Preparation and characterization of a titanium-substituted hydroxyapatite photocatalyst

Microwave-assisted synthesis of dual responsive luminomagnetic rare earth metal ions (Nd3+, Dy3+) co-doped nanohydroxyapatite for biomedical applications

The existing demand for the development of innovative multimodal imaging nanomaterial probes for biomedical applications stems from their unique combination of dual response modalities, i.e., photoluminescence (PL) and magnetic resonance imaging (MRI). In this study, for the first time, neodymium (Nd3+) and dysprosium (Dy3+) rare earth (RE) metal ions were co-doped into a hydroxyapatite (HAp) crystal lattice using a simple microwave-assisted synthesis technique to incorporate the essential properties of both the lanthanides in HAp. Theoretical as well as experimental studies were performed on novel Nd:Dy:HAp nanoparticles (NPs) to understand their photoluminescence and magnetic behaviour. Through co-precipitation, RE (Nd3+, Dy3+) ions were effectively integrated into the HAp crystal lattice, where they preferentially occupied the calcium ion (Ca2+) sites. The as-synthesized HAp, Nd:HAp, Dy:HAp, and Nd:Dy:HAp samples were characterized using different analytical tools. The PL and magnetic characteristics of Nd:Dy:HAp were dependent on the RE dopant ion type and concentration. In comparison with the pure HAp, the RE co-doped (Nd:Dy:HAp) NPs displayed multimodal features due to efficient energy transfer from the Nd3+ (sensitizer) to the Dy3+ (activator) ions. Furthermore, Nd:Dy:HAp NPs had good antimicrobial properties and they also displayed low cell toxicity effects. Hence, Nd:Dy:HAp NPs are attractive biomaterials for PL and MRI applications (e.g. permanent bone and tooth implants) and they can effectively be utilized in the biomedical industry for target-specific drug delivery, bioimaging, functional antimicrobial coatings etc. due to their tunable PL, magnetic, antimicrobial, and biocompatible capabilities.

Stearic acid-modified hollow hydroxyapatite particles with enhanced hydrophobicity for oil adsorption from oil spills

Oil spills lead to a substantial depletion of aquatic biodiversity. The mitigation of an oil spill can entail considerable financial outlays, give rise to consequential environmental impacts, and present formidable operational complexities. In this research, hollow hydroxyapatite particles with enhanced oil adsorption characteristics were prepared by surface modification with stearic acid. Peanut and vacuum pump oils were used to imitate oil spills and conduct adsorption tests. The 50% stearic acid-modified hydroxyapatite (Sa/HAP) adsorbent showed superior hydrophobic properties with respect to water contact angle data. Adsorption isotherm analysis revealed that the adsorption processes of peanut and vacuum pump oils matched well with the Sips isotherm model, with regression coefficients of 0.992 and 0.996, respectively. The oil adsorption by the modified hydroxyapatite (HAP) adsorbent was found to be 9.85 g·g-1 for peanut oil and 12.13 g·g-1 for vacuum pump oil. Furthermore, the adsorption kinetics performance was determined by chemical interaction, whereas the adsorption equilibrium capacities were 8.97 g·g-1 and 11.41 g·g-1, respectively. Recycling of the spent adsorbent was performed with toluene stripping. The synthesized oil-adsorbents were analyzed by SEM, FTIR, XRD, contact angle, and TGA analyses. Hence, the efficacy of the Sa/HAP material as a potential adsorbent for the purification of oil-contaminated water was established, attributed to its commendable oil adsorption capability.

