SiC nanoparticle-reinforced Al2O3–Nb composite as a potential femoral head material in total hip arthroplasty

A ceramic–metal composite consisting of SiC nanoparticle-reinforced Al₂O₃ and Nb (referred to as SiC/Al₂O₃–Nb), was prepared and evaluated in vitro for potential application as a femoral head material in total hip arthroplasty. Dense bi-layer laminates of SiC nanoparticle-reinforced Al₂O₃ and Nb were fabricated by hot pressing of powders (1425 °C; 35 MPa), and evaluated using scanning electron microscopy, microchemical analysis, and mechanical testing. The flexural strength of the SiC/Al₂O₃–Nb laminate (960 ± 20 MPa) was higher than the value (720 ± 40 MPa) for an Al₂O₃–Nb laminate, and far higher than the value (620 ± 50 MPa) for SiC nanoparticle-reinforced Al₂O₃ (SiC/Al₂O₃). The Vickers hardness of SiC/Al₂O₃ was 17 ± 2 GPa, compared to 12 ± 1 GPa for Al₂O₃. A high interfacial shear strength of the SiC/Al₂O₃–Nb laminate (310 ± 100 MPa), coupled with SEM observation of the interfacial region, showed strong bonding between the SiC/Al₂O₃ and Nb layers. Composite femoral heads consisting of a SiC/Al₂O₃ surface layer and a Nb core could potentially lead to a reduction in the tendency for brittle failure as well as to lower wear, when compared to Al₂O₃ femoral heads.     

Three-phase polymer–ceramic–metal composite for embedded capacitor applications

This paper addresses the materials and processes for printed wiring board compatible embedded capacitor using ceramic, polymer and metal. The Ca[(Li_1/3Nb_2/3)_0.8Ti_0.2]O_3?δ (CLNT)–epoxy–silver, three-phase composites were prepared by two step mixing and thermosetting technique. The dielectric properties of the three-phase composites were investigated in terms of volume fraction of silver, temperature and frequency. The dielectric properties of epoxy–CLNT composites were compared with theoretical predictions. The relative permittivity of the three-phase composites increased with silver loading. Addition of 0.28 volume fraction of silver increases the relative permittivity of epoxy–CLNT composites from 8 to 142 at 1 MHz. This composite is flexible and can be fabricated into various shapes with low processing temperature.     

Carbon–carbon composite bearing materials in hip arthroplasty: analysis of wear and biological response to wear debris

Ultra-high molecular weight polyethylene wear particles have been implicated as the major cause of osteolysis, implant loosening and late aseptic failure in total hip arthroplasties in vivo. This study initially screened 22 carbon-carbon composite materials as alternatives for UHMWPE in joint bearings. New bearing materials should satisfy certain criteria--they should have good wear properties that at least match UHMWPE, and produce wear particles with low levels of cytotoxic and osteolytic activity. Initial screening was based on wear resistance determined in short-term tribological pin-on-plate tests. Three materials (HMU-PP(s), HMU-RC-P(s), and SMS-RC-P(s)) which had superior wear resistance were selected for long-term testing. All materials had very low wear factors and SMS-RC-P(s), which had a wear factor of 0.08 +/- 0.56 x 10(-7) mm3/Nm, was selected for the subsequent biological testing and particle size analysis. SMS-RC-P(s) showed good biocompatibility in bulk material form and also the wear particles had low cytotoxicity for L929 fibroblasts in culture compared to metal wear particles. Wear debris size analysis by transmission electron microscopy showed that the particles were very small, with the vast majority being under 100 nm in size, similar to metal wear particles. The potential osteolytic effect of SMS-RC-P(s) wear particles was investigated by culturing particles with human peripheral blood mononuclear cells and measuring TNFalpha production. SMS-RC-P(s) did not significantly stimulate TNFalpha production at a particle volume to cell number ratio of 80:1, indicating that the debris had a low osteolytic potential. The results of this study suggest that carbon-carbon composites, particularly those composed of PAN-based fibers may be important biomaterials in the development of next generation bearing surfaces for use in total joint replacements that have very low wear rates and reduced osteolytic and cytotoxic potential.     

