Diffusion Kinetics of Carbonate Hydroxyapatite (CHAP) for Adsorbing F^- Dissolved in Water

A systematic research was performed about diffusion kinetics of adsorbing F^- dissolved in water for carbonate hydroxyapatite （CHAP） from the natural hydroxyapatite which was modified by adulterating with CO3^2-. The result shows that the speed of F^- adsorption is controlled by membrane diffusion when F^- concentration is relatively low, which is expressed by the kinetic equation of diffusion Q=0.0005（Ci-C）（t-ti）＋0.3967, or by vacancy diffusion when F^- concentration is relatively high, which is expressed by the kinetic equation of diffusion In[C（o, t）]=8.4718-0.5048Int. Based on the feature of CHAP for adsorbing F^- dissolved in water and its special channel of the structure of CO3^3- modified hydroxyapatite, models of vacancy diffusion and membrane diffusion were established.

Statistical Studies of the Physicochemical Analytic Results of a Series of Synthetic Calcium Hydroxyapatite Containing Carbonate and Sodium

The objective of this study is to present a simple method of statistical calculation that allowed us to determine the relationship between the different data obtained from the characterization of the synthetic carbonated apatites containing sodium, in order to find the fundamental substitution mechanism(s) for incorporation of Na+ and?CO32- and to establish the general formula. For that, a series of hydroxyapatites containing carbonate and sodium (Na-CO3HAps) has been obtained by the precipitation method. All the compounds were characterized by infrared spectra (IR), powder X-ray diffraction (PXRD) and elemental analysis. The statistical treatment of the experiment result allows us to determine the relationship between one variable and the change in the other and to found the fundamental substitution mechanism(s) for incorporation of Na+ and?CO32- . Analysis of variance (ANOVA) allows us to test the models proposed.

Removal Mechanism of Aqueous Lead by a Novel Eco-material: Carbonate Hydroxyapatite

Kinetics and mechanisms on the removal of aqueous lead ion by carbonate hydroxyapatite （CHap） are investigated in the present work. Experimental results show that, in the whole pH range, the lead removal percentage increases with decreasing pH values and reaches a maximum at pH=2-3. Under some conditions, the lead residual concentration is below national integrated wastewater discharge standard, even drinking water standard. The removal behavior is a complicated non-homogeneous solid/liquid reaction, which can be described by two stages from kinetic point of view. At the earlier stage, reaction rate is so fast that its kinetic course is intricate, which requires further study. At the latter stage, the rate of reaction becomes slow and the process of reaction accords with one order reaction kinetic equation. Experimental results show that the relationship between reaction rate constant k1 and temperature T accords to Arrhenius Equation, and the activation energy of sorption （Ea） is 11.93 kJ/mol and frequency factor （A） is 2.51 s^-1. X-ray diffraction （XRD）, scanning electron microscopy with an energy dispersive X-ray fluoresence spectrometer （SEM-EDS） and toxicity characteristic leaching procedure （TCLP） test were conducted in this work. It is indicated that the main mechanism is dissolution-precipitation, accompanying with superficial sorption.

Nanometre Carbonated Hydroxyapatite Powders Synthesis Controlled by Lecithin in Synthetic Body Fluids

Nanocrystal carbonated hydroxyapatite was prepared by lecithin-controlled chemical precipitation in synthetic body fluid （SBF）. The reactant was aged and heated at 850℃ for crystallization. The morphology and microstructure of the carbonated hydroxyapatite were investigated using transmission electron microscope （TEM）, X-ray diffraction （ XRD ） and FTIR. The experimental results demonstrate that the shapes of carbonated hydroxyapdtite particles display spheres with the average size of 20- 28 nm, and carbonated hydroxyapatite contained carbonate ions, similar to mineral of bone tissues.

Synthesis of Crystalline Hydroxyapatite from CaCO_3 and CaHPO_4·2H_2O by Mechanochemical Method

The mixture of CaHPO 4·2H 2O and CaCO 3 was ground in an aqueous system under appropriate conditions to investigate the mechanochemical reaction for the synthesis of crystalline hydroxyapatite (HA) powder. Hydroxyapatite of high crystallinity powder including trace Ca 10 (PO 4) 6CO 3(OH) and Ca 9HPO 4(PO 4) 6OH can be synthesized by mechanical activation without further thermal treatment at a high temperature. The synthesis reaction during the grinding process was almost completed within 1h. The as-ground powder exhibits a particle distribution of 20-100nm in size with a spherical or rodlike morphology. The composition and degree of crystallinity of the mechanochemical synthesized hydroxyapatite powders were coincident with the cement-type hydroxyapatite.

