A simple sol-gel technique for synthesis of nanostructured hydroxyapatite, tricalcium phosphate and biphasic powders

Hydroxyapatite (HAP), β-tricalcium phosphate (β-TCP) and biphasic calcium phosphate (BCP) nanocrystalline powders were prepared by a simple sol-gel approach. Because of the unique characteristic of the phosphorous source ((CH₃O)₃P) and the proper uses of calcic and phosphorous sources with Ca/P molar ratio between 1.4 and 1.67, three different kinds of nanostructured calcium phosphate powders were achieved by changing the ratio of calcic and phosphorous sources. For HAP and β-TCP, pure phases were prepared. For BCP, the proportion of HAP and β-TCP could be changed by thermal treatment.     

多孔β-TCP生物陶瓷成骨过程的研究

主要对多孔β-TCP生物陶瓷在体内对新骨生成的诱导性进行研究.首先,人为造成兔股骨髁部骨腔洞,建立骨缺损模型,将自制β-TCP多孔陶瓷植入,然后逐月取一系列处死、取材,并综合运用扫描电镜观察(SEM)、电子探针X显微分析(EPMA)、甲苯胺蓝染色(toluidine blue staining,TBS)和四环素双标记法(tetracycline double labeling,TDL)等测试手段,对材料植入区进行研究,试图探明β-TCP多孔陶瓷修复骨缺损时的成骨过程.     

Microsphere-based scaffolds encapsulating tricalcium phosphate and hydroxyapatite for bone regeneration

Bioceramic mixtures of tricalcium phosphate (TCP) and hydroxyapatite (HAp) are widely used for bone regeneration because of their excellent cytocompatibility, osteoconduction, and osteoinduction. Therefore, we hypothesized that incorporation of a mixture of TCP and HAp in microsphere-based scaffolds would enhance osteogenesis of rat bone marrow stromal cells (rBMSCs) compared to a positive control of scaffolds with encapsulated bone-morphogenic protein-2 (BMP-2). Poly(d,l-lactic-co-glycolic acid) (PLGA) microsphere-based scaffolds encapsulating TCP and HAp mixtures in two different ratios (7:3 and 1:1) were fabricated with the same net ceramic content (30 wt%) to evaluate how incorporation of these ceramic mixtures would affect the osteogenesis in rBMSCs. Encapsulation of TCP/HAp mixtures impacted microsphere morphologies and the compressive moduli of the scaffolds. Additionally, TCP/HAp mixtures enhanced the end-point secretion of extracellular matrix components relevant to bone tissue compared to the “blank” (PLGA-only) microsphere-based scaffolds as evidenced by the biochemical, gene expression, histology, and immunohistochemical characterization. Moreover, the TCP/HAp mixture groups even surpassed the BMP-2 positive control group in some instances in terms of matrix synthesis and gene expression. Lastly, gene expression data suggested that the rBMSCs responded differently to different TCP/HAp ratios presented to them. Altogether, it can be concluded that TCP/HAp mixtures stimulated the differentiation of rBMSCs toward an osteoblastic phenotype, and therefore may be beneficial in gradient microsphere-based scaffolds for osteochondral regeneration.     

Hydrothermal synthesis and biocompatibility of hydroxyapatite nanorods

A facile micelle precursor having cyclohexane/ethanol/cetyl trimethyl ammonium bromide/aqueous phase was treated hydrothermally to form nanohydroxyapatite. The synthesized products were characterized by means of X-ray diffraction, thermogravimetric analysis, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that the synthesized products display the crystalline structure and vibration modes of hydroxyapatite. Transmission electron micrograph revealed that nanohydroxyapatite exhibits elongated rod morphology with large aspect ratios. Nanohydroxyapatite prepared from a surfactant of 1.25 millimole showed good thermal stability at 1000 degrees C on the basis of thermogravimetric analysis. Simulated body fluid immersion test indicated that an apatite layer can be readily deposited on the nanohydroxyapatite surface demonstrating its good bio-resorbability.     

An investigation of the chemical synthesis and high-temperature sintering behaviour of calcium hydroxyapatite (HA) and tricalcium phosphate (TCP) bioceramics

The experimental conditions for the synthesis of sub-micrometre,spherical particles of calcium hydroxyapatite[Ca10(PO4)6(OH)2] (HA) andtricalcium phosphate [Ca3(PO4)2] (TCP) areinvestigated through chemical coprecipitation from the aqueous solutions ofcalcium nitrate and di-ammonium hydrogen phosphate salts. The precipitationprocess employed was also found to be suitable for the production ofsub-micrometre HA/TCP composite powders in situ. The synthesized pureHA and TCP powders were found to be stable even at 1300°C in air forprolonged heating times. Bioceramic sample characterization was achieved bypowder X-ray diffraction (XRD), scanning electron microscopy (SEM), energydispersive X-ray spectroscopy (EDX), and density and surface area measurements.Crystallographic analyses of HA powders were performed by the Rietveld method onthe powder XRD data.     

