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Bone and tooth enamel surface are made up of different crystallographically hydroxyapatite (HA), whereby bone comprises a(b)-planes of HA whilst tooth enamel comprises c-planes of HA. The reason behind the difference between HA orientations in both tissues are still yet to be discovered. We report the fabrication of anisotropic coatings of a-plane oriented HA according to the following process: (i) synthesis of a-plane oriented HA powders via a hydrothermal reaction and (ii) fabrication of a-plane oriented HA coatings via a Drop-on-Demand (DoD) micro-dispensing technique. Two types of HAs with high a-plane orientation degree of 72.2 and 75.6% (HA10 and HA84, respectively) was synthesised for the DoD coatings. The HA84 coating demonstrated more uniform and flatter surface than HA10 coating. The heat treatment of HA10 and HA84 coatings prepared with mesh-sieved particles led to a low adhesion strength for the substrates. However, the orientation degrees of those coatings (96.0 and 94.6%, respectively) were higher than the coatings without mesh-sieving. [ABSTRACT FROM AUTHOR]

Substitution of inorganic ions into β-tricalcium phosphate (β-TCP) is a well-known approach for facilitating biological functions of bioceramics. However, the dissolution mechanism of those β-TCPs is still under intensive debates. In the present study, the effect of copper substitution into β-TCP crystal structure on the local chemical structure and dissolution property of the copper-doped β-TCP (CuTCP) was investigated to clarify the dissolution mechanism of β-TCP. A copper-dependent decrease in the dissolution rate of CuTCP with time was observed. The 1H → 31P nuclear magnetic resonance (NMR) spectra of 10 mol% copper-doped β-TCP after the dissolution test demonstrated an amorphous hydrated layer on the surface of β-TCP core particles, which contained hydroxyapatite and dicalcium phosphate dihydrate and anhydrate. As such, all the dissolution curves could be curve-fitted by a heterogeneous dissolution model composing of fast and slow dissolution components. Overall, dissolution mechanism could be proposed as follows: the CuTCP particles initially dissolved by hydrolysis based on the fast dissolution component. Subsequently, the amorphous hydrated layers were formed on their surface, and caused the diffusion-controlled dissolution. As the result, the slow dissolution component would be dominant, and led to the decreased dissolution rate. Understanding the dissolution mechanism of copper doped β-tricalcium phosphate (CuTCP) is crucial for designing an angiogenetic controlled copper release CuTCP for therapeutic biomaterials. However, dissolution mechanism of β-TCP or CuTCP is still under intensive debates. This study demonstrated for the first time, that amorphous hydrated layers were formed on the CuTCP particle surface during its dissolution process, which caused a diffusion-controlled dissolution, and decreased the dissolution rate of CuTCP. This work not only provided a novel dissolution mechanism of β-TCP or CuTCP, but also a new finding for designing an angiogenetic controlled copper release CuTCP for therapeutic biomaterials. [ABSTRACT FROM AUTHOR]

Abstract: Moldable and injectable calcium‐phosphate cements (CPCs) are material candidates for bone replacement applications. In the present study, we examined the effectiveness of sodium alginate and sodium citrate additives to the liquid phase of CPC, in improving its handling property as well as mechanical strength. The use of these additives enhanced the handling property significantly, in terms of consistency as compared to CPC without additives due to the liquefying effect caused by the adsorption of citrate ions on the cement particles. Sodium alginate and sodium citrate were added to CPC, which was set by the chelate‐bonding capability of inositol phosphate, and was composed of mainly α‐tricalcium phosphate (α‐TCP) phase (>90%). The compressive strength of the CPC containing sodium alginate and sodium citrate was 3.4 ± 0.3 MPa, which was significantly higher than cement without additives. Furthermore, this cement exhibited favorable osteoconductivity and bioresorbability, and remained the α‐TCP phase after 4‐week implantation in a pig tibiae model. These results suggested that the cement is a potential candidate as a bioresorbable paste‐like artificial bone. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2361–2370, 2018. [ABSTRACT FROM AUTHOR]

An injectable chelate-setting hydroxyapatite cement (IP6-HAp), formed by chelate-bonding capability of inositol phosphate (IP6), was developed. The effects of ball-milling duration of starting HAp powder and IP6 concentration on the material properties such as injectability and mechanical strength of the cement were examined. The cement powder was prepared by ball-milling the as-synthesized HAp powder for 5 min using ZrO2 beads with a diameter of 10 mm, followed by another 60 min with ZrO2 beads with a diameter of 2 mm, and thereafter surface-modified with 5000 ppm of IP6 solution. Injectable cement was then fabricated with this HAp powder and 2.5 mass% chitosan as a mixing solution, with a setting time of 36.3 ± 4.7 min and a compressive strength of 19.0 ± 2.1 MPa. The IP6-HAp cements prepared with chitosan showed favorable biocompatibility in vitro using an osteoblast cell model, and osteoconductivity in vivo using a pig tibia model. [ABSTRACT FROM AUTHOR]

