Poly Methyl Methacrylate Particles Research Articles

Homogenous alumina tube with controlled pore morphology

Porous alumina tubes with homogenous microstructures were prepared from commercial alumina and polymethylmethacrylate (PMMA) powders with two kinds of particle sizes using a centrifugal molding technology. PMMA powders were used as the pore-forming agent and the proportion of fine to coarse particles was adjusted to control the pore morphology of the alumina tubes. The open porosity and air permeability was optimized with respect to the proportion of PMMA powders. The fracture strength decreased with increasing porosity and was insensitive to the proportion of fine to coarse PMMA powders despite the changing pore morphology. Analysis of the Weibull statistics showed that specimens with higher porosity exhibit a narrower scatter in fracture strength. A 50:50 mixture (v/v) of fine and coarse PMMA particles showed the lowest fluctuation in fracture strength. The present study paves the way to more reliable material design using porous materials.

An electronic pollen detection method using Coulter counting principle

Abstract A method for detecting and counting pollen particles based on Coulter counting principle is presented. This approach also provides information on the size and surface charges of the micro particles, allowing for preliminary differentiation of pollens from other micro particles. Three samples are studied: polymethyl methacrylate particles, tree pollens from Juniperus Scopulorum and grass pollens from Secale Cerale. The samples, suspended in diluted KCl aqueous solutions in an electrochemical cell, were allowed to pass through a microchannel and the conductance of the microchannel was sampled with a Gamry ® Potentiostat. The changes in the conductance due to the passing of the micro particles was thus recorded and analyzed. The experimental results showed that tree pollens and grass pollens display distinctive behaviors. The phenomena may be attributed to the differences in the surface characteristics of the pollens and is potentially useful for counting and differentiating different micro particles.

Effect of volume fraction and particle size on wall slip in flow of polymeric suspensions

AbstractFor especially highly concentrated suspensions, slip at the wall is the controlling phenomenon of their rheological behavior. Upon correction for slip at the wall, concentrated suspensions were observed to have non‐Newtonian behavior. In this study, to determine the true rheological behavior of model concentrated suspensions, “multiple gap separation method” was applied using a parallel‐disk rheometer. The model suspensions studied were polymethyl methacrylate particles having average particle sizes, in the range of 37–231 μm, in hydroxyl terminated polybutadiene. The effects of particle size and solid particle volume fraction on the wall slip and the true viscosity of model concentrated suspensions were investigated. It is observed that, as the volume fraction of particles increased, the wall slip velocity and the viscosity corrected for slip effects also increased. In addition, for model suspensions in which the solid volume fraction was ≥81% of the maximum packing fraction, non‐Newtonian behavior was observed upon wall slip correction. On the other hand, as the particle size increased, the wall slip velocity was observed to increase and the true viscosity was observed to decrease. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 439–448, 2005

FLAME PROPAGATION IN SPRAYS AND PARTICLE CLOUDS OF LESS VOLATILE FUELS

ABSTRACT Flame propagation mechanisms in spray and particle clouds of less volatile condensed fuels are discussed, based on microgravity experimental results obtained in tests using the Japan Microgravity Center with a microgravity test duration of 10 seconds and its microgravity quality of 10−5 g. First, n-decane sprays were tested under microgravity using a flame propagation tube with an inner diameter of 62 mm and a length of 605 mm. A flame front was observed in which there were many envelope flames surrounding droplets. It was suggested that the whole spray flame proceeded by a droplet-to-droplet propagation of envelope flames. The flame propagation speed had a maximum at a certain Sauter mean diameter (SMD) when the total equivalence ratio was kept constant. All experimental flame propagation speeds could be arranged on a curve when the mean droplet spacing divided by the mean radius of envelope flames surrounding droplets was employed as an abscissa. Second, to examine the fundamental mechanism of spray combustion mentioned above, we analyzed the flame spread rate of droplet arrays under various conditions. The flame spread rate had a maximum at a certain droplet spacing, and so the spread rate decreased when the spacing was large or small. This supports the observation of the above-mentioned flame propagation of spray. Third, to confirm the mechanism of flame propagation of dispersed less volatile fuels, we rearranged our previous experimental data of Polymethylmethacrylate (PMMA) particle clouds in microgravity. Although we were not able to arrange the data by means of flame radii since the measurements were difficult, the flame propagation speeds had a maximum at a certain mean particle spacing divided by the mean particle diameter.

