Mechanical properties, in vitro corrosion and biocompatibility of newly developed biodegradable Mg-Zr-Sr-Ho alloys for biomedical applications

Our previous studies have demonstrated that Mg-Zr-Sr alloys can be anticipated as excellent biodegradable implant materials for load-bearing applications. In general, rare earth elements (REEs) are widely used in magnesium (Mg) alloys with the aim of enhancing the mechanical properties of Mg-based alloys. In this study, the REE holmium (Ho) was added to an Mg-1Zr-2Sr alloy at different concentrations of Mg1Zr2SrxHo alloys (x = 0, 1, 3, 5 wt. %) and the microstructure, mechanical properties, degradation behaviour and biocompatibility of the alloys were systematically investigated. The results indicate that the addition of Ho to Mg1Zr2Sr led to the formation of the intermetallic phases MgHo3, Mg2Ho and Mg17Sr2 which resulted in enhanced mechanical strength and decreased degradation rates of the Mg-Zr-Sr-Ho alloys. Furthermore, Ho addition (≤5 wt. %) to Mg-Zr-Sr alloys led to enhancement of cell adhesion and proliferation of osteoblast cells on the Mg-Zr-Sr-Ho alloys. The in vitro biodegradation and the biocompatibility of the Mg-Zr-Sr-Ho alloys were both influenced by the Ho concentration in the Mg alloys; Mg1Zr2Sr3Ho exhibited lower degradation rates than Mg1Zr2Sr and displayed the best biocompatibility compared with the other alloys

Numerical observation of non-axisymmetric vesicles in fluid membranes

By means of Surface Evolver (Exp. Math,1,141 1992), a software package of brute-force energy minimization over a triangulated surface developed by the geometry center of University of Minnesota, we have numerically searched the non-axisymmetric shapes under the Helfrich spontaneous curvature (SC) energy model. We show for the first time there are abundant mechanically stable non-axisymmetric vesicles in SC model, including regular ones with intrinsic geometric symmetry and complex irregular ones. We report in this paper several interesting shapes including a corniculate shape with six corns, a quadri-concave shape, a shape resembling sickle cells, and a shape resembling acanthocytes. As far as we know, these shapes have not been theoretically obtained by any curvature model before. In addition, the role of the spontaneous curvature in the formation of irregular crenated vesicles has been studied. The results shows a positive spontaneous curvature may be a necessary condition to keep an irregular crenated shape being mechanically stable.Comment: RevTex, 14 pages. A hard copy of 8 figures is available on reques

Expression of Foot-and-Mouth Disease Virus Capsid Proteins in Silkworm-Baculovirus Expression System and Its Utilization as a Subunit Vaccine

Background: Foot-and-mouth disease (FMD) is a highly contagious disease of livestock that causes severe economic loss in susceptible cloven-hoofed animals. Although the traditional inactivated vaccine has been proved effective, it may lead to a new outbreak of FMD because of either incomplete inactivation of FMDV or the escape of live virus from vaccine production workshop. Thus, it is urgent to develop a novel FMDV vaccine that is safer, more effective and more economical than traditional vaccines. Methodology and Principal Findings: A recombinant silkworm baculovirus Bm-P12A3C which contained the intact P1-2A and 3C protease coding regions of FMDV Asia 1/HNK/CHA/05 was developed. Indirect immunofluorescence test and sandwich-ELISA were used to verify that Bm-P12A3C could express the target cassette. Expression products from silkworm were diluted to 30 folds and used as antigen to immunize cattle. Specific antibody was induced in all vaccinated animals. After challenge with virulent homologous virus, four of the five animals were completely protected, and clinical symptoms were alleviated and delayed in the remaining one. Furthermore, a PD50 (50 % bovine protective dose) test was performed to assess the bovine potency of the subunit vaccine. The result showed the subunit vaccine could achieve 6.34 PD50 per dose

Development of in-situ Zn–3Cu–10ZnO composite prepared by high-pressure solidification for orthopedic applications

Biodegradable zinc (Zn)-based composites are considered to be the next generation of promising orthopedic implant materials due to their degradability and the multiple functionality of combining metal and ceramic phases. However, its clinical bone-implant application is seriously limited due to their poor interface binding ability and mechanical properties. Herein, we developed the biodegradable in-situ Zn–3Cu–10ZnO composite through powder metallurgy using Zn and copper (Cu) powder combined with hot forging, followed by the high-pressure solidification (HPS) process for bone-implant application. Microstructural characterization showed that the HPS process can densify composite, form a uniform distribution of fine ZnO particle, and increase Cu atom solid solubility in the Zn matrix. Mechanical test revealed that the HPS composite exhibited a high compression performance with a compressive yield strength of 340.8 MPa, an ultimate compressive strength of 514.2 MPa, and a failure strain of ≥70%. The HPS composite exhibited the lowest corrosion rate of 25.8 μm/y and 44.3 μm/y measured by electrochemical corrosion and immersion tests, respectively, among these composites. Moreover, the diluted extracts of HPS composite with a concentration of ent% showed a higher cytocompatibility among these composites and better antimicrobial capability than those of the as-cast pure Zn. Accordingly, the HPS Zn–3Cu–10ZnO composite is expected to be a potential biodegradable material for orthopedic applications

