Rod-like Hydroxyapatite Research Articles

Synthesis of Hydroxyapatite Nanoparticles by Controlled Precipitation in the Presence of Sodium Dodecyl Sulfate

Hydroxyapatite nanoparticles (NPs) have been synthesized by controlled precipitation in the presence of a surfactant, sodium dodecyl sulfate. The sizes, shapes, and structures of the NPs depend on the sequence of mixing the reagents . When the addition of sodium phosphate to a surfactant solution is followed by the addition of calcium nitrate, rodlike hydroxyapatite NPs are formed, the length of which decreases with a rise in surfactant concentration. As the sodium dodecyl sulfate concentration increases, the ζ-potential of the NPs decreases to zero; then, its absolute value grows to –55 mV. This suggests that a surfactant bilayer is formed on the NP surface, with the bilayer shielding the surface of the growing crystals. The shielding leads to the formation of smaller NPs at high surfactant concentrations. When the addition of calcium nitrate to the surfactant solution is followed by the addition of sodium phosphate, the synthesis most likely occurs on the surface of micelles, which partially consist of calcium dodecyl sulfate. Therefore, the sulfate phase remains preserved in the synthesized particles, which is confirmed by X-ray diffraction analysis. At higher surfactant concentrations in the reaction medium, the presence of flexible cylindrical micelles is possible. The precipitation of hydroxyapatite on the surface of such micelles results in the formation of wavy threadlike particles.

Development of an apatitic calcium phosphate cements: effect of liquid/powder ratio on the setting time

Calcium phosphate cement (CPC) sets in situ to form resorbable hydroxyapatite with chemical and crystallographic similarity to the apatite in human bones, hence it is highly promising for clinical applications. Among the clinical requirements for calcium phosphate bone cements are initial setting time and final setting time. α-tricalcium phosphate (α-TCP) and hydroxyapatite (HA) were mixed with dicalcium phosphate dehydrate (DCPD) to form the cement powder which is mixed with aqueous solutions of 3% Na 2 HPO 4 .2H 2 O in weight at four different liquid-to‐powder ratios (0.35, 0.40, 0.45 and 0.50 mL/g). The cement powder, on wetting with the medium, formed a workable putty. X-ray diffraction (XRD), Energy dispersive X-ray spectroscopic (EDS) , transmission electron microscope (TEM) and scanning electron microscopy (SEM) techniques were employed to evaluate the phase composition and surface morphology of the cements. The results revealed similar phase composition for all samples before and after soaking in distilled water at 37°C. According to the results, it is shown that almost complete transformation of cements in calcium-deficient hydroxyapatite (CDHA) occur after soaking 7 days in destilled water with nanosized rod-like hydroxyapatite crystals. Also by reducing the L/P ratio from 0.50 to 0.35, initial and final setting times of the CPCs decreased 11 and 10 minutes respectively.

Characterization of Nano-Scale Hydroxyapatite Coating Synthesized from Eggshells Through Hydrothermal Reaction on Commercially Pure Titanium

Commercially pure titanium (c.p. Ti) is often used in biomedical implants, but its surface cannot usually combine with the living bone. A coating of hydroxyapatite (HA) on the surface of titanium implants provides excellent mechanical properties and has good biological activity and biocompatibility. For optimal osteocompatibility, the structure, size, and composition of HA crystals should be closer to those of biological apatite. Our results show that the surface of c.p. Ti was entirely covered by rod-like HA nanoparticles after alkali treatment and subsequent hydrothermal treatment at 150 °C for 48 h. Nano-sized apatite aggregates began to nucleate on HA-coated c.p. Ti surfaces after immersion in simulated body fluid (SBF) for 6 h, while no obvious precipitation was found on the uncoated sample. Higher apatite-forming ability (bioactivity) could be acquired by the samples after HA coating. The HA coating featured bone-like nanostructure, high crystallinity, and carbonate substitution. It can be expected that HA coatings synthesized from eggshells on c.p. Ti through a hydrothermal reaction could be used in dental implant applications in the future.

