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.

Deep Cryogenic Treatment Characteristics of a Deformation-Processed Cu-Ni-Co-Si Alloy.

This paper investigated the influence of deep cryogenic treatments (DCT) on the tensile strength, elongation to fracture and conductivity of a deformation-processed Cu-Ni-Co-Si alloy. The tensile properties were measured using a mechanical testing machine. The conductivity was evaluated using a low-resistance tester. The microstructure and precipitated phases were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), an energy dispersive spectrometer (EDS) and an X-ray diffractometer (XRD). The tensile strength, elongation to fracture and conductivity of the Cu-1.34Ni-1.02Co-0.61Si alloy before and after cold rolling at 47% reduction increased with increasing DCT time and tended to be stable at about 36 h. The microstructure became more uniform after the DCT. The grain size was refined and was smallest after DCT for 48 h. The DCT promoted the precipitation of the solid solution elements Ni, Co and Si from the Cu matrix to form many fine and evenly distributed 20-70 nm spherical second-phase particles in the grains and grain boundaries.

Design, mechanical and degradation requirements of biodegradable metal mesh for pelvic floor reconstruction.

Pelvic organ prolapse is the herniation of surrounding tissue and organs into the vagina and/or rectum and is a result of the weakening of pelvic floor muscles, connective tissue, and fascia. It is widely accepted that 50% of women will develop prolapse, with the prevalence increasing with age, and up to 10-20% of those seek evaluation for their condition. Suture repairs of pelvic floor defects are associated with a high failure rate, and permanent meshes were introduced to reduce the recurrence rate. The meshes were successful in reducing the rate of recurrence but were also associated with a higher rate of complications (pain or erosion into surrounding organs) and as such have been banned in many countries. New materials that are able to provide tissue support without complications are urgently required. A promising new material may be a biodegradable metal, which provides support during healing and subsequently completely degrades. We summarise pelvic mesh usage, and evaluate the use of a biodegradable metal, which has advantages of biocompatibility, antibacterial properties, and mechanical properties. The remaining challenges are discussed as follows: (1) degradation rate, (2) stiffness, (3) corrosion fatigue, (4) zinc aging, and (5) MRI artifacts.

Influence of Si, Cu, B, and Trace Alloying Elements on the Conductivity of the Al-Si-Cu Alloy.

The influence of Si, Cu, B, and trace alloying elements on the conductivity of aluminum die cast 12 (ADC12) alloy was investigated. The conductivity decreased linearly with increasing volume fraction of the Si phase attributed to a linear decrease of the volume of the more conductive Al phase through a rule of mixtures. The conductivity also decreased with increasing Cu content, between 0~3%. The conductivity increased with increasing B content, reached the peak at 0.02% B and thereafter decreased somewhat. The mechanism was that B reacted with the transition element in the Al phase to form boride, decreasing the transition element concentration in the Al lattice, and decreasing the lattice constant. The thermal conductivity, λ, was related to the electrical conductivity, σ, by means of λ=LTσ+λg, where L is the apparent Lorentz constant, 1.86 × 10-8; T is the absolute temperature, 293 K; λg is the lattice conductivity, 42.3 W/(m·K).

Study on a Novel Biodegradable and Antibacterial Fe-Based Alloy Prepared by Microwave Sintering.

This research produced a porous Fe-8 wt.% Cu alloy by microwave sintering in order to achieve (i) an increased biodegradation rate, and (ii) an antibacterial function. The Fe-8Cu alloy had higher density, hardness and degradation rate (about 2 times higher) but smaller and fewer surface pores, compared to the pure Fe. The Fe-8Cu alloy had a strong antibacterial function (the antibacterial rates against E. coli were up to 99.9%) and good biocompatibility. This work provides a novel approach of alloy design and processing to develop novel antibacterial Fe-based alloys.

Comparison on Tensile Characteristics of Plain C-Mn Steel with Ultrafine Grained Ferrite/Cementite Microstructure and Coarse Grained Ferrite/Pearlite Microstructure.

This work investigated the tensile characteristics of plain C-Mn steel with an ultrafine grained ferrite/cementite (UGF/C) microstructure and coarse-grained ferrite/pearlite (CGF/P) microstructure. The tensile tests were performed at temperatures between 77 K and 323 K. The lower yield and the ultimate tensile strengths were significantly increased when the microstructure was changed from the CGF/P to the UGF/C microstructures, but the total elongation and the uniform elongation decreased. A microstructural change from the CGF/P microstructure to the UGF/C microstructure had an influence on the athermal component of the lower yield and the ultimate tensile strengths but not on the thermal component. The UGF/C microstructure with a higher carbon content provided a higher strength without losing ductility because cementite particles restrained necking.