Effects of Various Ripening Media on the Mesoporous Structure and Morphology of Hydroxyapatite Powders

Mesoporous hydroxyapatite (HA) materials demonstrate advantages as catalysts and as support systems for catalysis, as adsorbent materials for removing contamination from soil and water, and as nanocarriers of functional agents for bone-related therapies. The present research demonstrates the possibility of the enlargement of the Brunauer-Emmett-Teller specific surface area (SSA), pore volume, and average pore diameter via changing the synthesis medium and ripening the material in the mother solution after the precipitation processes have been completed. HA powders were investigated via chemical analysis, X-ray diffraction analysis, Fourier-transform IR spectroscopy, transmission electron microscopy (TEM), and scanning (SEM) electron microscopy. Their SSA, pore volume, and pore-size distributions were determined via low-temperature nitrogen adsorption measurements, the zeta potential was established, and electron paramagnetic resonance (EPR) spectroscopy was performed. When the materials were synthesized in water-ethanol and water-acetone media, the SSA and total pore volume were 52.1 m²g^-1 and 116.4 m²g^-1, and 0.231 and 0.286 cm³g^-1, respectively. After ripening for 21 days, the particle morphology changed, the length/width aspect ratio decreased, and looser and smaller powder agglomerates were obtained. These changes in their characteristics led to an increase in SSA for the water and water-ethanol samples, while pore volume demonstrated a multiplied increase for all samples, reaching 0.593 cm³g^-1 for the water-acetone sample.

Titanium-Containing Silicate-Based Sol-Gel Bioactive Glass: Development, Characterization, and Applications

Bioactive glasses are surface-reactive glasses that, when placed in physiological fluid, undergo a transformation from glass to hydroxyapatite. Doping the bioactive glass with metallic ions can impart desirable and unique properties that are not inherent to natural hydroxyapatite. Once such ion is titanium. Titanium exists in trace amounts in native dental enamel, and its presence has been correlated with increased tooth hardness and brightness, both desirable clinical properties. Synthetic titanium-substituted hydroxyapatite exhibits better mechanical and antibacterial properties and demonstrates potential for an improved cellular response when compared to unmodified hydroxyapatite with applications in the broader field of bone tissue engineering. In this work, we use the sol-gel method to synthesize a titanium-containing silicate-based bioactive glass aimed at generating titanium-substituted hydroxyapatite on the glass surface upon immersion in body fluid. Titanium is homogeneously distributed throughout our glass, which keeps its amorphous nature. After 14 days of immersion in simulated body fluid, the glass forms a titanium-substituted hydroxyapatite on its surface. Enamel surfaces treated with the titanium-containing glass show significantly increased microhardness compared to enamel surfaces treated with a control glass, confirming the potential for the proposed glass in enamel remineralization. We also show that the presence of titanium in the glass promotes cell differentiation toward bone formation, suggesting further applications for this material in the broader field of bone tissue engineering.

Nanomixture of 0-D ternary metal oxides (TiO2- SnO2-Al2O3) cooperating with 1-D hydroxyapatite (HAp) nanorods for RhB removal from synthetic wastewater and hydrogen evolution via water splitting

This work was carried out to devise a feasible alternative to remove cationic dyes from industrial wastewater. A nanomixture of (TiO₂-SnO₂-Al₂O₃) cooperating with Hydroxyapatite (HAp) nanorods was synthesized in this regard as a catalyst to degrade Rhodamine B (RhB) dye from aqueous medium. The physicochemical properties of the hydrothermally prepared Hydroxyapatite Nano Mixture (HNM) were revealed through XRD, FESEM, TEM, XPS, FTIR, BET-BHJ, UV-Vis, and Raman spectroscopy techniques. The synthesized material which was found to be nanorods of average crystallite size 12.53 nm and BET Specific Surface area 60.81 m² g^-1 proved to be very effective for the removal of RhB at various pH conditions (acid, basic, and neutral). Maximum removal of 97% was achieved within 30 min of UV irradiation using 5 ppm RhB in acidic medium while at a higher concentration (20 ppm), it takes just 90 min to achieve 98% degradation of RhB under the same reaction conditions. A further catalytic potential of the prepared nanomixture for hydrogen (H₂) evolution via water splitting was explored where 129.45 μmol g^-1 of H₂ was evolved within 60 min. Our findings suggest that the prepared nanomixture could be used as an efficient catalyst for removing spent dyes used in industrial processes and also as a catalyst for hydrogen gas production.

