Effect of ball milling process on the microstructure of titanium-nanohydroxyapatite composite powder

Titaninm-nanohydroxyapatite （Ti-nHA） composite powders, composed of titanium with 10 vol.% and 20 vol.% of nano-hydroxyapatite, were milled in a planetary ball mill using alcohol media to avoid excessive heat. XRD and SEM were performed for characterization of the microstructure, and the homogeneity of Ti/HA nanocomposite powder was evaluated by EPMA with prolonged ball milling time. The results show that under the condition of wet milling, the grain size of Ti-nHA composite powders is decreased with the increase in ball milling time and the amount of the addition of nHA. While for milling of 30 h, the nanocomposite powder with free structure, which consists of the nano-hydroxyapatite （nHA） particles and titanium （Ti） phase, is obtained. Three stages of milling can be observed from the dement mapping of Ti, Ca, and P by EPMA; meanwhile, it is found that the nHA would be more homogenously distributed after milling for 30 h.     

In vitro degradation and cytotoxicity of Mg-5Zn-0.3Ca/nHA biocomposites prepared by powder metallurgy

Mg-5Zn-0.3Ca/nHA biocomposites were prepared from pure Mg, Zn, Ca and nano-hydroxyapatite (nHA) powders by powder metallurgy method. The effect of various mass fractions of nHA (1%, 2.5%, 5%) as reinforcement on the corrosion properties of Mg-5Zn-0.3Ca alloy was investigated. The corrosion resistance of biocomposite samples was investigated by immersion tests and electrochemical techniques in SBF solution. The results showed that the corrosion resistance of Mg alloy was improved by adding 1% and 2.5% nHA. Bioactive nHA motivated the formation of stable phosphate and carbonate layers on surface and improved corrosion resistance of nanocomposites. However, addition of large contents of nHA in Mg alloy as reinforcement increased the density of this precipitated layer, so gases produced from localized corrosion were accumulated underneath this layer and decreased its adhesiveness and lowered its corrosion resistance. Indirect cytotoxicity evaluation for Mg alloy and its nanocomposites also showed that their extraction was not toxic and nanocomposite with 1% nHA indicated almost similar behavior as negative control.     

仿生纳米纤维支架促进骨组织再生

人口老龄化,疾病以及交通事故等造成大量的人体骨组织损伤和丢失。如何实现骨组织缺损的快速修复与再生成为临床医学研究的重要课题和目标,而生物医用材料在其中发挥着极其重要的作用。目前临床上常用的骨组织修复材料如自体骨、异体骨、合成材料（金属,陶瓷,高分子）等都存在各种各样的问题,无法实现大规模的应用和骨组织的快速有效再生。而骨组织工程学科研究多孔支架结合细胞和生长因子来实现骨组织再生,以鳃决骨科临床面临的问题为目的。最近十多年来,三维纳米纤维支架由于可以仿天然细胞外基质的结构和形态而显示出较强的促进细胞增殖、成骨分化以及骨组织修复再生的能力。主要综述具有仿生的纳米纤维及其复合支架材料的制备技术以及他们在增强细胞功能、干细胞成骨分化、及其骨组织再生中的应用。     

Microstructures and Properties of Cold Spray Nanostructured HA Coatings

Nanostructured hydroxyapatite (nHA) coatings on implant surface are highly desirable owing to their excellent osteoconductive properties in association with intrinsic small crystals. Low processing temperature of cold spray makes it an ideal technique to prepare nHA coatings with nanostructured feedstock. This work demonstrated that dense and thick nHA coatings were achievable by cold spraying nanostructured feedstock onto TC4 alloy surface. Coating formation mechanisms were explored by investigating the deposition of individual particles. Microstructures, mechanical profiles and biological properties of the coatings were comprehensively investigated. A porous Ti buffer layer significantly enhanced the bonding between nHA coatings and the substrate. As-deposited nHA coatings exhibited a high wear resistance when slid against polyurethane or polycarbonate and a strong apatite-forming ability when being immersed in simulated body fluid (SBF). Findings of this work will contribute to a comprehensive understanding of building mechanisms, structures and properties of cold sprayed nHA coatings.     

Microstructure,Mechanical Properties and Corrosion Behavior of Porous Mg-6 wt.% Zn Scaffolds for Bone Tissue Engineering

Porous Mg-based scaffolds have been extensively researched as biodegradable implants due to their attractive biological and excellent mechanical properties. In this study, porous Mg-6 wt.% Zn scaffolds were prepared by powder metallurgy using ammonium bicarbonate particles as space-holder particles. The effects of space-holder particle content on the microstructure, mechanical properties and corrosion resistance of the Mg-6 wt.% Zn scaffolds were studied. The mean porosity and pore size of the open-cellular scaffolds were within the range 6.7-52.2% and 32.3-384.2 µm, respectively. Slight oxidation was observed at the grain boundaries and on the pore walls. The Mg-6 wt.% Zn scaffolds were shown to possess mechanical properties comparable with those of natural bone and had variable in vitro degradation rates. Increased content of space-holder particles negatively affected the mechanical behavior and corrosion resistance of the Mg-6 wt.% Zn scaffolds, especially when higher than 20%. These results suggest that porous Mg-6 wt.% Zn scaffolds are promising materials for application in bone tissue engineering.     

