Effects of hydroxyapatite particulate debris on the production of cytokines and proteases in human fibroblasts

Cytokine expression of soft tissue cells cultured with titanium discs and their respective supernatants in vitro

OBJECTIVE

Titanium surface modifications improve osseointegration in dental and orthopedic implants. However, soft tissue cells can also reach the implant surface in immediate loading protocols. While previous research focused on osteogenic cells, the early response of soft tissue cells still needs to be better understood.

MATERIAL AND METHODS

We have established a bioassay to this aim where human gingival fibroblasts, HSC2 oral squamous carcinoma cells, and murine bone marrow cells were cultured onto titanium discs or exposed to the respective supernatants for overnight. Modifications were double acid-etching (SLA), and coating with simulated body fluid (SBF) with or without odanacatib (ODN), a selective cathepsin K inhibitor reducing bone resorption.

RESULTS

Our findings indicate that direct contact with titanium discs, with all surface modifications, slightly reduces cell viability. Growing gingival fibroblasts on discs consistently showed a trend toward increased IL8 expression. In HSC2 cells, this setting significantly increased IL1 and IL8 expression, confirmed by the immunoassay. Murine bone marrow macrophages also showed an increase in IL1 and IL6 expressions. Supernatants of the respective discs failed to cause these changes. Although ODN coating inhibited cathepsin K, osteoclastogenesis remained unchanged.

CONCLUSIONS

These findings suggest that titanium discs do not provide a favorable in vitro surface for oral soft tissue cells as they lose viability and respond with a moderately increased expression of inflammatory cytokines.

CLINICAL RELEVANCE

The soft tissue surrounding a dental implant can impact rehabilitation success. Understanding how soft tissue cells respond to titanium surface is potentially relevant to understand clinical outcomes.

Novel 3D printed bioactive SiC orthopedic screw promotes bone growth associated activities by macrophages, neurons, and osteoblasts

Ceramic additive manufacturing currently relies on binders or high-energy lasers, each with limitations affecting final product quality and suitability for medical applications. To address these challenges, our laboratory has devised a surface activation technique for ceramic particles that eliminates the necessity for polymer binders or high-energy lasers in ceramic additive manufacturing. We utilized this method to 3D print bioactive SiC orthopedic screws and evaluated their properties. The study's findings reveal that chemical oxidation of SiC activated its surface, enabling 3D printing of orthopedic screws in a binder jet printer. Post-processing impregnation with NaOH and/or NH4OH strengthened the scaffold by promoting silica crystallization or partial conversion of silicon oxide into silicon nitride. The silica surface of the SiC 3D printed orthopedic screws facilitated osteoblast and neuron adhesion and extensive axon synthesis. The silicate ions released from the 3D printed SiC screws favorably modulated macrophage immune responses toward an M1 phenotype as indicated by the inhibition of TNFα secretions and of reactive oxygen species (ROS) expression along with the promotion of IL6R shedding. In contrast, under the same experimental conditions, Ti ions released from Ti6Al4V discs promoted macrophage TNFα secretion and ROS expression. In vivo tests demonstrated direct bone deposition on the SiC scaffold and a strong interfacial bond between the implanted SiC and bone. Immunostaining showed innervation, mineralization, and vascularization of the newly formed bone at the interface with SiC. Taken altogether, the 3D printed SiC orthopedic screws foster a favorable environment for wound healing and bone regeneration. The novel 3D printing method, based on ceramic surface activation represents a significant advancement in ceramic additive manufacturing and is applicable to a wide variety of materials.

Protective effect of zinc supplementation on tricalcium phosphate particles-induced inflammatory osteolysis in mice

Zinc (Zn), an essential trace element, can stimulate bone formation and inhibit osteoclastic bone resorption, which controls the growth and maintenance of bone. However, the effect of Zn supplementation on tricalcium phosphate (TCP) wear particles-induced osteolysis remains unknown. Here, we doped Zn into TCP particles (ZnTCP), and explore the protective effects of Zn on TCP particles-induced osteolysis in vivo. TCP particles and ZnTCP particles were embedded under the periosteum around the middle suture of the mouse calvaria. After 2 weeks, blood, the periosteal tissue, and the calvaria were collected to determine serum levels of Zn and osteocalcin, pro-inflammatory cytokines, bone biochemical markers, osteoclastogenesis and bone resorption area, and to explain its mechanism. Data revealed that Zn significantly prevented TCP particles-induced osteoclastogenesis and bone loss, and increased bone turnover. The Zn supplement remarkably suppressed the release of pro-inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6. Immunoblotting demonstrated that Zn alleviated expression levels of ER stress-related proteins such as glucose-regulated protein 78 (GRP78), PKR-like ER kinase (PERK), phospho-PERK (p-PERK), eukaryotic initiation factor 2α (eIF2α), phospho-eIF2α (p-eIF2α), activating transcription factor 4 (ATF4), inositol-requiring enzyme 1α (IRE1-α) and transcription factor X-box binding protein spliced (XBP1s), leading to decreasing the ratios of p-PERK/PERK and p-eIF2α/eIF2α. Taken together, Zn supplementation strongly prevents TCP particles-induced periprosthetic osteolysis via inhibition of the ER stress pathway, and it may be a novel therapeutic approach for the treatment of aseptic prosthesis loosening.

Naringin inhibits titanium particles-induced up-regulation of TNF-α and IL-6 via the p38 MAPK pathway in fibroblasts from hip periprosthetic membrane

AIMS

Inflammatory responses to wear debris cause osteolysis that leads to aseptic loosening and hip arthroplasty failure. Wear debris stimulate macrophages and fibroblasts to secret proinflammatory cytokines, including TNF-α and IL-6, which have been specifically implicated in periprosthetic osteolysis and osteoclast differentiation. Naringin has anti-inflammatory effect in macrophages. Moreover, naringin inhibited osteoclastogenesis and wear particles-induced osteolysis. In this study, we examined the potential inhibitory effects of naringin on titanium (Ti) particle-induced proinflammatory cytokines secretion in fibroblasts and the possible underlying molecular mechanisms.

MATERIALS AND METHODS

Fibroblasts were isolated from periprosthetic membrane at the time of revision surgery performed due to aseptic loosening after hip arthroplasty and were cultured in the presence or absence of Ti particles, naringin and mitogen-activated protein kinase (MAPK) inhibitors, PD98059 (a selective inhibitor of ERK), SP600125 (a selective inhibitor of JNK), and SB203580 (a selective inhibitor of p38). TNF-α and IL-6 assays were performed using enzyme-linked immunosorbent assay kits. The phosphorylation levels of p38 and nuclear factor kappa B p65 (NF-κB p65) were examined by western blot.

RESULTS

Naringin or SB203580 pretreatment significantly suppressed the secretion of TNF-α and IL-6 induced by titanium particles in fibroblasts, while inhibition of ERK or JNK pathways showed no effect on production of TNF-α and IL-6. Moreover, naringin inhibited Ti particle-induced phosphorylation of p38 and p65.