Hydroxyapatite composites with carbon allotropes:Preparation,properties,and applications

Hydroxyapatite(HA)and its composites with inorganic additives,dopants,and polymers is a rapidly developing branch in the materials chemistry.In particular,carbon allotropes are widely used in these composites being widely applied for medical purposes.Observing a gap of insufficient generalization of recent achievements in the field of the HA/Carbon composites,in this review we present the state of the art of the field of HA composites and hybrids with classic carbon allotropes and nanocarbons.These composites are known for carbon nanotubes,nanofibers,graphene and its oxidized forms,as well as,in a lesser grade,for graphite,fullerenes,nanodiamonds,carbon nanofoams,etc.These composites can be fabricated by a variety of classic and less-common methods,such as co-precipitation(with or without ultrasonic treatment),CVD,hot isostatic pressing,hydrothermal,spark plasma sintering,biomimetic mineralization,thermal and plasma spray,electrochemical and electrophoretic deposition,self-assembling,3D printing,electrospinning,and lyophilisation,among others.Combination of various synthesis techniques can be also carried out for composite preparation.Natural or synthetic HA can be used as it is for further interaction with carbon allotropes or it can be first prepared and then reacted with carbon counterpart;similarly,carbon allotropes can be introduced into the interaction with HA directly or they can be first synthesized,in particular from biomass.Resulting biocompatible composites can be produced in the form of coatings,powders,and scaffolds and can additionally contain quantitative amounts of third phases,frequently natural or synthetic polymers.In these composites,especially with O-containing functionalizing groups,HA disadvantages could be considerably decreased with simultaneous enhancement of mechanical properties,becoming similar to human bone,chemical stability and biocompatibility,as well as possessing antibacterial effect.GO→G reduction and higher HA decoration were observed in several experiments.The morphology of polymer-containing HA/GO composites can be tuned by variations of GO:polymer ratios.Predominant number of resulting applications of formed HA composites corresponds to the biomedical area,mainly for orthopedic applications/implants,osteoporosis treatment,myocardial,skin and dental regeneration,etc.Other important uses include applications as adsorbents for the elimination of impurities from wastewaters and/or removal/uptake of heavy metal cations,loading several medicines,and energy storage materials.Biocompatibility and hemocompatibility aspects of HA/Carbon composites are also discussed and future developments are proposed.

Bi-/multi-modal pore formation of PLGA/hydroxyapatite composite scaffolds by heterogeneous nucleation in supercritical CO_2 foaming

Scaffolds with multimodal pore structure are essential to cells differentiation and proliferation in bone tissue engineering. Bi-/multi-modal porous PLGA/hydroxyapatite composite scaffolds were prepared by supercritical C02 foaming in which hydroxyapatite acted as heterogeneous nucleation agent. Bimodal porous scaffolds were prepared under certain conditions, i.e. hydroxyapatite addition of 5%, depressurization rate of 0.3 MPa. min-1, soaking temperature of 55 ℃, and pressure of 9 MPa. And scaffolds presented specific structure of small pores （122 μM ± 66 μm） in the cellular walls of large pores （552 μm ±127 μm）. Furthermore, multimodal porous PLGA scaffolds with micro-pores （37 μM ± 11μM） were obtained at low soaking pressure of 7.5 MPa. The interconnected porosity of scaffolds ranged from （52.53 ± 2.69）% to （83.08±2.42）% by adjusting depressurization rate, while compression modulus satisfied the requirement of bone tissue engineering. Solvent-free CO2 foaming method is promising to fabricate bi-/multi-modal porous scaffolds in one step, and bioactive particles for osteogenesis could serve as nucleation agents.

