Porous Lithium Disilicate Glass-Ceramics Prepared by Cold Sintering Process Associated with Post-Annealing Technique.

Using melt-derived LD glass powders and 5-20 M NaOH solutions, porous lithium disilicate (Li2Si2O5, LD) glass-ceramics were prepared by the cold sintering process (CSP) associated with the post-annealing technique. In this novel technique, H2O vapor originating from condensation reactions between residual Si-OH groups in cold-sintered LD glasses played the role of a foaming agent. With the increasing concentration of NaOH solutions, many more residual Si-OH groups appeared, and then rising trends in number as well as size were found for spherical pores formed in the resultant porous LD glass-ceramics. Correspondingly, the total porosities and average pore sizes varied from 25.6 ± 1.3% to 48.6 ± 1.9% and from 1.89 ± 0.68 µm to 13.40 ± 10.27 µm, respectively. Meanwhile, both the volume fractions and average aspect ratios of precipitated LD crystals within their pore walls presented progressively increasing tendencies, ranging from 55.75% to 76.85% and from 4.18 to 6.53, respectively. Young's modulus and the hardness of pore walls for resultant porous LD glass-ceramics presented remarkable enhancement from 56.9 ± 2.5 GPa to 79.1 ± 2.1 GPa and from 4.6 ± 0.9 GPa to 8.1 ± 0.8 GPa, whereas their biaxial flexural strengths dropped from 152.0 ± 6.8 MPa to 77.4 ± 5.4 MPa. Using H2O vapor as a foaming agent, this work reveals that CSP associated with the post-annealing technique is a feasible and eco-friendly methodology by which to prepare porous glass-ceramics.

A copper-containing analog of the biomineral whitlockite: dissolution-precipitation synthesis, structural and biological properties.

In the present work, copper whitlockite (Cu-WH, Ca18Cu2(HPO4)2(PO4)12) was successfully synthesized and comprehensively characterized, founding the base knowledge for its future studies in medicine, particularly for bone regeneration. This material is a copper-containing analog of the well-known biomineral magnesium whitlockite (Mg-WH, Ca18Mg2(HPO4)2(PO4)12). The synthesis of powders was performed by a dissolution-precipitation method in an aqueous medium under hydrothermal conditions. Phase conversion from brushite (CaHPO4·2H2O) to Cu-WH took place in an acidic medium in the presence of Cu2+ ions. Optimization of the synthesis conditions in terms of medium pH, temperature, time, Ca/Cu molar ratio and concentration of starting materials was performed. The crystal structure of the synthesized products was confirmed by XRD, FTIR and Raman spectroscopy, 1H and 31P solid-state NMR, and EPR. Morphological features and elemental distribution of the synthesized powders were studied by means of SEM/EDX analysis. The ion release in SBF solution was estimated using ICP-OES. Cytotoxicity experiments were performed with MC3T3-E1 cells. The study on thermal stability revealed that the synthesized material is thermally unstable and gradually decomposes upon annealing to Cu-substituted ß-Ca3(PO4)2 and Ca2P2O7.

Development of bioinspired damage-tolerant calcium phosphate bulk materials.

Improving the damage tolerance and reliability of ceramic artificial bone materials, such as sintered bodies of hydroxyapatite (HAp), that remain in vivo for long periods of time is of utmost importance. However, the intrinsic brittleness and low damage tolerance of ceramics make this challenging. This paper reports the synthesis of highly damage tolerant calcium phosphate-based materials with a bioinspired design for novel artificial bones. The heat treatment of isophthalate ion-containing octacalcium phosphate compacts in a nitrogen atmosphere at 1000°C for 24 h produced an HAp/ß-tricalcium phosphate/pyrolytic carbon composite with a brick-and-mortar structure (similar to that of the nacreous layer). This composite exhibited excellent damage tolerance, with no brittle fracture upon nailing, likely attributable to the specific mechanical properties derived from its unique microstructure. Its maximum bending stress, maximum bending strain, Young's modulus, and Vickers hardness were 11.7 MPa, 2.8 × 10‒2, 5.3 GPa, and 11.7 kgf/mm2, respectively. The material exhibited a lower Young's modulus and higher fracture strain than that of HAp-sintered bodies and sintered-body samples prepared from pure octacalcium phosphate compacts. Additionally, the apatite-forming ability of the obtained material was confirmed in vitro, using a simulated body fluid. The proposed bioinspired material design could enable the fabrication of highly damage tolerant artificial bones that remain in vivo for long durations of time.

