Macrophage/particle interactions: effect of size, composition and surface area

Proinflammatory and osteoclastogenic effects of beta-tricalciumphosphate and hydroxyapatite particles on human mononuclear cells in vitro

Particulate wear debris can activate defence cells and osteoclasts at the bone-implant interface possibly leading to bone resorption and implant failure. Cellular responses and inflammatory effects have been reported for particulate hydroxyapatite (HA). However, the immunological effects of particulate beta-tricalciumphosphate (beta-TCP) have not been studied and the question of whether beta-TCP is more biocompatible in this regard as is HA remains to be determined. Therefore the present work investigates effects of endotoxin-free HA and beta-TCP particles of the same size (d(50)=1 microm) and dose (SAR 10:1) on human peripheral blood mononuclear cells in vitro. The production of proinflammatory cytokines (TNF-alpha, IL-1beta, IL-8) and cytokines connected to osteoclast and dendritic cell differentiation (OPG, RANKL, M-CSF, GM-CSF) was determined by ELISA. After 6 and 18 h of incubation HA and beta-TCP caused a quite similar induction of TNF-alpha, IL-1beta and IL-8. Effects of particles on the production of M-CSF and OPG were not detectable. However, in sharp contrast to HA, beta-TCP caused less induction of GM-CSF and not any of RANKL, both known for promoting dendritic cells and osteoclastogenesis respectively. Therefore these in vitro data suggest that wear debris of beta-TCP poses lesser risk of the detrimental effects of osteoclast induction known from HA.

Soluble and particulate Co-Cr-Mo alloy implant metals activate the inflammasome danger signaling pathway in human macrophages: a novel mechanism for implant debris reactivity

Immune reactivity to soluble and particulate implant debris remains the primary cause of aseptic inflammation and implant loosening. However, the intracellular mechanisms that trigger immune cells to sense and respond to exogenous nonbiological agents such as metal particles or metal ions released from orthopedic implants remain unknown. Recent studies in immunology have outlined the importance of the intracellular inflammasome complex of proteins in sensing danger/stress signals triggered by nonbiological agents in the cytosol of macrophages. We hypothesized that metal implant debris can activate the inflammasome pathway in macrophages that causes caspase-1-induced cleavage of intracellular pro-IL-1beta into its mature form, resulting in IL-1beta secretion and induction of a broader proinflammatory response. We tested this hypothesis by examining whether soluble cobalt, chromium, molybdenum, and nickel ions and Co-Cr-Mo alloy particles induce inflammasome- mediated macrophage reactivity. Our results demonstrate that these agents stimulate IL-1beta secretion in human macrophages that is inflammasome mediated (i.e., NADPH-, caspase-1-, Nalp3-, and ASC-dependent). Thus, metal ion- and particle-induced activation of the inflammasome in human macrophages provides evidence of a novel pathway of implant debris-induced inflammation, where contact with implant debris is sensed and transduced by macrophages into a proinflammatory response.

Polymorphonuclear neutrophil response to hydroxyapatite particles, implication in acute inflammatory reaction

Hydroxyapatite (HA) is widely used as a bone substitute or coating biomaterial in bone diseases or prosthesis metal parts. The release of HA particles induces an inflammatory response and, if uncontrolled, could result in implant loss. Among the hallmarks of such inflammatory response is early recruitment of the polymorphonuclear cells (PMNs). The purpose of this work is to investigate the response of PMNs following exposure to HA in terms of secreted mediators. Our study shows that HA particles increase the release of pro-inflammatory mediators such as interleukin-1alpha, as well as chemotactic factors such as interleukin-8, macrophage inflammatory protein-1alpha and macrophage inflammatory protein-1beta. HA also induces an increase in matrix metalloproteinase 9 expression. Taken together, our data demonstrate for the first time that HA is capable of activating PMNs, a phenomenon that could potentially contribute to the onset of implant-associated inflammation.

Targeted lipid-coated nanoparticles: delivery of tumor necrosis factor-functionalized particles to tumor cells

Polymeric nanoparticles displaying tumor necrosis factor on their surface (TNF nanocytes) are useful carrier systems capable of mimicking the bioactivity of membrane-bound TNF. Thus, TNF nanocytes are potent activators of TNF receptor 1 and 2 leading to a striking enhancement of apoptosis. However, in vivo applications are hampered by potential systemic toxicity. Here, using TNF nanocytes as a model system, we developed a procedure to generate targeted lipid-coated particles (TLP) in which TNF activity is shielded. The TLPs generated here are composed of an inner single-chain TNF (scTNF)-functionalized, polymeric nanoparticle core surrounded by a lipid coat endowed with polyethylene glycol (PEG) for sterical stabilization and a single-chain Fv (scFv) fragment for targeting. Using a scFv directed against the tumor stroma marker fibroblast activation protein (FAP) we show that TLP and scTNF-TLP specifically bind to FAP-expressing, but not to FAP-negative cells. Lipid coating strongly reduced nonspecific binding of particles and scTNF-mediated cytotoxicity towards FAP-negative cells. In contrast, an increased cytotoxicity of TLP was observed for FAP-positive cells. Thus, through liposome encapsulation, nanoparticles carrying bioactive molecules, which are subject to nonselective uptake and activity towards various cells and tissues, can be converted into target cell-specific composite particles exhibiting a selective activity towards antigen-positive target cells. Besides safe and targeted delivery of death ligands such as TNF, TLP should be suitable for various diagnostic and therapeutic applications, which benefit from a targeted delivery of reagents embedded into the particle core or displayed on the core particle surface.

Highly crosslinked vs conventional polyethylene particles: relative in vivo inflammatory response

Crosslinked polyethylenes have been introduced to reduce wear and osteolysis. The osteolysis rate depends on many factors including the biologic activity of the wear particles. This study examines the relative inflammatory potential of highly crosslinked and non-crosslinked polyethylene particles. Polyethylene particles were crosslinked and characterized. Dose-response curves were generated for endotoxin-positive and endotoxin-negative particles at each degree of cross-linking using an in vivo model. The 10-MRad crosslinked polyethylene was more inflammatory than an identical dose (25 mg/mL) of non-crosslinked polyethylene (P = .05). Endotoxin increased the inflammatory response to crosslinked and non-crosslinked polyethylene in a similar fashion. These data suggest that the improved wear characteristics of highly crosslinked polyethylenes may be offset somewhat by the modestly increased inflammatory profile of the highly crosslinked compared with non-crosslinked particles.

Highly crosslinked vs conventional polyethylene particles--an in vitro comparison of biologic activities

Highly cross-linked polyethylenes (HXPEs) have been introduced to reduce wear after hip arthroplasty. The improved wear characteristics of HXPEs are well documented, but the relative biologic activity of HXPE and conventional polyethylene (CPE) particles remains unclear. Longevity (Zimmer, Warsaw, Ind; HXPE) and GUR 1050 (Zimmer; CPE) particles were isolated and characterized from a hip simulator and their in vitro inflammatory responses (tissue necrosis factor *, interleukin 1*, and vascular endothelial growth factor levels) were compared using macrophages. The average diameter of Longevity particles (0.111 microm) was smaller than CPE particles (0.196 microm), and both were predominantly round (granular appearance). The inflammatory response to HXPE and CPE was concentration-dependent. No statistically significant differences were noted at low (0.1 surface area ratio [SAR]) and intermediate (0.75 SAR) doses. At the highest dose tested (2.5 SAR), HXPE was significantly more inflammatory than CPE based on relative tissue necrosis factor alpha and vascular endothelial growth factor secretion levels. Further study is needed to determine if similar findings would be noted in vivo over a broad concentration range.