Synthesis, microstructure and mechanical properties of tricalcium phosphate–hydroxyapatite (TCP/HA) composite ceramic

Tricalcium phosphate-hydroxyapatite (TCP/HA) is an important composite ceramic ubiquitously applied in biomedicine research. In this work, a novel design and synthesizing method for preparation of TCP/HA composites is proposed consisting in suspension mixing amorphous calcium phosphate (ACP) and hydroxyapatite (HA) ceramic powders with different weight ratios, and their compaction under a uniaxial pressure of 200 MPa and sintering at 1150 °C for 2 h. The obtained sintered bodies exhibited optimum hardness and fracture toughness of 5 GPa and 1.27 MPa m1/2, and values significantly improved as compared with those obtained with the traditional mechanical mixing method. The mechanical enhancement mechanism was mainly attributed to the good ACP and HA phase dispersion and ACP crystallization. SEM and HRTEM observations showed the suspension mixing method to allow amorphous spherical ACP and crystalline rod-like HA particles with size around 50 nm to uniformly disperse at the nano scale in the composite powder, which contributes to the excellent sinter ability. Furthermore, XRD results indicate that after sintering, nearly 100% of amorphous spherical ACP transformed to the crystalline β-TCP, which results in the nanoparticle shrinkage, porosity reduction and composite densification.

Ultrasonic assisted functionalization of MWCNT and synergistic electrocatalytic effect of nano-hydroxyapatite incorporated MWCNT-chitosan scaffolds for sensing of nitrofurantoin.

In the present work, we report the fabrication of stable composite of chitosan hydrogels (CHI) on multiwalled carbon nanotubes (MWCNT) using a simple ultrasonic-assisted method. Also, rod-like hydroxyapatite nanoparticles (HA NPs) were synthesised using a hydrothermal route and were incorporated into the highly conductive MWCNT-CHI scaffolds using an ultrasonication method. The functionalization of MWCNT and preparation of HA NPs on MWCNT-CHI nanocomposite were done using the sonication over the frequency of 37 kHz with the ultrasonic power capable of 150 W (Elmasonic Easy 60H bath sonicator). The resulting hybrid HA NPs/MWCNT-CHI nanocomposites have an excellent surface area and high surface to volume ratio, which leads to the sensitive detection of nitrofurantoin than pristine MWCNT and HA NPs. The complete elemental and morphological analyses of the HA NPs/MWCNT-CHI nanocomposites were characterised by XRD, FTIR, RAMAN, FESEM, TEM, EDX, and elemental mapping techniques. Electrochemical analysis of the HA NPs/MWCNT-CHI nanocomposites was carried out by cyclic voltammetry, electrochemical impedance spectroscopy and amperometry methods. The modified glassy carbon electrode (GCE) of HA NPs/MWCNT-CHI nanocomposites exhibit the nitrofurantoin detection activity at the linear range of 0.005-982.1 µM with the detection limit of 1.3 nM. The synergistic electrocatalytic activity of HA NPs/MWCNT-CHI nanocomposites modified GCE is correlated to the sensitivity of 0.16 µAµM-1 cm-2 with excellent precision and accuracy towards the sensing of nitrofurantoin.

