In-situ deposition of apatite layer to protect Mg-based composite fabricated via laser additive manufacturing

Biodegradable magnesium(Mg) and its alloy show huge potential as temporary bone substitute due to the favorable biocompatibility and mechanical compatibility. However, one issue deserves attention is the too fast degradation. In this work, mesoporous bioglass(MBG)with high pore volume(0.59 cc/g) and huge specific surface area(110.78 m^(2)/g) was synthesized using improved sol-gel method, and introduced into Mg-based composite via laser additive manufacturing. Immersion tests showed that the incorporated MBG served as powerful adsorption sites, which promoted the in-situ deposition of apatite by successively adsorbing Ca2+and HPO42-. Such dense apatite film acted as an efficient protection layer and enhanced the corrosion resistance of Mg matrix, which was proved by the electrochemical impedance spectroscopy measurements. Thereby, Mg based composite showed a significantly decreased degradation rate of 0.31 mm/year. Furthermore,MBG also improved the mechanical properties as well as cell behavior. This work highlighted the advantages of MBG in the fabrication of Mg-based implant with enhanced overall performance for orthopedic application.

A bifunctional bone scaffold combines osteogenesis and antibacterial activity via in situ grown hydroxyapatite and silver nanoparticles

Hydroxyapatite(HA)nanoparticles and silver(Ag)nanoparticles are expected to enable desirable bioactivity and antibac-terial properties on biopolymer scaffolds.Nevertheless,interfacial adhesion between HA/Ag and the biopolymer is poor due to the large physicochemical differences between these components.In this study,poly L-lactic acid(PLLA)powder was first surface-modified with bioactive polydopamine(PDA)in an alkaline environment.Next,HA and Ag nanoparticles were grown in situ on the PDA-coated PLLA powder,which was then adhered to the porous bone scaffold using a selective laser-sintering process.Results showed that HA and Ag nanoparticles were homogenously distributed in the matrix,with enhanced mechanical properties.Simulated body fluid bioactivity tests showed that the in situ grown HA-endowed scaffold shows excellent bioactivity.In vitro tests confirmed that the scaffold exhibits favorable biocompatibility with human umbilical cord mesenchymal stem cells,as well as strong antibacterial activity against Gram-negative Escherichia coli.Furthermore,in vivo assays indicated that the scaffold promoted bone generation,with a new bone area fraction of 71.8%after 8 weeks’implantation,without inflammation.

一种对空气中复合材料层合椭圆壳声振分析的统一预测方法

提出了一种半解析法对空气中的复合材料层合椭圆壳进行振动声分析。采用变分法和分段技术建立动力学模型。采用基尔霍夫-亥姆霍兹积分公式计算了外部流场的声辐射。用傅立叶级数和切比雪夫正交多项式组合展开了包含位移和声压的变量。引入配置点构造声积分方程代数系统,这些点分布在切比雪夫多项式的根上,并用组合亥姆霍兹积分消除系统的非唯一解。给出了复合材料层合椭圆壳声辐射问题的数值算例,并给出了周向模态对复合材料层合椭圆壳声学结果的影响。研究了几何参数和材料参数对复合材料层合椭圆壳声辐射的影响。

Advances in biocermets for bone implant applications

As two promising biomaterials for bone implants,biomedical metals have favorable mechanical properties and good machinability but lack of bioactivity;while bioceramics are known for good biocompatibility or even bioactivity but limited by their high brittleness.Biocermets,a kind of composites composing of bioceramics and biomedical metals,have been developed as an effective solution by combining their complementary advantages.This paper focused on the recently studied biocermets for bone implant applications.Concretely,biocermets were divided into ceramic-based biocermets and metal-based biocermets according to the phase percentages.Their characteristics were systematically summarized,and the fabrication methods for biocermets were reviewed and compared.Emphases were put on the interactions between bioceramics and biomedical metals,as well as the performance improvement mechanisms.More importantly,the main methods for the interfacial reinforcing were summarized,and the corresponding interfacial reinforcing mechanisms were discussed.In addition,the in vitro and in vivo biological performances of biocermets were also reviewed.Finally,future research directions were proposed on the advancement in component design,interfacial reinforcing and forming mechanisms for the fabrication of high-performance biocermets.

Construction of Fe/Ag galvanic couple by mechanochemical in-situ reduced Ag to accelerate the degradation of Fe-based implant

Orthopedic applications of Fe have been hindered by the insufficient degradation rate.Alloying with noble elements(such as Ag,Au,and Pt)to generate galvanic couples is a feasible approach.However,the direct preparation of homogenous alloys by mechanical alloying or metallurgy is difficult because of the differences in strength,density,and toughness.In this study,Ag_(2)O was selected as the precursor phase for incorporation into Fe to achieve a homogeneous distribution of Ag,which was then reduced in situ to Ag via a mechanochemical reduction reaction during mechanical alloying.The composite powders were printed as implants by selective laser melting,where a fast cooling rate contributed to the retention of the phase distribution of the obtained powder.The electrochemical tests showed that the Fe-Ag_(2)O implant had a high corrosion current density(21.88±0.12μA/cm^(2))and instantaneous corrosion rate(0.23±0.05 mm/year).Moreover,the implant exhibited a faster degradation rate(0.22 mm/year)than Fe(0.15 mm/year)and Fe-Ag(0.21 mm/year)after immersion for 28 d.The acceleration mechanism of the implant could be attributed to the uniformly distributed Ag particles triggering many galvanic couples with the Fe grains,which was confirmed by the observation of the corrosion surface.In addition,the composite implants exhibited good biocompatibility and antibacterial properties.