磁性介孔碳负载羟基磷灰石的制备及对U(Ⅵ)的吸附性能

采用共沉淀法研究制备了不同质量比的磁性介孔碳(MMC)与羟基磷灰石(HAP)复合材料(MMC@HAP-x,x=1、4和6)并用于去除溶液中U(Ⅵ)。采用XRD、FT-IR、Zeta等方法表征了MMC、HAP和MMC@HAP-x的结构、功能基团及表面电位等理化性质。探讨了MMC@HAP-x吸附U(Ⅵ)的动力学、热力学及吸附机制。结果表明:MMC@HAP-x对U(Ⅵ)的吸附最佳pH均为4.0,达到吸附平衡所需时间均小于10 min,MMC@HAP-6的理论饱和吸附量可达1164.62 mg/g,且吸附过程是自发的化学吸附过程。U(Ⅵ)在MMC@HAP-x的固定是由于HAP与UO_(2)^(+2)相互作用形成了Ca(UO_(2))_(2)(PO_(4))_(2)·3H_(2)O。MMC@HAP-6是一种快速的铀吸附剂,有望用于放射性废水中铀的去除。

修复材料与牙体组织力学适配性的研究进展

牙齿作为发挥咀嚼功能的主要器官,可承受无数次功能性接触,这与它的力学性能和组织结构密切相关。牙釉质和牙本质的硬度较高,并且它们具有梯度化的结构,这使得牙齿既能承受咬合力,又不致轻易折裂。当牙体组织缺损时,往往需要全冠修复体来恢复牙齿正常的形态与功能。常用的全冠修复材料有金属材料、陶瓷材料以及最近兴起的聚醚醚酮材料。金属材料在美学方面存在一定劣势,目前在临床上应用相对较少。不同组成成分的陶瓷材料在性能及美学上的表现有所差异,但弹性模量与硬度过高,在力学性能方面都超过了牙体组织,与牙体组织学力学性能不匹配。与此不同,聚醚醚酮材料的弹性模量低于牙体组织,与骨组织相似,但通过纤维增强等方式能够提高它的性能。当修复材料与牙体组织的力学性能并不完全适配时,两者之间的界面往往形成潜在的薄弱环节,最终影响修复的稳定性和长期效果。本文介绍了牙釉质和牙本质的力学性能以及相对应的结构特点,并在此基础上,分析现有修复材料的优势与局限性,进一步探究口腔全冠仿生设计的可能性。

Ag-doped CNT/HAP nanohybrids in a PLLA bone scaffold show significant antibacterial activity

Bacterial infection is a major problem following bone implant surgery.Moreover,poly-l-lactic acid/carbon nanotube/hydroxyapatite(PLLA/CNT/HAP)bone scaffolds possess enhanced mechanical properties and show good bioactiv-ityregardingbonedefectregeneration.Inthisstudy,wesynthesizedsilver(Ag)-dopedCNT/HAP(CNT/Ag-HAP)nanohybrids via the partial replacing of calcium ions(Ca2+)in the HAP lattice with silver ions(Ag+)using an ion doping technique under hydrothermal conditions.Specifically,the doping process was induced using the special lattice structure of HAP and the abundant surface oxygenic functional groups of CNT,and involved the partial replacement of Ca2+in the HAP lattice by doped Ag+as well as the in situ synthesis of Ag-HAP nanoparticles on CNT in a hydrothermal environment.The result-ing CNT/Ag-HAP nanohybrids were then introduced into a PLLA matrix via laser-based powder bed fusion(PBF-LB)to fabricate PLLA/CNT/Ag-HAP scaffolds that showed sustained antibacterial activity.We then found that Ag+,which pos-sesses broad-spectrum antibacterial activity,endowed PLLA/CNT/Ag-HAP scaffolds with this activity,with an antibacterial effectiveness of 92.65%.This antibacterial effect is due to the powerful effect of Ag+against bacterial structure and genetic material,as well as the physical destruction of bacterial structures due to the sharp edge structure of CNT.In addition,the scaffold possessed enhanced mechanical properties,showing tensile and compressive strengths of 8.49 MPa and 19.72 MPa,respectively.Finally,the scaffold also exhibited good bioactivity and cytocompatibility,including the ability to form apatite layers and to promote the adhesion and proliferation of human osteoblast-like cells(MG63 cells).