CONCLUSIONS

These results indicated that naringin could inhibit Ti particle-induced inflammation in fibroblasts by inhibiting p38 MAPK/NF-κB p65 activity and might be a potential drug for the treatment of inflammatory periprosthetic osteolysis after arthroplasty.

Current Challenges and Innovative Developments in Hydroxyapatite-Based Coatings on Metallic Materials for Bone Implantation: A Review

Biomaterials are in use for the replacement and reconstruction of several tissues and organs as treatment and enhancement. Metallic, organic, and composites are some of the common materials currently in practice. Metallic materials contribute a big share of their mechanical strength and resistance to corrosion properties, while organic polymeric materials stand high due to their biocompatibility, biodegradability, and natural availability. To enhance the biocompatibility of these metals and alloys, coatings are frequently applied. Organic polymeric materials and ceramics are extensively utilized for this purpose due to their outstanding characteristics of biocompatibility and biodegradability. Hydroxyapatite (HAp) is the material from the ceramic class which is an ultimate candidate for coating on these metals for biomedical applications. HAp possesses similar chemical and structural characteristics to normal human bone. Due to the bioactivity and biocompatibility of HAp, it is used for bone implants for regenerating bone tissues. This review covers an extensive study of the development of HAp coatings specifically for the orthopaedic applications that include different coating techniques and the process parameters of these coating techniques. Additionally, the future direction and challenges have been also discussed briefly in this review, including the coating of HAp in combination with other calcium magnesium phosphates that occur naturally in human bone.

Fibroblast-like cells change gene expression of bone remodelling markers in transwell cultures

Introduction

Periprosthetic fibroblast-like cells (PPFs) play an important role in aseptic loosening of arthroplasties. Various studies have examined PPF behavior in monolayer culture systems. However, the periprosthetic tissue is a three-dimensional (3D) mesh, which allows the cells to interact in a multidirectional way. The expression of bone remodeling markers of fibroblast-like cells in a multilayer environment changes significantly versus monolayer cultures without the addition of particles or cytokine stimulation. Gene expression of bone remodeling markers was therefore compared in fibroblast-like cells from different origins and dermal fibroblasts under transwell culture conditions versus monolayer cultures.

Methods

PPFs from periprosthetic tissues (n = 12), osteoarthritic (OA) synovial fibroblast-like cells (SFs) (n = 6), and dermal fibroblasts (DFs) were cultured in monolayer (density 5.5 × 10³/cm²) or multilayer cultures (density 8.5 × 10⁵/cm²) for 10 or 21 days. Cultures were examined via histology, TRAP staining, immunohistochemistry (anti-S100a4), and quantitative real-time PCR.

Results

Fibroblast-like cells (PPFs/SFs) and dermal fibroblasts significantly increased the expression of RANKL and significantly decreased the expression of ALP, COL1A1, and OPG in multilayer cultures. PPFs and SFs in multilayer cultures further showed a higher expression of cathepsin K, MMP-13, and TNF-α. In multilayer PPF cultures, the mRNA level of TRAP was also found to be significantly increased.

Conclusion

The multilayer cultures are able to induce significant expression changes in fibroblast-like cells depending on the nature of cellular origin without the addition of any further stimulus. This system might be a useful tool to get more in vivo like results regarding fibroblast-like cell cultures.

Organically modified hydroxyapatite (ormoHAP) nanospheres stimulate the differentiation of osteoblast and osteoclast precursors: a co-culture study

Isolated nanospheres consisting of organically modified hydroxyapatite (ormoHAP), prepared by an electric field-assisted ion double migration process, were embedded in foamed gelatin to form a composite scaffold. Degradation rates have been demonstrated to correlate with the crosslinking degree (40%, 80%) as well as with the mineral content of the scaffolds (0%, 20%, 40%). A human co-culture model of osteoblasts and osteoclasts, derived from bone marrow stromal cells and monocytes, respectively, without external addition of the factors RANKL and M-CSF, was run for up to 42 d in order to characterize the action of the ormoHAP-gelatin scaffolds on the co-culture. Examination was performed by quantitative biochemical methods (DNA, LDH, ALP, TRAP5b), gene expression analysis (ALP, BSP II, RANKL, IL-6, VTNR, CTSK, TRAP, OSCAR, CALCR) and confocal laser scanning microscopy (cell nuclei, actin, CD68, TRAP). Results confirm that ormoHAP embedded in the gelatin matrix enhanced TRAP 5b activity. As a feedback, ALP activity and gene expression of BSP II of osteoblasts increased. Finally, a sequence of cell cross-talk actions is suggested, which can explain the behavior of the formed vital co-culture and moreover the influence of the presence and concentration of ormoHAP.

Correlation of the composition of biominerals with their ability of stimulating intracellular DNA sensors and inflammatory cytokines

Biominerals (or microcalcification) deposited in soft tissues are associated with a number of pathogeneses and cancer progressions. Biominerals have also shown promise for DNA delivery and tissue engineering. Biominerals themselves may stimulate NALP3 inflammasomes, and DNA delivered by biominerals can potentially engage with intracellular DNA sensors, resulting in unwanted inflammatory responses. In this study, a library of biominerals doped with or without DNA is formed through surface-induced biomineralization. It is demonstrated that empty biominerals stimulate NALP3 inflammasomes and induce the production of IL-1β. They are also able to activate mouse embryonic fibroblasts (MEFs) and induce inflammatory cytokines, i.e. IL-6. DNA delivered by biominerals escapes the detection of TLR9, but activates DAI and inflammasomes. Furthermore, it is shown that the level of both IL-1β and IL-6 is correlated with the composition of biominerals, in particular the ratio of Mg(Sr) to Ca, and the pH sensitivity of biominerals. These results provide insights into the design of safe and effective DNA delivery systems and biocompatible implants as well as the understanding of the pathogeneses of biominerals deposited in soft tissues.

Biocompatibility of pure and mixed hydroxyapatite and α-tricalcium phosphate implanted in rabbit bone

