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

Silver/gold nanoalloy implant coatings with antibiofilm activity via pH-triggered silver ion release

Implant infections are a major challenge for the healthcare system. Biofilm formation and increasing antibiotic resistance of common bacteria cause implant infections, leading to an urgent need for alternative antibacterial agents. In this study, the antibiofilm behaviour of a coating consisting of a silver (Ag)/gold (Au) nanoalloy is investigated. This alloy is crucial to reduce uncontrolled potentially toxic Ag+ ion release. In neutral pH environments this release is minimal, but the Ag+ ion release increases in acidic microenvironments caused by bacterial biofilms. We perform a detailed physicochemical characterization of the nanoalloys and compare their Ag+ ion release with that of pure Ag nanoparticles. Despite a lower released Ag+ ion concentration at pH 7.4, the antibiofilm activity against Escherichia coli (a bacterium known to produce acidic pH environments) is comparable to a pure nanosilver sample with a similar Ag-content. Finally, biocompatibility studies with mouse pre-osteoblasts reveal a decreased cytotoxicity for the alloy coatings and nanoparticles.

Atomic Layer Deposition of Antibacterial Nanocoatings: A Review

In recent years, antibacterial coatings have become an important approach in the global fight against bacterial pathogens. Developments in materials science, chemistry, and biochemistry have led to a plethora of materials and chemical compounds that have the potential to create antibacterial coatings. However, insufficient attention has been paid to the analysis of the techniques and technologies used to apply these coatings. Among the various inorganic coating techniques, atomic layer deposition (ALD) is worthy of note. It enables the successful synthesis of high-purity inorganic nanocoatings on surfaces of complex shape and topography, while also providing precise control over their thickness and composition. ALD has various industrial applications, but its practical application in medicine is still limited. In recent years, a considerable number of papers have been published on the proposed use of thin films and coatings produced via ALD in medicine, notably those with antibacterial properties. The aim of this paper is to carefully evaluate and analyze the relevant literature on this topic. Simple oxide coatings, including TiO2, ZnO, Fe2O3, MgO, and ZrO2, were examined, as well as coatings containing metal nanoparticles such as Ag, Cu, Pt, and Au, and mixed systems such as TiO2-ZnO, TiO2-ZrO2, ZnO-Al2O3, TiO2-Ag, and ZnO-Ag. Through comparative analysis, we have been able to draw conclusions on the effectiveness of various antibacterial coatings of different compositions, including key characteristics such as thickness, morphology, and crystal structure. The use of ALD in the development of antibacterial coatings for various applications was analyzed. Furthermore, assumptions were made about the most promising areas of development. The final section provides a comparison of different coatings, as well as the advantages, disadvantages, and prospects of using ALD for the industrial production of antibacterial coatings.

Hazards Associated With Nanotechnology in Clinical Dentistry

Nanotechnology has transformed the field of dentistry with immense potential to provide comprehensive oral health care using nanomaterials, advanced clinical tools, and devices. New materials with superior properties can be developed using nanotechnology by making use of their atomic or molecular properties. Although there are numerous ways in which nanomaterials impact our health, the primary cause is that they comprise chemicals that may have an inadvertent reaction in the body. Moreover, they are used on a daily basis, increasing human contact with them. It is observed to be smaller in size than the physiological barrier in our bodies, making it much simpler for them to pass through and enter the body and they are being used more frequently. It is observed to be smaller in size than the physiological barrier in our bodies, making it much simpler for them to pass through and enter the body and being used more frequently. Although there are numerous ways in which nanomaterials impact our health, the primary cause is they comprise chemicals that may have an inadvertent reaction in the body. The review discusses various types of toxicity, including the cytotoxicity of composites, carbon nanoparticles, silver nanoparticles (SNPs), and quantum dots. It also covers genotoxicity, the effect of nanoparticles on salivary secretion, oral and gastrointestinal mucosa passage of nanoparticles, the tooth surface microenvironment, and interactions with engineered nanomaterials (ENMs). It is concluded that there is scarce information regarding the presence of chemicals that are released from nanoparticles used in dental materials. Nanotechnology is at an infant stage, although it has progressed by leaps and bounds, hailing a new age that provides better treatment modalities in various branches of dentistry. Although the development and application of nanodentistry are of considerable interest, knowledge regarding the possible toxicity of such materials must be meticulously evaluated, and potential benefits must be weighed against the risks to identify potential gaps in the safety assessment. Further research is needed on workplace exposure to nanoparticles in dentistry.

