The influence of elementary silver versus titanium on osteoblasts behaviour in vitro using human osteosarcoma cell lines

Effect of the Synergistic Interaction of Micro- and Nanostructures with Silver Ions on the Biocompatibility and Antimicrobial Properties of Ti-15Mo-2.5Ag

Titanium and titanium alloys have the advantages of a low density and a close elastic modulus to natural bone, which can reduce the stress-shielding effect and become one of the first choices for human hard tissue replacement and repair. However, implant site infection is still one of the main reasons for implantation failure. In this paper, 2.5 wt % Ag element was added to Ti-15Mo to obtain a low modulus, and a surface anodization was applied to improve the surface biocompatibility. The elastic modulus, micromorphology, surface elemental valence, corrosion resistance, antimicrobial properties, and cytocompatibility were investigated by mechanical tests, scanning electron microscopy, X-ray photoelectron spectroscopy, electrochemical tests, inductively coupled plasma spectroscopy, plate counting method, and cellular tests. The experimental results showed that the anodized Ti-15Mo-2.5Ag sample exhibited an elastic modulus of 79 GPa, a strong corrosion resistance, a strong antimicrobial ability of ≥99.99%, and good biocompatibility. It was demonstrated that the formation of Ag2O on the surface and Ag ion release improved the antimicrobial properties and that the structural synergism of silver ions with micro- and nanostructures played an important role in promoting the early spreading of cells and improving the cytocompatibility.

Human T-Cell Responses to Metallic Ion-Doped Bioactive Glasses

Biomaterials are extensively used as replacements for damaged tissue with bioactive glasses standing out as bone substitutes for their intrinsic osteogenic properties. However, biomaterial implantation has the following risks: the development of implant-associated infections and adverse immune responses. Thus, incorporating metallic ions with known antimicrobial properties can prevent infection, but should also modulate the immune response. Therefore, we selected silver, copper and tellurium as doping for bioactive glasses and evaluated the immunophenotype and cytokine profile of human T-cells cultured on top of these discs. Results showed that silver significantly decreased cell viability, copper increased the T helper (Th)-1 cell percentage while decreasing that of Th17, while tellurium did not affect either cell viability or immune response, as evaluated via multiparametric flow cytometry. Multiplex cytokines assay showed that IL-5 levels were decreased in the copper-doped discs, compared with its undoped control, while IL-10 tended to be lower in the doped glass, compared with the control (plastic) while undoped condition showed lower expression of IL-13 and increased MCP-1 and MIP-1β secretion. Overall, we hypothesized that the Th1/Th17 shift, and specific cytokine expression indicated that T-cells might cross-activate other cell types, potentially macrophages and eosinophils, in response to the scaffolds.

Silver-integrated EDM processing of TiAl6V4 implant material has antibacterial capacity while optimizing osseointegration

Periprosthetic joint infections (PJI) are a common reason for orthopedic revision surgeries. It has been shown that the silver surface modification of a titanium alloy (Ti-6Al-4V) by PMEDM (powder mixed electrical discharge machining) exhibits an antibacterial effect on Staphylococcus spp. adhesion. Whether the thickness of the silver-modified surface influences the adhesion and proliferation of bacteria as well as the ossification processes and in-vivo antibacterial capacity has not been investigated before. Therefore, the aim of this work is to investigate the antibacterial effect as well as the in vitro ossification process depending on the thickness of PMEDM silver modified surfaces. The attachment of S. aureus on the PMEDM modified surfaces was significantly lower than on comparative control samples, independently of the tested surface properties. Bacterial proliferation, however, was not affected by the silver content in the surface layer. We observed a long-term effect of antibacterial capacity in vitro, as well as in vivo. An induction of ROS, as indicator for oxidative stress, was observed in the bacteria, but not in osteoblast-like cells. No influence on the in vitro osteoblast function was observed, whereas osteoclast formation was drastically reduced on the silver surface. No changes in cell death, the metabolic activity and oxidative stress was measured in osteoblasts. We show that already small amounts of silver exhibit a significant antibacterial capacity while not influencing the osteoblast function. Therefore, PMEDM using silver nano-powder admixed to the dielectric represents a promising technology to shape and concurrently modify implant surfaces to reduce infections while at the same time optimizing bone ingrowth of endoprosthesis.