Calcium phosphates and hydroxyapatite, in particular, are used as substitute materials in experimental implantology. These materials are primarily used in hard tissue replacement because their chemical and crystallographic characteristics are considered to be similar to the mineral content, osteoconductivity and bioactivity of normal bone. Cytokines, such as interleukin (IL)-1, IL-6, IL-8, IL-10 and antimicrobial protein β-defensin-2 (βDef-2), are used as biomarkers of non-specific reactogenicity. Other biomarkers, including bone morphogenetic protein-2/4 (BMP-2/4), bone regeneration protein osteoprotegerin (OPG), bone matrix protein osteopontin (OP) and osteocalcin (OC), are regarded as specific factors of reactogenicity in bone substitution. The aim of our study was to assess the changes in the distribution and expression of the aforementioned proteins in the lower jaws of rabbits following implantation with pure hydroxyapatite (HAP), α-tricalcium phosphate (α-TCP) or a mix of the two (HAP/α-TCP) manufactured under different temperatures. Our results reveal osteoblast proliferation and regions of granulation tissue formation between biomaterial granules close to the original implantation site, but in the control tissue these changes were less noticeable. Our study showed low variability in the distribution of βDef-2, OPG and all of the tested interleukins and these proteins were less expressed than BMP2/4, OP and OC. But across all experiments, no statistically significant difference in mean βDef-2, IL-1, IL-6, IL-8, IL-10, OP, OC, BMP-2/4 and OPG expression in osteocytes was detected between experimental and control groups. We concluded that pure and mixed HAP and α-TCP sintered at different temperatures do not affect the production of cytokines and bone-specific proteins; regions with osteoblast proliferation and low levels of anti-inflammatory cytokines IL-6 and IL-10 indicates better biocompatibility for HAP/α-TCP and α-TCP-2 biomaterials and the moderate number of BMP-2/4- and a prevalence of OC- and OP-positive osteocytes in experimental tissues implanted with HAP at 3 months after implantation indicates potential bone regeneration stimulated by pure HAP.

On the fate of particles liberated from hydroxyapatite coatings in vivo

PURPOSE

Hydroxyapatite (HA) has been used as a coating for orthopaedic implants for over 30 years to help promote the fixation of orthopaedic implants into the surrounding bone. However, concerns exist about the fate of the hydroxyapatite coating and hydroxyapatite particles in vivo, especially in the wake of recent concerns about particulates from metal-on-metal bearings.

METHODS

Here, we assess the mechanisms of particle detachment from coated orthopaedic devices as well as the safety and performance concerns and biomedical implications arising from the liberation of the particles by review of the literature.

FINDINGS

The mechanisms that can result in the detachment of the HA coating from the implant can be mechanical or biochemical, or both. Mechanical mechanisms include implant insertion, abrasion, fatigue and micro-motion. Biochemical mechanisms that contribute to the liberation of HA particles include dissolution into extra-cellular fluid, cell-mediated processes and crystallisation of amorphous phases. The form the particles take once liberated is influenced by a number of factors such as coating method, the raw powder morphology, processing parameters, coating thickness and coating structure.

CONCLUSIONS

This review summarises and discusses each of these factors and concludes that HA is a safe biomimetic material to use as a coating and does not cause any problems in particulate form if liberated as debris from an orthopaedic implant.

Inflammatory cell response to calcium phosphate biomaterial particles: an overview

Bone is a metabolically active and highly organized tissue consisting of a mineral phase of hydroxyapatite (HA) and amorphous calcium phosphate (CaP) crystals deposited in an organic matrix. One objective of bone tissue engineering is to mimic the chemical and structural properties of this complex tissue. CaP ceramics, such as sintered HA and beta-tricalcium phosphate, are widely used as bone substitutes or prosthesis coatings because of their osteoconductive properties. These ceramic interactions with tissues induce a cell response that can be different according to the composition of the material. In this review, we discuss inflammatory cell responses to CaP materials to provide a comprehensive overview of mechanisms governing the integration or loosening of implants, which remains a major concern in tissue engineering. A focus on the effects of the functionalization of CaP biomaterials highlights potential ways to increase tissue integration and limit rejection processes.

The effect of impaction and a bioceramic coating on bone ingrowth in porous titanium particles

BACKGROUND AND PURPOSE

Porous titanium (Ti) particles can be impacted like cancellous allograft bone particles, and may therefore be used as bone substitute in impaction grafting. We evaluated the effect of impaction and of a thin silicated biphasic calcium phosphate coating on osteoconduction by Ti particles.

METHODS

The bone conduction chamber of Aspenberg was used in goats and filled with various groups of coated or uncoated small Ti particles (diameter 1.0-1.4 mm). Impacted allograft bone particles and empty chambers were used in control groups. Fluorochromes were administered at 4, 8, and 12 weeks. Maximum bone ingrowth distance was evaluated by histomorphometric analysis.

RESULTS

Histology of Ti particle graft cylinders showed a dense matrix with narrow inter-particle and intra-particle pores (< 100 μm), occluding the lumen of the bone chamber. Bone ingrowth distances gradually increased with time in all groups. Maximum bone ingrowth distance was higher in originally empty chambers than those with allograft bone particles (p = 0.01) and Ti particles (p < 0.001). Maximum bone ingrowth in allograft bone particles was higher than in all Ti groups (p ≤ 0.001). Impaction reduced osteoconduction and the coating partially compensated for the negative effect of impaction, but these differences were not statistically significant. No osteolytic reactions were found.

INTERPRETATION

Osteoconduction in the bone conduction chamber was reduced more by the insertion of small Ti particles than by insertion of small allograft bone particles. The osteoconductive potential of porous Ti particles should be studied further with larger-sized particles, which may allow bone ingrowth after impaction through larger inter-particle pores.

Size dependent induction of proinflammatory cytokines and cytotoxicity of particulate beta-tricalciumphosphate in vitro

Cellular responses to particulate calcium phosphate ceramics can lead to inflammatory reactions under certain conditions that depend on particle composition, size and morphology. In this context, the potential influence of varying sizes of particulate beta-tricalciumphosphate (beta-TCP) on the induction of inflammation and cytotoxicity remains to be determined. The present work investigates the effects of beta-TCP particles of five different sizes (1, 3, 13, 32 and 40 μm) on human peripheral blood mononuclear cells (PBMC) in vitro concerning the release of TNF-alpha, IL-1beta and IL-8 after six and 18 h of incubation (ELISA) as well as intracellular TNF-alpha, IFN-gamma, IL-1alpha, IL-1beta and IL-8 levels within distinct PBMC subpopulations after 12 h (FACS). Potential cytotoxic effects were determined by assaying lactate dehydrogenase (LDH) and morphological analyses (electron microscopy). Beta-TCP 1 μm did not induce any cytokine after 6 h but slightly increases TNF-alpha, IL-1beta and IL-8 release after 18 h. Larger particles (32 and 40 μm) consistently caused higher levels of cytokine release by increasing the fraction of cytokine producing monocytes. They also caused higher levels of LDH release as did smaller, phagocytosable particles. These data suggest a less inflammatory and cytotoxic profile of beta-TCP devices with a smaller primary particle size when compared to larger particles.

The efficacy of host response modulation therapy (omega-3 plus low-dose aspirin) as an adjunctive treatment of chronic periodontitis (clinical and biochemical study)

BACKGROUND AND OBJECTIVE

Regeneration of lost periodontal tissues is considered to be one of the most challenging aspects of periodontal therapy. Our current understanding of the role of the host immuno-inflammatory response in periodontal diseases forms the basis of new therapeutic approaches. The aim of this study was to evaluate the efficacy of systemic administration of omega-3 polyunsaturated fatty acids plus low-dose aspirin as an adjunctive treatment to regenerative therapy of furcation defects.

