Alumina Ceramic Particles Research Articles

Numerical simulation of mold filling process for high chromium cast iron matrix composite reinforced by ZTA ceramic particles

The mold filling process of high chromium cast iron matrix composites reinforced by zirconia toughened alumina (ZTA) ceramic particles (referred as HCCI/ZTAP composites hereinafter) by infiltration casting were simulated using finite element analysis software in this paper. Volume of fluid (VOF) method and porous medium model were used to describe the flow phenomenon during infiltration process. Multiphase flow and heat transfer equations were solved by finite element method. The comparison between the experimental observations and simulation results indicates that the formulated model and method could provide a solution with acceptable accuracy, thus a promising tool to optimize the processing parameters. After trial calculations, the optimal parameters and pouring system were determined eventually. A complete casting without any defects was prepared at the pouring temperature of 1843K and pouring velocity of 0.2m/s by top filling in an enclosed gating system.

In vitro comparison of the biological activity of alumina ceramic and titanium particles associated with aseptic loosening

Prosthetic wear particles are thought to play a central role in the initiation and development of periprosthetic osteolysis, leading to aseptic loosening of prostheses. This study aimed to compare the biological activity of ceramic and titanium particles that are associated with particle-induced, aseptic joint loosening. Different sizes of alumina-ceramic particles and titanium particles were prepared to stimulate murine macrophage cells RAW 264.7, of which the expressions of tumor necrosis factor alpha (TNF-alpha) and receptor activator of nuclear factor-κB ligand (RANKL) were measured by qPCR and ELISA at various time points. In the presence of all particles, the expression of TNF-alpha increased in a time-dependent manner, whereas the expression of RANKL showed no regular expression patterns. Notably, particles of smaller sizes provoked significantly higher levels of TNF-alpha and RANKL than those of larger sizes. Compared to the titanium particles, the ceramic particles provoked a significantly lower production of TNF-alpha. Thus, the bioactivities of titanium and alumina ceramic particles were inversely proportional to the sizes of the particles, and the expression of RANKL was not parallel to that of TNF-alpha. The successful outcome of ceramic-on-ceramic artificial joint prostheses may be attributed to the low biological activity of ceramic particles, as evidenced here.

Hybrid plasma-catalytic systems for converting substances of high stability, greenhouse gases and VOC

Three kinds of plasma-catalytic hybrid systems were examined with purpose of improving the techniques for the reduction of greenhouse gases and volatile organic compound (VOC) emissions: (1) A new reactor was developed and used for combining the reagent activation in gliding discharges (GD) with the catalytic action of particles moving in the discharge zone. Non-oxidative methane coupling by plasma action in the presence of a moving bed of Pt and Pd catalysts was examined. Acetylene and soot were the main products formed in the homogeneous plasma system (without a catalyst) and with alumina-ceramic particles. In the presence of Pt and Pd supported on alumina ceramic particles, two effects were noticed: ethylene and ethane became the main products instead of acetylene, and the soot formation was strongly reduced. (2) Plasma-catalytic methane conversion with CO 2 was studied in a dielectric-barrier discharge (DBD) reactor which was packed with selected materials: alumina ceramic carrier, Ag, Fe, and Pd catalysts, and Na-ZSM-5 zeolite. It was found that the tested catalysts were active under the process conditions. The catalytic action of palladium was the most pronounced. (3) The conversion of trichloromethane in mixtures with air was investigated with the use of a hybrid system composed of GD and a stable bed of catalysts containing Cr 2O 3, MnO 2 and platinum. Chlorine was the main reaction product with a minor share of hydrogen chloride and tetrachloromethane. Due to the catalysts used in this experiment, the overall CHCl 3 conversion was increased, whereas the unwanted CCl 4 formation was nearly constant. On the basis of these experiments, one can conclude that hybrid systems which combine plasma activation of reagents with the action of solid catalysts may be useful for processing gaseous substances, including those of high stability. It was confirmed that the catalyst localization inside or near the plasma zone is the indispensable condition for high efficiency of the hybrid systems.