In Vitro and In Vivo Studies of Antibacterial Coatings on Titanium Alloy Implants for Veterinary Application

The aim of this work was the evaluation of biological properties of hybrid coatings modified with Ag, Cu, and Zn nanoparticles (NPs) applied on TPLO medical implants by the sol-gel process. The implant coatings enriched with various concentrations of metallic NPs were investigated in the in vitro bactericidal efficacy tests against Gram+ and Gram- bacteria and pathogenic yeast. Next, the designed materials were tested on human osteosarcoma cell lines. The cells adhesion, proliferation, viability, and differentiation were investigated. The cell growth wasevaluated using SEM, and the metallic ion release was measured. The results revealed that the NPs concentration in the hybrid layers decreased with the incubation time. In the last stage, the implants were tested in vivo on six canine patients. Three months after the operation, the radiological evaluation of the performed anastomosis was carried out as well as the histopathological evaluation of tissue regeneration. The strongest bactericidal efficacy was observed for the layers containing AgNPs. Along with an increased concentration of metallic additives, a growing toxic effect was clearly observed. The most pronounced toxic effect was especially evident with the AgNPs concentration exceeding 1 mol %. In all the operated patients, no deviations were found during the follow-up examinations in the postoperative period. The low dose of AgNPs in the hybrid layer facilitated the tissue healing process. It was proven that silver nanoparticles may accelerate the bone healing process. The correct tissue reparation was observed.

Antibacterial Adhesion Strategy for Dental Titanium Implant Surfaces: From Mechanisms to Application

Dental implants are widely used to restore missing teeth because of their stability and comfort characteristics. Peri-implant infection may lead to implant failure and other profound consequences. It is believed that peri-implantitis is closely related to the formation of biofilms, which are difficult to remove once formed. Therefore, endowing titanium implants with anti-adhesion properties is an effective method to prevent peri-implant infection. Moreover, anti-adhesion strategies for titanium implant surfaces are critical steps for resisting bacterial adherence. This article reviews the process of bacterial adhesion, the material properties that may affect the process, and the anti-adhesion strategies that have been proven effective and promising in practice. This article intends to be a reference for further improvement of the antibacterial adhesion strategy in clinical application and for related research on titanium implant surfaces.

Development of Silver-Containing Hydroxyapatite-Coated Antimicrobial Implants for Orthopaedic and Spinal Surgery

The prevention of surgical site infections is directly related to the minimization of surgical invasiveness, and is in line with the concept of minimally invasive spine therapy (MIST). In recent years, the incidence of postoperative infections has been increasing due to the increased use of spinal implant surgery in patients at high risk of infection, including the elderly and easily infected hosts, the limitations of poor bone marrow transfer of antibiotics, and the potential for contamination of surgical gloves and instruments. Thus, the development of antimicrobial implants in orthopedic and spinal surgery is becoming more and more popular, and implants with proven antimicrobial, safety, and osteoconductive properties (i.e., silver, iodine, antibiotics) in vitro, in vivo, and in clinical trials have become available for clinical use. We have developed silver-containing hydroxyapatite (Ag-HA)-coated implants to prevent post-operative infection, and increase bone fusion capacity, and have successfully commercialized antibacterial implants for hip prostheses and spinal interbody cages. This narrative review overviews the present status of available surface coating technologies and materials; describes how the antimicrobial, safety, and biocompatibility (osteoconductivity) of Ag-HA-coated implants have been demonstrated for commercialization; and reviews the clinical use of antimicrobial implants in orthopedic and spinal surgery, including Ag-HA-coated implants that we have developed.

Antibacterial metals and alloys for potential biomedical implants

Metals and alloys, including stainless steel, titanium and its alloys, cobalt alloys, and other metals and alloys have been widely used clinically as implant materials, but implant-related infection or inflammation is still one of the main causes of implantation failure. The bacterial infection or inflammation that seriously threatens human health has already become a worldwide complaint. Antibacterial metals and alloys recently have attracted wide attention for their long-term stable antibacterial ability, good mechanical properties and good biocompatibility in vitro and in vivo. In this review, common antibacterial alloying elements, antibacterial standards and testing methods were introduced. Recent developments in the design and manufacturing of antibacterial metal alloys containing various antibacterial agents were described in detail, including antibacterial stainless steel, antibacterial titanium alloy, antibacterial zinc and alloy, antibacterial magnesium and alloy, antibacterial cobalt alloy, and other antibacterial metals and alloys. Researches on the antibacterial properties, mechanical properties, corrosion resistance and biocompatibility of antibacterial metals and alloys have been summarized in detail for the first time. It is hoped that this review could help researchers understand the development of antibacterial alloys in a timely manner, thereby could promote the development of antibacterial metal alloys and the clinical application.

