In vitro anti-bacterial and biological properties of magnetron co-sputtered silver-containing hydroxyapatite coating

Magnesium Doped Hydroxyapatite-Based Coatings Obtained by Pulsed Galvanostatic Electrochemical Deposition with Adjustable Electrochemical Behavior

The aim of this study was to adapt the electrochemical behavior in synthetic body fluid (SBF) of hydroxyapatite-based coatings obtained by pulsed galvanostatic electrochemical deposition through addition of Mg in different concentrations. The coatings were obtained by electrochemical deposition in a typical three electrodes electrochemical cell in galvanic pulsed mode. The electrolyte was obtained by subsequently dissolving Ca(NO3)2·4H2O, NH4H2PO4, and Mg(NO3)2·6H2O in ultra-pure water and the pH value was set to 5. The morphology consists of elongated and thin ribbon-like crystals for hydroxyapatite (HAp), which after the addition of Mg became a little wider. The elemental and phase composition evidenced that HAp was successfully doped with Mg through pulsed galvanostatic electrochemical deposition. The characteristics and properties of hydroxyapatite obtained electrochemically can be controlled by adding Mg in different concentrations, thus being able to obtain materials with different properties and characteristics. In addition, the addition of Mg can lead to the control of hydroxyapatite bioactive ceramics in terms of dissolution rate.

Biomaterials against Bone Infection

Chronic bone infection is considered as one of the most problematic biofilm-related infections. Its recurrent and resistant nature, high morbidity, prolonged hospitalization, and costly medical care expenses have driven the efforts of the scientific community to develop new therapies to improve the standards used today. There is great debate on the management of this kind of infection in order to establish consistent and agreed guidelines in national health systems. The scientific research is oriented toward the design of anti-infective biomaterials both for prevention and cure. The properties of these materials must be adapted to achieve better anti-infective performance and good compatibility, which allow a good integration of the implant with the surrounding tissue. The objective of this review is to study in-depth the antibacterial biomaterials and the strategies underlying them. In this sense, this manuscript focuses on antimicrobial coatings, including the new technological advances on surface modification; scaffolding design including multifunctional scaffolds with both antimicrobial and bone regeneration properties; and nanocarriers based on mesoporous silica nanoparticles with advanced properties (targeting and stimuli-response capabilities).

Crestal bone loss due to abutment manipulation and an internal silver deposition implant design in a canine model

OBJECTIVE

The study aimed to evaluate the effect of internal silver coating as a countermeasure to crestal bone loss around implants with or without multiple abutment disconnections/reconnections.

MATERIALS AND METHODS

Following tooth extraction, 48 implants with connected healing abutments (24 implants internally coated with elemental silver) were placed in the mandible of eight beagle dogs. Two months after implant surgery one side of the mandible was randomly assigned to four abutment manipulations (disconnection/reconnection) on a weekly basis. At 4 months postoperative, biopsies were obtained and prepared for histomorphometric analysis.

RESULTS

Healing abutment manipulation increased crestal bone remodeling when compared to no abutment manipulation (1.28 mm versus 0.92 mm, respectively), although the difference was not statistically significant (p = 0.0836). Overall, an internal silver coating did not provide a statistically sufficient implant treatment characteristic as a countermeasure to crestal bone loss (p = 0.7801).

CONCLUSIONS

These findings indicate that the controlled variables explored here (abutment manipulation/internal silver coating) have a limited effect on initial crestal bone loss.

CLINICAL RELEVANCE

Abutment manipulation during prosthetic work does not seem to harm the peri-implant soft and hard tissues.

Biological and antibacterial properties of TiO2 coatings containing Ca/P/Ag by one-step and two-step methods

The porous TiO₂ coatings containing Ca/P/Ag were separately prepared on titanium (Ti) surface by one-step (micro-arc oxidation) and two-step methods (micro-arc oxidation and cathodic deposition), and then their surface morphology, composition, biological and antibacterial properties were compared. The results showed that the porous coatings containing Ca/P/Ag achieved by different methods showed similar surface morphology and elemental composition, however, by one-step method, silver existed in the coating as silver phosphate, while in the coatings prepared by two-step method, silver existed as metallic silver. Although both coatings showed excellent antibacterial property (the antimicrobial rate is over 99.9%), the surface coating prepared by one-step method had a more suitable release curve of Ag. In addition, the surface coating prepared by one-step method also presented better biological property, which was due to its enhanced surface roughness and hydrophilicity. Combining with its easy operation and long-term antibacterial property, its prospect for clinical application is more promising.

Substituted hydroxyapatite coatings of bone implants

Surface modification of orthopedic and dental implants has been demonstrated to be an effective strategy to accelerate bone healing at early implantation times. Among the different alternatives, coating implants with a layer of hydroxyapatite (HAp) is one of the most used techniques, due to its excellent biocompatibility and osteoconductive behavior. The composition and crystalline structure of HAp allow for numerous ionic substitutions that provide added value, such as antibiotic properties or osteoinduction. In this article, we will review and critically analyze the most important advances in the field of substituted hydroxyapatite coatings. In recent years substituted HAp coatings have been deposited not only on orthopedic prostheses and dental implants, but also on macroporous scaffolds, thus expanding their applications towards bone regeneration therapies. Besides, the capability of substituted HAps to immobilize proteins and growth factors by non-covalent interactions has opened new possibilities for preparing hybrid coatings that foster bone healing processes. Finally, the most important in vivo outcomes will be discussed to understand the prospects of substituted HAp coatings from a clinical point of view.

