基于SLM的梯度多孔牙种植体力学特性

目的 确定既满足强度要求又能够有良好长期稳定性的梯度多孔牙种植体最佳孔隙值。方法 设计4组不同孔隙率(G30、G40、G50、G60)的梯度多孔结构样件及均质多孔样件S30,选区激光熔化(SLM)成型后通过准静态压缩试验对其力学性能进行研究,测量出样件的弹性模量和屈服强度。通过有限元分析评估不同孔隙率种植体及对应下颌骨组织的应力分布。结果 相较于实体钛合金结构(110 GPa),多孔结构的弹性模量(13.47~15.88 GPa)已完全符合人体自然骨组织(2~20 GPa)范围,多孔结构屈服强度(484.81~834.47 MPa)远高于皮质骨(180.5~211.7 MPa);梯度多孔结构样件弹性模量相较于均质多孔结构略有提升,屈服强度(834.47 MPa)比均质多孔结构样件(730.56 MPa)提高了约14%。梯度多孔种植体周围皮质骨最大等效应力值分布在43.362 9~45.015 4 MPa之间,松质骨最大等效应力值分布在4.756 58~ 5.055 6 MPa之间,完全满足2~60 MPa范围内的最大应力,适合骨组织生长。种植体与下颌骨之间的应力差值随着孔隙率的增大而逐渐变大,孔隙率为30%的TPMS–G型梯度多孔牙种植体与下颌骨应力差值最小,生物力学特性最佳,有利于形成稳定的骨整合。结论 通过试验及仿真模拟,确定了适用于种植体的最佳梯度多孔结构,既满足强度要求,又具有良好的长期稳定性。     

基于SLM的髋臼杯多孔结构设计与力学性能分析

目的 获得长期稳定性更优的医用多孔髋臼杯。方法 利用三周期极小曲面方法设计出更适合应用于髋臼杯的多孔结构,采用选区激光熔化方法进行加工成形。对样件进行测量得到其力学性能参数。对得到的弹性模量、屈服强度进行分析,得出不同结构的变形模型及设计参数对多孔结构力学性能的影响,选择力学性能和生物相容性均符合髋臼杯多孔需求的一组多孔结构。结果 制造出的多孔结构弹性模量为3.27~7.44 GPa,屈服强度为164.84~407.21 MPa。试验结果表明,TPMS设计的多孔结构力学性能优良,除了70%与75%孔隙率的P结构之外,均可以在力学性能上满足髋臼杯的制造。从变形模式看,P结构变形模式以拉伸为主,G结构与D结构为混合模式变形。其中,G结构设计参数对多孔样件的力学性能影响最大。结论 得到最适合制造髋臼杯多孔结构的是TPMS的G结构,并将G结构应用于髋臼杯的三维模型中。     

胞元结构准静态压缩力学行为及吸能特性研究

为探究结构构型和规格参数对胞元结构综合力学特性的影响,设计了7种体积相等、结构构型不同的胞元结构,开展了准静态压缩试验,得到了各胞元结构的变形破坏过程和应力应变关系,分析了胞元构型和壁厚变化对结构承载能力及能量吸收性能的影响,结果表明：内凹鼓形、内凹六边形、内凹弧形胞元结构均呈现出宏观负泊松比特性,外凸六边形、外凸鼓形、正方形胞元结构呈现出宏观正泊松比特性,外凸弧形胞元结构呈现出近似零泊松比特性;胞元结构的直立壁面和曲面(折线面)共同承担压缩载荷,直立壁面主要发生失稳变形,曲面(折线面)主要发生弯曲外张变形或弯曲回缩变形,直立壁面的失稳临界载荷和屈曲模式对结构承载力和平台应力起主导作用;在各个宏观正泊松比胞元中,外凸六边形胞元的结构承载能力较强,外凸鼓形胞元的结构吸能特性较好,在各个宏观负泊松比胞元中,内凹弧形胞元的结构承载能力和结构吸能特性均较好。     

负泊松比材料和结构的研究进展

该文提出一种多弧段曲边内凹可调泊松比新型胞元。通过调整弧角,可以设计得到正泊松比、零泊松比和负泊松比的胞元结构。利用能量法求得结构的等效泊松比与等效弹性模量解析表达式,所得结果与有限元结果吻合较好。基于提出的新型胞元构建多胞蜂窝结构,利用数值方法讨论了低速和高速冲击作用下,正泊松比、零泊松比和负泊松比结构的冲击变形失效行为与单位质量能量吸收率。研究发现：低速冲击时,三种泊松比(正/零/负)结构的局部变形不同;高速冲击时,惯性效应使局部变形集中在冲击端,三种泊松比(正/零/负)结构的胞元变形模式不同。不论低速还是高速冲击,负泊松比结构都表现出优异的吸能效果。随着壁厚的增加,结构的吸能效果显著增强。     