Silk fibroin protein from mulberry and non-mulberry silkworms: cytotoxicity, biocompatibility and kinetics of L929 murine fibroblast adhesion

Silks fibers and films fabricated from fibroin protein of domesticated mulberry silkworm cocoon have been traditionally utilized as sutures in surgery and recently as biomaterial films respectively. Here, we explore the possibility of application of silk fibroin protein from non-mulberry silkworm cocoon as a potential biomaterial aid. In terms of direct inflammatory potential, fibroin proteins from Antheraea mylitta and Bombyx mori are immunologically inert and invoke minimal immune response. Stimulation of murine peritoneal macrophages and RAW 264.7 murine macrophages by these fibroin proteins both in solution and in the form of films assayed in terms of nitric oxide and TNFalpha production showed comparable stimulation as in collagen. Kinetics of adhesion of L929 murine fibroblasts, for biocompatibility evaluation, monitored every 4 h from seeding and studied over a period of 24 h, reveal A. mylitta fibroin film to be a better substrate in terms of rapid and easier cellularization. Cell viability studies by MTT assay and flow cytometric analyses indicate the ability of fibroin matrices to support cell growth and proliferation comparable to collagen for long-term culture. This matrix may have potential to serve in those injuries where rapid cellularization is essential.

Cell (A549)-particle (Jasada Bhasma) interactions using Raman spectroscopy

Current methods for the evaluation of cell interactions with particles are nonspecific, slow, and invasive to the cells. Raman spectroscopy is a noninvasive technique, and is used in the present study to investigate particle-cell interactions. The main focus of the present study is to employ Raman spectroscopy for investigating the interaction of human lung adenocarcinoma cell line (A549) with the particulate system Jasada Bhasma, a traditional Indian medicine. Jasada Bhasma is a unique preparation of zinc and is traditionally used for the treatment of various diseases like diabetes, age-related eye diseases, and as a health promotional tonic. The Raman spectral analysis is executed by identifying the difference in intracellular DNA/RNA, and proteins and lipids concentration between particles--treated and untreated cells. Comparison between Bhasma-treated and -untreated cells indicates that vibrational peaks corresponding to the DNA/RNA molecule show a significant increase in cells treated with the Jasada Bhasma. Apart from the DNA molecule, several other vibrational peaks related to the protein molecules also show a significant increase in A549 cells after treatment with Bhasma. These results indicate that Bhasma treatment of A549 possibly delays DNA degradation and enables retention of higher amount of protein molecules in the cells.

Evaluation of surgically retrieved temporomandibular joint alloplastic implants: pilot study

PURPOSE

The purpose of this study was to perform a retrieval analysis of temporomandibular joint (TMJ) alloplastic interpositional implants and test possible correlation between implant failure features and patient clinical outcomes. In addition, we investigated the implants' surface and examined the foreign body reaction associated with different types of alloplastic materials.

MATERIALS AND METHODS

Twelve implants (Proplast/Teflon [Vitek, Houston, TX] and Silastic [Dow Corning, Midland, MI]) were surgically removed from the patients' TMJs. Implant surface failure features (fracture length, perforation of the implants) were observed using stereomicroscopy and recorded for description of the failure mechanisms and to statistically compare with clinical outcomes. Patients' clinical data (pain symptoms and mandibular function) were collected and examined. Clinical outcomes were obtained relative to symptom severity (Symptom Severity Index [SSI]) and jaw function (modified Mandibular Function Impairment Questionnaire [mMFIQ]). Peri-implant soft tissues and implants were analyzed with light microscopy and stereo zoom microscopy. Electron microprobe analysis of implant fragments and peri-implant tissues was performed.

RESULTS

The statistical results showed that only the presence of implant perforation was statistically associated with the SSI, specifically with the pain tolerability dimension. No statistical association was seen between any of the other implant failure predictors and the SSI and between the predictors and the mMFIQ. Stereo zoom microscopy suggested that Proplast/Teflon implants (n = 7) were susceptible to perforation, layer tearing, fracture and fiber extrusion. The Silastic implants (n = 3) revealed a possible center perforation with fracture lines towards the periphery and fiber extrusion. Teflon implant wear debris particles appear to trigger a multinucleated giant cell foreign body reaction.

CONCLUSION

Facial pain was a significant correlate to perforation and breakdown of the alloplastic TMJ interpositional implants, and most likely was the reason for implant removal.

Mesenchymal stem cell interaction with ultra-smooth nanostructured diamond for wear-resistant orthopaedic implants

Ultra-smooth nanostructured diamond (USND) can be applied to greatly increase the wear resistance of orthopaedic implants over conventional designs. Herein we describe surface modification techniques and cytocompatibility studies performed on this new material. We report that hydrogen (H)-terminated USND surfaces supported robust mesenchymal stem cell (MSC) adhesion and survival, while oxygen- (O) and fluorine (F)-terminated surfaces resisted cell adhesion, indicating that USND can be modified to either promote or prevent cell/biomaterial interactions. Given the favorable cell response to H-terminated USND, this material was further compared with two commonly used biocompatible metals, titanium alloy (Ti-6Al-4V) and cobalt chrome (CoCrMo). MSC adhesion and proliferation were significantly improved on USND compared with CoCrMo, although cell adhesion was greatest on Ti-6Al-4V. Comparable amounts of the pro-adhesive protein, fibronectin, were deposited from serum on the three substrates. Finally, MSCs were induced to undergo osteoblastic differentiation on the three materials, and deposition of a mineralized matrix was quantified. Similar amounts of mineral were deposited onto USND and CoCrMo, whereas mineral deposition was slightly higher on Ti-6Al-4V. When coupled with recently published wear studies, these in vitro results suggest that USND has the potential to reduce debris particle release from orthopaedic implants without compromising osseointegration.

Polyethylene and cobalt-chromium molybdenium particles elicit a different immune response in vitro

Periprosthetic osteolysis is a major clinical problem that limits the long-term survival of total joint arthroplasties. Particles of prosthetic material stimulate immune competent cells to release cytokines, which may cause bone loss and loosening of the prosthesis. This study examined the following hypothesis. Polyethylene and titanium particles elicit a different immune response in vitro. To test these hypotheses, we used the human bone marrow cell culture model that we have established and previously used to examine particle associated cytokine release. Ultra high molecular weight polyethylene (UHMW-PE) induced a proliferation of CD14 positive cells (monocytes/macrophages) whereas cobalt chromium molybdenium (CoCrMb) particles demonstrated an increased proliferation of CD66b positive cells (granulocytes). Light and scanning microscopic evaluation revealed that the UHMW-PE particles, which have built large clusters of particles (Ø7, 5 microm), were mainly surrounded by the cells and less phagocytosed. On the other hand the smaller particles from CoCrMb have been phagocytosed by the cells. These results provide strong support for our hypothesis: that wear particles derived from prosthetic materials of different material can elicit significantly different biologic responses. In summary the results suggest that the "in vitro" response to wear particles of different biomaterials should be investigated by culture systems of various lineages of cells.