基于SLM的Ti-6Al-4V人工骨支架的结构设计

设计了6种Ti-6Al-4V人工骨支架,利用SLM(选择性激光熔化)进行制备。采用万能材料实验机结合高速摄像机分析支架的压缩过程,并利用Ansys进行分析。结果表明：支架的立柱直径对支架的力学性能参数影响较大,横梁直径对其影响较小;在相同高度下,支架横梁直径增大、层数增多或立柱直径增大,均使结构长径比减小,使结构稳固且支架承载能力提高;支架的力学性能应与周围骨组织相匹配,经过分析,3种结构的支架力学性能参数与人体股骨相近,故可作为股骨的人工骨支架。     

Reaction kinetics and properties of VN/CrN nanocomposite via microwave in situ synthesis

VN/CrN nanocomposite was prepared by microwave in situ synthesis for the first time. The reaction kinetics and structure evolution in the preparation of the nanocomposite were researched, and the composite was applied to the ceramic bond. VN/CrN nanocomposite can be prepared at a temperature about 400 °C lower than that of traditional synthesis methods. The structure evolution of the nanocomposite follows the order from oxides to carbides to nitrides. The flexural strength of ceramic bond can be improved obviously by adding appropriate amount of the nanocomposite. The activation energies of VN and CrN reactions are 29.18KJ/mol and 41.57 kJ/mol, respectively.     

钛合金变形Gyroid单元梯度多孔结构设计与分析

研究一种具有径向和轴向孔径梯度的变形Gyroid单元多孔结构参数化设计方法,采用激光选区熔化成形(selective laser melting, SLM)技术,制备出孔隙率为60%和75%的钛合金变形Gyroid单元梯度多孔结构样件。使用有限元法(finiteelementmethod,FEM)对4组梯度多孔支架模型及2组均质模型进行静力学仿真分析,对制备的钛合金梯度多孔样件进行力学性能测试,并与已测试过的均质样件进行力学性能对比分析。有限元计算结果与力学性能试验结果共同表明：变形Gyroid单元多孔结构力学性能随孔隙率的升高而降低,孔隙率相同时,径向梯度多孔支架力学性能优于均质多孔支架,更适用于皮质骨的骨缺损修复,轴向梯度多孔支架力学性能相比均质多孔支架有所减弱,更适用于松质骨。     

Novel fabrication of forsterite scaffold with improved mechanical properties

In this study, the macroporous forsterite scaffolds with highly interconnected spherical pores, with sizes ranged from 50 to 200 μm have been successfully fabricated via gelcasting method. The crystallite size of the forsterite scaffolds was measured in the range 26-35 nm. Total porosity of different bodies sintered at different sintering temperatures was calculated in the range 81-86%, while open porosity ranges from 69 to 78%. The maximum values of compressive strength and elastic modulus of the prepared scaffolds were found to be about 2.43 MPa and 182 MPa, respectively, which are close to the lower limit of the compressive strength and elastic modulus of cancellous bone and the compressive strength is equal to the standard for a porous bioceramic bone implant (2.4 MPa). Transmission electron microscopy analyses showed that the particle sizes are smaller than 100 nm. In vitro test in the simulated body fluid proved the good bioactivity of the prepared scaffold. It seems that, the mentioned properties could make the forsterite scaffold appropriate for tissue engineering applications, but cell culture and in vivo tests are needed for more confidence.     

纳米羟基磷灰石/壳聚糖-明胶复合支架材料缓释基因的研究

用冷冻干燥法制备不同比例的纳米羟基磷灰石/壳聚糖-明胶(n-HA/CS-Gel)三维多孔支架材料,加入含骨形态发生蛋白-2(BMP-2)基因的质粒后再次冷冻干燥,制成具有基因缓释功能的组织工程支架材料.对支架材料的形貌结构、力学性能、体外降解特性、质粒的体外释放特性及质粒完整性进行检测.结果显示:纳米羟基磷灰石均匀分散在支架材料中,随着其含量的增加,孔隙率减少,抗压强度提高,在体外降解速度减慢.质粒DNA在体外1～3d快速释放,并能够维持释放5周以上,随着纳米羟基磷灰石含量的增加,释放时间延长,释放出的质粒DNA能够保持完整性.具有基因缓释功能的n-HA/CS-Gel支架材料是一种有望用于临床的新型骨组织工程支架材料.     