Bone ongrowth of a cementless silver oxide-containing hydroxyapatite-coated antibacterial acetabular socket

BACKGROUND

The silver oxide-containing hydroxyapatite-coated socket (KYOCERA, Osaka, Japan) is a cementless antibacterial implant that has both the osteoconductivity of the HA and the antibacterial activity of silver. The silver oxide-containing hydroxyapatite coating was shown to have good osteoconductivity and new bone formation in vitro and in vivo. However, the histological bone ongrowth of this implant has not been proven in a clinical study.

METHODS

We analyzed bone ongrowth using two silver oxide-containing hydroxyapatite-coated sockets that were removed in revision total hip arthroplasty for recurrent dislocation. A histomorphometric analysis was performed using a scanning electron microscope (SEM) connected to a CCD camera and an elemental analysis was performed by energy-dispersive elemental spectrometry (EDS).

RESULT

A white structure thought to be osseous tissue was attached to the retrieved socket surface macroscopically, and histological bone ongrowth of the silver oxide-containing hydroxyapatite coating of the socket was confirmed by SEM. In addition, the presence of silver in the silver oxide-containing hydroxyapatite coating was confirmed in an elemental analysis by EDS.

CONCLUSION

Histologically, the silver oxide-containing hydroxyapatite-coated socket presented bone ongrowth in this clinical study.

Review of titanium surface modification techniques and coatings for antibacterial applications

Implanted biomaterials play a key role in the current success of orthopedic and dental procedures. Pure titanium and its alloys are the most commonly used materials for permanent implants in contact with bone. However, implant-related infections remain among the leading reasons for failure. The most critical pathogenic event in the development of infection on biomaterials is biofilm formation, which starts immediately after bacterial adhesion. In the last decade, numerous studies reported the ability of titanium surface modifications and coatings to minimize bacterial adhesion, inhibit biofilm formation and provide effective bacterial killing to protect implanted biomaterials. In the present review, the different strategies to prevent infection onto titanium surfaces are reported: surface modification and coatings by antibiotics, antimicrobial peptides, inorganic antibacterial metal elements and antibacterial polymers. STATEMENT OF SIGNIFICANCE: Implanted biomaterials play a key role in the current success of orthopedic and dental procedures. Pure titanium and its alloys are the most commonly used materials for permanent implants in contact with bone. Microbial infection is one of the main causes of implant failure. Currently, the global infection risk is 2-5% in orthopedic surgery. Numerous solutions exist to render titanium surfaces antibacterial. The LBPS team is an expert on the functionalization of titanium surfaces by using bioactive polymers to improve the biologiocal response. In this review, the different strategies to prevent infection are reported onto titanium and titanium alloy surfaces such as surface modification by antibiotics, antimicrobial peptides, inorganic antibacterial metal elements and antibacterial polymers.

Silver-coated (Agluna®) tumour prostheses can be a protective factor against infection in high risk failure patients

INTRODUCTION

Endoprostheses in the treatment of extremity sarcomas are associated with late complications including periprosthetic infection. This study analysed the incidence of infection in patients undergoing endoprosthetic replacement (EPR) with a silver-coated prosthesis.

MATERIALS AND METHODS

The study comprised a retrospective single centre study of 394 consecutive patients treated with resection and EPR for primary extremity bone tumours.

RESULTS

89 patients at risk for infection were treated with a silver-coated (Agluna®) EPR (22.6%), compared to 305 patients treated with a non-silver EPR (77.4%). The incidence of periprosthetic infection, requiring revision as the primary endpoint was 34/394 (8.6%); 11 patients (12.4%) in the silver group and 23 patients (7.5%) in the non-silver group (p = 0.154). Overall implant survival was 90.9% and 95.3% at 1-year and 86.8% and 91.8% at 5-years in the silver-coated and non-silver coated group, respectively (p = 0.193). Infection was treated in the silver group by washout of the prosthesis in 2/11, debridement and implant retention (DAIR) in 1/11 and single-stage revision in 1/11, and in the non-silver group by washout in 1/23 or DAIR in 2/23. Two-stage revision was successful in 2/11in the silver group, and in 11/23 in the non-silver group. Amputation was required in 4/11 in the silver group and 9/23 in the non-silver group. One patient in the silver group died due to disease with an infected EPR.

