In vitro evaluation of Ag-containing calcium phosphates: Effectiveness of Ag-incorporated β-tricalcium phosphate

Preparation and Characterization of Mono- and Biphasic Ca1-xAgxHPO4·nH2O Compounds for Biomedical Applications

This study aimed to explore the effects of the full-scale replacement (up to 100%) of Ca2+ ions with Ag1+ ions in the structure of brushite (CaHPO4·2H2O). This substitution has potential benefits for producing monophasic and biphasic Ca1-xAgxHPO4·nH2O compounds. To prepare the starting solutions, (NH4)2HPO4, Ca(NO3)2·4H2O, and AgNO3 at different concentrations were used. The results showed that when the Ag/Ca molar ratio was below 0.25, partial substitution of Ca with Ag reduced the size of the unit cell of brushite. As the Ag/Ca molar ratio increased to 4, a compound with both monoclinic CaHPO4·2H2O and cubic nanostructured Ag3PO4 phases formed. There was a nearly linear relationship between the Ag ion ratio in the starting solutions and the wt% precipitation of the Ag3PO4 phase in the resulting compound. Moreover, when the Ag/Ca molar ratio exceeded 4, a single-phase Ag3PO4 compound formed. Hence, adjusting the Ag/Ca ratio in the starting solution allows the production of biomaterials with customized properties. In summary, this study introduces a novel synthesis method for the mono- and biphasic Ca1-xAgxHPO4·nH2O compounds brushite and silver phosphate. The preparation of these phases in a one-pot synthesis with controlled phase composition resulted in the enhancement of existing bone cement formulations by allowing better mixing of the starting ingredients.

Silver-Containing Biomaterials for Biomedical Hard Tissue Implants

Bacterial infection caused by biomaterials is a very serious problem in the clinical treatment of implants. The emergence of antibiotic resistance has prompted other antibacterial agents to replace traditional antibiotics. Silver is rapidly developing as an antibacterial candidate material to inhibit bone infections due to its significant advantages such as high antibacterial timeliness, high antibacterial efficiency, and less susceptibility to bacterial resistance. However, silver has strong cytotoxicity, which can cause inflammatory reactions and oxidative stress, thereby destroying tissue regeneration, making the application of silver-containing biomaterials extremely challenging. In this paper, the application of silver in biomaterials is reviewed, focusing on the following three issues: 1) how to ensure the excellent antibacterial properties of silver, and not easy to cause bacterial resistance; 2) how to choose the appropriate method to combine silver with biomaterials; 3) how to make silver-containing biomaterials in hard tissue implants have further research. Following a brief introduction, the discussion focuses on the application of silver-containing biomaterials, with an emphasis on the effects of silver on the physicochemical properties, structural properties, and biological properties of biomaterials. Finally, the review concludes with the authors' perspectives on the challenges and future directions of silver in commercialization and in-depth research.

Antimicrobial Natural Hydrogels in Biomedicine: Properties, Applications, and Challenges-A Concise Review

Natural hydrogels are widely used as biomedical materials in many areas, including drug delivery, tissue scaffolds, and particularly wound dressings, where they can act as an antimicrobial factor lowering the risk of microbial infections, which are serious health problems, especially with respect to wound healing. In this review article, a number of promising strategies in the development of hydrogels with biocidal properties, particularly those originating from natural polymers, are briefly summarized and concisely discussed. Common strategies to design and fabricate hydrogels with intrinsic or stimuli-triggered antibacterial activity are exemplified, and the mechanisms lying behind these properties are also discussed. Finally, practical antibacterial applications are also considered while discussing the current challenges and perspectives.

Hydrogels for Antitumor and Antibacterial Therapy

As a highly absorbent and hydrophobic material with a three-dimensional network structure, hydrogels are widely used in biomedical fields for their excellent biocompatibility, low immunogenicity, adjustable physicochemical properties, ability to encapsulate a variety of drugs, controllability, and degradability. Hydrogels can be used not only for wound dressings and tissue repair, but also as drug carriers for the treatment of tumors. As multifunctional hydrogels are the focus for many researchers, this review focuses on hydrogels for antitumor therapy, hydrogels for antibacterial therapy, and hydrogels for co-use in tumor therapy and bacterial infection. We highlighted the advantages and representative applications of hydrogels in these fields and also outlined the shortages and future orientations of this useful tool, which might give inspirations for future studies.