Production of High Silicon-Doped Hydroxyapatite Thin Film Coatings via Magnetron Sputtering: Deposition, Characterisation, and In Vitro Biocompatibility

In recent years, it has been found that small weight percent additions of silicon to HA can be used to enhance the initial response between bone tissue and HA. A large amount of research has been concerned with bulk materials, however, only recently has the attention moved to the use of these doped materials as coatings. This paper focusses on the development of a co-RF and pulsed DC magnetron sputtering methodology to produce a high percentage Si containing HA (SiHA) thin films (from 1.8 to 13.4 wt.%; one of the highest recorded in the literature to date). As deposited thin films were found to be amorphous, but crystallised at different annealing temperatures employed, dependent on silicon content, which also lowered surface energy profiles destabilising the films. X-ray photoelectron spectroscopy (XPS) was used to explore the structure of silicon within the films which were found to be in a polymeric (SiO2; Q4) state. However, after annealing, the films transformed to a SiO44−, Q0, state, indicating that silicon had substituted into the HA lattice at higher concentrations than previously reported. A loss of hydroxyl groups and the maintenance of a single-phase HA crystal structure further provided evidence for silicon substitution. Furthermore, a human osteoblast cell (HOB) model was used to explore the in vitro cellular response. The cells appeared to prefer the HA surfaces compared to SiHA surfaces, which was thought to be due to the higher solubility of SiHA surfaces inhibiting protein mediated cell attachment. The extent of this effect was found to be dependent on film crystallinity and silicon content.

Microstructure, mechanical properties, and degradation of Mg-Ag alloy after equal-channel angular pressing

Enhancing the strength of Mg-based biodegradable alloys without decreasing their corrosion resistance is a major engineering challenge. In addition, the growing demand for effective reduction of infections and inflammation after implant placement motivates the design of alloys with appropriate compositions or coatings. One promising alloying element is silver, whose antibacterial effect has long been known. Therefore, a Mg-4% Ag alloy was selected for this study. The alloy was investigated under three conditions: as-cast, after T4 treatment, and after T4 treatment with subsequent equal-channel angular pressing (ECAP) using a newly developed double-ECAP die, which offers an equivalent strain per pass of 1.6. The first pass through the double-ECAP die was conducted at 370 °C and the second at 330 °C using route B_C. The microstructure of the as-cast Mg-4% Ag consisted of large grains (several hundred microns) and a dendritic structure with micron-sized Mg₅₄Ag₁₇ precipitates. T4 heat treatment caused dissolution of the dendrites and formation of a solid solution without changing the grain size. Consequently, the ultimate compressive strength (UCS) was increased by approximately 30%, and the compressive strain at fracture reached approximately 23%. The compressive yield strength (CYS) remained nearly constant at approximately 30 MPa. Subsequent ECAP led to strong grain refinement (from 350 μm to 38 μm after one pass and 15 μm after two passes) and further increases in the CYS and UCS, to 45 and 300 MPa after the first pass and 62 and 325 MPa after the second pass, respectively. The as-cast alloy exhibited a very high degradation rate in a simulated body fluid at approximately 36 °C. The degradation rate of the alloy after T4 treatment was much lower. Subsequent ECAP had no significant effect on the degradation properties. Thus, it can be concluded that grain refinement has little effect on the degradation rate.

Approaches based on passive and active antibacterial coating on titanium to achieve antibacterial activity

Titanium (Ti) and its alloys are widely applied as orthopedic implants for hip and knee prosthesis, fixation, and dental implants. However, Ti and its alloys are bioinert and susceptible to bacteria and biofilm formation. Strategies for improving the antibacterial properties of Ti can be divided into two approaches, namely, passive coating and active coating on the Ti surface. Passive coating on Ti mainly kills the bacteria in contact but does not kill plankton or bacteria dwell in the bone tissue around the Ti implant. Active coating mainly involves the release of antibacterial agents to kill the bacteria, but this may result in the development of bacterial resistance. Both strategies include advantages and disadvantages. This article reviews the current and potential future approaches for improving antibacterial activity on Ti. We mainly focus on current approaches for fabricating antibacterial Ti and its limitations and countermeasures, and provide direction for further studies of biofunctionalization of Ti with antibacterial properties. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2531-2539, 2018.

Properties of silver contained coatings on CoCr alloys prepared by vacuum plasma spraying

The silver contained coatings on cast Cobalt Chrome (CoCr) alloys were prepared by vacuum plasma spraying technique. The Scanning Electron Microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), energy dispersive spectrometry (EDS), properties of corrosion resistance, wear resistance and effect of vitro antibacterial on the surface of silver contained coating were investigated. The cytotoxicity of the coatings was performed with L-929 fibroblasts by MTT assay. SEM showed that the surfaces of the coatings were dense, smooth, no obvious cracks except only a few pores. XRD analysis indicated that the contents of the surface were mainly Ag and Cr except a small amount of Ag₂O, Cr₂O₃. EDS analysis indicated that the distributions of Cr and Ag were uniform without any large-scale clustering. The wear resistance of silver coatings is similar to that of CoCr alloys, and the corrosion resistance is slightly better than that of CoCr alloys. The Ag coating had no significant effect on the proliferation of L929 cells. The antibacterial results indicated that the number of S. mutans and C. albicans were significantly reduced on the surface of silver contained coating than that of CoCr alloys. All the results indicated that the silver contained coatings can be achieved by vacuum plasma spraying technique with good surface characteristic and antibacterial properties and have promising applications in biomedical area.

High Bactericidal Self-Assembled Nano-Monolayer of Silver Sulfadiazine on Hydroxylated Material Surfaces

Anti-infective surfaces are a modern strategy to address the issue of infection related to the clinical use of materials for implants and medical devices. Nanocoatings, with their high surface/mass ratio, lend themselves to being mono-layered on the material surfaces to release antibacterial molecules and prevent bacterial adhesion. Here, a “layer-by-layer” (LbL) approach to achieve a self-assembled monolayer (SAM) with high microbicidal effect on hydroxylated surfaces is presented, exploiting the reaction between a monolayer of thiolic functions on glass/quartz surfaces and a newly synthesized derivative of the well-known antibacterial compound silver sulfadiazine. Using several different techniques, it is demonstrated that a nano-monolayer of silver sulfadiazine is formed on the surfaces. The surface-functionalized materials showed efficient bactericidal effect against both Gram-positive and Gram-negative bacteria. Interestingly, bactericidal self-assembled nano-monolayers of silver sulfadiazine could be achieved on a large variety of materials by simply pre-depositing glass-like SiO₂ films on their surfaces.

