Needle-like Hydroxyapatite Crystals Research Articles

Biocompatibility of dental implants coated with hydroxyapatite using pulsed Er:YAG laser deposition.

We aimed to improve the biocompatibility and osteoinductive potential of Ti implants using a simulated intraoral hydroxyapatite (HAp) coating. We devised a novel surface treatment for aggressive induction of osteoblast adhesion and bone regeneration on the implant surface. A thin α-tricalcium phosphate (α-TCP) film was deposited on the implant surface using a pulsed Er:YAG laser. The coating was converted to HAp through artificial saliva immersion, which was confirmed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM showed needle-like HAp crystals on the Ti disks and sandblasted implant surfaces after immersion in artificial saliva for 96 h. Microcomputed tomography and histological evaluation 4 and 8 weeks after implantation into beagle dog mandibles showed that the HAp-coated implant was biocompatible and exhibited superior osteoinduction compared to that of sandblasted implants. Coating the implant surface with HAp using an Er:YAG laser has potential as a new method of the implant-surface debridement.

Modeling of Ca/P and deposit size responses of electrodeposited calcium-phosphate coating using full factorial design

PurposeThis study aims to investigate the effect of electrodeposition parameters (i.e. time and voltage) on the properties of hydroxyapatite (HA) coating fabricated on Ti6Al4V surface.Design/methodology/approachA full factorial design along with response surface methodology was utilized to evaluate the main effect of independent variables and their relative interactions on response variables. The effect of electrodeposition voltage and deposition time on HA coatings Ca/P molar ratio and the size of deposited HA crystals were examined by structural equation modeling (SEM). The formation of plate-like and needle-like HA crystals was observed for all experiments.FindingsThe results obtained showed that the higher electrodeposition voltage leads to lower Ca/P values for HA coatings. This is more significant at lower deposition times, where at a 20-minute deposition time, the voltage increased from 2 to 3 V and the Ca/P decreased from 2.27 to 1.52. Full factorial design results showed that electrodeposition voltage has a more significant effect on the size of the deposited HA crystal. With increasing the voltage from 2 to 3 V at a deposition time of 20 min, the HA crystal size varied from 99 to 36 µm.Originality/valueThe investigation delved into the impact of two critical parameters, deposition time and voltage, within the electrodeposition process on two paramount properties of HA coatings. Analyzing the alterations in coating characteristics relative to variations in these process parameters can serve as a foundational guide for subsequent research in the domain of calcium-phosphate deposition for implants.

Synthesis of Micro-/Nanohydroxyapatite Assisted by the Taylor-Couette Flow Reactor.

Hydroxyapatite (HAP) has received increasing attention as an essential chemical product with good biocompatibility and adsorption properties. Generally, amorphous calcium phosphate (ACP) was generated first in the reactor and transformed into HAP after a period of crystallization. In this work, a series of Taylor-Couette flow reactors with different inner diameters were designed to assist in synthesizing HAP micro-/nanocrystals. ACP was obtained in a Taylor-Couette flow reactor at Re = 247 and successfully transformed into needle-like HAP crystals with a length of about 200 nm and a uniform particle size distribution after crystallization transformation. The yield of a single reactor can reach 2.16 kg per day. The finite element analysis results and time-space diagram of flow pattern variation showed that the Taylor-Couette flow reactor could improve the mixing behavior and the flow field distribution. The Taylor-Couette flow reactor provides a valuable reference for synthesizing inorganic micro-/nanomaterials.