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.

Silver Decorated βTCP-Poly(3hydroxybutyrate) Scaffolds for Bone Tissue Engineering

Implantations in orthopedics are associated with a high risk of bacterial infections in the surgery area. Therefore, biomaterials containing antibacterial agents, such as antibiotics, bactericidal ions or nanoparticles have been intensively investigated. In this work, silver decorated β tricalcium phosphate (βTCP)-based porous scaffolds were obtained and coated with a biopolymer-poly(3-hydroxybutyrate)-P(3HB). To the best of our knowledge, studies using silver-doped βTCP and P(3HB), as a component in ceramic-polymer scaffolds for bone tissue regeneration, have not yet been reported. Obtained materials were investigated by high-temperature X-ray diffraction, X-ray fluorescence, scanning electron microscopy with energy dispersive spectroscopy, hydrostatic weighing, compression tests and ultrahigh-pressure liquid chromatography with mass spectrometry (UHPLC-MS) measurements. The influence of sintering temperature (1150, 1200 °C) on the scaffolds' physicochemical properties (phase and chemical composition, microstructure, porosity, compressive strength) was evaluated. Materials covered with P(3HB) possessed higher compressive strength (3.8 ± 0.6 MPa) and surgical maneuverability, sufficient to withstand the implantation procedures. Furthermore, during the hydrolytic degradation of the composite material not only pure (R)-3-hydroxybutyric acid but also its oligomers were released which may nourish surrounding tissues. Thus, obtained scaffolds were found to be promising bone substitutes for use in non-load bearing applications.

Effect of Precursor Deficiency Induced Ca/P Ratio on Antibacterial and Osteoblast Adhesion Properties of Ag-Incorporated Hydroxyapatite: Reducing Ag Toxicity

Ag-containing hydroxyapatite (HA) can reduce risks associated with bacterial infections which may eventually require additional surgical operations to retrieve a failed implant. The biological properties of HA in such applications are strongly affected by its composition in terms of dopants as well as Ca/P stoichiometry, which can be easily controlled by altering processing parameters, such as precursor concentrations. The objective of this in vitro study was to understand the effect of variations in HA precursor solutions on antibacterial properties against Escherichia coli (E. coli) and for promoting osteoblast (bone-forming cell) adhesion on Ag incorporated HA (AgHA) which has not yet been investigated. For this, two groups of AgHAs were synthesized via a precipitation method by adjusting precursor reactants with a stoichiometric value of 1.67, being either (Ca + Ag)/P (Ca-deficient) or Ca/(P + Ag) (P-deficient), and were characterized by XRD, FTIR, and SEM-EDS. Results showed that Ag⁺ incorporated into the Ca²⁺ sites was associated with a corresponding OH⁻ vacancy. Additional incorporation of CO₃²⁻ into PO₄³⁻ sites occurred specifically for the P-deficient AgHAs. While antibacterial properties increased, osteoblast adhesion decreased with increasing Ag content for the Ca-deficient AgHAs, as anticipated. In contrast, significant antibacterial properties with good osteoblast behavior were observed on the P-deficient AgHAs even with a lower Ag content, owing to carbonated HA. Thus, this showed that by synthesizing AgHA using P-deficient precursors with carbonate substitution, one can keep the antibacterial properties of Ag in HA while reducing its toxic effect on osteoblasts.

The Influence of Nanometals, Dispersed in the Electrophoretic Nanohydroxyapatite Coatings on the Ti13Zr13Nb Alloy, on Their Morphology and Mechanical Properties

In this work, nanohydroxyapatite coatings with nanosilver and nanocopper have been fabricated and studied. The presented results concern coatings with a chemical composition that has never been proposed before. The present research aims to characterize the effects of nanosilver and nanocopper, dispersed in nanohydroxyapatite coatings and deposited on a new, non-toxic Ti13Zr13Nb alloy, on the physical and mechanical properties of coatings. The coatings were obtained by a one-stage electrophoretic process. The surface topography, and the chemical and phase compositions of coatings were examined with scanning electron microscopy, atomic force microscopy, X-ray diffractometry, glow discharge optical emission spectroscopy, and energy-dispersive X-ray spectroscopy. The mechanical properties of coatings were determined by nanoindentation tests, while coatings adhesion was determined by nanoscratch tests. The results demonstrate that copper addition increases the hardness and adhesion. The presence of nanosilver has no significant influence on the adhesion of coatings.

