Fabrication of multilevel porous structure networks on Nb-Ta-Ti alloy scaffolds and the effects of surface characteristics on behaviors of MC3T3-E1 cells.

Porous Nb-25Ta-25Ti alloys (60% porosity and 100-600 µm pore size) for bone implant applications were manufactured combining impregnation and sintering methods. Surfaces with porous micro-nanostructured networks on Nb-Ta-Ti alloys were successfully modified by various surface pre-treatments (acid etching, alkali-heat treatment and annealing treatment). Surface characteristics and Ca-P layer deposition behaviors of the multilevel structured porous Nb-Ta-Ti alloys were investigated by conducting various tests, including x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray, atomic force microscopy and optical contact angle measurement. In particular, bulk Nb-Ta-Ti alloys were also used as mutual control. The results demonstrated that the porous alloy exhibited a unique multilevel porous structure with macro-networks and micro-pits after pre-treatments. The surface passive TiO2/Nb2O5/Ta2O5layers on Nb-Ta-Ti alloys were partially dissolved by the corrosive attack of hydroxyl ions during alkali heat treatment. In addition, subsequent annealing treatment increased the density of the gel layers formed during alkali heat treatment. After immersion in SBF for 14 d, a continuous relatively uniform apatite layer was formed on the multilevel structured surfaces. Moreover, the mechanism of surface mineralization can be construed as electrostatic interactions between substrates and ions. Furthermore,in vitrocell culture showed that Nb-Ta-Ti alloys had a good biocompatibility and the multilevel porous structure could enhance the cellular behaviors including: cell adhesion and spreading.

Fur Protein Regulates the Motility of Avian Pathogenic Escherichia coli AE17 Through Promoter Regions of the Flagella Key Genes flhD.

Avian pathogenic Escherichia coli (APEC) is an important pathogen causing several diseases in birds. It is responsible for local and systemic infections in poultry, seriously impeding the development of the poultry industry, and poses a potential risk to public health. The iron absorption regulatory protein Fur and the noncoding RNA, RyhB, that it negatively regulates are important factors in bacterial iron uptake, but the regulation of bacterial virulence genes varies greatly among different bacteria. We found that Fur is very important for the mobility of APEC. The expression of fur and RyhB is extensively regulated in APEC, and RyhB expression is also negatively regulated by Fur. A transcriptomic analysis showed that the genes significantly differentially regulated by Fur are related to cell movement, including pilus- or flagellum-dependent cell motility. To verify these results, we examined the effects of fur knockdown on cell movement by measuring the diameter of the bacteria colonies. Consistent with the RNA sequencing results, the mobility of AE17Δfur was significantly reduced compared with that of the wild type, and it had almost lost its ability to move. Using an electrophoretic mobility assay, we confirmed that the Fur protein directly binds to the promoter region of the key flagellum-related gene flhD, thereby affecting the assembly and synthesis of the APEC flagellum. This study extends our understanding of gene regulation in APEC.

Bone response in vivo of Ti-45Zr alloy as dental implant material.

Ti-Zr alloys have gained increasing attention as a new metallic biomaterial, being used as implants for both orthopedics and dentistry. More recently, our group found promising results for the Ti-45Zr alloy, which presented a low elastic modulus, a pronounced and excellent mechanic character, and excellent cell compatibility in vitro. However, its biocompatibility and potential to promote osteogenesis in vivo remained unclear. In the present study, the biocompatibility, osteointegration ability, and immune response effects of the Ti-45Zr alloy were evaluated in animal experiments. The results showed that the alloy had good blood compatibility and no body side effects. After implantation in vivo, the inflammation turned out well and was beneficial to the polarization of macrophages. Additionally, the Ti-45Zr alloy presented a good osteointegration ability. Overall, these results confirmed that the Ti-45Zr alloy can be used as a dental implant material.

Microstructure, mechanical properties and osseointegration ability of Ta-20Zr alloy used as dental implant material.