Live Visualization of the Nucleation and Growth of Needle-Like Hydroxyapatite Crystals in Solution by In Situ TEM

Live Visualization of the Nucleation and Growth of Needle-Like Hydroxyapatite Crystals in Solution by In Situ TEM

3D printing of hierarchical porous biomimetic hydroxyapatite scaffolds: Adding concavities to the convex filaments

Porosity plays a key role on the osteogenic performance of bone scaffolds. Direct Ink Writing (DIW) allows the design of customized synthetic bone grafts with patient-specific architecture and controlled macroporosity. Being an extrusion-based technique, the scaffolds obtained are formed by arrays of cylindrical filaments, and therefore have convex surfaces. This may represent a serious limitation, as the role of surface curvature and more specifically the stimulating role of concave surfaces in osteoinduction and bone growth has been recently highlighted. Hence the need to design strategies that allow the introduction of concave pores in DIW scaffolds. In the current study, we propose to add gelatin microspheres as a sacrificial material in a self-setting calcium phosphate ink. Neither the phase transformation responsible for the hardening of the scaffold nor the formation of characteristic network of needle-like hydroxyapatite crystals was affected by the addition of gelatin microspheres. The partial dissolution of the gelatin resulted in the creation of spherical pores throughout the filaments and exposed on the surface, increasing filament porosity from 0.2 % to 67.9 %. Moreover, the presence of retained gelatin proved to have a significant effect on the mechanical properties, reducing the strength but simultaneously giving the scaffolds an elastic behavior, despite the high content of ceramic as a continuous phase. Notwithstanding the inherent difficulty of in vitro cultures with this highly reactive material an enhancement of MG-63 cell proliferation, as well as better spreading of hMSCs was recorded on the developed scaffolds. Statement of significanceRecent studies have stressed the role that concave surfaces play in tissue regeneration and, more specifically, in osteoinduction and osteogenesis. Direct ink writing enables the production of patient-specific bone grafts with controlled architecture. However, besides many advantages, it has the serious limitation that the surfaces obtained are convex. In this article, for the first time we develop a strategy to introduce concave pores in the printed filaments of biomimetic hydroxyapatite by incorporation and partial dissolution of gelatin microspheres. The retention of part of the gelatin results in a more elastic behavior compared to the brittleness of hydroxyapatite scaffolds, while the needle-shaped nanostructure of biomimetic hydroxyapatite is maintained and gelatin-coated concave pores on the surface of the filaments enhance cell spreading.

Polyvinyl Alcohol/Graphene Oxide Interlayer for Enhancing Adhesive Performance of HA Coating on C/C Composites Prepared by Hydrothermal Electrodeposition/Hydrothermal Treatment.

Hydroxyapatite (HA) coatings directly deposited by hydrothermal electrochemical technology (HET) onto carbon/carbon (C/C) composites exhibited a catastrophic failure occurring at the interface of the HA and C/C. To overcome this problem, a polyvinyl alcohol (PVA)/graphene oxide (GO) interlayer (P/G interlayer) was applied on the (NH4)2S2O8-pretreated C/C substrate (named P/G-C/C) by using a dipping method. Subsequently, a calcium phosphate coating was deposited on P/G-C/C, shortened as M-P/G-C/C, by HET, and then converted into HA coating (abbreviated as HA-P/G-C/C) through posthydrothermal treatment. For comparison, HA coating was prepared onto C/C without a P/G interlayer through the same process, which was denoted as HA-C/C. The composition, microstructure, and morphology of the samples were characterized by X-ray diffractometry (XRD), energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), Raman spectra, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). The adhesive performance of the coatings on C/C was measured by a scratch test. Finally, an in vitro bioactivity of the coatings was evaluated in a simulated body fluid solution at 37 °C. Results showed no apparent differences in the morphology and phase of the posttreated coatings, both of which are composed of a dense structure containing needle-like HA crystals. However, the HA-P/G-C/C sample possessed a higher Ca/P ratio and denser interface, thereby exhibiting higher adhesive performance and better bioactivity. The adhesive strength of the HA-P/G coating was observed at a critical load of 41.04 N, which increased by 29.3% relative to the HA coating. Moreover, the failure site was on the HA-P/G coating rather than at the interface. The enhanced adhesive performance was ascribed to the PVA/GO-repairing pits on C/C and PVA and GO toughening effects on the HA coating. In vitro and in vivo tests revealed no statistical significance for the two HA-coated C/C samples, although the HA-P/G coating exhibited better bioactivity, inducing the growth of bonelike apatite than the HA coating.