Anodic Voltage Dependence of Ti-6Al-4V Substrates and Hydroxyapatite Coating

Ti-6Al-4V alloys were anodized in a solution containing 0.15 M HF and 2 M H₃PO₄ for 30 min under different voltages and then coated with hydroxyapatite (HA) by hydrothermal-electrochemical deposition. The effects of anodizing voltage on the morphology and bioactivity of the HA coating and on the bonding strength between the HA coating and the anodized substrates were investigated. Results indicated that highly ordered amorphous TiO₂ nanotube arrays formed on the Ti-6Al-4V surface after anodic oxidation. The pore size of the nanotube increased up to approximately 100 nm with increasing anodic voltage until 25 V. The nanotube was damaged at anodic voltages above 25 V. The crystal structure of TiO₂ changed from amorphous to anatase when the anodized substrates were heated at 450 °C for 3 h. The contact angle between the Ti-6Al-4V surfaces and the simulated body fluid evidently decreased after anodic oxidation. The roughness increased with increasing anodic voltage, and Ra reached about 0.56 μm under 25 V. The HA coating exhibited layered growth. The deposition of rod-like HA crystals as well as the crystallinity of the HA coating initially increased and then decreased with the further increase of the anodic volatage. The degree of crystallinity reached the maximum of approximately 73% at 25 V. The bonding strength between the coating and the anodized substrates increased and then slightly decreased with increasing voltage. The bonding strength was about 20.0 MPa when titanium substrate was anodized under 25 V. The results of simulated body fluid immersing experiments suggest that the HA coating exhibits promising bioactivity.

Preparation of bioactive hydroxyapatite@halloysite and its effect on MC3T3-E1 osteogenic differentiation of chitosan film.

Halloysite nanotubes (HNTs) are widely used in biomedical field due to their special tubular structure and high reinforcing ability, while hydroxyapatite (HAP) is generally used in tissue engineering owing to its excellent biocompatibility and biological activity. In this work, hydroxyapatite@halloysite nanotubes(HAP@HNTs) hybrid was synthesized via a facial hydrothermal reaction process. The morphology, particle size, specific surface area, and chemical composition of the hybrid were thoroughly characterized by different techniques. Rod-like HAP nanoparticles can be anchored on the outer surface of the clay tubes, which lead to a maximum increase of 4.7 m2/g in the specific surface area of HAP@HNTs over that of HNTs. HAP nanoparticles have little effect on the pores of HNTs, but diffraction peak strength of HNTs is covered by the HAP crystals. HAP@HNTs exhibit improved cytocompatibility and possess osteogenic differentiation ability towards MC3T3-E1 preosteoblasts. Chitosan/HAP@HNTs composite films were then prepared by doping of HAP@HNTs into chitosan by solution mixing. HAP@HNTs can serve as a functional phase which enhances mechanical properties of chitosan films and osteogenic differentiation of MC3T3-E1 cells. This work provides a facial synthesis routine of bioactive HAP@HNTs, which combines the osteogenic activity of HAP and the good mechanical properties of HNTs. HAP@HNTs can be used a novel bone regeneration biomaterial as local delivery systems with improved osteoinductive properties.

Bone-like nano-hydroxyapatite coating on low-modulus Ti–5Nb–5Mo alloy using hydrothermal and post-heat treatments

Titanium and its alloys are widely used as biomaterials for orthopedic and dental implants because of their excellent biocompatibility and mechanical properties. However, they are considered to be bioinert; when they are inserted into the human body these implants cannot bond directly to the surrounding living bone. Through hydrothermal reaction and heat treatment, this study aimed to improve the bioactivity of a low-modulus Ti–5Nb–5Mo alloy with a hydroxyapatite (HA) surface coating that used eggshells as a Ca source. The results showed that after hydrothermal reaction at 200 °C for 48 h, the entire alkali-treated alloy surface was covered with amorphous calcium phosphate nanoparticles. When later heat-treated at various temperatures (400, 500 or 600 °C) for 48 h, the surface coating of Ti–5Nb–5Mo alloy was transformed into crystalline, rod-like HA nanoparticles. Additionally, FTIR analysis confirmed the production of HA with mixed AB-type carbonate substitutions. The HA coating exhibited a carbonate-containing composition, rod-like morphology, and nano-sized particles, all of which indicate a bone-like structure. To evaluate the bioactivity of the bone-like HA-coated Ti–5Nb–5Mo alloy, the capability of apatite formation on the alloy surface was assessed by immersion in a simulated body fluid (SBF). A dune-like apatite layer was densely deposited on the surface of the HA-coated Ti alloy after 6 h of immersion in the SBF. Notably, the ability of a Ti–5Nb–5Mo alloy subjected to sequential processing with alkali, hydrothermal, and heat treatments to form a bone-like HA nanoparticle coating was close to double that of its counterpart without an HA coating.