Human macrophage response to UHMWPE, TiAlV, CoCr, and alumina particles: analysis of multiple cytokines using protein arrays

Aseptic loosening of total joint replacements is believed to be initiated by a macrophage response to prosthetic wear debris. To better characterize the early response to clinically relevant wear debris, we challenged primary human macrophages from four donors with ultra high molecular weight polyethylene (UHMWPE), TiAlV, CoCr, and alumina particles. After a 24-h culture, protein arrays were used to quantify the secretion of 30 different cytokines and chemokines. Macrophages secreted detectable levels of nine mediators in culture: Interleukin-1alpha (IL-1alpha), tumor necrosis factor-alpha (TNF-alpha), IL-1beta, MCP-1, IL-8, IL-6, GM-CSF, IL-10, and IL-12p40. TiAlV particles were the most stimulatory, causing 5- to 900-fold higher cytokine expression compared with nonstimulated cells and uniquely eliciting high levels of IL-1alpha, IL-6, IL-10, and GM-CSF. CoCr and alumina were mildly stimulatory and typically elicited two- to fivefold greater levels than nonstimulated cells. Surprisingly, UHMWPE did not elicit a significant increase in cytokine release. Our data suggests that IL-1alpha, TNF-alpha, IL-1beta, and MCP-1 are the primary initiators of osteolysis and implicates metallic debris as an important trigger for their release.

Are there biological markers of wear?

Potential systemic markers of implant wear include products of the wear process (particles and ions) and mediators of the inflammatory reaction that can be induced by wear. Ions from polymers used in arthroplasty are not specific, but high metal ion levels may help identify patients with unexpectedly high wear of metal-on-metal implants. The kinetics of ion production, transport, and excretion are complex, however, so it is currently difficult to interpret the significance of mild elevations in metal ions. Indices of bone turnover (eg, collagen fragments) and mediators involved in the inflammatory reaction to particles (eg, osteoprotegerin, RANKL, interleukins) may be associated with osteolysis, but systemic disorders (eg, osteoarthritis) and the use of medications that influence bone remodeling limit the predictive value of these analytes with respect to the consequences of implant wear. Using genomic and proteomic methods to measure multiple analytes offers promise, but the challenge is to identify markers specifically associated with wear that are not elevated by other conditions that often coexist in this patient population.

Tribo-electrochemical technique for studying tribocorrosion behavior of biomaterials

Tribocorrosion is the term which describes the synergy between tribological and electrochemical processes. An apparatus was designed and built to study the tribocorrosion behavior of biomaterials. Electrochemical set-up with three electrodes is used for controlling the potential of the surface of a conducting material subjected to classical wear testing. Using this equipment, it is possible to carry out friction and wear tests in electrolytic solution under well-defined electrochemical conditions determined by the applied electrode potential. In this paper, this apparatus was described and the tests of deposited TiN on pure Ti for corrosion and tribocorrosion behavior under simulated body fluid were conducted. The presence of TiN layer on the surface of Ti has increased the open circuit potential. The charge transfer resistance (R(ct)) determined using electrochemical impedance spectroscopy (EIS) was higher for the nitrided surfaces than for the Ti substrates. However after wear test, R(ct) was significantly reduced because the protective layer was damaged.

Biocompatibility of dental casting alloys

Most cast dental restorations are made from alloys or commercially pure titanium (cpTi). Many orthodontic appliances are also fabricated from metallic materials. It has been documented in vitro and in vivo that metallic dental devices release metal ions, mainly due to corrosion. Those metallic components may be locally and systemically distributed and could play a role in the etiology of oral and systemic pathological conditions. The quality and quantity of the released cations depend upon the type of alloy and various corrosion parameters. No general correlation has been observed between alloy nobility and corrosion. However, it has been documented that some Ni-based alloys, such as beryllium-containing Ni alloys, exhibit increased corrosion, specifically at low pH. Further, microparticles are abraded from metallic restorations due to wear. In sufficient quantities, released metal ions-particularly Cu, Ni, Be, and abraded microparticles-can also induce inflammation of the adjacent periodontal tissues and the oral mucosa. While there is also some in vitro evidence that the immune response can be altered by various metal ions, the role of these ions in oral inflammatory diseases such as gingivitis and periodontitis is unknown. Allergic reactions due to metallic dental restorations have been documented. Ni has especially been identified as being highly allergenic. Interestingly, from 34% to 65.5% of the patients who are allergic to Ni are also allergic to Pd. Further, Pd allergy always occurrs with Ni sensitivity. In contrast, no study has been published which supports the hypothesis that dental metallic materials are mutagenic/genotoxic or might be a carcinogenic hazard to man. Taken together, very contradictory data have been documented regarding the local and systemic effects of dental casting alloys and metallic ions released from them. Therefore, it is of critical importance to elucidate the release of cations from metallic dental restorations in the oral environment and to determine the biological interactions of released metal components with oral and systemic tissues.

Wear analysis of failed acetabular polyethylene: a comparison of analytical methods

There are many methods for analysing wear volume in failed polyethylene acetabular components. We compared a radiological technique with three recognised ex vivo methods of measurement. We tested 18 ultra-high-molecular-weight polyethylene acetabular components revised for wear and aseptic loosening, of which 13 had pre-revision radiographs, from which the wear volume was calculated based upon the linear wear. We used a shadowgraph technique on silicone casts of all of the retrievals and a coordinate measuring method on the components directly. For these techniques, the wear vector was calculated for each component and the wear volume extrapolated using mathematical equations. The volumetric wear was also measured directly using a fluid-displacement method. The results of each technique were compared. The series had high wear volumes (mean 1385 mm(3); 730 to 1850) and high wear rates (mean 205 mm(3)/year; 92 to 363). There were wide variations in the measurements of wear volume between the radiological and the other techniques. Radiograph-derived wear volume correlated poorly with that of the fluid-displacement method, co-ordinate measuring method and shadowgraph methods, becoming less accurate as the wear increased. The mean overestimation in radiological wear volume was 47.7% of the fluid-displacement method wear volume. Fluid-displacement method, coordinate measuring method and shadowgraph determinations of wear volume were all better than that of the radiograph-derived linear measurements since they took into account the direction of wear. However, only radiological techniques can be used in vivo and remain useful for monitoring linear wear in the clinical setting. Interpretation of radiological measurements of acetabular wear must be done judiciously in the clinical setting. In vitro laboratory techniques, in particular the fluid-displacement method, remain the most accurate and reliable methods of assessing the wear of acetabular polyethylene.

Neo-capsule tissue reactions in metal-on-metal hip arthroplasty

BACKGROUND

Modern-generation metal-on-metal articulations have a high wear resistance and may therefore be able to improve the long-term performance of artificial joints. However, the biological effects are still under debate. This study was undertaken to review the histopathological changes in neo-capsule tissues of different metal-on-metal hip arthroplasties.

METHODS

Neo-capsule tissue samples from 46 hips with modern second-generation metal-on-metal articulations (39 hip resurfacings and 7 non-cemented total hip replacements) with a variety of failure mechanisms were examined histopathologically and immunohistochemically.

RESULTS

A distinct lymphocytic infiltration was found in all cases with in situ times of more than 7 months, consisting of CD20-positive B-lymphocytes and CD3-positive T-lymphocytes and sometimes thinly distributed CD138-positive plasma cells without dominant T-cell or plasma cell infiltrates.