Nanotechnology enabled radioprotectants to reduce space radiation-induced reactive oxidative species

Interest in space exploration has seen substantial growth following recent launch and operation of modern space technologies. In particular, the possibility of travel beyond low earth orbit is seeing sustained support. However, future deep space travel requires addressing health concerns for crews under continuous, longer-term exposure to adverse environmental conditions. Among these challenges, radiation-induced health issues are a major concern. Their potential to induce chronic illness is further potentiated by the microgravity environment. While investigations into the physiological effects of space radiation are still under investigation, studies on model ionizing radiation conditions, in earth and micro-gravity conditions, can provide needed insight into relevant processes. Substantial formation of high, sustained reactive oxygen species (ROS) evolution during radiation exposure is a clear threat to physiological health of space travelers, producing indirect damage to various cell structures and requiring therapeutic address. Radioprotection toward the skeletal system components is essential to astronaut health, due to the high radio-absorption cross-section of bone mineral and local hematopoiesis. Nanotechnology can potentially function as radioprotectant and radiomitigating agents toward ROS and direct radiation damage. Nanoparticle compositions such as gold, silver, platinum, carbon-based materials, silica, transition metal dichalcogenides, and ceria have all shown potential as viable radioprotectants to mitigate space radiation effects with nanoceria further showing the ability to protect genetic material from oxidative damage in several studies. As research into space radiation-induced health problems develops, this review intends to provide insights into the nanomaterial design to ameliorate pathological effects from ionizing radiation exposure. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Nanotechnology Approaches to Biology > Cells at the Nanoscale Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

In-vivo processing of nanoassemblies: a neglected framework for recycling to bypass nanotoxicological therapeutics

The proof-of-concept of nanomaterials (NMs) in the fields of imaging, diagnosis, treatment, and theranostics shows the importance in biopharmaceuticals development due to structural orientation, on-targeting, and long-term stability. However, biotransformation of NMs and their modified form in human body via recyclable techniques are not explored owing to tiny structures and cytotoxic effects. Recycling of NMs offers advantages of dose reduction, re-utilization of the administered therapeutics providing secondary release, and decrease in nanotoxicity in human body. Therefore, approaches like in-vivo re-processing and bio-recycling are essential to overcome nanocargo system-associated toxicities such as hepatotoxicity, nephrotoxicity, neurotoxicity, and lung toxicity. After 3-5 stages of recycling process of some NMs of gold, lipid, iron oxide, polymer, silver, and graphene in spleen, kidney, and Kupffer's cells retain biological efficiency in the body. Thus, substantial attention towards recyclability and reusability of NMs for sustainable development necessitates further advancement in healthcare for effective therapy. This review article outlines biotransformation of engineered NMs as a valuable source of drug carriers and biocatalyst with critical strategies like pH modification, flocculation, or magnetization for recovery of NMs in the body. Furthermore, this article summarizes the challenges of recycled NMs and advances in integrated technologies such as artificial intelligence, machine learning, in-silico assay, etc. Therefore, potential contribution of NM's life-cycle in the recovery of nanosystems for futuristic developments require consideration in site-specific delivery, reduction of dose, remodeling in breast cancer therapy, wound healing action, antibacterial effect, and for bioremediation to develop ideal nanotherapeutics.

Development of Silver Doped Hydroxyapatite Thin Films for Biomedical Applications

Silver doped hydroxyapatite [AgHAp, Ca10−xAg(PO4)6(OH)2], due to its antimicrobial properties, is an advantageous material to be used for various coatings. The AgHAp thin films with xAg = 0.05 and xAg = 0.1 were achieved using the spin-coating method. The resulting samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XRD analysis revealed that the particles of both samples are ellipsoidal. Also, in agreement with the results obtained by XRD measurements, the results of the SEM studies have shown that the particles shape is ellipsoidal. Optical properties of silver doped hydroxyapatite thin films deposited on Si substrate were investigated through Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The results obtained by the two complementary techniques highlighted that the molecular structure of the studied samples is not influenced by the increase of the silver concentration in the samples. Our studies revealed that the surface morphology of the obtained samples consist of uniform and continuous layers. The biocompatibility of the obtained thin films was also evaluated with the aid of human osteosarcoma MG63 (ATCC CRL 1427) cell line. Moreover, the in vitro antifungal activity against Candida albicans fungal strain of the AgHAp thin films was studied and the obtained results revealed their antifungal effect. The results of the biological assays showed that the AgHAp thin films are a very promising material for biomedical applications.