Bioadaptive nanorod array topography of hydroxyapatite and TiO2 on Ti substrate to preosteoblast cell behaviors.

Bioadaptive nanostructure coatings of hydroxyapatite (HAP) and TiO2 on titanium (Ti) implants are essential for biomaterial-tissue osteointegration. However, there is no specific report, so far, that focuses on the different influences of the two bioadaptive coatings on preosteoblast behaviors. Herein, adhesion, proliferation, and osteogenic potential of preosteoblast on HAP and TiO2 coatings with nanorod array topography were studied. XRD, TEM, and SAED analysis indicated that rod-like HAP nanoarray and anatase TiO2 nanoarray coatings were fabricated successfully, and there was insignificant difference in roughness and fibronectin adsorption of the two coatings. Adhesion and proliferation of MC3T3-E1 cells on the two coatings were of no significant difference, besides a larger projected area of the cells on HAP coating. MC3T3-E1 cells cultured on the HAP coating displayed significantly higher expression of runt-related transcription factor-2 (Runx2), osteocalcin (OCN) and collagen type-1 (Col I) after culture for 21 days compared with those on TiO2 coating, except alkaline phosphatase (ALP). This study provides beneficial suggestion for intelligent selection of biocoatings.

Fabrication of hybrid ultrafiltration membranes with improved water separation properties by incorporating environmentally friendly taurine modified hydroxyapatite nanotubes

In this work, hydroxyapatite nanotubes (HANTs) were explored as a novel environment-friendly additive for the fabrication of ultrafiltration (UF) membranes. Hydrophilic modification was conducted to the prepared HANTs, which includes the polydopamine (PDA) coating and the following grafting of taurine (TA), a kind of amino acid with -SO3H group. Subsequently, the modified HANTs (HANTs-DA-TA) were mixed with polyethersulfone (PES) to fabricate nanocomposite UF membranes. The prepared membranes were fully characterized, including the porosity, hydrophilicity, membrane morphology, and practical UF capability. The fabricated PES/HANTs-DA-TA membranes exhibited remarkably elevated water flux (up to 439 L m−2 h−1), which was ~2.6 times that of PES membrane (169 L m−2 h−1), whereas the rejection of PES/HANTs-DA-TA membranes was still kept at a high state. The improved flux mainly benefited from the more porous membrane structure, declined skin layer thickness, and the enhanced hydrophilicity. Meanwhile, the PES/HANTs-DA-TA membranes exhibited increased antifouling capability and the highest flux recovery ratio (FRR) reached 77.9% due to the improved surface hydrophilicity. Furthermore, the short rod-like nano hydroxyapatite (HA) was prepared and functionalized the same way as the HANTs-DA-TA. It was found that compared to rod-like HA, the tubular nano HA was more efficient in facilitating the membrane permeation due to the superiority of nanotubular structure. This work reveals that as a novel green additive, the HANTs have great application potential in fabricating water treatment membranes and can be employed for further studies.

Improved Multicellular Response, Biomimetic Mineralization, Angiogenesis, and Reduced Foreign Body Response of Modified Polydioxanone Scaffolds for Skeletal Tissue Regeneration.