CONCLUSIONS

Silver-coated prostheses in high risk patients show similar infection free survival as non-silver coated prosthesis in standard sites in primary bone tumours of the extremities.

Biocompatible Nanocomposite Implant with Silver Nanoparticles for Otology-In Vivo Evaluation

The aim of this work was to investigate of biocompatibility of polymeric implants modified with silver nanoparticles (AgNPs). Middle ear prostheses (otoimplants) made of the (poly)acrylonitrile butadiene styrene (ABS) and ABS modified with silver nanoparticles were prepared through extrusion and injection moulding process. The obtained prostheses were characterized by SEM-EDX, micro-CT and mechanical tests, confirming their proper shape, good AgNPs homogenization and mechanical parameters stability. The biocompatibility of the implants was evaluated in vivo on rats, after 4, 12, 24 and 48 weeks of implantation. The tissue-healing process and cytotoxicity of the implants were evaluated on the basis of microscopic observations of the materials morphology after histochemical staining with cytochrome c oxidase (OCC) and acid phosphatase (AP), as well as via micro-tomography (ex vivo). The in vivo studies confirmed biocompatibility of the implants in the surrounding tissue environment. Both the pure ABS and nanosilver-modified ABS implants exhibited a distinct decrease in the area of granulation tissue which was replaced with the regenerating muscle tissue. Moreover, a slightly smaller area of granulation tissue was observed in the surroundings of the silver-doped prosthesis than in the case of pure ABS prosthesis. The kinetics of silver ions releasing from implants was investigated by ICP-MS spectrometry. The measurement confirmed that concentration of the silver ions increased within the implant’s immersion period. Our results showed that middle ear implant with the nanoscale modification is biocompatible and might be used in ossicular reconstruction.

Comparative cytotoxicity and apoptotic pathways induced by nanosilver in human liver HepG2 and L02 cells

Silver nanoparticles are used in many commercial products in daily life. Exposure to nanosilver has hepatotoxic effects in animals. This study investigated the cytotoxicity associated with polyvinylpyrrolidone-coated nanosilver (23.44 ± 4.92 nm in diameter) exposure in the human hepatoma cell line (HepG2) and normal hepatic cell line (L02), and the molecular mechanisms induced by nanosilver in HepG2 cells. Nanosilver, in doses of 20-160 μg mL^-1 for 24 and 48 h, reduced cell viability in a dose- and time-dependent manner and induced cell membrane leakage and mitochondria injury in both cell lines; these effects were more pronounced in HepG2 cells than in L02 cells. Intracellular oxidative stress was documented by reactive oxygen species (ROS) being generated in HepG2 cells but not in L02 cells, an effect possibly due to differential uptake of nanosilver by cancer cells and normal cells. In HepG2 cells, apoptosis was documented by finding that ROS triggered a decrease in mitochondrial membrane potential, an increase in cytochrome c release, activation of caspase 3 and caspase 9, and a decrease in the ratio of Bcl-2/Bax. Furthermore, nanosilver activated the Fas death receptor pathway by downregulation of nuclear factor-κB and activation of caspase 8 and caspase 3. These results suggest that apoptosis induced by nanosilver in HepG2 cells is mediated via a mitochondria-dependent pathway and the Fas death receptor pathway. These findings provide toxicological and mechanistic information that can help in assessing the effects of nanosilver in biological systems, including the potential for anticancer activities.

Biotransformation of Silver Released from Nanoparticle Coated Titanium Implants Revealed in Regenerating Bone

Antimicrobial silver nanoparticle coatings have attracted interest for reducing prosthetic joint infection. However, few studies report in vivo investigations of the biotransformation of silver nanoparticles within the regenerating tissue and its impact on bone formation. We present a longitudinal investigation of the osseointegration of silver nanoparticle-coated additive manufactured titanium implants in rat tibial defects. Correlative imaging at different time points using nanoscale secondary ion mass spectrometry, transmission electron microscopy (TEM), histomorphometry, and 3D X-ray microcomputed tomography provided quantitative insight from the nano- to macroscales. The quality and quantity of newly formed bone is comparable between the uncoated and silver coated implants. The newly formed bone demonstrates a trabecular morphology with bone being located at the implant surface, and at a distance, at two weeks. Nanoscale elemental mapping of the bone-implant interface showed that silver was present primarily in the osseous tissue and colocalized with sulfur. TEM revealed silver sulfide nanoparticles in the newly regenerated bone, presenting strong evidence that the previously in vitro observed biotransformation of silver to silver sulfide occurs in vivo.