No-Observed-Effect Level of Silver Phosphate in Carbonate Apatite Artificial Bone on Initial Bone Regeneration

Fracture-related infections require both treatments for bacteria removal and bone reconstruction. The use of combined broad-spectrum antibacterial silver compounds and artificial bone with high osteogenic activity is considered to be an effective strategy for achieving these treatments in one surgery. However, silver compounds are toxic for living tissues even at low concentrations. Herein, we investigated the no-observed-effect level (NOEL) of silver phosphate (Ag₃PO₄) in a bone substitute composed of carbonate apatite (CO₃Ap), a bone mineral, using in vitro and in vivo experiments. In vitro experiments demonstrated that the CO₃Ap artificial bone containing ≥0.1 wt % Ag₃PO₄ exerted antibacterial effects against Staphylococcus epidermidis, while those containing ≤0.3 wt % Ag₃PO₄ did not affect cellular adhesion, proliferation, differentiation, and calcification of osteoblast-like MC3T3-E1 cells. In vivo experiments demonstrated that the CO₃Ap artificial bone containing ≤0.3 wt % Ag₃PO₄ replaced a new bone to the same levels as those without Ag₃PO₄ 4 weeks after implantation into the bone defect of the rabbit femur condyle. However, the CO₃Ap artificial bone containing 0.3 wt % Ag₃PO₄ caused an inflammatory reaction, whereas those containing ≤0.1 wt % Ag₃PO₄ did not. Thus, both bone regeneration and infection control without any adverse effects were achieved using the CO₃Ap artificial bone containing 0.1 wt % Ag₃PO₄, indicating that the NOEL of Ag₃PO₄ was 0.1 wt %. Our results provide an effective strategy for the treatments of fracture-related infections.

Fate and transformation of silver nanoparticles in different biological conditions

The exploitation of silver nanoparticles (AgNPs) in biomedicine represents more than one third of their overall application. Despite their wide use and significant amount of scientific data on their effects on biological systems, detailed insight into their in vivo fate is still lacking. This study aimed to elucidate the biotransformation patterns of AgNPs following oral administration. Colloidal stability, biochemical transformation, dissolution, and degradation behaviour of different types of AgNPs were evaluated in systems modelled to represent biological environments relevant for oral administration, as well as in cell culture media and tissue compartments obtained from animal models. A multimethod approach was employed by implementing light scattering (dynamic and electrophoretic) techniques, spectroscopy (UV-vis, atomic absorption, nuclear magnetic resonance) and transmission electron microscopy. The obtained results demonstrated that AgNPs may transform very quickly during their journey through different biological conditions. They are able to degrade to an ionic form and again reconstruct to a nanoparticulate form, depending on the biological environment determined by specific body compartments. As suggested for other inorganic nanoparticles by other research groups, AgNPs fail to preserve their specific integrity in in vivo settings.

Surface ligand rigidity modulates lipid raft affinity of ultra-small hydrophobic nanoparticles: insights from molecular dynamics simulations

Differential preferences between lipids and proteins drive the formation of dynamical nanoscale membrane domains (lipid rafts), which play key roles in the proper functioning of cells. On the other hand, due to the potent physicochemical properties of nanoparticles (NPs), they have been widely used in drug delivery, bio-imaging and regulating various essential biological processes of the cells. Hence, in this work, we aim to design ultra-small hydrophobic NPs with tunable raft affinity, which is supposed to partition into the hydrophobic region of lipid membranes and be able to regulate the dynamics of the lipid raft domains. A series of μs-scale coarse-grained molecular dynamics simulations and umbrella sampling free energy calculations were performed to investigate the role of surface ligand rigidity of ultra-small hydrophobicNPs in their raft affinity. Our results indicated that the preferred localization of NPs can be tuned by adjusting their surface ligand rigidity. Generally, rigid NPs tended to target the raft domain, while soft NPs preferred the interface of the raft and non-raft domains. The free energy analysis further indicated that the surface ligand rigidity of NPs can enhance their targeting to lipid raft domains. Besides, we found that these ultra-small NPs had no significant effects on the phase separation of the lipid membrane although they might cause some local interference to surrounding lipids. These results indicate that the targeting to the lipid raft domain can be achieved by the surface ligand rigidity of NPs, which provides helpful insights for further regulations of lipid raft-mediated biological processes.