Effects of Aloe Vera Gel Extract in Doped Hydroxyapatite-Coated Titanium Implants on in Vivo and in Vitro Biological Properties

Hydroxyapatite-coated titanium alloys have been a popular choice as bone implants for load-bearing applications for the compositional similarity of hydroxyapatite to natural bone. The limited osteoinductive properties exhibited by the hydroxyapatite (HA) coatings have led to the incorporation of growth factor or dopants for improved osseointegration. This study aims to investigate the effects of a naturally occurring aloe vera gel extract, acemannan, in doped hydroxyapatite coatings on the in vitro osteoblast cell viability and in vivo new bone formation in a rat distal femur model. Silver oxide and silica-doped hydroxyapatite coatings were developed by the induction plasma spray coating method on Ti alloys to introduce antibacterial properties along with induction of angiogenic properties, respectively. The doped coating was further consecutively dip coated with acemannan to analyze its effects on the in vivo early stage osseointegration and chitosan to control the burst release of the acemannan from the calcium phosphate matrix. The results show controlled release of acemannan from the chitosan coatings, with enhanced osteoblast cell viability by the incorporation of acemannan in vitro. Improved osseointegration with a seamless implant interface and improved new bone formation was noted by the acemannan and chitosan coating in vivo, 5 weeks after implantation. Our results demonstrate the efficacy of a combination of natural medicine and naturally occurring polymer in a doped hydroxyapatite-coated titanium implant on the bone tissue regeneration for load-bearing orthopedic applications.

Enhancement effect on antibacterial property of gray titania coating by plasma-sprayed hydroxyapatite-amino acid complexes during irradiation with visible light

The aim of this study was to reveal the mechanism of enhancement of antibacterial properties of gray titania by plasma-sprayed hydroxyapatite (HAp)-amino acid fluorescent complexes under irradiation with visible light. Although visible-light-sensitive photocatalysts are applied safely to oral cavities, their efficacy is not high because of the low energy of irradiating light. This study proposed a composite coating containing HAp and gray titania. HAp itself functioned as bacteria catchers and gray titania released antibacterial radicals by visible-light irradiation. HAp-amino acid fluorescent complexes were formed on the surface of the composite coating in order to increase light intensity to gray titania by fluorescence, based on an idea bioinspired by deep-sea fluorescent coral reefs. A cytotoxicity assay on murine osteoblastlike cells revealed that biocompatibility of the HAp-amino acid fluorescent complexes was identical with the that of HAp. Antibacterial assays involving Escherichia coli showed that the three types of HAp-amino acid fluorescent complexes and irradiation with three types of light-emitting diodes (blue, green, and red) significantly decreased colony-forming units. Furthermore, kelvin probe force microscopy revealed that the HAp-amino acid fluorescent complexes preserved the surface potentials even after irradiation with visible light, whereas those of HAp were significantly decreased by the irradiation. Such a preservative effect of the HAp-amino acid fluorescent complexes maintained the bacterial-adhesion performance of HAp and consequently enhanced the antibacterial action of gray titania.

Bioinspired surface modification of orthopedic implants for bone tissue engineering

Biomedical implants have been widely used in various orthopedic treatments, including total hip arthroplasty, joint arthrodesis, fracture fixation, non-union, dental repair, etc. The modern research and development of orthopedic implants have gradually shifted from traditional mechanical support to a bioactive graft in order to endow them with better osteoinduction and osteoconduction. Inspired by structural and mechanical properties of natural bone, this review provides a panorama of current biological surface modifications for facilitating the interaction between medical implants and bone tissue and gives a future outlook for fabricating the next-generation multifunctional and smart implants by systematically biomimicking the physiological processes involved in formation and functioning of bones.

Evolving concepts in bone infection: redefining "biofilm", "acute vs. chronic osteomyelitis", "the immune proteome" and "local antibiotic therapy"

Osteomyelitis is a devastating disease caused by microbial infection of bone. While the frequency of infection following elective orthopedic surgery is low, rates of reinfection are disturbingly high. Staphylococcus aureus is responsible for the majority of chronic osteomyelitis cases and is often considered to be incurable due to bacterial persistence deep within bone. Unfortunately, there is no consensus on clinical classifications of osteomyelitis and the ensuing treatment algorithm. Given the high patient morbidity, mortality, and economic burden caused by osteomyelitis, it is important to elucidate mechanisms of bone infection to inform novel strategies for prevention and curative treatment. Recent discoveries in this field have identified three distinct reservoirs of bacterial biofilm including: Staphylococcal abscess communities in the local soft tissue and bone marrow, glycocalyx formation on implant hardware and necrotic tissue, and colonization of the osteocyte-lacuno canalicular network (OLCN) of cortical bone. In contrast, S. aureus intracellular persistence in bone cells has not been substantiated in vivo, which challenges this mode of chronic osteomyelitis. There have also been major advances in our understanding of the immune proteome against S. aureus, from clinical studies of serum antibodies and media enriched for newly synthesized antibodies (MENSA), which may provide new opportunities for osteomyelitis diagnosis, prognosis, and vaccine development. Finally, novel therapies such as antimicrobial implant coatings and antibiotic impregnated 3D-printed scaffolds represent promising strategies for preventing and managing this devastating disease. Here, we review these recent advances and highlight translational opportunities towards a cure.