The Chemical and Biological Properties of Nanohydroxyapatite Coatings with Antibacterial Nanometals, Obtained in the Electrophoretic Process on the Ti13Zr13Nb Alloy

The risk of an early inflammation after implantation surgery of titanium implants has caused the development of different antimicrobial measures. The present research is aimed at characterizing the effects of nanosilver and nanocopper dispersed in the nanohydroxyapatite coatings, deposited on the Ti13Zr13Nb alloy, and on the chemical and biological properties of the coatings. The one-stage deposition process was performed by the electrophoretic method at different contents of nanomaterials in suspension. The surface topography of the coatings was examined with scanning electron microscopy. The wettability was expressed as the water contact angle. The corrosion behavior was characterized by the potentiodynamic technique. The release rate of copper and silver into the simulated body fluid was investigated by atomic absorption spectrometry. The antibacterial efficiency was evaluated as the survivability and adhesion of the bacteria and the growth of the biofilm. The cytotoxicity was assessed for osteoblasts. The results demonstrate that silver and copper increase the corrosion resistance and hydrophilicity. Both elements together effectively kill bacteria and inhibit biofilm growth but appear to be toxic for osteoblasts. The obtained results show that the nanohydroxyapatite coatings doped with nanosilver and nanocopper in a one-stage electrophoretic process can be valuable for antibacterial coatings.

Tunable Microstructure and Morphology of the Self-Assembly Hydroxyapatite Coatings on ZK60 Magnesium Alloy Substrates Using Hydrothermal Methods

Hydroxyapatite coatings have been widely used to improve the corrosion resistance of biodegradable magnesium alloys. In this paper, in order to manufacture the ideal hydroxyapatite (HA) coating on the ZK60 magnesium substrate by hydrothermal method, formation mechanism of enhanced hydroxyapatite (HA) coatings, influence of pH values of the precursor solution on the HA morphology, corrosion resistance and cytotoxicity of HA coatings have been investigated. Results show that the growth pattern of the HA is influenced by the local pH value. HA has a preferential c-axis and higher crystallinity in the alkaline environment developing a nanorod-like structure, while in acid and neutral environments it has a preferential growth along the a(b)-plane with a lower crystallinity, developing a nanosheet-like structure. The different morphology and microstructure lead to different degradation behavior and performance of HA coatings. Immersion and electrochemical tests show that the neutral environment promote formation of HA coatings with high corrosion resistance. The cell culture experiments confirm that the enhanced corrosion resistance assure the biocompatibility of the substrate-coating system. In general, the HA coating prepared in neutral environment shows great potential in surface modification of magnesium alloys.

Using HAADF-STEM for atomic-scale evaluation of incorporation of antibacterial Ag atoms in a β-tricalcium phosphate structure

Structural evaluation of ionic additions in calcium phosphates that enhance their performance is a long-lasting area of research in the field of biomedical materials. Ionic incorporation in β-tricalcium phosphate (β-TCP) structures is indispensable for obtaining desirable properties for specific functions and applications. Owing to its complex structure and beam-sensitive nature, determining the extent of ion incorporation and its corresponding location in the β-TCP structure is challenging. Further, very few experimental studies have been able to estimate the location of Ag atoms incorporated in a β-TCP structure while considering the associated changes in lattice parameters. Although the incorporation alters the lattice parameters, the alteration is not significant enough for estimating the location of the incorporated Ag atoms. Here, Ag incorporation in a β-TCP structure was evaluated on atomic scale using scanning transmission electron microscopy (STEM). To the best of our knowledge, this is the first report to unambiguously determine the location of the incorporated Ag atoms in the β-TCP structure by comparing z-contrast profiles of the Ag and Ca atoms by combining the state-of-art STEM observations and STEM image simulations. The Ag incorporation in the Ca(4) sites of β-TCP, as estimated by the Rietveld refinement, was in good agreement with the high-angle annular dark-field STEM observations and the simulations of the location of Ag atoms for [001] and [010] zone axes.