Characterization of a calcium phosphate–TiO2 nanotube composite layer for biomedical applications

Well-ordered nanotube arrays of titania ~ 0.7 μm high and about 40 or 110 nm in diameter were prepared via electrochemical oxidation at constant voltage (10, 15, 20 or 25 V) in a mixture of 0.86 wt.% of NH₄F, glycerol and deionized water. The effect of annealing the nanotubes at 600 °C on their morphology and structure was examined using SEM and TEM techniques. These substrates are suitable supports for a calcium phosphate coating deposited by a simple immersion in Hank solution.The nucleation and growth of a calcium phosphate (Ca–P) coating deposited on TiO₂ nanotubes (NT) from Hanks' solution was investigated using SEM. XPS and FTIR surface analytical techniques were used to characterize the self-organized porous TiO₂ layers covered with calcium phosphate coatings before and after protein adsorption. Our results confirm that the nanotubular titania layer became stable after annealing at 600 °C, while its internal structure changed from amorphous to crystalline anatase, and eventually, a mixture of anatase and rutile. These thermally stabilized TiO₂ nanotubes significantly enhance apatite formation in Hanks' Balanced Salt Solution as compared to pure Ti covered with a native oxide layer. The Ca–P/TiO₂ NT/Ti surface adsorbs a higher amount of protein (bovine serum albumin, BSA) for a geometric surface area than does the Ti surface. The above difference in protein adsorption suggests a more promising initial cellular response for a Ca–P/TiO₂ NT/Ti composite than for a typical Ti implant surface.     

Nickel–Silver Monotectic in Alumina Crucible for Use with Contact Thermometry

Previously, the authors have published work describing a pure Ni fixed point within alumina crucibles. The success of this study stimulated working with the Ni–Ag monotectic point in alumina crucibles. Similar to eutectic points, the Ni–Ag monotectic temperature is an invariant point but it differs from a eutectic reaction in such a way that the monotectic phase change takes place from Ni–Ag liquid solution to Ni–Ag solid solution and Ag rich Ni–Ag liquid solution. In the phase diagram references, the Ni–Ag monotectic phase transition temperature is assigned to be about 20 \(^{\circ }\)C below the pure Ni melting/freezing point. As is the case for pure Ni, mechanical stability is one of the concerns. Therefore, proper cell design is necessary to avoid breakage of the alumina crucible. The techniques used for the fabrication and measurement of the pure Ni cell were applied to the Ni–Ag cell as well. The cells have been successfully fabricated and the temperature measurement at the fixed point was carried out for more than 20 thermal cycles in total. A Pt/Pd thermocouple was used to measure the temperature and was calibrated from the tin point to the gold point to measure the ITS-90. Freezing plateaus are realized with the technique of “recurrent offset freezing method with reserved solid”. The duration of each freezing plateau is a minimum of 30 min. The monotectic transformation temperature for the best performed cell is determined as 1428.27 \(^{\circ }\)C with a combined uncertainty of ±0.06 \(^{\circ }\)C (\({k}=1\)).     

Preparation and comparative characterization of keratin–chitosan and keratin–gelatin composite scaffolds for tissue engineering applications

We report fabrication of three dimensional scaffolds with well interconnected matrix of high porosity using keratin, chitosan and gelatin for tissue engineering and other biomedical applications. Scaffolds were fabricated using porous Keratin–Gelatin (KG), Keratin–Chitosan (KC) composites. The morphology of both KG and KC was investigated using SEM. The scaffolds showed high porosity with interconnected pores in the range of 20–100 μm. They were further tested by FTIR, DSC, CD, tensile strength measurement, water uptake and swelling behavior. In vitro cell adhesion and cell proliferation tests were carried out to study the biocompatibility behavior and their application as an artificial skin substitute. Both KG and KC composite scaffolds showed similar properties and patterns for cell proliferation. Due to rapid degradation of gelatin in KG, we found that it has limited application as compared to KC scaffold. We conclude that KC scaffold owing to its slow degradation and antibacterial properties would be a better substrate for tissue engineering and other biomedical application.     