Silver Doping Mechanism in Bioceramics—From Ag+: Doped HAp to Ag°/BCP Nanocomposite

The results presented in this paper, based on the powder X-ray diffraction technique followed by Rietveld analyses, are devoted to the mechanism of silver incorporation in biphasic calcium phosphates. Results were confirmed by SEM observation. Samples were synthesized via the sol-gel route, followed by heat treatments. Two incorporation sites were highlighted: Ca2+ replacement by Ag+ into the calcium phosphates (HAp: hydroxyapatite and β-TCP: tricalcium phosphate), and the other as metallic silver Ag° nanoparticles (formed by autogenous reduction). The samples obtained were thus nanocomposites, written Ag°/BCP, composed of closely-mixed Ag° particles of about 100 nm at 400 °C (which became micrometric upon heating) and calcium phosphates, themselves substituted by Ag+ cations. Between 400 °C and 700 °C the cationic silver part was mainly located in the HAp phase of the composition Ca10-xAgx(PO4)6(OH)2-x (written Ag+: HAp). From 600 °C silver cations migrated to β-TCP to form the definite compound Ca10Ag(PO4)7 (written Ag+: TCP). Due to the melting point of Ag°, the doping element completely left our sample at temperatures above 1000 °C. In order to correctly understand the biological behavior of such material, which is potentially interesting for biomaterial applications, its complex doping mechanism should be taken into consideration for subsequent cytotoxic and bacteriologic studies.

Ion-substituted calcium phosphate coatings by physical vapor deposition magnetron sputtering for biomedical applications: A review

Coatings based on ion-substituted calcium phosphate (Ca-P) have attracted great attention in the scientific community over the past decade for the development of biomedical applications. Among such Ca-P based structures, hydroxyapatite (HA) has shown significant influence on cell behaviors including cell proliferation, adhesion, and differentiation. These cell behaviors determine the osseointegration between the implant and host bone and the biocompatibility of implants. This review presents a critical analysis on the physical vapor deposition magnetron sputtering (PVDMS) technique that has been used for ion-substituted Ca-P based coatings on implants materials. The effect of PVDMS processing parameters such as discharge power, bias voltage, deposition time, substrate temperature, and post-heat treatment on the surface properties of ion-substituted Ca-P coatings is elucidated. Moreover, the advantages, short comings and future research directions of Ca-P coatings by PVDMS have been comprehensively analyzed. It is revealed that the topography and surface chemistry of amorphous HA coatings influence the cell behavior, and ion-substituted HA coatings significantly increase cell attachment but may result in a cytotoxic effect that reduces the growth of the cells attached to the coating surface areas. Meanwhile, low-crystalline HA coatings exhibit lower rates of osteogenic cell proliferation as compared to highly crystalline HA coatings developed on Ti based surfaces. PVDMS allows a close reproduction of bioapatite characteristics with high adhesion strength and substitution of therapeutic ions. It can also be used for processing nanostructured Ca-P coatings on polymeric biomaterials and biodegradable metals and alloys with enhanced corrosion resistance and biocompatibility. STATEMENT OF SIGNIFICANCE: Recent studies have utilized the physical vapor deposition magnetron sputtering (PVDMS) for the deposition of Ca-P and ion-substituted Ca-P thin film coatings on orthopedic and dental implants. This review explains the effect of PVDMS processing parameters, such as discharge power, bias voltage, deposition time, substrate temperature, and post-heat treatment, on the surface morphology and crystal structure of ion-substituted Ca-P and ion-substituted Ca-P thin coatings. It is revealed that coating thickness, surface morphology and crystal structure of ion-substituted Ca-P coatings via PVDMS directly affect the biocompatibility and cell responses of such structures. The cell responses determine the osseointegration between the implant and host bone and eventually the success of the implants.

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.

Multifunctional Coatings and Nanotopographies: Toward Cell Instructive and Antibacterial Implants

In biomaterials science, it is nowadays well accepted that improving the biointegration of dental and orthopedic implants with surrounding tissues is a major goal. However, implant surfaces that support osteointegration may also favor colonization of bacterial cells. Infection of biomaterials and subsequent biofilm formation can have devastating effects and reduce patient quality of life, representing an emerging concern in healthcare. Conversely, efforts toward inhibiting bacterial colonization may impair biomaterial-tissue integration. Therefore, to improve the long-term success of medical implants, biomaterial surfaces should ideally discourage the attachment of bacteria without affecting eukaryotic cell functions. However, most current strategies seldom investigate a combined goal. This work reviews recent strategies of surface modification to simultaneously address implant biointegration while mitigating bacterial infections. To this end, two emerging solutions are considered, multifunctional chemical coatings and nanotopographical features.

Recent updates for biomaterials used in total hip arthroplasty

Background

Total hip arthroplasty (THA) is probably one of the most successful surgical interventions performed in medicine. Through the revolution of hip arthroplasty by principles of low friction arthroplasty was introduced by Sir John Charnley in 1960s. Thereafter, new bearing materials, fixation methods, and new designs has been improved. The main concern regarding failure of THA has been the biological response to particulate polyethylene debris generated by conventional metal on polyethylene bearing surfaces leading to osteolysis and aseptic loosening of the prosthesis. To resolve these problems, the materials of the modern THA were developed since then.

Methods

A literature search strategy was conducted using various search terms in PUBMED. The highest quality articles that met the inclusion criteria and best answered the topics of focus of this review were selected. Key search terms included ‘total hip arthroplasty’, ‘biomaterials’, ‘stainless steel’, ‘cobalt-chromium’, ‘titanium’, ‘polyethylene’, and ‘ceramic’.

Results

The initial search retrieved 6921 articles. Thirty-two articles were selected and used in the review.

Conclusion

This article introduces biomaterials used in THA and discusses various bearing materials in currentclinical use in THA as well as the newer biomaterials which may even further decrease wear and improve THA survivorship.

