Poly Methyl Methacrylate Particles Research Articles

Structure Formation of Blend and Sheath/Core Conjugated Fibers in High-Speed Spinning of PET, Including a Small Amount of PMMA

The blend of poly(ethylene terephthalate) (PET) and a small amount of polymer that has higher T g than PET, such as polymethylmethacrylate (PMMA)—and is dispersed finely as immiscible particles in PET—exhibits lower molecular orientation than pure PET under high-speed fiber spinning. To obtain insight into the mechanism of the lower molecular orientation of the blend fiber, the sheath/core structure of PET (sheath)/PMMA (core) conjugated fiber (the same PET/PMMA weight ratio as in the blend fiber), was produced as a model. The thinning profile of the fiber diameter along the spinning line and the birefringence distribution of the cross-section were examined and compared among pure PET fiber, the conjugated fiber, and the blend fiber. The conjugated fiber had the lowest molecular orientation of PET in the sheath part, and its thinning process was accelerated similar to the blend fiber. As a result of the distribution of molecular orientation across the diameter of the conjugated fiber, it is considered that PMMA, having the high T g , tends to solidify at a higher temperature (upstream) than PET in the thinning process, making the flow of PET accelerate as if it was pushed by PMMA. This causes the maximum dv/dx just before the solidification point to be smaller; therefore, the lower spinning stress, resulting in smaller birefringence of PET, can be considerable. This acceleration was generated at the interface of PET and PMMA, and spread toward the fiber surface as both polymers were thinning in elongational flow (in melt). On the other hand, close to the interface, molecules of PET were stretched by PMMA, resulting in an increase of birefringence. Such discussion is also considered to apply to the blend fiber. However, because the blend fiber had a significantly larger interface area compared with the conjugated fiber, it is considered that the increase of birefringence of PET by the interface drag force cannot be neglected. The larger particles of PMMA dispersed in PET results in the lower birefringence of PET that is supported by the elongation effect (i.e., the interface drag force).

The Role of Dynamic Membrane in Cross-Flow Microfiltration of Macromolecules

The effects of dynamic membrane formed by fine particles on the filtration rate and the rejection of macromolecules in cross-flow microfiltration are studied. Experiments were carried out using the binary suspensions prepared by polymethyl methacrylate (PMMA) particles and the Dextran macromolecules. The filtration rates, the rejections of Dextran and the cake properties under various operating conditions, such as the cross-flow velocity and the filtration pressure, are measured and discussed. The filtration rate increases with increases of the cross-flow velocity and the filtration pressure but decreases when the molecular weight of Dextran is increased. On the other hand, the rejection of Dextran increases with the increase of filtration pressure but decreases with the increase of cross-flow velocity. The standard capture equation for deep-bed filtration is adopted to relate the rejection of Dextran and the properties of dynamic membrane. The results show that the mass of the dynamic membrane is the most important factor on the rejection of Dextran. Using the experimental data obtained under various cross-flow velocities, the rejection of Dextran can be regressed as a single function of cake mass. It can be concluded that the rejection of macromolecules increases due to the presence of fine particles, and that the magnitude of the rejection increases with increasing the mass of cake.

Investigations on the wear behaviour of the temporary PMMA-based hip Spacer-G®

Total hip replacement has become one of the most successful orthopaedic procedures. However, complications due to infections may give serious problems and have devastating consequences for the hip implant. The use of a temporary three-dimensional polymethylmethacrylate (PMMA) cement spacer may be an alternative to solve infections in hip implants, improving the lives of patients awaiting reimplantation. In order to evaluate their wear behaviour, five PMMA Spacer-G femoral heads were tested against five post-mortem pelves in a hip joint simulator with bovine calf serum as lubricant. The surface of the worn spacers was characterized by scanning electron microscopy (SEM) analysis; all the samples revealed a similar morphology, showing areas characterized by different degrees of wear. Particle debris was isolated from the lubricant and PMMA particles and bone fractions were quantified. The amount of debris was found to be higher than where no-temporary prostheses were used. However, this result is acceptable since wear debris is removed by lavage irrigation when the Spacer-G is explanted. On the basis of these data, it is considered that the use of the cement Spacer-G could be a promising approach to the treatment of complicated infections of the hip joint. Therefore, Spacer-G is worthy of further research.

Modeling of Cross-Flow Microfiltration of Fine Particle/Macromolecule Binary Suspension.