Hydrothermal synthesis and nanostructure of carbonated calcium hydroxyapatite

The influence of precursor concentration, pressure, temperature and time of hydrothermal synthesis on the development of calcium hydroxyapatite structure has been analyzed. The obtained results show that it is possible to adjust the conditions of hydrothermal synthesis from solutions of relatively high concentrations to obtain calcium hydroxyapatite nanopowders of well-defined structure. The relationship between the synthesis and the lattice parameters, as well as the crystallite size and the microstructure of synthesized hydroxyapatite has been established. The synthesized powders are preferentially carbonated hydroxyapatite of the B type in the form of agglomerates that accommodate two-modal size pores of 1.5–10 and 50–200 nm. The structure of calcium hydroxyapatite particles consists of crystallites 8–22 nm in size, bound within prime particles, which size is between 10 and 63 nm, that in turn form bigger agglomerates 200 nm in size, which further cluster building up agglomerates 5–20 μm in size.     

Hydrothermal synthesis of hydroxyapatite from natural source

Dicalcium phosphate dihydrate (DCPD) and anhydrous dicalcium phosphate (DCPA) extracted from a by-product in a manufacture of gelatin from bovine bone are used as starting materials for the hydrothermal synthesis of hydroxyapatite (HA) at temperatures of 160 and 200 °C under vapor pressures of 1 and 2 MPa, respectively. The suspension of DCPA with water gives a mixture of DCPA and HA as product but after adjusting the Ca/P molar ratio to 1.50 and 1.67 by addition of Ca(OH)₂, a single phase of HA with needle-like crystals is obtained. DCPA whiskers are produced in the suspension of DCPD with water but, on addition of Ca(OH)₂, the product obtained is again, a mixture of DCPA and HA. The coexistence of DCPA and HA is observed not only in the acidic region at pH 4.6 which is close to the known quasi-invariant point but also in the basic region at pH 12.3. Without addition of Ca(OH)₂ to the system, the complete conversion of DCPA or DCPD to HA is not possible.     

羟基磷灰石纳米棒的水热制备及其晶体生长机理研究EI北大核心CSCD

以无水CaCl 2和(NH 4)2HPO 4为原料,尿素为均相沉淀剂,十六烷基三甲基溴化铵(CTAB)为模板剂,利用水热法制备了羟基磷灰石(HA)纳米棒。采用X射线衍射仪(XRD)、扫描电镜(SEM)和透射电镜(TEM)对产物的物相组成、微观形貌进行了表征。结果表明:通过改变反应温度和时间,可实现HA纳米形貌的可控微调。在120℃水热反应12 h可以制备出单晶密排六方结构HA纳米棒,其长约为0.5~1.0μm,直径约为15~30 nm。并从晶体结构的角度详细研究了CTAB在合成纳米棒结构中所起的作用,并通过实验进行了验证。     

Hydrothermal synthesis of composites of well-crystallized hydroxyapatite and poly(vinyl alcohol) hydrogel

Composites of hydroxyapatite (HAp) and poly(vinyl alcohol) (PVA) hydrogel were fabricated by the hydrothermal treatment of calcium phosphate powder. Alpha-tricalcium phosphate (α-TCP) or beta-tricalcium phosphate (β-TCP) powder was dispersed in PVA hydrogel and exposed to water vapor at 120 °C, 140 °C or 160 °C for 6 h. Low crystallinity HAp was formed in specimens prepared from α-TCP and PVA hydrogel prior to hydrothermal treatment, which was caused by hydrolysis of α-TCP. This allowed specimen shape to be retained after hydrothermal treatment. β-TCP showed less reactivity in forming HAp in the PVA hydrogel, which led to the formation of large rod-shaped crystals approximately 15 μm in length. Specimens from β-TCP and PVA were too soft to retain their shape after hydrothermal treatment. HAp with controlled morphology was prepared using different types of tricalcium phosphate precursor. The application of α-TCP allowed the in situ fabrication of HAp/PVA composites.     

Hydrothermal synthesis of hydroxyapatite whiskers with sharp faceted hexagonal morphology

We report an effective method for the synthesis of hydroxyapatite whiskers with sharp faceted hexagonal shape employing a low temperature (90 °C) hydrothermal route with calcium nitrate tetrahydrate, diammonium phosphate and urea as starting materials. The key parameters of the synthesis process i.e. duration, temperature cycle of the treatment and starting pH value are carefully varied and the end products are investigated using powder X-ray diffraction (XRD), Raman-scattering, infrared spectroscopy (IR), elemental analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), electron diffraction (ED), and high-resolution TEM (HRTEM) in order to find the optimal reaction conditions that lead to the desired hexagonal morphology of HA whiskers. The results demonstrate that gradual and greater increase in solution pH during the hydrothermal process favors large quantity of the single-crystalline hydroxyapatite whiskers with well defined hexagonal morphology.     