Preparation and Oxidation of Novel Electrodeposited Cu–Ni–Cr Nanocomposites

The poor oxidation resistance of Cu-base alloys limits their applications at high temperatures, and it cannot be improved by conventional Cr alloying because that requires an extremely high Cr content. In this work a chromia scale has been formed on novel Cu-base nanocomposites which contain much less chromium. Cu–Ni–Cr nanocomposites, with the weight percentage ratio of Cu/Ni ≈1 and various amounts of Cr, were produced by co-electrodeposition of Cu–Ni alloy with Cr nanoparticles which subsequently acted as “seeds” for chromia formation. The results of oxidation tests in air at 800°C showed that only 15 wt.% Cr in the nanocomposite was required to form an external chromia scale. Furthermore, the scale consisted only of chromia rather than the duplex scales which form on the conventional alloy even when it contains significantly more chromium.     

Electrochemical deposition of octacalcium phosphate micro-fiber/chitosan composite coatings on titanium substrates

Calcium phosphate/chitosan composites have been extensively studied as bone substitutes, tissue engineering scaffolds, or bone cements. In the present study, we have prepared octacalcium phosphate (OCP) micro-fiber/chitosan composite coatings through an electrochemical deposition method. OCP coatings with microporous structure, which are woven by micro-fibers with 20-30 μm in length and 0.1-1 μm in width, have a good ability to incorporate chitosan. This novel OCP micro-fiber/chitosan composite coating could have broad applications in the biomedical engineering.     

多孔钛骨组织工程支架设计及孔结构表征

针对目前骨组织工程支架微孔结构难以准确设计制备的问题,提出了一种基于点云的参数化建模+3D打印新方法。通过提取cube(C)、diamond(D)、gyroid(G)3种结构的型面函数点云数据,完成对不同孔结构特征的参数化建模。通过对模型有限元力学分析,对不同孔结构特征的多孔钛骨组织支架进行力学设计与订制。借助激光选区熔融(SLM)3D打印技术,完成对不同孔特征的骨组织支架快速成型。对多孔钛骨组织支架进行了相关材料学表征,包括孔结构表征与力学性能测试。结果表明:参数化模型的快速成型制造,能够有效地设计制备钛合金骨组织工程支架的孔结构特性,且可有效设计订制支架的力学性能,从仿生的角度实现多孔钛合金骨组织工程支架生物学功能的设计优化。     

钽涂层多孔钛合金支架的制备与表征

钽金属是一种理想的医用金属材料,能够与人体软/硬组织发生整合。利用化学气相沉积方法,在可控多孔结构的Ti6Al4V合金支架表面沉积涂覆钽金属涂层,使其同时具备理想的三维孔隙结构和力学相容性,以及钽金属优异的生物学性能。研究结果显示,多孔钛合金支架表面涂层前后色泽发生明显变化,涂层后支架呈现钽金属色泽。扫描电镜和XRD分析进一步证明了多孔钛合金支架表面沉积物为钽金属。与美国Zimmer公司生产的多孔钽小梁金属相比,钽涂层多孔钛合金支架具备与人体皮质骨更相似的弹性模量和抗压强度,是一种理想的骨修复替代物。     

NiTi with 3D-interconnected microchannels produced by liquid phase sintering and electrochemical dissolution of steel tubes

A process was developed for fabricating 3D fully interconnected microchannels in superelastic NiTi-Nb for bone implant applications by combining spaceholder powder metallurgy and liquid-phase sintering. Prealloyed NiTi powders were blended with 3.1 at.% Nb and cold-pressed around a 3D scaffold of carburized steel tubes acting as space-holders. The tubes were then electrochemically dissolved to form orthogonally interconnected microchannels with 400 μm diameter and ∼34% volume fraction. Finally, the powder preform was heated to 1185 °C to form a quasi-binary NiTi-Nb eutectic liquid, which liquid-phase-sintered the NiTi powders without filling the microchannels. The resulting continuously bonded matrix contains an additional 16% porosity, for a total structure porosity of ∼50%. NiTi-Nb micro-architectured structures have excellent potential as bone implant scaffolds due to the high versatility in channel size, fraction, and spatial arrangement. Fully interconnected 3D microchannels also increase fluid transport within the scaffold, assisting in nutrient delivery and waste transport to and from cells deep within the scaffold.     