The potential of electrospun polydioxanone (PDX) mats as scaffolds for skeletal tissue regeneration was significantly enhanced through improvement of the cell-mediated biomimetic mineralization and multicellular response. This was achieved by blending PDX ( i) with poly(hydroxybutyrate- co-valerate) (PHBV) in the presence of hydroxyapatite (HA) and ( ii) with aloe vera (AV) extract containing a mixture of acemannan/glucomannan. In an exhaustive study, the behavior of the most relevant cell lines involved in the skeletal tissue healing cascade, i.e. fibroblasts, macrophages, endothelial cells and preosteoblasts, on the scaffolds was investigated. The scaffolds were shown to be nontoxic, to exhibit insignificant inflammatory responses in macrophages, and to be degradable by macrophage-secreted enzymes. As a result of different phase separation in PDX/PHBV/HA and PDX/AV blend mats, cells interacted differentially. Presumably due to varying tension states of cell-matrix interactions, thinner microtubules and significantly more cell adhesion sites and filopodia were formed on PDX/AV compared to PDX/PHBV/HA. While PDX/PHBV/HA supported micrometer-sized spherical particles, nanosized rod-like HA was observed to nucleate and grow on PDX/AV fibers, allowing the mineralized PDX/AV scaffold to retain its porosity over a longer time for cellular infiltration. Finally, PDX/AV exhibited better in vivo biocompatibility compared to PDX/PHBV/HA, as indicated by the reduced fibrous capsule thickness and enhanced blood vessel formation. Overall, PDX/AV blend mats showed a significantly enhanced potential for skeletal tissue regeneration compared to the already promising PDX/PHBV/HA blends.

Hydroxyapatite coating on titanium endosseous implants for improved osseointegration: Physical and chemical considerations.

For many years, hydroxyapatite (HA) has been used as a bioactive endosseous dental implant coating to improve osseointegration. As such, the coating needs to be of high purity, adequate thickness, crystalline, and of a certain roughness in order to stimulate rapid fixation and form a strong bond between the host bone and the implant. There are a number of ways of preparing the HA coating, resulting in various coating properties. Herein, we report the preparation of the HA coating using a direct electrochemical method without the need for subsequent heat treatment. The aim of this study was to investigate the physicochemical properties of the HP coating, deposited on titanium implants by a modified electrochemical method. The coating was characterized in terms of surface chemical composition, structure, morphology, coating thickness and roughness. The coating was found to be composed of homogenous HA with Ca/P and Ca/O ratios of 1.62 and 0.35, respectively. No other forms of calcium phosphate were detected. The degree of crystallinity of HA was 92.4%. The surface roughness was moderate (Sa = 1.04 μm) with the coating thickness of 2-3 μm. The scanning electron microscopy (SEM) analysis revealed a uniform, integrated layer of rod-like HA crystals with the longitudinal axes parallel to the implant surface. The coating reported herein was found to have potentially favorable chemical and physical characteristics fostering osseointegration.

Study on Rare Earth Doped Nano - hydroxyapatite Biosignal Tracer

In recent years, bioluminescent probes with labeled traces have been one of the research hotspots for doping rare earth ions into hydroxyapatite (HA) nanomaterials. Because the 20~40nm HA nanomaterials can easily enter the interior of the cells, the role of the rare earth doped, well - dispersed, 20 ~ 40nm spherical or short rod-like nano HA bioluminescent probe materials for the role of Mechanisms and other studies provide good experimental basis and theoretical support.

Fabrication of two distinct hydroxyapatite coatings and their effects on MC3T3-E1 cell behavior.

How the surface topography of hydroxyapatite (HAP) coatings remodels hard tissue is of utmost importance and a contributing factor to ambiguity regarding this subject. Here, HAP coatings with different topographies of a rod-like nanoarray with c-axis orientation and a flake-like micro-flower array with a(b)-axis orientation on a Ti substrate were synthesized via hydrothermal-electrodeposition by controlling the concentration of electrolytes. XRD, TEM and SAED analyses indicated that the rod-like HAP nanoarray was predominant with an orientation of (001), while the HAP micro-flower samples were based on an orientation of (100). Compared to the flake-like HAP, the rod-like nanoarray HAP possessed better hydrophilic properties and lower roughness, which not only enhanced adsorption of specific fibronectin proteins but also promoted the spreading and growth of MC3T3-E1 cells. Runx2, alkaline phosphatase, collagen and osteocalcin were also analyzed by RT-PCR on the two distinctive HAP-coated samples. MC3T3-E1 cells on the rod-like nanoarray coating had higher osteo-related gene expression. This finding suggested that the ordered assembly structure of the HAP might cause topography-dependent coordination with biomolecules for enhancing osteoblast-like cell proliferation and osteogenic differentiation. This study provided an understanding of the surface's features for biomaterials to ensure better bioactivity.