The in vitro genotoxicity of orthopaedic ceramic (Al2O3) and metal (CoCr alloy) particles

One of the biggest problems with orthopaedic joint replacements has been the tendency for metal-on-polyethylene implants to produce particulate wear debris. These particles stimulated adjacent macrophage infiltration, which caused destruction of bone and soft tissue, resulting in aseptic loosening of the implant. This problem led to the development of new implants with articulating surfaces that produce less volumetric wear (metal-on-metal, MOM, and ceramic-on-ceramic, COC). To determine whether there could be adverse biological effects from exposure to particulate wear debris after total hip replacement (THR), we investigated the in vitro genotoxic effects of alumina ceramic (Al2O3) particles in comparison with cobalt–chrome metal (CoCr alloy) particles.Primary human fibroblasts were exposed to Al2O3 nanoparticles or CoCr alloy particles (0.1–10mg/T-75 flask) for 5 days. There were no significant differences in cell viability between control and ceramic-treated cells, at all doses and time-points studied. Cells exposed to CoCr alloy particles showed both dose- and time-dependent cytotoxicity. There was a small but significant increase in micronucleated binucleate cells after 24h of treatment with >1mg/T-75 flask of alumina particulates compared with controls, although no clear dose–response was observed. The induction of micronuclei was unaffected by the size or shape of the ceramic particles. The increase in micronucleated binucleate cells was much greater after exposure to CoCr particles for 24h, showing a clear dose–response curve. No increase in gamma-H2AX foci was noted in cells exposed to ceramic particles, in contrast with a significant increase of these foci in cells exposed to CoCr particles at comparable mass/surface doses. Cytogenetic analysis showed that both types of particle caused mainly numerical rather than structural chromosomal aberrations, with a greater number and variation of lesions induced by CoCr particles. In conclusion, our results show that alumina (Al2O3) ceramic particles are only weakly genotoxic to human cells in vitro when compared with metal (CoCr alloy) particles.

The hybrid plasma–catalytic process for non-oxidative methane coupling to ethylene and ethane

Non-oxidative methane coupling in hybrid plasma–catalytic reactors was studied. The hybrid system which combined the gliding discharge (GD) and mobile (spouted) bed of catalyst particles revealed high efficiency in the methane conversion. Two catalysts from Pt and Pd supported by alumina ceramics were prepared and tested. The methane conversion was investigated in two GD reactors supplied by 1-phase or 3-phase circuits (50 Hz). In a homogeneous gas system and with a mobile bed of alumina–ceramic particles, mainly acetylene was produced from the CH 4 + H 2 mixture with none or a minor share of other C 2 hydrocarbons. The formation of non-volatile products (mainly soot) was also observed. In the presence of Pt and Pd catalysts, the soot formation was strongly reduced. Owing to these catalysts, ethylene and ethane became the main gaseous products replacing a major part of acetylene.

Histomorphometric analysis of the osseointegration of four different implant surfaces in the femoral epiphyses of rabbits

The surface properties of titanium dental implants are key parameters for rapid and intimate bone-implant contact. The osseointegration of four implant surfaces was studied in the femoral epiphyses of rabbits. Titanium implants were either grit-blasted with alumina or biphasic calcium phosphate (BCP) ceramic particles, coated with a thin octacalcium phosphate (OCP) layer, or prepared by large-grit sand blasting and acid-etched (SLA). After 2 and 8 weeks of implantation, the bone-implant contact and bone growth inside the chambers were compared. Scanning electron microscopy (SEM) and profilometry showed distinct microtopographies. The alumina-Ti, BCP-Ti and OCP-Ti groups had similar average surface roughness in the 1-2 mum range whereas the SLA surface was significantly higher with a roughness averaging 4.5 microm. Concerning the osseointegration, the study demonstrated a significantly greater bone-to-implant contact for both the SLA and OCP-Ti surfaces as compared with the grit-blasted surfaces, alumina- and BCP-Ti at both 2 and 8 weeks of healing. In this animal model, a biomimetic calcium phosphate coating gave similar osseointegration to the SLA surface. This biomimetic coating method may enhance the apposition of bone onto titanium dental implants.