TC4/Ag Metal Matrix Nanocomposites Modified by Friction Stir Processing: Surface Characterization, Antibacterial Property, and Cytotoxicity in Vitro

Numerous antibacterial biomaterials have been developed, but a majority of them suffer from poor biocompatibility. With the purpose of reducing biomaterial-related infection and cytotoxicity, friction stir processing (FSP) was employed to embed silver nanoparticles (Ag NPs) in a Ti-6Al-4V (TC4) substrate. Characterization using scanning electron microscopy, transmission electron microscopy, and three-dimensional atom probe tomography illustrates that NPs are distributed more homogeneously on the surface of TC4 as the groove depth increases, and silver-rich NPs with a size from 10 to 20 nm exist as metallic silver diffused into the substrate, where the silver content is 4.3-5.6%. Electrochemical impedance spectroscopy shows that both FSP and the addition of silver have positive effects on corrosion resistance. The modified samples effectively inhibit both Staphylococcus aureus and Escherichia coli strains and slightly reduce their adhesion while not displaying any cytotoxicity to bone mesenchymal stem cells in vitro. The antibacterial effect is independent of Ag-ion release and is likely due to the number of embedded silver NPs on the surface, which directly contact and subsequently destroy the cell membrane. Our study shows that the TC4/Ag metal matrix nanocomposite is a potential infection-related biomaterial and that embedding Ag NPs tightly on a biomaterial surface is an effective strategy for striking a balance between the antibacterial effect and biocompatibility, providing an innovative approach for accurately controlling the cytotoxicity of infection-related biomaterials.

Remineralisation of enamel with silver diamine fluoride and sodium fluoride

OBJECTIVE

To evaluate the remineralising effect of the adjunctive application of 38% silver diamine fluoride (SDF) solution and 5% sodium fluoride (NaF) varnish on artificial enamel caries lesions.

METHODS

Forty-eight demineralised enamel specimens were allocated into four groups. Group 1 received 38% SDF and 5% NaF; Group 2 received 38% SDF; Group 3 received 5% NaF; and Group 4 received deionized water. After pH cycling, the surface morphology and fluoride content of the specimens were studied via scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS). The lesion depth and crystal characteristics were assessed using micro-computed tomography and X-ray diffraction (XRD) respectively. The crystallization reaction was performed by incubating hydroxyapatite powder with NaF or SDF for 48h. The precipitates were studied via transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).

RESULTS

SEM demonstrated the destruction of the enamel surface in Group 4. EDS revealed that the mean fluoride weight percentage of Groups 1-4 were 1.28±0.15, 1.33±0.19, 1.03±0.09 and 0.87±0.04 respectively. The mean lesion depths of Groups 1-4 were 129±14μm, 131±16μm, 153±10μm and 181±21μm respectively. The addition of NaF to SDF did not reduce the lesion depths (p=0.779). XRD revealed that silver chloride formed as a main product in Groups 1 and 2. Meanwhile, TEM analysis indicated that silver nanoparticles were incorporated into hydroxyapatite crystal in SDF-treated hydroxyapatite. XPS spectra suggested that the chemical state of the silver was metallic.

SIGNIFICANCE

The adjunctive application of SDF and NaF varnish had a similar remineralising effect to that of SDF on enamel caries.

Cationic Substitutions in Hydroxyapatite: Current Status of the Derived Biofunctional Effects and Their In Vitro Interrogation Methods

High-performance bioceramics are required for preventing failure and prolonging the life-time of bone grafting scaffolds and osseous implants. The proper identification and development of materials with extended functionalities addressing socio-economic needs and health problems constitute important and critical steps at the heart of clinical research. Recent findings in the realm of ion-substituted hydroxyapatite (HA) could pave the road towards significant developments in biomedicine, with an emphasis on a new generation of orthopaedic and dentistry applications, since such bioceramics are able to mimic the structural, compositional and mechanical properties of the bone mineral phase. In fact, the fascinating ability of the HA crystalline lattice to allow for the substitution of calcium ions with a plethora of cationic species has been widely explored in the recent period, with consequent modifications of its physical and chemical features, as well as its functional mechanical and in vitro and in vivo biological performance. A comprehensive inventory of the progresses achieved so far is both opportune and of paramount importance, in order to not only gather and summarize information, but to also allow fellow researchers to compare with ease and filter the best solutions for the cation substitution of HA-based materials and enable the development of multi-functional biomedical designs. The review surveys preparation and synthesis methods, pinpoints all the explored cation dopants, and discloses the full application range of substituted HA. Special attention is dedicated to the antimicrobial efficiency spectrum and cytotoxic trade-off concentration values for various cell lines, highlighting new prophylactic routes for the prevention of implant failure. Importantly, the current in vitro biological tests (widely employed to unveil the biological performance of HA-based materials), and their ability to mimic the in vivo biological interactions, are also critically assessed. Future perspectives are discussed, and a series of recommendations are underlined.

State-of-the-Art, and Perspectives of, Silver/Plasma Polymer Antibacterial Nanocomposites

Urgent need for innovative and effective antibacterial coatings in different fields seems to have triggered the development of numerous strategies for the production of such materials. As shown in this short overview, plasma based techniques arouse considerable attention that is connected with the possibility to use these techniques for the production of advanced antibacterial Ag/plasma polymer coatings with tailor-made functional properties. In addition, the plasma-based deposition is believed to be well-suited for the production of novel multi-functional or stimuli-responsive antibacterial films.

A reversible fluorescent probe for monitoring Ag(I) ions

Silver-containing nanomaterials are of interest for their antibiotic properties, for a wide range of applications from medicine to consumer products. However, much remains to be learnt about the degradation of such materials and their effects on human health. While most analyses involve measurement of total silver levels, it is important also to be able to measure concentrations of active free Ag(I) ions. We report here the preparation of a coumarin-based probe, thiocoumarin silver sensor 1 (TcAg1), that responds reversibly to the addition of silver ions through the appearance of a new fluorescence emission peak at 565 nm. Importantly, this peak is not observed in the presence of Hg(II), a common interferent in Ag(I) sensing. To establish the utility of this sensor, we prepared silver-doped phosphate glasses with demonstrated bactericidal properties, and observed the Ag(I) release from these glasses in solutions of different ionic strength. TcAg1 is therefore a useful tool for the study of the environmental and medical effects of silver-containing materials.