Metallic-nanoparticle release systems for biomedical implant surfaces: effectiveness and safety

The current focus of bioengineering for implant devices involves the development of functionalized surfaces, bioactive coatings, and metallic nanoparticles (mNPs) with a controlled release, together with strategies for the application of drugs in situ, aiming at reducing infection rates, with an improvement of clinical outcomes. Controversially, negative aspects, such as cytotoxicity, mNP incorporation, bioaccumulation, acquired autoimmunity, and systemic toxicity have gained attention at the same status of importance, concerning the release of mNPs from these surface systems. The balance between the promising prospects of system releasing mNPs and the undesirable long-term adverse reactions require further investigation. The scarcity of knowledge and the methods of analysis of nanoscale-based systems to control the sequence of migration, interaction, and nanoparticle incorporation with human tissues raise hesitation about their efficacy and safety. Looking ahead, this innovative approach requires additional scientific investigation for permitting an evolution of implants without counterpoints, while updating implant surface technologies to a new level of development. This critical review has explored the promising properties of metals at the nano-scale to promote broad-spectrum bacterial control, allowing for a decrease in using systemic antibiotics. Attempts have also been made to discuss the existing limitations and the future challenges regarding these technologies, besides the negative findings that are explored in the literature.

Combined NMR and Computational Study of Cysteine Oxidation during Nucleation of Metallic Clusters in Biological Systems

The widespread biomedical applications of silver and gold nanoparticles (AgNPs and AuNPs, respectively) prompt the need for mechanistic evaluation of their interaction with biomolecules. In biological media, metallic NPs are known to transform by various pathways, especially in the presence of thiols. The interplay between metallic NPs and thiols may lead to unpredictable consequences for the health status of an organism. This study explored the potential events occurring during biotransformation, dissolution, and reformation of NPs in the thiol-rich biological media. The study employed a model system evaluating the interaction of cysteine with small-sized AgNPs and AuNPs. The interplay of cysteine on transformation and reformation pathways of these NPs was experimentally investigated by nuclear magnetic resonance (NMR) spectroscopy and supported by light scattering techniques and transmission electron microscopy (TEM). As the main outcome, Ag- or Au-catalyzed oxidation of cysteine to cystine was found to occur through generation of reactive oxygen species (ROS). Computational simulations confirmed this mechanism and the role of ROS in the oxidative dimerization of biothiol during NPs reformation. The obtained results represent valuable mechanistic data about the complex events during the transport of metallic NPs in thiol-rich biological systems that should be considered for the future biomedical applications of metal-based nanomaterials.

Are silver nanoparticles better than triclosan as a daily antimicrobial? Answers from the perspectives of gut microbiome disruption and pathogenicity

As an alternative to triclosan (TCS), the widespread use of silver nanoparticles (AgNPs) in daily products shows genuine potential. However, information regarding whether AgNPs are substantially better than TCS in their potential disruption of the gut microbiome and health effects is lacking. Using a simulator of the human intestinal microbial ecosystem (SHIME), we systemically compared the effects of TCS and AgNPs (at 1 μg/L and 30 μg/L) on the human gut microbiome in terms of changes in gut homeostasis, microbial community structure, antibiotic resistance profiles and abundances of opportunistic pathogens. Generally, TCS exerted more severe effects than AgNPs on gut disturbances (i.e., decreased production of short-chain fatty acids, increased contents of ammonium and total bile acids, and increased β-glucosidase activities) in a dose-dependent manner, whereas no clear dose effect was observed for the AgNP treatment because of potential nanoparticle transformation. The more serious effect of TCS than AgNPs on the microbiota composition was indicated by the dynamic increase in the Firmicutes/Bacteroidetes ratio determined using 16S rDNA sequencing. Metagenomic analyses revealed a more pronounced effect of TCS than AgNPs on the selection and dissemination of multiple resistance genes to antibiotics, TCS, and even Ag via the enrichment of genes encoding efflux pumps and mobile genetic elements. Consequently, the overgrowth of opportunistic pathogens was observed upon TCS exposure due to an imbalanced microbiome, in contrast to a slight increase in the abundance of some beneficial bacteria (i.e., Bifidobacterium) induced by the AgNP treatment. In conclusion, from the perspective of effects on gut health, AgNPs may prevail over TCS to some extent. However, the stress and potential selection of Ag resistance indicates the need for targeted surveillance of AgNP commercialization for daily use.