Advances in Nanoalumina Ceramic Particle Fabrication Using Sonofragmentation

The present study is focused on fabrication of high-purity submicrometer alumina ceramic particles (predominantly in sub-100 nm range) from micrometer-sized feed (e.g., 70-80 mum) using sonofragmentation. The effects of various parameters such as ultrasonic frequency, feed concentration, sonication time, surfactant, and applied ultrasonic power on sonofragmentation were investigated. Sub-100 nm particle production by sonofragmentation was validated via three metrics, i.e., laser particle size analysis, high-resolution transmission electron microscopy, and turbidimetry. There is a significant change in color and shape of alumina ceramic particles as a result of sonofragmentation. Higher size reduction ratios are obtained at lower frequencies and at higher input power. Submicrometer particle generation increases as concentration of the feed particles increases, indicating that attrition by interparticle collision is a significant mechanism. The shape of the particles changes from angular to spherical as sonofragmentation time increases. Probe-type sonication produces fragmentation effects that are less uniform than those induced by tank-type ultrasonics. Surfactant plays a significant role in preventing agglomeration, especially as finer fragments are produced with prolonged sonication.

Alumina ceramic particles, in comparison with titanium particles, hardly affect the expression of RANK‐, TNF‐α‐, and OPG‐mRNA in the THP‐1 human monocytic cell line

Particle-induced osteolysis is the most frequent cause of aseptic loosening after total joint replacement. We performed a study to illuminate the effect of ceramic particles with different diameters and concentrations on the mRNA expression of certain key regulators in particle-induced aseptic osteolysis (RANK, RANKL, OPG, and TNF-alpha) in THP-1 macrophage-like cells. Titanium particles were used as a positive control. RNA was analyzed by quantitative RTPCR. Our results demonstrate that alumina ceramic particles, regardless of particle size, caused only slight upregulations of RANK, TNF-alpha, and OPG mRNA, whose levels were significantly lower in comparison with those of titanium particles (p < 0.05). The continuous increasing tendency to time and particle-dependent mRNA expression of all the parameters stimulated by titanium particles was not found after stimulation with ceramic materials. Even after the concentration of ceramic particles was increased, only a mild upregulation of mRNA expression was found. Furthermore, we observed that the bioinert properties of ceramic particles did not change much in diameters ranging from 0.5 to 1.5 microm. At most of the measuring time points, there was no significant difference between the reactions of the large and small particles in this range. Our results support the theory about the relative bioinert properties of alumina ceramic particles.

Effect of bisphosphonates on the stimulation of macrophages by alumina ceramic particles: A comparison with ultra-high-molecular-weight polyethylene

Wear particle-induced osteolysis and loosening is a critical process that limits the longevity of total hip arthroplasty. Despite their potential value in the management of aseptic loosening, little is known about the cellular response to bisphosphonates (BPs) in the presence of particulate debris. In the present study, we compared the effect of pamidronate and clodronate, two structurally different bisphosphonates, on the induction of TNF-alpha release by alumina ceramic (Al(2)O(3)) and ultra-high-molecular-weight-polyethylene (UHMWPE) particles. We also looked, by Trypan blue exclusion, at the viability of J774 mouse macrophages incubated with Al(2)O(3) and UHMWPE particles in combination with pamidronate or clodronate. Results showed that pamidronate and clodronate can inhibit UHMWPE particle-induced TNF-alpha release while they had no effect on Al(2)O(3)-stimulated TNF-alpha release. The co-incubation of pamidronate or clodronate and Al(2)O(3) had no effect on the induction by Al(2)O(3) of poly(ADP-ribose)polymerase (PARP) proteolysis and DNA fragmentation. On the other hand, UHMWPE particles had no effect on these apoptotic markers. However, the co-incubation of pamidronate or clodronate with UHMWPE particles led to the appearance of these markers of apoptosis. Al(2)O(3) and UHMWPE particles had no effect on macrophage cell death or the number of macrophages at the end of experiments. Co-incubation of UHMWPE particles with pamidronate and clodronate led to a significant increase in cell death. Interestingly, the number of macrophages co-incubated with particles and pamidronate or clodronate significantly decreased. In conclusion, our results suggest that the effect of BPs on particle-stimulated macrophages is, at least in part, particle composition dependent.

