Multiscale characterization of a chimeric biomimetic polypeptide for stem cell culture.

Mesenchymal stem cells have attracted great interest in the field of tissue engineering and regenerative medicine because of their multipotentiality and relative ease of isolation from adult tissues. The medical application of this cellular system requires the inclusion in a growth and delivery scaffold that is crucial for the clinical effectiveness of the therapy. In particular, the ideal scaffolding material should have the needed porosity and mechanical strength to allow a good integration with the surrounding tissues, but it should also assure high biocompatibility and full resorbability. For such a purpose, protein-inspired biomaterials and, in particular, elastomeric-derived polypeptides are playing a major role, in which they are expected to fulfil many of the biological and mechanical requirements. A specific chimeric protein, designed starting from elastin, resilin and collagen sequences, was characterized over different length scales. Single-molecule mechanics, aggregation properties and compatibility with human mesenchymal stem cells were tested, showing that the engineered compound is a good candidate as a stem cell scaffold to be used in tissue engineering applications.

Novel soybean/gelatine-based bioactive and injectable hydroxyapatite foam: material properties and cell response.

Despite their known osteoconductivity, clinical use of calcium phosphate cements is limited both by their relatively slow rate of resorption and by rheological properties incompatible with injectability. Bone in-growth and material resorption have been improved by the development of porous calcium phosphate cements. However, injectable formulations have so far only been obtained through the addition of relatively toxic surfactants. The present work describes the response of osteoblasts to a novel injectable foamed bone cement based on a composite formulation including the bioactive foaming agents soybean and gelatine. The foaming properties of both defatted soybean and gelatine gels were exploited to develop a self-hardening soy/gelatine/hydroxyapatite composite foam able to retain porosity upon injection. After setting, the foamed paste produced a calcium-deficient hydroxyapatite scaffold, showing good injectability and cohesion as well as interconnected porosity after injection. The intrinsic bioactivity of soybean and gelatine was shown to favour osteoblast adhesion and growth. These findings suggest that injectable, porous and bioactive calcium phosphate cements can be produced for bone regeneration through minimally invasive surgery.

Response of human bone marrow stromal cells to a resorbable P(2)O(5)-SiO(2)-CaO-MgO-Na(2)O-K(2)O phosphate glass ceramic for tissue engineering applications.

This work focuses on the synthesis and characterization of a novel bioresorbable glass ceramic phosphate-based material (GC-ICEL). More specifically, its solubility in different aqueous media (water, Tris-HCl and acellular simulated body fluid) and the response of human stromal cells cultured on it were investigated. X-ray diffraction analysis showed the presence of two crystalline phases identified as Na(2)Mg(PO(4))(3) and Ca(2)P(2)O(7) and dissolution tests highlighted a preferential dissolution of the Na(2)Mg(PO(4))(3) phase and of the residual amorphous phase in all the chosen media. Soaking tests in simulated body fluid showed precipitation of a hydroxyapatite layer, demonstrating the bioactivity of GC-ICEL, which is partially due to the reported bioactivity of Ca(2)P(2)O(7). The effect of GC-ICEL on adhesion, proliferation and osteoblastic gene expression of human bone marrow-derived stromal cells was also studied. Combining molecular and biochemical analyses, it was found that bone marrow cell differentiation was stimulated over proliferation on GC-ICEL. Moreover, the expression of bone-related genes in cells cultured on GC-ICEL confirmed the bioactivity of this phosphate-based glass ceramic, which might have a stimulatory effect on osteogenesis.

Innovative silicate-based cements for endodontics: a study of osteoblast-like cell response.

Silicate-based filling materials were designed to obtain new endodontic sealers and root-end filling materials with adequate workability and consistency. Four different formulations (TC, TC 1%, TCf 1%, and TCf) were prepared incorporating calcium chloride as accelerant agent. A plasticizing compound (phyllosilicate) was added to TC 1% and TCf 1%. TC and TC 1% were prepared with water, whereas TCf and TCf 1% were mixed with a latex polymer as fluidizing agent. The aim of this study was to assess the in vitro biological compatibility of designed materials. White-MTA and AH Plus were tested as reference materials. Human osteoblast-like Saos-2 cells were challenged in short-term cultures (72 h) with solid materials and with material extracts in culture medium, and cell viability and number, cellular adhesion, and morphology were assessed. The new cements exerted no acute toxicity in the assay systems. Saos-2 like cells adhered and proliferated on solid samples of the experimental cements and MTA whilst AH Plus did not allowed cell growth. The extracts from the latex-containing cements showed some toxicity. By SEM analysis, osteoblast-like cells appeared adherent and spread on the new materials, and showed the maintenance of polygonal osteoblastic phenotype. Similar morphology was observed for cells on MTA, whereas only few cells were noted on the AH Plus surface. In conclusion, the new materials proved non toxic and supported the growth of bone-like cells, and resulted suitable to be used as endodontic sealers and root-end filling materials.

