Dynamic study of calcium phosphate formation on porous HA/TCP ceramics

Bone-like apatite formation on porous calcium phosphate ceramics was investigated in static simulated body fluid (SBF) and dynamic SBF at different flowing rates. The results of a 14-day immersion in static SBF showed that the formation of bone-like apatite occurred both on the surface and in the pores of the samples. When SBF flow at the physiological flow rate in muscle (2 ml/100 ml min1), bone-like apatite could be detected only in internal surface of the pores of samples. The result that bone-like apatite formation could only be found in the pores when SBF flown at physiological flow rate was consistent with that of porous calcium phosphate ceramics implanted in vivo: osteoinduction was only detected inside the pores of the porous calcium phosphate ceramics. This result implicates that the bone-like apatite may play an important role in the osteoinduction of Ca-P materials. The dynamic model used in this study may be better than usually used static immersion model in imitating the physiological condition of bone-like apatite formation. Dynamic SBF method is very useful to understand bone-like apatite formation in vivo and the mechanism of ectopic bone formation in calcium phosphate ceramics.     

Dynamic study of calcium phosphate formation on porous HA/TCP ceramics

Bone-like apatite formation on porous calcium phosphate ceramics was investigated in static simulated body fluid (SBF) and dynamic SBF at different flowing rates. The results of a 14-day immersion in static SBF showed that the formation of bone-like apatite occurred both on the surface and in the pores of the samples. When SBF flowed at the physiological flow rate in muscle (2 ml/100 ml⋅min), bone-like apatite could be detected only in internal surface of the pores of samples. The result that bone-like apatite formation could only be found in the pores when SBF flowed at physiological flow rate was consistent with that of porous calcium phosphate ceramics implanted in vivo: osteoinduction was only detected inside the pores of the porous calcium phosphate ceramics. This result implicates that the bone-like apatite may play an important role in the osteoinduction of Ca-P materials. The dynamic model used in this study may be better than usually used static immersion model in imitating the physiological condition of bone-like apatite formation. Dynamic SBF method is very useful to understand bone-like apatite formation in vivo and the mechanism of ectopic bone formation in calcium phosphate ceramics.     

Mechanical examinations on dental implants with porous titanium coating

Due to its good biocompatibility, porous titanium is an interesting material for biomedical applications. Bone tissue can grow inside the porous structure and maintain a long and stable connection between the implant and the human bone. To investigate its long term stability, the mechanical behavior of porous titanium was tested under static and dynamic conditions and was compared to human bone tissue. A promising application of this material is the coating of dental implants. A manufacturing technique was developed and implants were produced. These implants were fatigue tested according to modified ISO 14801 and the micro structural change was examined. The fatigue test was statically modeled using finite element analysis (FEA). The results show that the implants resist a continuous load which is comparable to the loading conditions in the human jaw. The experiments show that the porous titanium has bone-like mechanical properties. Additionally the porous titanium shows an anisotropic behavior of its mechanical properties depending on the alignment of the pores. Finally, other potential applications of porous titanium are outlined.     

Effect of MgO contents on the mechanical properties and biological performances of bioceramics in the MgO–CaO–SiO2 system

The aim of this research was to investigate the effect of the chemical composition on the mechanical properties, bioactivity, and cytocompatibility in vitro of bioceramics in the MgO–CaO–SiO₂ system. Three single-phase ceramics (merwinite, akermanite and monticellite ceramics) with different MgO contents were fabricated. The mechanical properties were tested by an electronic universal machine, while the bioactivity in vitro of the ceramics was detected by investigating the bone-like apatite-formation ability in simulated body fluid (SBF), and the cytocompatibility was evaluated through osteoblast proliferation and adhesion assay. The results showed that their mechanical properties were improved from merwinite to akermanite and monticellite ceramics with the increase of MgO contents, whereas the apatite-formation ability in SBF and cell proliferation decreased. Furthermore, osteoblasts could adhere, spread and proliferate on these ceramic wafers. Finally, the elongated appearance and minor filopodia of cells on merwinite ceramic were more obvious than the other two ceramics.     

磷酸钙陶瓷在不同动物的模拟体液中类骨磷灰石的形成研究

根据人、狗、猪、猴和兔五种动物体液的钙离子浓度和pH值的差异,配制了不同组分的模拟体液,将孔壁致密和有微孔的多孔磷酸钙陶瓷分别浸泡在这些模拟体液中,研究陶瓷孔隙表面类骨磷灰石的形成情况.结果表明:在模拟体液中浸泡14天后,孔壁致密的材料未见有类骨磷灰石层形成;有微孔的多孔磷酸钙陶瓷,材料孔壁表面(包括陶瓷表面较深孔隙)有类骨磷灰石层的形成,这与体内植入实验观察到的类骨磷灰石层形成和诱导成骨情况相似,可以推论类骨磷灰石层的形成的确是骨诱导的先决条件.随着钙离子浓度的增加,其孔壁表面类骨磷灰石层的形成也更为均匀,但类骨磷灰石生长快慢顺序与动物组织学观察到的骨诱导性高低的次序不完全一致.     

