Impacts of permeability and effective diffusivity of porous scaffolds on bone ingrowth: In silico and in vivo analyses.

The permeability and the effective diffusivity of a porous scaffold are critical in the bone-ingrowth process. However, design guidelines for porous structures are still lacking due to inadequate understanding of the complex physiological processes involved. In this study, a model integrating the fundamental biological processes of bone regeneration was constructed to investigate the roles of permeability and effective diffusivity in regulating bone deposition in scaffolds. The in silico analysis results were confirmed in vivo by examining bone depositions in three diamond lattice scaffolds manufactured using selective laser melting. The findings show that the scaffolds with better permeability and effective diffusivity had deeper bone ingrowth and greater bone volume. Compared to permeability, effective diffusivity exhibited greater sensitivity to the orientation of porous structures, and bone ingrowth was deeper in the directions with higher effective diffusivity in spite of identical pore size. A 4.8-fold increase in permeability and a 1.6-fold increase in effective diffusivity by changing the porous structure led to a 1.5-fold increase in newly formed bone. The effective diffusivity of the porous scaffold affects the distribution of osteogenic growth factor, which in turn impacts cell migration and bone deposition through chemotaxis effects. Therefore, effective diffusivity may be a more suitable indicator for porous scaffolds because our study shows changes in this parameter determine changes in bone distribution and bone volume.

Advances in functional coatings on biliary stents.

Biliary stenting is an important interventional method for the prevention and treatment of biliary tract diseases. However, complications, such as postoperative biliary infection and restenosis, frequently occur due to the extensive scope of the biliary system and the complex composition of bile. The combination of coating technology and biliary stents is expected to bring new approaches to the solution of these problems. The cutting-edge advance on functional coatings on biliary stents is reviewed from seven perspectives: anticorrosion, -bacterial, -tumor, stone-dissolving, X-ray visibility, antistent migration and functional composite coatings. The development trend is also discussed. Overall, the performance of the numerous functional coatings for various purposes is generally up to expectations, but the balance between the medications' effectiveness and their safety needs to be further adjusted. Many contemporary investigations have advanced to the level of animal experiments, offering crucial fundamental assurance for broader human studies. The combination of biliary stents and functional coatings is an innovative idea with great potential for future development.

Facile synthesis of multi-phase (Si+SiO2)@C anode materials for lithium-ion batteries.

To bring about a revolution in energy storage through Li-ion batteries, it is crucial to develop a scalable preparation method for Si-based composite anodes. However, the severe volume expansion and poor ionic transport properties of Si-based composites present significant challenges. Previous research focused on SiO and nano Si/C composites to address these issues. In this study, mechanical milling was used to introduce a SiOx layer onto the surface of Si by mixing Si and SiO2 in a 1 : 1 mass ratio. The resulting Si+SiO2 composites (denoted as SS50) exhibited an initial coulombic efficiency (ICE) of 73.5% and high rate performance. To further stabilize the overall structure, kerosene was introduced as a carbon source precursor to generate a coating layer. The resulting multiphase composite structure (SiOx+SiO2+C), designated as SS50-900C, demonstrated a capacity retention of 79.5% over 280 cycles at its capacity of 487 mA h g-1. These results suggest that a cost-effective mechanical ball milling refinement of Si+SiO2 and a gas-phase encapsulation process can significantly improve the electrochemical performance of Si-based composites.

Enhanced Mechanical Properties, Corrosion Resistance, Cytocompatibility, Osteogenesis, and Antibacterial Performance of Biodegradable Mg-2Zn-0.5Ca-0.5Sr/Zr Alloys for Bone-Implant Application.

Magnesium (Mg) alloys are widely used in bone fixation and bone repair as biodegradable bone-implant materials. However, their clinical application is limited due to their fast corrosion rate and poor mechanical stability. Here, the development of Mg-2Zn-0.5Ca-0.5Sr (MZCS) and Mg-2Zn-0.5Ca-0.5Zr (MZCZ) alloys with improved mechanical properties, corrosion resistance, cytocompatibility, osteogenesis performance, and antibacterial capability is reported. The hot-extruded (HE) MZCZ sample exhibits the highest ultimate tensile strength of 255.8 ± 2.4 MPa and the highest yield strength of 208.4 ± 2.8 MPa and an elongation of 15.7 ± 0.5%. The HE MZCS sample shows the highest corrosion resistance, with the lowest corrosion current density of 0.2 ± 0.1 µA cm-2 and the lowest corrosion rate of 4 ± 2 µm per year obtained from electrochemical testing, and a degradation rate of 368 µm per year and hydrogen evolution rate of 0.83 ± 0.03 mL cm-2 per day obtained from immersion testing. The MZCZ sample shows the highest cell viability in relation to MC3T3-E1 cells among all alloy extracts, indicating good cytocompatibility except at 25% concentration. Furthermore, the MZCZ alloy shows good antibacterial capability against Staphylococcus aureus.