Si_(3)N_(4)nanowires@pyrolytic carbon nanolayers coupled withhydroxyapatite nanosheets as reinforcement for carbon matrixcomposites with boosting mechanical and friction properties

Extensive attention has been drawn to the development of carbon-matrix composites for application in the aerospace and military industry,where a combination of high mechanical strength and excellent frictional properties are required.Herein,carbon-matrix composites reinforced by Si_(3)N_(4)nanowires@pyrolytic carbon nanolayers(Si_(3)N_(4nws)@PyCnls)coupled with hydroxyapatite nanosheets is reported.The Si_(3)N_(4nws)@PyCnls(SP)with coaxial structure could increase the surface roughness of Si_(3)N_(4nws)and promote the stress transfer to the carbon matrix,whereas the porous hydroxyapatite nanosheets favor the infiltration of the carbon matrix and promote the interfacial bonding between the SP and carbon matrix.The carbon matrix composites reinforced by SP coupled with hydroxyapatite nanosheets(Si_(3)N_(4nws)@PyCnls-HA-C)exhibit excellent mechanical strength.Compare with the conventional Si_(3)N_(4nws)reinforced carbon composites,Si_(3)N_(4nws)@PyCnls-HA-C(SPHC)have 162%and 249%improvement in flexural strength and elastic modulus,respectively.Moreover,the friction coefficient and wear rate decreased by 53%and 23%,respectively.This study provides a co-reinforcement strategy generated by SP coupled with hydroxyapatite nanosheets for effective improvement of mechanical and frictional properties of carbon matrix composites that are used for aerospace and military industry applications.

Effect of Synthesis Technique and Carbonate Content on the Crystallinity and Morphology of Carbonated Hydroxyapatite

The syntheses of nanosized carbonated hydroxyapatite （CHA） were performed by comparing dropwise and direct pouring of acetone solution of Ca（NO3）2·4H2O into mixture of （NH4）2HPO4 and NH4HCO3 at room temperature controlled at pH 11. Direct pouring method was later applied to study the increment of carbonate content in syntheses. The as-synthesized powders were characterized by various characterization techniques. The crystallographic results of the produced powders were obtained from X-ray diffraction analysis, whilst the carbonate content in the produced powders was determined by the CHNS/O elemental analyzer. Fourier transform infrared analysis confirmed that the CHA powders formed were B-type. Field emission scanning electron microscopy revealed that the powders were highly agglomerated in nanosized range and hence energy filtered transmission electron microscopy was employed to show elongated particles which decreased with increasing carbonate content.

Co-substitution of carbonate and fluoride in hydroxyapatite： Effect on substitution type and content

The nanosized hydroxyapatite substituted by fluoride and carbonate ions （CFHA） had been synthesized by aqueous precipitation method. CFHA had been considered as potential bone graft material for orthopedic and dental applications. The objective of this study was to determine the effects of simultaneously incorporated CO2/3- and F- on the substitution type and content. The morphologies of CFHAs were observed by TEM. The carbonate substitution type and content were characterized by FTIR. The fluoride contents were determined by F-selective electrode. The phase compositions and crystallinity of the samples were investigated by XRD. The fluoride and carbonate contents of CFHA increase with the dopant concentrations nonlinearly, The carbonate substitution has much more obvious effect on morphology compared with the fluoride substitution. The co-existence of CO2/3-and F- ions can influence the corresponding substitution fraction. The isomorphic substitution of sodium for calcium in the substitution process of CO2/3-can improve crystal degree and favor the B-type substitutions. Due to the closeness of the ion radii and equivalent substitution of F- and OH-, F- will occupy the OH- sites of HA crystals more easily, compelling most of the CO2/3- to be located in the B sites.

Facile Template-free Synthesis of Carbonated Hydroxyapatite Spheres in Aqueous Solution

Prickly carbonated hydroxyapatite（CHAp） spheres were obtained via a facile template-free self-assembly method with Na2HPO4 and self-made cubic CaCO3 as reactants. X-ray diffraction results of the product revealed CHAp with high crystallinity could be successfully prepared in a short reaction time. A nucleation mechanism was proposed according to the results of characterizing the resultant powders and analyzing the growth process. It shows that the self-made CaCO3 particles play an important role in the template-free synthesis of prickly spheres.