Imaging inorganic nanomaterial fate down to the organelle level

Nanotoxicology remains an important and emerging field since only recent years have seen the improvement of biological models and exposure setups toward real-life scenarios. The appropriate analysis of nanomaterial fate in these conditions also required methodological developments in imaging to become sensitive enough and element specific. In the last 2-4 years, impressive breakthroughs have been achieved using electron microscopy, nanoscale secondary ion mass spectrometry, X-ray fluorescence microscopy, or fluorescent sensors. In this review, basics of the approaches and application examples in the study of nanomaterial fate in biological systems will be described to highlight recent successes in the field.

Atomic layer deposition on dental materials: Processing conditions and surface functionalization to improve physical, chemical, and clinical properties - A review

Surface functionalization is an effective approach to improve and enhance the properties of dental materials. A review of atomic layer deposition (ALD) in the field of dental materials is presented. ALD is a well-established thin film deposition technique. It is being used for surface functionalization in different technologies and biological related applications. With film thickness control down to Ångström length scale and uniform conformal thin films even on complex 3D substrates, high quality thin films and their reproducibility are noteworthy advantages of ALD over other thin film deposition methods. Low temperature ALD allows temperature sensitive substrates to be functionalized with high quality ultra-thin films too. In the current work, ALD is elaborated as a promising method for surface modification of dental materials. Different aspects of conventional dental materials that can be enhanced using ALD are discussed. Also, the influence of different ALD thin films and their microstructure on the surface properties, corrosion-resistance, antibacterial activity, biofilm formation, and osteoblast compatibility are addressed. Depending on the stage of advancement for the studied materials reported in the literature, these studies are then categorized into four stages: fabrication & characterization, in vitro studies, in vivo studies, and human tests. Materials coated with ALD thin films with potential dental applications are also presented here and they are categorized as stage 1. The purpose of this review is to organize and present the up to date ALD research on dental materials. The current study can serve as a guide for future work on using ALD for surface functionalization and resulting property tuning of materials in real world dental applications.

Biofunctional Elements Incorporated Nano/Microstructured Coatings on Titanium Implants with Enhanced Osteogenic and Antibacterial Performance

Bone fracture is prevalent among athletes and senior citizens and may require surgical insertion of bone implants. Titanium (Ti) and its alloys are widely used in orthopedics due to its high corrosion resistance, good biocompatibility, and modulus compatible with natural bone tissues. However, bone repair and regrowth are impeded by the insufficient intrinsic osteogenetic capability of Ti and Ti alloys and potential bacterial infection. The physicochemical properties of the materials and nano/microstructures on the implant surface are crucial for clinical success and loading with biofunctional elements such as Sr, Zn, Cu, Si, and Ag into nano/microstructured TiO2 coating has been demonstrated to enhance bone repair/regeneration and bacterial resistance of Ti implants. In this review, recent advances in biofunctional element-incorporated nano/microstructured coatings on Ti and Ti alloy implants are described and the prospects and limitations are discussed.

Novel fast-acting pyrazole/pyridine-functionalized N-heterocyclic carbene silver complexes assembled with nanoparticles show enhanced safety and efficacy as anticancer therapeutics

In this study, we designed and synthesized four novel multi-nuclear silver complexes (1-4) coordinated with pyrazole- or pyridine-functionalized N-heterocyclic carbene (NHC) ligands. The crystal structures of the silver-NHC complexes were confirmed by X-ray diffraction analysis. In vitro assays showed that the silver-NHC complexes effectively killed a broad range of cancer cells after short-term drug exposure, serving as fast-acting cytotoxic agents. Of note, in cisplatin-resistant A549 cancer cells, the silver complexes were not cross-resistant with the clinically used cisplatin agent. Detailed mechanistic studies revealed that complex 2 triggered caspase-independent cell necrosis associated with intracellular reactive oxygen species (ROS) production and mitochondrial membrane potential (MMP) depletion. By exploiting a facile nano-assembly process, silver-NHC complexes 1, 2 and 4 were successfully integrated into the hydrophobic cores of amphiphilic matrices (DSPE-PEG2K), enabling systemic injection. The silver complex-loaded nanotherapeutics (1-NPs, 2-NPs, and 4-NPs) showed high safety margins with reduced systemic drug toxicities relative to cisplatin in animals. Furthermore, in a xenograft model of human colorectal cancer, the administration of the nanotherapeutics resulted in a marked inhibition of tumor progression.