INTERPRETATION

This distinct lymphocytic infiltration has not been reported in tissue analyses of metal- or ceramic-on-polyethylene hip replacements, and may therefore be considered to be a characteristic histological pattern of tissue reactions on metal particles and/or ions around metal-on-metal bearings.

Modeling UHMWPE wear debris generation

It is widely recognized that polyethylene wear debris is one of the main causes of long-term prosthesis loosening. The noxious bioreactivity associated with this debris is determined by its size, shape, and quantity. The aim of this study was to develop a numerical tool that can be used to investigate the primary polyethylene wear mechanisms involved. This model illustrates the formation of varying flow of polyethylene debris with various shapes and sizes caused by elementary mechanical processes. Instead of using the classical continuum mechanics formulation for this purpose, we used a divided materials approach to simulate debris production and release. This approach involves complex nonlinear bulk behaviors, frictional adhesive contact, and characterizes material damage as a loss of adhesion. All the associated models were validated with various benchmark tests. The examples given show the ability of the numerical model to generate debris of various shapes and sizes such as those observed in implant retrieval studies. Most of wear mechanisms such as abrasion, adhesion, and the shearing off of micro-asperities can be described using this approach. Furthermore, it could be applied to study the effects of friction couples, macroscopic geometries, and material processing (e.g. irradiation) on wear.

The potential role of phagocytic capacity in the osteolytic process induced by polyethylene wear particles

Osteolysis induced by ultra-high molecular weight polyethylene wear particles is the major cause of long-term failure of artificial joints. We examined the effects of wear particles on bioactivity by analysing the biophysical aspects of particle phagocytosis. We estimated the maximum number of internalized particles (the phagocytic capacity) for particles of various sizes and shapes. We demonstrated that elongated particles had a smaller phagocytic capacity than spherical particles of the same volume. A review of the literature showed that the ratio of particle concentration (number of particles/number of cells) to phagocytic capacity is critical for particle-induced biological responses. When this ratio was < 1, the biological response was approximately proportional to the ratio itself. When this ratio was > 1, limited changes in the biological response were observed. The saturation level of the phagocytic capacity for a particle population appears to reflect the degree of polyethylene particle-induced biological response.

Mechanisms of Disease: molecular insights into aseptic loosening of orthopedic implants

Despite the success of treating rheumatic disorders with biologic therapies, joint replacement surgery still remains the final treatment option in many cases. Approximately 1.5 million joint arthroplastic operations are performed annually worldwide. Implant failure due to massive bone loss and aseptic loosening of prostheses, however, is a major complication of joint replacement, which can lead to high socioeconomic burdens both for the individual patient and for health-care systems. To date, there is no approved drug therapy to prevent or inhibit periprosthetic osteolysis, and aseptic loosening of prostheses can only be overcome by surgical revision. Research during the past decade, however, has unravelled much of the pathogenesis of aseptic prosthesis loosening and preclinical studies have identified potential targets for pharmaceutical treatments. This article highlights the importance of a cooperative interaction between rheumatologists and orthopedic surgeons, and presents novel insights into the molecular mechanisms behind aseptic loosening of prostheses. In addition, we outline potential perspectives for the development of future therapeutic strategies for this devastating complication.

The cellular and molecular biology of periprosthetic osteolysis

The generation of prosthetic implant wear after total joint arthroplasty is recognized as the major initiating event in development of periprosthetic osteolysis and aseptic loosening, the leading complication of this otherwise successful surgical procedure. We review current concepts of how wear debris causes osteolysis, and report ideas for prevention and treatment. Wear debris primarily targets macrophages and osteoclast precursor cells, although osteoblasts, fibroblasts, and lymphocytes also may be involved. Molecular responses include activation of MAP kinase pathways, transcription factors (including NFkappaB), and suppressors of cytokine signaling. This results in up-regulation of proinflammatory signaling and inhibition of the protective actions of antiosteoclastogenic cytokines such as interferon gamma. Strategies to reduce osteolysis by choosing bearing surface materials with reduced wear properties should be balanced by awareness that reducing particle size may increase biologic activity. There are no approved treatments for osteolysis despite the promise of therapeutic agents against proinflammatory mediators (such as tumor necrosis factor) and osteoclasts (bisphosphonates and molecules blocking receptor activator of NFkappaB ligand [RANKL] signaling) shown in animal models. Considerable efforts are underway to develop such therapies, to identify novel targets for therapeutic intervention, and to develop effective outcome measures.

Titanium particles and surface-bound LPS activate different pathways in IC-21 macrophages

It is still unknown if wear-debris particles themselves induce osteolysis or if they serve a functional role as receptors for ligands that incite an inflammatory response that ultimately leads to bone resorption. In this study, commercially pure titanium particles (cpTi) were subjected to a serial combination of different cleaning methods to remove Lipopolysaccharide (LPS) or were incubated in LPS solutions of known concentrations. Then, the response of the macrophage cell line IC-21 to the cleaned particles, LPS-bound Ti particles, and soluble LPS was examined. It was found that cleaned particles up to 1000 particles per cell did not stimulate macrophages to release Tumor necrosis factor-alpha (TNF-alpha) or Interleukin 6 (IL-6), but they significantly increased the release of Prostaglandin E(2) (PGE(2)) when the particle concentration was higher than 500 particles per cell. At one particle per cell, Ti particles bound with LPS stimulated the release of IL-6 and TNF-alpha by macrophages. The level of released cytokines was dependent on, and correlated with, the amount of LPS present on the particles. The macrophages were more sensitive to soluble LPS than to particle-bound LPS, and the simultaneous addition of cleaned Ti particles did not have additional effects on the effects of soluble LPS. This study shows evidence that, cpTi particles and LPS have distinct mechanisms of action on the IC-21 macrophages, but that both contribute to the development of an inflammatory response.

The central role of wear debris in periprosthetic osteolysis

Periprosthetic osteolysis remains the leading complication of total hip arthroplasty, often resulting in aseptic loosening of the implant, and a requirement for revision surgery. Wear-generated particular debris is the main cause of initiating this destructive process. The purpose of this article is to review recent advances in our understanding of how wear debris causes osteolysis, and emergent strategies for the avoidance and treatment of this disease. The most important cellular target for wear debris is the macrophage, which responds to particle challenge in two distinct ways, both of which contribute to increased bone resorption. First, it is well known that wear debris activates proinflammatory signaling, which leads to increased osteoclast recruitment and activation. More recently, it has been established that wear also inhibits the protective actions of antiosteoclastogenic cytokines such as interferon gamma, thus promoting differentiation of macrophages to bone-resorbing osteoclasts. Osteoblasts, fibroblasts, and possibly lymphocytes may also be involved in responses to wear. At a molecular level, wear particles activate MAP kinase cascades, NFkappaB and other transcription factors, and induce expression of suppressors of cytokine signaling. Strategies to reduce osteolysis by choosing bearing surface materials with reduced wear properties (such as metal-on-metal) should be balanced by awareness that reducing particle size may increase biological activity. Finally, although therapeutic agents against proinflammatory mediators [such as tumor necrosis factor (TNF)] and osteoclasts (bisphosphonates and molecules blocking RANKL signaling) have shown promise in animal models, no approved treatments are yet available to osteolysis patients. Considerable efforts are underway to develop such therapies, and to identify novel targets for therapeutic intervention.