Titanium-niobium pentoxide composites for biomedical applications

The strength of titanium scaffolds with the introduction of high porosity decreases dramatically and may become inadequate for load bearing in biomedical applications. To simultaneously meet the requirements of biocompatibility, low elastic modulus and appropriate strength for orthopedic implant materials, it is highly desirable to develop new biocompatible titanium based materials with enhanced strength. In this study, we developed a niobium pentoxide (Nb2O5) reinforced titanium composite via powder metallurgy for biomedical applications. The strength of the Nb2O5 reinforced titanium composites (Ti-Nb2O5) is significantly higher than that of pure titanium. Cell culture results revealed that the Ti-Nb2O5 composite exhibits excellent biocompatibility and cell adhesion. Human osteoblast-like cells grew and spread healthily on the surface of the Ti-Nb2O5 composite. Our study demonstrated that Nb2O5 reinforced titanium composite is a promising implant material by virtue of its high mechanical strength and excellent biocompatibility

Improvements in mechanical, corrosion, and biocompatibility properties of Mg–Zr–Sr–Dy alloys via extrusion for biodegradable implant applications

In this study, extrusion was performed on Mg‒Zr‒Sr‒Dy alloys for improving their mechanical, corrosion, and biocompatibility properties. Effects of extrusion and alloying elements on the microstructural characteristics, tensile and compressive strengths, corrosion behavior, and biocompatibility were investigated. The Mg‒Zr‒Sr‒Dy alloys were composed of an α-Mg matrix containing {101¯2} extension twins and secondary phases of intermetallic compounds Mg17Sr2 and Mg2Dy. Evolution of basal and rare earth (RE) textures was observed in the extruded alloys and an increase in Dy content to 2 wt.% resulted in texture randomization and strengthening of the RE component, mainly due to particle-stimulated nucleation and a change from discontinuous dynamic recrystallization to continuous dynamic recrystallization, which also led to an improved tension–compression yield asymmetry of 0.87. Extrusion of the alloys significantly enhanced their tensile and compressive properties due to improved distribution of alloying elements and formation of textures. Corrosion rates tested by hydrogen evolution testing, potentiodynamic polarization, and electrical impedance spectroscopy showed similar trends for each composition, and the lowest corrosion rate of 3.37 mmy−1 was observed for the Mg-1Zr-0.5Sr-1Dy in the potentiodynamic polarization testing. Dy2O3 was observed in the inner layers of the Mg(OH)2 protective films, whose protective efficacy was confirmed by charge-transfer and film resistances. A comparison among the minimum CRs observed in this study and previously studied as-cast Mg‒Zr‒Sr‒Dy and extruded Mg‒Zr‒Sr alloys, demonstrates that both the extrusion process and addition of Dy in Mg‒Zr‒Sr improved the CR. Similarly, extruded Mg–Zr–Sr–Dy alloys showed improved cell viability and adhesion of human osteoblast–like SaOS2 cells due to increased corrosion resistance and enhanced Sr distribution within the Mg matrix

Impact of scandium and terbium on the mechanical properties, corrosion behavior, and biocompatibility of biodegradable Mg-Zn-Zr-Mn alloys

Magnesium (Mg)-based bone implants degrade rapidly in the physiological environment of the human body which affects their structural integrity and biocompatibility before adequate bone repair. Rare earth elements (REEs) have demonstrated their effectiveness in tailoring the corrosion and mechanical behavior of Mg alloys. This study methodically investigated the impacts of scandium (Sc) and terbium (Tb) in tailoring the corrosion resistance, mechanical properties, and biocompatibility of Mg–0.5Zn–0.35Zr–0.15Mn (MZZM) alloys fabricated via casting and hot extrusion. Results indicate that addition of Sc and Tb improved the strength of MZZM alloys via grain size reduction and solid solution strengthening mechanisms. The extruded MZZM–(1–2)Sc–(1–2)Tb (wt.%) alloys exhibit compressive strengths within the range of 336–405 MPa, surpassing the minimum required strength of 200 MPa for bone implants by a significant margin. Potentiodynamic polarization tests revealed low corrosion rates of as–cast MZZM (0.25 mm/y), MZZM–2Tb (0.45 mm/y), MZZM–1Sc–1Tb (0.18 mm/y), and MZZM–1Sc–2Tb (0.64 mm/y), and extruded MZZM (0.17 mm/y), MZZM–1Sc (0.15 mm/y), MZZM-2Sc (0.45 mm/y), MZZM-1Tb (0.17 mm/y), MZZM-2Tb (0.10 mm/y), MZZM–1Sc-1Tb (0.14 mm/y), MZZM-1Sc-2Tb (0.40 mm/y), and MZZM–2Sc–2Tb (0.51 mm/y) alloys, which were found lower compared to corrosion rate of high-purity Mg (∼1.0 mm/y) reported in the literature. Furthermore, addition of Sc, or Tb, or Sc and Tb to MZZM alloys did not adversely affect the viability of SaOS2 cells, but enhanced their initial cell attachment, proliferation, and spreading shown via polygonal shapes and filipodia. This study emphasizes the benefits of incorporating Sc and Tb elements in MZZM alloys, as they effectively enhance corrosion resistance, mechanical properties, and biocompatibility simultaneously