Potential of FeAlCr intermetallics reinforced with nanoparticles as new biomaterials for medical devices.

Novel FeAlCr oxide dispersion strengthened intermetallics that are processed by powder metallurgy have been developed as potential biomaterials. The alloys exhibit a small grain size and a fine dispersion of yttria provides the material with a high yield strength and depending on the alloy composition good ductility (up to 5%). The biocompatibility of the alloy was assessed in comparison with commercial alumina. Saos-2 osteoblast-like cells were either challenged with mechanically alloyed particles, or seeded onto solid samples. Viability and proliferation of cells were substantially unaffected by the presence of a high concentration of particles (1 mg/mL). Solid samples of novel FeAlCr intermetallic have shown a good biocompatibility in vitro, often approaching the behavior of materials well known for their biological acceptance (e.g. alumina). It has been found that osteoblasts are able to produce ALP, a specific marker of cells with bone-forming activity. In this respect, ALUSI alloys hold the promise to be suitable substrate for bone integration. The finding of no cytotoxic effect in the presence of the alloy particles is a reliable proof of the absence of acute toxicity of the material.

Improved osteogenic differentiation of human marrow stromal cells cultured on ion-induced chemically structured poly-epsilon-caprolactone.

The ability to control cell proliferation/differentiation, using material surface, is a main goal in tissue engineering. The objective of this study was to evaluate the attachment, proliferation and differentiation to the osteoblastic phenotype of human marrow stromal cells (MSC) when seeded on poly-epsilon-caprolactone (PCL) thin films before and after irradiation with 10 keV He+. The polymeric surface was characterized as surface chemical structure and composition, roughness and morphology on the micro- and nano-scale, wettability and surface free energy parameters. MSC were obtained from patients undergoing routine hip replacement surgery, expanded in vitro and cultured on untreated PCL and He+ irradiated PCL films for up to 4-5 weeks in osteogenic medium. He+-irradiation led to slight smoothening of the surface and different nanoscale surface chemical structure, while surface free energy resulted unchanged in comparison to untreated PCL. The results from biological testing demonstrated that early attachment and further proliferation, as well as osteoblastic markers, were higher for MSC on He+-irradiated PCL. In conclusion, the change of PCL surface properties induced by ion beam irradiation is confirmed to enhance the adhesion of MSC and support their differentiation.

Human bone marrow stromal cells: In vitro expansion and differentiation for bone engineering.

Stromal cells from marrow hold a great promise for bone regeneration. Even if they are already being exploited in many clinical settings, the biological basis for the source and maintenance of their proliferation/differentiation potential after in vitro isolation and expansion needs further investigation. Most studies on osteogenic differentiation of marrow stromal cells (MSC) have been performed using bone marrow from the iliac crest. In this study, MSC were derived from spare femoral bone marrow obtained during hip replacement surgery from 20 adult donors. After in vitro isolation the cells were grown in osteogenic medium, and their proliferation and differentiation analysed during in vitro expansion. We found that MSC isolated from the femur of adult patients consistently maintain an osteogenic potential. Using biochemical signals, these cells turn to fully differentiated osteoblasts with a predictable set of molecular and phenotypic events of in vitro bone deposition. When seeded on polycaprolactone-based scaffold or surfaces, the proliferation and mineralization of femur-derived MSC were modulated by the surface chemistry/topography. Despite remarkable differences between individual colony-forming ability, alkaline phosphatase production, and mineralization ability, these cells are a potential source for bone engineering, either by direct autologous reimplantation or by ex vivo expansion and reimplantation combined to a proper scaffold.

Poly-epsilon-caprolactone/hydroxyapatite composites for bone regeneration: in vitro characterization and human osteoblast response.