Ag nanoparticles incorporated tannic acid/nanoapatite composite coating on Ti implant surfaces for enhancement of antibacterial and antioxidant properties

Implant infections caused by bacteria and oxidative stress induced by reactive oxygen species (ROS) would seriously hinder the osseointegration at the interface of bone and titanium (Ti) implant, leading to a failure. Therefore, it is highly desirable to develop an implant surface modification with antibacterial and antioxidant functions. Silver (Ag), which exhibit a broad spectrum of antibacterial properties, was used in this work. Tannic acid (TA) was selected as the reducing agent to realize the generation of Ag nanoparticles, and as an antioxidant to achieve the antioxidative activity of Ti implants. So, a layer of anatase titanium dioxide (TiO2) nanotubes with a diameter of 138.72 ± 14.02 nm was formed on the surface of Ti substrate by anodization and annealing, followed by loading Ag nanoparticles, growing bioactive hydroxyapatite (HA) crystals, and finally forming Ag-HA/TA composite coatings. Morphology and phase composition investigations detected the presence of Ag nanoparticles and HA crystals in the coatings. The results reveal the uniformly distributed Ag particles with a diameter of about 20– 80 nm and needle-like HA crystals with a diameter of about 18– 20 nm. Results of total antioxidant capacity tests indicate that the slow release of TA from the composite coatings leads to a persistent antioxidative activity. The antibacterial and cell compatibility tests in vitro reveal that the Ag-HA/TA coating has high antibacterial activity against both Escherichia coli and Staphylococcus aureus and good cytocompatibility effect with MC3T3-E1 cell lines. This study presents a simple and effective method for the incorporation of antibacterial agents and antioxidant into HA coatings to modify metallic implant surfaces.

Use of experimental-resin-based materials doped with carboxymethyl chitosan and calcium phosphate microfillers to induce biomimetic remineralization of caries-affected dentin

This study investigated carboxymethyl chitosan (CMC)-induced biomimetic mineralization of collagen fibrils, with the aim of synthesizing experimental resins doped with CMC and calcium phosphate microfillers to remineralize artificial caries-affected dentin (ACAD) and enhance resin–dentin bonding durability. A size exclusion test provided evidence for the rejection of CMC (Mw 150 kDa) by collagen fibrils. Transmission electron microscopy and selected area electron diffraction conducted on reconstituted two-dimensional collagen showed typical deposition of needle-like hydroxyapatite crystals within collagen fibrils through CMC-induced biomimetic mineralization. The Vickers hardness test revealed significant improvement (P < 0.001) of the hardness of ACAD treated with CMC-containing experimental resins. Confocal laser scanning microscopy showed reduced dentin permeability and defect sites after biomimetic mineralization. On microtensile bond strength testing, the CMC-remineralized ACAD had better bonding with resin than ACAD and traditionally remineralized ACAD in both self-etch and etch-and-rinse bonding modes (P < 0.001). In conclusion, CMC is efficient in directing the biomimetic mineralization of collagen fibrils. The experimental resins containing CMC can induce dentin biomimetic remineralization and improve the bonding performance of ACAD.