Effect of graphene nanoplatelet addition on properties of thermo-responsive shape memory polyurethane-based nanocomposite

Graphene nanoplatelet (GNP) was added as reinforcement to novel blend of polyurethane (PU) and poly(ethylene-co-ethyl acrylate-co-maleic anhydride) (PEEAMA) with an intended application for heat-induced shape recovery. Objective of the study was to explore the effect of GNP addition on morphology, mechanical properties, and heat-induced shape recovery. Physical inter-linking of GNP platelets to blend components directed unique self-assembled pattern. Neat blend revealed gyroid morphology while addition of functional GNP initiated well-defined double gyroid pattern on folds of primary gyroid structure. At a concentration of 5 wt.% GNP, the nanocomposite film showed highest improvement in tensile strength (54%) and Young's modulus (57%) as compared to blend. The nanocomposite samples showed shape recovery phenomenon at T_m (60°C). In 5 wt.% GNP-loaded nanocomposite, the original shape of samples was nearly 96% recovered within 7 s.     

孔径对球体开孔泡沫铝压缩及吸能性能的影响

目的 研究在准静态压缩过程中,不同孔径（泡沫铝内部胞孔的直径）对球体开孔泡沫铝压缩性能及吸能性能的影响。方法 针对3种不同孔径的泡沫铝试样进行准静态压缩实验。通过准静态压缩试验得出泡沫铝的应力-应变曲线,并通过应力-应变曲线计算得到吸能-应变曲线。结果 当泡沫铝孔径从5 mm增加到9 mm时,球形孔开孔泡沫铝的屈服强度增加了4.6862 MPa,最大吸能效率由24.45%提升到27.71%,力学性能和吸能性能均得到提升。结论 泡沫铝的压缩性能和吸能性能随着球体开孔泡沫铝孔径的增加而增强。     

Mechanical properties of the double gyroid phase in oriented thermoplastic elastomers

We investigate the mechanical properties of triblock copolymers with oriented double gyroid (DG) morphology in poly(styrene-b-isoprene-b-styrene) (SIS) triblock copolymers by deforming textured samples along both the [111] direction and transverse to this direction. The modulus anisotropy for the two directions of this cubic material is approximately a factor of 5. Deformation along [111] causes the sample to form a distinct neck and draw, while the deformation in the transverse direction proceeds without neck formation. In addition, the mechanical hysteresis of the [111] stretch is 50% higher than that transverse to the [111] direction. Upon unloading and annealing above the polystyrene Tg, the DG structure recovers fully, both macroscopically and microscopically. The mechanical properties of the DG are compared to those of the classical block copolymer morphologies to gain insight into the deformation mechanism.     

Insight into the effects of pore size and distribution on mechanical properties of austenite stainless steels

While conventional Gibson–Ashby models provide a general insight into how elastic modulus and yield strength degrade with increasing overall porosity in materials, very limited work has investigated the effects of pore size and distribution on the mechanical properties of metals. One key question is whether and how pores can be utilized for improved mechanical properties rather than being eliminated or minimized for full densification. To fill in this gap, austenitic stainless steel 316L samples with intentional pores of varying diameters and distributions were fabricated by spark plasma sintering using starting powders with different morphologies. Characterization of pore features was not limited to the total volume percentage but also addressed the pore size, shape, interpore spacing, and pore surface area. The mechanical properties of those samples were investigated at multiple length scales to investigate the effect of pore characteristics, including macro-scale compression testing, Vickers micro-indentation, nanoindentation, and nanoscratch. Results suggested incorporating submicron pores improved both the yield strength and strength to weight ratio. The sample containing submicron pores represented an outlier in the classical Hall–Petch relation between yield strength and grain size, and it achieved a yield strength of 482 MPa, compressive strength of?~?1.4GPa at a strain of 0.3 without fracture, and a specific yield strength of 67.7 MPa cm³/g. The mechanism was attributed to local stiffening and (Cr, Mn)-rich precipitates surrounding the submicron pores. It was discovered, for the first time, the specific yield strength and the pore diameter followed a Hall–Petch type correlation.