Effects of Argon Gas Plasma Treatment on Biocompatibility of Nanostructured Titanium.

In this study, we applied argon plasma treatment to titanium surfaces with nanostructures deposited by concentrated alkali treatment and investigated the effects on the surface of the material and the tissue surrounding an implant site. The results showed that the treatment with argon plasma removed carbon contaminants and increased the surface energy of the material while the nanoscale network structure deposited on the titanium surface remained in place. Reactive oxygen species reduced the oxidative stress of bone marrow cells on the treated titanium surface, creating a favorable environment for cell proliferation. Good results were observed in vitro evaluations using rat bone marrow cells. The group treated with argon plasma exhibited the highest apatite formation in experiments using simulated body fluids. The results of in vivo evaluation using rat femurs revealed that the treatment improved the amount of new bone formation around an implant. Thus, the results demonstrate that argon plasma treatment enhances the ability of nanostructured titanium surfaces to induce hard tissue differentiation and supports new bone formation around an implant site.

Porphyrin covalent organic nanodisks synthesized using acid-assisted exfoliation for improved bactericidal efficacy.

Porphyrin covalent organic nanodisks (CONs) were synthesized by exfoliating covalent organic frameworks (COFs) in acidic aqueous solutions at pH 4. The synthesized CONs showed remarkable bactericidal activity against Escherichia coli owing to enhanced generation of singlet oxygen upon visible light irradiation.

A facile bottom-up method for synthesis of peroxo-potassium titanate nanoribbons and visible light photocatalytic activity derived from a peroxo-titanium bond.

Low-dimensional titanate nanostructures are gaining attention as a promising material for various photocatalytic applications. However, these conventional titanium oxide-based materials cannot utilize visible light because of their wide bandgap, and their synthesis generally requires high-alkali (10 mol L-1) and high-temperature (160-200 °C) conditions. Here, we report facile bottom-up synthesis for the visible light-activated peroxo-titanate nanoribbon (PTNR). The use of the peroxo-titanium complex ion containing the potassium ion as a precursor can induce the formation of a layered potassium titanate structure (K2-x H x Ti2O5) based on the self-organization reaction between titanium complex ions and potassium ions under mild synthetic conditions (0.29-4.39 mol L-1 KOH, 100 °C). Furthermore, the requirement of potassium ions in the formation of layered potassium titanate was stoichiometrically examined. The layered titanate crystals could be grown anisotropically, which depended on the radius of the cation used. Our results newly revealed that the larger radius of the interlayer cation promotes anisotropic crystal growth. As a result, in the case of the potassium base, a nanoribbon structure with a higher aspect ratio and larger specific surface area than those of lithium and sodium bases was formed. The formed peroxo-titanium functional groups significantly reduced the bandgap of titanate to 2.64 eV. In a photocatalytic decolorization test, the PTNR showed excellent photocatalytic performance based on the large surface area and enhanced light absorption in the visible light range while still performing well under UV light. These findings show not only that the proposed synthetic process has a low environmental impact but also that it contributes to the development of highly functionalized materials for photochemical applications.

Enhanced Photocatalytic Activity of Porphyrin Nanodisks Prepared by Exfoliation of Metalloporphyrin-Based Covalent Organic Frameworks.