Biomimetic Enamel Regeneration Mediated by Leucine-Rich Amelogenin Peptide

We report here a novel biomimetic approach to the regeneration of human enamel. The approach combines the use of inorganic pyrophosphate (PPi) to control the onset and rate of enamel regeneration and the use of leucine-rich amelogenin peptide (LRAP), a nonphosphorylated 56–amino acid alternative splice product of amelogenin, to regulate the shape and orientation of growing enamel crystals. This study builds on our previous findings that show LRAP can effectively guide the formation of ordered arrays of needle-like hydroxyapatite (HA) crystals in vitro and on the known role mineralization inhibitors, like PPi, play in the regulation of mineralized tissue formation. Acid-etched enamel surfaces of extracted human molars, cut perpendicular or parallel to the direction of the enamel rods, were exposed to a PPi-stabilized supersaturated calcium phosphate (CaP) solution containing 0 to 0.06 mg/mL LRAP for 20 h. In the absence of LRAP, PPi inhibition was reversed by the presence of etched enamel surfaces and led to the formation of large, randomly distributed plate-like HA crystals that were weakly attached, regardless of rod orientation. In the presence of 0.04 mg/mL LRAP, however, densely packed mineral layers, comprising bundles of small needle-like HA crystals, formed on etched surfaces that were cut perpendicular to the enamel rods. These crystals were strongly attached, and their arrangement reflected to a significant degree the underlying enamel prism pattern. In contrast, under the same conditions with LRAP, little to no crystal formation was found on enamel surfaces that were cut parallel to the direction of the enamel rods. These results suggest that LRAP preferentially interacts with ab surfaces of mature enamel crystals, inhibiting their directional growth, thus selectively promoting linear growth along the c-axis of enamel crystals. The present findings demonstrate a potential for the development of a new approach to regenerate enamel structure and properties.

Mineralization on polylactide/gelatin composite nanofibers using simulated body fluid containing amino acid

From physiological point of view, organic–inorganic composite nanofibers are envisioned promising substrates for bone tissue engineering. Biomineralization on polymeric nanofibers using simulated body fluid (SBF) is a common technique to obtain the composite nanofibers. Many factors, however, will affect the nucleation and crystal growth of deposited apatite, such as the additives like amino acids in SBF. In this study, electrospun composite nanofibers consisting of poly(l-lactide) (PLLA, 50wt%) and gelatin (50wt%) were soaked in 2.5 times SBF (2.5SBF) for different time periods (1, 2, 3, 5 and 7 days) to perform the biomineralization. Three amino acids (glycine, aspartic acid, or arginine) of different charge characteristics were introduced into the SBF, and their effects on nucleation and transformation of calcium phosphate depositions were systematically investigated. The results revealed that amino acids could take part in the early stage formation of pre-nucleation clusters, leading to different assemblies dependent closely on the feature of amino acid. In comparison with normal 2.5SBF, the presence of amino acid was able to enhance the preferred orientation of hydroxyapatite (HA) crystal along c axis and the transformation from amorphous calcium phosphate to hierarchical HA. The incorporation of glycine had promoted the formation of the well-evolved needle-like HA crystals in comparison with aspartic acid or arginine. It was suggested that the addition of amino acids into SBF might be a useful tool to regulate the biomineralizaiton for preparing organic–inorganic composite nanofibers.

An Electrophoresis-Aided Biomineralization System for Regenerating Dentin- and Enamel-Like Microstructures for the Self-Healing of Tooth Defects

It is the challenging and desirable aim of biomineralization studies to regenerate tooth tissue microstructures and to accelerate the speed of available biomimetic remineralization protocols for potential use in clinical dentistry. In this study, we developed a novel electrophoresis-aided calcium and phosphate agarose hydrogel system that can be used to quickly regenerate tooth tissue microstructure. After remineralization for 12 h, a demineralized dentin collagen matrix was remineralized with intrafibrillar and interfibrillar hydroxyapatites that mimicked the structure of the original calcified dentin collagen matrix. The precipitated hydroxyapatites were densely packed, occluded the exposed dentinal tubules, and regularly and homogeneously distributed along the collagen fibrils in a “string-of-beads” structure within the dentin collagen matrix. Needle-like hydroxyapatite crystals were densely packed, with their c-axis parallel to one another, to form the enamel-like tissue that precipitated onto the rem...