The aim of this study was to evaluate the application prospect of a tantalum (Ta) and zirconium (Zr) alloy as a dental implant material. The Ta-20Zr (wt.%) alloy was prepared by powder metallurgy, and its microstructure and mechanical properties were analyzed by standard techniques. The effect of Ta-20Zr alloy on inflammation, bone remodeling and osseointegration was analyzed in rat and rabbit models by biochemical, histological and imaging tests. The Ta-20Zr alloy showed excellent mechanical compatibility with the bone tissue on account of similar elastic modulus (49.2 GPa), thereby avoiding the 'stress shielding effect'. Furthermore, Ta-20Zr alloy enhanced the inflammatory response by promoting secretion of interleukin-6 (IL-6) and IL-10, and facilitated the balance between the M1/M2 macrophage phenotypes. Finally, Ta-20Zr also showed excellent osseointegration and osteogenic ability without any systemic side effects, making it an ideal dental implant material.

Microstructures and Mechanical Properties of H13 Tool Steel Fabricated by Selective Laser Melting.

H13 stool steel processed by selective laser melting (SLM) suffered from severe brittleness and scatter distribution of mechanical properties. We optimized the mechanical response of as-SLMed H13 by tailoring the optimisation of process parameters and established the correlation between microstructure and mechanical properties in this work. Microstructures were examined using XRD, SEM, EBSD and TEM. The results showed that the microstructures were predominantly featured by cellular structures and columnar grains, which consisted of lath martensite and retained austenite with numerous nanoscale carbides being distributed at and within sub-grain boundaries. The average size of cellular structure was ~500 nm and Cr and Mo element were enriched toward the cell wall of each cellular structure. The as-SLMed H13 offered the yield strength (YS) of 1468 MPa, the ultimate tensile strength (UTS) of 1837 MPa and the fracture strain of 8.48%. The excellent strength-ductility synergy can be attributed to the refined hierarchical microstructures with fine grains, the unique cellular structures and the presence of dislocations. In addition, the enrichment of solute elements along cellular walls and carbides at sub-grain boundaries improve the grain boundary strengthening.

Synthesis, structure, and properties of carbon/carbon composites artificial rib for chest wall reconstruction.

In this work, braided carbon fiber reinforced carbon matrix composites (3D-C/C composites) are prepared by chemical vapor infiltration process. Their composite structure, mechanical properties, biocompatibility, and in vivo experiments are investigated and compared with those of traditional 2.5D-C/C composites and titanium alloys TC4. The results show that 3D-C/C composites are composed of reinforced braided carbon fiber bundles and pyrolytic carbon matrix and provide 51% open pores with a size larger than 100 µm for tissue adhesion and growth. The Young's modulus of 3D-C/C composites is about 5 GPa, much smaller than those of 2.5D-C/C composites and TC4, while close to the autogenous bone. 3D-C/C composites have a higher tensile strength (167 MPa) and larger elongation (5.0%) than 2.5D-C/C composites (81 MPa and 0.7%), and do not show obvious degradation after 1 × 106 cyclic tensile loading. The 3D-C/C composites display good biocompatibility and have almost no artifacts on CT imaging. The in vivo experiment reveals that 3D-C/C composites artificial ribs implanted in dogs do not show displacement or fracture in 1 year, and there are no obvious proliferation and inflammation in the soft tissues around 3D-C/C composites implant. Our findings demonstrate that 3D-C/C composites are suitable for chest wall reconstruction and present great potentials in artificial bones.

Influence of Cr3C2 and VC Content on WC Grain Size, WC Shape and Mechanical Properties of WC-6.0 wt. % Co Cemented Carbides.