Vacancy-Induced Visible Light-Driven Fluorescence in Toxic Ion-Free Resorbable Magnetic Calcium Phosphates for Cell Imaging Applications

Multifunctional nanosized particles are very beneficial in the field of biomedicine. Bioactive and highly biocompatible calcium phosphate (CaP) nanoparticles (∼50 nm) exhibiting both superparamagnetic and fluorescence properties were synthesized by incorporating dual ions (Fe³⁺ and Sr²⁺) in HAp (hydroxyapatite) [Ca₁₀(PO₄)₆(OH)₂]. Insertion of Fe³⁺ creates oxygen vacancies at the PO₄^3- site, thereby destabilizing the structure. Thus, in order to maintain the structural stability, Sr²⁺ has been incorporated. This incorporation of Sr²⁺ leads to an intense emission at 550 nm. HAp nanoparticles when subjected to thermal treatment (800 °C) transform to β-TCP, exhibiting emission at 710 nm due to the emergence of an intermediate band. Moreover, these nanoparticles exhibit fluorescence in visible light when compared to the other UV and IR fluorescence excitation sources which could damage the tissues. The synthesis involving the combination of ultrasound and microwave techniques resulted in the distribution of Fe³⁺ in the interstitial sites of CaP, which is responsible for the excellent fluorescent properties. Moreover, thermally treated CaP becomes superparamagnetic, without affecting the desired optical properties. The bioactive, biocompatible, magnetic, and fluorescent properties of this resorbable CaP which is free from toxic heavy metals (Eu, Gd, etc.) could help in overcoming the long-term cytotoxicity. This could also be useful in tracking the location of the nanoparticles during drug delivery and magnetic hyperthermia. The bioactive fluorescent CaP nanoparticle helps in monitoring the bone growth and in addition, it could be employed in cell imaging applications. The in vitro MCF-7 imaging using the nanoparticles after 24 h of uptake at 465 nm evidences the bioimaging capability of the prepared nanoparticles. The reproducibility of the defect level is essential for the defect-induced emission properties. The synthesis of nontoxic fluorescent CaP is highly reproducible with the present synthesis method. Hence, it could be safely employed in various biomedical applications.

Iron Oxide/Phosphatic Materials Composites with Potential Applications in Environmental Protection

Currently, hydroxyapatite is probably the most researched material, due to its multiple applications in medical, environmental, or cultural heritage, when the classical structure is modified and calcium is displaced partially or totally with different metals. By changing the classical structure of the hydroxyapatite, new morphologies can be obtained, thus allowing final applications different from those of the initial hydroxyapatite material. However, their properties should be tuned for the desired application. In this context, the present paper describes the synthesis and characterization (through energy-dispersive X-ray fluorescence, X-ray diffraction, FTIR, thermal analysis, and transmission electron microscopy) of iron oxide/manganese-containing phosphatic phase composite materials, developed in order to obtain the enhancement of final environmental applications (photodegradation of dyes, adsorption of organic compounds). The composite material was tested for photocatalytic properties, after embedding in hydrosoluble film-forming materials. Photocatalytic coatings show different activity during the photodecomposition of Methylene Blue, used as a model of a contaminant. The photocatalytic activities of the materials were discussed in relationship with both the phosphatic materials and the magnetic components. Finally, other environmental applications were studied for the developed materials (adsorption of non-steroidal anti-inflammatory drugs—paracetamol and ibuprofen), revealing an enhancement of the adsorption capacity of the phosphatic material upon addition of the magnetic phase.