Regulation of calcium phosphate formation by native amelogenins in vitro

Our previous in vitro studies have shown that recombinant full-length porcine amelogenin rP172 can transiently stabilize amorphous calcium phosphate (ACP) and uniquely guide the formation of well-aligned bundles of hydroxyapatite (HA) crystals, as seen in the secretory stage of amelogenesis. This functional capacity is dependent on the hydrophilic C-terminal domain of full-length amelogenin. However, we have also found that native phosphorylated (single S-16 site) forms of full-length (P173) and C-terminal cleaved (P148) amelogenins can stabilize ACP for > 2 d and prevent HA formation. The present study was carried out to test the hypothesis that, at reduced concentrations, native full-length P173 also has the capacity to guide ordered HA formation. The effect of P148 and P173 concentrations (0.2–2.0 mg/ml) on the rate of spontaneous calcium phosphate precipitation was monitored via changes in solution pH, while mineral phases formed were assessed using TEM. At higher P173 concentrations (1.0–2.0 mg/ml), limited mineral formation occurred and only ACP nanoparticles were observed during a 48 h period. However, at 0.4 mg/ml P173, a predominance of organized bundles of linear, needle-like HA crystals were observed. At 0.2 mg/ml of P173, limited quantities of less organized HA crystals were found. Although P148 similarly stabilized ACP, it did not guide ordered HA formation, like P173. Hence, the establishment of the hierarchical enamel structure during secretory stage amelogenesis may be regulated by the partial removal of full-length amelogenin via MMP20 proteolysis, while predominant amelogenin degradation products, like P148, serve to prevent uncontrolled mineral formation.

Scratch resistance and electrochemical corrosion behavior of hydroxyapatite coatings on Ti6Al4V in simulated physiological media

Using an electrochemical process, needle-like hydroxyapatite crystals with Ca/P ratio of 1.67 were synthesized on Ti6Al4V without the formation of any precursor. In vitro dissolution/precipitation process was investigated by immersion of the coated substrate into Hank’s solution up to 14 days. Physical and chemical characterizations were performed by scanning electron microscope coupled with energy dispersive X-ray spectroscopy and by X-ray diffraction. In particular, through a sequence of reactions including dissolution, precipitation, and ions exchange during immersion tests, a precipitated bone-like apatite coating homogenous and less porous was formed. Further, the corrosion behavior of the untreated and HA-coated specimens in simulated body fluid was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that the corrosion rates of the samples with HA layer before and after immersion tests were 72 and 80 % lower than that of the bare titanium alloy. At last, the adhesion of the HA layer was determined through the use of scratch tests. A particular tribological behavior and a strong link to the substrate were revealed.

Effect of Hydroxide Ion Concentration on the Morphology of the Hydroxyapatite Nanorods Synthesized Using Electrophoretic Deposition

The effect of OH- concentration on the morphology of the hydroxyapatite (HA) nanorod synthesized using electrophoretic deposition (EPD) method has been investigated. The growth of HA nanorods was achieved on polished titanium substrates. The electrolyte used in this study was prepared by dissolving calcium acetate (Ca (CH3COO)2H)2O), and Ammonium dihydrogen phosphate (NH4H2PO4) in distilled water without any surfactant, and was maintained at 80-130°C. Two electrolytes with OH- concentration of 10-4 and 10-10 were prepared. A highly homogeneous HA nanorods deposited on the titanium substrates were obtained after 1 h in the electrolytes with higher OH- concentration of 10-4. On the other hand, a flower-shaped HA nanostructures composed of needle-like HA crystals were obtained in the electrolyte of lower OH- concentration of 10-10. The deposits were identified as HA crystal rods grown along the c axis and perpendicular to the substrate. The HA deposits were characterized by scanning electron microscopy (SEM) while detailed structural characterization was done using a transmission electron microscope (TEM) equipped with selected area electron diffraction (SAED) patterns.

Electrochemical Characteristics of the Hydroxyapatite Coatings Prepared by Mg Sacrificial Anode

Abstract The hydroxyapatite (HA) coating, one of the most important biomaterials, was prepared on Ti6Al4V alloy by Mg sacrificial anode to improve the anticorrosion electrochemical characteristics. Energy dispersive X-ray analysis (EDX), electron probe microanalyzer (EPMA), Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) were used to analyze the HA coating. The results show that the HA coating is composed of needle-like hydroxyapatite crystals with the Ca/P ratio of 1.4063. After the immersion test of 30 d, the crystals become larger in Hank's solution, from needle-like to sheet-like in Ringer's solution and column-like in Tyrode's solution. The tests of open circuit potential, polarizing curves and EIS method in Hank's solution, Ringer's solution, Tyrode's solution and human blood show that the Ti6Al4V alloy with HA coating has better electrochemical characters than Ti6Al4V alloy.

