Abstract Metals and ceramics are commonly used in orthopaedics, dentistry and other load bearing applications. However, the use of ceramic matrix composites reinforced with biocompatible metals for ...heavy load-bearing hard tissue replacement applications has not previously been reported. In order to improve the reliability and the mechanical properties of biomedical implants, new zirconia–Nb composites have been recently developed. The aim of this study was to investigate the biological tolerance of these new zirconia/Nb biocermets implants with both in vitro and in vivo approaches. At first, human bone marrow derived mesenchymal stem cells were cultured on sintered biocermet discs with polished surfaces and were compared with responses to niobium metal. In vitro, the biocermets showed no deleterious effect on cell proliferation, extra-cellular matrix production or on cell morphology. Furthermore, the biocermet showed a higher percentage of cell proliferation than Nb metal. On the other hand, the bone response to these new zirconia/Nb biocermets was studied. Cylinders of biocermets, as well as commercially Nb rod were implanted in the tibiae of New Zealand white rabbits. All the animals were euthanatized after 6 months. The specimens were processed to obtain thin ground sections. The slides were observed in normal transmitted light microscope. A newly formed bone was observed in close contact with material surfaces. No inflamed or multinucleated cells were present. This study concluded that zirconia/Nb composites are biocompatible and osteoconductive. The ceramic-metal composite has even better osteointegration ability than pure Nb. In conclusion, zirconia–Nb biocermet is suitable for heavy load-bearing hard tissue replacement from the point of view of both mechanical properties and biocompatibility.
Hierarchical tantalum-graphene flakes reinforced zirconia (3Y-TZP) ceramic matrix composites were fabricated by wet processing route and freeze drying followed by spark plasma sintering (SPS). The ...microstructures and mechanical properties were investigated. The results show that graphene and Ta particles are homogeneously dispersed in the ceramic matrix and the optimum sintering temperature for complete densification of composites and thermal reduction of the graphene oxide is 1500 °C. The addition of dual reinforcements of tantalum microflakes and graphene nanoflakes results in significant improvement in the mechanical properties of the ZrO2 matrix. Approximately a 30% increase in flexural strength vs the zirconia-Ta composite and a 175% increase in fracture toughness vs the monolithic zirconia have been achieved by introducing 0.5 vol% GO and 20 vol% Ta particles.
Dense (>98 th%) and homogeneous ceramic/metal composites were obtained by spark plasma sintering (SPS) using ZrO2 and lamellar metallic powder of tantalum (20 vol%) as starting materials. Composites ...showed a fracture toughness value of 16 MPa m1/2 mainly due to crack bridging of the elastic–plastic deformations of ductile metal particles. This fracture toughness was accompanied by a simultaneous enhancement in damage tolerance and fatigue resistance of 3Y-TZP/Ta composites.
Besides exceptional mechanical properties, SPS sintered 3Y-TZP/Ta composites also showed the electrical conductivity suited to wire electrical discharge machining (WEDM). Therefore, they are suitable to be produced in mechanically performant, complex shape components with the required tolerance while reducing machining costs. The aim of this work was the study of the electrical properties of the materials as well as the characteristics of the machining process and the machined surfaces influence on the bending strength of composites. The results show that workpieces can be machined with high accuracy and without a drop in mechanical strength.
•Fully dense and homogeneous ceramic-metal composites were successfully fabricated.•Composites showed outstanding value of fracture toughness of 16 MPa m1/2.•3Y-TZP/Ta composites suited to wire electrical discharge machining (WEDM).•WEDM cut specimens showed insignificant degradation in the bending strength.
Dense (>98 th%) and homogeneous ceramic/metal composites were obtained by spark plasma sintering (SPS) using ZrO
and lamellar metallic powders of tantalum or niobium (20 vol.%) as starting materials. ...The present study has demonstrated the unique and unpredicted simultaneous enhancement in toughness and strength with very high flaw tolerance of zirconia/Ta composites. In addition to their excellent static mechanical properties, these composites also have exceptional resistance to fatigue loading. It has been shown that the major contributions to toughening are the resulting crack bridging and plastic deformation of the metallic particles, together with crack deflection and interfacial debonding, which is compatible with the coexistence in the composite of both, strong and weak ceramic/metal interfaces, in agreement with predictions of ab-initio calculations. Therefore, these materials are promising candidates for designing damage tolerance components for aerospace industry, cutting and drilling tools, biomedical implants, among many others.