Different particle determinants induce apoptosis and cytokine release in primary alveolar macrophage cultures

Background

Particles are known to induce both cytokine release (MIP-2, TNF-α), a reduction in cell viability and an increased apoptosis in alveolar macrophages. To examine whether these responses are triggered by the same particle determinants, alveolar macrophages were exposed in vitro to mineral particles of different physical-chemical properties.

Results

The crystalline particles of the different stone types mylonite, gabbro, basalt, feldspar, quartz, hornfels and fine grain syenite porphyr (porphyr), with a relatively equal size distribution (≤ 10 μm), but different chemical/mineral composition, all induced low and relatively similar levels of apoptosis. In contrast, mylonite and gabbro induced a marked MIP-2 response compared to the other particles. For particles of smaller size, quartz (≤ 2 μm) seemed to induce a somewhat stronger apoptotic response than even smaller quartz (≤ 0.5 μm) and larger quartz (≤ 10 μm) in relation to surface area, and was more potent than hornfels and porphyr (≤ 2 μm). The reduction in cell viability induced by quartz of the different sizes was roughly similar when adjusted to surface area. With respect to cytokines, the release was more marked after exposure to quartz ≤ 0.5 μm than to quartz ≤ 2 μm and ≤ 10 μm. Furthermore, hornfels (≤ 2 μm) was more potent than the corresponding hornfels (≤ 10 μm) and quartz (≤ 2 μm) to induce cytokine responses. Pre-treatment of hornfels and quartz particles ≤ 2 μm with aluminium lactate, to diminish the surface reactivity, did significantly reduce the MIP-2 response to hornfels. In contrast, the apoptotic responses to the particles were not affected.

Conclusion

These results indicate that different determinants of mineral/stone particles are critical for inducing cytokine responses, reduction in cell viability and apoptosis in alveolar macrophages. The data suggest that the particle surface reactivity was critical for cytokine responses, but contributed less to cell death for the types of particles tested. The size-dependent variations, specially in cytokine release, seem not to be explained only by particle surface area.

Wear particles from metal-on-metal total hip replacements: effects of implant design and implantation time

Detailed characterization of wear particles is necessary to understand better the implant wear mechanisms and the periprosthetic tissue response. The purposes of the present study were to compare particle characteristics of current with older designs of metal-on-metal (MM) total hip replacements (THRs), and to determine the effect of implantation time on wear particle characteristics. Metal wear particles isolated from periprosthetic tissues from 19 patients with MM THRs of current and older designs and at different implantation times (very short, longer, and very long) were studied using transmission electron microscopy and energy dispersive X-ray analysis. The particles from the current design implants with implantation times of not more than 15 months (very short-term) were almost exclusively round to oval chromium oxide particles. In all other cases, although the predominance was still round to oval chromium oxide particles, greater proportions of cobalt-chromium-molybdenum (Co-Cr-Mo) particles, mainly needle-shaped, were detected. Very long-term THRs implanted for more than 20 years had the highest percentage of needle-shaped Co-Cr-Mo particles. Particle lengths were not markedly different between the different designs and implantation times except for the current design implants of not more than 15 months, which had a significantly smaller mean length of 39 nm. In conclusion, the implant design did not seem to have a significant influence on particle characteristics whereas the implantation time appeared to have the most effect on the particles. It should be noted that, because of the limited number of tissue retrievals available, some uncertainty remains regarding the generality of these findings.

Periprosthetic osteolysis: an immunologist's update

PURPOSE OF REVIEW

Inflammation-induced osteolysis is a problem in both inflammatory arthritis and total joint arthroplasty. New drug therapies have been shown to slow, halt, or even reverse the osteolysis associated with inflammatory arthritis. Unfortunately, similar advances in the medical treatment of periprosthetic osteolysis have not occurred. This review will update the state of periprosthetic osteolysis.

RECENT FINDINGS

Preliminary results with phase I and II clinical trials with AMG-162, a human IgG2 that binds receptor activator of nuclear factor kappaB (RANK) ligand, have been reported. Based on these results AMG-162 appears to be safe and to have a potent effect on osteoclast function. Based on animal studies, it is expected that regents such as AMG-162 that block RANK-ligand/RANK interaction will have activity in inflammation-induced osteolysis. Volumetric three-dimensional and magnetic resonance imaging scans for detecting and quantifying periprosthetic osteolysis have been validated in cadaver studies. Lymphocytic infiltrates and positive skin tests to cobalt have been found in patients with periprosthetic osteolysis after second generation metal-on-metal prostheses. These findings again raise the question of whether metal allergy may contribute to implant failure in these patients. A new subset of T helper cells that are neither Th1 nor Th2, but secrete a unique pattern of cytokines including IL-17, has recently been discovered. The importance of these cells in modifying particle-induced osteolysis remains to be determined.

SUMMARY

There have been significant advances in our understanding of periprosthetic osteolysis, imaging technology to quantify osteolysis, and drug development. The time now seems ripe to translate these advances in clinical trials.

Effect of toothbrushing on titanium surface: An approach to understanding surface properties of brushed titanium

OBJECTIVES

This in vitro study aimed to characterize the surface morphology and composition of tooth-brushed titanium casting and thereby to elucidate interactions between the metal and abrasive material in dentifrice.

METHODS

Specimens were cast from CP Ti ingots and then mirror-finished. Two fluoride-free toothpastes containing crystalline CaHPO4.2H2O and amorphous SiO2 particles as abrasive were slurried with distilled water (15 g/30 mL). While toothbrushes were reciprocated at 120 strokes/min for 350,400 strokes, the specimens were brushed with the respective slurries under a load of 2.45 N. The brushed and non-brushed surfaces were characterized by means of SPM, EPMA, and XPS. SPM data were analyzed using one-way ANOVA, followed by post hoc Tukey test (p<0.01).

RESULTS

Irrespective of toothpastes, toothbrushing had a significant influence on surface roughness. The CaHPO4.2H2O-containing paste produced much rougher surface than the SiO2-containing paste. Both the surfaces were chemically altered due to reactions with the respective abrasive materials. Abrading chips had dimensions of micron to submicron order. A number of chips were attached to abrasive particles.

SIGNIFICANCE

The alterations of surface morphology and composition may affect biological responses of titanium in the oral environment. Dentifrice with lower abrasivity might be advisable for daily oral hygiene practice of patients with dental titanium devices.

Hydroxy apatite microspheres enhance gap junctional intercellular communication of human osteoblasts composed of connexin 43 and 45

The aseptic loosening of artificial joints with associated periprosthetic bone resorption may be partly due to the suppression of osteoblast function to form new bone by wear debris from the joint. To assess the effect of wear debris on osteoblasts, effects of model wear debris on gap junctional intercellular communication (GJIC) of normal human osteoblasts were estimated. The GJIC activity of the osteoblasts after a 1-day incubation with the microspheres was similar to that of normal osteoblasts. However, hydroxy apatite particles, which have been reported to enhance the differentiation of osteoblasts in contact with them, enhanced the GJIC function of the osteoblasts. From RT-PCR studies, not only connexin 43 but also connexin 45 is suggested to play a role in the GJIC of the osteoblasts in an early stage of coculture with the microspheres, although it is still unclear how these connexins work and are regulated in the GJIC and differentiation. However, this study suggests that there is a relationship between the early levels of GJIC and the differentiation of the cells. Therefore, estimating the effect of biomaterials, even in the microsphere form, on the GJIC of model cells, with which the biomaterials may be in contact in vivo, can provide important information about their biocompatibility.