Organic polymers derived from covalent organic frameworks (COFs) have various applications, including photocatalysis. The synthesis of organic polymer materials from COFs to obtain higher activity for photocatalysis by changing the unit molecule has been investigated. The choice of the unit molecule is important to characterize the photochemical properties. Among various such unit molecules, porphyrins have attracted much attention as organic chromophores commonly used in photocatalytic reactions with COFs. Although COFs with various organic chromophores have been synthesized and attempts have been made to improve their photocatalytic activity, enhancing the photocatalytic activity by adjusting the layer thickness through exfoliation of COFs has yet to be fully studied. In the present study, the exfoliation of metalloporphyrin-based COFs with pyridine as the axial ligand and adjustment of the layer thickness were found to enhance the photocatalytic activity. Hydrogen generation and 3,3',5,5'-tetramethylbenzidine oxidation reactions were investigated as representative photocatalytic reactions, with the photocatalytic activity up to 7 times that of the original free-base porphyrin COFs. These results indicate that the different thicknesses synthesized by exfoliating COFs increased the photocatalytic effect of polymers.

Immunomodulatory Properties and Osteogenic Activity of Polyetheretherketone Coated with Titanate Nanonetwork Structures.

Polyetheretherketone (PEEK) is a potential substitute for conventional metallic biomedical implants owing to its superior mechanical and chemical properties, as well as biocompatibility. However, its inherent bio-inertness and poor osseointegration limit its use in clinical applications. Herein, thin titanium films were deposited on the PEEK substrate by plasma sputtering, and porous nanonetwork structures were incorporated on the PEEK surface by alkali treatment (PEEK-TNS). Changes in the physical and chemical characteristics of the PEEK surface were analyzed to establish the interactions with cell behaviors. The osteoimmunomodulatory properties were evaluated using macrophage cells and osteoblast lineage cells. The functionalized nanostructured surface of PEEK-TNS effectively promoted initial cell adhesion and proliferation, suppressed inflammatory responses, and induced macrophages to anti-inflammatory M2 polarization. Compared with PEEK, PEEK-TNS provided a more beneficial osteoimmune environment, including increased levels of osteogenic, angiogenic, and fibrogenic gene expression, and balanced osteoclast activities. Furthermore, the crosstalk between macrophages and osteoblast cells showed that PEEK-TNS could provide favorable osteoimmunodulatory environment for bone regeneration. PEEK-TNS exhibited high osteogenic activity, as indicated by alkaline phosphatase activity, osteogenic factor production, and the osteogenesis/osteoclastogenesis-related gene expression of osteoblasts. The study establishes that the fabrication of titanate nanonetwork structures on PEEK surfaces could extract an adequate immune response and favorable osteogenesis for functional bone regeneration. Furthermore, it indicates the potential of PEEK-TNS in implant applications.

Mechanism investigation of the enhanced oxygen storage performance of YBaCo4O7+δ synthesized by a glycine-complex decomposition method.

A YBaCo4O7 oxygen storage material has been synthesized by the glycine-complex decomposition method at a low temperature of 800 °C and its crystal structure and reaction kinetics were investigated. This sample showed the highest storage/release speed among all the reported YBaCo4O7+δ materials.

Synthesis of Octacalcium Phosphate Containing Glutarate Ions with a High Incorporation Fraction.

Octacalcium phosphate (OCP) has received considerable attention in the field of ceramic biomaterials as an advanced functional material. It exhibits a layered structure composed of apatitic and hydrated layers and can incorporate various dicarboxylate ions into the hydrated layer. Saturated dicarboxylic acids (HOOC(CH2)nCOOH) with an odd number of methylene groups (-CH2-) exhibit lower incorporation fractions than those with an even number of methylene groups, possibly owing to a compositional dependence on the synthetic method. In this study, calcium carbonate, phosphoric acid, and various amounts of glutaric acid were used to produce glutarate-ion-incorporated OCP by a wet chemical method, which is different from the conventional synthetic strategy. While utilising 1-20 mmol of glutaric acid during synthesis did not produce the desired product, using 25 mmol of glutaric acid resulted in the formation of single-phase glutarate-ion-incorporated OCP with a Ca/P molar ratio of 1.57 and a 90% incorporation fraction of glutarate ions. This glutarate-ion-incorporation fraction is significantly higher than that reported in the previous studies (35%). Thus, the synthetic procedure proposed herein was able to produce single-phase OCP containing glutarate ions with a high incorporation fraction. Our findings can contribute to development of novel functional ceramic biomaterials in the future.