Photocatalytic degradation and kinetic modeling of azo dye using bimetallic photocatalysts: effect of synthesis and operational parameters

Industrial wastewaters are the major source polluting the surface and ground water resources. Pollutants released along with the untreated textile industry wastewaters are responsible for the great damage to the natural resources like water. Considering the hazardous effects of the azo dyes (textile coloring agents) and their byproducts, there is a need to develop cost-effective and efficient treatment method for the textile wastewaters as such dyes have been reported as toxic, mutagenic, and carcinogenic and can cause direct demolition of aquatic communities. One of the possible and effective treatment methods is the use of TiO₂ photocatalysis due to its chemical stability, low cost, and non-toxic nature. The present study explored the photocatalytic potential of anatase-type of bimetallic Cu-Ni/TiO₂ photocatalysts under visible light irradiation for possible photocatalytic degradation and mineralization of Methyl Orange (MO), as model azo dye. The focus was to correlate the synthesis (different calcination temperatures, phase composition of TiO₂ either anatase or rutile, and metal ion loading in terms of concentration and composition (Cu:Ni)) and operational parameters (photocatalyst loading, pollutant concentration, and irradiation time) that were believed responsible for the enhanced photocatalytic performance. Blank experiments were carried out to check the effect of metal loading in comparison to bare TiO₂ and effect of absence or presence of light and photocatalysts on MO photodegradation. Results obtained using bimetallic photocatalysts are promising as compared to bare TiO₂ as 100% MO removal and ~ 90% %COD removal were obtained in 90 min of irradiation, obeying a pseudo-first-order kinetics with photocatalytic reaction via the Langmuir-Hinshelwood mechanism with a good linear fit. Photocatalysts synthesized using anatase TiO₂ were reported with improved performance compared to rutile phase. It is evident that synthesis parameters influence photocatalyst performance directly. The higher rate constant (> 1) that proves the excellent adsorption capacity of the tested photocatalysts for tested pollutants on the surface may have a great prospective for photocatalytic water purification at neutral pH.

Opposite influences of mineral-associated and dissolved organic matter on the transport of hydroxyapatite nanoparticles through soil and aggregates

The mechanism by which soil organic matter (SOM) controls nanoparticle transport through natural soils is unclear. In this study, we distinguished the specific effects of two primary SOM fractions, mineral-associated organic matter (MOM) and dissolved organic matter (DOM), on the transport of hydroxyapatite nanoparticles (nHAP) through a loamy soil under the conditions of saturated steady flow and environmentally relevant solution chemistry (1 mM NaCl at pH 7). The results showed that MOM could inhibit the transport of nHAP by decreasing electrostatic repulsion and increasing mechanical straining and hydrophobic interactions. Specifically, the presence of MOM reduced the mobility of nHAP in the bulk soil and its macroaggregates by ~4 fold and ~6 fold, respectively, and this hindered effect became further conspicuous in microaggregates (~36 fold decrease). An analysis of extended Derjaguin-Landau-Vervey-Overbeek (abbreviated as XDLVO) interactions indicated that MOM could decrease the primary energy barrier (Φ_max1), primary minimum (Φ_min1), and secondary minimum (Φ_min2) to promote nHAP attachment. Conversely, DOM (10-50 mg L^-1) favored nHAP mobility due to an increase in electrostatic repulsion among nHAP particles and between nHAP and soil surfaces. Pre-flushing soil with DOM (causing DOM sorption on soil) increased nHAP mobility by ~2 fold in the bulk soil and its macroaggregates, and this facilitated effect was furthered in microaggregates (~11 fold increase). The results of XDLVO interactions showed that DOM increased Φ_max1, Φ_min1, and Φ_min2, producing an unfavorable effect on nHAP attachment. Mass recovery data revealed that the MOM-hindered effect was stronger than the DOM-facilitated effect on nHAP transport. This study suggested that changing SOM fractions could control the mobility of nanoparticles in the subsurface considerably.

Waste-to-wealth: biowaste valorization into valuable bio(nano)materials

The waste-to-wealth concept aims to promote a future sustainable lifestyle where waste valorization is seen not only for its intrinsic benefits to the environment but also to develop new technologies, livelihoods and jobs.

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.