Abstract: The effect of concentration of sodium inositol hexaphosphate (IP6-Na) on material properties of calcium-phosphate cement (CPC) was investigated. The starting cement powder (IP6-HAp) was prepared by grinding and surface modifying hydroxyapatite (HAp) powder in various concentrations of IP6-Na solution. To prepare the IP6-HAp cement paste, the IP6-HAp powder was mixed with water under various powder/liquid ratios (P/L= [g/mL]). Amount of IP6 adsorbed on the surface of HAp powders increased with an increment of IP6-Na concentration, leading to negative surface charge. Dispersion of IP6-HAp powders was improved with an increase of IP6-Na concentration. As for cement fabrication, the IP6-HAp powder with negative charge enabled putty-like cement paste to be prepared at the higher P/L ratio. The compressive strength fabricated from IP6-HAp powders with negative surface charge at -20mV or lower was higher than that fabricated from IP6-HAp powders with negative surface charge at -10mV or higher. This improvement of the CS may be due to the increase of packing density. [Copyright &y& Elsevier]

Abstract: The dense hydroxyapatite (HAp) ceramics with preferred orientation to a-plane were fabricated using composite powders of single-crystal apatite fibers (AF) and wet-synthesized apatite gels (AG). AF was synthesized by homogeneous precipitation method. The composites of AF and AG were prepared as the following process. Aqueous (NH4)2HPO4 solutions were added into the AF slurry with the amount of 1 mass%. In addition, aqueous Ca(NO3)2 solutions were added dropwise to the slurry to precipitate the AG on the AF at room temperature, and then aged at room temperature for 24h with stirring. The dried powders were uniaxially pressed at 200MPa of compaction pressure and then fired at 1300 ¼C for 5h. All the resulting ceramics were identified with HAp single phases. The (100), (200) and (300) reflections which correspond to a-plane were more intense than those of a standard HAp ceramics. With increasing the additive amount of AG, the orientation degree of a-plane decreased, and the relative density increased. Furthermore, the ultrastructure of the resulting ceramics was examined by high-resolution transmission electron microscopy. The selected area electron diffraction patterns showed clear spots corresponding to [110] zone axis direction of HAp crystal with high crystallinity. The lattice spacings of crystal grains were determined to be 0.34nm or 0.68nm which corresponds to the lattice constant of (002) or (001) plane of HAp crystal. Therefore, the resulting ceramics were HAp single phases with preferred orientation to a-plane. [Copyright &y& Elsevier]

Autograft has been carried out for anterior cruciate ligament (ACL) reconstruction surgery. However, it has negative aspect because patients lose their healthy ligaments from other part. We focus on a chitosan-hydroxyapatite (HAp) composite fiber as a scaffold of ligament regeneration. Chitosan- HAp composite fiber was made by using coagulation method. Chitosan-NaH 2 PO 4 solution was coagulated with coagulation bath including calcium ion to get the mono-fiber and then treated with sodium hydroxide solution to form HAp in fiber matrix. The mechanical property of the fiber was improved by the stretching of the wet one because of the orientation of chitosan molecule and the interaction between chitosan and HAp. Maximum stress was improved with increasing of sodium dihydrogen phosphate until 0.03 M. The swelling ratio of the fiber was inhibited by composited with HAp. Additionally, bone-bonding ability was confirmed by SBF soaking tests. [ABSTRACT FROM AUTHOR]

Abstract: Hydroxyapatite (HAp), with its high biocompatibility and osteoconductivity, readily absorbs proteins, amino acids and other substances, which in turn favor the adsorption and colonization of bacteria. To prevent bacterial growth and biofilm formation on HAp discs, silver-containing (1–20mol%) HAp (Ag-HAp) powders were synthesized using an ultrasonic spray pyrolysis (USSP) technique. The X-ray diffraction (XRD) peaks were very broad, indicating low crystallinity, and this induced the release of Ag+ ions from Ag-HAp powders. In addition, a gradual increase in Ca2+ ion release was observed. These results suggest that dissolution of Ca2+ ion in Ag-HAp triggered the release of Ag+ ions. The antimicrobial efficacy of Ag-HAp disc was tested against Staphylococcus aureus. Samples with Ag contents of more than 5mol% were found to be highly effective against bacterial colonization and biofilm formation in vitro. In vivo antibacterial tests using bioluminescent strains also showed reductions in the viability of bacteria with Ag-HAp (5mol%) discs. Biocompatibility tests using a modified Transwell® insert method showed that Ag-HAp (5mol%) discs have negative effects on osteoblast proliferation. These results indicate that Ag-HAp (5mol%) has effective antibacterial activity and good biocompatibility both in vitro and in vivo together with good biocompatibility, thus confirming its utility as a bactericidal material. [Copyright &y& Elsevier]

We have succeeded in improving the material properties of a chelate-setting calcium-phosphate cement (CPC), which is composed of hydroxyapatite (HAp) the surface of which has been modified with inositol hexaphosphate (IP6) by adding α-tricalcium phosphate (α-TCP) powder. In order to create a novel chelate-setting CPC with sufficient bioresorbability, gelatin particles were added into the IP6-HAp/α-TCP cement system to modify the material properties. The effects of adding polysaccharides (chitosan, chondroitin sulfate, and sodium alginate) into the sodium dihydrogen phosphate mixing solution on the material properties of the gelatin-hybridized CPC were evaluated. The results of mechanical testing revealed that chondroitin sulfate would be the most suitable for fabricating the hybridized CPC with higher compressive strength. Moreover, further addition of an appropriate amount of citric acid could improve the anti-washout capability of the cement paste. In summary, a gelatin-hybridized IP6-HAp/α-TCP cement system prepared with a mixing solution containing chondroitin sulfate and citric acid is expected to be a beneficial CPC, with sufficient bioresorbability and material properties., Competing Interests: The authors declare no conflicts of interest.