MATERIAL AND METHODS

Forty patients displaying at least a single grade II furcation defect were enrolled in the study. They were randomly allocated into two groups: an experimental group receiving decalcified freeze-dried bone allograft (DFDBA) + omega-3 polyunsaturated fatty acids combined with low-dose aspirin; and a control group receiving DFDBA + placebo. Clinical parameters were monitored at baseline, and at 3 and 6 mo following therapy, and included plaque index, gingival index, gingival bleeding index, probing pocket depth and clinical attachment level. The biochemical markers assessed in gingival crevicular fluid samples were interleukin-1β and interleukin-10.

RESULTS

The experimental intervention resulted in a greater mean probing pocket depth reduction (P < 0.001) and gain in clinical attachment (P < 0.05) compared with the control at 6 mo. Furthermore, the experimental protocol was able to achieve a significant modulatory effect on the levels of interleukin-1β and interleukin-10 compared with control therapy.

CONCLUSION

The findings suggest that the combination therapy demonstrated successful reduction of gingival inflammation, reduction of pocket depth and attachment level gain, accompanied by a trend for modulation of the cytokines profile in gingival crevicular fluid.

Hypoxia-like effect of cobalt chromium alloy micro particles on fibroblasts in vitro

Periprosthetic osteolysis leading to asceptic loosening remains the primary cause of failure of joint replacement. Although many inflammatory cell types have been implicated, the exact pathomechanisms of asceptic loosening have not been delineated. In the present study we have adopted a proteomic approach to elucidate the initial signals that are expressed to particulate material, using an in vitro cell culture system. Human lung fibroblasts MRC-5 were cultured with Cobalt Chromium (CoCr ASTM F-75, 1-7 µm) particles. Cells were harvested after 72 h incubation and total cellular proteins extracted for downstream analysis via 2D Gel Electrophoresis and tandem mass spectrometry using MALDI-TOF-TOF-MS. Thirteen protein spots showed greater than twofold increase, following 72 h incubation of fibroblast with CoCr particles. Four of these proteins were identified by tandem mass spectrometry. These were Annexin II, Pyruvate kinase, Triose phosphate isomerase, and N-myc downstream regulated gene 1 protein. Cobalt is a hypoxia mimicking agent and N-myc downstream regulated gene 1 protein, Triose phosphate isomerase, Pyruvate kinase, and Annexin II are important hypoxia regulated gene products that are found to be over expressed in cellular oxidative stress response. Our data indicates that exposure of fibroblast to CoCr alloy induces the transition of these cells into a hypoxia like state and oxidative stress even in normoxic culture conditions. The study reflects the possibility of the presence of a hypoxic environment in the periprosthetic tissue surrounding metallic implants.

PGE2 signaling through the EP4 receptor on fibroblasts upregulates RANKL and stimulates osteolysis

Periprosthetic osteolysis is the most common cause of aseptic loosening in total joint arthroplasty. The role of inflammatory mediators such as prostaglandin E2 (PGE2) and osteoclast promoting factors including RANKL in the pathogenesis of osteolysis has been well characterized. However, the PGE2 receptor (EP1, EP2, or EP4), and cell type in which it is expressed, which is responsible for PGE2 induction of RANKL during wear debris-induced osteolysis, has yet to be elucidated. To address this, we used mice genetically deficient in these EP receptors to assess PGE2 and wear debris responses in vitro and in vivo. Wear debris-induced osteolysis and RANKL expression were observed at similar levels in WT, EP1(-/-), and EP2(-/-) mice, indicating that these receptors do not mediate PGE2 signals in this process. A conditional knockout approach was used to eliminate EP4 expression in FSP1(+) fibroblasts that are the predominant source of RANKL. In the absence of EP4, fibroblasts do not express RANKL after stimulation with particles or PGE2, nor do they exhibit high levels of osteoclasts and osteolysis. These results show that periprosthetic fibroblasts are important mediators of osteolysis through the expression of RANKL, which is induced after PGE2 signaling through the EP4 receptor.

Basic research methods and current trends of dental implant surfaces

Among dental implant design alterations, surface modifications have been by far the most investigated topic. Regarding implant surface research, the lack of hierarchical approaches relating in vitro, in vivo, clinical trials, and ex vivo analyses has hindered biomaterials scientists with clear informed rationale guidelines for implant surface design. This manuscript provides a critical hierarchical overview of the in vitro, laboratory in vivo, clinical, and ex vivo methodologies used to investigate the performance of novel biomaterials aiming to allow dental professionals to better evaluate the past, present, and future dental implant surface research. This manuscript also contains an overview of the commercially available surface texture and chemistry modifications including novel nanotechnology-based fabrication processes. Over the last decade, surface texturing has been the most utilized parameter for increasing the host-to-implant response. Recently, dental implant surfaces utilizing reduced length scale physico/chemical features (atomic and nanometric) have shown the potential to synergistically use both texture and the inclusion of bioactive ceramic components on the surface. Although surface modifications have been shown to enhance osseointegration at early implantation times, information concerning its long-term benefit to peri-implant tissues is lacking due to the reduced number of controlled clinical trials. Given the various implants/surfaces under study, the clinician should ask, founded on the basic hierarchical approach described for the in vitro, laboratory in vivo data, as well as the results of clinical studies to effectiveness before use of any dental implant.

Injectable iron-modified apatitic bone cement intended for kyphoplasty: cytocompatibility study

In this study, the cytocompatibility of human ephitelial (HEp-2) cells cultured on new injectable iron-modified calcium phosphate cements (IM-CPCs) has been investigated in terms of cell adhesion, cell proliferation, and morphology. Quantitative MTT-assay and scanning electron microscopy (SEM) showed that cell adhesion and viability were not affected with culturing time by iron concentration in a dose-dependent manner. SEM-cell morphology showed that HEp-2 cells, seeded on IM-CPCs, were able to adhere, spread, and attain normal morphology. These results showed that the new injectable IM-CPCs have cytocompatible features of interest to the intended kyphophasty application, for the treatment of osteoporotic vertebral compression fractures.