Phase transformations in Fe–Ni–Cr heat-resistant alloys for reformer tube applications

Fe–35Ni–25Cr–0.4C alloys with different compositions are aged between 750 and 1150°C up to ～10,000?h. As-cast microstructure contains interdendritic carbides of type M₇C₃ (‘Cr₇C₃’) and MC (‘NbC’). At service temperatures, M₇C₃ transform into M₂₃C₆ (‘Cr₂₃C₆’) within hours. Then, a hardening precipitation of secondary intragranular M₂₃C₆ occurs over hundreds of hours, the nose of the ‘temperature-time-hardening’ curve being around 1000°C. G phase forms after long aging; its solvus temperature and formation kinetics depend on silicon content. Z phase is observed after long aging at 950°C or above. G and Z phases form at the expense of MC. Very long aging causes nitridation under air, with first a transformation of M₂₃C₆ into chromium-rich M₂X carbonitrides (X?=?C,N), then of MC into chromium-rich MX carbonitrides.     

Magnet–PNIPA hydrogels for bioengineering applications

Temperature-sensitive Poly (N-isopropylacrylamide), PNIPA gels were synthesized with micron-sized iron and iron oxide (Fe₃O₄) particles to investigate their viability for hyperthermia applications. Induction heating of the magnetic hydrogels with varying concentration of magnetic powder was conducted at a frequency of 375  kHz for magnetic field strength varying from 1.7 kA/m (21 Oe) to 2.5 kA/m (31.4 Oe). It was observed that the maximum temperature induced in the magnetic hydrogels increased with the concentration of magnetic particles and magnetic field strength. The PNIPA gel underwent a collapse transition at 34 °C. It was found that a 2.5 wt.% Fe₃O₄ in PNIPA composite took 260 s to be heated to 45 °C under a magnetic field strength of 1.7 kA/m, the specific absorption rate (SAR) was found to be 1.83. SAR of iron oxide was found to be higher than the SAR of iron.     

Fabrication and oxidation behavior of a reaction derived graphite–ZrC composite for ultrahigh temperature applications

Graphite containing nominally 40 vol.% ZrC (graphite–ZrC) was prepared from commercially available ZrO₂ and graphite powders by hot pressing at 2000 °C in a vacuum. The oxidation behavior of the graphite–ZrC composite was carried out in dry stagnant air at the temperatures of 1200 and 2200 °C. Compared with the pure graphite, the graphite–ZrC composite exhibited good oxidation resistance because the mass loss of the composite powder was significantly lower than that of the pure graphite. The mass loss of graphite–ZrC at 2200 °C was lower than pure graphite at 1200 °C. Furthermore, the introduction of ZrC also improved the strength of the graphite–ZrC composite.     

The optimum dose of gamma radiation–heavy doses to low wear polyethylene in total hip prostheses

Wear volume, surface area and coefficient of friction of UHMWPE cup crosslinked with gamma radiation of 0, 50, 75, 100, 125, 150 and 200 Mrad sliding against an alumina ball were measured using a sphere-on-flat reciprocating type tribology testing machine. The effects of gamma radiation were scarcely observed in coefficient of friction. The coefficient of friction under lubricated (distilled water) and non-lubricated testing conditions was 0.08 to 0.12 and 0.20 to 0.25, respectively. The wear volume of UHMWPE with radiation of 50 Mrad, 75 to 150 Mrad, and 200 Mrad was 70 to 80%, 18 to 25%, and 12 to 15%, respectively, in comparison to non-irradiated specimens. Elongation and tensile strength of UHMWPE with radiation of 100 Mrad decreased to 6%, and 50% of that without radiation, respectively. The hardness increased with increase of the radiation dose. From several kinds of tribological findings, mechanical strength tests, and studies of long-term clinical findings, it is concluded that approximately 200 Mrad is the optimum dose of gamma radiation for clinical use in total hip prostheses.     