Accelerated degradation of HAP/PLLA bone scaffold by PGA blending facilitates bioactivity and osteoconductivity

The incorporation of hydroxyapatite(HAP)into poly-L-lactic acid(PLLA)matrix serving as bone scaffold is expected to exhibit bioactivity and osteoconductivity to those of the living bone.While too low degradation rate of HAP/PLLA scaffold hinders the activity because the embedded HAP in the PLLA matrix is difficult to contact and exchange ions with body fluid.In this study,biodegradable polymer poly(glycolic acid)(PGA)was blended into the HAP/PLLA scaffold fabricated by laser 3D printing to accelerate the degradation.The results indicated that the incorporation of PGA enhanced the degradation rate of scaffold as indicated by the weight loss increasing from 3.3%to 25.0%after immersion for 28 days,owing to the degradation of high hydrophilic PGA and the subsequent accelerated hydrolysis of PLLA chains.Moreover,a lot of pores produced by the degradation of the scaffold promoted the exposure of HAP from the matrix,which not only activated the deposition of bone like apatite on scaffold but also accelerated apatite growth.Cytocompatibility tests exhibited a good osteoblast adhesion,spreading and proliferation,suggesting the scaffold provided a suitable environment for cell cultivation.Furthermore,the scaffold displayed excellent bone defect repair capacity with the formation of abundant new bone tissue and blood vessel tissue,and both ends of defect region were bridged after 8 weeks of implantation.

Microstructure evolution and texture tailoring of reduced graphene oxide reinforced Zn scaffold

Zinc(Zn)possesses desirable degradability and favorable biocompatibility,thus being recognized as a promising bone implant material.Nevertheless,the insufficient mechanical performance limits its further clinical application.In this study,reduced graphene oxide(RGO)was used as reinforcement in Zn scaffold fabricated via laser additive manufacturing.Results showed that the homogeneously dispersed RGO simultaneously enhanced the strength and ductility of Zn scaffold.On one hand,the enhanced strength was ascribed to(i)the grain refinement caused by the pinning effect of RGO,(ii)the efficient load shift due to the huge specific surface area of RGO and the favorable interface bonding between RGO and Zn matrix,and(iii)the Orowan strengthening by the homogeneously distributed RGO.On the other hand,the improved ductility was owing to the RGO-induced random orientation of grain with texture index reducing from 20.5 to 7.3,which activated more slip systems and provided more space to accommodate dislocation.Furthermore,the cell test confirmed that RGO promoted cell growth and differentiation.This study demonstrated the great potential of RGO in tailoring the mechanical performance and cell behavior of Zn scaffold for bone repair.

Halloysite nanotubes loaded with nano silver for the sustained-release of antibacterial polymer nanocomposite scaffolds

It is challenging for antibacterial polymer scaffolds to achieve the drug sustained-release through directly coating or blending.In this work,halloysite nanotubes(HNTs),a natural aluminosilicate nanotube,were utilized as a nano container to load nano silver(Ag)into the lumen through vacuum negativepressure suction&injection and thermal decomposition of silver acetate.Then,the nano Ag loaded HNTs(HNTs@Ag)were introduced to poly-l-lactic acidide)(PLLA)scaffolds prepared by additive manufacturing for the sustained-release of Ag^+.Acting like a’shield’,the tube walls of HNTs not only retarded the erosion of external aqueous solution on internal nano Ag to generate Ag^+but also postponed the generated Ag^+to diffuse outward.The results indicated the PLLA-HNTs@Ag nanocomposite scaffolds achieved a sustained-release of Ag^+over 28 days without obvious initial burst release.Moreover,the scaffolds exhibited a long-lasting antibacterial property without compromising the cytocompatibility.Besides,the degradation properties,biomineralization ability and mechanical properties of the scaffolds were increased.This study suggests the potential application of inorganic nanotubes as drug carrier for the sustained-release of functional polymer nanocomposite scaffolds.

A Review on Distortion and Residual Stress in Additive Manufacturing

Additive manufacturing(AM)has gained extensive attention and tremendous research due to its advantages of fabricating complex-shaped parts without the need of casting mold.However,distortion is a known issue for many AM technologies,which decreases the precision of as-built parts.Like fusion welding,the local high-energy input generates residual stresses,which can adversely affect the fatigue performance of AM parts.To the best of the authors’knowledge,a comprehensive review does not exist regarding the distortion and residual stresses dedicated for AM,despite some work has explored the interrelationship between the two.The present review is aimed to fill in the identified knowledge gap,by first describing the evolution of distortion and residual stresses for a range of AM processes,and second assessing their influencing factors.This allows us to elucidate their formation mechanisms from both the micro-and macro-scales.Moreover,approaches which have been successfully adopted to mitigate both the distortion and residual stresses are reviewed.It is anticipated that this review paper opens many opportunities to increase the success rate of AM parts by improving the dimension precision and fatigue life.