An in vitro evaluation of the Ca/P ratio for the cytocompatibility of nano-to-micron particulate calcium phosphates for bone regeneration

Calcium phosphate based bioceramics have been widely used for orthopedic applications due to their chemical similarity to natural bone. The Ca/P stoichiometry of calcium phosphates strongly influences their performance under biological conditions, which have not yet been fully elucidated to date. For this reason, the objective of this in vitro study was to understand the relationship between the Ca/P ratio of nano-to-micron particulate calcium phosphate substrates and their biological properties, such as osteoblast (bone-forming cell) viability, collagen production, alkaline phosphatase activity and nitric oxide (NO) production. A group of calcium phosphates with Ca/P ratios between 0.5 and 2.5 were obtained by intentionally adjusting the Ca/P stoichiometry of the initial reactants necessary for calcium phosphate precipitation. For samples with 0.5 and 0.75 Ca/P ratios, tricalcium phosphate (TCP) and Ca(2)P(2)O(7) phases were observed. In contrast, for samples with 1.0 and 1.33 Ca/P ratios, the only stable phase was TCP. For samples with a 1.5 Ca/P ratio, the TCP phase was dominant; however, small amounts of the hydroxyapatite (HA) phase started to appear. For samples with a 1.6 Ca/P ratio, the HA phase was dominant. Lastly, for samples with 2.0 and 2.5 Ca/P ratios, the CaO phase started to appear in the HA phase which was the dominant phase. Moreover, the average grain size and the average pore size decreased from micron-scale (e.g. 1370nm for a 0.5 Ca/P ratio) to nano-scale (e.g. 262nm for a 2.5 Ca/P ratio) with increasing Ca/P ratios. The porosity (%) of calcium phosphate substrates also decreased with increasing Ca/P ratios. Previous in vitro results demonstrated increased osteoblast adhesion on calcium phosphates with higher Ca/P ratios (up to 2.5). The present study showed that the collagen production by osteoblasts was similar between all the calcium phosphates but slightly lower with a 1.6 Ca/P ratio. Greater alkaline phosphatase activity by osteoblasts was observed in all the cultures with various calcium phosphates (0.5-2.5 Ca/P ratios) than in the control (only cells in culture). Ca/P ratios of <2 and 1 optimized osteoblast viability and promoted alkaline phosphatase activity in osteoblasts, respectively. However, the presence of the CaO phase in Ca/P ratios 2.0 increased osteoblast NO production and decreased osteoblast viability. In summary, this study provided evidence that the Ca/P ratio of calcium phosphate is a very important factor that should be considered when selecting nano-to-micron particulate calcium phosphates for various orthopedic applications.

Osteointegration of poly(L: -lactic acid)PLLA and poly(L: -lactic acid)PLLA/poly(ethylene oxide)PEO implants in rat tibiae

Natural or synthetic materials may be used to aid tissue repair of fracture or pathologies where there has been a loss of bone mass. Polymeric materials have been widely studied, aiming at their use in orthopaedics and aesthetic plastic surgery. Polymeric biodegradable blends formed from two or more kinds of polymers could present faster degradation rate than homopolymers. The purpose of this work was to compare the biological response of two biomaterials: poly(L: -lactic acid)PLLA and poly(L: -lactic acid)PLLA/poly(ethylene oxide)PEO blend. Forty four-week-old rats were divided into two groups of 20 animals, of which one group received PLLA and the other PLLA/PEO implants. In each of the animals, one of the biomaterials was implanted in the proximal epiphysis of the right tibia. Each group was divided into subgroups of 5 animals, and sacrificed 2, 4, 8 and 16 weeks after surgery, respectively. Samples were then processed for analysis by light microscopy. Newly formed bone was found around both PLLA and PLLA/PEO implants. PLLA/PEO blends had a porous morphology after immersion in a buffer solution and in vivo implantation. The proportion 50/50 PLLA/PEO blend was adequate to promote this porous morphology, which resulted in gradual bone tissue growth into the implant.

Substance P stimulates production of interleukin 1beta and tumor necrosis factor alpha in fibroblasts from hip periprosthetic membrane

Aseptic loosening remains the primary cause of failure in total joint arthroplasty. Substance P (SP)-immunoreactive nerve fibers have been detected in the pseudomembrane and pseudocapsular tissues of aseptic loose hip prostheses, suggesting that SP might be involved in the process of aseptic loosening. We isolated fibroblasts from periprosthetic membrane at the time of revision hip arthroplasty performed because of aseptic loosening. Fibroblasts were incubated in the presence of various concentrations of SP, and the levels of interleukin 1beta, and tumor necrosis factor alpha in the media were determined using enzyme-linked immunosorbent assay kit. We found that the levels of interleukin 1beta and tumor necrosis factor alpha increased in a time- and concentration-dependent manner. Our results suggested that SP might be involved in the pathogenesis of aseptic loosening.

In Vitro Study on Different Cell Response to Spherical Hydroxyapatite Nanoparticles

Hydroxyapatite (HA) is widely used in filling of bone defects and coating on metal parts of prosthetic implants due to its excellent biocompatibility, bioactivity, and bone-bonding properties. It has been demonstrated that micro-sized HA particles cause inflammatory reaction, especially for the needle shaped particles. However, little effort has been concentrated on the cell responses of the spherical HA nanoparticles. The aim of the present work is to chemically and physically characterize the synthesized HA nanoparticles and to investigate the in vitro cell responses. X-ray diffraction, electron microscopy, nitrogen adsorption, and Fourier transform infrared spectroscopy revealed that the particles consisted of nearly spherical crystallites of carbonate-substituted HA with size of 20—40 nm and specific surface area of 75 m2/g. L929 cell proliferation experiments demonstrate that the spherical HA nanoparticles is more biocompatible than commercially available HA. On the other hand, U2-OS cell test results show that the inhibition rate of the spherical HA nanoparticles increases with time and concentration. The half effective inhibitory concentration (IC50) of the nanoparticles was determined to be 50.8 μg/mL at 72 h. All these data indicated that the synthesized spherical nanocrystalline HA particles can function as an effective biomaterial for bone tumorectomy repair, while having little adverse effect.

Biocompatibility of novel polymer-apatite nanocomposite fibers

On the basis of the bioactivity of hydroxyapatite (HA) and the excellent mechanical and biocompatible performance of polyethylene terephthalate (PET), composite microfibers made of nanograde HA with PET was designed and fabricated to mimic the structure of biological bone, which exhibits a composite of nanograde apatite crystals and natural polymer. The PET/HA nanocomposite was molded into fibers so that the bulk structures' mechanical properties can be custom tailored by changing the final 3D orientation of the fibbers. This study focused on the in vitro biocompatibility evaluation of the PET/HA composite fibers as potential bone fixation biomaterial for total hip replacement prosthesis surfaces. The MTT assay was performed with the extracts of the composite fibers in order to evaluate the short-term effects of the degradation products. The cell morphology of L929 mouse fibroblast cell line was analyzed after direct contact with the fiber scaffolds for different time periods, and the cell viability was also analyzed by the Alamar Blue assay. The release of the inflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), from RAW 264.7 macrophages in the presence of fiber extracts and fibers was used as a measure of the inflammatory response. The ability of the fiber matrices to support L929 attachment, spreading, and growth in vitro, combined with the compatible degradation extracts and low inflammation potential of the fibers and extracts, suggests potential use of these fibers as load-baring bone fixation biomaterial structures.