Mechanical analysis of fracture in an automotive radiator head produced from a nylon–glass fibre composite

The fracture during assembly of a radiator head produced from a nylon–short glass fibre composite is studied in the framework of complexities such as determining elastic constants and fracture stresses on the one hand and manufacturing problems such as distortion after moulding and deformations induced during assembly on the other. The combination of in situ measurements, SEM observation of fracture surfaces and reverse modelling of non-linear material properties permitted to make a sufficiently accurate estimate of the real mechanical behaviour of the material, as opposed to the properties mentioned in its data sheet. While the method was applied to solve a particular production problem, its applicability in process evaluation and redesign of injection-moulded short fibre composites is general.     

Doped calcium–aluminium–phosphate cements for biomedical applications

Calcium–aluminium–phosphate cements (CAPCs) for biomedical applications, mainly intended for applications in the dental field as non-resorbable fillers, were obtained by reacting Ca-aluminates compounds, i.e. CaO·Al₂O₃ (CA) and CaO·2 Al₂O₃ (CA₂), with Al(H₂PO₄)₃ aqueous solution. Hydroxyapatite was also introduced as a bioactive dispersed phase. Suitable elements like Sr and La were used to increase the radiopacity of the set yielded pastes towards X-ray wavelength used in clinical diagnostic radiographic equipments. La and Sr doped Ca-aluminates powders have been synthesized by solid state reaction at 1,400°C from a mixture of CaCO₃, Al₂O₃, La₂O₃ and SrCO₃. The characteristics of the obtained powders were analyzed and related to the starting compositions and synthesis procedures. The microstructure, setting time, radiopacity and compressive strength of the CAPCs have been investigated and discussed.     

Layered dielectric–magnetic composite structures for Rf-applications

In this paper multilayer magnetic–dielectric composite structures for high frequency applications are introduced. The 0–3 type dielectric and magnetic composites with homogeneously distributed ceramic inclusions were fabricated by mixing extrusion and injection moulding. Magnetic Yttrium Iron Garnet (YIG) and Z-type Hexaferrite (HexaZ) as well as paraelectric Barium Strontium Titanate (BST) powders were used to enhance the permittivity and permeability of the composites. The magnetic–dielectric multilayer composites were constructed by hot-laminating magnetic and dielectric layers in turn to create a solid 2-2 type composite structure. The microstructure, high frequency dielectric and magnetic properties of individual layers and 2-2 composites were investigated and measured. The measurement results indicate that such multimaterial multilayer structures are good candidates for components with reduced dielectric and magnetic losses. Moreover, the observed good frequency stability and the cut-off frequencies above 1 GHz suggested that the composites could be utilized in, e.g., sophisticated functional circuit boards and RF devices.     

Dielectric tunable properties of Ba0.5Sr0.5TiO3–MgMoO4 composite ceramics for microwave applications

(1?x) Ba_0.5Sr_0.5TiO₃–xMgMoO₄ (x = 0, 5, 10, 20 and 30 wt%) composite ceramics were prepared via solid state reaction processing. Their structure and dielectric properties were systematically characterized. The introduction of MgMoO₄ resulted in a change in lattice constant of the perovskite phase and partial reaction between MgMoO₄ and Ba_0.5Sr_0.5TiO₃ occurred in the sintering process. Both X-Ray Diffraction (XRD) and Back-scattered Electron Images (BEI) analysis show the co-existence of three phase structures of BST, MgMoO₄ and BaMoO₄. With increasing of MgMoO₄ content, the tunability of the composite ceramics was decreased due to the increase of the amount of non-ferroelectric phases. The Curie temperature Tc of the samples gradually shifted to low temperatures with increasing of MgMoO₄ content. Dielectric constant can be adjusted in the range from 2035 to 150, meanwhile maintain a relatively high tunability and Q values. The sample with 20 wt% MgMoO₄ possesses a tunability of 10 %, a low dielectric constant of 111 and an appropriate Q value of 183 (2.240 GHz), which meet the requirements of high power and impedance matching, thus making it a promising candidate for applications as electrically tunable microwave devices.     