Influence of the Microstructure and Silver Content on Degradation, Cytocompatibility, and Antibacterial Properties of Magnesium-Silver Alloys In Vitro

Implantation is a frequent procedure in orthopedic surgery, particularly in the aging population. However, it possesses the risk of infection and biofilm formation at the surgical site. This can cause unnecessary suffering to patients and burden on the healthcare system. Pure Mg, as a promising metal for biodegradable orthopedic implants, exhibits some antibacterial effects due to the alkaline pH produced during degradation. However, this antibacterial effect may not be sufficient in a dynamic environment, for example, the human body. The aim of this study was to increase the antibacterial properties under harsh and dynamic conditions by alloying silver metal with pure Mg as much as possible. Meanwhile, the Mg-Ag alloys should not show obvious cytotoxicity to human primary osteoblasts. Therefore, we studied the influence of the microstructure and the silver content on the degradation behavior, cytocompatibility, and antibacterial properties of Mg-Ag alloys in vitro. The results indicated that a higher silver content can increase the degradation rate of Mg-Ag alloys. However, the degradation rate could be reduced by eliminating the precipitates in the Mg-Ag alloys via T4 treatment. By controlling the microstructure and increasing the silver content, Mg-Ag alloys obtained good antibacterial properties in harsh and dynamic conditions but had almost equivalent cytocompatibility to human primary osteoblasts as pure Mg.

Silver-coated megaprostheses: review of the literature

Periprosthetic infection remains one of the most serious complications following megaendoprostheses. Despite a large number of preventive measures that have been introduced in recent years, it has not been possible to further reduce the rate of periprosthetic infection. With regard to metallic modification of implants, silver in particular has been regarded as highly promising, since silver particles combine a high degree of antimicrobial activity with a low level of human toxicity. This review provides an overview of the history of the use of silver as an antimicrobial agent, its mechanism of action, and its clinical application in the field of megaendoprosthetics. The benefits of silver-coated prostheses could not be confirmed until now. However, a large number of retrospective studies suggest that the rate of periprosthetic infections could be reduced by using silver-coated megaprostheses.

First Clinical Experience With Thermal-Sprayed Silver Oxide-Containing Hydroxyapatite Coating Implant

BACKGROUND

Prosthetic joint infection is a serious complication of implant therapy. To prevent prosthetic joint infection, we previously reported the features of silver oxide-containing hydroxyapatite (Ag-HA), which was prepared by mixing silver (a metal with antimicrobial activity) with HA. In this study, we evaluated the potential issues of total hip arthroplasty (THA) with an Ag-HA-coated implant.

METHODS

We prepared an implant for THA that was coated with Ag-HA. In this study, the implant contained silver at a maximum quantity of 2.9 mg/implant. In this prospective interventional study, we performed THA with this implant in 20 patients and investigated the effects of silver.

RESULTS

Blood silver levels peaked at 2 weeks after THA and gradually decreased thereafter. The highest blood silver level recorded during the postoperative follow-up was 6.0 ng/mL, which was within the normal range. The Harris Hip Scores increased in all cases, and activities of daily living improved markedly after THA with Ag-HA-coated implants. Implant failure was absent on radiography. No adverse reaction to silver was noted, and argyria was not observed in any case. No patients have developed infection after surgery.

CONCLUSION

This is the first clinical study of Ag-HA-coated implants in THA. Our Ag-HA-coated implants markedly improved patients' activities of daily living without causing any adverse reactions attributable to silver in the human body. Ag-HA is expected to reduce postoperative infections and prevent decreased quality of life in patients undergoing prosthetic arthroplasty, thus leading to more favorable outcomes.