The cross-flow microfiltration of fine particle/macromolecule binary suspension is analyzed and modeled in this study. The filtration rate, the cake thickness and the rejection of macromolecules can be estimated from the operating variables by modeling the cake formation, the concentration polarization and the penetration of macromolecules through the filter cake. Based on the force balance model, the thickness of the filter cake formed by fine particles can be related to the operating conditions. The formed cake plays the major roles on the filtration resistances and on the rejection of macromolecules. A reversible concentration polarization layer is constructed with the macromolecules near the cake surface. The concentration profile in this layer can be calculated using the mass transfer equation once the mass transfer coefficient is obtained from the analogy analysis. The standard capture equation for depth filtration is adopted to simulate the retention and the penetration of macromolecules in the filter cake. Experiments are carried out using the binary suspensions prepared by polymethyl methacrylate (PMMA) particles and the Dextran macromolecules. The filtration rates, the rejection of Dextran and the cake properties under various operating conditions are measured and discussed. The predicted values using the proposed models agree fairly well with the experimental data under various operating conditions.

‘Unsticking’ a colloidal glass, and sticking it again

We study glass formation in hard spheres with short-range attraction. Thesystem consists of nearly-hard-sphere polymethylmethacrylate particles andnon-adsorbing random-coil polystyrene which induced a depletion attractionbetween the particles. The experiments reveal a re-entrant glass transitionand two qualitatively distinct glassy states. Dynamic light scattering,covering eleven orders of magnitude in time, gives insight into the kinds ofparticle motion responsible for these observations. The possible relevance ofour results to generic issues, such as the distinction between fragile andstrong glass formers, the nature of the underlying ‘free energy landscape’,and the relative importance of temperature and pressure, is discussed.

Rearrangements in hard-sphere glasses under oscillatory shear strain.

We investigate particle rearrangements in colloidal glasses subjected to oscillatory shear strain by the technique of light scattering (LS) echo. LS echo directly follows the motion of the particles through peaks (echoes) in the intensity autocorrelation function; the height of the peak measures the reversible motion in the sample. Polydisperse hard-sphere poly-methylmethacrylate particles were used to avoid crystallization under shear. The yielding behavior is monitored through irreversible particle rearrangements at several volume fractions in the glass phase region. At high volume fractions the glasses are found to yield at strains as high as 15% while the irreversible rearrangements have a more gradual onset with strain for low volume fraction glasses. The behavior of high order echoes at long times is related to the effects of shear on the frozen-in fluctuations of the glass.

Yielding and flow of colloidal glasses.

We investigate the yielding and flow of hard-sphere colloidal glasses by combining rheological measurements with the technique of light scattering echo. The polymethylmethacrylate particles used are sufficiently polydisperse that crystallization is suppressed. Creep and recovery measurements show that the glasses can tolerate surprisingly large strains, up to at least 15%, before yielding irreversibly. We attribute this behaviour to 'cage elasticity', the ability of a particle and its cage of neighbours to retain their identity under quite large distortion. Results from light scattering echo, which measures the extent of irreversible particle rearrangement under oscillatory shear, support the notion of cage elasticity. In the lower concentration glasses we find that particle trajectories are partly reversible under strains which significantly exceed the yield strain.

Human monocyte response to retrieved polymethylmethacrylate particles.

The purpose of this study was to compare retrieved polymethylmethacrylate (PMMA) particles from failed total hip arthroplasties in terms of size, shape, and the response of human monocytes with commercially available particles. PMMA particles were isolated from peri-implant tissues of five failed cemented total hip arthroplasties using tissue digestion and a sucrose density gradient technique. Prepolymerized cement powder and those from which barium sulfate had been removed were examined for comparison. After exposure of peripheral human monocytes to PMMA particles, tumor necrosis factor-alpha and interleukin-6 in medium were measured by using enzyme-linked immunosorbent assays. Image analysis revealed that retrieved particles were larger (retrieved: 1.24 microm; prepolymerized cement powder: 0.83 microm; barium sulfate-free powder: 0.87 microm) and were more irregular in shape and rougher than commercially available particles. Cytokine release was increased by all PMMA particle species. However, commercially available PMMA particles stimulated the release of necrosis factor-alpha and interleukin-6 more strongly than did retrieved particles at very high doses. The observed difference in monocyte response might be due to the volume of the challenged particles. Another possible reason for the difference might be alteration of the surface chemistry of particles in situ and the difference in surface morphology between them.

Phagocytosis of different particulate dermal filler substances by human macrophages and skin cells.