Biodegradable Zn-5Dy Alloy with Enhanced Osteo/Angio-Genic Activity and Osteointegration Effect via Regulation of SIRT4-Dependent Mitochondrial Function.

Zinc (Zn)-dysprosium (Dy) binary alloys are promising biodegradable bone fracture fixation implants owing to their attractive biodegradability and mechanical properties. However, their clinical application is a challenge for bone fracture healing, due to the lack of Zn-Dy alloys with tailored proper bio-mechanical and osteointegration properties for bone regeneration. A Zn-5Dy alloy with high strength and ductility and a degradation rate aligned with the bone remodeling cycle is developed. Here, mechanical stability is further confirmed, proving that Zn-5Dy alloy can resist aging in the degradation process, thus meeting the mechanical requirements of fracture fixation. In vitro cellular experiments reveal that the Zn-5Dy alloy enhances osteogenesis and angiogenesis by elevating SIRT4-mediated mitochondrial function. In vivo Micro-CT, SEM-EDS, and immunohistochemistry analyses further indicate good biosafety, suitable biodegradation rate, and great osteointegration of Zn-5Dy alloy during bone healing, which also depends on the upregulation of SIRT4-mediated mitochondrial events. Overall, the study is the first to report a Zn-5Dy alloy that exerts remarkable osteointegration properties and has a strong potential to promote bone healing. Furthermore, the results highlight the importance of mitochondrial modulation and shall guide the future development of mitochondria-targeting materials in enhancing bone fracture healing.

A biodegradable Zn-5Gd alloy with biomechanical compatibility, cytocompatibility, antibacterial ability, and in vitro and in vivo osteogenesis for orthopedic applications.

Zinc (Zn) and some of its alloys are recognized as promising biodegradable implant materials due to their acceptable biocompatibility, facile processability, and moderate degradation rate. Nevertheless, the limited mechanical properties and stability of as-cast Zn alloys hinder their clinical application. In this work, hot-rolled (HR) and hot-extruded (HE) Zn-5 wt.% gadolinium (Zn-5Gd) samples were prepared by casting and respectively combining with hot rolling and hot extrusion for bone-implant applications. Their microstructure evolution, mechanical properties, corrosion behavior, cytotoxicity, antibacterial ability, and in vitro and in vivo osteogenesis were systematically evaluated. The HR and HE Zn-5Gd exhibited significantly improved mechanical properties compared with those of their pure Zn counterparts and the HR Zn-5Gd showed a unique combination of tensile properties with an ultimate tensile strength of ∼311.6 MPa, yield strength of ∼236.5 MPa, and elongation of ∼40.6%, all of which are greater than the mechanical properties required for bone-implant materials. The HR and HE Zn-5Gd showed higher corrosion resistance than their pure Zn counterpart in Hanks' solution and the HE Zn-5Gd had the lowest corrosion rate of 155 µm/y measured by electrochemical corrosion and degradation rate of 26.9 µm/y measured by immersion testing. The HR and HE Zn-5Gd showed high cytocompatibility toward MC3T3-E1 and MG-63 cells, high antibacterial effects against S. aureus, and better in vitro osteogenic activity than their pure Zn counterparts. Furthermore, the HE Zn-5Gd exhibited better in vivo biocompatibility, osteogenesis, and osteointegration ability than pure Zn and pure Ti. STATEMENT OF SIGNIFICANCE: This work reports the mechanical properties, corrosion behaviors, cytocompatibility, antibacterial ability, in vitro and in vivo osteogenesis of biodegradable Zn-Gd alloy for bone-implant applications. Our findings demonstrate that the hot-rolled (HR) Zn-5Gd showed a unique combination of tensile properties with an ultimate tensile strength of ∼311.6 MPa, yield strength of ∼236.5 MPa, and elongation of ∼40.6%. The HR and HE Zn-5Gd showed higher corrosion resistance than their pure Zn counterpart in Hanks' solution. The HR and HE Zn-5Gd showed high cytocompatibility toward MC3T3-E1 and MG-63 cells, good antibacterial effects against S. aureus, and better in vitro osteogenic activity. Furthermore, the HE Zn-5Gd exhibited better in vivo biocompatibility, osteogenesis, and osteointegration ability than pure Zn and pure Ti.