Polycaprolactone (PCL), a semicrystalline linear resorbable aliphatic polyester, is a good candidate as a scaffold for bone tissue engineering, due to its biocompatibility and biodegradability. However, the poor mechanical properties of PCL impair its use as scaffold for hard tissue regeneration, unless mechanical reinforcement is provided. To enhance mechanical properties and promote osteoconductivity, hydroxyapatite (HA) particles were added to the PCL matrix: three PCL-based composites with different volume ratio of HA (13%, 20%, and 32%) were studied. Mechanical properties and structure were analysed, along with biocompatibility and osteoconductivity. The addition of HA particles (in particular in the range of 20% and 32%) led to a significant improvement in mechanical performance (e.g., elastic modulus) of scaffold. Saos-2 cells and osteoblasts from human trabecular bone (hOB) retrieved during total hip replacement surgery were seeded onto 3D PCL samples for 1-4 weeks. Following the assessment of cell viability, proliferation, morphology, and ALP release, HA-loaded PCL was found to improve osteoconduction compared to the PCL alone. The results indicated that PCL represents a potential candidate as an efficient substrate for bone substitution through an accurate balance between structural/ mechanical properties of polymer and biological activities.

Advanced nanocomposite materials for orthopaedic applications. I. A long-term in vitro wear study of zirconia-toughened alumina.

The use of ceramic-on-ceramic (alumina- and zirconia-based) couplings in hip joint prostheses has been reported to produce lower wear rates than other combinations (i.e., metal-on-polyethylene and ceramic-on-polyethylene). The addition of zirconia into an alumina matrix (zirconia-toughened alumina, ZTA) has been reported to result in an enhancement of flexural strength, fracture toughness, and fatigue resistance. The development of new processing routes in nonaqueous media has allowed to obtain high-density ZTA nanocomposites with a very homogeneous microstructure and a significantly smaller and narrower particle-size distribution of zirconia than conventional powder mixing methods. The aim of the present study was to set up and validate a new ZTA nanocomposite by testing its biocompatibility and wear behavior in a hip-joint simulator in comparison with commercial alumina and experimental alumina specimens. The primary osteoblast proliferation onto ZTA nanocomposite samples was found to be not significantly different from that onto commercial alumina samples. After 7 million cycles, no significant differences were observed between the wear behaviors of the three sets of cups. In this light, it can be affirmed that ZTA nanocomposite materials can offer the option of improving the lifetime and reliability of ceramic joint prostheses.

Effects of activated platelet concentrates on human primary cultures of fibroblasts and osteoblasts.

BACKGROUND: Platelet alpha granules contain growth factors released into the surrounding environment during activation. This property has been used in clinical medicine to accelerate the repair process by activating in vitro autologous platelets with thrombin and has also been proposed to promote the proliferation of bone cells. The aim of this research was to assess the effect of platelet concentrates activated with thrombin on human gingival fibroblasts and human osteoblasts from trabecular bone. METHODS: Platelet concentrates, activated with bovine thrombin, were added to the cells in serum-free medium. The cultures were assessed for proliferation by vital stain and cell count after 72-hour incubation. Alkaline phosphatase activity was tested after 72-hour incubation on the osteoblast lysates by a colorimetric assay. After 21 days the formation of mineral nodules was tested in the osteoblast cultures by alizarin red staining. The effects of the activated platelet concentrates (APC) were compared with the serum-free medium (SF), or with platelet-poor plasma added medium (PPP). RESULTS: The fibroblast growth in the presence of APC was higher, though not significantly, than SF. APC resulted in a nonsignificant decrease in proliferation and alkaline phosphatase expression in osteoblasts, compared both to serum free medium, and PPP. Mineralization was only modestly increased after incubation with APC in comparison with serum-free medium. CONCLUSIONS: There were no statistical differences in fibroblast proliferation, or in osteoblast growth and functions between serum-free conditions and the platelet gel treatment. Therefore, neither fibroblast proliferation nor osteoblast growth and functions were affected by the activated platelet concentrates in vitro.

Evaluation of mechanical properties and biological response of an alumina-forming Ni-free ferritic alloy.