Chemokine IL-8 induction by particulate wear debris in osteoblasts is mediated by NF-kappaB

Chemokines, or chemotactic cytokines, are major regulators of the inflammatory response and have been identified as pathogenic factors in the periprosthetic soft tissue. Particulate wear debris induced NF-kappaB activation, the major transcriptional regulator of IL-8 and MCP-1 pro-inflammatory genes and, indeed, both IL-8 and MCP-1 chemokine gene expressions were upregulated in titanium particulate-stimulated human osteoblasts. Here, we demonstrate that phagocytosed particles activate the IL-8 gene promoter via a NF-kappaB-mediated mechanism. Transfection of a dominant negative mutant IkappaBalpha protein that cannot be serine phosphorylated led to suppression of IL-8 promoter activity. The p65/RelA NF-kappaB subunit activity was affected in both a time- and titanium particle concentration-dependent fashion. Titanium particles led to increased ERK, JNK, and p38 activation in MG-63 osteoblast cells, and IL-8 protein release was suppressed by specific inhibitors of the ERK and p38 MAPK pathways. Together, our results suggest that wear debris particles induce chemokine expression in osteoblasts via NF-kappaB-mediated transcriptional activation, which is controlled by the MAPK signal transduction pathway.

Activation of NF-kappaB signalling and TNFalpha-expression in THP-1 macrophages by TiAlV- and polyethylene-wear particles

Wear particles are believed to induce periprosthetic inflammation which contributes to periprosthetic osteolysis. TNFalpha plays a pivotal role in the pathogenesis of this process. The molecular mechanisms leading to the development of periprosthetic inflammation with upregulated TNFalpha expression in monocytic cells in response to different wear particles have yet to be defined. In this study we evaluated the effects of polyethylene- and TiAlV-particles on activation of NF-kappaB signalling pathways and TNFalpha biosynthesis and release in monocytic cells with respect to periprosthetic osteoclastogenesis. THP-1 monocytic cells were differentiated to macrophage-like cells and exposed to LPS-detoxified polyethylene and prosthesis-derived TiAlV-particles. TNFalpha release was analyzed in culture supernatant by ELISA. NF-kappaB activation was examined by electrophoretic mobility shift assay (EMSA), and NF-kappaB target promoter activities including transactivation of the TNFalpha promoter were determined by luciferase reporter gene assays. Differentiated THP-1 macrophages were exposed to increasing numbers of particles for 0, 60, 180 and 360 min. Both, polyethylene- and TiAlV-particles induced a significant activation of both NF-kappaB and TNFalpha promoters at 180 min. A significant TNFalpha release was detected after 360 min exposure to polyethylene- and TiAlV-particles in a dose dependent manner. In comparison, LPS induced a much greater activation of NF-kappaB and TNFalpha promoters, and TNFalpha secretion into the supernatant was strongly induced. These results provide evidence that induction of the NF-kappaB signal transduction pathway in macrophages plays a major role in initiating and mediating the inflammatory response leading to periprosthetic osteolysis.

Gene expression clustering using self-organizing maps: analysis of the macrophage response to particulate biomaterials

The most common cause of total joint replacement failure is peri-implant bone loss causing pain and prosthesis loosening. This process, known as osteolysis or aseptic loosening, is characterized by macrophage phagocytosis of particulate implant wear debris. In an incompletely defined step, particulate biomaterial debris induces macrophages to release a variety of inflammatory mediators and signaling proteins that lead to bone loss. In an in vitro model of this process, we used microarray technology and data analysis techniques, including the use of self-organizing maps (SOMs), to understand the mRNA gene expression changes occurring in macrophages exposed to clinically relevant particles of ultra-high molecular weight polyethylene and TiAlV alloy. Earlier studies have been limited by technology that only allowed analysis of a few genes at a time, but the microarray techniques used in this paper generate the quantitative analysis of over a thousand genes simultaneously. Our microarray analysis utilized an SOM clustering to elucidate general patterns in the data, lists of top up- and down-regulated genes for each time point and genes with differential expression under different biomaterial exposures. The expression levels of the majority of genes (>95%) did not vary over time or with exposure to different biomaterials, but a few important genes, such as TNF-alpha, IL-1beta, IL-6, and MIP1alpha, proved to be highly regulated in response to biomaterial exposure. We also uncovered a novel set of genes, which not only validates and logically extends the current model of the pathogenesis of osteolysis and aseptic loosening, but also provides new targets for further research and therapeutics.

In vitro studies on the effect of delaminated a-C:H film fragments on bone marrow cell cultures

Amorphous hydrogenated carbon (a-C:H) films have many outstanding properties required for a protective coating material on load bearing medical implants. Recently, titanium doped a-C:H films have been evaluated regarding their effects on bone marrow cell cultures. But many materials that are well-tolerated in bulk form are able to induce toxic reaction if present particulate form. In order to further assess biocompatibility aspects of these two coatings, film delamination has been mimicked in exposure to fluids. In the present study, particles from a-C:H, a-C:H/Ti and a-C:H-a-C:H/Ti bilayer films were added to bone marrow cell cultures in vitro. The results showed that plain a-C:H and to a certain extent a-CH/Ti particles were inert. Both kinds of particles did not significantly stimulate the osteoclast-related enzyme tartrate resistant acid phosphatase (TRAP). A slight increase in cell proliferation and total culture TRAP was found in cultures treated by a-C:H-a-C:H/Ti bilayer films. Latter effect can probably be traced back by the relative high percentage of small particles of a size of around 2 microm. However, if corrected by the cell number also no differences between particle-treated and untreated control cultures could be found, indicating the absence of a toxic effect from delaminated a-C:H coatings.

Importance of the surface area ratio on cytokines production by human monocytes in vitro induced by various hydroxyapatite particles

A possible complication associated with the implantation of hydroxyapatite (HA)-based prosthesis is the release of particles. Those particles can be phagocyted by monocytes that are among the first cells to colonize the inflammatory site. The activated monocytes produce inflammatory mediators, such as cytokines, which cause osteoclasts activation. It has previously been demonstrated using a surface area ratio (ratio of the total surface of the given particles to the surface area of cells) of 1 to 1 that there was a correlation between the expression and production of cytokines induced by HA. The present work studies the effect of physical characteristics of HA particles on the production of various inflammatory cytokines (tumour necrosis factor-alpha, interleukin (IL)-6, and IL-8) and anti-inflammatory cytokine (IL-10). However, the experiments were performed using a surface area ratio of 10 to 1. Our data demonstrate that all the particles, whatever their characteristics, induced a high expression of cytokines but the production was different, meaning that there was a post-transcriptional regulation. The size and sintering temperature seemed to be a characteristics that were less important compared to the shape; the needle particles appeared to induce the most important production of all the cytokines studied.