Mechanical properties, corrosion behavior, and cytotoxicity of biodegradable Zn/Mg multilayered composites prepared by accumulative roll bonding process.

Zinc (Zn), magnesium (Mg), and their respective alloys have attracted great attention as biodegradable bone-implant materials due to their excellent biocompatibility and biodegradability. However, the poor mechanical strength of Zn alloys and the rapid degradation rate of Mg alloys limit their clinical application. The manufacture of Zn and Mg bimetals may be a promising way to improve their mechanical and degradation properties. Here we report on Zn/Mg multilayered composites prepared via an accumulative roll bonding (ARB) process. With an increase in the number of ARB cycles, the thicknesses of the Zn layer and the Mg layer were reduced, while a large number of heterogeneous interfaces were introduced into the Zn/Mg multilayered composites. The composite samples after 14 ARB cycles showed the highest yield strength of 411±3 MPa and highest ultimate tensile strength of 501±3 MPa among all the ARB processed samples, significantly higher than those of the Zn/Zn and Mg/Mg multilayered samples. The Zn and Mg layers remained continuous in the Zn/Mg composite samples after annealing at 150 °C for 10 min, resulting in a decrease in yield strength from 411±3 MPa to 349±3 MPa but an increase in elongation from 8±1% to 28±1%. The degradation rate of the Zn/Mg multilayered composite samples in Hanks' solution was ranged from 127±18 µm/y to 6±1 µm/y. The Zn/Mg multilayered composites showed over 100% cell viability with their 25% and 12.5% extracts in relation to MG-63 cells after culturing for 3 d, indicating excellent cytocompatibility. STATEMENT OF SIGNIFICANCE: This work reports a biodegradable Zn/Mg multilayered composite prepared by accumulative roll bonding (ARB) process. The yield and ultimate tensile strength of the Zn/Mg multilayered composites were improved due to grain refinement and the introduction of a large number of heterogeneous interfaces. The composite samples after 14 ARB cycles showed the highest yield strength of 411±3 MPa and highest ultimate tensile strength of 501±3 MPa among all the ARB processed samples. The degradation rate of the Zn/Mg multilayered composite meets the required degradation rate for biodegradable bone-implant materials. The results demonstrated that it is a very promising approach to improve the strength and biocompatibility of biodegradable Zn-based alloys.

Mechanical properties, corrosion and degradation behaviors, and in vitro cytocompatibility of a biodegradable Zn-5La alloy for bone-implant applications.

Zinc (Zn) and its alloys are used in bone-fixation devices as biodegradable bone-implant materials due to their good biosafety, biological function, biodegradability, and formability. Unfortunately, the clinical application of pure Zn is hindered by its insufficient mechanical properties and slow degradation rate. In this study, a Zn-5 wt.% lanthanum (Zn-5La) alloy with enhanced mechanical properties, suitable degradation rate, and cytocompatibility was developed through La alloying and hot extrusion. The hot-extruded (HE) Zn-5La alloy showed ultimate tensile strength of 286.3 MPa, tensile yield strength of 139.7 MPa, elongation of 35.7%, compressive yield strength of 262.7 MPa, and microhardness of 109.7 HV. The corrosion resistance of the HE Zn-5La in Hanks' and Dulbecco's modified Eagle medium (DMEM) solutions gradually increased with prolonged immersion time. Further, the HE Zn-5La exhibited an electrochemical corrosion rate of 36.7 µm/y in Hanks' solution and 11.4 µm/y in DMEM solution, and a degradation rate of 49.5 µm/y in Hanks' solution and 30.3 µm/y in DMEM solution, after 30 d of immersion. The corrosion resistance of both HE Zn and Zn-5La in DMEM solution was higher than in Hanks' solution. The 25% concentration extract of the HE Zn-5La showed a cell viability of 106.5%, indicating no cytotoxicity toward MG-63 cells. We recommend the HE Zn-5La alloy as a promising candidate material for biodegradable bone-implant applications. STATEMENT OF SIGNIFICANCE: This work reports the mechanical properties, corrosion and degradation behaviors, in vitro cytocompatibility and antibacterial ability of biodegradable Zn-5La alloy for bone-implant applications. Our findings demonstrate that the hot-extruded (HE) Zn-5La alloy showed an ultimate tensile strength of 286.3 MPa, a yield strength of 139.7 MPa, an elongation of 35.7%, compressive yield strength of 262.7 MPa, and microhardness of 109.7 HV. HE Zn-5La exhibited appropriate degradation rates in Hanks' and DMEM solutions. Furthermore, the HE Zn-5La alloy showed good cytocompatibility toward MG-63 and MC3T3-E1 cells and greater antibacterial ability against S. aureus.