Current perspectives regarding the application and incorporation of silver nanoparticles into dental biomaterials

INTRODUCTION

The key idea of nanotechnology is to construct and preserve functional structures by means of exploiting atoms and molecules. Nanotechnology has proven to be crucial in pharmacological medicine, tissue engineering, clinical diagnosis, long term conservation of biological tissues in a cryogenic state, protein detection, tumor destruction and magnetic resonance imaging.The aim of this paper is to review the literature on the specific characteristics of nanostructured materials, their applications and advantages that they bring to dentistry.

METHOD

We conducted an electronic scientific database research that included PubMed, Cochrane and Medline. The following keywords were used: nanotechnology, nanodentistry and silver nanoparticles. Initially 1650 original articles were retrieved from the these mentioned international databases, which were screened in detail. We included literature reviews that dealt with the comprehensive applications of nanostructured particles and silver nanoparticles in particular, in all fields of contemporary dentistry. Case reports, clinical trials, editorials and opinion letters were excluded in the first phase of our research. Fifty two articles met all the selection criteria and were ultimately selected and reviewed.

RESULTS

Nanotechnology deals with the production of various types of nanomaterials with potential applications in the field of biomedicine. Silver nanoparticles have the capacity to eliminate dental caries producing bacteria or repair teeth enamel with signs of dental decay. Nanodentistry will allow better oral health by use of nanostructured materials. Treatment opportunities that nanotechnology has to offer in contemporary dentistry include local anesthesia, permanent treatment of dental hypersensitivity, orthodontic and oral health care with nanorobotic dentifrice.

CONCLUSION

The studies that we reviewed are largely in favor of nanotechnology and nanostructured materials, highlighting their qualities and enhancements they bring to the field of dentistry. Although many of these products that benefit from silver nanoparticles properties are still expensive and exclusive, we can foresee major improvements and demand regarding dental biomaterials with nanoparticles incorporated in the near future.

Synthesizing selenium- and silver-substituted hydroxyapatite-based bone grafts and their effects on antibacterial efficiency and cell viability

Hydroxyapatite (HA)-based biografts with selenium (Se) and silver (Ag) substitutions were synthesized using the sol-gel method. The synthesized HA-based biografts at various Se and Ag quantity ratios (wt%) were characterized via Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDX). Escherichia coli (JM103) and Gram-positive Staphylococcus aureus (ATCC29293) bacteria were used for the cell viability tests by performing the MTT assay. During antibacterial tests, it was determined that the synthesized biografts showed significant antimicrobial activity on E. coli and S. aureus; however, some materials were effective on Gram-negative E. coli, but had no effect on Gram-positive S. aureus. In vitro cell viability tests revealed that some of the synthesized biografts such as H30Ag10Se15 and H40Ag20Se10 provided the highest cell viability rates compared to those in the control group.

Arresting Dentine Caries with Silver Diamine Fluoride: What’s Behind It?

Unlike other fluoride-based caries preventive agents, silver diamine fluoride (SDF) can simultaneously prevent and arrest coronal and root dentine caries. The profound clinical success of SDF has drawn many clinicians and researchers to study the mechanism of SDF in arresting dentine caries. This critical review discusses how silver and fluoride contribute to caries arrest, in terms of their effects on bacteria as well as on the mineral and organic content of dentine. Silver interacts with bacterial cell membrane and bacterial enzymes, which can inhibit bacterial growth. Silver can also dope into hydroxyapatite and have an antibacterial effect on silver-doped hydroxyapatite. Furthermore, silver is also a strong inhibitor of cathepsins and inhibits dentine collagen degradation. Early studies proposed that silver hardened caries lesions by forming silver phosphate. However, recent studies found that little silver phosphate remained on the arrested dentine lesion. The principal silver precipitate was silver chloride, which could not contribute to the significant hardening of the arrested lesions. On the other hand, fluoride enhances mineral formation by forming fluorohydroxyapatite with reduced solubility. A significant increase in microhardness occurs with an elevated level of calcium and phosphorus but not silver on the surface layer of the arrested dentine caries lesion following SDF treatment. Fluoride also inhibits matrix metalloproteinases activities and therefore inhibits dentine collagen degradation. The combination of silver and fluoride in an alkaline solution has a synergistic effect in arresting dentine caries. The alkaline property of SDF provides an unfavorable environment for collagen enzyme activation. Understanding the mechanisms of SDF in arresting dentine caries helps clinicians to develop appropriate protocols for the use of SDF in clinical care.

Nanostructured Ag+-substituted fluorhydroxyapatite-TiO2 coatings for enhanced bactericidal effects and osteoinductivity of Ti for biomedical applications

Background

Poor mechanical properties, undesirable fast dissolution rate, and lack of antibacterial activity limit the application of hydroxyapatite (HA) as an implant coating material. To overcome these limitations, a hybrid coating of Ag⁺-substituted fluorhydroxyapatite and titania nanotube (TNT) was prepared.

Methods

The incorporation of silver into the HA-TiO₂ hybrid coating improves its antimicrobial properties. The addition of F as a second binary element increases the structural stability of the coating. The TNT/F-and-Ag-substituted HA (FAgHA) bilayer coating on the Ti substrate was confirmed by X-ray diffraction, scanning electron microscope, energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS).