Cobalt and chromium ions induce nitration of proteins in human U937 macrophages in vitro

The in situ localization of nitrotyrosine, a product of the nitration of tyrosine residues by peroxynitrite, in the interface membranes from Co--Cr--Mo and Ti--Al--V prostheses provided evidence of nitric oxide-induced oxidative damage in the periprosthetic environment. In the present study, we compared the effects of different wear products from hip prostheses on the nitration of proteins in macrophages in vitro. Nitration of proteins was measured by Western blot using a polyclonal antibody directed against nitrotyrosines. Results showed that Co(2+) and Cr(3+) ions induced the nitration of a 79 +/- 4 kDa protein in a time- and dose-dependent manner. Indeed, the stimulation was significant (p < 0.05) after 24 h with 10 ppm Co(2+) and reached a plateau level between 48 and 72 h. With Cr(3+), the stimulation was significant (p < 0.05) only after 48 and 72 h. The effect of both Co(2+) and Cr(3+) ions was inhibited by glutathione monoethyl-ester that provides protection against oxidative stress. However, ultrahigh-molecular-weight-polyethylene and alumina ceramic particles had no significant effect on the nitration of proteins. Finally, the results showed that nitrated proteins are mainly found in the cytoplasmic fraction of cells and are absent from the nucleus. In conclusion, our results show that Co(2+) and Cr(3+) ions induce the nitration of cytoplasmic proteins in human U937 macrophages, suggesting that metal ions from MM prostheses have the potential to modify protein function in the periprosthetic environment and in circulating cells.

Serious metallosis of a metal head due to fragmented ceramic screws in a cemented THA

We reported a rare revision case necessitated by massive metallosis of a metal head due to a fragmented ceramic screw which had been extraarticularily used in the primary THA here and reviewed previous literature about metallosis of metal heads associated with ceramic materials. The ceramic screw had been used for the fixation of a bone graft and reattachment of the greater trochanter in the primary THA. Scanning electron microscope analysis revealed large alumina ceramic particles embedded on the bearing surface of the polyethylene. It has previously been pointed out that metallosis of an inner head occurred in bipolar case due to a fracture of the ceramic screws in contact with a proximally migrated outer head. However, this case showed that if a ceramic screw fragmented even though it was used outside of the hip joint, the fragments could migrate into bearing surface and cause serious metallosis of the metal head. Thus, we recommend that surgeons should pay special attention to the radiographic signs of ceramic failure or metallosis such as a change of the metal head contour, if an aseptic loosening or severe osteolysis is observed in a THA in which ceramic materials were used near the hip joint. And, when a surgical revision is planned, the surgeon should be prepared to exchange with a new ceramic head.

Auswirkungen von klinisch relevanten Aluminium Keramik-, Zirkonium Keramik- und Titanpartikel unterschiedlicher Größe und Konzentration auf die TNFα-Ausschüttung in einem humanen Makrophagensystem / Effects of clinically relevant alumina ceramic particles, circonia ceramic particles and titanium particles of different sizes and concentrations on TNFα release in a human monocytic cell line

Aseptic loosening is considered to be the main problem of modern endoprothesis. Tumor necrosis factor alpha (TNFalpha) seems to be the initiator protein of particle disease. The aim of our study was to investigate the TNFalpha response of macrophage like cells (MLC) after stimulation with periprosthetic particles, typically found during revision surgery. For this purpose alumina ceramic (Al2O3), zirconia ceramic (ZrO2) and titanium (Ti) particles of different sizes and concentrations were used. Important was to study the effects of different sizes due to TNFalpha secretion and the comparison of the biological effects of alumina ceramic and titanium. To obtain an TNFalpha profile we used an established macrophage model (Rader et al.) with THP-1 cells (human monocytic cell line). Therefore 106 MLC were incubated with different particle concentrations and sizes for 6 h. The supernatant was then investigated for TNF using ELISA assay. Ti-particles provoked in both sizes (0.2 microm and 2.5 microm) the greatest TNFalpha response, 8 times and 17 times as high in comparison with control. But substantially more 0.2 microm sized Ti-particles were necessary to get the above mentioned results. Al2O3-particles were not as effective as Ti, but they released fourfold more TNFalpha compared to control. There was no difference in TNFalpha-secretion comparing Al2O3-particles of different sizes (0.6 microm and 2 microm), but a 1000 times greater concentration of the 0.6 microm sized particles were needed. Using Al2O3- and Ti-particles of the same size and concentration, Ti provoked a significant higher TNFalpha response. ZrO2 showed no effects on TNFalpha release. Because of our results we recommend ceramic articulating surfaces, which are superior to metal on metal matings ion term of biological reactions. Additionally bigger wear particles should be avoided. Revisionoperation should be done early to avoid huge amount of wear particles and to minimize local osteolysis.