Biodegradable Zn–3Cu and Zn–3Cu–0.2Ti alloys with ultrahigh ductility and antibacterial ability for orthopedic applications

Zinc (Zn) and its alloys have been proposed as biodegradable implant materials due to their unique combination of biodegradability, biocompatibility, and biofunctionality. However, the insufficient mechanical properties of pure Zn greatly limit its clinical application. Here, we report on the microstructure, mechanical properties, friction and wear behavior, corrosion and degradation properties, hemocompatibility, and cytocompatibility of Zn–3Cu and Zn–3Cu–0.2Ti alloys under three different conditions of as-cast (AC), hot-rolling (HR), and hot-rolling plus cold-rolling (HR + CR). The HR + CR Zn–3Cu–0.2Ti exhibited the best set of comprehensive properties among all the alloy samples, with yield strength of 211.0 MPa, ultimate strength of 271.1 MPa, and elongation of 72.1 %. Immersion tests of the Zn–3Cu and Zn–3Cu–0.2Ti alloys in Hanks’ solution for 3 months indicated that the AC samples showed the lowest degradation rate, followed by the HR samples, and then the HR + CR samples, while the HR + CR Zn–3Cu exhibited the highest degradation rate of 23.9 μm/a. Friction and wear testing of the Zn–3Cu and Zn–3Cu–0.2Ti alloys in Hanks’ solution indicated that the AC samples showed the highest wear resistance, followed by the HR samples, and then the HR + CR samples, while the AC Zn–3Cu–0.2Ti showed the highest wear resistance. The diluted extracts of HR + CR Zn–3Cu and Zn–3Cu–0.2Ti at a concentration of ≤25 % exhibited non-cytotoxicity. Furthermore, both the HR + CR Zn–3Cu and Zn–3Cu–0.2Ti exhibited effective antibacterial properties against S. aureus

A social-semantic working-memory account for two canonical language areas

Language and social cognition are traditionally studied as separate cognitive domains, yet accumulative studies reveal overlapping neural correlates at the left ventral temporoparietal junction (vTPJ) and the left lateral anterior temporal lobe (lATL), which have been attributed to sentence processing and social concept activation. We propose a common cognitive component underlying both effects: social-semantic working memory. We confirmed two key predictions of our hypothesis using functional MRI. First, the left vTPJ and lATL showed sensitivity to sentences only when the sentences conveyed social meaning; second, these regions showed persistent social-semantic-selective activity after the linguistic stimuli disappeared. We additionally found that both regions were sensitive to the socialness of non-linguistic stimuli and were more tightly connected with the social-semantic-processing areas than with the sentence-processing areas. The converging evidence indicates the social-semantic working-memory function of the left vTPJ and lATL and challenges the general-semantic and/or syntactic accounts for the neural activity of these regions. In a series of human functional MRI studies, Zhang et al. find that the activation of two brain areas typically involved in language comprehension reflects working memory of social semantics rather than general semantic or syntactic processing

Enhancing mechanical strength, tribological properties, cytocompatibility, osteogenic differentiation, and antibacterial capacity of biodegradable Zn-5RE (RE = Nd, Y, and Ho) alloys for potential bone-implant application

Degradable zinc (Zn) based metals exhibit great promise as potential load-bearing bone-implant materials due to their suitable biodegradability, good fabricate-friendliness, biocompatibility, and favorable osteogenesis-promoting capacity. Nevertheless, most as-cast Zn-based metals display poor mechanical properties due to their coarse grain size and few slip systems, which is challenging to meet bone-implant application requirements. Herein, the alloying using rare earth (RE) elements of neodymium (Nd), yttrium (Y), and holmium (Ho) combined with hot-rolling was used to prepare the hot-rolled (HR) Zn-5RE binary alloys for load-bearing bone fixation or bone repair applications. HR Zn–5Y sample demonstrated the best mechanical properties matching with an ultimate tensile strength of ∼260 MPa, yield strength of ∼200 MPa, elongation of ∼43.5%, strength-elongation product of ∼11.3 GPa%, and macro-hardness of ∼104.7 HB among the HR samples, close to the requirements of mechanical properties for degradable bone-implant materials. HR Zn–5Y sample exhibited the lowest corrosion rate of ∼178 μm/y measured by electrochemical polarization testing, the degradation rate of ∼29 μm/y measured by static immersion testing, and high tribological properties in Hanks’ solution. The diluted Zn–5Y extract showed an appropriate cytocompatibility to 3T3 and MG-63 cells and moderate osteogenic differentiation ability to 3T3 cells among HR Zn-5RE and pure Zn extracts. Meanwhile, the HR Zn–5Y sample showed a suitable and effective antibacterial capacity against S. aureus and E. coli. Overall, the HR Zn–5Y sample is a promising moderate load-bearing bone-implant material for bone pins, plates, and guiding bone regeneration membrane application