In this paper, the influences of Cr3C2/VC content on WC grain size, WC grain shape and mechanical properties of WC-6 wt. % Co cemented carbides were investigated. The results showed that the grain size first rapidly decreased and then slightly decreased with the increasing Cr3C2/VC content, and VC led to finer grain size and narrower size distribution. HRTEM/EDS analysis of the WC/Co interface indicates that the segregation concentration of V is much larger than that of Cr, which may be a strong response to the higher inhibition efficiency of VC. The addition of Cr3C2 induced triangular prism shape WC grains while VC generated stepped triangular prism grains. Despite the grain growth inhibitor (GGI) mechanisms of Cr3C2/VC have been extensively studied in the literature, the doping amount, especially the doping limit, has not been systematically investigated. In this work, the saturated solubilities of Cr and V in cobalt binder phase along with carbon content hare been predicted based on thermodynamic calculations. Based on the theoretical calculations, the doping amount of Cr3C2/VC is designed to be gradually increasing until more or less over their maximum solubilities in the binder phase, thereby investigating the subsequent microstructure and mechanical properties. When the doping of Cr3C2/VC exceeds the maximum solubility in Co phase, Co-rich Cr-carbides and Co-deficient V-carbides would form respectively, which were detrimental to the transverse rupture strength (TRS) and impact toughness. The hardness increased with the increasing Cr3C2/VC content, while the fracture toughness decreased with the increasing Cr3C2/VC content. The TRS initially enhanced and then declined, but the stepped triangular prism shape grains and low fraction of WC/Co interface in WC-6Co-VC cemented carbide led to a more pronounced decline in the TRS. The sample with 0.6 wt. % Cr3C2 addition had good comprehensive mechanical properties, its hardness, fracture toughness and TRS were 1880 kg/mm2, 9.32 MPa·m1/2 and 3450 MPa, respectively.

Cytocompatibility of Ti-xZr alloys as dental implant materials.

Ti-xZr (x = 5, 15, 25, 35, 45% wt%) alloys with low elastic modulus and high mechanical strength were fabricated as a novel implant material. The biocompatibility of the Ti-xZr alloys was evaluated by osteoblast-like cell line (MG63) in terms of cytotoxicity, proliferation, adhesion, and osteogenic induction using CCK-8 and live/dead cell assays, electron microscopy, and real-time PCR. The Ti-xZr alloys were non-toxic and showed superior biomechanics compared to commercially pure titanium (cpTi). Ti-45Zr had the optimum strength/elastic modulus ratio and osteogenic activity, thus is a promising to used as dental implants.

Nb-Ti-Zr alloys for orthopedic implants.

Niobium (Nb), Titanium (Ti), and Zirconium (Zr) have attracted much attention as implant materials due to it's excellent mechanical properties and biocompatibility. However, little attention has been paid to high Nb-containing biomedical alloys. Here, the 50 wt.%Nb-XTi-Zr ternary alloy(x = 20wt.%, 30 wt.%, 40 wt.%) with relative density over 90% was prepared by powder metallurgy method. The massive α(Zr) distributed along the grain boundaries and lamellar ß(Zr) appeared in the grains of ß(Nb) in the 50 wt.%Nb-20wt.%Ti-Zr alloy. The acicular α phase is mainly distributed in the ß-grain of 50 wt.%Nb-30wt.%Ti-Zr alloy. And α(Ti)-colonies in the ß-grains and continuous α(Ti)GB at ß-grain boundary can be observed in the 50 wt.%Nb-40wt.%Ti-Zr alloy. Comparing with Nb-20wt.%Ti-Zr alloy and 50 wt.%Nb-40wt.%Ti-Zr alloy, the 50 wt.%Nb-30wt.%Ti-Zr alloy showed lower Vickers hardness and elastic modulus. Furthermore, the as-sintered 50 wt.%Nb-XTi-Zr alloy promoted the cell proliferation and cell adhesion of MG-63 cells on the surface of alloys. In conclusion, the 50 wt.%Nb-XTi-Zr alloy combines excellent mechanical and biological properties, and the 50 wt.%Nb-30wt.%Ti-Zr alloy with lower elastic modulus (close to the bone) is a more promising candidate for bone implant material.

Cytocompatibility, stability and osteogenic activity of powder metallurgy Ta-xZr alloys as dental implant materials.