Nanosized-Ag-doped porous β-tricalcium phosphate for biological applications

The treatment of infectious or potentially infective bone defects remains a major problem in clinical practice. Silver has the ability to potentiate antibiotics against resistant bacterial strains. In order to reduce the risk of long-term infections, it is necessary for the biomaterial scaffold to release Ag⁺ in a controlled manner during the entire healing process. In this study, given the antimicrobial characteristics of nanosized Ag (NSAg), we synthesized β-tricalcium phosphate (β-TCP) doped with 5 and 10 wt% NSAg (5 wt% NSAgTCP and 10 wt% NSAgTCP, respectively). The NSAgTCP composites exhibited similar macroporous structures to pure β-TCP. The NSAgTCP samples were examined by scanning electron microscopy at 10,000-times magnification, which revealed that silver was still present at the nanometer scale. X-ray diffraction revealed that silver does not change the crystalline properties of β-TCP. In addition, we observed that the mechanical strength of NSAgTCP increased with increasing amounts of added Ag. The antibacterial, physical, and chemical properties of NSAgTCP were investigated in vitro. We found that NSAgTCP is effective at inhibiting the growth of Staphylococcus aureus and Escherichia coli and is not cytotoxic to human bone marrow mesenchymal stem cells. Moreover, it does not hinder liver or kidney function when tested in vivo. As the bioceramic degrades, Ag ions are slowly released and new bone is formed. No significant cytotoxic effects were observed even when 10 wt% NSAgTCP was used. NSAgTCP has the ability to simultaneously repair bone defects and act as an anti-infective agent; hence, we expect that this material, with its good bone-repairing and anti-infective properties, will find wide spread use as a novel bone substitute.

Ionic Substitutions in Non-Apatitic Calcium Phosphates

Calcium phosphate materials (CaPs) are similar to inorganic part of human mineralized tissues (i.e., bone, enamel, and dentin). Owing to their high biocompatibility, CaPs, mainly hydroxyapatite (HA), have been investigated for their use in various medical applications. One of the most widely used ways to improve the biological and physicochemical properties of HA is ionic substitution with trace ions. Recent developments in bioceramics have already demonstrated that introducing foreign ions is also possible in other CaPs, such as tricalcium phosphates (amorphous as well as α and β crystalline forms) and brushite. The purpose of this paper is to review recent achievements in the field of non-apatitic CaPs substituted with various ions. Particular attention will be focused on tricalcium phosphates (TCP) and "additives" such as magnesium, zinc, strontium, and silicate ions, all of which have been widely investigated thanks to their important biological role. This review also highlights some of the potential biomedical applications of non-apatitic substituted CaPs.

In vitro performance of Ag-incorporated hydroxyapatite and its adhesive porous coatings deposited by electrostatic spraying

Bacterial infection of implanted materials is a significant complication that might require additional surgical operations for implant retrieval. As an antibacterial biomaterial, Ag-containing hydroxyapatite (HA) may be a solution to reduce the incidences of implant associated infections. In this study, pure, 0.2mol% and 0.3mol% Ag incorporated HA powders were synthesized via a precipitation method. Colloidal precursor dispersions prepared from these powders were used to deposit porous coatings onto titanium and stainless steel substrates via electrostatic spraying. The porous coating layers obtained with various deposition times and heat treatment conditions were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Scratch tests were conducted to assess the adhesion strength of the coating. Antibacterial activity of Ag-incorporated HA was tested towards Escherichia coli (E. coli) at various incubation times. Osteoblast adhesion on Ag-incorporated HA was evaluated to assess biocompatibility. Improvement in adhesion strength of the coating layer was observed after the heat treatment process due to mutual ionic diffusion at the interface. The Ag-incorporated HA killed all viable E. coli after 24h of incubation, whereas no antibacterial activity was detected with pure HA. In addition, in vitro cell culture tests demonstrated osteoblast adhesion similar to pure HA, which indicated good cytocompatibility. In summary, results of this study provided significant promise for the future study of Ag-incorporated HA for numerous medical applications.