Role of fibroblasts and fibroblast-derived growth factors in periprosthetic angiogenesis

The periprosthetic granulomatous soft tissue [designated iterfacial membrane (IFM) in this study] exhibits heterogeneous histopathological features, in which highly vascularized areas with dense cellularity alternate with fibrotic and pseudocapsule-like tissue structures. Although macrophage/monocyte activation is a prominent event in the periprosthetic environment, fibroblasts also phagocytose particulate wear debris both in vivo and in vitro. Particulate wear debris and/or cytokines/growth factors alone or in combination (e.g., in conditioned media of explant cultures of IFMs) stimulated normal synovial and IFM fibroblasts to express inflammatory mediators and growth factors such as interleukin (IL)-1beta, IL-6, IL-8, three isoforms of vascular endothelial growth factor (VEGF), monocyte/macrophage chemoattractant protein-1 (MCP-1), macrophage-colony-stimulating factor (M-CSF), cycloxygenases (Cox-1 and Cox-2), acid- and basic-fibroblast growth factors (FGF-1 and FGF-2), leukemia inhibitory factor-1 (LIF-1), transforming growth factor beta-1 (TGF-beta1), receptor activator of nuclear factor-kappa B ligand (RANKL), and osteoprotegerin (OPG). Thus, the fibroblast is capable of expressing a wide array of angiogenic and osteoclastogenic factors which are involved in the detrimental processes of the periprosthetic osteolysis.

Effects of platelet factors on biodegradation and osteogenesis in metaphyseal defects filled with nanoparticular hydroxyapatite--an experimental study in minipigs

There are no studies on the cellular activity in the early phase of biodegradation and bone healing of bone substitutes loaded with platelet factors (PLF). The purpose of this study was to evaluate the cellular effects of PLF in combination with nanoparticulate hydroxyapatite (HA) on the biodegradation and bone formation after 20 days. Autogenous PLFs were obtained by centrifugation of miniature pig blood samples and subsequent degranulation of platelets by calcium and thrombin. A cylindrical bone defect with a diameter of 8.9 mm was created in the distal femoral condyle of 20 miniature pigs. Four of the defects were left empty, 8 were filled with HA with loading and 8 with HA loaded with PLF. The distal femur was harvested after 20 days and TRAP-staining, cathepsin-K and CD44 staining and scanning electron microscopy were performed for cellular assessment of biodegradation was done. Histomorphometry of new bone formation and of biodegradation of HA material was performed. PLF loading of HA led to statistically significant more TRAP-positive cells with enhanced biodegradation of the nanoparticulate HA but no statistically enhanced new bone formation compared to unloaded HA. Furthermore, there was a higher number of CD44 and cathepsin-K positive cells by PLF-loading. In summary, PLF led to stimulation of the cellular process of the biodegradation of HA.

Growth of human osteoblast-like cells on beta-tricalciumphosphate (TCP) membranes with different structures

Bioresorb, a bioactive, bioresorbable bone replacement material, consisting of pure beta-tricalciumphos phate (TCP) ceramic, was evaluated in cell culture with human osteoblast-like cells. The aim of our study was to investigate the influence of TCP on the growth behavior of human osteoblast-like cells. Different granule sizes and plate sizes were used in this study: Granule sizes 500-1000 microm, 1000-2000 microm and 2000-5000 microm; plate sizes 1.7 mm, 2.0 mm and 2.2 mm. Under scanning electron microscopic (SEM) observations the cell colonization on the surface of the biomaterial and the tissue compatibility were studied. Thin sections were used to study the growth of human osteoblast-like cells inside the biomaterial. It could be clearly shown that all investigated biomaterials are tissue compatible and that the size and structure (granule or plate) of the biomaterial effects the colonization rate. Bioresorb plates enhance the colonization comparable to granule. The results obtained by SEM and thin sections were confirmed immunhistochemically by the nonradioactive assay EZ4U - EASY FOR YOU.In conclusion, all investigated sizes and structures of Bioresorb are tissue compatible but the cell growth is much better on plates than on granule small in size. The results suggest that the plates may be favourable useful as scaffold for regrowth of bone.

Substance P augments PGE2 and IL-6 production in titanium particles-stimulated fibroblasts from hip periprosthetic membrane

Aseptic loosening remains the primary cause of failure in total joint arthroplasty. Implant-derived particles are thought to be a main cause of osteolysis that leads to failure of total joint arthroplasty. The nervous system has been implicated in the etiology and pathogenesis of joint diseases. Substance P (SP) immunoreactive nerve fibers have been detected in the pseudomembrane and pseudocapsular tissues of aseptic loose hip prostheses, suggesting that SP might be involved in the process of aseptic loosening. Fibroblasts are abundant in periprosthetic membrane. Neuropeptides are able to modulate cytokine production by fibroblasts. In this study, we isolated fibroblasts from periprosthetic membrane at the time of revision hip arthroplasty performed because of aseptic loosening. Fibroblasts were stimulated with titanium (Ti) particles or SP. Prostaglandin (PG) E2 and interleukin-6 (IL-6) assays were performed using enzyme-linked immunosorbent assay kit. PGE2 and IL-6 secretion by fibroblasts have been significantly increased in the presence of Ti particles or SP. Moreover SP caused significant increase in PGE2 and IL-6 production by Ti particles-stimulated fibroblasts. Thus, SP and Ti particles acted synergistically to increase PGE2 and IL-6 secretion in fibroblasts from periprosthetic membrane.

Plasma cytokines as markers of aseptic prosthesis loosening

The proinflammatory cytokines IL-1beta, IL-8, and TNF-alpha play a major role in the process of bone resorption during aseptic loosening of large joint prostheses. These cytokines secreted locally during bone resorption in aseptic loosening may enter peripheral circulation. Increased concentration of IL-1gamma, IL-8, and TNF-alpha in peripheral circulation may indicate aseptic loosening. We determined whether bone resorption could be verified by cytokine presence in plasma. We recruited 50 patients with aseptic prosthesis loosening, 50 with stable prostheses, 50 with osteoarthritis, and 50 healthy individuals. Cytokine levels were determined in plasma by ELISA tests. Patients with prosthesis loosening had higher plasma levels (IL-10, 3.7 +/- 5.5 pg/mL; IL-8, 14.7 +/- 9 pg/mL; TNF-alpha, 32.7 +/-+/- 32.4 pg/mL) than patients with stable prostheses (IL-1beta, 1.5 +/- 2 pg/mL; IL-8, 8.1 +/- 4.7 pg/mL; TNF-alpha, 22.9 +/- 18.7 pg/mL), patients with osteoarthritis (IL-1beta, 0.7 +/- 1.1 pg/mL; IL-8, 5.8 +/- 3.8 pg/mL; TNF-alpha, 9.8 +/- 7.7 pg/mL) and healthy individuals (IL-1beta, 0.7 +/- 1.1 pg/mL; IL-8, 4.2 +/- 1.3 pg/mL; TNF-alpha, 3.9 +/- 3.9 pg/mL). Our data suggest elevated plasma levels of proinflammatory cytokines may be useful as markers of bone resorption in the laboratory diagnosis of prosthesis loosening.

The role of fibroblasts and fibroblast-derived factors in periprosthetic osteolysis

OBJECTIVE

This study was undertaken to investigate how fibroblasts respond to stimulation with particulate wear debris and/or conditioned media obtained from pathologic tissue, and whether these activated fibroblasts express compounds that are involved in bone resorption.