Tantalum (Ta) and zirconium (Zr) alloys were found to had low elastic modulus and similar biomechanical characteristics as the human bone. However, the biocompatibility and osteogenic potential of Ta-xZr alloyswith different proportions (20, 30, 40 and 50% Zr by atom) remains to be investigated. In this study, the biocompatibility of Ta-xZr alloys and commercially pure titanium (cpTi) was evaluated in vitro by cell counting kit-8 assay. The adhesion of MG63 osteoblasts to the surface of the alloys was observed by fluorescence microscopy, and their morphology was analyzed by scanning electron microscopy (SEM). The expressions of alkaline phosphatase (ALP), Ki67, osteocalcin (OC), collagen-I (Col-I) and Integrin ß1 mRNA in the cultured cells were determined by RT-PCR. As a result, Ta-xZr (x = 20, 30, 40 and 50 at%) alloys were non-toxic and supported proliferation of the MG63 cells. The osteoblasts adhered to the Ta-xZr alloys, and subsequently spread and proliferated rapidly. Furthermore, the cells grown on Ta-20Zr and Ta-30Zr expressed high levels of ALP, Col I and OC, indicating that the Ta-xZr alloys can induce osteogenesis. In conclusion, Ta-xZr alloys promoted the adhesion, proliferation and osteogenic differentiation of MG63 cells. The Ta-xZr composites with a higher proportion of Ta exhibited superior osteogenic activity, and Ta-30Zr is therefore a promising alternative for Ti implants.

Evaluation of biocompatibility and osseointegration of Nb-xTi-Zr alloys for use as dental implant materials.

The aim of this study was to evaluate the biocompatibility and osteogenic potential of 50%Nb-xTi-Zr (NTZ,x= 20%, 30%, 40% by weight) alloys as compared with dental commercial pure titanium (cpTi). Cell cytotoxicity assay, fluorescence microscopy and electron microscopy were used to measure thein vitrobiocompatibility of NTZ. The expression of alkaline phosphatase (ALP), integrin ß1, osteocalcin (OC), Ki67 and collagen-I (Col-I) at the mRNA level was measured by real-time reverse transcription-polymerase chain reaction. Osseointegration ability was determined using x-ray evaluation and histological analysisin vivo. Compared with the MG63 cells grown on cpTi on day 3, the viability, adherence and proliferation rates of cells cultured on NTZ alloys were significantly improved (p< 0.05). Furthermore, similar expression levels of Ki67, Col-I, OC and ALP were found in the MG63 cells grown on NTZ alloys and those grown on cpTi. The Cbfα1 level was significantly higher for the 50%Nb-30%Ti-Zr (NTZ3) than for the cpTi group on day 6 (p< 0.01), indicating that NTZ alloys can induce osteogenesis. A considerable amount of new bone formation and osseointegration was observed around NTZ3 implants compared with cpTi implantsin vivo. Collectively, NTZ3 showed superior biocompatibility and osteogenic activity; therefore, NTZ3 may be an excellent replacement for dental Ti implants.

In vitro cell response and in vivo primary osteointegration of highly porous Ta-Nb alloys as implant materials.

By combining the biocompatibility of Ta and excellent performance of Nb, the ß-type Ta-xNb (x = 5, 10, and 15 wt %) alloys with three-dimensional network structure was successfully fabricated. This work was designed to carry out the systematic study of in vitro/vivo biocompatibility of highly porous Ta-Nb alloys. In the present study, the in vitro biological response was characterized by cell attachment, cytotoxicity test, and gene expression. Cells were well distributed on porous alloy surface and both bulk/porous Ta-15Nb alloys showd a 0-1 RGR level. Moreover, the upregulated gene expression may reveal an increase in bone regeneration. An assessment of primary osteogenic response in vivo was achieved by histological evaluation and pull-out test. In vivo results demonstrated that the porous Ta-15Nb alloy showed a higher pull-out force than bulk Ta-15Nb alloy and exhibited a more extensive contact between implants and bones after 12 weeks. Based on the present experiments, porous Ta-Nb alloy scaffolds had a good biocompatibility and were promising for biomedical applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 573-581, 2019.

Microstructure, mechanical properties, and preliminary biocompatibility evaluation of binary Ti-Zr alloys for dental application.

The microstructure, mechanical properties, and in vitro biocompatibility of vacuum-sintered Ti-xZr binary alloys (x = 5, 15, 25, 35, 45 wt%) were investigated. The results indicated that α and α' phase existed in Ti-xZr alloys. The hardness of the Ti-Zr alloys increased as the contents increased and ranged from 473 HV (Ti-5Zr) to 525 HV (Ti-45Zr). Increasing Zr content could lead to an increase in compressive and bending strength. Additionally, the Ti-45Zr alloy exhibited the maximum bending strength of 867.1 MPa and the maximum compressive strength of 1599.8 MPa which were much larger than that of CP-Ti. Moreover, all Ti-Zr alloys showed a lower elastic modulus (ranging from 53.5 to 59.3 GPa) compared with CP-Ti (103 GPa). The in vitro cytotoxicity tests were carried out for biocompatibility evaluation. The alloys presented no cytotoxic effects and the surface of the alloys exhibited great growth conditions for MG-63 cells. The Ti-45Zr alloy exhibited better mechanical properties and biocompatibility. In conclusion, Ti-45Zr alloy is of great potential for dental applications.