Novel manipulation in environmental scanning electron microscope for measuring mechanical properties of single nanoparticles

A novel nanomanipulation technique has been developed to measure the mechanical properties of single nanoparticles. The principle of this technique is to compress single nanoparticles between two flat surfaces comprising a glass slide and the tip of a calibrated glass cantilever inside the chamber of an environmental scanning electron microscope (ESEM), so that the force being imposed on them and their deformation can be determined by a series of images of the particles and the position of the cantilever. The cantilever is held by a nanomanipulator that has a resolution of 0·5 nm. The novel nanomanipulation technique, and a previously developed micromanipulation technique, were first used to measure the force required to compress single microparticles (ranging from 1 to 3 μm in diameter) of methacrylic acid copolymer Eudragit E100 to different deformations under dry mode conditions, to validate results from the former. Results showed that there is no significant difference in the data obtained using these two techniques, which implies that the new nanomanipulation technique is highly reliable. The new technique was then applied to single polymethylmethacrylate (PMMA) particles ranging from 530 to 950 nm in diameter. They were compressed and held, compressed and released, and compressed to different deformations, and the force imposed on the particles was determined simultaneously. This work demonstrates the feasibility of measuring the mechanical properties of single nanoparticles, and the developed technique can find wide application in mechanical characterisation of different nanoparticles.

Inter-individual and intra-individual variability in TNF-alpha production by human peripheral blood cells in vitro

Background Two assays—isolated peripheral blood mononuclear cells (PBMC) and a whole blood assay (WBA)—are commonly used to study TNF-alpha production by an individual in order to distinguish between high and low cytokine producers. We assessed the reliability and reproducibility of these assays. Methods The PBMC assays ( n=5) were performed weekly over a period of 6 weeks and the WBAs ( n=4) weekly over a 4-week period. Polymethylmethacrylate particles (approx. 6×10 2 particles/cell) and optimal concentrations of endotoxin (6.25 and 12.5 ng/ml) were used as the stimulatory agents in PBMC and WBAs, respectively. TNF-alpha production was measured by ELISA. Results There was a high degree of both intra- and inter-individual variability of TNF-alpha secretion, with unpredictable changes in the amount of the cytokine produced by cells from the same donor. This variability could not be eliminated by correcting for cell numbers. Conclusion The PBMC and WBA models of TNF-alpha production by human peripheral blood cells cannot be used for the evaluation of inter-individual variability in cytokine secretion due to the high intra-individual variability observed. In the case of PBMC this is partly due to differences in the confluency of the cells between individuals.

In vitro and in vivo biological responses to a novel radiopacifying agent for bone cement.

Iodixanol (IDX) and iohexol (IHX) have been investigated as possible radiopacification agents for polymethylmethacrylate (PMMA) bone cement, to replace the currently used barium sulphate and zirconia. IDX and IHX are both water-soluble iodine-based contrast media and for the last 20 years have been used extensively in clinical diagnostic procedures such as contrast media enhanced computed tomography, angiography and urography. One of the major reasons to remove the current radiopacifying agents is their well-documented cytotoxicity and their potential to increase bone resorption. Using in vitro bone resorption assays, the effect of PMMA particles plus IDX or IHX to induce osteoclast formation and lacunar resorption on dentine slices has been investigated. These responses have been compared with the in vitro response to PMMA particles containing the conventional radiopacifying agents, that is, barium sulphate and zirconia. In parallel, the in vivo reaction, in terms of new bone formation, to particles of these materials has been tested using a bone harvest chamber in rabbit tibiae. In vitro cell culture showed that PMMA containing IHX resulted in significantly less bone resorption than PMMA containing the conventional opacifiers. In vivo testing, however, showed no significant differences between the amounts of new bone formed around cement samples containing the two iodine-based opacifying agents in particulate form, although both led to fewer inflammatory cells than particles of PMMA containing zirconia. Our results suggest that a non-ionic radiopacifier could be considered as an alternative to the conventional radiopacifying agents used in biomaterials in orthopaedic surgery.