Electrodeposition of hydroxyapatite on nickel foam and further modification with conductive polyaniline for non-enzymatic glucose sensing

A hybrid material of hydroxyapatite, nickel foam and polyaniline (PANI/HAP/NF) were assembled for non-enzymatic glucose sensing. First, we prepared rod-like hydroxyapatite (HAP) on the surface of nickel foam (NF) through cathode electrodeposition. The 3D network of NF enlarges the area of nickel, and the plentiful active sites on HAP surface are helpful to adsorb glucose molecules. Second, the surface of HAP/NF was modified by a self-assembled polyaniline (PANI) membrane to improve the ability of HAP to transform charges. The hybrid shows an excellent synergistic effect on non-enzymatic glucose sensing in alkaline electrolyte. The assembled PANI/HAP/NF sensing electrode presents a broad glucose concentration-dependent current linear range from 1 μmol dm−3 to 30 mmol dm−3. The sensitivity and detection limit reach 1704 μA mM-1 cm-2 and 0.32 μmol dm−3 (S/N = 3), respectively. The response of current to glucose concentration is much more prominent than that of common interference compounds, such as l-ascorbic acid, dopamine, sucrose, lactose. Further, the experiments of durability and repeatability also present satisfactory results.

Study of Endochondral Ossification in Human Fetalcartilage Anlagen of Metacarpals: Comparative Morphology of Mineral Deposition in Cartilage and in the Periosteal Bone Matrix.

The progression of mineral phase deposition in hypertrophic cartilage and periosteal bone matrix was studied in human metacarpals primary ossification centers before vascular invasion began. This study aimed to provide a morphologic/morphometric comparative analysis of the calcification process in cartilage and periosteal osteoid used as models of endochondral ossification. Thin, sequential sections from the same paraffin inclusions of metacarpal anlagen (gestational age between the 20th and 22nd weeks) were examined with light microscopy and scanning electron microscopy, either stained or heat-deproteinated. This process enabled the analysis of corresponding fields using the different methods. From the initial CaPO4 nucleation in cartilage matrix, calcification progressed increasing the size of focal, globular, randomly distributed deposits (size range 0.5-5µm), followed by aggregation into polycyclic clusters and finally forming a dense, compact mass of calcified cartilage. At the same time, the early osteoid calcification was characterized by a fine granular pattern (size range 0.1-0.5µm), which was soon compacted in the layer of the first periosteal lamella. Scanning electron microscopy of heat-deproteinated sections revealed a rod-like hydroxyapatite crystallite pattern, with only size differences between the early globular deposits of the two calcifying matrices. The morphology of the early calcium deposits was similar in both cartilage and osteoid, with variations in size and density only. However, integration of the reported data with the actual hypotheses of the mechanisms of Ca concentration suggested that ion transport was linked to the progression of the chondrocyte maturation cycle (with recall of H2 O from the matrix) in cartilage, while ions transport was an active process through the cell membrane in osteoid. Other considered factors were the collagen type specificity and the matrix fibrillar texture. Anat Rec, 301:571-580, 2018. © 2017 Wiley Periodicals, Inc.

Chitosan based hydrogel assisted spongelike calcium phosphate mineralization for in-vitro BSA release

New chitosan-g- poly (3-sulfopropyl methacrylate), CHI-g-P(SPMA), hydrogel was prepared by free radical polymerization process and investigated as a template for biomimetic spongelike calcium phosphate mineralization in a solution mimicking physiological condition. Infrared spectroscopy, scanning electron microscopy, X-ray diffraction and transmission electron microscopy confirmed the predominant formation of rod-like hydroxyapatite. The swelling behavior of the nanocomposite was evaluated at different pHs and different saline concentrations. Bovine serum albumin (BSA), as a model protein drug, was loaded in the CHI-g-P(SPMA)/calcium phosphate hybrid. The BSA release behavior was investigated and the results suggested CHI-g-P(SPMA)/calcium phosphate hybrid as controlled release carrier. These results suggest that next generation of polysaccharides based hybrid materials could be interesting for biomedical applications.