多弧段曲边内凹蜂窝可调泊松比结构的力学性能研究

该文提出一种多弧段曲边内凹可调泊松比新型胞元。通过调整弧角,可以设计得到正泊松比、零泊松比和负泊松比的胞元结构。利用能量法求得结构的等效泊松比与等效弹性模量解析表达式,所得结果与有限元结果吻合较好。基于提出的新型胞元构建多胞蜂窝结构,利用数值方法讨论了低速和高速冲击作用下,正泊松比、零泊松比和负泊松比结构的冲击变形失效行为与单位质量能量吸收率。研究发现：低速冲击时,三种泊松比(正/零/负)结构的局部变形不同;高速冲击时,惯性效应使局部变形集中在冲击端,三种泊松比(正/零/负)结构的胞元变形模式不同。不论低速还是高速冲击,负泊松比结构都表现出优异的吸能效果。随着壁厚的增加,结构的吸能效果显著增强。     

SLM成形不同孔隙结构骨支架的仿真与实验研究

目的确定多孔骨骼支架的最佳结构及孔隙率。方法建立不同孔隙率、不同结构的18个多孔支架模型,通过有限元对多孔支架分别进行应力、应变模拟分析,通过选择性激光熔化(SLM)技术制备A,B,C这3种不同结构、孔隙率范围相近(65%～90%)、支架直径相同(300μm)的多孔316L支架。通过压缩试验、微观组织分析、X射线衍射试验(XRD)对不同多孔支架进行表面微观组织分析及力学性能研究。通过有限元模拟获得适用于人体皮质骨及松质骨的不同多孔支架结构及孔隙率。结果 A类结构孔隙率为90%的多孔骨骼支架弹性模量为7.5 GPa,抗压强度为11.62 MPa,与人体松质骨相吻合;B类结构孔隙率为80%的多孔骨骼支架弹性模量为18.9 GPa,抗压强度为127.01 MPa,与皮质骨相吻合。结论通过模拟及试验,确定了适用于不同骨骼部位的最佳结构及孔隙率,并且多孔结构有利于营养物质及血液的运输,保证了骨骼替代物的生物力学性能,有助于患者的康复。     

数值模拟碳纳米管增强铝基复合材料的力学性能

本文根据连续介质理论,采用代表性体积元的方法计算了碳纳米管增强铝基复合材料的力学性能。使用有限元软件ABAQUS对代表性体积元模型进行分析,研究了不同碳纳米管体积分数对复合材料弹性模量、屈服强度、泊松比及剪切模量的影响。结果表明碳纳米管体积分数对复合材料力学性能有显著影响,随着碳纳米管体积分数的增加,复合材料的弹性模量、屈服强度及剪切强度都明显提高,泊松比略有下降。     

新型负泊松比多孔吸能盒平台区力学性能

提出了一种具有负泊松比效应的汽车前纵梁吸能盒(NPRC)结构,通过对元胞平台区的失效模式和平台应力的分析,研究了此结构在失效时的力学性能,即等效弹性模量和平台应力在面内加载过程中均能得到一定程度的增强,表现出较好的能量吸收能力。根据NPRC元胞在平台区的力学模型,分别建立了发生弹性屈曲和塑性塌陷时的临界应力公式,得出塑性塌陷是该结构的主要失效模式。通过Matlab程序建立了NPRC元胞的参数化有限元模型,研究了元胞几何参数与平台应力的关系,即元胞的平台应力与长度系数和元胞夹角呈反比,与厚度系数呈正比。通过NPRC结构3×3样件的面内轴向准静态压缩实验验证了有限元分析结果,实验结果表明:NPRC样件等效负泊松比为-11.97,产生密实化现象,平台应力的峰值随着应变的增加逐渐增大,这对提高能量吸收性能具有重要的研究意义。     

内凹-反手性蜂窝结构的面内动态压溃性能研究

通过内凹六边形蜂窝与反手性蜂窝的结合得到一种内凹-反手性蜂窝(re-entrant anti-trichiral honeycomb,RATH)结构。利用显式动力有限元软件LS-DYNA对不同冲击速度和不同相对密度下内凹-反手性蜂窝的变形模式、抗冲击性能及拉胀性能进行了研究。结果表明,引入内凹结构可以显著增强中低速冲击时反手性蜂窝的局部“颈缩”现象,且在靠近内凹-反手性蜂窝的冲击端呈现出明显的“V形”变形带。与三边反手性蜂窝及传统蜂窝相比,内凹-反手性蜂窝的能量吸收性能更强,负泊松比效应更明显。基于一维冲击波理论,推导了内凹-反手性蜂窝的临界冲击速度和平台应力的经验公式。此外,讨论了冲击速度和胞壁厚度对平台应力及平台应变的影响。该研究将为混合变形机制拉胀蜂窝结构的设计提供新的思路。     