Reducing bone cancer cell functions using selenium nanocomposites

Cancer recurrence at the site of tumor resection remains a major threat to patient survival despite modern cancer therapeutic advances. Osteosarcoma, in particular, is a very aggressive primary bone cancer that commonly recurs after surgical resection, radiation, and chemotherapeutic treatment. The objective of the present in vitro study was to develop a material that could decrease bone cancer cell recurrence while promoting healthy bone cell functions. Selenium is a natural part of our diet which has shown promise for reducing cancer cell functions, inhibiting bacteria, and promoting healthy cells functions, yet, it has not been widely explored for osteosarcoma applications. For this purpose, due to their increased surface area, selenium nanoparticles (SeNP) were precipitated on a very common orthopedic tissue engineering material, poly-l-lactic acid (or PLLA). Selenium-coated PLLA materials were shown to selectively decrease long-term osteosarcoma cell density while promoting healthy, noncancerous, osteoblast functions (for example, up to two times more alkaline phosphatase activity on selenium coated compared to osteoblasts grown on typical tissue culture plates), suggesting they should be further studied for replacing tumorous bone tissue with healthy bone tissue. Importantly, results of this study were achieved without the use of chemotherapeutics or pharmaceutical agents, which have negative side effects.

Cytotoxicity and apoptosis induced by silver nanoparticles in human liver HepG2 cells in different dispersion media

Silver nanoparticles (Ag NPs) have been widely used in medical and healthcare products owing to their unique antibacterial activities. However, their safety for humans and the environment has not yet been established. This study evaluated the cellular proliferation and apoptosis of Ag NPs suspended in different solvents using human liver HepG2 cells. The ionization of Ag NPs in different dispersion media [deionized water, phosphate-buffered saline (PBS), saline and cell culture] was measured using an Ag ion selective electrode. The MTT assay was used to examine the cell proliferation activities. The effects of Ag NPs on cell cycle, induction of apoptosis, production of reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) were analyzed using flow cytometry. The degree of Ag NPs ionization differed with dispersion media, with the concentrations of silver ions in deionized water being the highest in all suspensions. Ag NPs could inhibit the viability of HepG2 cells in a time- and concentration-dependent manner. Ag NPs (40, 80 and 160 µg ml(-1)) exposure could cause cell-cycle arrest in the G2/M phase, significantly increasing the apoptosis rate and ROS generation, and decreasing the MMP in HepG2 cells more sensitive to deionized water than in cell culture. These results suggested that the cellular toxicological mechanism of Ag NPs might be related to the oxidative stress of cells by the generation of ROS, leading to mitochondria injury and induction of apoptosis. It also implies that it is important to assess the physicochemical properties of NPs in the media where the biological toxicity tests are performed.

Evaluation of osseous integration of PVD-silver-coated hip prostheses in a canine model

Infection associated with biomaterials used for orthopedic prostheses remains a serious complication in orthopedics, especially tumor surgery. Silver-coating of orthopedic (mega)prostheses proved its efficiency in reducing infections but has been limited to surface areas exposed to soft tissues due to concerns of silver inhibiting osseous integration of cementless stems. To close this gap in the bactericidal capacity of silver-coated orthopedic prostheses extension of the silver-coating on surface areas intended for osseous integration seems to be inevitable. Our study reports about a PVD- (physical-vapor-deposition-) silver-coated cementless stem in a canine model for the first time and showed osseous integration of a silver-coated titanium surface in vivo. Radiological, histological, and biomechanical analysis revealed a stable osseous integration of four of nine stems implanted. Silver trace elemental concentrations in serum did not exceed 1.82 parts per billion (ppb) and can be considered as nontoxic. Changes in liver and kidney functions associated with the silver-coating could be excluded by blood chemistry analysis. This was in accordance with very limited metal displacement from coated surfaces observed by laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) 12 months after implantation. In conclusion our results represent a step towards complete bactericidal silver-coating of orthopedic prostheses.

Osseointegration of titanium with an antimicrobial nanostructured noble metal coating

Nanometer scale surface features on implants and prostheses can potentially be used to enhance osseointegration and may also add further functionalities, such as infection resistance, to the implant. In this study, a nanostructured noble metal coating consisting of palladium, gold and silver, never previously used in bone applications, was applied to machined titanium screws to evaluate osseointegration after 6 and 12 weeks in rabbit tibiae and femurs. Infection resistance was confirmed by in vitro adhesion test. A qualitatively and quantitatively similar in vivo bone response was observed for the coated and uncoated control screws, using histology, histomorphometry and electron microscopy. The bone-implant interface analysis revealed an extensive bone formation and direct bone-implant contact. These results demonstrate that the nanostructured noble metal coating with antimicrobial properties promotes osseointegration and may therefore be used to add extra implant functionality in the form of increased resistance to infection without the use of antibiotics.

FROM THE CLINICAL EDITOR

The authors of this paper demonstrate that nanostructured noble metal coating of implants and prostheses used in orthopedic procedures promotes osseointegration and may be used to add extra implant functionality in the form of increased resistance to infection without the use of antibiotics.