Foreign substances have been introduced into the human body with varying degrees of success. Polymethylmethacrylate (PMMA) microspheres of different sizes recently have been manufactured for use as a filler substances in the skin and other organs. To establish whether the size of PMMA microspheres determines whether various cell types initiate phagocytosis. The capacity of three different cell lines-U-937 cells, XS 106 and XS 52 Langerhans cells, and HaCaT keratinocytes-to phagocytose microspheres of varying sizes was examined using light and confocal microscopy as well as fluorescence-activated cell sorter (FACS) analysis. Tumor necrosis factor (TNF)-alpha secretion was also determined. The U-937 cells, keratinocytes, and Langerhans cells could phagocytose PMMA particles of 20 microm or smaller. Microspheres larger than 20 microm were not ingested by any of the cells. Microspheres larger than 20 microm have a lower likelihood of being phagocytosed. Thus this study suggests that microspheres 40-50 microm in diameter are less likely to initiate an inflammatory reaction when injected into the dermis and subdermis as a filler substance. On the other hand, microparticles made of silicone and polymethacrylate were phagocytosed, possibly because of their different structure.

Tumor necrosis factor-α mediates polymethylmethacrylate particle-induced NF- κB activation in osteoclast precursor cells

Tumor necrosis factor-α (TNF) is a potent osteoclastogenic cytokine that has a fundamental role in the pathogenesis of implant particle-induced osteolysis. The nuclear transcription factor NF- κB mediates TNF signaling and this transcription complex is necessary for osteoclastogenesis. Because polymethylmethacrylate (PMMA) particles cause osteolysis, we reasoned the PMMA would induce NF- κB activation. In fact, we find that exposure of osteoclast precursors, in the form of colony stimulating factor-1 (CSF-1) dependent murine bone marrow macrophages, to PMMA particles prompts nuclear translocation and activation of NF- κB. Supershift assays confirm the presence of the p50 and p65 NF- κB subunits in the activated transcription factor. Particle-induced NF- κB activation is equal in both wild type and LPS- hyporesponsive cells indicating that the phenomenon does not represent endotoxin contamination. A soluble, competitive inhibitor of TNF (huTNFr:Fc) dampens particle-directed NF- κB activation and this response is also abrogated in TNF −/− osteoclast precursors. Thus, PMMA particle activation of NF- κB is a secondary event resulting from enhanced TNF expression and is independent of LPS contamination.

Synthesis of Monodisperse Polymethyl Methacrylate Particles in Buffer Solutions under the Action of Carboxyl-Containing Initiator

Influence exerted by salts with buffering action and by the initial pH of the reaction mixture on the polymerization kinetics, viscosity-average molecular weight, and amount and degree of surface carboxylation of polymethyl methacrylate particles formed in the course of emulsifier-free emulsion polymerization of methyl methacrylate initiated by 4,4'-azobis(4-cyanoisovaleric acid) was studied.

Fiber Structure in High Speed Melt Spinning of Poly(ethylene terephthalate)/Polymethylmethacrylate.

The effect of a small amount of Polymethylmethacrylate (PMMA) additive on the fiber structure formation of poly(ethylene terephthalate) (PET) has been studied by means of birefringence, tensile properties, wide-angle-X-ray scattering, and DSC profiles. The investigations have been carried out under various spinning speeds (1000-5000m/min) and temperatures (275-295°C). A small amount of PMMA, which is immiscible with PET, suppressed the structure formation of PET at spinning speeds higher than 3000m/min, in that the birefringence and the melting point became lower and the wide angle X-ray scattering pattern was not clear compared with those of pure PET. Higher spinning temperature led to higher tenacity, the smaller elongation at break, and higher birefringence in PET/PMMA blend fiber. These tendencies were quite opposite to those in pure PET. To understand the cause of the suppression of structure formation of PET and the opposite tendencies with respect to the increase in spinning temperature by the presence of a small amount of PMMA, the melt viscosity of PET/PMMA blend, the deformation of PMMA particles after spinning were examined. Also the effect of solidification temperature of blend polymer on the orientation was investigated by using some PMMAs having different Tgs. These results suggested that PMMA does not work as plasticizer, and that the dispersed PMMA particles at higher spinning temperature had larger aspect ratio (L/D) compared with those of spun at low temperature. The molecular orientation decreased with increasing Tg(80-116°C) of PMMA. Taking these facts into consideration, the major cause for the less oriented PET(Tg=65°C) structure was considered that the formation of PET fiber structure should be finished before the solidification of PMMA due to its higher solidification temperature compared with those of PET itself, and the elongation flow of PET on the spinning line was restricted by the PMMA which deformed in parallel with PET.

