Wh kg^?1, and excellent cycling stability. The cactus‐like NiCoP/NiCo‐OH 3D electrode presents a great potential for ECs and is promising for other functional applications such as catalysts and batteries.     

Extremely Low‐Threshold Amplified Spontaneous Emission of 9,9′‐Spirobifluorene Derivatives and Electroluminescence from Field‐Effect Transistor Structure

By doping 2,7‐bis[4‐(N‐carbazole)phenylvinyl]‐9,9′‐spirobifluorene (spiro‐SBCz) into a wide energy gap 4,4′‐bis(9‐carbazole)‐2,2′‐biphenyl (CBP) host, we demonstrate an extremely low ASE threshold of E_th = (0.11 ± 0.05) μJ cm^–2 (220 W cm^–2) which is the lowest ASE threshold ever reported. In addition, we confirmed that the spiro‐SBCz thin film functions as an active light emitting layer in organic light‐emitting diode (OLED) and a field‐effect transistor (FET). In particular, we succeeded to obtain linear electroluminescence in the FET structure which will be useful for future organic laser diodes.     

Chemical and Structural Investigations of Biomimetically Grown Fluorapatite–Gelatin Composite Aggregates

Deeper understanding of the basic principles of biomineralization is a major challenge for present and future research. The high complexity of in‐vivo conditions calls for simplified model systems that still involve dynamic processes like reorganization, formation, self‐organization, and development of patterns, respectively. The present contribution deals with hierarchically ordered spherical aggregates of fluorapatite–gelatin composites with fractal architecture that are grown in gelatin matrices. The model system was chosen to mimic formation conditions on a lower level of complexity compared with the natural formation of calcified tissue (bone, teeth). In order to gain insight into structure formation and the motif for this special kind of morphogenesis we investigated the interaction of the organic and inorganic components of aggregates in different growth stages by detailed chemical analyses, thermoanalytical measurements, X‐ray diffraction on solitary particles, and scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM) investigations. The close relation of the results and observations to calcified tissue may stimulate advanced interests in the fields of medical and materials development.     

3D Hierarchical Co3O4 Twin‐Spheres with an Urchin‐Like Structure: Large‐Scale Synthesis,Multistep‐Splitting Growth,and Electrochemical Pseudocapacitors

Novel, 3D hierarchical Co₃O₄ twin‐spheres with an urchin‐like structure are produced successfully on the large scale for the first time by a solvothermal synthesis of cobalt carbonate hydroxide hydrate, Co(CO₃)_0.5(OH)·0.11H₂O, and its subsequent calcination. The morphology of the precursor, which dominates the structure of the final product, evolves from nanorods to sheaf‐like bundles, to flower‐like structures, to dumbbell‐like particles, and eventually to twin‐spheres, accompanying a prolonged reaction time. A multistep‐splitting growth mechanism is proposed to understand the formation of the 3D hierarchical twin‐spheres of the precursor, based on the time effect on the morphologies of the precursor. The 3D hierarchical Co₃O₄ twin‐spheres are further used as electrode materials to fabricate supercapacitors with high specific capacitances of 781, 754, 700, 670, and 611 F g^?1 at current densities of 0.5, 1, 2, 4, and 8 A g^?1, respectively. The devices also show high charge‐discharge reversibility with an efficiency of 97.8% after cycling 1000 times at a current density of 4 A g^?1.     

Study of the Hole Transport Processes in Solution‐Processed Layers of the Wide Bandgap Semiconductor Copper(I) Thiocyanate (CuSCN)