Biological responses of silver-coated thermosets: an in vitro and in vivo study

Bisphenol A glycidylmethacrylate (BisGMA)/triethyleneglycol dimethacrylate (TEGDMA) thermosets are biomaterials commonly employed for orthopedic and dental applications; for both these fields, bacterial adhesion to the surface of the implant represents a major issue for the outcome of the surgical procedures. In this study, the antimicrobial properties of a nanocomposite coating formed by polysaccharide 1-deoxylactit-1-yl chitosan (Chitlac) and silver nanoparticles (nAg) on methacrylate thermosets were studied. The Chitlac-nAg system showed good anti-bacterial and anti-biofilm activity although its biocidal properties can be moderately, albeit significantly, inhibited by serum proteins. In vitro studies on the silver release kinetic in physiological conditions showed a steady metal release associated with a gradual loss of antimicrobial activity. However, after 3weeks there was still effective protection against bacterial colonization which could be accounted for by the residual silver. This time-span could be considered adequate to confer short-term protection from early peri-implant infections. Preliminary in vivo tests in a mini-pig animal model showed good biological compatibility of Chitlac-nAg-coated materials when implanted in bony tissue. The comparison was made with implants of titanium Ti6Al4V alloy and with a Chitlac-coated thermoset. Bone healing patterns and biocompatibility parameters observed for nAg-treated material were comparable with those observed for control implants.

Osteoconductivity of thermal-sprayed silver-containing hydroxyapatite coating in the rat tibia

A silver-containing hydroxyapatite (Ag-HA) coating has been developed using thermal spraying technology. We evaluated the osteoconductivity of this coating on titanium (Ti) implants in rat tibiae in relation to bacterial infection in joint replacement.

At 12 weeks, the mean affinity indices of bone formation of a Ti, an HA, a 3%Ag-HA and a 50%Ag-HA coating were 97.3%, 84.9%, 81.0% and 40.5%, respectively. The mean affinity indices of bone contact of these four coatings were 18.8%, 83.7%, 77.2% and 40.5%, respectively. The indices of bone formation and bone contact around the implant of the 3%Ag-HA coating were similar to those of the HA coating, and no significant differences were found between them (bone formation, p = 0.99; bone contact, p = 0.957). However, inhibition of bone formation was observed with the 50%Ag-HA coating.

These results indicate that the 3%Ag-HA coating has low toxicity and good osteoconductivity, and that the effect of silver toxicity on osteoconductivity depends on the dose.

Osteoblast adhesion to functionally graded hydroxyapatite coatings doped with silver

Silver-doped functionally graded hydroxyapatite (Ag-FGHA) coatings have been prepared on glass and titanium substrates by ion beam assisted deposition (IBAD) method with in situ heat treatment, and the biological response and dissolution properties of the coatings have been examined. Three Ag-FGHA coatings with different percentages of silver (1, 3, and 6.6 wt % Ag) were compared with pure FGHA (without Ag) as a control. MC 3T3-E1 murine osteoblast cells were cultured on FGHA and Ag-FGHA coating surfaces, and the number of adhered cells after 1, 4, and 7 days was counted. Micromanipulation of live single cells was performed to quantitatively compare cell affinity among the four coating compositions. Results showed that FGHA-Ag1 coating (with 1 wt % Ag) had the highest number of adhered cells after each incubation period, as well as the highest cell affinity after 24-h incubation. Surface profilometry was performed to determine surface roughness average (R(a) ) of coating surfaces before and after immersion in high-purity water, showing that all surfaces initially had roughness averages below 200 nm, while after immersion, roughness average of FGHA-Ag1 surface was significantly increased (R(a) = 404 +/- 100.8 nm), attributed to the highest rate of dissolution. Release rate of Ag+ ions in solution was measured, showing release rates of silver ions for all Ag-doped coatings were initially high and then gradually decreased to a minimum over time, which is the expected dissolution of functionally graded coatings. It is concluded that FGHA-Ag1 coating promoted the highest degree of osteoblast adhesion because of optimal dissolution rate and nontoxic Ag percentage.