Particle classification in Taylor vortex flow with an axial flow

Particle classification phenomenon in Taylor vortex flow with an axial flow was investigated experimentally and numerically. The flow-visualization experiment by a laser-induced fluorescence method clearly revealed that there existed two distinct mixing regions at low Reynolds numbers. The tracer near the vortex cell boundary was rapidly transported axially owing to the bypass flow effect. On the other hand, the fluid element was confined to the vortex core region without being exchanged with the outer flow region. In order to observe particle classification phenomenon, polymethyl methacrylate (PMMA) particles suspended in the same aqueous solution of glycerol as the working fluid were fed into the top of the apparatus. Particle size was initially ranging from 10 to 80 µm. The ratio of the particle density to the fluid density was 1.04–1.05, which means the density difference between particle and fluid is very small. The suspended solution was withdrawn using a hypodermic needle every a certain time period at 30 mm above the bottom of apparatus. The fluid was sampled both near the outer wall and in vortex core. The particles sampled at 42 min having the size of 20–50 µm were mainly observed in the vortex core region. On the other hand, a large population of particles having the size of about 50–80 µm could be seen in the outer region of vortex. It was found that large particles located near the outer edge of vortices were quickly transported axially owing to the bypass flow effect. Numerical simulation also revealed that the loci of particles depended on the particle size.

Influence of orthopedic particulate biomaterials on inflammation and synovial microcirculation in the murine knee joint.

The purpose of the present study was to examine changes in the synovial microcirculation as well as synovial tissue responses to exposure to titanium, polymethylmethacrylate (PMMA), ceramic (Al(2)O(3)), cobalt-chromium alloy (Co-Cr), and polyethylene (PE) particles in an in vivo model. The particulate biomaterials were injected into the left knee joint of female Balb/c mice and assessment of the synovial microcirculation using intravital fluorescence microscopy as well as histological evaluation of the synovial tissue response were performed on day 7 after particle administration. Intravital microscopic measurements revealed that all tested biomaterials caused significantly (p < 0.05) enhanced leukocyte-endothelial cell interactions and an increase of functional capillary density compared to controls. In the histological examination PMMA, Al(2)O(3), PE, and Co-Cr particles provoked significantly (p < 0.05) enhanced inflammatory tissue responses in comparison to tissue from control animals. Titanium particles showed significantly (p < 0.05) less leukocyte-endothelial cell interactions than the other particulate biomaterials and caused significantly (p < 0.05) minor membrane thickening compared to PE and PMMA particles. In conclusion, all tested particulate biomaterials were capable of inducing inflammatory responses in the present study. Our data suggest that titanium particles may cause less leukocyte activation and inflammatory tissue responses than other particulate biomaterials used in total joint arthroplasty.

Quantification of inflammatory cellular responses using real-time polymerase chain reaction.

The introduction of tissue engineering strategies for the repair and replacement of human body components extends the application and importance of biomaterials. Implanted biomaterials frequently evoke inflammatory responses that are complex and not well understood at present. The goals of this work were to develop improved measurement methods for the quantification of cellular inflammatory responses to biomaterials and obtain data that lead to an enhanced understanding of the ways in which the body responds to the introduction of biomaterials. To evaluate the biocompatibility of materials, we established a system that allows for the analysis and quantitation of cellular inflammatory responses in vitro. In this study, the inflammatory responses of murine macrophages (RAW 264.7) were analyzed. The cells were incubated with polymethylmethacrylate (PMMA) microspheres in the presence and absence of lipopolysaccharide (LPS) at 8 and 18 h. The analysis of the genetic material obtained from the cells was quantitated using real-time reverse transcription polymerase chain reaction (RT-PCR). The cell populations treated with LPS or PMMA microspheres singly resulted in an elevation of cytokine levels compared to the untreated control. LPS resulted in a 258-fold increase, while PMMA resulted in an 87.9-fold increase at 8 h. RAW 264.7 cells incubated with LPS and PMMA particles demonstrated a synergistic effect by producing a marked increase in the level of cytokine expression, 336-fold greater than that of the untreated control at 8 h. Fluorescence microscopy studies that assessed cellular viability were also performed and are consistent with the RT-PCR results.