Human Body-Fluid-Assisted Fracture of Zinc Alloys as Biodegradable Temporary Implants: Challenges, Research Needs and Way Forward.

Alloys of magnesium, zinc or iron that do not contain toxic elements are attractive as construction material for biodegradable implants, i.e., the type of implants that harmlessly dissolve away within the human body after they have completed their intended task. The synergistic influence of mechanical stress and corrosive human body fluid can cause sudden and catastrophic fracture of bioimplants due to phenomena such as stress corrosion cracking (SCC) and corrosion fatigue (CF). To date, SCC and CF of implants based on Zn have scarcely been investigated. This article is an overview of the challenges, research needs and way forward in understanding human body-fluid-assisted fractures (i.e., SCC and CF) of Zn alloys in human body fluid.

Metallurgical manipulation of surface Volta potential in bimetals and cell response of human mesenchymal stem cells.

Bioelectricity plays an overriding role in directing cell migration, proliferation, differentiation etc. Tailoring the electro-extracellular environment through metallurgical manipulation could modulate the surrounding cell behaviors. In this study, different electric potential patterns, in terms of Volta potential distribution and gradient, were created on the metallic surface as an electric microenvironment, and their effects on adherent human mesenchymal stem cells were investigated. Periodically and randomly distributed Volta potential pattern, respectively, were generated on the surface through spark plasma sintering of two alternatively stacked dissimilar metals films and of a mixture of metallic powders. Actin cytoskeleton staining demonstrated that the Volta potential pattern strongly affected cell attachment and deformation. The cytoskeletons of cells were observed to elongate along the Volta potential gradient and across the border of adjacent regions with higher and lower potentials. Moreover, the steepest potential gradient resulting from the drastic compositional changes on the periodic borders gave rise to the strongest osteogenic tendency among all the samples. This study suggests that tailoring the Volta potential distribution and gradient of metallic biomaterials via metallurgical manipulation is a promising approach to activate surrounding cells, providing an extra degree of freedom for designing desirable bone-repairing metallic implants.

An Optimized Method for Microcomputed Tomography Analysis of Trabecular Parameters of Metal Scaffolds for Bone Ingrowth.

Owing to its superior mechanical and biological properties, titanium metal is widely used in dental implants, orthopedic devices, and bone regenerative materials. Advances in 3D printing technology have led to more and more metal-based scaffolds being used in orthopedic applications. Microcomputed tomography (µCT) is commonly applied to evaluate the newly formed bone tissues and scaffold integration in animal studies. However, the presence of metal artifacts dramatically hinders the accuracy of µCT analysis of new bone formation. To acquire reliable and accurate µCT results that reflect new bone formation in vivo, it is crucial to lessen the impact of metal artifacts. Herein, an optimized procedure for calibrating µCT parameters using histological data was developed. In this study, the porous titanium scaffolds were fabricated by powder bed fusion based on computer-aided design. These scaffolds were implanted in femur defects created in New Zealand rabbits. After 8 weeks, tissue samples were collected to assess new bone formation using µCT analysis. Resin-embedded tissue sections were then used for further histological analysis. A series of deartifact two-dimensional (2D) µCT images were obtained by setting the erosion radius and the dilation radius in the µCT analysis software (CTan) separately. To get the µCT results closer to the real value, the 2D µCT images and corresponding parameters were subsequently selected by matching the histological images in the particular region. After applying the optimized parameters, more accurate 3D images and more realistic statistical data were obtained. The results demonstrate that the newly established method of adjusting µCT parameters can effectively reduce the influence of metal artifacts on data analysis to some extent. For further validation, other metal materials should be analyzed using the process established in this study.