[Evaluation of osseointegration of domestic porous tantalum-niobium alloy].

PURPOSE: To evaluate the osseointegration of domestic porous tantalum-niobium(PTa-Nb) alloy. METHODS: A total of 36 adult New Zealand rabbits were selected and divided into 3 groups. Pta-Nb rods(3.5 mm×10 mm) were implanted into the femoral condyle of each rabbit.The rabbits were sacrificed successively at 4,8,12 weeks after operation. X-ray, hard tissue slices stained with toluidine blue, scanning electron microscope(SEM), X-ray energy disperse spectroscopy(XEDS) and push-out test were used to test the osseointegration of PTa-Nb. SPSS19.0 software package was used for statistical analysis. RESULTS: X-ray films showed no obvious inflammation,as well as implants loosing and bone resorption. Density of the bone around implants increased. Hard tissue slices displayed chimeric shape in the implant-bone interface. New bone contacted directly to the surface of PTa-Nb and got more and more closer with the increase of healing time. Osteoid formed in the inner pores at 4 weeks after operation,and more mature bone tissue grew into inner part of PTa-Nb at 12 weeks. SEM showed bone tissue was more denser and closer to the Pta-Nb,which was similar to the results of hard tissue slices. XEDS analysis showed the percent content of the calcium and phosphate of the tissue within PTa-Nb increased gradually in the three groups.The ratio of Ca/P at 8 and 12 weeks was significantly higher than at 4 weeks (P<0.05); Push-out test showed the shear-strength of PTa-Nb implants increased from (8.26±0.75) MPa at 4 weeks to (21.04±1.46) MPa at 12 weeks (P<0.05). CONCLUSIONS: The domestic PTa-Nb alloy has good osseointegration with both bone tissue ongrowth and ingrowth,which may be a high potential biomimetic bone material.

Porous Nb-Ti-Ta alloy scaffolds for bone tissue engineering: Fabrication, mechanical properties and in vitro/vivo biocompatibility.

Porous Nb-Ti-Ta (at.%) alloys with the pore size of 100-600µm and the porosity of 50%-80% were fabricated by the combination of the sponge impregnation technique and sintering method. The results revealed that the pores were well connected with three-dimensional (3D) network structure, which showed morphological similarity to the anisotropic porous structure of human bones. The results also showed that the alloys could provide the compressive Young's modulus of 0.11±0.01GPa to 2.08±0.09GPa and the strength of 17.45±2.76MPa to 121.67±1.76MPa at different level of porosity, indicating that the mechanical properties of the alloys are similar to those of human bones. Pore structure on the compressive properties was also discussed on the basis of the deformation mode. The relationship between compressive properties and porosity was well consistent with the Gibson-Ashby model. The mechanical properties could be tailored to match different requirements of the human bones. Moreover, the alloys had good biocompatibility due to the porous structure with higher surface, which were suitable for apatite formation and cell adhesion. In conclusion, the porous Nb-Ti-Ta alloy is potentially useful in the hard tissue implants for the appropriate mechanical properties as well as the good biocompatible properties.

Reconstruction of Large-scale Defects with a Novel Hybrid Scaffold Made from Poly(L-lactic acid)/Nanohydroxyapatite/Alendronate-loaded Chitosan Microsphere: in vitro and in vivo Studies.