Opsonization of polyethylene wear particles regulates macrophage and osteoblast responses in vitro

The cellular reaction to wear debris may result in the failure of an artificial joint's fixation to the skeleton. The influence of debris opsinization on cell activity has received little attention. This study seeks to establish whether different proteinaceous culture environments may invoke variant cellular responses to debris challenge. Consideration of the zeta potential of a low density polyethylene particle group and an ex vitro ultrahigh molecular weight polyethylene particle group revealed that the nature of the protein adsorbants is related to the concentration of the proteins in solution. Furthermore, the composition of the adsorbed layer was shown to vary with the spectra of proteins in solution. In standard cell culture conditions zeta potential approached zero, indicating the high probability of particle agglomeration. Cell challenge studies with U937 macrophages showed that BSA and FCS protein adsorption mediated increased cell adhesion, while bovine IgG showed little change over control values. No changes in behavior of osteoblastic cells were observed in similar experiments.

The role of macrophages in osteolysis of total joint replacement

The osteolysis associated with conventional polyethylene on metal total joint replacements is associated with the formation of an inflamed periprosthetic membrane rich in macrophages, cytokines and implant-derived wear particles. There is a wealth of evidence to indicate that the presence and activation of macrophages in the periprosthetic tissues around joint replacements is stimulated by UHMWPE particles. Particles within the size range 0.1-1.0 microm have been shown to be the most reactive. Animal studies have provided increasing evidence that, of the milieu of cytokines produced by particle-stimulated macrophages, TNF-alpha is a key cytokine involved in osteolysis. Recent advances in the understanding of the mechanisms of osteoclastogenesis and osteoclast activation at the cellular and molecular level have indicated that bone marrow-derived macrophages may play a dual role in osteolysis associated with total joint replacement. Firstly, as the major cell in host defence responding to UHMWPE particles via the production of cytokines and secondly as precursors for the osteoclasts responsible for the ensuing bone resorption.

Particles of all sizes provoke inflammatory responses in vivo

The aim of this study was to investigate whether all sizes of wear particles are capable of provoking inflammatory responses and whether there are different responses among different particle sizes. The knees of 40 female Balb/c mice were injected with polystyrene particles of three different diameters, 0.5 microm, 2.0 microm, and 75 microm, using a 0.1% vol/vol concentration. Seven days after particle injection, assessment of the synovial microcirculation using intravital microscopy, and histologic examination, were done. All the mice injected with polystyrene particles had enhanced leukocyte-endothelial cell interactions and histologic scores regardless of particle size when compared with control animals injected with sterile phosphate buffered saline. Polystyrene particles 0.5 microm in size provoked stronger membrane thickening and increased leukocyte-endothelial cell interactions than 75-microm particles. The fraction of rolling leukocytes was enhanced in the 2.0-microm particle group when compared with the 75-microm particle group. These results indicate that polystyrene particles of all sizes (0.5 microm, 2.0 microm, and 75 microm) are capable of inducing an inflammatory response. Small particles (0.5 microm, 2.0 microm) seem to provoke a stronger inflammatory response than larger particles (75 microm) in conditions with equal particle volume.

Flow cytometric measurement of phagocytosis reveals a role for C3b in metal particle uptake by phagocytes

A methodology for the quick and efficient study of phagocytosis has been developed. It uses the flow cytometer to exploit the change in size and granularity that occurs in cells upon the ingestion of particulate material. The numbers of cells that have phagocytosed particles can be calculated from the distinct shift in regions that occurs. The method also allows the factors governing phagocytosis to be studied in detail through the use of blocking agents or antibodies. Blood-derived monocytes were studied to investigate the role of complement in metal particle phagocytosis to further understand aseptic loosening. Factor C3b was found to be fundamental to the opsonization and phagocytosis of metal particles by monocytes.

The effect of the physical characteristics of hydroxyapatite particles on human monocytes IL-18 production in vitro

Hydroxyapatite (HA) is widely used to coat the metal parts of prosthetic implants in order to improve their biocompatibility and as a bone defect filling material. HA has been demonstrated to produce particles at the prosthetic interface that lead to an activation of phagocytic cells that induce a cascade reaction leading to bone resorption and aseptic loosening. Monocytes/macrophages are commonly observed in the interface tissue, and are among the first cells to colonize the inflammatory site where they play a key role in the immune response. IL-18 is a pro-inflammatory cytokine. Monocytes/macrophages were described as IL-18 producing cells. IL-18 works antagonistically to IL-6, which activates osteoclastogenesis. In the present study, we investigated the ability of HA particles to induce the production of active IL-18 by human monocytes according to particle characteristics (size, sintering temperature and shape). Our study demonstrates, for the first time, that HA particles are capable of stimulating the production of the proinflammatory cytokine IL-18 in human monocytes according to their particle characteristics. The expression and the production of IL-18 was modified by the parameter studied. The difference observed between the expression and the production could be explain by the production of ICE. The needle shaped particles induced the larger production of IL-18.

Effect of titanium surface topography on macrophage activation and secretion of proinflammatory cytokines and chemokines

The macrophage has a major role in normal wound healing and the reparative process around implants. Murine macrophage-like cells RAW 264.7 were used to investigate the effect of titanium surfaces on macrophage activation and secretion of proinflammatory cytokines [interleukin (IL)-1 beta, IL-6, and tumor necrosis factor (TNF)-alpha] and chemokines (monocyte chemoattractant protein-1 and macrophage inflammatory protein-1 alpha). Four topographies were used: those produced by mechanically polishing, coarse sand blasting, acid etching, and sandblasting and acid etching (SLA). Macrophages were plated on the four titanium surfaces at a population density of 5 x 10(5) cells/mL/well. Tissue culture plastic and tissue culture plastic plus lipopolysaccharide (LPS) served as negative and positive control, respectively. In addition, all surfaces were tested for their effects on macrophages in the presence of LPS. Supernatants were collected for assays after 6, 24, and 48 h and the numbers of macrophages attached to the surfaces were quantified using the DAPI (4,6-di-amidino-2-phenylindole) assay. Cytokine and chemokine levels were measured with sandwich enzyme-linked immunosorbent assays. Statistical comparison between the surfaces and the controls was determined by using the two-way analysis of variance including interaction effect (two tailed and p < or = 0.05). Unstimulated macrophages increased their secretion of the proinflammatory cytokine (TNF-alpha) when attached to rough surfaces (acid etching and SLA, p < or = 0.05). In macrophages stimulated with LPS, the roughest surface SLA produced higher levels of IL-1 beta, IL-6, and TNF-alpha at 24 and 48 h than all other surfaces (p < or = 0.05). Surface topography also modulated the secretion of the chemokines monocyte chemoattractant protein-1 and macrophage inflammatory protein-1 alpha by macrophages. Unstimulated macrophages attached to the SLA surface down-regulated their production of chemokines (p < or = 0.05) whereas LPS-stimulated macrophages attached to the SLA surface up-regulated their production (p < or = 0.05). Moreover, the SLA surface was found to act synergistically with LPS as well as the combination of blasting and etching features of the SLA surface resulted in significant release of proinflammatory cytokines and chemokines by stimulated macrophages at 24 and 48 h (p < or = 0.05). This in vitro study has demonstrated that surface topography, in particular the SLA surface, modulated expression of proinflammatory cytokines and chemokines by macrophages in a time-dependent manner.