Wide bandgap hole‐transporting semiconductor copper(I) thiocyanate (CuSCN) has recently shown promise both as a transparent p‐type channel material for thin‐film transistors and as a hole‐transporting layer in organic light‐emitting diodes and organic photovoltaics. Herein, the hole‐transport properties of solution‐processed CuSCN layers are investigated. Metal–insulator–semiconductor capacitors are employed to determine key material parameters including: dielectric constant [5.1 (±1.0)], flat‐band voltage [?0.7 (±0.1) V], and unintentional hole doping concentration [7.2 (±1.4) × 10¹⁷ cm^?3]. The density of localized hole states in the mobility gap is analyzed using electrical field‐effect measurements; the distribution can be approximated invoking an exponential function with a characteristic energy of 42.4 (±0.1) meV. Further investigation using temperature‐dependent mobility measurements in the range 78–318 K reveals the existence of three transport regimes. The first two regimes observed at high (303–228 K) and intermediate (228–123 K) temperatures are described with multiple trapping and release and variable range hopping processes, respectively. The third regime observed at low temperatures (123–78 K) exhibits weak temperature dependence and is attributed to a field‐assisted hopping process. The transitions between the mechanisms are discussed based on the temperature dependence of the transport energy.     

Novel p–p Heterojunctions Self‐Powered Broadband Photodetectors with Ultrafast Speed and High Responsivity

Novel inorganic/organic self‐powered UV–vis photodetectors based on single Se microtube and conducting polymers—polyaniline (PANI), polypyrrole (PPy), and poly(3,4‐ethylenedioxythiophene) (PEDOT)—are fabricated. The conducting polymers are directly coated on the surface of a single Se microtube via a facile and low‐cost in situ polymerization method. The integrated Se/PANI photodetector with 45‐nm‐thick PANI layer shows excellent self‐powered behavior under UV–vis light illumination. In particular, it exhibits high on/off ratio of 1.1 × 10³, responsivity (120 mA W^?1), large detectivity (3.78 × 10¹¹ Jones), and ultrafast response speed (rise time of 4.5 µs and fall time of 2.84 ms) at zero bias at 610 nm (0.434 mW cm^?2)‐light illumination. Moreover, the individual Se/PPy and Se/PEDOT self‐powered photodetectors also exhibit fast and stable responses, including responsivity of 70 and 5.5 mA W^?1, rise time of 0.35 and 1.00 ms, fall time of 16.97 and 9.78 ms, respectively. Given the simple device architecture and low cost fabrication process, this work provides a promising way to fabricate inorganic/organic, high‐performance, self‐powered photodetectors.     

Fluorescent,Carrier‐Trapping Dopants for Highly Efficient Single‐Layer Polyfluorene LEDs

Two fluorescent molecules with an alkynylanthracene core and pyrene end‐cappers have been synthesized and fully characterized. Carbazole moieties are introduced into one molecule at the C9 position of the fluorene linkages to enhance the hole‐transport ability of the molecule and to reduce intermolecular interactions. Both compounds exhibit high thermal stabilities and narrow energy bandgaps. Single‐layer polymer light‐emitting diodes (PLEDs) based on poly(9,9‐dioctylfluorene) (PFO) doped with the synthesized compounds exhibit excellent performance. A PLED with 0.2 % of dopant 7 had a high luminance efficiency of 10.7 ± 0.3 cd A^–1 as well as a brightness of 1400 cd m^–2 at a current density of 13 mA cm^–2, and a low turn on voltage (3.1 V) at a brightness of 10 cd m^–2. A maximum brightness of 20 500 ± 1400 cd m^–2 at 7 V was also measured. The high efficiency of the device's performance is attributed to the good electron and hole trapping ability of the dopants, which possess suitable energy levels as compared to those of PFO.     

Highly Sensitive,Photocontrolled, Organic Thin‐Film Transistors Using Soluble Star‐shaped Conjugated Molecules

The highly photosensitive characteristics of organic thin‐film transistors (OTFTs) made using soluble star‐shaped oligothiophenes with four‐armed π‐conjugation paths, 4(HPBT)‐benzene and 4(HP3T)‐benzene molecules having a relatively high quantum yield, are reported. 4(HPBT)‐benzene‐based organic phototransistors (OPTs) exhibited high photosensitivity (～2500–4300 A W^?1) even with low optical powers (～6.8–30 µW cm^?2) at zero gate bias. The measured photosensitivity of the devices was much higher than that of inorganic single‐crystal Si‐based phototransistors, as well as that of other OPTs reported earlier. With the highly photosensitive characteristics of the 4(HPBT)‐benzene‐based OPTs, a high ratio of the on and off current switching of ～4 × 10⁴ with low optical power and low gate bias was observed. The slow relaxation of the photoinduced charges and charge‐trapping phenomena at the interface could lead to a reproducible memory operation for 4(HPBT)‐benzene‐based OPTs.     