PM 2000 is a Ni-free oxide dispersion strengthened Fe-20Cr-5Al alloy able to develop a fine, dense and tightly adherent alpha-alumina scale during high-temperature oxidation. Despite the high temperature involved during thermal oxidation (1100 degrees C), microstructural changes in the candidate material, a hot rolled product, hardly occurs. Consequently, the good mechanical properties of the as-received material are not significantly affected. Moreover, due to the high compressive residual stresses at the alumina scale, an increase in the fatigue limit from 500 to 530 MPa is observed. Such stresses also account for the high capability of the coating/metal system to withstand more than 1% tensile deformation without cracking. The biocompatibility of the alloy was assessed in comparison to commercial alumina. Saos-2 osteoblast-like cells were either challenged with PM 2000 particles, or seeded onto PM 2000 (with and without scale) solid samples. Viability, growth, and ALP release from cells were assessed after 3 or 7 days, while mineralization was checked at 18 days. This study has demonstrated that PM 2000 with and without scale are capable of supporting in vitro growth and function of osteoblast-like cells over a period of 18 days. Results from this study suggest that the resulting alumina/alloy system combines the good mechanical properties of the alloy with the superior biocompatibility of the alpha-alumina, for which there is very good clinical experience.

Quantitative assessment of the response of osteoblast- and macrophage-like cells to particles of Ni-free Fe-base alloys.

In the present study, the effect of mechanically alloyed particles of new FeAlCr alloys developed for potential applications as surgical implants has been tested on osteoblast- and macrophage-like cells and compared to particles of the Ti6Al4V alloy, for which there is a good clinical experience. After microstructural characterisation of the particles, cells were cultured with particles for 24-48 h using three different concentrations of particles, and the response of cells was quantified by assessment of viability, proliferation, and morphology. Mineralisation by osteoblasts was verified after 21 days. The amount of aluminium and chromium ions in the culture medium of macrophages was measured by graphite furnace atomic absorption and phagocytosis of particles assessed by light microscopy. Viability and proliferation of osteoblast- and macrophage-like cells were substantially unaffected by the presence of particles of the new alloys, which were phagocytosed according to their size. Aluminium and chromium ions were released in the culture medium, but no direct correlation with the cell behaviour was found. In vitro mineralisation was achieved by osteoblasts in due time. The new alloys are well tolerated in in vitro systems, and, due to their chemical and mechanical characteristics, they are under development for surgical implants.

Evaluation of magnetic behaviour and in vitro biocompatibility of ferritic PM2000 alloy.

PM2000 is a ferritic alloy obtained by powder metallurgy and is being investigated for potential applications as a biomaterial. This work aimed to assess the biological compatibility and to determine the influence of the processing route and further recrystallisation treatment on the magnetic behaviour. The magnetic behaviour has been analysed as a function of the hysteresis loop obtained by using an inductive method. The biocompatibility has been tested using human osteoblast-like cells seeded onto discs of PM2000. The ability of cells, on its surface, to attach, grow, and produce alkaline phosphatase (ALP) was determined. It is shown that PM2000 is a soft magnetic material irrespective of its material condition, its remanent magnetisation being very low (up to about 3% for the recrystallised swaged material). Fields close to 200 Oe are required to saturate the material. The saturation magnetisation is about 135 emu g(-1). In vitro tests indicate that cells are able to attach and grow onto its surface, and produce ALP, a specific marker of cells with bone-forming activity. In this respect, PM2000 holds promise as a suitable substrate for bone integration. These properties could make PM2000 a useful candidate for the preparation of medical devices where biocompatible and soft magnetic materials are sought. Applications for dental magnetic attachments could be envisaged.

Evaluation of osteoblast-like cell response to Proroot MTA (mineral trioxide aggregate) cement.

Some endodontic sealers have been shown to cause local and systemic effects, mainly due to microleakage of chemicals from the sealer. To avoid the risk of toxic effects in vivo, the biological compatibility of filling materials has to be assessed. In vitro compatibility of Proroot MTA cement in comparison with two different fillers used in clinical practice, was examined by testing the adherence, viability, proliferation and secretion of collagen of osteoblast-like cells. In our experimental system, Saos-2 cells challenged with Proroot MTA for 24 and 72 h showed a better behaviour than the cells exposed to the other compounds under assay. We found that the cells attached to the rough surface of Proroot MTA cement and spread onto the rough surface. Moreover, the cells on Proroot MTA were viable, grew, and released some collagen even at 72 h, while cell metabolism and growth was dramatically reduced onto sEBA and amalgam surfaces. A parallel behaviour was found after the cells were challenged with extracts of the different fillers. In conclusion, according to our in vitro study, Proroot MTA showed a good interaction with bone-forming cells: such behaviour may partially account for its satisfying clinical performance.