Erythrocyte Membrane-Wrapped Magnetic Nanotherapeutic Agents for Reduction and Removal of Blood Cr(VI)

The hazard of hexavalent chromium (Cr(VI)) from environmental pollution and medical implanted metal has been recognized widely. However, removal of trace amount of Cr(VI) in the blood circumstance faces tremendous difficulties for that most of Cr(VI) located in erythrocytes, thus there is almost no literature to report the removal of Cr(VI) in blood. Herein, a removal strategy, named as reduction-adsorption-separation, is proposed to realize the removal of Cr(VI) in blood. First, magnetic core-shell mesoporous nanocomposite is fabricated by using Fe₃O₄ nanoparticles as magnetic core and mesoporous silica (MS) as shell, hyperbranched polyamide (HPA) as mesoporous channel modifier and ascorbic acid (ASC) as the reductant drug loaded in the mesoporous channels, which is also denoted as Fe/MS/HPA/ASC. Then, on the basis of the bionic idea, the erythrocyte membrane (EM)-wrapped Fe/MS/HPA/ASC to protect ASC from deactivation is obtained and named as the therapeutic agent (Fe/MS/HPA/ASC@EM). During removal process, the therapeutic agent can enter in erythrocytes to use ASC to reduce Cr(VI) to Cr(III) and HPA in mesoporous channels to adsorb Cr(III) and can then be recollected from blood by magnetic separation. Finally, an animal model of blood Cr(VI) poisoning is constructed and used to test the removal ability of Cr(VI) from pig blood in vivo, verifying the effectiveness of this blood Cr(VI) removal strategy, providing a possible way to design more efficient and biosafe therapeutic agents for blood purification.

The Impact of Engineered Silver Nanomaterials on the Immune System

Over the last decades there has been a tremendous volume of research efforts focused on engineering silver-based (nano)materials. The interest in silver has been mostly driven by the element capacity to kill pathogenic bacteria. In this context, the main area of application has been medical devices that are at significant risk of becoming colonized by bacteria and subsequently infected. However, silver nanomaterials have been incorporated in a number of other commercial products which may or may not benefit from antibacterial protection. The rapid expansion of such products raises important questions about a possible adverse influence on human health. This review focuses on examining currently available literature and summarizing the current state of knowledge of the impact of silver (nano)materials on the immune system. The review also looks at various surface modification strategies used to generate silver-based nanomaterials and the immunomodulatory potential of these materials. It also highlights the immune response triggered by various silver-coated implantable devices and provides guidance and perspective towards engineering silver nanomaterials for modulating immunological consequences.

Materials for Orthopedic Bioimplants: Modulating Degradation and Surface Modification Using Integrated Nanomaterials

Significant research and development in the field of biomedical implants has evoked the scope to treat a broad range of orthopedic ailments that include fracture fixation, total bone replacement, joint arthrodesis, dental screws, and others. Importantly, the success of a bioimplant depends not only upon its bulk properties, but also on its surface properties that influence its interaction with the host tissue. Various approaches of surface modification such as coating of nanomaterial have been employed to enhance antibacterial activities of a bioimplant. The modified surface facilitates directed modulation of the host cellular behavior and grafting of cell-binding peptides, extracellular matrix (ECM) proteins, and growth factors to further improve host acceptance of a bioimplant. These strategies showed promising results in orthopedics, e.g., improved bone repair and regeneration. However, the choice of materials, especially considering their degradation behavior and surface properties, plays a key role in long-term reliability and performance of bioimplants. Metallic biomaterials have evolved largely in terms of their bulk and surface properties including nano-structuring with nanomaterials to meet the requirements of new generation orthopedic bioimplants. In this review, we have discussed metals and metal alloys commonly used for manufacturing different orthopedic bioimplants and the biotic as well as abiotic factors affecting the failure and degradation of those bioimplants. The review also highlights the currently available nanomaterial-based surface modification technologies to augment the function and performance of these metallic bioimplants in a clinical setting.