选区激光熔化成型正六方柱体多孔TC4合金结构及力学性能研究

为了改善植入物与人体骨的力学相容性,避免应力屏蔽效应,采用选区激光熔化(SLM)技术制备了多孔Ti6Al4V合金。利用扫描电子显微镜对多孔钛试样的孔隙结构进行分析,并且测试了试样的力学性能。结果表明,测得的多孔件孔隙率约为46%,与原始设计相比,孔隙率降低16%;孔隙率降低主要来自激光扫描路径、熔池形状与尺寸以及粘粉等因素的影响;多孔件纵截面(平行于堆积方向)的硬度值高于横截面(垂直于堆积方向)的硬度值;压缩实验显示,其弹性模量为8.8GPa、屈服强度为348 MPa,力学性能与理论预测值有偏差,但较相同的致密合金与自然骨更为接近。     

Porous bioceramics reinforced by coating gelatin

Porous bioceramics with high porosity for bone tissue engineering were fabricated by the foam impregnation technique, but their mechanical strength was poor, only a mean compressive strength of 1.04 ± 0.15 MPa and an mean elastic modulus of 0.1 GPa. In order to reinforce porous ceramics, the ceramic samples were immerged in 5% gelatin solution and gelatin coatings were formed on the inter-surface of their pores. It was found that the mean compressive strength value and the mean elastic modulus value of porous samples coated with gelatin were improved to 5.17 ± 0.17 MPa and 0.3 GPa respectively without sacrificing their porosity greatly. Moreover composite samples were not as fragile as sintered ceramics. The results indicated that the gelatin coatings on the inter-surface of pores reinforced porous bioceramics effectively.     

Physical and mechanical characterisation of 3D-printed porous titanium for biomedical applications

The elastic modulus of metallic orthopaedic implants is typically 6–12 times greater than cortical bone, causing stress shielding: over time, bone atrophies through decreased mechanical strain, which can lead to fracture at the implantation site. Introducing pores into an implant will lower the modulus significantly. Three dimensional printing (3DP) is capable of producing parts with dual porosity features: micropores by process (residual pores from binder burnout) and macropores by design via a computer aided design model. Titanium was chosen due to its excellent biocompatibility, superior corrosion resistance, durability, osteointegration capability, relatively low elastic modulus, and high strength to weight ratio. The mechanical and physical properties of 3DP titanium were studied and compared to the properties of bone. The mechanical and physical properties were tailored by varying the binder (polyvinyl alcohol) content and the sintering temperature of the titanium samples. The fabricated titanium samples had a porosity of 32.2–53.4 % and a compressive modulus of 0.86–2.48 GPa, within the range of cancellous bone modulus. Other physical and mechanical properties were investigated including fracture strength, density, fracture toughness, hardness and surface roughness. The correlation between the porous 3DP titanium-bulk modulus ratio and porosity was also quantified.     

Fabrication and characterization of porous Ti–7.5Mo alloy scaffolds for biomedical applications

Porous titanium and titanium alloys are promising scaffolds for bone tissue engineering, since they have the potential to provide new bone tissue ingrowth abilities and low elastic modulus to match that of natural bone. In the present study, porous Ti–7.5Mo alloy scaffolds with various porosities from 30 to 75 % were successfully prepared through a space-holder sintering method. The yield strength and elastic modulus of a Ti–7.5Mo scaffold with a porosity of 50 % are 127 MPa and 4.2 GPa, respectively, being relatively comparable to the reported mechanical properties of natural bone. In addition, the porous Ti–7.5Mo alloy exhibited improved apatite-forming abilities after pretreatment (with NaOH or NaOH + water) and subsequent immersion in simulated body fluid (SBF) at 37 °C. After soaking in an SBF solution for 21 days, a dense apatite layer covered the inner and outer surfaces of the pretreated porous Ti–7.5Mo substrates, thereby providing favorable bioactive conditions for bone bonding and growth. The preliminary cell culturing result revealed that the porous Ti–7.5Mo alloy supported cell attachment.     

Cancellous bone from porous T{i}6Al4V by multiple coating technique

A highly porous T{i}6Al4V with interconnected porous structure has been developed in our previous study. By using a so-called “Multiple coating” technique, the porous T{i}6Al4V can be tailored to resemble cancellous bone in terms of porous structure and mechanical properties. A thin layer of T{i}6Al4V slurry was coated on the struts of base porous T{i}6Al4V to improve the pore structure. After two additional coating, pore sizes ranged from 100 μm to 700 μm, and the porosity was decreased from ∼90% to ∼ 75%, while the compressive strength was increased from 10.3 ± 3.3 MPa to 59.4 ± 20.3 MPa and the Young's modulus increased from 0.8 ± 0.3 GPa to 1.8 ± 0.3 GPa. The pore size and porosity are similar to that of cancellous bone, meanwhile the compressive strength is higher than that of cancellous bone, and the Young's modulus is between that of cancellous bone and cortical bone. Porosity, pore size and mechanical properties can be controlled by the parameters in such multiple coating processes. Therefore the porous T{i}6Al4V with the characteristics of cancellous bone is expected to be a promising biomaterial for biomedical applications. Author to whom all correspondence should be addressed.     