Deactivated sintering by particle coating: the significance of static and dynamic surface phenomena

The suppression of bonding of micron-sized host particles due to the application of heat at temperatures below their melting point (deactivated sintering) when coated with submicron guest particles is theoretically predicted and confirmed by experiments. It was possible to preserve individual particles of polymethylmethacrylate (PMMA) at 150°C, about 45°C above the minimum sintering temperature (MST) of the uncoated particles, and individual glass beads at 750°C, about 175°C above the minimum sintering temperature of the uncoated glass beads, by applying a surface coating of silicon carbide.A dense monolayer of submicron particles coated onto the surfaces of much larger host particles prevents contact of their surfaces (host–host contact) and suppress the dilation of their mobile surfaces. At the temperature at which the host particle material starts to flow, the coated particles behave as solid colloid particles sitting on the surface of a liquid. If the adhesion energy at the interface between the host and guest particles is not small in comparison to the cohesion energy, i.e., when the contact angle is not very large, the decrease in bonding energy due to the coating is small and sintering deactivation is weak. If the contact angle is very large, i.e., the work of adhesion is very small compared to the work of cohesion, the decrease in bonding energy is large resulting in appreciable sintering deactivation. This deactivation is only temporary, however, because of the forced intrusion of the host fluid into the pores of the coating layer (CL). This process is similar to the intrusion of mercury, which occurs in mercury porosimetry. Models for the intrusion dynamics are developed for both a dense coating monolayer and polylayers with account for different pore size distributions.

Polymethylmethacrylate Particles

Polymethylmethacrylate Particles

Self-Supporting Liquid Crystal Composite

Colloid-liquid crystal composites are a novel type of soft condensed matter, formed from dispersions of colloidal particles in liquid crystalline hosts. Here, we investigate the kinetics of network formation in mixtures of the thermotropic liquid crystal 5CB and nearly hard sphere colloids (polymethylmethacrylate particles), occurring as the liquid crystal undergoes a transition from the isotropic to the nematic phase. In the isotropic phase the particles (volume fraction <0.2) are homogeneously distributed. While cooling through the isotropic-nematic phase transition the particles are expelled by the liquid crystal, forming a three dimensional network structure. Using time-resolved laser scanning confocal microscopy (LSCM) we image the dynamics of the network formation at single particle resolution, for the first time. In the isotropic phase the particles perform Brownian motion, whereas in the network they remain frozen in position. We observe a broad distribution of the size of the liquid crystal domains of up to ∼50 micrometers. Heating shows although the network breaks up clusters of particles remain. DSC measurements show that the particles do not change TNI, suggesting that the particles do not alter the bulk properties of the liquid crystal. These observations provide an important step towards characterising the material properties of this novel composite.

Preparation and Properties of Cross-Linked Fluorescent Poly(methyl methacrylate) Latex Colloids

We report a single step preparation of monodisperse fluorescent poly(methyl)methacrylate (PMMA) lattices cross-linked with ethylene glycol dimethacrylate with radii in the range 150-1000 nm using dispersion polymerization. The particles are applied as fluorescent cores in core-shell PMMA particles for confocal microscopy (Dullens et al. Langmuir 2003, 19, 5963). Contrary to un-cross-linked particles, these cross-linked colloids are stable in good solvents for PMMA as well. Therefore we studied the properties of the cross-linked PMMA particles in the good solvents tetrahydrofuran (THF), chloroform, and toluene using light scattering and confocal scanning laser microscopy. We show that the particles swell instantaneously and that their volume can increase up to more than seven times their volume in poor solvents. Further, it is very likely that the particles are charged in THF.