Graphical abstract

     

Multiscale Geometric Design Principles Applied to 3D Printed Schwarzites

Schwartzites are 3D porous solids with periodic minimal surfaces having negative Gaussian curvatures and can possess unusual mechanical and electronic properties. The mechanical behavior of primitive and gyroid schwartzite structures across different length scales is investigated after these geometries are 3D printed at centimeter length scales based on molecular models. Molecular dynamics and finite elements simulations are used to gain further understanding on responses of these complex solids under compressive loads and kinetic impact experiments. The results show that these structures hold great promise as high load bearing and impact‐resistant materials due to a unique layered deformation mechanism that emerges in these architectures during loading. Easily scalable techniques such as 3D printing can be used for exploring mechanical behavior of various predicted complex geometrical shapes to build innovative engineered materials with tunable properties.     

Challenges and Solutions for the Additive Manufacturing of Biodegradable Magnesium Implants

Due to their capability of fabricating geometrically complex structures, additive manufacturing (AM) techniques have provided unprecedented opportunities to produce biodegradable metallic implants—especially using Mg alloys, which exhibit appropriate mechanical properties and outstanding biocompatibility. However, many challenges hinder the fabrication of AM-processed biodegradable Mg-based implants, such as the difficulty of Mg powder preparation, powder splash, and crack formation during the AM process. In the present work, the challenges of AM-processed Mg components are analyzed and solutions to these challenges are proposed. A novel Mg-based alloy (Mg–Nd–Zn–Zr alloy, JDBM) powder with a smooth surface and good roundness was first synthesized successfully, and the AM parameters for Mg-based alloys were optimized. Based on the optimized parameters, porous JDBM scaffolds with three different architectures (biomimetic, diamond, and gyroid) were then fabricated by selective laser melting (SLM), and their mechanical properties and degradation behavior were evaluated. Finally, the gyroid scaffolds with the best performance were selected for dicalcium phosphate dihydrate (DCPD) coating treatment, which greatly suppressed the degradation rate and increased the cytocompatibility, indicating a promising prospect for clinical application as bone tissue engineering scaffolds.     

In vivo biological responses of plasma sprayed hydroxyapatite coatings with an electric polarized treatment in alkaline solution

The plasma sprayed hydroxyapatite coatings were post-treated by an electric polarized treatment in alkaline solution (PAS). The compositions, stabilities, surface charges, bone-like apatite formation abilities of the PAS coatings were investigated. The bioactivity of the PAS coatings was characterized in vivo. The results showed that the stabilities of the PAS coatings were improved because of the increased crystallinity and the decreased impurity phase. The bone-like apatite formation abilities were also improved after the PAS treatment because of the negative charges formed on the coating surfaces. Animal experiments showed that the PAS coatings could accelerate the initial fixation of the implant. The results indicated that the PAS is a promising post-treatment method to improve the biological properties of the plasma sprayed hydroxyapatite coatings.     

间接SLS金属件的树脂增强研究

间接选择性激光烧结制造的金属零件毛坯经脱脂和高温烧结,所得零件存在大量的孔隙,故其致密度和强度较差,本文采用改性环氧树脂对上述方法制造的零件进行致密化浸渗,并采用DSC、TGA和SEM分析方法研究了不同配比的树脂渗剂的浸渗及渗后零件的力学性能。结果表明,渗剂环氧树脂和酚醛树脂的比例为2∶1时,所得零件的性能最佳,此时最佳渗入温度和固化温度分别为100℃和160℃,渗入后零件的耐热温度达200℃,而且零件的致密度也得到提高,浸渗前后零件的拉伸强度分别为7.64MPa和29.51MPa。该方法对制造注塑模具有一定的参考价值。     

Tensile Properties of 3D-Projected 4-Polytopes: A New Class of Mechanical Metamaterial

In this article, we research the tensile behavior mechanical metamaterial based on the 3D projections of 4D geometries (4-polytopes). The specific properties of these mechanical metamaterials can be enhanced by more than fourfold when optimized within a framework powered by an evolutionary algorithm. We show that the best-performing metamaterial structure, the 8-cell (tesseract), has specific yield strength and specific stiffness values in a similar range to those of hexagonal honeycombs tested out-of-plane. The 8-cell structures are also cubically symmetrical and have the same mechanical properties in three orthogonal axes. The effect of structure is quantified by comparing metamaterial tensile strength against the Young's modulus of constituent solid material. We find that the strength-to-modulus value of the 8-cell structures exceeds that of the hexagonal honeycomb by 76%. The 5-cell (pentatope) and 16-cell (orthoplex) metamaterials are shown to be more effective under tensile loading than gyroid structures, while 24-cell (octaplex) structures display the least optimal structure-properties relationships. The findings presented in this paper showcase the importance of macro-scale architecture and highlight the potential of 3D projections of 4-polytopes as the basis for a new class of mechanical metamaterial.     