Antiviral activity of multifunctional composite based on TiO2-modified hydroxyapatite

An antiviral activity of TiO₂-modified hydroxyapatite composite (HA/TiO₂) had been investigated. The HA/TiO₂ composite (HA50:Ti50) was prepared by a solid state reaction method followed by calcination at 650 °C for 2 h. Phase formations and morphologies of the obtained HA/TiO₂ composite powders were determined using XRD and SEM. XRD result confirmed that HA/TiO₂ composite was successfully prepared. SEM revealed small crystals of anatase TiO₂ embedded in larger HA crystals. A strong antiviral activity against H1N1 Influenza A Virus was observed at 0.5 mg/ml concentration of the composite under the UV irradiation for 60 min. It showed the highest rate of reducing virus titer approximately more than 2 log/h. Results obtained from this study indicated that HA/TiO₂ composite could be a promising material to be used as antimicrobial filtration applications such as in face masks.

Biomineralization of a titanium-modified hydroxyapatite semiconductor on conductive wool fibers

Metal ions are frequently incorporated into crystalline materials to improve their electrochemical properties and to confer new physicochemical properties. Naturally-occurring phosphate apatite, which is formed geologically and in biomineralization processes, has extensive potential applications and is therefore an attractive functional material. In this study, we generate a novel building block for flexible optoelectronics using bio-inspired methods to deposit a layer of photoactive titanium-modified hydroxyapatite (TiHA) nanoparticles (NPs) on conductive polypyrrole(PPy)-coated wool yarns. The titanium concentration in the reaction solution was varied between 8-50 mol% with respect to the phosphorous, which led to titanate ions replacing phosphate in the hydroxyapatite lattice at levels up to 17 mol%. PPy was separately deposited on wool yarns by oxidative polymerization, using two dopants: (i) anthraquinone-2,6-disulfonic acid to increase the conductivity of the PPy layer and (ii) pyroglutamic acid, to reduce the resistivity of the wool yarns and to promote the heterogeneous nucleation of the TiHA NPs. A specific titanium concentration (25 mol% wrt P) was used to endow the TiHA NPs on the PPy-coated fibers with a desirable band gap value of 3.68 eV, and a specific surface area of 146 m² g^-1. This is the first time that a thin film of a wide-band gap semiconductor has been deposited on natural fibers to create a fiber-based building block that can be used to manufacture flexible electronic devices.

Calcium hydroxyapatite-based photocatalysts for environment remediation: Characteristics, performances and future perspectives

Calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (HAp) is a material widely used in biomedicine, for bone implants manufacture, due to its biocompatibility. HAp has also application for environmental remediation, as it can be employed as metal removal; moreover, it has the capability of effectively adsorbing organic molecules its surface. In recent years, the photocatalytic properties of HAp have been investigated; indeed several studies report of HAp used as photocatalyst, either on its own or combined with other photocatalytic materials. Although in the majority of cases the activity was induced by UV light, some reports of visible light-activated materials were reported. Here we present a critical review of the latest developments for HAp-based photocatalysts; the materials discussed are undoped single phase HAp, doped HAp and HAp-containing composites. For undoped single phase HAp, the possible surface treatment and lattice defects which can lead to a photoactive material are discussed. Considering doped HAp, the use of Ti⁴⁺ (the most common dopant) is described, with particular attention to the effects that this metal have on the characteristics of the material (i.e. crystallinity) and on its photocatalytic behaviour. The use of other dopants is also discussed. For the multiphasic materials, the combination of HAp with other photocatalysts is discussed, mainly but not only with titanium dioxide TiO₂. Overall, HAp is a compound with high potential as photocatalyst; this property, combined with its capability for heavy metal removal, makes it a multifunctional material for environmental remediation. As future perspectives, further studies, based on the results obtained until present, should be performed, to improve the performance of the materials and/or shift the band gap into the visible. The use of other dopants and/or the combination with other photocatalysts, for instance, are features which is worth exploring.