Synthesis and characterization of silica–lead sulfide core–shell nanospheres for applications in optoelectronic devices

Nanoscale miniaturization of chalcogenide semiconductors such as lead sulfide (galena) can generate interesting quantum confinement effects in the field of optoelectronic applications. In this work, we developed a process in order to obtain SiO₂ nanospheres coated with Galena, as the denominated core–shell system; this process is based on Stöber’s method, where the magnetic stirring was replaced by an ultrasonic bath to achieve well rounded and highly stable silica nanoparticles with diameters average of 70 nm. The PbS shell cover presents a thickness of 10 nm around. The nanostructures’ chemical composition, morphology, and optical properties were determined by transmission electron microscopy and UV–Vis spectroscopy. As a result, the nanoshells correspond to cubic PbS, presenting some interplanar distances of 2.95 Å and 3.41 Å; this nanoshell also shown an optical spectrum shift toward blue and a remarkable increase of 3.75 eV in its band gap, compared with the PbS bulk value. The chemical composition is studied by energy scattering spectroscopy and X-ray photoelectron spectroscopy analysis.

     

Sol–gel synthesis of tantalum oxide and phosphonic acid-modified carbon nanotubes composite coatings on titanium surfaces

Carbon nanotubes used as fillers in composite materials are more and more appreciated for the outstanding range of accessible properties and functionalities they generate in numerous domains of nanotechnologies. In the framework of biological and medical sciences, and particularly for orthopedic applications and devices (prostheses, implants, surgical instruments, …), titanium substrates covered by tantalum oxide/carbon nanotube composite coatings have proved to constitute interesting and successful platforms for the conception of solid and biocompatible biomaterials inducing the osseous regeneration processes (hydroxyapatite growth, osteoblasts attachment). This paper describes an original strategy for the conception of resistant and homogeneous tantalum oxide/carbon nanotubes layers on titanium through the introduction of carbon nanotubes functionalized by phosphonic acid moieties (P(O)(OH)₂). Strong covalent CP bonds are specifically inserted on their external sidewalls with a ratio of two phosphonic groups per anchoring point. Experimental results highlight the stronger “tantalum capture agent” effect of phosphonic-modified nanotubes during the sol–gel formation process of the deposits compared to nanotubes bearing oxidized functions (OH, CO, C(O)OH). Particular attention is also paid to the relative impact of the rate of functionalization and the dispersion degree of the carbon nanotubes in the coatings, as well as their wrapping level by the tantalum oxide matrix material. The resulting effect on the in vitro growth of hydroxyapatite is also evaluated to confirm the primary osseous bioactivity of those materials. Chemical, structural and morphological features of the different composite deposits described herein are assessed by X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission (TEM) electronic microscopies, energy dispersive X-rays analysis (EDX) and peeling tests.     

Ti–25Ta alloy with the best mechanical compatibility in Ti–Ta alloys for biomedical applications

The microstructures, dynamic elastic modulus, and mechanical properties of the Ti–25Ta (mass%) alloy are investigated in this study in order to assess its mechanical compatibility for biomedical applications. The microstructures are examined by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The dynamic elastic modulus is measured by the resonance vibration method and the mechanical properties are determined from uniaxial tensile tests. The experimental results indicate that the Ti–25Ta alloy exhibits an orthorhombic martensite (α″) twinned structure after solution treatment. The Ti–25Ta alloy has the lowest elastic modulus and the highest ratio of strength to modulus among Ti–Ta alloys. Thus, the Ti–25Ta alloy exhibits the best mechanical compatibility among Ti–Ta alloys and is a promising candidate for novel metallic biomaterials.     