New aspects in the histological examination of polyethylene wear particles in failed total joint replacements

The most important long-term complication in total joint replacements is aseptic osteolysis. Wear particles such as polyethylene (PE) debris are considered to be one of the causes that play a central role. Several studies indicated that PE can be visualised in paraffin-embedded tissue sections not only by polarised light, but also after oil red staining. To determine whether oil red staining enables sensitive detection of PE, we examined staining of mechanically-produced PE particles by oil red. Furthermore, we studied oil red staining of paraffin-embedded tissue specimens of patients with failed uncemented and cemented total knee and hip prostheses. We applied double labelling of sections by immunohistochemistry using the macrophage marker anti-CD68 and oil red staining. We found that oil red stains both isolated PE particles and PE particles in paraffin-embedded tissue sections. Polymethylmethacrylate particles in failed cemented arthroplasties did not stain in paraffin sections. Double labelling showed strong colocalisation of CD68 and PE. We suggest that oil red staining is a sensitive method to detect PE particles. Oil red staining is particularly helpful in these cases which show a characteristic histological feature of aseptic prosthesis loosening without particles being detectable with routine microscopy and polarised light. We also established that immunohistochemical methods can be applied together with the oil red staining method.

Inflammatory responses to orthopaedic biomaterials in the murine air pouch

An in vivo model of the inflammatory response to orthopaedic biomaterials was used to examine cellular and cytokine responses to polymer particles of ultra high molecular weight polyethylene (UHMWPE) and polymethylmethacrylate (PMMA), and metal particles of cobalt–chrome (Co–Cr) and titanium alloy (Ti–6Al–4V). Responses were determined separately and in combinations, to examine interactions between different forms of biomaterials. Murine air pouches were injected with particle suspensions, and reactions evaluated using histological, immunological, and molecular techniques. All particulate biomaterials caused significant increases in membrane thickness compared with control (saline) air pouches, with the highest reaction seen in response to Ti–6Al–4V particles. A synergistic increase in membrane thickness was observed when PMMA was combined with UHMWPE, suggesting that multiple biomaterial stimuli markedly increase the inflammatory reaction. Cellular analysis indicated that all particles increased the absolute number and the percentage of macrophages in the membrane over the control level, with the most pronounced increase due to individual biomaterial occurring with UHMWPE particles. Cytokine analysis revealed that biomaterials provoked a strong IL-1 response. Ti–6Al–4V stimulated the highest IL-6 gene transcription and the lowest IL-1 gene transcription. The data suggest that synergism in the inflammatory response to biomaterials may be important in adverse responses to orthopaedic wear debris.

Ceramic and PMMA particles differentially affect osteoblast phenotype

There is increasing evidence that wear debris particles present in periprosthetic tissues have direct effects on osteoblasts. The nature of the cell response varies with the chemistry of the particle and the number of particles. Most studies have used Ti, Ti–6Al–4V, and ultrahigh molecular weight polyethylene (UHMWPE) particles since these materials are most frequently used in implants and as a result, these particles predominate in peri-prosthetic tissues. Ceramics have also been used successfully as load-bearing surfaces in implants for years, although it is unknown how wear debris from these surfaces may contribute to aseptic bone loss. Further, particles resulting from polymethylmethacrylate (PMMA) cements used for fixation may also be involved in aseptic loosening of implants, but how these particles may affect bone formation is unknown. In the present study, we examined whether aluminum oxide (Al2O3), zirconium oxide (ZrO2), and PMMA particles exert effects on osteoblast proliferation, phenotypic expression, and local factor production, and if so, whether the effects were specific to the particle type. ZrO2 particles were produced in a custom-made axial mixer in which ZrO2 containers were filled with ZrO2 bars and 95% ethanol and then rotated continuously at room temperature. PMMA particles were prepared in a ZrO2 roller mill. Al2O3 was produced and provided by Aesculap AG. Particles were endotoxin-free with equivalent circle diameters <3μm; Al2O3 particles were significantly smaller than ZrO2 or PMMA particles. Particle suspensions were added to confluent cultures of MG63 osteoblast-like cells after diluting them 1:100, 1:10, and 1:1 with culture medium. Cells were incubated with the particles for 24h. Transmission electron microscopy showed that MG63 cells phagocytosed Al2O3 particles and exhibited ultrastructural changes consistent with cytotoxicity. This was supported by biochemical changes as well. Proliferation, alkaline phosphatase activity, and TGF-β1 levels were decreased. ZrO2 and PMMA particles increased proliferation and alkaline phosphatase specific activity. The effect of ZrO2 on alkaline phosphatase was targeted to matrix vesicles; the effect of PMMA was greater on the cells. All particles increased prostaglandin E2 production. These results show that Al2O3, ZrO2, and PMMA particles elicit direct effects on osteoblasts and that cell response depends on the particle type. None of the particles tested had the same effect as noted previously for UHMWPE: increased proliferation and decreased alkaline phosphatase. These results may indicate that the response of peri-prosthetic tissues to wear particles may be modulated by the relative contributions of the various particle types present.