Cesium carbonate supported on hydroxyapatite coated Ni_(0.5)Zn_(0.5)Fe_2O_4 magnetic nanoparticles as an efficient and green catalyst for the synthesis of pyrano[2,3-c]pyrazoles

Cesium carbonate supported on hydroxyapatite coated Nio.sZno.sFe2O4 magnetic nanoparticles （Nio.sZno.sFe2O4@Hap-Cs2CO3） was found to be magnetically separable, highly efficient, green and recyclable heterogeneous catalyst. The synthesized nanocatalyst has been characterized with several methods （FT-IR, SEM, TEM, XRD and XRF） and these analyzes confirmed which the cesium carbonate is well supported to catalyst surface. After full characterization, its catalytic activity was investigated in the synthesis of pyranopyrazole derivatives and the reactions were carried out at room temperature in 50：50 water/ethanol with excellent yields （88-95%）. More importantly, the Nio.5Zno.sFe204@Hap-Cs2CO3 was easily separated from the reaction mixture by external magnetic field and efficiently reused at least six runs without any loss of its catalytic activity. Thus, the developed nanomagnetic base catalyst is potentially useful for the green and economic production of organic compounds.

<i>In Silico</i>Experiments of Carbon Dioxide Atmosphere and Buffer Type Effects on the Biomimetic Coating with Simulated Body Fluids

The formation of calcium phosphate phases is extremely important in a biomedical engineering context. These phosphates are used in many applications, such as grafts, drug-delivery processes and evaluation of the bioactivity of metallic surfaces. Considering this scenario, it is useful to evaluate the thermodynamic conditions for the precipitation of phosphates of biomedical interest, mainly hydroxyapatite. In this work, we investigate the effects of two important factors using a thermodynamic framework: 1) carbon dioxide partial pressure;and 2) buffer type (2-Amino-2-hydroxy- methyl-propane-1,3-diol, known as TRIS and 2-[4-(2-hydroxyethyl)piperazin-1-yl] ethanesulfonic acid, also called HEPES), on the driving force behind the precipitation of calcium phosphates in simulated body fluids. The in silico results show that the pH value is governed by carbon dioxide content, as expected to occur in vivo. Moreover, the buffers can deplete the free calcium available in solution and, consequently, can cause difficulties in the calcium phosphate precipitation.

Fabrication and Characterization of Hierarchically Nanostructured Porous Carbonated Hydroxyapatite Coatings

Hierarchically nanostructured porous carbonated hydroxyapatite coatings (HNPCs) on Ti6Al4V substrate were fabricated by a two-stage application route: fabrication of nacre coatings (NCs) on Ti6Al4V substrate by electrophoretic technique, and conversion of NCs to HNPCs in a phosphate buffer solution (PBS) by microwave irradiation method. Their samples were characterized by using XRD, FT-IR, SEM, TEM, and N2 adsorption-desorption isotherms. The results show that the microwave irradiation technique improves obviously the conversion rate of NCs to HNPCs as compared with conventional method. After soaking the NCs in the PBS, calcium ions are released from the nacre particles and react with phosphate ions to form carbonated hydroxyapatite nanoparticles. These nanoparticles aggregate to form the plate-like carbonated apatite. The mesopores with a size of about 3.9 nm and macropores with the diameters of 1~4μm exist within and among the carbonated apatite plates, respectively. Simulated body fluid immersion tests reveal that the HNPCs have a good in vitro bioactivity.

Adhesion of bone marrow mesenchymal stem cells on porous titanium surfaces with strontium-doped hydroxyapatite coating

Objective: To determine the adhesion behavior of bone marrow mesenchymal stem cells(MSCs) on a titanium surface with a nanostructured strontium-doped hydroxyapatite(Sr-HA) coating. Methods: Sr-HA coatings were applied on roughened titanium surfaces using an electrochemical deposition method. Primary cultured rat MSCs were seeded onto Sr-HA-, HA-coated titanium, and roughened titanium surfaces, and they were then cultured for 1,6, and 24 h.3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT) assay was used to determine the metabolic condition of the cells. Scanning electron microscopy(SEM) was used to observe the cell morphology. The cytoskeletal structure was analyzed using fluorescence actin staining to characterize cell adherence. Quantitative real-time reverse transcription polymerase chain reaction(RT-q PCR) was used to analyze the gene expression levels of FAK(focal adhesion kinase), vinculin, integrin β1, and integrin β3 after culturing for 24,48, and 72 h. Results: MSCs cultured on the Sr-HA surface showed better cell proliferation and viability. Improvement of cell adhesion and structural rearrangement of the cytoskeleton were observed on the Sr-HA surface. The gene expression of FAK, vinculin, integrin β1, and integrin β3 was also elevated on the Sr-HA surface. Conclusions: Cell viability, adhesion, cell morphology, and the cytoskeletal structure were all upregulated considerably by the titanium surface modified with a Sr-HA coating.