Results

The results indicate that the FAgHA/TNT nanocomposite coating has a dense and uniform morphology with a nano-rod-like structure. The solubility measurement result shows that the substitution of F⁻ ions into the AgHA structure has a positive effect on the dissolution resistance of HA. The adhesion strength of FAgHA/TNT has significantly increased because of the interlocking of the roughened surface with nano-rod-like particles that entered into the voids of the TiO₂ nanotubes. Compared with that of the bare Ti, the corrosion current density of FAgHA/TNT-coated Ti substrate decreased from 3.71 to 0.18 μA, and its corrosion resistance increased by almost two orders of magnitude. Moreover, despite pure HA, the FAgHA killed all viable Staphylococcus aureus after 24 hours of incubation. Although the fabricated FAgHA/TNT coating is hydrophobic, it induced deposition of the typical spherical apatite when immersed in a simulated body fluid (SBF); the osteoblasts spread very well on the surface of the coating. In addition, in vitro cell culture tests demonstrated cell viability and alkaline phosphatase (ALP) similar to pure HA, which indicated good cytocompatibility. Interestingly, compared with bare Ti, FAgHA/TNT-coated Ti surface was innocent for cell vitality and even more beneficial for cell osteogenesis in vitro.

Conclusion

Enhancing the osseointegration and preventing infection in implants, the FAgHA/TNT-coated Ti makes implants more successful.

Silver nanoparticle deposited implants to treat osteomyelitis

In this study, electrolytically deposited strongly adherent silver nanoparticles on stainless-steel (SS) implants were used for in situ osteomyelitis treatment. Samples were heat treated to enhance adhesion of silver on 316 L SS. Ex vivo studies were performed to measure silver-release profiles from the 316 L SS screws inserted in equine cadaver bones. No change in the release profiles of silver ions were observed in vitro between the implanted screws and the control. In vivo studies were performed using osteomyelitic rabbit model with 3 mm diameter silver-deposited 316 L SS pins at two different doses of silver: high and low. Infection control ability of the pins for treating osteomyelitis in a rabbit model was measured using bacteriologic, radiographic, histological, and scanning electron microscopic studies. Silver-coated pins, especially high dose, offered a promising result to treat infection in animal osteomyelitis model without any toxicity to major organs. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1073-1083, 2018.

Silver-nanoparticles increase bactericidal activity and radical oxygen responses against bacterial pathogens in human osteoclasts

Bone infections are difficult to treat and can lead to severe tissue destruction. Acute bone infections are usually caused by Staphylococcus aureus. Osteoclasts, which belong to the monocyte/macrophage lineage, are the key cells in bone infections. They are not well equipped for killing bacteria and may serve as a reservoir for bacterial pathogens. Silver has been known for centuries for its bactericidal activity. Here, we investigated the bactericidal effects of nano-silver particles in bacteria infected human osteoclasts. We found that nano-silver in per se non-toxic concentration enhanced the bactericidal activity in osteoclasts against intracellular Methicillin-resistant, virulent Staphylococcus aureus. The reduced bacterial survival in nano-silver pretreated cells correlated with increased reactive oxygen responses towards the invading pathogens. Overall, these results indicate that nano-silver compounds should be considered as an effective treatment and prevention option for bacterial bone and orthopedic implant infections.

Silver doped hydroxyapatite coatings by sacrificial anode deposition under magnetic field

Uniform distribution of silver (Ag) in the hydroxyapatite (HA) coated Ti surface has been a concern for which an attempt has been made to dope Ag in HA coating with and without magnetic field. Cathodic deposition technique was employed to coat Ag incorporated hydroxyapatite coating using a sacrificial silver anode method by using NdFeB bar magnets producing 12 Tesla magnetic field. While uniform deposition of Ag was observed in the coatings under magnetic field, dense coating was evident in the coating without magnetic field conditions. Uniformly distributed Ag incorporated HA in the present study has potential to fight microorganism while providing osseoconduction properties of the composite coating.

Silver Oxide Coatings with High Silver-Ion Elution Rates and Characterization of Bactericidal Activity

This paper reports the synthesis and characterization of silver oxide films for use as bactericidal coatings. Synthesis parameters, dissolution/elution rate, and bactericidal efficacy are reported. Synthesis conditions were developed to create AgO, Ag₂O, or mixtures of AgO and Ag₂O on surfaces by reactive magnetron sputtering. The coatings demonstrate strong adhesion to many substrate materials and impede the growth of all bacterial strains tested. The coatings are effective in killing Escherichia coli and Staphylococcus aureus, demonstrating a clear zone-of-inhibition against bacteria growing on solid media and the ability to rapidly inhibit bacterial growth in planktonic culture. Additionally, the coatings exhibit very high elution of silver ions under conditions that mimic dynamic fluid flow ranging between 0.003 and 0.07 ppm/min depending on the media conditions. The elution of silver ions from the AgO/Ag₂O surfaces was directly impacted by the complexity of the elution media, with a reduction in elution rate when examined in complex cell culture media. Both E. coli and S. aureus were shown to bind ~1 ppm Ag⁺/mL culture. The elution of Ag⁺ resulted in no increases in mammalian cell apoptosis after 24 h exposure compared to control, but apoptotic cells increased to ~35% by 48 and 72 h of exposure. Taken together, the AgO/Ag₂O coatings described are effective in eliciting antibacterial activity and have potential for application on a wide variety of surfaces and devices.