공침법을 이용한 마그네슘이 첨가된 biphasic calcium phosphate의 적합성 평가

Mg-BCP(Mg Substituted BCP)를 제조하기 위하여 <TEX>$Ca(NO_3)_2{\cdot}4H_2O$</TEX>(Katayama chemical, Japan)과 <TEX>$(NH_4)_2{\cdot}HPO_4$</TEX> (Junsei chemical, Japan), <TEX>$Mg(NO_3)_2{\cdot}6H_2O$</TEX>(Junsei chemical, Japan)를 출발물질로 공침법(co-precipitation process)을 이용하여 합성하였다. 제조된 분말의 마그네슘의 첨가에 따른 분말의 분광학적 특성은 FT-IR(MAGNA-IR 560, Nicolet)을 통하여 분석하였으며, SEM(S-4200, Hitachi)을 통하여 미세구조를 분석하였다. XRD 회절피크의 면적적분강도를 Integral Analysis (Rigaku, Japan)를 이용하여 HAp와 <TEX>${\beta}$</TEX>-TCP의 비율을 확인하였다. 1.0 wt% 마그네슘이 첨가된 BCP 샘플의 경우 Hank's solution에서의 2주 침적 후 표면에 침상의 HAp로 추정되는 결정이 성장하였다. 이러한 미세구조의 변화는 생활성을 가지는 마그네슘의 첨가가 BCP 조직 내에서 표면의 활성을 증가시켜 결정의 성장을 촉진시킨 것으로 판단된다. Magnesium-substituted BCP (biphasic calcium phosphate) powders were prepared by incorporating small amounts of magnesium into the structure of different hydroxyapatite (HAp)/<TEX>${\beta}$</TEX>-tricalcium phosphate (<TEX>${\beta}$</TEX>-TCP) ratios through coprecipitation method. A series of magnesium substitutions ranging from 0, 0.5, and 1.0 wt%, which are comparable to the measured magnesium contents, were performed. The obtained powders were characterized by the following analytical techniques: X-ray diffraction analysis (XRD), Thermo Gravimetric Analyzer (TGA) and Fourier transform infrared spectroscopy (FT-IR). The results have shown that substitution of magnesium in the calcium-deficient apatites resulted in the formation of biphasic mixtures of different HAP/<TEX>${\beta}$</TEX>-TCP ratios after heating above <TEX>$1000^{\circ}C$</TEX>. The 1.0 wt% magnesiumsubstituted-BCP were soaked in Hank's solutions after 2 weeks to observe the morphology of the biocement, especially needle-like hydroxyapatite crystals and to estimate the length and diameter of nanoneedle crystals.

Microstructure of hydroxyapatite- and octacalcium phosphate-coatings formed on magnesium by a hydrothermal treatment at various pH values

Hydroxyapatite (HAp) coatings with and without octacalcium phosphate (OCP) were uniformly formed on pure magnesium by a hydrothermal treatment using a Ca-EDTA solution. The crystal structure, crystallographic orientation and lattice images were investigated using transmission electron microscopy (TEM) and high-resolution TEM. It was demonstrated that the crystal phase and microstructure of the calcium phosphate-coatings can vary with the pH of the treatment solution. In a weak acid treatment solution, a dual-layer structure was formed: an outer coarse layer consisting of plate-like OCP crystals and an inner dense layer consisting primarily of HAp crystals. One piece of the OCP plate corresponded to a single OCP crystal growing parallel to the (1 0 0) OCP. In a weak alkali treatment solution, a dual-layer structure was also formed: an outer coarse layer consisting of rod-like HAp crystals and an inner dense layer consisting of HAp crystals. One piece of the HAp rod corresponded to a single HAp crystal growing along [0 0 2] HAp. In a strong alkali treatment solution, needle-like HAp crystals were formed. No defect was observed in the lattice image of the OCP and HAp. The corrosion current density of pure magnesium in a 3.5 wt.% NaCl solution decreased with the HAp coating more significantly than the OCP + HAp coating. It is revealed that the degree of protection afforded by calcium phosphate-coatings varies with their crystal phase and microstructure.