The deposition of strontium and zinc Co-substituted hydroxyapatite coatings

The in vitro and in vivo performance of hydroxyapatite (HAp) coatings can be modified by the addition of different trace ions, such as silicon (Si), lithium (Li), magnesium (Mg), zinc (Zn) or strontium (Sr) into the HAp lattice, to more closely mirror the complex chemistry of human bone. To date, most of the work in the literature has considered single ion-substituted materials and coatings, with limited reports on co-substituted calcium phosphate systems. The aim of this study was to investigate the potential of radio frequency magnetron sputtering to deposit Sr and Zn co-substituted HAp coatings using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The FTIR and XPS results highlight that all of the Sr, Zn and Sr-Zn co-substituted surfaces produced are all dehydroxylated and are calcium deficient. All of the coatings contained HPO₄^2- groups, however; only the pure HAp coating and the Sr substituted HAp coating contained additional CO₃^2- groups. The XRD results highlight that none of the coatings produced in this study contain any other impurity CaP phases, showing peaks corresponding to that of ICDD file #01-072-1243 for HAp, albeit shifted to lower 2θ values due to the incorporation of Sr into the HAp lattice for Ca (in the Sr and Sr-Zn co-substituted surfaces only). Therefore, the results here clearly show that RF magnetron sputtering offers a simple means to deliver Sr and Zn co-substituted HAp coatings with enhanced surface properties. (a) XRD patterns for RF magnetron sputter deposited hydroxyapatite coatings and (b)-(d) for Sr, Zn and Sr-Zn co-substituted coatings, respectively. The XPS spectra in (b) confirms the presence of a HA sputter deposited coating as opposed to

Plasmon induced enhanced photocatalytic activity of gold loaded hydroxyapatite nanoparticles for methylene blue degradation under visible light

A facile surfactant free wet-precipitation process was employed to prepare hydroxyapatite (HAp) nanoparticles.

Photodegradation of pharmaceutical persistent pollutants using hydroxyapatite-based materials

Pharmaceutical persistent pollutants pose a serious threat to the environment. The aim of this study was to use, for the first time, hydroxyapatite-based biomaterials as photocatalysts to degrade micropollutants. Diclofenac and fluoxetine were selected for these initial tests. Hydroxyapatite (Ca10(PO4)(OH)2, HAp) is one of the most commonly used biomaterials/bioceramics, being a major constituent of bone. In this work sustainable HAp-based materials of marine origin, obtained from cod fish bones, were used; these photocatalysts were previously fully studied and characterised. Both single-phase HAp and HAp-titania multicomponent materials (1 wt% TiO2) were employed as UV light photocatalysts, the latter showing better performance, indicated by higher degradation rates of both compounds. The HAp-titania photocatalyst showed excellent degradation of both persistent pollutants, the maximum degradation performance being 100% for fluoxetine and 92% for diclofenac, with pollutant and photocatalyst concentrations of 2 ppm and 4 g/L, respectively. Variations in features such as pollutant and photocatalyst concentrations were investigated, and results showed that generally fluoxetine was degraded more easily than diclofenac. The photocatalyst's crystallinity was not affected by the photodegradation reaction; indeed the material exhibited good photostability, as the degradation rate did not decrease when the material was reused. Tests were also performed using actual treated wastewater; the photocatalyst was still effective, even if with lower efficiency (-20% and -4% for diclofenac and fluoxetine, respectively). TOC analysis showed high but incomplete mineralisation of the pollutants (maximum 60% and 80% for DCF and FXT, respectively).

Immobilization of cadmium ions to synthesis hierarchical flowerlike cadmium phosphates microspheres and their application in the degradation of organic pollutants under light irradiation

Hierarchical flowerlike Cd₅H₂(PO₄)₄·4H₂O and Cd₅(PO₄)₂P₂O₇ microspheres were prepared by cadmium ion immobilization followed by an annealing treatment. Cd₅(PO₄)₂P₂O₇ was applied as a novel photocatalyst toward dye degradation under light irradiation.

An effective route to the synthesis of carbonated apatite crystals with controllable morphologies and their growth mechanism

CHAp powders with controllable morphologies and sizes were synthesized using HMT as a hydroxide anion-generating agent in a phosphate-surplus solution.