Biodegradation, Antibacterial Performance, and Cytocompatibility of a Novel ZK30-Cu-Mn Biomedical Alloy Produced by Selective Laser Melting.

In the present study, an antibacterial biomedical magnesium (Mg) alloy with a low biodegradation rate was designed, and ZK30-0.2Cu-xMn (x = 0, 0.4, 0.8, 1.2, and 1.6 wt%) was produced by selective laser melting, which is a widely applied laser powder bed fusion additive manufacturing technology. Alloying with Mn evidently influenced the grain size, hardness, and biodegradation behavior. On the other hand, increasing Mn content to 0.8 wt% resulted in a decrease of biodegradation rate which is attributed to the decreased grain size and relatively protective surface layer of manganese oxide. Higher Mn contents increased the biodegradation rate attributed to the presence of the Mn-rich particles. Taken together, ZK30-0.2Cu-0.8Mn exhibited the lowest biodegradation rate, strong antibacterial performance, and good cytocompatibility.

Microstructure and Strengthening Model of Cu-Fe In-Situ Composites.

The tensile strength evolution and strengthening mechanism of Cu-Fe in-situ composites were investigated using both experiments and theoretical analysis. Experimentally, the tensile strength evolution of the in-situ composites with a cold deformation strain was studied using the model alloys Cu-11Fe, Cu-14Fe, and Cu-17Fe, and the effect of the strain on the matrix of the in-situ composites was studied using the model alloys Cu-3Fe and Cu-4.3Fe. The tensile strength was related to the microstructure and to the theoretical strengthening mechanisms. Based on these experimental data and theoretical insights, a mathematical model was established for the dependence of the tensile strength on the cold deformation strain. For low cold deformation strains, the strengthening mechanism was mainly work hardening, solid solution, and precipitation strengthening. Tensile strength can be estimated using an improved rule of mixtures. For high cold deformation strains, the strengthening mechanism was mainly filament strengthening. Tensile strength can be estimated using an improved Hall-Petch relation.

Absorbable Mg surgical tack: Proof of concept &in situ fixation strength.

A prototype magnesium (Mg) surgical tack is tested comparatively against commercially available tacks made of titanium (ProTacktm, Medtronic) and PLGA (AbsorbaTacktm, Medtronic). The pull-out force is measured in situ in a lap-shear pull-out test, using porcine abdominal muscle tissue as a model. The Mg tack had a pull-out force comparable to those of the commercially available tacks. The majority of the Mg tacks also had a more ductile failure mode (i.e. the tacks deformed prior to failure), compared to the commercial tacks which pulled directly from the tissue with no deformation. The Mg tacks deformed as they were removed from the tissue, causing less damage to the tissue in the process. This is the first reported use of a Mg alloy in this application, and the proof of concept indicates that this is an area that deserves further interest and study.

Effect of Boron on the Grain Refinement and Mechanical Properties of as-Cast Mg Alloy AM50.

The effect of B addition on the microstructure and mechanical properties of AM50 was investigated, and the mechanism of grain refinement was clarified. Optical microscopy, X-ray diffraction, scanning electron microscopy, and electron probe microanalysis were used to characterize the microstructure evolution. The grain size of as-cast AM50 decreased from 550 µm to 100 µm with the B content increasing from 0 to 0.15 wt.%. AlB2 particles in the Al-3B master alloy transformed to Mg-B, and acted as the grain refiner. The addition of B to as cast AM50 alloy results in improved mechanical properties of AM50 + xB alloys. For instance, the YTS (yield tensile strength), UTS (ultimate tensile strength), and elongation of as cast AM50 + 0.15 wt.% B alloy was 94 MPa, 215 MPa, and 12.3%.

Novel ß-Ti35Zr28Nb alloy scaffolds manufactured using selective laser melting for bone implant applications.