Chondrogenesis of articular chondrocytes in hydroxyapatite/chitin/chitosan scaffolds supplemented with pituitary extract

AbstractThis study analyzes the effects of pituitary extract supplement on the cultivation of bovine knee chondrocytes (BKCs) in three‐dimensional chitin/chitosan biomaterials. Transforming growth factor‐β1 (TGF‐β1) in the supplement was identified by Western blot near 23 kDa, and the immunoassayed concentration of TGF‐β1 in the supplement was about 33 ng/mL. The typical pore diameter of the chitin/chitosan scaffolds was 250 μm, indicating an apposite void space for chondrocyte growth. The characteristic width of needlelike hydroxyapatite crystals was 85 nm after chemical co‐precipitation of hydroxyapatite on the pore surfaces of the scaffolds. Over 4‐wk cultivation, the amounts of proliferated BKCs, secreted glycosaminoglycans and produced collagen were improved with the concentration of TGF‐β1 in culture medium. In addition, the cultivated constructs revealed mature neocartilage with lacunas enclosing BKCs, demonstrating chondrogenesis. Pituitary extract supplement was more efficient in the synthesis of extracellular matrix than pure TGF‐β1. Hence, an appropriate addition of the supplement can enhance the formation of cartilaginous components in the scaffolds to regenerate articular cartilage.

Synthesis of nanorod and needle-like hydroxyapatite crystal and role of pH adjustment

Nanorod and needle-like hydroxyapatite (HAp) crystals were successfully synthesized at 85 °C through a simple and mild pathway. Single-phase HAp powder with high crystallinity was obtained without thermal treatment. The effect of urea concentration on the crystal component was investigated. X-ray diffraction (XRD) results indicated that pH adjustment played a key role in controlling the composition of final products. The fast adjustment on pH by NH 3·H 2O resulted in formation of single-phase HAp with nanorod and needle-like shapes while the slow adjustment by urea led to a mixture of octacalcium phosphate (OCP) and HAp with ribbon-like morphology. Ribbon-like OCP crystal was the intermediate for the transformation from monetite (DCPA) to HAp.

Formation of hydroxyapatite on low Young's modulus Ti–30Nb–1Fe–1Hf alloy via anodic oxidation and hydrothermal treatment

Hydroxyapatite (HA) on the Ti–30Nb–1Fe–1Hf alloy has been fabricated via anodic oxidation followed with the hydrothermal treatment. The anodic oxide film (AOF) containing Ca and P was formed by anodic oxidation in a solution consisting of β-glycerophosphate disodium pentahydrate(β-GP), and calcium acetate monohydrate(CA). The AOF was formed by a 2-stage growth: (1) a thin oxide film that intimately contacted the substrate formed prior to sparking; (2) after sparking, the thickness of AOF increased rapidly, accompanying with the formation of numerous craters in the AOF. When anodizing to 300 V, the AOF had a glassy amorphous structure. Increasing anodizing potential increased the Ca/P ratio and contents of Ca and P, but decreased the adhesion strength between the AOF and the substrate. After 6 h of hydrothermal treatment at 250 °C, a great number of crystalline HA precipitated on the surface of AOF anodized to 300 V. The shapes and population density of HA crystals can be controlled by modifying the anodizing potential and the solution pH of hydrothermal treatment. Increasing the pH of the solution in hydrothermal treatment enhanced the precipitation of HA crystals. Numerous needle-like HA crystals that nearly covered the surface of AOF were obtained when hydrothermally treated in the pH 13 solution.