Interface Engineering for Solid‐State Dye‐Sensitized Nanocrystalline Solar Cells: The Use of Ion‐Solvating Hole‐Transporting Polymers

The control of interfacial charge transfer is central to the design of photovoltaic devices. This charge transfer is strongly dependent upon the local chemical environment at each interface. In this paper we report a methodology for the fabrication of a novel nanostructured multicomponent film, employing a dual‐function supramolecular organic semiconductor to allow molecular‐level control of the local chemical composition at a nanostructured inorganic/organic semiconductor heterojunction. The multicomponent film comprises a lithium ion doped dual‐functional hole‐transporting material (Li⁺–DFHTM), sandwiched between a dye‐sensitized nanocrystalline TiO₂ film and a mono‐functional organic hole‐transporting material (MFHTM). The DFHTM consists of a conjugated organic semiconductor with ion supporting side chains, designed to allow both electronic and ionic charge transport properties. The Li⁺–DFHTM layers provide a new and versatile way to control the interface electrostatics, and consequently the charge transfer, at a nanostructured dye‐sensitized inorganic/organic semiconductor heterojunction.     

Development of a Multifunctional Platform Based on Strong,Intrinsically Photoluminescent and Antimicrobial Silica‐Poly(citrates)‐Based Hybrid Biodegradable Elastomers for Bone Regeneration

Biodegradable biomaterials with intrinsically multifunctional properties such as high strength, photoluminescent ability (bioimaging monitoring), and antimicrobial activity (anti‐infection), as well as high osteoblastic differentiation ability, play a critical role in successful bone tissue regeneration. However, fabricating a biomaterial containing all these functions is still a challenge. Here, urethane cross‐linked intrinsically multifunctional silica‐poly(citrate) (CMSPC)‐based hybrid elastomers are developed by first one‐step polymerization and further chemical crosslinked using isocyanate. CMSPC hybrid elastomers demonstrate a high modulus of 976 ± 15 MPa, which is superior compared with most conventional poly(citrate)‐based elastomers. Hybrid elastomers show strong and stable intrinsic photoluminescent ability (emission 400–600 nm) due to the incorporation of silica phase. All elastomers exhibit high inherent antibacterial properties against Staphylococcus aureus. In addition, CMSPC hybrid elastomers significantly enhance the proliferation and metabolic activity of osteoblasts (MC3T3‐E1). CMSPC hybrid elastomers significantly promote the osteogenic differentiation of MC3T3‐E1 by improving alkaline phosphatase activity and calcium biomineralization deposits, as well as expressions of osteoblastic genes. These hybrid elastomers also show a minimal inflammatory response indicated by subcutaneous transplantation in vivo. These optimized structure and multifunctional properties make this hybrid elastomer highly promising for bone tissue regeneration and antiinfection and bioimaging applications.     

Hierarchically Structured Self‐Healing Actuators with Superfast Light‐ and Magnetic‐Response

Despite the tremendous advancement of intelligent robots, it remains a great challenge to integrate living organisms‐like multistimuli responsive actuation and excellent self‐healing ability into one single material system, which will greatly benefit and broaden the development of smart biomimetic materials. Herein, a novel self‐healable multistimuli responsive actuator is developed based on hierarchical structural design and interfacial supramolecular crosslinking. The resulting biomimetic actuator shows a record high photothermal efficiency (η_PT = 79.1%) and thermal conductivity (31.92 W m^?1 K^?1), and presents a superfast actuating response (near‐infrared light: 0.44 s; magnetic field: 0.36 s). In addition, the supramolecular crosslinking endows excellent self‐healing performance in both mechanical and actuating properties to the material. This biomimetic actuator with its hierarchical structure design provides great potential for various applications, such as artificial muscles, soft robotics, and biomedical microdevices.