Titanium (Ti) based tissue engineering scaffolds can be used to repair damaged bone. However, successful orthopedic applications of these scaffolds rely on their ability to mimic the mechanical properties of trabecular bone. Selective laser melting (SLM) was used to manufacture scaffolds of a new ß-Ti35Zr28Nb alloy for biomedical applications. Porosity values of the scaffolds were 83% for the FCCZ structure (face centered cubic unit cell with longitudinal struts) and 50% for the FBCCZ structure (face and body centered cubic unit cell with longitudinal struts). The scaffolds had an elastic modulus of ∼1 GPa and a plateau strength of 8-58 MPa, which fall within the values of trabecular bone (0.2-5 GPa for elastic modulus and 4-70 MPa for compressive strength). The SLM-manufactured ß-Ti35Zr28Nb alloy showed good corrosion properties. MTS assay revealed that both the FCCZ and FBCCZ scaffolds had a cell viability similar to the control. SEM observation indicated that the osteoblast-like cells adhered, spread and grew healthily on the surface of both scaffolds after culture for 7, 14 and 28 d, demonstrating good biocompatibility. Overall, the SLM-manufactured Ti35Zr28Nb scaffolds possess promising potential as hard-tissue implant materials due to their appropriate mechanical properties, good corrosion behavior and biocompatibility. STATEMENT OF SIGNIFICANCE: Novel ß Ti35Zr28Nb alloy scaffolds with FCCZ and FBCCZ structures were successfully fabricated by selective laser melting (SLM) for biomedical applications. The scaffolds showed values of elastic modulus of ∼1 GPa and plateau strength of 8-58 MPa, which fall within the ranges of the mechanical properties of trabecular bone. The SLM-manufactured ß Ti35Zr28Nb alloy showed good corrosion properties. Both SLM-manufactured FCCZ and FBCCZ scaffolds exhibited good biocompatibility, with osteoblast-like cells attaching, growing, and spreading in a healthy way on their surfaces after culturing for different periods up to 28 d.

A Graphene Spin Coatings for Cost-Effective Corrosion Protection for the Magnesium Alloy AZ31.

A graphene coating, prepared via spin coating on the Mg alloy AZ31, was characterized using Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The Raman spectra indicated that the graphene spin coatings were uniform over the surface of AZ31. The SEM indicated the chemical composition of the graphene coating. The XPS analysis indicated that the carbon was mainly composed of conjugated double bonds. The corrosion behavior was evaluated from potentio-dynamic polarization curves and electrochemical impedance spectroscopy (EIS). The graphene coating decreased the corrosion rate of AZ31 by three orders of magnitude.

The influence of two common sterilization techniques on the corrosion of Mg and its alloys for biomedical applications.

This paper studied the influence of two common sterilization techniques, ethylene oxide (EO) and gamma irradiation (GI), on the corrosion rate of four Mg-based materials in CO2 -bicarbonate buffered Hanks' solution. The four materials were: high-purity (HP)-Mg, ZE41, ultra-high purity (XHP)-Mg, and XHP-ZX00. The corrosion rate was measured through mass loss (Pm ) and hydrogen evolution (PH ). Two-way analysis of variance (ANOVA) was conducted to assess the effect of the sterilization techniques on the corrosion rates across the four materials. The ANOVA analyzed the variables of (1) material, (2) sterilization condition (EO, GI, and an unsterilized control group), and (3) the interaction between these two independent variables. Neither sterilization technique (EO and GI) significantly influenced the corrosion rate as measured by Pm (p < 0.84) nor PH (p < 0.08). This result was consistent across the four materials tested, as there was no interaction between the test variables of material and sterilization condition for Pm (p < 0.49) or PH (p < 0.27). As neither EO nor GI influenced the corrosion rates, either of these techniques warrants consideration for use on Mg-based medical implants and devices. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1907-1917, 2018.

Sealing of anodized magnesium alloy AZ31 with MgAl layered double hydroxides layers.

In this work, anodized magnesium alloy AZ31 with and without boiling water sealing was pre-prepared, and then MgAl-layered double hydroxide (LDH) films were fabricated on it through hydrothermal chemical conversion of the pre-prepared anodic layer. The morphology, structure, and composition of the films were characterized by XRD, SEM, EDS, FT-IR, XPS and GDOES. It was found that the porosity of the films was reduced after in situ fabrication of the LDHs. The effects of boiling water sealing treatment on the anodized substrate were also discussed. Moreover, the polarization curve, EIS, and immersion tests showed that LDHs fabricated on the anodized substrate with boiling water sealing treatment exhibited a significant long period of protection for the substrate.