Particle analysis for the determination of UHMWPE wear

Three types of ultrahigh molecular weight polyethylene (UHMWPE) acetabular liners were tested against cobalt-chrome (CoCr) femoral heads on a hip simulator to approximately 20 million cycles. The materials included (1) conventional, nonirradiated liners (C-PE); (2) 5 Mrad gamma-irradiated, remelted, and artificially aged liners (5-XPE); and (3) 10 Mrad gamma-irradiated, remelted, and artificially aged liners (10-XPE). Wear was quantified by gravimetric analysis and wear particle characterization. Particle number and morphology were quantified by scanning electron microscopy (SEM) and compared between groups. Atomic force microscopy (AFM) was used to measure particle height in an effort to improve the total wear volume estimation. The wear debris, as characterized by SEM, was predominantly submicron and round, with occasional fibrils documented in the C-PE material. AFM analysis showed that particle height was approximately one-third of the particle equivalent circular diameter for all three materials. This correlation was used to improve the estimation of volumetric wear rate through SEM particle analysis. This technique is particularly useful for high-dose crosslinked UHMWPE, such as 10-XPE, which show weight gain due to fluid absorption during wear testing. This study has shown that particle analysis provides additional particle morphology and quantity information that cannot be obtained through gravimetric analysis.

Characterization of mode II – wear particles and cytokine response in a human macrophage – like cell culture / Charakterisierung von Mode II – Abriebpartikeln und der Zytokinantwort in einer humanen Makrophagen – ähnlichen Zellkultur

Informations about wear particles in metallosis (mode II wear) and their effects in vitro and in vivo are limited. The aim of this study was to characterize wear particles obtained intraoperatively and to analyse their effects on cytokine response in an established human macrophage-like cell culture model.

METHOD

Wear particles were obtained intraoperatively from four patients with metallosis resulting from CrCoMo/PE/TiAIV-implants (mode II wear) (3 knee, 1 hip prosthesis). After purification, particles were characterized regarding to their composition and size (particle size analyser, electron microscopy, edx-analysis, histological slices). The effects of particles on the release of cytokines (PDGF, IL-1beta, IL-8, TNF alpha) were determined in an established human macrophage-like cell culture system by ELISA-assays.

RESULTS

The metal wear particles consisted of TiAIV with a mean size of 0.1 +/- 0.15 microm, independent of the prosthesis location. CrCoMo particles could not be detected. In the cell culture model 1456 x 10(8) particles per 1 x 10(6) macrophages released maximum amounts of TNFalpha (8-fold) and IL-8 and IL-1beta (5-fold) while the survival rate of the cells was more than 90 percent. A particle-dependent increase of PDGF-levels could not be detected.

CONCLUSION

As already shown for mode I wear particles (contact between primary bearing surfaces), also mode II wear particles cause release of bone resorbing cytokines in a macrophage-like cell culture model. Because their local and systemic effects in vivo are still not completely understood, we recommend a complete removal of wear particles in cases of metallosis to avoid possible immunological reactions of the body as well as periprosthetic osteolysis.

Metal-on-metal total hip replacement

Metal-on-metal bearings have wear rates that are 20 to 100 times lower than metal-on-conventional polyethylene. The amount of wear generally is the same order of magnitude for the head and the cup. There is an initial run-in period of higher wear followed by lower, steady-state wear. Wear rate is a function of the interplay of material(s), macrogeometry, microgeometry, and the resultant type and amount of lubrication. The wear resistance and clinical performance of a metal-on-metal bearing are more sensitive to macrogeometry and lubrication than a metal-on-polyethylene bearing. Metal wear particles are nanometers in linear dimension. They are much smaller and more numerous than the submicron polyethylene wear particles, but the volume of periprosthetic inflammatory tissue is less. Osteolysis seems to be relatively rare. Little is known about the systemic distribution of metal particles and ions. The significance of systemic distribution also is not known. The levels of serum and urine Co and Cr ions are elevated in patients with metal-on-metal bearings, but the long-term, steady-state levels are not much higher than those from corrosion of modular femoral components. Because of the elevated levels of Co and Cr ions, there is a greater risk of delayed type hypersensitivity. There also is concern about the potential for malignant degeneration secondary to prolonged exposure to these elements. The available data are insufficient to address this concern. Rigorous long-term studies are needed. It will take decades of close clinical observation to determine if the benefits of metal-on-metal bearings outweigh the associated risks.

In vitro interaction between surface-treated Ti-6Al-4V titanium alloy and human peripheral blood mononuclear cells

The Ti-6Al-4V titanium alloy is widely employed as an implant material. The effects of Ti-6Al-4V samples, tested in both an untreated state and one in which the samples were subjected to a glow-discharge treatment performed with the use of air, on human peripheral blood mononuclear cells (PBMC) were studied. Apoptosis, undetectable after 24-h contact of PBMC with the two sample types, is induced after 48 h by treated samples, and, after 48 h, but in the presence of 1.5 microg/mL PHA, by both sample types. The expression of intercellular adhesion molecule-1 (ICAM-1) always increases, in comparison with control, in PBMC put in contact with the two sample types. In the same way, a remarkable increase in tumor necrosis-alpha (TNF-alpha) release in the culture medium is registered, when PBMC are put in contact with the two sample types for 24 and 48 h. Human umbilical-vein endothelial cells (HUVEC) cocultured for 48 h with PBMC, previously incubated with the two sample types for 24 h, show an increase in ICAM-1 and vascular cell adhesion molecule-1 (VCAM-1) protein expression in comparison with control (HUVEC cocultured with control PBMC), indicating that inflammatory phenomena might occur. Taken together, these results suggest that, although plasma-treated titanium alloy shows a better biocompatibility in comparison with the untreated one, attention must be paid to the careful control of the first signs of inflammation.

Regulation of osteoclast activity in peri-implant tissues

Implants, particularly joint replacement prostheses, are one of the great success stories of modern medicine. However, too many implants fail prematurely, mainly due to aseptic bone loss around the implant. This paper reviews our current understanding of the role of osteoclasts in this peri-implant bone lysis. Prosthetic particles, often produced by articulating prostheses, are one of the major causes of elevated osteoclast lysis of peri-implant bone. Over the past decade there have been major advances in our understanding of the factors that regulate osteoclast activity, many of which were found to be important in osteoclast formation and activity in the peri-implant tissues. These factors are targets of a number of recently developed drugs that have been used successfully to prevent and treat peri-implant bone lysis in experimental models. Treatments such as these are being used in a number of bone loss pathologies in humans and have the potential for successful treatment of peri-implant osteolysis. In addition, understanding how different biomaterials influence the expression of key osteoclastogenic factors may allow us to select biomaterials for implantation that will last the lifetime of the recipient.

Regulation of osteoclast activity in peri-implant tissues

Implants, particularly joint replacement prostheses, are one of the great success stories of modern medicine. However, too many implants fail prematurely, mainly due to aseptic bone loss around the implant. This paper reviews our current understanding of the role of osteoclasts in this peri-implant bone lysis. Prosthetic particles, often produced by articulating prostheses, are one of the major causes of elevated osteoclast lysis of peri-implant bone. Over the past decade there have been major advances in our understanding of the factors that regulate osteoclast activity, many of which were found to be important in osteoclast formation and activity in the peri-implant tissues. These factors are targets of a number of recently developed drugs that have been used successfully to prevent and treat peri-implant bone lysis in experimental models. Treatments such as these are being used in a number of bone loss pathologies in humans and have the potential for successful treatment of peri-implant osteolysis. In addition, understanding how different biomaterials influence the expression of key osteoclastogenic factors may allow us to select biomaterials for implantation that will last the lifetime of the recipient.