Superhydrophobic Mechano-Bactericidal Surface with Photodynamic Antibacterial Capability.

Bacterial invasion and proliferation on various surfaces pose a serious threat to public health worldwide. Conventional antibacterial strategies that mainly rely on bactericides exhibit high bacteria-killing efficiency but might trigger the well-known risk of antibiotic resistance. Here, we report a superhydrophobic mechano-bactericidal surface with photodynamically enhanced antibacterial capability. First, bioinspired nanopillars with polycarbonate as the bulk material were replicated from anodized alumina oxide templates via a simple hot-pressing molding method. Subsequently, a facile bovine serum albumin phase-transition method was used to introduce chlorin e6 onto the nanopillar-patterned surface, which was then perfluorinated to render the surface superhydrophobic. Benefiting from its strong liquid super-repellency and photodynamically enhanced mechano-bactericidal properties, the superhydrophobic nanopillar-patterned surface exhibits 100% antibacterial efficiency after 30 min visible light irradiation (650 nm, 20 mW cm-2). More strikingly, the surface exhibited impressive long-lasting antimicrobial performance, maintaining a very high bactericidal efficiency (≥99%) even after 10 cycles of bacterial contamination tests. Also, the superhydrophobic nanopillar-patterned surface displays good hemocompatibility with a much lower than the 5% hemolysis rate. Overall, this work offers a new method for significantly enhancing the antibacterial efficiency of structural antimicrobial surfaces without involving any bactericidal agents, and this functional surface shows great potential in the field of advanced medical materials and hospital surfaces.

Improvement of stability and capacity of Co-free, Li-rich layered oxide Li1.2Ni0.2Mn0.6O2 cathode material through defect control.

Layered oxides based on manganese (Mn), rich in lithium (Li), and free of cobalt (Co) are the most promising cathode candidates used for lithium-ion batteries due to their high capacity, high voltage and low cost. These types of material can be written as xLi2MnO3·(1 - x) LiTMO2 (TM = Ni,Mn,etc.). Though, Li2MnO3 is known to have poor cycling stability and low capacity, which hinder its industrial application commercially. In this work, Li1.2Ni0.2Mn0.6O2 materials with different amounts of structural defects was successfully synthesized using powder metallurgy followed by different cooling processes in order to improve its electrochemical properties. Microstructural analyses and electrochemical measurements were carried out on the study samples synthesized by a combination of X-ray diffraction, transmission electron microscopy, and cyclic voltammetry. It is found that the disorder of the transition metal layer in Li2MnO3 promotes its electrochemical activity, whereas the Li/Ni antisites of the Li layer maintain the stability of its local structure. The material with optimal amount of structural defects had an initial capacity of 188.2 mAh g-1, while maintaining an excellent specific capacity of 144.2 mAh g-1 after 500 cycles at 1C. In comparison, Li1.2Ni0.2Mn0.6O2 without structural defect only gives a capacity of 40.8 mAh g-1 after cycling. This microstructural control strategy provides a simple and effective route to develop high-performance Co-free, Li-rich Mn-based cathode materials and scale-up manufacturing.

Biodegradable Zn-Dy binary alloys with high strength, ductility, cytocompatibility, and antibacterial ability for bone-implant applications.