Quasi-static Torsional Deformation Behavior of Porous Ti6Al4V alloy

Laser processed Ti6Al4V alloy samples with total porosities of 0%, 10% and 20% have been subjected to torsional loading to determine mechanical properties and to understand the deformation behavior. The torsional yield strength and modulus of porous Ti alloy samples was found to be in the range of 185-332 MPa and 5.7-11 GPa, respectively. With an increase in the porosity both the strength and the modulus decreased, and at 20% porosity the torsional modulus of Ti6Al4V alloy was found to be very close to that of human cortical bone. Further, the experiments revealed clear strain hardening and ductile deformation in all the samples, which suggests that the inherent brittleness associated solid-state sintered porous materials can be completely eliminated via laser processing for load bearing metal implant applications.     

Fabrication and characterization of porous Co–Cr–Mo/58S bioglass nano-composite by using NH4HCO3 as space-holder

In the present study, Co–Cr–Mo/58S porous nano-composites were successfully fabricated by the use of space-holder and powder metallurgy techniques. The cold compacted Samples were heated at 175 °C for 2 h and then was raised to 1250 °C and held for 2 h. Scanning electron microscope (SEM) and optical microscope (OM) images of porous samples showed interconnected, isolated pores and appropriate range of pore sizes. The results of compressive strength and Young's modulus were in the range of 33–566 MPa and 0.19–4.46 GPa, respectively. In particular, the compressive strength and Young's modulus at the porosity of 38.5% were found to be similar to those of bone. The SEM images, pH values and Fourier-transform infrared spectroscopy (FTIR) results showed that apatite crystallites were formed on the surface of sample with 38.5% porosity during immersion in simulated body fluid which revealed bioactivity of this sample. In vitro cytocompatibility of the sample with 38.5% porosity was evaluated and cell growth was examined. SEM images revealed that cells grew on the surface and inside the pores. The present investigation has shown that this porous nano-composite is a promising biomaterial for bone tissue engineering by virtue of its porous structure, appropriate mechanical properties, bioactivity and biocompatibility.     

Three‐Dimensional Printing of Complex‐Shaped Alumina/Glass Composites

Alumina/glass composites were fabricated by three‐dimensional printing (3DP?) and pressureless infiltration of lanthanum‐alumino‐silicate glass into sintered porous alumina preforms. The preforms were printed using an alumina/dextrin powder blend as a precursor material. They were sintered at 1600 °C for 2 h prior to glass infiltration at 1100 °C for 2 h. The influence of layer thickness and sample orientation within the building chamber of the 3D‐printer on microstructure, porosity, and mechanical properties of the preforms and final composites was investigated. The increase of the layer thickness from 90 to 150 µm resulted in an increase of the total porosity from ～19 to ～39 vol% and thus, in a decrease of the mechanical properties of the sintered preforms. Bending strength and elastic modulus of sintered preforms were found to attain significantly higher values for samples orientated along the Y‐axis of the 3D‐printer compared to those orientated along the X‐ or the Z‐axis, respectively. Fabricated Al₂O₃/glass composites exhibit improved fracture toughness, bending strength, Young's modulus, and Vickers hardness up to 3.6 MPa m^1/2, 175 MPa, 228 GPa, and 12 GPa, respectively. Prototypes were fabricated on the basis of computer tomography data and computer aided design data to show geometric capability of the process.     

Preparation,microstructure and mechanical properties of porous titanium sintered by Ti fibres

Open-cell porous Ti with a porosity ranging from 35 to 84% was successfully manufactured by sintering titanium fibres. The microstructure of the porous titanium was observed by SEM and the compressive mechanical properties were tested. By adjusting the spiral structure of the porous titanium, the pore size can be controlled in a range of 150–600 μm. With the increasing of the porosity, compressive yield strength and modulus decrease as predicated. However, high mechanical properties were still obtained at a medium porosity, e.g. the compressive yield strength and the modulus are as high as 100–200 MPa and 3.5–4.2 GPa, respectively, when the porosity is in the range of 50–70%. It was suggested that the porous titanium be strong enough to resist handing during implantation and in vivo loading. It is expected to be used as biocompatible implant, because their interconnected porous structures permit bone tissues ingrowth and the body fluids transportation.