Microstructure ofin situ MoSi2/SiC nanocomposite coating formed on Mo substrate by displacement reaction

The microstructure of an in-situ Mosi₂/β-SiC nanocomposite coating formed by the solid-state displacement reactions of Si deposited by chemical vapor deposition (CVD) with Mo-carbide layers at 1100°C, which had previously been formed on the surface of a Mo substrate by a CVD process, was investigated. The Mo-carbide layers formed by the simultaneous CVD of Mo and carbon at 900°C for 5 h using a gas mixture of C₂H₄−MoCl₅−Ar consisted of two layers, an inner layer of Mo₂C and an outer layer of MoC. While the monolithic MoSi₂ coating showed a typical colummar microstructure perpendicular to the Mo substrate, the MoSi₂/β-SiC nanocomposite coating formed by the solid-state displacement reactions between the Mo-carbide layers and Si was composed of equiaxed MoSi₂ grains with an average size of 150–500 nm and β-SiC particles with an average size of 80–105 nm. The β-SiC particles exhibited an oblate-spheroidal shape and were located mostly at the grain boundaries of MoSi₂. The volume percentage of β-SiC particles ranged from 18.5 to 29.2% with respect to the carbon concentration in Mo-carbide layers.     

Antibacterial Property of Cold-Sprayed HA-Ag/PEEK Coating

The antibacterial behavior of HA-Ag (silver-doped hydroxyapatite) nanopowder and their composite coatings were investigated against Escherichia coli (DH5α). HA-Ag nanopowder and PEEK (poly-ether-ether-ketone)-based HA-Ag composite powders were synthesized using in-house powder processing techniques. Bacteria culture assay of HA-Ag nanopowder and their composite powders displayed excellent bacteriostatic activity against E. coli. The antibacterial activity increased with increasing concentration of HA-Ag nanoparticle in these composite powders. These nanocomposite powders were subsequently used as feedstock to generate antibacterial coatings via cold spray technology. The ratios of HA-Ag to PEEK in their composite powders were 80:20, 60:40, 40:60, and 20:80 (wt.%). Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out using FESEM/EDX and XRD. Antibacterial nanocomposite HA-Ag/PEEK coatings were successfully deposited using cold spraying parameters of 11-12 bars at preheated air temperature between 150 and 160 °C. These as-sprayed coatings of HA-Ag/PEEK composite powders comprising varying HA-Ag and PEEK ratios retained their inherent antibacterial property as verified from bacterial assay. The results indicated that the antibacterial activity increased with increasing HA-Ag nanopowder concentration in the composite powder feedstock and cold-sprayed coating.     

Semi-solid casting (SSC) of zinc alloy nanocomposites

An innovative casting method that combines semi-solid casting (SSC) and metal matrix nanocomposite (MMNC) technology was successfully demonstrated. The method uses the grain refining properties of the nanoparticles in the MMNC to produce slurry with the appropriate globular structure for semi-solid casting. In this way no additional material processing or mechanical agitation is necessary to achieve the desirable slurry microstructure. The grain refining attributes of the nanoparticles were shown to stem from the promotion of nucleation in the solidifying matrix alloy. Differential scanning calorimetry (DSC) showed a reduced undercooling necessary for nucleation owing to the nucleation catalytic potency of the nanoparticles. Using this method zinc alloy AC43A nanocomposite with 0.5 wt.% SiC β nanoparticle additions were cast at a 30% solid fraction. The resulting castings showed increased ductility, reduced shrinkage, and increased strength compared to their monolithic liquid cast counterparts.     

Calcium phosphate scaffolds for bone repair

Calcium phosphates, with their chemical similarity to bone mineral, show biocompatibility with hard and soft tissues and offer massive potential for bone repair, both as scaffolds to be implanted directly into the defect and as structures for cell transplantation or to guide new bone growth in tissue engineering. This paper reviews the requirements and motivation for synthetic bone graft alternatives and the production routes for, particularly, hydroxyapatite porous scaffolds. It also considers the important role of substitution of ions such as silicate into calcium phosphates so as to more closely mirror the chemistry of bone mineral and to elicit specific biological responses.     

Ion beam assisted deposition of TiN-Ni nanocomposite coatings

Hard and tough nanocomposite coatings consisting of hard TiN nanograins embedded in a soft metallic intergranular phase of Ni have been produced using ion beam assisted deposition. The chemical composition has been obtained by Rutherford Backscattering and the microstructural properties: phases, grain size, and texture of the coatings have been investigated by X-Ray Diffraction. In the composition range 0-22.5 at.% Ni, δ-TiN is the only crystalline phase and Ni appears as an X Ray amorphous phase. The hardness increases up to a maximum of 41 GPa at ~ 7 at.% Ni which corresponds to a TiN crystallite size of ~ 8 nm and a Ni intergranular phase thickness of roughly 1 monolayer. It is shown that the hardness enhancement in TiN-Ni nanocomposite coatings is not correlated with residual stresses, but rather with the intrinsic properties of the nanostructure. An important improvement in wear resistance is obtained for the coatings exhibiting the highest toughness and not the highest hardness. These results show that ion assisted processing is an effective tool for producing dense TiN-Ni nanocomposite coatings and tailoring their structure and mechanical properties.