Silver and gold doped hydroxyapatite nanocomposites for enhanced bone regeneration

We report the osteogenic potential of silver (Ag), gold (Au), or silver-gold doped hydroxyapatite nanoparticles (Ag-Au-HA) in zebrafish (ZF) jawbone regeneration (JBR) model. The hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂), Ag-HA, Au-HA, and Ag-Au-HA nanomaterials were synthesized by the co-precipitation procedure. The surface structures of Ag-HA, Au-HA, HA, and Ag-Au-HA were analysed by scanning electron microscopy, transmission-electron microscopy (TEM), x-ray diffraction, Fourier transform infrared (FTIR), UV-vis, energy dispersive x-ray spectroscopy (EDS), elemental mapping, and laser fluorescent spectroscopy. The TEM and EDS analysis confirmed that the Ag and Au are associated with the surface of HA nanoparticle. The chemical structure of HA, Ag-HA, Au-HA, and Ag-Au-HA nanoparticles was validated by FTIR and EDS analysis. We observed that Ag and Au are associated with HA nanoparticles by electrostatic, wander wall, and electrostatic and H-bonding interaction. The effect of Ag-HA, Au-HA, and Ag-Au-HA nanoparticles on bone regeneration was confirmed by ZF JBR model. The significant growth of ZF bone regeneration was observed in Ag-Au-HA nanoparticles as compared with HA, Ag-HA, and Au-HA nanoparticles. These results indicating a therapeutic potential of Ag-Au-HA compositions suggest these nanomaterials would be excellent for bone regeneration and fracture healing.

Silver-loaded nanoparticles affect ex-vivo mechanical behavior and mineralization of dentin

Background

The aim was to evaluate the effect of silver loaded nanoparticles (NPs) application on the triboscopic, crystallographic and viscoelastic properties of demineralized dentin. Polymethylmetacrylate-based NPs and Ag loaded NPs were applied on demineralized dentin.

Material and Methods

Treated and untreated surfaces were probed by a nanoindenter to test viscoelasticity, and by atomic force microscopy to test nanoroughness and collagen fibril diameter. X-ray diffraction and transmission electron microscopy through selected area diffraction and bright-field imaging were also used.

Results

Dentin treated with Ag-NPs attained the lowest complex modulus, and the highest tan delta values after 7 days of storage. Dentin treated with undoped-NPs achieved the lowest nanoroughness and the greatest collagen bandwidths among groups. Crystals were identified as hydroxyapatite with the highest crystallographic maturity and crystallite size in dentin treated with undoped-NPs. Texture increased in all samples from 24 h to 7 d, except in dentin surfaces treated with Ag-NPs at 310 plane. Polyhedral, block-like, hexagonal or plate-like shaped apatite crystals constituted the bulk of minerals in dentin treated with Ag-NPs, after 7 d. Polyhedral or rounded/drop-like, and polymorphic in strata crystal apatite characterized the minerals when undoped-NPs were used, with more crystalline characteristics after 7 d than that found when Ag-NPs were applied. Ag-NPs application did not improve the mechanical performance of dentin and did not produce dentin remineralization. However, energy was dissipated through the dentin without showing stress concentration; contrary was occurring at dentin treated with undoped-NPs, that provoked bridge-like mineral deposits at the dentin surface.

Conclusions

Ag-NPs application did not enhance the mechanical properties of cervical dentin, though the energy dissipation did not damage the dentin structure. Remineralization at dentin was not produced after Ag-NPs application, though improved crystallinity may lead to increase stability of the apatite that was generated at the dentin surface.

Key words:Dentin, mechanical, mineralization, roughness, silver, viscoelastic.

Long-Term Prevention of Bacterial Infection and Enhanced Osteoinductivity of a Hybrid Coating with Selective Silver Toxicity

Antibacterial and osteogenic design is required for ideal orthopedic implants. The excellent antimicrobial performance of silver nanoparticles (AgNPs) has attracted interest for the treatment of implant-related infections. However, the dose-dependent cytotoxicity of silver and its negative impact on bone implants restrict the further use of AgNPs coatings. Therefore, a hybrid coating containing polydopamine (PDA), hydroxyapatite (HA), AgNPs, and chitosan (CS) is prepared. Organic chelators CS and PDA that have promising biocompatibility are used to prevent the rapid release of silver ions from the AgNPs coating. The double chelating effect of PDA and CS significantly reduces silver ion release from the hybrid coating. The coating exhibits excellent anti-biofilm efficiency of 91.7%, 89.5%, and 92.0% for Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli, respectively. In addition, the coating can significantly stimulate osteogenic differentiation of MC3T3-E1 cells and promote bone-implant osseointegration in vivo as compared to that in the control group. The longitudinal biosafety of the coating is confirmed in vivo by histological evaluation and blood tests. The results of this study indicate that the hybrid coating exhibits antibacterial properties as well as allow bone-implant osseointegration, thereby providing insight into the design of multifunctional implants for long-term orthopedic applications.