微波等离子体烧结多孔HA/β-TCP双相生物陶瓷的研究

针对常规马弗炉烧结钙磷生物陶瓷温度高、烧结时间长,制品晶粒粗、强度和生物学活性难于同时提高的问题,采用微波等离子体新技术烧结了多孔HA/β-TCP双相生物陶瓷。实验结果显示,和常规马弗炉烧结法相比,微波等离子体烧结可在极短的加热时间内,制得线收缩率较大,晶粒尺寸小,抗压强度更大的多孔HA/β-TCP双相生物陶瓷。通过模拟体液的浸泡实验发现,其类骨磷灰石形成量也明显多于常规马弗炉烧结。这预示微波等离子体烧结是一种既能提高钙磷材料的力学强度,同时又可能增加其生物学活性的新烧结方法。     

Fabrication and characterization of magnesium–fluorapatite nanocomposite for biomedical applications

Recent studies indicate that there is a high demand for magnesium alloys with adjustable corrosion rates, suitable mechanical properties, and the ability for precipitation of a bone-like apatite layer on the surface of magnesium alloys in the body. An approach to this challenge might be the application of metal matrix composites based on magnesium alloys. The aim of this work was to fabricate and characterize a nanocomposite made of AZ91 magnesium alloy as the matrix and fluorapatite nano particles as reinforcement. A magnesium–fluorapatite nanocomposite was made via a blending–pressing–sintering method. Mechanical, metallurgical and in vitro corrosion measurements were performed for characterization of both the initial materials and the composite structure. The results showed that the addition of fluorapatite nano particle reinforcements to magnesium alloys can improve the mechanical properties, reduce the corrosion rate, and accelerate the formation of an apatite layer on the surface, which provides improved protection for the AZ91 matrix. It is suggested that the formation of an apatite layer on the surface of magnesium alloys can contribute to the improved osteoconductivity of magnesium alloys for biomedical applications.     

Influence of cell aspect ratio on architecture and compressive strength of titanium foams

Titanium foams have been of interest in dental and orthopedic implants over the past few decades on account of their excellent mechanical properties, chemical stability, and biocompatibility. A powerful tool, X-ray computed microtomography was used to measure quantitatively the effect of pore morphology on foam architecture. Mechanical properties of titanium foams with varying pore structure were investigated. Aspect ratio of the pores was quantitatively demonstrated to affect strength, degree of anisotropy and strain-rate sensitivity of the produced titanium foams. Needle-like pored foams showed 30-55% lower strength when compared to the foams having lower aspect ratio pores. Lower aspect ratio pored foams were 3-11%, higher aspect ratio pored foams were 17-34% weaker in the direction parallel to the compaction direction when compared to the perpendicular one. High aspect ratio pores also resulted in more pronounced strain-rate sensitivity.     

多孔PZT95/5铁电陶瓷的机械性能和铁电性能研究

采用添加造孔剂的方法制备多孔锆钛酸铅(PZT95/5)铁电陶瓷, 研究了孔结构包括孔隙率、孔径及孔形状对多孔PZT95/5陶瓷机械性能和电性能的影响及机理, 并揭示多孔PZT95/5陶瓷微观结构、机械性能和铁电性能的内在联系。研究表明: 孔隙率的增加降低了多孔PZT95/5陶瓷的声阻抗, 改善了陶瓷与封装材料的声阻抗匹配. 孔隙率增加, 多孔PZT95/5陶瓷的屈服应力和剩余极化强度降低, 矫顽场强增大。孔结构对多孔PZT95/5陶瓷屈服应力的影响可由应力集中理论解释; 多孔PZT95/5陶瓷剩余极化强度随孔结构的变化可用内应力结合空间电荷理论加以解释。     

高温等静压后处理液相烧结SiC陶瓷的结构与性能表征

本文研究了高温等静压（HIP）后处理工艺对液相烧结SiC陶瓷的显微结构及力学性能的影响．实验表明,HIP后处理的效果随烧结助剂的不同及液相烧结温度的变化而改变．Ar气氛条件下的HIP后处理可以提高液相烧结SiC的密度,减少或消除内部气孔等结构缺陷,但不引起晶粒的长大．N₂条件下的HIP后处理除了具有Ar－HIP后处理的优点外,由于表面SiC与N₂之间的反应生成的Si₃N₄可以有效地改善表面状态,从而达到表面改性,提高SiC陶瓷的力学性能．结构分析表明,经N₂-HIP后处理,表面氮化层中晶粒细小,结构致密．同时,HIP后处理的效果还受液相烧结SiC陶瓷显微结构的影响,当液相烧结SiC的烧结温度较低,晶粒较细时,经HIP后处理,尤其是N₂-HIP后处理,强度和韧性均有较大幅度的提高．     

气孔对1420铝锂合金焊接接头力学性能的影响

采用不同的清理方法揭示焊接接头气孔的产生情况，并且研究了气孔对接接头力学性能的影响。