Understanding long-term silver release from surface modified porous titanium implants

Prevention of orthopedic device related infection (ODRI) using antibiotics has met with limited amount of success and is still a big concern during post-surgery. As an alternative, use of silver as an antibiotic treatment to prevent surgical infections is being used due to the well-established antimicrobial properties of silver. However, in most cases silver is used in particulate form with wound dressings or with short-term devices such as catheters but not with load-bearing implants. We hypothesize that strongly adherent silver to load-bearing implants can offer longer term solution to infection in vivo. Keeping that in mind, the focus of this study was to understand the long term release study of silver ions for a period of minimum 6months from silver coated surface modified porous titanium implants. Implants were fabricated using a LENS™ system, a powder based additive manufacturing technique, with at least 25% volume porosity, with and without TiO2 nanotubes in phosphate buffer saline (pH 7.4) to see if the total release of silver ions is within the toxic limit for human cells. Considering the fact that infection sites may reduce the local pH, silver release was also studied in acetate buffer (pH 5.0) for a period of 4weeks. Along with that, the osseointegrative properties as well as cytotoxicity of porous titanium implants were assessed in vivo for a period of 12weeks using a rat distal femur model. In vivo results indicate that porous titanium implants with silver coating show comparable, if not better, biocompatibility and bonding at the bone-implant interface negating any concerns related to toxicity related to silver to normal cells. The current research is based on our recently patented technology, however focused on understanding longer-term silver release to mitigate infection related problems in load-bearing implants that can even arise several months after the surgery.

STATEMENT OF SIGNIFICANCE

Prevention of orthopedic device related infection using antibiotics has met with limited success and is still a big concern during post-surgery. Use of silver as an antibiotic treatment to prevent surgical infections is being explored due to the well-established antimicrobial properties of silver. However, in most cases silver is used in particulate form with wound dressings or with short-term devices such as catheters but not with load-bearing implants. We hypothesize that strongly adherent silver to load-bearing implants can offer longer-term solution towards infection in vivo. Keeping that in mind, the focus of this study was to understand the long-term release of silver ions, for a period of minimum 6months, from silver coated surface modified porous titanium implants.

Ultralong Hydroxyapatite Nanowires-Based Paper Co-Loaded with Silver Nanoparticles and Antibiotic for Long-Term Antibacterial Benefit

Hydroxyapatite is a kind of biocompatible, environmentally friendly, and versatile inorganic biomaterial. Herein, the preparation of ultralong hydroxyapatite nanowires (HAPNWs)-based antibacterial paper co-loaded with silver nanoparticles (AgNPs) and antibiotic is reported. HAPNWs are used to prepare AgNPs in situ using an aqueous solution containing AgNO₃ under the sunlight without added reducing agent at room temperature. Subsequently, ciprofloxacin (CIP) as an antibiotic is loaded on the HAPNWs@AgNPs. The resultant HAPNWs@AgNPs-CIP paper possesses several unique properties, including high flexibility, high Brunauer-Emmett-Teller (BET) specific surface area (47.9 m² g^-1), high drug loading capacity (447.4 mg g^-1), good biocompatibility, sustained and pH-responsive drug release behavior (5.40-6.75% of Ag⁺ ions and 37.7-76.4% of CIP molecules at pH values of 7.4-4.5 at day 8, respectively), and reusable recycling. In the antibacterial tests against Escherichia coli and Staphylococcus aureus, the HAPNWs@AgNPs-CIP paper exhibits large diameters of inhibition zones and low minimum inhibitory concentrations (30 and 40 μg mL^-1), revealing the high antibacterial activity. Besides, the consecutive agar diffusion tests (8 cycles), long-term stability tests (over 56 days), and continuous contamination tests (5 cycles) demonstrate the excellent recycling performance and long-term antibacterial activity of the HAPNWs@AgNPs-CIP paper. These results indicate a promising potential of the HAPNWs@AgNPs-CIP bactericidal paper for tackling public health issues related to bacterial infections.

pH dependent silver nanoparticles releasing titanium implant: A novel therapeutic approach to control peri-implant infection

Peri-implant infection control is crucial for implant fixation and durability. Antimicrobial administration approaches to control peri-implant infection are far from satisfactory. During bacterial infection, pH level around the peri-implant surface decreases as low as pH 5.5. This change of pH can be used as a switch to control antimicrobial drug release from the implant surface. Silver nanoparticles (AgNPs) have broad-spectrum antimicrobial properties. In this study, we aimed to design a pH-dependent AgNPs releasing titania nanotube arrays (TNT) implant for peri-implant infection control. The nanotube arrays were fabricated on the surface of titanium implant as containers; AgNPs were grafted on TNT implant surface via a low pH-sensitive acetal linker (TNT-AL-AgNPs). SEM, TEM, AFM, FTIR as well as XPS data showed that AgNPs have been successfully linked to TNT via acetal linker without affecting the physicochemical characteristics of TNT. The pH 5.5 enhanced AgNPs release from TNT-AL-AgNPs implant compared with pH 7.4. AgNPs released at pH 5.5 robustly increased antimicrobial activities against gram-positive and gram-negative bacteria compared with AgNPs released at pH 7.4. TNT-AL-AgNPs implant enhanced osteoblast proliferation, differentiation, and did not affect osteoblast morphology in vitro. In conclusion, incorporation of AgNPs in TNT via acetal linker maintained the surface characteristics of TNT. TNT-AL-AgNPs implant was biocompatible to osteoblasts and showed osteoinductive properties. AgNPs were released from TNT-AL-AgNPs implant in high dose at pH 5.5, and this release showed strong antimicrobial properties in vitro. Therefore, this novel design of low pH-triggered AgNPs releasing TNT-AL-AgNPs could be an infection-triggered antimicrobial releasing implant model to control peri-implant infection.

Mussel-inspired nano-multilayered coating on magnesium alloys for enhanced corrosion resistance and antibacterial property

Magnesium alloys are promising candidates for load-bearing orthopedic implants due to their biodegradability and mechanical resemblance to natural bone tissue. However, the high degradation rate and the risk of implant-associated infections pose grand challenges for their clinical applications. Herein, we developed a nano-multilayered coating strategy through polydopamine and chitosan assisted layer-by-layer assembly of osteoinductive carbonated apatite and antibacterial sliver nanoparticles on the surface of AZ31 magnesium alloys. The fabricated nano-multilayered coating can not only obviously enhance the corrosion resistance but also significantly increase the antibacterial activity and demonstrate better biocompatility of magnesium alloys.