Antibacterial ability of supported silver nanoparticles by functionalized hydroxyapatite with 5-aminosalicylic acid

Antimicrobial performance of silver nanoparticles supported by functionalized hydroxyapatite with 5-aminosalycile acid was tested against Gram-negative bacteria E. coli, Gram-positive bacteria S. aureus and yeast C. albicans. Thorough characterization of materials (electron microscopy, nitrogen adsorption–desorption isotherms, diffuse reflectance spectroscopy) followed each step during the course of nanocomposite preparation. Synthesized powder consists of rod-like hydroxyapatite particles (40–60 × 10–20 nm, length × diameter) decorated with nano-sized spherical silver particles whose content in nanocomposite was found to be 1.9 wt.-%. Concentration- and time-dependent bacterial reduction data indicated that use of silver nanoparticles even at concentration as low as 1 μg mL−1 lead to complete reduction of both bacteria (E. coli and S. aureus). On the other hand, non-toxic behavior of nanocomposite in broad concentration range (0.05–2.0 mg mL−1) was found towards C. albicans. Successful inactivation of E. coli and S. aureus in five repeated cycles proved that synthesized nanocomposite can perform under long-run working conditions.

The morphological effect of calcium phosphates as reinforcement in methacrylate-based dental composite resins on mechanical strength through thermal cycling

Abstract The rationale of this study was based on the hypothesis that mechanical strength and ion release in dental composite resins containing 50 wt% calcium phosphate fillers, including spherical micrometer-scale modified dicalcium phosphate anhydrous (Ms-DCPA) and synthetic micro- and nanometer-scale rod-like hydroxyapatite (HA) (respectively abbreviated as Mr-HA and Nr-HA), led to a superior ability to re-precipitate. The reinforced resin properties were measured before and after immersion for 24 h and further exposure to thermal fatigue between 5 and 55 °C for 600 and 2400 cycles. The groups of resins reinforced with Mr-HA and Nr-HA showed a significant increase in their microhardness and ability to re-precipitate after immersion and through thermal fatigue. The 50% Mr-HA sample had the highest anti-decline ability for flexural strength and modulus after thermal fatigue among all three types of fillers, whereas the Nr-HA sample had the lowest flexural strength and modulus. Filler morphologies that had a higher aspect ratio of length to width had better re-mineralization ability after immersion, but the Mr-HA sample showed the advantage of avoiding the agglomeration problems that occurred in the case of Nr-HA. Micro-rod HA-reinforced composite resins have superior potential applications in dental caries restoration.

Hydroxyapatite/chemically reduced graphene oxide composite: Environment-friendly synthesis and high-performance electrochemical sensing for hydrazine

It is unexpectedly found that, the in-situ growth of hydroxyapatite (HAP) on graphene oxide (GO) under a moderate temperature (85°C) can effectively trigger the reduction of GO, which needs neither extra reducing agents nor high-temperature thermal treatment. The transmission electron microscope (TEM) experiment demonstrates that the rod-like HAP particles are well attached on the surface of reduced GO (rGO) to form the composite. Electrochemical sensing assays show that the synthesized HAP-rGO nanocomposite presents excellent electrocatalytic capacity for the oxidation of a toxic chemical of hydrazine. When the HAP-rGO modified electrode was utilized as an electrochemical sensor for hydrazine detection, outstanding performances in the indexes of low fabrication cost, short response time (~2s), wide linear range, low detection limit (0.43μM), and good selectivity were achieved. The developed sensor also shows satisfactory results for the detection of hydrazine in real industrial wastewater sample were achieved.