Cement particles containing radio-opacifiers stimulate pro-osteolytic cytokine production from a human monocytic cell line

Proponents of the biological theory of aseptic loosening have in recent years tended to concentrate on the production and distribution of particulate ultra-high-molecular-weight polyethylene (UHMWPE) debris around the potential joint space. However, mechanical loading of cemented implants with the differing elastic moduli of metal stems, polymethylmethacrylate (PMMA) cement and bone can result in relative micromotion, implying the potential for production of metal and PMMA particles from the stem-cement interface by fretting wear. In order to investigate the production and biological reactivity of debris from this interface, PMMA and metal particulate debris was produced by sliding wear of PMMA pins containing barium sulphate and zirconium dioxide against a Vaquasheened stainless steel counterface. This debris was characterised by SEM, energy-dispersive analysis by X-ray (EDAX) and image analysis, then added to cell cultures of a human monocytic cell line, U937, and stimulation of proosteolytic cytokines measured by ELISA. Large quantities of PMMA cement debris were generated by the sliding wear of PMMA pins against Vaquasheened stainless steel plates in the method developed for this study. Both cements stimulated the release of pro-osteolytic TNFalpha from the U937 monocytic cell line, in a dose-dependent fashion. There was a trend towards greater TNFalpha release with Palacos cement than CMW cement at the same dose. Palacos particles also caused significant release of IL-6, another pro-osteolytic cytokine, while CMW did not. The particulate cement debris produced did not stimulate the release of GM-CSF or IL1beta from the U937 cells. These results may explain the cytokine pathway responsible for bone resorption caused by particulate PMMA debris. Radio-opaque additives are of value in surgical practice and clinical studies to quantify the relevance of these in vitro findings are required before the use of cement containing radio-opacifier is constrained.

NF-kB signaling blockade abolishes implant particle-induced osteoclastogenesis

In this study we investigated the effect of NF-kB signaling blockade on polymethylmethacrylate (PMMA) particle-induced osteoclastogenesis in vitro. We first established effective blockade of NF-kB activity as tested by electrophoretic mobility shift assays (EMSA). Particle-induced NF-kB activation in murine osteoclast precursor cells (CSF-1-dependent bone marrow macrophages) was markedly reduced by co-treatment of the cells with the NF-kB inhibitors N-tosyl- L-phenylalanine chloromethyl ketone (TPCK) and Calpain Inhibitor I (CPI). This inhibition of NF-kB activity was associated with blockade of p50 NF-kB subunit nuclear translocation. We then established a direct NF-kB inhibition approach by utilizing a TAT-bound, mutant IkB (TAT:IkB 46-317), and demonstrated an inhibitory effect evidenced by decreased NF-kB DNA binding activity. Having established that these strategies (TPCK, CPI, TAT: IkB 46-317) effectively block NF-kB activation, we next investigated the effect of these agents on particle-stimulated osteoclast formation. PMMA particle stimulation of mature osteoclast formation from RANKL-primed osteoclast precursor cells was blocked by all three inhibitors. To further test the efficacy of NF-kB blockade, experiments were performed with the TAT:IkB 46-317 mutant peptide in whole bone marrow cultures that contain supporting stromal cells. Again, this inhibitor efficiently blocked particle-induced osteoclastogenesis. Thus, we have shown that pharmaceutical and molecular blockade of NF-kB activation inhibits PMMA particle-directed osteoclastogenesis in vitro.