The unique combination of biodegradability, biocompatibility, and functionality of zinc (Zn)-based alloys makes them highly desirable for a wide range of medical applications. However, a long-standing problem associated with this family of biodegradable alloys in the as-cast state is their limited mechanical strength and slow degradation rate. Here we report the development of Zn-xDy (x = 1, 3, and 5 wt.%) alloys with high strength, ductility, cytocompatibility, antibacterial ability, and appropriate degradation rate for biodegradable bone-implant applications. Our results indicate that the mechanical properties of Zn-xDy alloys were effectively improved with increasing Dy addition and hot-rolling due to the second-phase strengthening. The hot-rolled (HR) Zn-3Dy alloy showed the best combined mechanical performance with an ultimate tensile strength of 270.5 MPa, a yield strength of 214.8 MPa, an elongation of 55.1%, and Brinell hardness of 75.9 HB. The corrosion and degradation rates of HR Zn-xDy alloys in Hanks' solution gradually increased with increasing Dy addition due to the intensification of galvanic corrosion. The HR Zn-3Dy alloy showed high antibacterial ability against S. aureus and cytocompatibility toward MC3T3-E1 cells among all the HR alloys. Overall, the HR Zn-3Dy alloy can be considered a promising biodegradable material for bone implants. STATEMENT OF SIGNIFICANCE: This work reports on Zn-xDy (x = 1, 3, and 5%) alloys fabricated by Dy alloying followed by hot-rolling for biodegradable bone-implant applications. Our findings demonstrate that the hot-rolled (HR) Zn-3Dy alloy showed the best combined mechanical performance with an ultimate tensile strength of 270.5 MPa, a yield strength of 214.8 MPa, an elongation of 55.1%, and Brinell hardness of 75.9 HB. The corrosion and degradation rates of HR Zn-xDy alloys in Hanks' solution gradually increased with increasing Dy addition due to the intensification of galvanic corrosion. Furthermore, the HR Zn-3Dy alloy showed greater antibacterial ability against S. aureus and the best cytocompatibility toward MC3T3-E1 cells among all the HR alloys.

Microstructures, mechanical and corrosion properties of graphene nanoplatelet-reinforced zinc matrix composites for implant applications.

Zinc (Zn)-based alloys and composites are gaining increasing interest as promising biodegradable implant materials due to their appropriate biodegradation rates and biological functionalities. However, the inadequate mechanical strength and ductility of pure Zn have restricted its application. In this study, Zn matrix composites (ZMCs) reinforced with 0.1-0.4 wt.% graphene nanoplatelets (GNP) fabricated via powder metallurgy were investigated as potential biodegradable implant materials. The microstructures, mechanical properties, and corrosion behaviors of the GNP-reinforced ZMCs were characterized using optical microscopy, scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, Raman spectroscopy, compression testing, and electrochemical and immersion testing in Hanks' balanced salt solution (HBSS). The microstructural study revealed that the GNP was uniformly dispersed in the ZMCs after ball milling and sintering at 420°C for 6 h. The microhardness, compressive yield strength, ultimate compressive strength, and compressive strain of the ZMC-0.2GNP were 69 HV, 123 MPa, 247 MPa, and 23 %, respectively, improvements of ∼ 18 %, 50%, ∼ 28%, and ∼ 15% compared to pure Zn. The corrosion rate of the ZMCs were lower than that of the pure Zn in HBSS, and the ZMC-0.2GNP composite exhibited the lowest corrosion rate of 0.09 mm/y as measured by electrochemical testing. Biocompatibility assessment indicated that the diluted extracts of pure Zn and GNP-reinforced ZMCs with concentrations of 12.5% and 6.25% exhibited no cytotoxicity after cell culturing for up to 5 days, and the diluted extracts of ZMC-0.2 GNP composite revealed more than 90% cell viability after cell culturing of 3 days, showing the satisfying cytocompatibility. STATEMENT OF SIGNIFICANCE: Biodegradable Zn is a promising candidate material for orthopedic implant applications. Nonetheless, the inadequate mechanical strength and ductility of pure Zn limited its clinical application. In this study, Zn matrix composites (ZMCs) reinforced with 0.1-0.4 wt.% graphene nanoplatelets (GNP) were developed via powder metallurgy, and the reinforcing efficacy of GNP on their mechanical properties was investigated. The addition of GNP significantly improved the compressive properties of ZMCs, with the Zn-0.2GNP composite exhibiting the best compressive properties, including 123 MPa compressive yield strength, 247 MPa ultimate compressive strength, and 22.9% compressive strain. Further, the 12.5% concentration extract of the ZMCs exhibited no cytotoxicity after cell culturing for 5 d toward SaOS2 cells.

Mechanical, corrosion, nanotribological, and biocompatibility properties of equal channel angular pressed Ti-28Nb-35.4Zr alloys for biomedical applications.