Densification, phase stability and in vitro biocompatibility property of hydroxyapatite-10 wt% silver composites

In this paper, we demonstrate how a simple fabrication route, i.e., pressureless sintering of mechanically mixed powders can be employed to develop hydroxyapatite (HAp, Ca(10)(PO(4))(6)(OH)(2))-silver (Ag) bioceramic composites with superior combination of physical (hardness, toughness), non-cytotoxicity, cytocompatiblity and anti-microbial property. The densification results show that such composites can be sintered at 1200 degrees C for 2 h near to theoretical density (>98% rho(th).) An important observation is that the dissociation of HAp phase can be prevented during sintering up to 1300 degrees C for 2 h in HAp-10 wt% Ag composites. The stability of HAp in presence of silver is discussed in reference to the results obtained using XRD, FTIR and Raman spectroscopy. The hardness values of the composites are comparable (approximately 6.5 GPa) to that of pure HAp, despite of the presence of softer Ag particles. The sintered composites exhibit modest crack growth resistance property and their toughness varies in the range of 0.9-1.2 MPa m(0.5), depending on sintering temperature. For selected samples, the in vitro characterization was performed using mouse fibroblast (L929) and human osteosarcoma (MG63) cell lines. The combination of biochemical assays (MTT, ALP and osteocalcin) confirm that HAp-10 wt% Ag biocomposites have comparable or even better cellular viability, osteogenic differentiation and bone mineralization as well as osteoinduction property. Antibacterial experiments involving gram-negative bacteria, Escherichia coli confirm excellent bactericidal property of HAp-10 wt% Ag composites, sintered using mechanically mixed powders.

The apoptotic effect of nanosilver is mediated by a ROS- and JNK-dependent mechanism involving the mitochondrial pathway in NIH3T3 cells

Nanomaterials and nanoparticles have received considerable attention recently because of their unique properties and diverse biotechnology and life sciences applications. Nanosilver products, which have well-known antimicrobial properties, have been used extensively in a range of medical settings. Despite the widespread use of nanosilver products, relatively few studies have been undertaken to determine the biological effects of nanosilver exposure. The purpose of this study was to evaluate the toxicity of nanosilver and to elucidate possible molecular mechanisms underlying the biological effects of nanosilver. Here, we show that nanosilver is cytotoxic, inducing apoptosis in NIH3T3 fibroblast cells. Treatment with nanosilver induced the release of cytochrome c into the cytosol and translocation of Bax to mitochondria, indicating that nanosilver-mediated apoptosis is mitochondria-dependent. Nanosilver-induced apoptosis was associated with the generation of reactive oxygen species (ROS) and JNK activation, and inhibition of either ROS or JNK attenuated nanosilver-induced apoptosis. In nanosilver-resistant HCT116 cells, up-regulation of the anti-apoptotic proteins, Bcl-2 appeared to be associated with a diminished apoptotic response. Taken together, our results provide the first evidence for a molecular mechanism of nanosilver cytotoxicity, showing that nanosilver acts through ROS and JNK to induce apoptosis via the mitochondrial pathway.

Divergent effects of orthosilicic acid and dimethylsilanediol on cell survival and adhesion in human osteoblast-like cells

Although dietary silicon (Si) is recognized to be an important factor for the growth and development of bone and connective tissue, its biochemical role has yet to be identified. The predominant Si-containing species in blood and other biofluids is orthosilicic acid, Si(OH)(4). Dimethylsilanediol, (CH(3))(2)Si(OH)(2), is an environmental contaminant that results from decomposition of silicone compounds used in personal hygiene, health care and industrial products. We examined the in vitro effects of both Si species on the survival (colony forming efficiency), proliferation (DNA content), differentiation (alkaline phosphatase activity) and adhesion (relative protein content) of the human osteoblast-like cell lines Saos-2 and hFOB 1.19. Orthosilicic acid yielded a small, dose-dependent decrease in Saos-2 cell survivability up to its 1,700 micromol/L solubility limit, by which point survival was 20% less than that of untreated cells. This negative association, although small, correlated with a reduction in the proliferation and adhesion of Saos-2 cells as well as of hFOB 1.19 and osteoclast-like GCT cells. By contrast, dimethylsilanediol treatment had no discernable influence on Saos-2 survivability at concentrations up to 50 micromol/L, and yet significantly enhanced cell survival at higher doses. Moreover, dimethylsilanediol did not affect proliferation or adhesion of any cell line. The findings show that orthosilicic acid and dimethylsilanediol affect osteoblast-like cells very differently, providing insight into the mechanism by which silicon influences bone health, although the specific site of Si activity remains unknown. There was no evidence to suggest that dimethylsilanediol is cytotoxic at environmental/physiological concentrations.