Optimizing TiO2 through Water-Soluble Ti Complexes as Raw Material for Controlling Particle Size and Distribution of Synthesized BaTiO3 Nanocubes.

Barium titanate (BaTiO3) nanocubes with a narrow particle size distribution were synthesized using a three-step approach. First, a water-soluble Ti complex was synthesized using a hydrolysis method. Next, the titanium dioxide (TiO2) raw material was synthesized via a hydrothermal method using various water-soluble titanium (Ti) complexes. The TiO2 exhibited various particle sizes and crystal structures (anatase, rutile, or brookite) depending on the water-soluble Ti complex and the hydrothermal conditions used in its synthesis. Finally, BaTiO3 nanocubes were subsequently created through a hydrothermal method using the synthesized TiO2 particles and barium hydroxide octahydrate [Ba(OH)2·8H2O] as raw materials. The present study clarifies that the particle size of the BaTiO3 nanocubes depends on the particle size of the TiO2 raw material. BaTiO3 particles with a narrow size distribution were obtained when the TiO2 particles exhibited a narrow size distribution. We found that the best conditions for the creation of BaTiO3 nanocubes using TiO2 involved using lactic acid as a complexing agent, which resulted in a particle size of 166 nm on average. This particle size is consistent with an average of the width of the cubes measured from corner to corner diagonally, which corresponds to a side length of 117 nm. In addition, surface reconstruction of the BaTiO3 was clarified via electron microscopy observations, identifying the outermost surface as a Ti layer. Electron tomography using high-angle annular dark-field (HAADF)-scanning transmission electron microscopy (STEM) confirmed the three-dimensional (3D) structure of the obtained BaTiO3 nanocubes.

Bottom-up method for synthesis of layered lithium titanate nanoplates using ion precursor.

A facile bottom-up method for the synthesis of lithium titanate nanoplates using a peroxo titanium complex ion precursor is reported. Instead of employing complicated treatment with high alkali concentration, the self-organization reaction between lithium and titanium ions in the prepared ion precursor can enable the formation of layered lithium titanate crystals (Li2-xHxTi2O5, where x = 0.1 and 1.52 for as-synthesise and acid-treated samples, respectively) under low alkaline conditions. We demonstrate that layered lithium titanate crystals can be grown anisotropically into individual nanoplates. Our work presents an easy and useful platform for the production of titanate materials with various morphologies based on the interaction with ionic species.

UV/ozone irradiation manipulates immune response for antibacterial activity and bone regeneration on titanium.

The immunomodulatory antibacterial activity and osteoimmunomodulatory properties of implantable biomaterials significantly influence bone regeneration. Various types of ultraviolet (UV) instrument are currently in use to greatly enhance the antibacterial activity and osteoconductive capability of titanium, it remains unclear how UV treatment modulates immune response. Compared to traditional UV treatment, the combination of low-dose ozone with UV irradiation is considered a new option to give benefits to surface modification and reduce the drawbacks of UV and ozone individually. Herein, the aim of this study was to elucidate the immune-modulatory properties of macrophages on UV/ozone-irradiated titanium that serve as defense against S. aureus and the crosstalk between immune cells and osteoblasts. Three different cell and bacteria co-culture systems were developed in order to investigate the race between host cells and bacteria to occupy the surface. In vitro immunological experiments indicated that UV/ozone irradiation significantly enhanced the phagocytic and bactericidal activity of macrophages against S. aureus. Further, in vitro and in vivo studies evidenced the favorable osteoimmune environment for osteogenic differentiation and bone formation. This research suggests vital therapeutic potential of UV/ozone irradiation for preventing the biomaterial-associated infections and achieving favorable bone formation simultaneously.

Dissolution-Precipitation Synthesis and Characterization of Zinc Whitlockite with Variable Metal Content.