This study systematically investigated the effect of equal channel angular pressing (ECAP) on the microstructure, mechanical, corrosion, nano-tribological properties and biocompatibility of a newly developed ß Ti-28Nb-35.4Zr (hereafter denoted TNZ) alloy. Results indicated that ECAP of the ß TNZ alloy refined its microstructure by forming ultrafine grains without causing stress-induced phase transformation, leading to formation of a single ß phase. The ECAP-processed TNZ alloy exhibited a compressive yield strength of 960 MPa, and high plastic deformation capacity without fracturing under compression loads. Potentiodynamic polarization tests revealed the higher tendency of ECAP-processed TNZ alloys to form passive oxide films on its surface, which exhibited a lower corrosion rate (0.44±0.07 µm/y) in Hanks' balanced salt solution compared to its as-cast counterpart (0.71±0.10 µm/y). Nanotribological testing also revealed higher resistance of the ECAP-processed TNZ alloy to abrasion, wear and scratching, when compared to its as-cast counterpart. Cytocompatibility and cell adhesion assessments of the ECAP-processed TNZ alloys showed a high viability (111%) of human osteoblast-like SaOS2 cells after 7 d of culturing. Moreover, the ECAP-processed TNZ alloy promoted adhesion and spreading of SaOS2 cells, which exhibited growth and proliferation on alloy surfaces. In summary, significantly enhanced mechanical, corrosion, and biological properties of ECAP-processed TNZ alloy advocate its suitability for load-bearing implant applications. STATEMENT OF SIGNIFICANCE: Equal channel angular pressing (ECAP) provides a unique combination of enhanced mechanical and functional properties of materials by optimizing their microstructures and phase transformations. This study investigated the mechanical, nano-tribological, corrosion, and biocompatibility properties of a newly developed ß Ti-28Nb-35.4Zr (TNZ) alloy processed via ECAP. Our findings indicated that ECAP of the ß TNZ alloy refined its microstructure by forming ultrafine grains without causing stress-induced phase transformation. Compared to its as-cast counterpart, ECAP-processed TNZ exhibited significantly enhanced compressive yield strength, plastic deformation capacity, hardness, wear, and corrosion properties. Moreover, in vitro cytocompatibility and cell adhesion studies revealed high cellular viabilities, growth and proliferation of osteoblast-like SaOS2 cells on the ECAP-processed TNZ alloy.

Additive manufacturing of functionally graded porous titanium scaffolds for dental applications.

Graded porous titanium scaffolds are gaining increasing attention as dental implants due to their ability to mimic the mechanical and biological properties of human bone. In this study, we have developed titanium scaffolds with graded primitive structures with porosities of 50.7 %, 61.0 %, 70.5 %, and 80.3 % (denoted as P50, P60, P70, and P80, respectively) for dental applications. The simulation results in the oral environment showed that the maximum von Mises strains and stress of cortical bone tissue around P50, P60, and P70 were lower than 3000 µÎµ and 60 MPa, respectively, which was beneficial for bone regeneration. The elastic modulus and yield strength of P50, P60, and P70 ranged within 5.2-13.8 GPa and 88.6-217.8 MPa, respectively. Among these, P60 exhibited the most favorable mechanical properties with a compression yield strength of 163.2 MPa and an elastic modulus of 9.7 GPa, which are desirable mechanical properties for dental material applications. The tested permeabilities of the fabricated specimens were in the range 0.66-6.88 × 10-9 m2, which is within the range of human bone (0.01-12.10 × 10-9 m2). In vitro biocompatibility assay results showed that P60 and P70 had better potential for cell viability and osteogenesis than P50. It can be concluded that P60, which has a compatible elastic modulus, high yield strength, high permeability, good cytocompatibility, and osteogenesis properties, is a promising candidate for bone-tissue engineering applications in dentistry.

Recent Progress on Nanocrystalline Metallic Materials for Biomedical Applications.

Nanocrystalline (NC) metallic materials have better mechanical properties, corrosion behavior and biocompatibility compared with their coarse-grained (CG) counterparts. Recently, nanocrystalline metallic materials are receiving increasing attention for biomedical applications. In this review, we have summarized the mechanical properties, corrosion behavior, biocompatibility, and clinical applications of different types of NC metallic materials. Nanocrystalline materials, such as Ti and Ti alloys, shape memory alloys (SMAs), stainless steels (SS), and biodegradable Fe and Mg alloys prepared by high-pressure torsion, equiangular extrusion techniques, etc., have better mechanical properties, superior corrosion resistance and biocompatibility properties due to their special nanostructures. Moreover, future research directions of NC metallic materials are elaborated. This review can provide guidance and reference for future research on nanocrystalline metallic materials for biomedical applications.

A biodegradable in situ Zn-Mg2Ge composite for bone-implant applications.