METHODS

Conditioned media from explant cultures of synovial tissue, periprosthetic soft tissue (interface membranes), titanium particles, and proinflammatory cytokines were used to stimulate fibroblasts. RNase protection assay was used to measure altered gene expression, and enzyme-linked immunosorbent assay, Western blot hybridization, and flow cytometry were used to determine fibroblast protein expression. Tartrate-resistant acid phosphatase staining was used to identify multinucleated osteoclast-like cells.

RESULTS

The most dominant compounds measured in the conditioned media from interface membranes were tumor necrosis factor alpha (TNFalpha), monocyte chemoattractant protein 1 (MCP-1), interleukin-1beta (IL-1beta), IL-6, IL-8, and vascular endothelial growth factor. Fibroblasts phagocytosed particulate wear debris and responded to cytokine/chemokine stimulation. The most prominent up-regulated genes and proteins secreted by fibroblasts in response to stimulation were matrix metalloproteinase 1, MCP-1, IL-1beta, IL-6, IL-8, cyclooxygenase 1 (COX-1), COX-2, leukemia inhibitory factor 1, transforming growth factor beta1 (TGFbeta1), and TGFbeta receptor type I. In addition, interface membrane fibroblasts expressed RANKL and osteoprotegerin in response to stimulation with conditioned media, TNFalpha, or IL-1beta. Stimulated fibroblasts cocultured with bone marrow cells in the presence of macrophage colony-stimulating factor induced osteoclastogenesis.

CONCLUSION

Interface membrane fibroblasts respond directly to particulate wear debris, possibly via phagocytosis, expressing proinflammatory cytokines and RANKL. Thus, these cells may be actively involved in osteoclastogenesis and pathologic (periprosthetic) bone resorption.

Biodegradable Composite Implants

Biodegradable implants are established in the field of operative sports medicine. So-called composite implants are increasingly used. The idea to improve biocompatibility and osteoconductivity of biodegradable polymers by modifying them with a ceramic component, has led to the development of these composite implants. Today, an increasing variety of composite implants are available. They have substantially different material characteristics, which depend on matrix polymer choice and the additional ceramic. The material characteristics influence the mechanical properties, in vivo degradation, the osseous replacement and the host-tissue response. It is important to understand their biologic base for a better knowledge of the advantages and risks associated with using composite implants in the field of operative sports medicine. The purpose of this review is to focus on current developments in biodegradable composite implants and their biologic base.

Fibroblasts express RANKL and support osteoclastogenesis in a COX-2-dependent manner after stimulation with titanium particles

Synovial fibroblasts are possible mediators of osteolysis. Fibroblasts respond directly to titanium particles and increase RANKL expression through a COX-2/PGE2/EP4/PKA signaling pathway. Fibroblasts pretreated with titanium or PGE2 stimulated osteoclast formation, showing the functional importance of RANKL induction. Synovial fibroblasts and their activation pathways are potential targets to prevent osteolysis.

INTRODUCTION

Bone loss adjacent to the implant is a major cause of joint arthroplasty failure. Although the cellular and molecular response to microscopic wear debris particles is recognized as causative, little is known concerning role of synovial fibroblasts in these events.

MATERIALS AND METHODS

Murine embryonic fibroblasts and knee synovial fibroblasts in culture stimulated with titanium particles were examined by FACS, real time RT-PCR, Northern blot, and Western blot for expressions of vascular cell adhesion molecule (VCAM)1, RANKL, cyclooxygenase (COX)-1, and COX-2, and the four prostaglandin E2 (PGE2) receptor isoforms. Experiments were performed in the presence and absence of COX inhibitors, protein kinase A (PKA) and protein kinase C (PKC) inhibitors, and various EP receptor agonists. Osteoclast formation was examined in co-cultures of pretreated glutaraldehyde-fixed fibroblasts and primary murine spleen cells treated with macrophage-colony stimulating factor (M-CSF) for 7-days.

RESULTS

TNF-alpha stimulated VCAM1 expression, consistent with a synovial fibroblast phenotype. Titanium particles stimulated RANKL gene and protein expressions in fibroblasts in a dose-dependent manner. Gene expression was increased 5-fold by 4 h, and protein levels reached a maximum after 48 h. Within 1 h, titanium particles also induced COX-2 mRNA and protein levels, whereas both indomethacin and celecoxib blocked the stimulation of RANKL, suggesting a COX-2-mediated event. Furthermore, PGE2 induced RANKL gene and protein expression and rescued RANKL expression in titanium-treated cultures containing COX-2 inhibitors. Fibroblast cultures pretreated with either PGE2 or titanium particles enhanced osteoclast formation, indicating the functional importance of RANKL induction. EP4 was the most abundant PGE2 receptor isoform, EP1 and EP2 were expressed at low levels, and EP3 was absent. The EP1 selective agonist iloprost and the EP2 selective agonist butaprost minimally stimulated RANKL. In contrast, the EP2 and EP4 agonist misoprostol induced RANKL to a magnitude similar to PGE2. Finally, PKA antagonism strongly repressed RANKL stimulation by PGE2.

CONCLUSION

Fibroblasts respond directly to titanium particles and increase RANKL expression through a COX-2/PGE2/EP4/PKA signaling pathway. Thus, the synovial fibroblast is important mediator of osteolysis and target for therapeutic strategies.

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.

No effect of hydroxyapatite particles in phagocytosable sizes on implant fixation: An experimental study in dogs

The influence of wear debris on bone healing around orthopedic implants is debated. Hydroxyapatite (HA) particles and polyethylene (PE) particles have been shown to have a negative effect on osteoblast cultures in vitro. The present study investigated the in vivo effects of HA and PE particles on the mechanical fixation and gap healing around experimental HA implants. Nonloaded implants (n = 30) were inserted bilaterally into the proximal tibia of 15 dogs with a 2-mm gap to the bone. The peri-implant gap was either (1) empty (n = 6) or filled with (2) hyaluronic acid (n = 8), (3) hyaluronic acid and HA particles (n = 8), or (4) hyaluronic acid and PE particles (n = 8). After 4 weeks, the animals were killed. The implant interface was evaluated by pushout testing until failure and by histomorphometry. Both HA and PE particles were found to be phagocytosed by macrophage-like cells in the interfacial tissue. HA particles were also integrated in newly formed bone. We found no negative effect of the particulate material on mechanical fixation of the implants or on bone formation around the implants.