PIRAC Ti nitride coated Ti–6Al–4V head against UHMWPE acetabular cup–hip wear simulator study

Wear behaviour of TiN(titanium nitride)-coated Ti and Ti-6AI-4V alloy against UHMW polyethylene was studied in hip simulation test. Ti alloys possess an excellent combination of mechanical properties and biocompatibility, however, they suffer from inadequate wear resistance. Thus, their use as articulating components of total joint replacements requires surface hardening, e.g. by TiN. Thirty-two millimetre diameter cp-Ti and Ti-6AI-4V femoral heads were coated with several micrometre thick TiN layers employing an original PIRAC nitriding method based on interaction of Ti alloy substrate with highly reactive monatomic nitrogen. The heads were tested against UHMWPE cups at 37 degrees C in Ringer's solution or in distilled water. Simulator tests were performed at peak pressures of 1.5 and 2.0 MPa in a constant rotation mode at the frequency of 1.5 Hz. The wear of UHMWPE was estimated by weight loss, and the worn metallic and polyethylene surfaces were examined in SEM. The wear rate of UHMWPE cups articulating against PIRAC coated Ti and Ti-6AI-4V after up to 4 x 10(6) cycles was significantly lower than that of UHMWPE articulating against 316L stainless steel. No delamination of TiN coatings was observed after 4 x 10(6) cycles. These results suggest that TiN PIRAC coating on Ti-6AI-4V heads could minimise the wear of total hip replacements without compromising the mechanical properties of the femoral component.     

Laser-assisted synthesis of Ti–Mo alloys for biomedical applications

This paper presents the results of a laser-based combinatorial investigation of the Ti–Mo system, aiming at finding alloys with promising properties for orthopedic applications. Variable powder feed rate laser cladding was applied to synthesize Ti–xMo alloys with composition continuously varying in the range of 4–19 wt.% Mo. Screening was performed on the basis of the alloys' mechanical properties, in particular hardness and Young's modulus, measured by microindentation tests. Microstructural analysis showed that alloys with Mo content between 4 and 8 wt.% are composed of acicular martensite and retained β-phase, the proportion of the later phase increasing with increasing Mo content. Alloys with Mo content of 10 wt.% and higher consist entirely of β phase. All the alloys present a Mo segregation pattern indicating that solidification occurred with a cellular solid–liquid interface. Though β-phase alloys present lower values of Young's modulus and hardness than α′- or α″- containing alloys, minimum values of Young's modulus (75 GPa) and hardness (240 VHN) were achieved for the Ti–13 wt.% Mo alloy.     

Developing aluminium–zinc-based a new alloy for tribological applications

In order to develop aluminium–zinc-based a new alloy for tribological applications, six binary Al–Zn and seven ternary Al–25Zn–(1–5)Cu were prepared by permanent mould casting. Their microstructure and mechanical properties were investigated. Dry sliding friction and wear properties of the ternary alloys were investigated using a pin-on-disc machine. Surface and subsurface regions of the wear samples were studied with scanning electron microscopy (SEM). The highest hardness and tensile strength were obtained with the Al–25Zn alloy among the binary ones. The microstructure of this alloy consisted of aluminium-rich α and eutectoid α + η phases. Addition of copper to this alloy resulted in the formation of θ (CuAl₂) phase. The hardness of the ternary alloys increased with increasing copper content. The highest tensile and compressive strengths and wear resistance and the lowest friction coefficient were obtained from the ternary Al–25Zn–3Cu alloy. The dimensional change measured on ageing (stabilization) of this alloy was found to be much lower than that obtained from the copper containing zinc-based alloys. Microstructural changes were observed below the surface of the wear samples of the Al–25Zn–3Cu alloy. These changes were related to the heavy deformation of the surface material due to normal and frictional forces, and smearing and oxidation of wear material. Adhesion was found to be the main wear mechanism for the alloys tested.