The influence of alumina and ultra-high molecular weight polyethylene particles on osteoblast-osteoclast cooperation.

Particle-induced macrophage activation, mainly by UHMWPE wear, has been recognized as the biological mechanism leading to periprosthetic bone resorption, which is responsible for the loosening of the total hip replacements (THR). Ceramic-on-ceramic implants have been advocated as a means of reducing wear products. Many studies investigated the effect of alumina (Al(2)O(3)) particles on monocytes/macrophages, but only limited information are available on their participation to bone turnover. An in vitro model was performed to investigate how Al(2)O(3) and UHMWPE particles may influence the osteoblast-osteoclast interaction: human osteoblasts (HOB) were obtained from trabecular bone, while osteoclasts were derived from peripheral blood mononuclear cells (PBMC) of healthy donors. The amount of IL6, TNF alpha, GM-CSF, and other factors acting on the bone turnover, i.e. the 'receptor activator of NF kappa B' ligand (RANKL) and osteoprotegerin (OPG), was detected in culture medium of particle-challenged HOB (HOB-CM). The Al(2)O(3) and UHMWPE particles did not affect either cell viability or TNF and GM-CSF release, while the increase in IL6 release seemed to be dependent on the particle concentration. UHMWPE increased the release of RANKL from HOB, while OPG and OPG-to-RANKL ratio were significantly inhibited. The ability of HOB-CM to promote osteoclastogenesis was tested via osteoblast/monocyte cooperation: after seven days of culture UHMWPE HOB-CM induced a large amount of multinucleated TRAP-positive giant cells, as well as significantly reduced the amount of IL6, GM-CSF and RANKL in the supernatant. With regard to the inductive effect on the osteoclastogenesis, our results show that the Al(2)O(3) wear debris are less active.

Ability of restorative and fluoride releasing materials to prevent marginal dentine demineralization.

The study aimed to define the in vitro secondary caries inhibiting potential of restorative materials currently used in dental practice. Class V restorations were prepared in extracted human third molars and immersed in a demineralizing solution (lactic acid, pH 4.5) at 37 degrees C for 2 days to simulate secondary caries formation. The bonding and the restorative systems tested in the study were: Scotchbond 1+Z 250 (Group A), Scotchbond 1+F 2000 (Group B), ABF+APX (Group C), ABF+F2000 (Group D). Perimarginal dentine, immediately close to the margin of the restoration, and exposed dentine, at approximately 0.5 mm from the margins of the restoration, after exposure to the acid solution, were investigated; protected dentine, at approximately 4 mm from the margin in a varnish-covered area, was analysed as control. Polarized light microscopy and contact transverse microradiography (TMR) were employed. The output parameters were lesion shape and size (depth in microm) of the exposed dentine, dentine mineral volume%, and integrated mineral loss (Delta Z, in %volmicrom) of the lesions. Compomers (Groups B and D) showed a thinner demineralization of the outer lesions, a less demineralization along the perimarginal dentine (inner lesion) and more caries inhibition zones or CIZs (Delta Z positive values) compared to composites (Groups A and C). In conclusion, Groups B and D materials seemed to partially counteract the marginal demineralization induced by an acid solution and favourably influence the formation of CIZs along the restorations. On the contrary, composites did not show a protective effect, probably due to an insufficient marginal seal and the lack of fluoride release.

Ion release in stable hip arthroplasties using metal-on-metal articulating surfaces: a comparison between short- and medium-term results.

The use of metallic heads articulating with metallic cups could solve the problem of polyethylene (PE) wear in total hip replacement (THR) with metal-on-PE bearings. A conspicuous release of metal ions from new models of metal-on-metal bearings has been found in the short-term, but it is yet unclear whether the medium-term corrosion rate is high or, on the contrary, it becomes negligible, because of the continuous surface finishing. Our purpose was to compare the serum ion values (nanograms per milliliter) in 15 patients with metal-on-metal stable prosthesis (Group A), in the short-term (subgroup A(1); mean follow-up: 24 mo) and medium-term (subgroup A(2); mean follow-up: 52 mo), in order to determine whether the ion release decreased with time of implant. Chromium (Cr), cobalt (Co), molybdenum (Mo) and aluminum (Al) were analyzed. Twenty-two presurgical patients were used for comparison (Group B). The reference range was obtained from a population of 27 healthy subjects (Group C). Co and Cr levels in the medium-term (subgroup A(2)) were not decreased in comparison with the short-term values (subgroup A(1)) and were significantly higher (p < 0.001) than presurgical and reference values. Otherwise, Mo and Al concentrations were not significantly increased in comparison with reference values. In conclusion, despite the apparent advantage of metal-on-metal coupling, especially in younger patient populations, there is a major concern about the extent and duration of the relevant "internal" exposure to Cr and Co ions. This exposure should be carefully monitored, in order to clarify the biologic effects of ion dissemination and, consequently, to identify risks concerning long-term toxicity of metals.