Although bioactive glasses have been widely used for the surfaces of orthopaedic and dental implants, its limited mechanical strength, low toughness and wear resistance have prevented their use as ...load-bearing devices. Considering that even a small variation in the composition of such materials can deeply modify their features, inducing very different physicochemical or mechanical properties, the present research was conducted by modifying the glass network of 45S5 Bioglass® by adding Al2O3 and SrO to obtain a highly bioactive glass with improved mechanical and tribological performance for biomedical applications. The addition of 2% Al2O3 and 2% SrO produced a dense material with the same elastic modulus as 45S5 (~50 GPa). Moreover, the bending strength increased by 60% and the toughness doubled. The wear rate obtained against steel was found to be three times lower than that of 45S5. From the results, it can be assumed that both alumina and strontium synergistically play crucial roles in the mechanical and tribological properties of these new bioactive glasses.
We sought to identify the comorbidities associated with heart failure (HF) in a non-selected cohort of patients, and its influence on mortality and rehospitalization.
Data were obtained from the ...'Registro de Insuficiencia Cardiaca' (RICA) of the Spanish Society of Internal Medicine. The registry includes patients prospectively admitted in Internal Medicine units for acute HF. Variables included in Charlson Index (ChI) were collected and analysed according to age, gender, left ventricular ejection fraction (LVEF) and Barthel Index. The primary end point of study was the likelihood of rehospitalization and death for any cause during the year after discharge.
We included 2051 patients, mean age 78 and 53% females. LVEF was ⩾ 50% in 59.1% of the cohort. There was a high degree of dependency as measured by Barthel Index (14.8 % had an index ≤ 60). Mean ChI was 2.91 (SD ± 2.4). The most frequent comorbidities included in ChI were diabetes mellitus (44.3%), chronic renal impairment (30.8%) and chronic obstructive pulmonary disease (COPD) (27.4%). Age, myocardial infarction, peripheral artery disease, dementia, COPD, chronic renal impairment and diabetes with target-organ damage were all identified as independent prognostic factors for the combined end point of rehospitalization and death at 1 year. However, if multivariate analysis was done including ChI, only this remained as an independent prognostic factor for the combined end point (P < 0.001).
HF is a comorbid condition. ChI is a simple and feasible tool for estimating the burden of comorbidities in such population. We believe that a holistic approach to HF would improve prognosis and the relief the pressure exerted on public health services.
In the present work, the recent advances and promising potential applications of new developed ceramic (alumina, zirconia, spinel)/metal (Ni, Nb, W) micro/nanocomposites are discussed. We review the ...exotic properties of metal particles embedded into ceramic matrices and the effect of the percolation law, the nature of the interfaces and the size effect (micro/nano). This article discusses the material's mechanical and tribological properties, such as hardness, wear resistance and toughness.
The aim of this survey was to determine the effects of an aerobic physical training program of six months duration on the serum and urinary concentrations of essential trace elements among middle ...distance runners and untrained, non-sportsmen participants.
24 well-trained, middle-distance (1500 and 5000 m), aerobic male runners (AG) were recruited at the beginning of their training season and 26 untrained males formed the control group (CG). All participants were from the same region of Spain, and all of them had been living in this area for at least two years. Serum and urine of samples of Cobalt (Co), Copper (Cu), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Vanadium (V) and Zinc (Zn) were obtained at the beginning of the training season, and six months later, from all participants. All samples were analyzed with inductively coupled plasma mass spectrometry (ICP-MS).
Two-way ANOVA showed significant differences relative to group effect in serum concentrations of Co, Cu, Mn, Mo, Se and Zn. Attending to time effect, there were differences in Mn (p = 0.003) and Zn (p = 0.001). The group x time interaction revealed differences only in the case of Mn (p = 0.04). In urine, significant differences between group were obtained in Co, Cu, Mn, Se and V. Time effect showed changes in Co, Cy, Mo and Se. Finally, the group and time interaction revealed significant differences in urinary Cu (p = 0.001), Mn (p = 0.01) and Se (p = 0.001).
A six-month aerobic training program for well-trained athletes induced modifications in the body values of several minerals, a fact which may reflect adaptive responses to physical exercise. The obtained data could be interesting for physicians or coaches in order to consider specific modifications in sportsmen's diets as well as to determine specific nutritional supplementation strategies.
The addition of small amounts of niobia (Nb2O5) in borosilicate glasses was explored. By analysis on thermal and structural changes, we found evidences that niobium integrates the glass structure in ...octahedral NbO6 coordination. Adding up to 8.0 mol% of Nb2O5, the oxide partially ruptured the glass structure, interfering in the BO3/BO4 ratio, but the predominant network configuration was maintained. Thermally, there was an increase in the processing interval and the glasses became more resistant against crystallization, with the presence of niobia. Also, the oxide contributed to a notable decrease in the viscosity of the melts. The improvement of such properties were obtained by the controlled dispersion of the oxide in the glass network structure, avoiding large areas of phase-to-phase separation to preserve the desired ability of these glasses to incorporate a wide range of elements.
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