In the present work, a series of zinc whitlockite (CaxZny(HPO4)2(PO4)12) powders was synthesized by a low-temperature dissolution-precipitation process for the first time. The phase conversion from calcium hydroxyapatite to zinc whitlockite occurred in an acidic medium in the presence of Zn2+ ions. Variable chemical composition of the synthesis products was achieved by changing Ca-to-Zn molar ratio in the reaction mixture. Investigation of the phase evolution as a function of time demonstrated that phase-pure zinc whitlockite powders can be synthesized in just 3 h. It is also demonstrated that single-phase products can be obtained when the Ca-to-Zn ratio in the reaction medium is in the range from 9 to 30. With higher or lower ratios, neighboring crystal phases such as scholzite or calcium hydroxyapatite were obtained. The morphology of the synthesized powders was found to be dependent on the chemical composition, transforming from hexagonal to rhombohedral plates with the increase of Zn content. Thermal stability studies revealed that the synthesized compounds were thermally unstable and decomposed upon heat treatment.

In vivo bioresorbability and bone formation ability of sintered highly pure calcium carbonate granules.

Calcium carbonate-based bone substitutes derived from natural coral exoskeleton (aragonite) are resorbed and remodeled faster than calcium phosphate-based substitutes. However, coral species with structures appropriate for use as bone substitutes are very limited. Therefore, it is important to evaluate potential of artificial calcium carbonate ceramics as a bone substitute. In this study, calcium carbonate granules with various porosities and pore sizes were prepared by sintering a highly pure (>99.98%) calcium carbonate powder (calcite), and their resorption properties and bone formation abilities were examined in vivo for the first time. The sintered calcium carbonate was resorbed faster than ß-tricalcium phosphate, which has a similar structure. However, sintered calcium carbonate did not promote new bone formation during long-term implantation. Furthermore, both resorption and new bone formation were affected by the pore structure. The optimal structures of the artificially sintered calcium carbonate bone substitute were also discussed.

Stabilization of Size-Controlled BaTiO3 Nanocubes via Precise Solvothermal Crystal Growth and Their Anomalous Surface Compositional Reconstruction.

Crystal growth of barium titanate (BaTiO3) using a wet chemical reaction was investigated at various temperatures. BaTiO3 nanoparticles were obtained at an energy-efficient temperature of 80 °C. However, BaTiO3 nanocubes with a preferred size and shape could be synthesized using a solvothermal method at 200 °C via a reaction involving titanium tetraisopropoxide [(CH3)2CHO]4Ti for nucleation and fine titanium oxide (TiO2) nanoparticles for crystal growth. The BaTiO3 nanocubes showed a high degree of dispersion without the use of dispersants or surfactants. The morphology of BaTiO3 was found to depend on the reaction medium. The size of the BaTiO3 particles obtained using water as the reaction medium was the largest among the particles synthesized using various reaction media. In the case of alcohol reaction media, the BaTiO3 particle size increased in the order methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol. Furthermore, BaTiO3 powder obtained using alcohol reaction media resulted in cubic shapes as opposed to the round shapes obtained when water was used as the medium. We found that the optimal condition for the synthesis of BaTiO3 nanocubes involved the use of 1-butanol as the reaction medium, resulting in an average particle size of 52 nm, which is the average distance of the cubes measured diagonally from corner to corner, and gives an average side length of 37 nm, and a tetragonal crystal system as evidenced by the powder X-ray diffraction pattern obtained using high-energy synchrotron X-rays. The origin of the spontaneous polarization of the BaTiO3 tetragonal crystal structure was clarified by a pair distribution function analysis. In addition, surface reconstruction of BaTiO3 nanocubes led to an outermost surface comprising two layers of Ti columns.

Fluorescence and physical properties of thulium and erbium co-doped dental zirconia.

The fluorescence and physical properties of thulium and erbium co-doped dental zirconia were investigated. The high-translucency yttria-stabilized dental zirconia specimens co-doped with Tm2O3 powder 0.8 wt% and Er2O3 powder at proportions from 0.1 to 0.8 wt% were used. The specimens co-doped with Tm2O3 powder 0.8 wt% and Er2O3 from 0.3 to 0.5 wt% exhibited the fluorescence similar to that of natural tooth. All the specimens had a tetragonal peak and no major change in the Vickers hardness, fracture toughness and bending strength on addition of Tm2O3 and Er2O3. These results suggest that the method of co-doping trace amounts of Tm2O3 and Er2O3 into high-translucency dental zirconia powder can effectively improve the esthetics of zirconia monolithic fixed dental prothesis.