Biologic effects of surface roughness and fluorhydroxyapatite coating on osteointegration in external fixation systems: an in vivo experimental study.

The concomitant influence of surface roughness and fluorhydroxyapatite (FHA) coating of titanium (Ti) implants on bone response was investigated. For this purpose, titanium screw-shaped implants with a lower degree (Y371) and a higher degree (TiPore300) of surface roughness, coated with FHA and uncoated, were transversally inserted into the diaphyses of sheep tibiae for 12 weeks. Four sheep received Y371 (group A) and Y371 + FHA (group B) screws and four sheep received TiPore300 (group C) and TiPore300 + FHA (group D) screws. For each type of material, the morphology and microstructure of implant-facing bone were evaluated. The host bone of each tibia was used as a control. In all groups the bone tissue did not reach a complete maturation. The higher degree of roughness, perhaps due to an excessive irregularity of the surface, induced the worst osteointegration: a fibrous tissue layer between screw and new bone tissue was often present. Nevertheless, as viewed by XRD, no crystallographic change of the apatite lattice was observed in any of the implants. In contrast, the microhardness value, an index of bone mineralization, was higher in the uncoated screws and decreased progressively in the following order: group C > group A > group B > group D. The association of plasma spraying with roughness treatment constitutes a complex system that seems to interfere with bone mineralization. A chemical change of the surface, perhaps with more Ti release or more coating degradation, could be responsible for such impairment. The authors emphasize the necessity for simultaneous evaluation of surface topography and chemistry as well as an improvement in plasma-spraying and post-processing techniques and in standard procedures for materials characterization.

Osteoblast growth and function in porous poly epsilon -caprolactone matrices for bone repair: a preliminary study.

Current methods for the replacement of skeletal tissue involve the use of autografts, allografts and, recently, synthetic substitutes, which provide a proper amount of material to repair large bone defects. Engineered bone seems a promising approach, but a number of variables have to be set prior to any clinical application. In this study, four different poly caprolactone-based polymers (PCL) were prepared and tested in vitro using osteoblast-like Saos-2 cells. Differences among three-dimensional polymers include porosity, addition of hydroxyapatite (HA) particles, and treatment with simulated body fluid. Biochemical parameters to assess cell/material interactions include viability, growth, alkaline phosphatase release, and mineralization of osteoblastic cells seeded onto three-dimensional samples, while their morphology was observed using light microscopy and SEM. Preliminary results show that the polymers, though degrading in the medium, have a positive interaction with cells, as they support cell growth and functions. In the short-term culture (3-7 days) of Saos-2 on polymers, little differences were found among PCL samples, with the presence of HA moderately improving the number of cells onto the surfaces. In the long term (3-4 weeks), it was found that the HA-added polymers obtained the best colonization by cells, and more mineral formation was observed after coating with SBF. It can be concluded that PCL is a promising material for three-dimensional scaffold for bone formation, and the presence of bone-like components improves osteoblast activity.

Nitric oxide synthase in tissues around failed hip prostheses.

Nineteen patients who had undergone hip revision surgery for aseptic loosening of joint prostheses were studied. Tissue samples were harvested at the interface between bone and implant, either at the stem or at the cotyle level. Immunohistochemistry was performed on tissue sections to detect nitric oxide synthase (NOS), the enzyme which enables the synthesis of nitric oxide (NO), a molecule which can activate bone resorption. Quantitative analysis of the positive cells and correlation with the presence of particulate wear debris and radiological data were performed. The authors observed a trend towards a moderate increase in positive cells due to inducible NOS in tissues containing particulate wear debris, especially of a plastic material. This increase, however, did not achieve statistical significance. On the contrary, there was a statistical correlation between iNOS (inducible NOS) and the severity of osteolysis around the prosthetic implant. Pharmacological control of the biosynthesis of NO may be considered in the prevention or treatment of loosening.