Comparison of the response of primary human blood monocytes and the U937 human monocytic cell line to two different sizes of alumina ceramic particles

It is well recognized that wear particles derived from orthopaedic implants have the potential to induce inflammation, which may eventually lead to aseptic loosening of the artificial joint. We hypothesized that alumina ceramic particles of different sizes cause a differential cytokine response by human monocytes. To test this hypothesis a human monocytic cell line (U937) and primary human blood monocytes obtained from healthy volunteers were exposed to ceramic particles within the range known to be generated in vivo. Cellular responses were measured by quantifying the relative gene expression of 12 different cytokines using TAQman Real-Time Polymerase Chain Reaction (RT-PCR). Our results demonstrate that at a particle to cell ratio of 100:1, 0.5 μm ceramic particles consistently provoked higher amounts of Interleukin-1α (IL-1α), IL-1β, IL-8, IL-10 and Tumor necrosis factor-α (TNF-α) steady state mRNA by U937 cells. As expected, the variability of cytokine expression in primary blood monocytes was much higher compared to the cell line however, a similar trend was observed. These results show a differential response to ceramic particle size, which may imply that 0.5 μm particles are less biocompatible. New ceramic implants can be designed to generate a known particle size range in vivo. Implant materials of this type may induce relatively lower levels of production of inflammatory cytokines resulting in a reduced incidence of failure due to aseptic loosening.

Effects of clinically relevant alumina ceramic wear particles on TNF- α production by human peripheral blood mononuclear phagocytes

The recent introduction of microseparation of the components of ceramic-on-ceramic hip prostheses during hip simulations has produced clinically relevant wear rates, wear patterns and wear particles. This provided an opportunity to determine the response of primary human peripheral blood mononuclear cells to clinically relevant alumina ceramic wear particles in vitro. Alumina ceramic wear particles were generated in a hip joint simulator under microseparation conditions. The particles showed a bi-modal size distribution with nanometer sized (5– 20 nm ) and larger particles (0.2– >10 μm ). The particles were cultured with human peripheral blood mononuclear cells obtained from six different donors at particle volume to cell number ratios of 1, 10, 100 and 500 μm 3 . After 24 h incubation the viability of the cells and the levels of TNF- α were determined. The response to the microseparation wear particles was compared to that of commercially available alumina powder with a uniform morphology and mean size of 0.5 μm . All six Donors PBMNC produced significantly elevated levels of TNF- α when stimulated with 100 μm 3 of the alumina powder per cell. Volumetric concentrations of 10 and 1.0 μm 3 per cell failed to stimulate a significant response by the cells from any of the six donors. Three of the six Donors PBMNC secreted significantly elevated levels of TNF- α when stimulated with 100 μm 3 of the microseparation wear particles, whereas the other three failed to respond to the wear debris at this concentration. All of the Donors PBMNC produced significantly elevated levels of TNF- α when stimulated with 500 μm 3 of the microseparation wear particles per cell. Thus, a greater volume of the microseparation wear particles was required to activate the PBMNC than the alumina powder. This was probably due to the microseparation wear particles having fewer particles in the critical size range (0.1– 1 μm ) for macrophage activation compared to the alumina powder. It can be concluded that alumina ceramic wear particles generated under microseparation conditions are capable of inducing osteolytic cytokine production by human mononuclear phagocytes. However, the volumetric concentration of the particles needed to generate this response is extremely high and given the low wear rates ( <4 mm 3 per million cycles) of ceramic-on-ceramic bearings, even under severe microseparation conditions, it is unlikely that this concentration threshold will be achieved in vivo.

Characterization of silane coated hollow sphere alumina-reinforced ultra high molecular weight polyethylene composite as a possible bone substitute material

Silane coated hollow sphere alumina ceramic particles were moulded with ultra high molecular weight polyethylene (UHMWPE) to form a series of composites with alumina weight percent in the range from 15 to 50. The composites were prepared in a cylindrical mould using powder-processing technique. The composites were characterized for mechanical properties using destructive and non-destructive ultrasonic testing methods. The physical properties of the composite were determined and compared with those of cortical bone.