Effect of titanium and zirconium substitutions for calcium on the formation and structure of tricalcium phosphate and hydroxyapatite

The effect of Ti and Zr substitutions for Ca cations on the formation of tricalcium phosphate and hydroxyapatite has been studied in a wide concentration range: from 0.1 to 20 mol %. Upon the incorporation of Ti and Zr cations into tricalcium phosphate, the major forming phase is β-tricalcium phosphate. On the addition of low substituent concentrations to hydroxyapatite, we observe the formation of a single-phase material with the apatite structure. Increasing the substituent concentration to 10–20 mol % Ti or 20 mol % Zr leads to the formation of tricalcium phosphate. The unit-cell volume of the cation-substituted tricalcium phosphates has been shown to decrease with increasing substituent concentration. In the zirconium-containing hydroxyapatites, the unit-cell volume decreases with increasing zirconium concentration, whereas the titanium-containing hydroxyapatites exhibit an opposite tendency.     

Template-directed one-step synthesis of flowerlike porous carbonated hydroxyapatite spheres

Flowerlike porous carbonated hydroxyapatite (CHAp) spheres were first synthesized by the template-directed self-assembly method in a high-pressure system. The product was characterized via Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that flowerlike porous CHAp spheres were obtained, that the average granularity of porous CHAp spheres is about 20 μm, that the average aperture is about 1 μm, and that the average thickness of flakes is about 50 nm. Great amounts of OH channels, high special surface area and regular spherical shape imply potential applications.     

Hydrothermal synthesis of calcium hydroxyapatite nanorods in the presence of PVP

Calcium hydroxyphosphate (Ca₁₀(PO₄)₆(OH)₂, HAP) nanorods have been successfully synthesized by a simple and mild hydrothermal treatment in the presence of polyvinylpyrrolidone (PVP). A complex of calcium nitrate (Ca(NO₃)₂) and Na₂HPO₄ was used to supply the calcium and phosphate ions during the reactions. The synthesis of pure HAP nanorods was under near neutral condition. The morphology and structure of the samples were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy analysis. The nanorods were uniform with diameter of 20–25 nm and length ranging from several hundreds of nanometers to several micrometers. The influence of different experiment conditions, i.e., the PVP concentration, molar ratio of Ca²⁺ to HPO₄ ²⁻, reaction time, and temperature, on the morphology of the nanorods was investigated. The formation mechanism of rod-like HAP and effects of PVP on the crystal nucleation and growth have also been discussed.     

Fibrous growth of tricalcium phosphate ceramics

Structural transformation and sintering processes of tricalcium phosphate (TCP) ceramics prepared from defective hydroxyapatite (Ca9HPO4(PO4)5OH) were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). Starting powders with Ca/P ratio 1.5 were obtained by adding 0.5 l of 0.3 M H3PO4 solution to an equal volume of 0.45 M Ca(OH)2. In the prepared ceramics, the onset temperature for transformation of defective hydroxyapatite into TCP (witlokite) agrees with the onset temperature for sintering (800 °C). Sintering occurs through the formation of a fibrous structure, which resembles biological hard tissue. In the 1000–1200°C range, these fibres coalesce into grains of up to 0.6 m in size with a fibrous-laminar morphology. At the end of this sintering stage witlokite transforms into TCP. At about 1450°C, partial decomposition of TCP into Ca2P2O7+Ca4P2O9 is observed. AFM observations suggest that Ca2P2O7 is segregated in the liquid state and increases the velocity of grain growth (up to 12 m).     

Calcite as a bone substitute. Comparison with hydroxyapatite and tricalcium phosphate with regard to the osteoblastic activity

Close to the bone mineral phase, the calcic bioceramics, such as hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP), are commonly used as substitutes or filling materials in bone surgery. Besides, calcium carbonate (CaCO₃) is also used for their excellent biocompatibility and bioactivity. However, the problem with the animal-origin aragonite demands the new technique to synthesize pure calcite capable of forming 3D bone implant. This study aims to manufacture and evaluate a highly-pure synthetic crystalline calcite with good cytocompatibility regarding to the osteoblasts, comparing to that of HA and β-TCP. After the manufacture of macroporous bioceramic scaffolds with the identical internal architecture, their cytocompatibility is studied through MC3T3-E1 osteoblasts with the tests of cell viability, proliferation, vitality, etc. The results confirmed that the studied process is able to form a macroporous material with a controlled internal architecture, and this synthesized calcite is non-cytotoxic and facilitate the cell proliferation. Indeed requiring further improvement, the studied calcite is definitely an interesting alternative not only to coralline aragonite but also to calcium phosphate ceramics, particularly in bone sites with the large bone remodelling.     

Hydrothermal preparation of tailored hydroxyapatite

Hydrothermal vapor treatment method was applied for preparation of ceramic biomaterials. Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂; HA) ceramics prepared by sintering with random crystal surface have already been used as bone-repairing materials which can directly bond to natural bones. If materials of HA could have the tailored specific crystal surface, they should have the advantage of adsorptive activity and osteoconductivity in comparison with the sintered HA. In the present study, porous HA sheets of about 50 μm to 1 mm in thickness and porous HA granules of about 50 μm to 1 mm in size with tailored crystal surface were prepared by the hydrothermal vapor exposure method at temperatures below 200°C. Porous sheets and porous granules of HA with controlled crystal surface should be suitable for scaffold of cultured bone, for bone graft material and for drug delivery system (DDS).