Mechanical performance of additively manufactured meta-biomaterials

Additive manufacturing (AM) (=3D printing) and rational design techniques have enabled development of meta-biomaterials with unprecedented combinations of mechanical, mass transport, and biological properties. Such meta-biomaterials are usually topologically ordered and are designed by repeating a number of regular unit cells in different directions to create a lattice structure. Establishing accurate topology-property relationships is of critical importance for these materials. In this paper, we specifically focus on AM metallic meta-biomaterials aimed for application as bone substitutes and orthopaedic implants and review the currently available evidence regarding their mechanical performance under quasi-static and cyclic loading conditions. The topology-property relationships are reviewed for regular beam-based lattice structures, sheet-based lattice structures including those based on triply periodic minimal surface, and graded designs. The predictive models used for establishing the topology-property relationships including analytical and computational models are covered as well. Moreover, we present an overview of the effects of the AM processes, material type, tissue regeneration, biodegradation, surface bio-functionalization, post-manufacturing (heat) treatments, and loading profiles on the quasi-static mechanical properties and fatigue behavior of AM meta-biomaterials. AM meta-biomaterials exhibiting unusual mechanical properties such as negative Poisson's ratios (auxetic meta-biomaterials), shape memory behavior, and superelasitcity as well as the potential applications of such unusual behaviors (e.g. deployable implants) are presented too. The paper concludes with some suggestions for future research. STATEMENT OF SIGNIFICANCE: Additive manufacturing enables fabrication of meta-biomaterials with rare combinations of topological, mechanical, and mass transport properties. Given that the micro-scale topological design determines the macro-scale properties of meta-biomaterials, establishing topology-property relationships is the central research question when rationally designing meta-biomaterials. The interest in understanding the relationship between the topological design and material type on the one hand and the mechanical properties and fatigue behavior of meta-biomaterials on the other hand is currently booming. This paper presents and critically evaluates the most important trends and findings in this area with a special focus on the metallic biomaterials used for skeletal applications to enable researchers better understand the current state-of-the-art and to guide the design of future research projects.

Nanomaterials in dentistry: a cornerstone or a black box?

Aim: The studies on tooth structure provided basis for nanotechnology-based dental treatment approaches known as nanodentistry which aims at detection and treatment of oral pathologies, such as dental caries and periodontal diseases, insufficiently being treated by conventional materials or drugs. This review aims at defining the role of nanodentistry in the medical area, its potential and hazards. Materials & methods: To validate these issues, current literature on nanomaterials for dental applications was critically reviewed. Results: Nanomaterials for teeth restoration, bone regeneration and oral implantology exhibit better mechanical properties and provide more efficient esthetic outcome. However, still little is known about influence of long-term function of such biomaterials in the living organism. Conclusion: As application of nanomaterials in industry and medical-related sciences is still expanding, more information is needed on how such nano-dental materials may interfere with oral cavity, GI tract and general health.

Engineering of Micro- to Nanostructured 3D-Printed Drug-Releasing Titanium Implants for Enhanced Osseointegration and Localized Delivery of Anticancer Drugs

Primary and secondary bone cancers are major causes of pathological bone fractures which are usually treated through implant fixation and chemotherapy. However, both approaches face many limitations. On one hand, implants may suffer from poor osseointegration, and their rejection results in repeated surgery, patient's suffering, and extensive expenses. On the other hand, there are severe systemic adverse effects of toxic chemotherapeutics which are administrated systemically. In this paper, in order to address these two problems, we present a new type of localized drug-releasing titanium implants with enhanced implants' biointegration and drug release capabilities that could provide a high concentration of anticancer drugs locally to treat bone cancers. The implants are fabricated by 3D printing of Ti alloy followed by an anodization process featuring unique micro- (particles) and nanosurface (tubular arrays) topography. We successfully demonstrate their enhanced bone osseointegration and drug loading capabilities using two types of anticancer drugs, doxorubicin (DOX) and apoptosis-inducing ligand (Apo2L/TRAIL). In vitro study showed strong anticancer efficacy against cancer cells (MDA-MB-231-TXSA), confirming that these drug-releasing implants can be used for localized chemotherapy for treatment of primary and secondary bone cancers together with fracture support.