Zinc (Zn)-based composites have received extensive attention as promising biodegradable materials due to their unique combination of moderate biodegradability, biocompatibility, and functionality. Nevertheless, the low mechanical strength of as-cast Zn-based composites impedes their practical clinical application. Here we reported the mechanical properties, corrosion behavior, wear properties, and cytotoxicity of in situ synthesized biodegradable Zn-xMg2Ge (x = 1, 3, and 5 wt.%) composites for bone-implant applications. The mechanical properties of Zn-xMg2Ge composites were effectively improved by alloying and hot-rolling due to particle reinforcement of the Mg2Ge intermetallic phase and dynamic recrystallization. The hot-rolled (HR) Zn-3Mg2Ge composite exhibited the best mechanical properties, including a yield strength of 162.3 MPa, an ultimate tensile strength of 264.3 MPa, an elongation of 10.9%, and a Brinell hardness of 83.9 HB. With an increase in Mg2Ge content, the corrosion and degradation rates of the HR Zn-xMg2Ge composites gradually increased, while their wear rate decreased and then increased in Hanks' solution. The diluted extract (12.5% concentration) of the HR Zn-3Mg2Ge composite showed the highest cell viability compared to the other HR composites and their as-cast pure Zn counterparts. Overall, the HR Zn-3Mg2Ge composite can be considered a promising biodegradable Zn-based composite for bone-implant applications. STATEMENT OF SIGNIFICANCE: This paper reports the mechanical properties, corrosion behavior, wear properties, and cytotoxicity of in situ synthesized biodegradable Zn-xMg2Ge (x = 1, 3, and 5 wt.%) composites for bone-implant applications. Our findings demonstrated that the mechanical properties of Zn-xMg2Ge composites were effectively improved by alloying and hot-rolling due to Mg2Ge particle reinforcement and dynamic recrystallization. The hot-rolled Zn-3Mg2Ge composite showed superior cytocompatibility, satisfying corrosion and degradation rates, and the best mechanical properties including a yield strength of 162.3 MPa, an ultimate tensile strength of 264.3 MPa, and an elongation of 10.9%.

A biodegradable Fe/Zn-3Cu composite with requisite properties for orthopedic applications.

Zinc (Zn)-based metals and alloys are emerging as promising biodegradable implant materials due to their inherent biodegradability and good biocompatibility. However, this class of materials exhibits low mechanical strength and a slow degradation rate, which hinders their clinical application. Here we report the development of a new biodegradable Fe/Zn-3Cu composite fabricated by infiltration casting of a Zn-3Cu alloy into an Fe foam followed by hot-rolling. Our results indicate that the hot-rolled (HR) Fe/Zn-3Cu composite exhibited an α-Zn matrix phase, a secondary CuZn5 phase, and an α-Fe phase. The HR Fe/Zn-3Cu composite exhibited an ultimate tensile strength of 269 MPa, a tensile yield strength of 210 MPa, and an elongation of 27%. The HR Fe/Zn-3Cu composite showed a degradation rate of 228 µm/year after immersion in Hanks' solution for 30 d The diluted extract of the HR Fe/Zn-3Cu composite exhibited a higher cell viability than that of the HR Zn-3Cu alloy in relation to MC3T3-E1 and MG-63 cells. Furthermore, the HR Fe/Zn-3Cu composite showed significantly better antibacterial ability than that of the HR Zn-3Cu alloy in relation to S. aureus. Overall, the HR Fe/Zn-3Cu composite can be anticipated to be a promising biodegradable implant material for bone-fixation applications. STATEMENT OF SIGNIFICANCE: This work reports a new biodegradable Fe/Zn-3Cu composite fabricated by infiltration casting and followed by hot-rolling for biodegradable bone-fixation application. Our findings demonstrated that the hot-rolled (HR) Fe/Zn-3Cu composite exhibited an ultimate tensile strength of 269.1 MPa, a tensile yield strength of 210.3 MPa, and an elongation of 26.7%. HR Fe/Zn-3Cu composite showed a degradation rate of 227.6 µm/a, higher than HR Zn-3Cu alloy after immersion in Hanks' solution for 30 d The diluted extracts of the HR Fe/Zn-3Cu composite exhibited a higher cell viability than HR Zn-3Cu alloy toward MC3T3-E1 cells. Furthermore, the HR Fe/Zn-3Cu composite showed significantly better antibacterial ability than the HR Zn-3Cu alloy toward S. aureus.