Three-body wear of UHMWPE acetabular cups by PMMA particles against CoCr, alumina and zirconia heads in a hip joint simulator

Three-body abrasive wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups by loose polymethyl methacrylate (PMMA) bone cement particles is an important mechanism responsible for elevated wear debris generation in total hip arthroplasty. The resistance of the femoral head material to third-body damage has been considered critical for the wear performance of the polyethylene component. This study examines the effect of loose bone cement particles on the wear rate of UHMWPE acetabular cups against both metal and ceramic counterfaces in a hip joint simulator. Against the CoCr head, the UHMWPE cup showed a strong dependence of wear rate on the concentration of the PMMA particles in the lubricant. At a concentration less than 5g/l, the presence of the PMMA particles had no detrimental effect on the wear rate; higher concentrations of the PMMA particles greater than 5g/l led to an accelerated wear of the acetabular cups. Mild scratching damage was observed on the CoCr heads after testing with all PMMA-containing lubricants. However, no increased UHMWPE wear rate was found against these damaged femoral heads in a fresh lubricant without PMMA particles, indicating that femoral head scratching was not a major cause for the elevated wear observed under the three-body abrasive conditions. Against both alumina and zirconia ceramic heads, the wear rate of the UHMWPE was independent of the concentration of the PMMA particles. It was observed that a significant portion of the CoCr heads was covered with loose patches of PMMA particles. The higher the concentration of the PMMA particles, the greater the area of the head covered with PMMA particles. The attachment of PMMA particles to the ceramic heads was much reduced compared to the CoCr heads. It is therefore concluded that ceramic femoral heads are effective against potential run-away wear of the UHMWPE acetabular cups when an excessive amount of loose PMMA particles are present in the lubricant.

Contamination of polyethylene cups with polymethyl methacrylate particles: An experimental study

The articulating surfaces of 6 ultra–high molecular weight polyethylene cups were exposed to curing polymethyl methacrylate (PMMA) bone–cement and examined with scanning electron microscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Three of the cups were exposed to blood and bone–cement, and the rest were exposed to bone–cement only. After removal of the bone–cement bulk, PMMA particles were found and identified in all 6 cups. The particles were verified by identifying zirconium with energy-dispersive x-ray fluorescence spectroscopy in 5 cups and with LA-ICPMS in 1 cup. The degree of surface contamination was estimated with LA-ICPMS. The number of zirconium-containing particles detected was on average 10 to 20/mm2. PMMA bone–cement left in polyethylene cups during polymerization can contaminate the articulating surface with adherent PMMA particles.

Fibroblast expression of C–C chemokines in response to orthopaedic biomaterial particle challenge in vitro

C–C chemokines are soluble mediators that occur in a periprosthetic granuloma and influence recruitment, localization and activation of inflammatory cells. This study tested effects of titanium and polymethylmethacrylate (PMMA) particles on expression of selected C–C chemokines in cultured human fibroblasts. The C–C chemokines analyzed included monocyte chemoattractant protein-1, 2 (MCP-1, 2), monocyte inflammatory protein-1 alpha (MIP-1 alpha), and regulated on activation, normal T-cell expressed and secreted protein (RANTES). Interleukin-1 beta (IL-1 beta) served as a known stimulator of chemokine release while interleukin-6 (IL-6) expression served as a marker for fibroblast activation. Protein and mRNA signal levels were determined by ELISA and RT-PCR, respectively. The results demonstrated that exposure of fibroblasts to titanium and PMMA particles resulted in increased release of MCP-1 in a dose- and time-dependent manner. After 24 h, titanium particles maximally upregulated MCP-1 release 7-fold while PMMA particles increased MCP-1 levels 2-fold, when compared to unchallenged fibroblasts. MCP-2, MIP-1 alpha and RANTES levels remained unchanged following exposure of fibroblasts to titanium or PMMA particles at any concentration or time point tested. However, IL-1 beta stimulated release of MCP-1, MCP-2, and RANTES, but not MIP-1 alpha from the fibroblasts. IL-1 beta, not particles, exhibited the most prominent effect on MCP-1 mRNA levels. Increased release of MCP-1 from fibroblasts exposed to titanium and PMMA particles coincided with increased release of IL-6. This study suggests that release of chemoattractant factors from fibroblasts localized in periprosthetic membranes enhances the chronic inflammatory process leading to bone resorption and implant loosening.