A chitosan-based microsphere delivery system has been fabricated for controlled release of alendronate (AL). The present study aimed to incorporate the chitosan/hydroxyapatite microspheres-loaded with AL (CH/nHA-AL) into poly(L-lactic acid)/nanohydroxyapatite (PLLA/nHA) matrix to prepare a novel microspheres-scaffold hybrid system (CM-ALs) for drug delivery and bone tissue engineering application. The characteristics of CM-ALs scaffolds containing 10% and 20% CH/nHA-AL were evaluated in vitro, including surface morphology and porosity, mechanical properties, drug release, degradation, and osteogenic differentiation. The in vivo bone repair for large segmental radius defects (1.5 cm) in a rabbit model was evaluated by radiography and histology. In vitro study showed more sustained drug release of CM-AL-containing scaffolds than these of CM/nHA-AL and PLLA/nHA/AL scaffolds, and the mechanical and degradation properties of CM-ALs (10%) scaffolds were comparable to that of PLLA/nHA control. The osteogenic differentiation of adipose-derived stem cells (ASCs) was significantly enhanced as indicated by increased alkaline phosphates (ALP) activity and calcium deposition. In vivo study further showed better performance of CM-ALs (10%) scaffolds with complete repair of large-sized bone defects within 8 weeks. A microspheres-scaffold-based release system containing AL-encapsulated chitosan microspheres was successfully fabricated in this study. Our results suggested the promising application of CM-ALs (10%) scaffolds for drug delivery and bone tissue engineering.

Microstructure, mechanical behavior and biocompatibility of powder metallurgy Nb-Ti-Ta alloys as biomedical material.

Microstructures, mechanical properties, apatite-forming ability and in vitro experiments were studied for Nb-25Ti-xTa (x=10, 15, 20, 25, 35at.%) alloys fabricated by powder metallurgy. It is confirmed that the alloys could achieve a relative density over 80%. Meanwhile, the increase in Ta content enhances the tensile strength, elastic modulus and hardness of the as-sintered alloys. When increasing the sintering temperatures, the microstructure became more homogeneous for ß phase, resulting in a decrease in the modulus and strength. Moreover, the alloys showed a good biocompatibility due to the absence of cytotoxic elements, and were suitable for apatite formation and cell adhesion. In conclusion, Nb-25Ti-xTa alloys are potentially useful in biomedical applications with their mechanical and biological properties being evaluated in this work.

Preparation and characterization of biomedical highly porous Ti-Nb alloy.

The compressive strength and the biocompatibility were assessed for the porous Ti-25 wt%Nb alloy fabricated by the combination of the sponge impregnation technique and sintering technique. The alloy provided pore sizes of 300-600 µm, porosity levels of 71 ± 1.5%, in which the volume fraction of open pores was 94 ± 1.3%. The measurements also showed that the alloy had the compressive Young's modulus of 2.23 ± 0.5 GPa and the strength of 98.4 ± 4.5 MPa, indicating that the mechanical properties of the alloy are similar to those of human bone. The scanning electron microscopy (SEM) observations revealed that the pores were well connected to form three-dimension (3D) network open cell structure. Moreover, no obvious impurities were detected in the porous structure. The experiments also confirmed that rabbit bone mesenchymal stem cells (MSCs) could adhere and proliferate in the porous Ti-25 wt%Nb alloy. The interactions between the porous alloy and the cells are attributed to the porous structure with relatively higher surface. The suitable mechanical and biocompatible properties confirmed that this material has a promising potential in the application for tissue engineering.

Emulsion cross-linked chitosan/nanohydroxyapatite microspheres for controlled release of alendronate.

Sustained delivery of growth factors has emerged as an essential requirement for bone tissue engineering applications for the treatment of various kinds of bone defects. Chitosan (CH) has attracted particular attention for drug delivery and bone tissue engineering because of its favorable biocompatibility and biodegradability. In this study, a composite microsphere system containing CH and nanohydroxyapatite (nHA)-alendronate (AL) particles was fabricated by employing both emulsification and cross-linking strategies. The microspheres were characterized for their surface morphology, composition, size distribution, drug loading efficiency and release properties. The results showed that loading efficiency and sustained release of hydrophilic AL were significantly improved, which is ideal for locally sustained release in the bone microenvironment. In vitro osteogenic studies showed that the microspheres could enhance the osteogenic activity of rabbit adipose-derived stem cells. In conclusion, the CH/nHA-AL composite microspheres exhibit promising properties as a candidate for local treatment for bone defects.