Cytokine secretion from mononuclear cells culturedin vitro with starch-based polymers and poly-L-lactide

The cytokine network is one of the major controlling systems of the inflammatory process, driving the magnitude and duration of the host response against invading microorganisms, foreign materials, or altered internal stimuli. Pro- and antiinflammatory cytokines were quantified after in vitro culture of a mixed population of monocytes/macrophages and lymphocytes with biodegradable polymers. Different blends of starch-based polymers and their composites filled with hydroxyapatite were studied and compared with poly-L-lactide. Interleukin (IL)-1beta, IL-6, and tumour necrosis factor-alpha were investigated as the markers of immunological reactivity because they are known to act at the early stages of injury/invasion. Interferon-gamma, recognized as a proinflammatory cytokine, although not present during early responses was also investigated. Contrarily, IL-4 derived from T lymphocytes, was investigated because it is an immunoregulator that counteracts some aspects of inflammation. T lymphocyte activation was also determined by quantifying IL-2. The results support the hypothesis that different biodegradable polymers can affect mononuclear cell activation and the production of several cytokines associated with the inflammatory process. No IL-2 or interferon-gamma was found in the culture supernatants after 3, 7, and 14 days in the presence of any of the materials. IL-6 was detected in the highest amounts, for all the conditions, followed by tumour necrosis factor-alpha. IL-1beta was produced in very low amounts, being undetectable with some of the starch-based materials. IL-4 was the only cytokine that did not demonstrate any significant difference within this group of materials. Starch-based polymers and composites induced lower production of proinflammatory cytokines in comparison to poly-L-lactide.

MMP-2, MMP-9 and their inhibitors TIMP-2 and TIMP-1 production by human monocytes in vitro in the presence of different forms of hydroxyapatite particles

After calcium-phosphates biomaterials based implantation like hydroxyapatite (HA) coating, particles are released in the periprosthetic tissues. Wear-debris induced fibrous membranes contain macrophage subsets that can produce metalloproteinases (MMPs), which are considered to be key enzymes in extra-cellular matrix turnover. Tissue inhibitors of metalloproteinases (TIMPs) are important regulator of MMPs activity. Interleukin-1 mainly produced by monocytes can also regulate MMPs production. In the present work, we have evaluated the effect of HA particles characteristics (size, shape and sintering temperature) on the MMP-2, -9 and their respective inhibitors TIMP-2, -1 production. Our results demonstrate that sintering temperature (that modify crystal size and surface area) have little effect on MMPs and TIMPs production. Non-phagocytable particles induced more MMP-9, although phagocytable particles induced more IL-1beta release. The shape of the particles was the most important factor since needle-shaped particles induced the most significant up-regulated expression of MMPs and IL-1beta.

PGE2 and IL-6 production by fibroblasts in response to titanium wear debris particles is mediated through a Cox-2 dependent pathway

Aseptic loosening of orthopaedic implants is precipitated by wear debris-induced osteolysis. Central to this process are the pro-inflammatory mediators that are produced in response to wear by the fibroblastic cells, which comprise the majority of periprosthetic membranes. Since this pro-inflammatory cascade is mediated by a plethora of factors with redundant functions, it is imperative to establish a hierarchy. Two well-known fibroblast derived pro-inflammatory factors that stimulate wear debris-induced osteoclastic resorption are prostaglandin E2 (PGE2) and IL-6. However, their relationship to each other in this process is poorly defined. Here we show immunohistochemistry of retrieval membranes indicating that COX-2 is the principal cyclooxygenase responsible for PGE2 production in fibroblasts around failed implants. We also performed in vitro experiments with fibroblasts derived from wild-type (WT), COX-1 (-/-) and COX-2 (-/-) mice, which demonstrated that COX-2 is required for Ti wear debris-induced PGE2 production. Interestingly, COX-2 was also required for IL-6 production in these assays, which could be rescued by the addition of exogenous PGE2 (10(-6) M). Pharmacology studies that utilized the COX-1 selective inhibitor SC 560, the COX-2 selective inhibitor celecoxib, and the nonselective COX inhibitor indomethacin confirmed these results. Taken together, these results indicate that selective inhibition of prostaglandin signaling could favorably impact aseptic loosening beyond its direct effects on PGE2 synthesis, in that it inhibits downstream pro-inflammatory/pro-osteoclastic cytokine production.

Growth behavior, matrix production, and gene expression of human osteoblasts in defined cylindrical titanium channels

The purpose of the current study was to investigate the effect of different diameters of cylindrical titanium channels on human osteoblasts. Titanium samples having continuous drill channels with diameters of 300, 400, 500, 600, and 1000 microm were put into osteoblast cell cultures that were isolated from 12 adult human trauma patients. Cell migration into the drill channels was investigated by transmitted-light microscopy. The DNA content in the drill channels was measured photometrically, collagen type I production was analyzed by enzyme-linked immunosorbent assay (ELISA) and osteocalcin gene expression by reverse transcriptase-polymerase chain reaction (RT-PCR). Formation of mineralized tissue was assessed by microradiographs of histological sections. Within 20 days, cells grew an average of 838 microm (+/-128 microm) into the drill channels with a diameter of 600 microm and were significantly faster (p < 0.05) than in all other channels. Cells produced significantly more osteocalcin messenger RNA (mRNA) in 600-microm channels (p < 0.05) than they did in 1000-microm channels and demonstrated the highest osteogenic differentiation. The channel diameter did not influence collagen type I production. The highest cell density was found in 300-microm channels (p < 0.05). The DNA content of the channels linearly decreased with increasing channel diameters. After 40 days of culture, the proportion of mineralized tissue at the mouth section amounted to 6% in 300-microm channels and to 9-11% in 400-600-microm channels. In 1000-microm channels, only traces of mineralization were detected. Our data suggest that the diameter of cylindrical titanium channels has a significant effect on migration, gene expression, and mineralization of human osteoblasts.

Autologous osteoblasts enhance osseointegration of porous titanium implants

The goal of this study was to assess the osseointegration of porous titanium implants by means of coating with autologous osteoblasts. Titanium implants (8 x 5 x 4 mm) having drill channels with diameters of 400, 500, and 600 microm were coated with autologous osteoblasts obtained from spongiosa chips. The implants were inserted into the distal femora of 17 adult Chinchilla Bastard rabbits (group I). Uncoated implants were inserted as controls in the contralateral femur (group II). The animals were sacrificed after 5, 11, and 42 days. Intravital fluorochrome labeling and microradiography were used for the assessment of bone ingrowth into the titanium channels. In both groups, no bone tissue was formed in the channels up to day 5. On day 11, group I exhibited significantly more (p<0.05) bone tissue (19.8+/-14.0% vs. 5.8+/-9.1%) with greater bone-implant contact (13.3+/-15.1% vs. 5.7+/-5.3%, p<0.05) at the channel mouths than group II. Bone tissue was formed mainly between day 15 and 30 in group I, in group II between day 25 and 40. Six weeks after implantation, bone tissue filled on an average 68.8+/-15.1% of the mouths of the drill channels in implants in group I, the filling for group II was 49.8+/-18.1% (p<0.05). The average bone-implant contact at the channel mouths after six weeks was 56.5+/-13.5% in group I, 40.2+/-21.9% in group II (p<0.05). 600-microm channels showed at this time point the best osseous integration (p<0.05). Coating with autologous osteoblasts accelerates and enhances the osseointegration of titanium implants and could be a successful biotechnology for future clinical applications.