The performance of gamma- and EtO-sterilised UHMWPE acetabular cups tested under severe simulator conditions. Part 2: wear particle characteristics with isolation protocols

Ultra-high molecular-weight polyethylene (UHMWPE) has been used in total joint replacement for the last three decades. Despite the recent advancements in prosthesis design, the wear of UHMWPE remains a serious clinical problem; the release of wear debris may induce osteolysis and implant loosening. Controlling the quality of the polyethylene is essential to improve its wear resistance and any potential adverse effect caused by processing, manufacturing or sterilisation should be avoided. To evaluate the influence of the sterilisation method (gamma-irradiation and ethylene oxide (EtO)-treatment) and third-body particles, gamma- and EtO-sterilised UHMWPE acetabular cups were tested against CoCrMo femoral heads in a hip joint simulator run for 2.5 million cycles in bovine calf serum in the presence of third-body polymethylmethacrylate (PMMA) particles. A method not requiring ultra-centrifugation has been proposed for the isolation of polyethylene wear debris from the serum lubricant. SEM analysis allowed debris shape and morphology to be determined, and the wear mechanism operating in this study to be hypothesised. The morphological features of the wear debris were in agreement with clinical findings, enabling the hip simulator function to be validated. Micro-Raman spectroscopy coupled to PLS analysis showed that the mechanical friction during in vitro tests induced significant crystallinity changes in all the cups. The most significant changes were observed for the EtO-sterilised cups, which showed the highest weight loss.

Sub-picosecond shock interferometry of transparent thin films

Ultrafast spatial interferometric measurements of shock dynamics in transparent thin films exhibit phase shifts caused by both surface motion and the interference of multiple reflections off the moving shock wave interface. The interference effects are strong perturbations on the phase shift, which do not allow independent measurement of surface motion. Calculations of the time dependent phase shift that include reflective surface motion, shock wave transit through the transparent thin film, and thin film interference effects are shown to match experimental measurements in 625-nm-thick films of polymethylmethacrylate (PMMA) shocked to 19 GPa. Interferometric data obtained at two angles of incidence and two polarizations were sufficient to uniquely determine the PMMA shocked refractive index, shock speed, and particle velocity. Interferometric results as a function of shock strength, 2–20 GPa, suggest that submicron PMMA films have essentially the same material response to shock loading (Hugoniot) as macroscopic samples.

Field-induced structures in miscible ferrofluid suspensions with and without latex spheres.

We explore magnetic-field-induced ordering and microphase separation of aqueous ferrofluid and of aqueous mixtures of ferrofluid with nonmagnetic latex spheres. The ferrofluid is a surfactant stabilized aqueous suspension of magnetite (Fe3O4) particles with average diameter 20 nm (including the approximately 2.5-nm thick surfactant layer); the nonmagnetic latex spheres are charge stabilized polymethylmethacrylate (PMMA) particles with diameters of 42 nm, 108 nm, and 220 nm. In the presence of a uniform magnetic field, needlelike ferrofluid droplets formed that eventually grew to sample-traversing columns at fields of approximately 600 G; the two-dimensional structure of these columns was, however, glassy rather than hexagonal. In higher fields, approximately 1000 G, the columns stretched and coalesced into sheetlike striped liquids, but a true lamellar phase was not observed. The addition of nonmagnetic latex spheres to the ferrofluid suspension lowered substantially the critical field for the formation of columns, and induced lamellar (stripe) phases at relatively low applied fields. Image analysis was used to determine the spatial correlation functions, the average needle or column spacing, and the average lamellae spacing of these samples as a function of latex sphere size and concentration.

PMMA particles and pressure––a study of the osteolytic properties of two agents proposed to cause prosthetic loosening

Amongst the wear debris particles implicated in the particle hypothesis for prosthetic loosening are polymethylmethacrylate (PMMA), and particularly PMMA with barium sulphate contrast agent. Another suggested cause for loosening is hydrostatic pressure. PMMA particles were combined with hydrostatic pressure in a study to investigate whether there could be a synergistic or additive effect between these two factors. Titanium plates were fastened onto tibiae of 59 rats. After osseointegration, PMMA particles with barium sulphate were administered to the bone–implant interface. Further, PMMA particles were introduced into a previously published model for hydrostatic pressure induced osteolysis. There was measurable resorption in response to the PMMA particles but no additive or synergistic effect from introducing particles to the pressure model, and the effect of pressure was far greater than that of particles. These results suggest that, whereas particles can be shown to elicit an osteolytic response, the much less studied osteolytic effects of pressure could be far more important.