Comparison of the cytotoxicity of clinically relevant cobalt–chromium and alumina ceramic wear particles in vitro

Concern over polyethylene wear particle induced aseptic loosening of metal-on-polyethylene hip prostheses has led to renewed interest in alternative materials such as metal-on-metal and alumina ceramic-on-alumina ceramic for total hip replacement. This study compared the effects of clinically relevant cobalt–chromium and alumina ceramic wear particles on the viability of U937 histiocytes and L929 fibroblasts in vitro. Clinically relevant cobalt–chromium wear particles were generated using a flat pin-on-plate tribometer. The mean size of the clinically relevant metal particles was 29.5±6.3 nm (range 5– 200 nm ). Clinically relevant alumina ceramic particles were generated in the Leeds MkII anatomical hip simulator from a Mittelmieier prosthesis using micro-separation motion. This produced particles with a bimodal size distribution. The majority (98%) of the clinically relevant alumina ceramic wear debris was 5– 20 nm in size. The cytotoxicity of the clinically relevant wear particles was compared to commercially available cobalt–chromium (9.87 μm±5.67) and alumina ceramic (0.503±0.19 μm) particles. The effects of the particles on the cells over a 5 day period at different particle volume (μm 3) to cell number ratios were tested and viability determined using ATP-Lite TM. Clinically relevant cobalt–chromium particles 50 and 5 μm 3 per cell reduced the viability of U937 cells by 97% and 42% and reduced the viability of L929 cells by 95% and 73%, respectively. At 50 μm 3 per cell, the clinically relevant ceramic particles reduced U937 cell viability by 18%. None of the other concentrations of the clinically relevant particles were toxic. The commercial cobalt–chromium and alumina particles did not affect the viability of either the U937 histiocytes or the L929 fibroblasts. Thus at equivalent particle volumes the clinically relevant cobalt–chromium particles were more toxic then the alumina ceramic particles. This study has emphasised the fact that the nature, size and volume of particles are important in assessing biological effects of wear debris on cells in vitro.

Alumina–alumina artificial hip joints. Part II: Characterisation of the wear debris from in vitro hip joint simulations

Until recently it was not possible to reproduce clinically relevant wear rates and wear patterns in in vitro hip joint simulators for alumina ceramic-on-ceramic hip prostheses. The introduction of microseparation of the prosthesis components into in vitro wear simulations produced clinically relevant wear rates and wear patterns for the first time. The aim of this study was to characterise the wear particles generated from standard simulator testing and microseparation simulator testing of hot isostatically pressed (HIPed) and non-HIPed alumina ceramic-on-ceramic hip prostheses, and compare these particles to those generated in vivo.Standard simulation conditions produced wear rates of ≈0.1mm3 per million cycles for both material types. No change in surface roughness was detected and very few wear features were observed. In contrast, when microseparation was introduced into the wear simulation, wear rates of between 1.24 (HIPed) and 1.74mm3 per million cycles (non-HIPed) were produced. Surface roughness increased and a wear stripe often observed clinically on retrieved femoral heads was also reproduced. Under standard simulation conditions only nanometre-sized wear particles (2–27.5nm) were observed by TEM, and it was thought likely that these particles resulted from relief polishing of the alumina ceramic. However, when microseparation of the prosthesis components was introduced into the simulation, a bi-modal distribution of particle sizes was observed. The nanometre-sized particles produced by relief polishing were present (1–35nm), however, larger micrometre-sized particles were also observed by both transmission electron microscopy (TEM) (0.02–1μm) and scanning electron microscopy (SEM) (0.05–>10μm). These larger particles were thought to originate from the wear stripe and were produced by trans-granular fracture of the alumina ceramic.In Part I of this study, alumina ceramic wear particles were isolated from the periprosthetic tissues from around Mittelmeier ceramic-on-ceramic hip prostheses. Characterisation of the particles by TEM and SEM revealed a bi-modal size distribution. SEM analysis revealed particles in the 0.05–3.2μm size range, and TEM revealed particles in the 5–90nm size range, indicating that microseparation of the prosthesis components may be a common event in vivo. This study (Part II) has revealed that the introduction of microseparation of the prosthesis components during the swing phase of the wear simulation reproduced clinically relevant wear rates, wear patterns and wear particles in in vitro hip joint simulators.