Tissue reactions to particles of bone-substitute materials in intraosseous and heterotopic sites in rats: discrimination of osteoinduction, osteocompatibility, and inflammation

Two rat models were used to characterize tissue-specific reactions to particles of bone-substitute materials: one for osteocompatibility in a healing tibial wound and the other in a heterotopic, subcutaneous site. Small, unicortical tibial wounds in rats healed spontaneously, beginning with the rapid proliferation of intramedullary woven bone. That temporary bone was resorbed by osteoclasts and finally, the cortical wound was healed with lamellar bone and the medullary space was repopulated with marrow. When various particulate materials were implanted into fresh wounds, three types of reactions were observed. (1) Demineralized bone powder (DBP) and non-resorbable calcium phosphate (nrCP) were incorporated into the reactive medullary and cortical bone. (2) Polymethylmethacrylate (PMMA) particles were surrounded with a fibrous layer, but did not impair bone healing. (3) Polyethylene (PE) shards and resorbable calcium phosphates (rCPs) were inflammatory and inhibited osseous repair. Subcutaneous sites showed osteoinductive, fibrotic, or inflammatory responses to these materials. Only DBP induced endochondral osteogenesis subcutaneously. The nrCP evoked a fibrous reaction. In contrast, rCPs, PMMA, and PE shards generated inflammatory reactions with each particle being surrounded by fibrous tissue and large multinucleated giant cells. In conclusion, only DBP showed osteoinductive as well as osteocompatible properties. The nrCP was osteocompatible. The rCPs stimulated various degrees of inflammatory responses. PMMA was osteocompatible and did not interfere with the bone healing process. PE was not osteocompatible and generated foreign body reactions in both sites. Use of the two sites distinguishes osteoinductive, osteocompatible, and inflammatory properties of particles of bone-substitute materials.

Interleukin-10 inhibits polymethylmethacrylate particle induced interleukin-6 and tumor necrosis factor- α release by human monocyte/macrophages in vitro

Periprosthetic membranes commonly observed at sites of total joint implant loosening exhibit abundant macrophages and particulate debris. Macrophages phagocytose orthopedic debris and release the pro-inflammatory mediators interleukin-1, interleukin-6, tumor necrosis factor- α, and prostaglandin E 2. Populations of activated lymphocytes are often seen in periprosthetic membranes. These lymphocytes may modulate the monocyte/macrophage response to particulate debris and influence aseptic loosening. In addition, other immunologic agents, such as interleukin-10, are present in tissues harvested from the bone–implant interface of failed total joint arthroplasties. The present study examined the effects of interleukin-10 on polymethylmethacrylate (PMMA) particle challenged human monocyte/macrophages in vitro. Human monocyte/macrophages isolated from buffy coats of five healthy individuals were exposed to 1–10 μm PMMA particles. Interleukin-10 was added to the monocyte/macrophages with and without the addition of PMMA particles. Interleukin-10-induced alterations in monocyte/macrophage metabolism were determined measuring interleukin-6 and tumor necrosis factor- α release by the cells following exposure to PMMA particles. Exposure of the monocyte/macrophages to PMMA particles resulted in a dose-dependent release of interleukin-6 and tumor necrosis factor- α at 48 h. Interleukin-10 reduced the levels of interleukin-6 and tumor necrosis factor- α release by macrophages in response to PMMA particles in a dose-dependent manner. At 48 h, particle-induced interleukin-6 release was inhibited by 60 and 90% with 1.0 and 10.0 ng/ml treatments of interleukin-10, respectively. At 48 h, particle-induced tumor necrosis factor- α release was inhibited by 58 and 88% with 1.0 and 10.0 ng/ml treatments of interleukin-10, respectively. Interleukin-10 challenge alone did not significantly alter basal interleukin-6 or tumor necrosis factor- α release relative to control cultures. The data presented in this study demonstrate that the anti-inflammatory cytokine, interleukin-10, inhibits monocyte/macrophage release of the pro-inflammatory cytokines interleukin-6 and tumor necrosis factor- α in response to PMMA particle challenge in vitro.