Incorporation of tetracarboxylate ions into octacalcium phosphate for the development of next-generation biofriendly materials.

Octacalcium phosphate (OCP; Ca8(HPO4)2(PO4)4 ∙ 5H2O) is a precursor of hydroxyapatite found in human bones and teeth, and is among the inorganic substances critical for hard tissue formation and regeneration in the human body. OCP has a layered structure and can incorporate carboxylate ions into its interlayers. However, studies involving the incorporation of tetracarboxylic and multivalent (pentavalent and above) carboxylic acids into OCP have not yet been reported. In this study, we investigate the incorporation of pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), a type of tetracarboxylic acid, into OCP. We established that pyromellitate ions could be incorporated into OCP by a wet chemical method using an acetate buffer solution containing pyromellitic acid. The derived OCP showed a brilliant blue emission under UV light owing to the incorporated pyromellitate ions. Incorporation of a carboxylic acid into OCP imparted new functions, which could enable the development of novel functional materials for biomedical applications.

Sr2+ sorption property of seaweed-like sodium titanate mats: effects of crystallographic properties.

Layered sodium titanate is a typical ion-exchanger for water purification aimed at removing cationic heavy metals and radionuclides. The material design of an ion-exchanger is effective for cation removal. For that purpose, understanding the basic impacts of crystallographic properties such as crystal size, morphology, and phase is critical for developing highly functional nanoscale ion-exchangers. In this study, we investigate the principal relationship between the crystallographic properties of seaweed-like sodium titanate mats (SSTs), which consist of a dititanate (H x Na2-x Ti2O5) phase of nanofibers synthesised by the alkaline hydrothermal method and their Sr2+ sorption mechanism. A trititanate (H x Na2-x Ti3O7) phase, which has a micro-sized fibre morphology, was also synthesised using the same method by adjusting the NaOH concentration. The SST demonstrates a high ion-exchange selectivity of Sr2+ against H+ and a high maximum sorption capacity (2 mmol g-1), which was four times higher than that of the trititanate phase (0.49 mmol g-1). In contrast, the trititanate phase, which is the comparison target, had a low Sr2+ ion-exchange selectivity and precipitated SrCO3. We conclude that these differences in Sr2+ sorption mechanisms were derived from not only the unique morphology but also the crystal structure of sodium titanates. Although almost all of the Na+ in dititanate with lamellar structure was consumed by the ion-exchange reaction, some Na+ remained in the trititanate because there are two sites in the zigzag layered structure. These findings on the crystallographic properties of SST for Sr2+ sorption may contribute to the functionalisation of a nanoscale ion-exchanger.

Enhancing Visible Light Absorption of Yellow-Colored Peroxo-Titanate Nanotubes Prepared Using Peroxo Titanium Complex Ions.

Visible light-activated yellow titanate nanotubes (TNTs) modified by peroxo groups were directly synthesized via a facile chemical reaction route using peroxo titanium complex ions as a precursor. Obtained peroxo-modified TNTs (PTNTs) possessed a cylindrical-shaped tubular morphology with an outer diameter of approximately 10 nm. The peroxo titanium functional group (Ti-O-O) was formed between the interlayers of the lepidocrocite-type titanate crystal that was the base structure of TNTs, with the interlayer distance estimated at approximately 10.02 Å. The formation of the peroxo functional groups reduced the electron density adjacent to the titanium atom, raising the valence band to 1.35 eV and forming a band gap of 2.50 eV, which is lower than that of TNTs (3.19 eV). In addition, the peroxo titanium functional group had a negative potential, which increased the chemical adsorption performances with positively charged rhodamine B molecules in water. Meanwhile, the photocatalytic investigation indicated that the PTNTs have enhanced the photocatalytic performance for RhB decolorization under visible light irradiating in comparison with TNTs. These findings show not only the improvement in the photocatalytic performance but also the potential of processing design by selecting the precursor with arbitrary characteristics.