Production of hydroxyapatite layers on the plasma electrolytically oxidized surface of titanium alloys

Hydroxyapatite (HA) is a bioactive material that is widely used for improving the osseointegration of titanium dental implants. Titanium can be coated with HA by various methods, such as chemical vapor deposition (CVD), thermal spray, or plasma spray. HA coatings can also be grown on titanium surfaces by hydrothermal, chemical, and electrochemical methods. Plasma electrolytic oxidation (PEO), or microarc oxidation (MAO), is an electrochemical method that enables the production of a thick porous oxide layer on the surface of a titanium implant. If the electrolyte in which PEO is performed contains calcium and phosphate ions, the oxide layer produced may contain hydroxyapatite. The HA content can then be increased by subsequent hydrothermal treatment. The HA thus produced on titanium surfaces has attractive properties, such as a high porosity, a controllable thickness, and a considerable density, which favor its use in dental and bone surgery. This review summarizes the state of the art and possible further development of PEO for the production of HA on Ti implants.

Substituted hydroxyapatites with antibacterial properties

Reconstructive surgery is presently struggling with the problem of infections located within implantation biomaterials. Of course, the best antibacterial protection is antibiotic therapy. However, oral antibiotic therapy is sometimes ineffective, while administering an antibiotic at the location of infection is often associated with an unfavourable ratio of dosage efficiency and toxic effect. Thus, the present study aims to find a new factor which may improve antibacterial activity while also presenting low toxicity to the human cells. Such factors are usually implemented along with the implant itself and may be an integral part of it. Many recent studies have focused on inorganic factors, such as metal nanoparticles, salts, and metal oxides. The advantages of inorganic factors include the ease with which they can be combined with ceramic and polymeric biomaterials. The following review focuses on hydroxyapatites substituted with ions with antibacterial properties. It considers materials that have already been applied in regenerative medicine (e.g., hydroxyapatites with silver ions) and those that are only at the preliminary stage of research and which could potentially be used in implantology or dentistry. We present methods for the synthesis of modified apatites and the antibacterial mechanisms of various ions as well as their antibacterial efficiency.

Trace elements can influence the physical properties of tooth enamel

In previous studies, we showed that the size of apatite nanocrystals in tooth enamel can influence its physical properties. This important discovery raised a new question; which factors are regulating the size of these nanocrystals? Trace elements can affect crystallographic properties of synthetic apatite, therefore this study was designed to investigate how trace elements influence enamel's crystallographic properties and ultimately its physical properties. The concentration of trace elements in tooth enamel was determined for 38 extracted human teeth using inductively coupled plasma-optical emission spectroscopy (ICP-OES). The following trace elements were detected: Al, K, Mg, S, Na, Zn, Si, B, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se and Ti. Simple and stepwise multiple regression was used to identify the correlations between trace elements concentration in enamel and its crystallographic structure, hardness, resistance to crack propagation, shade lightness and carbonate content. The presence of some trace elements in enamel was correlated with the size (Pb, Ti, Mn) and lattice parameters (Se, Cr, Ni) of apatite nanocrystals. Some trace elements such as Ti was significantly correlated with tooth crystallographic structure and consequently with hardness and shade lightness. We conclude that the presence of trace elements in enamel could influence its physical properties.

Crystal structure of cobalt-substituted calcium hydroxyapatite nanopowders prepared by hydrothermal processing

A series of cobalt-exchanged hydroxyapatite (CoHAp) powders with different Ca/Co ratios and nominal unit-cell contents Ca10−xCox(PO4)6(OH)2,x= 0, 0.5, 1.0, 1.5 and 2.0, were synthesized by hydrothermal treatment of a precipitate at 473 K for 8 h. Based on ICP (inductively coupled plasma) emission spectroscopy analysis, it was established that the maximum amount of cobalt incorporation saturated at ∼12 at.% under these conditions. The effects of cobalt content on the CoHAp powders were investigated using ICP emission spectroscopy, particle size analysis, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) analyses as well as X-ray powder diffraction (XRPD) including Rietveld analysis. According to XRPD, all the materials are single-phase HAp and CoHAp of low crystallinity. Rietveld analysis shows that Co enrichment causes theccell parameter to decrease at a faster rate than theacell parameter. A microstructural analysis showed anisotropic X-ray line broadening due to crystallite size reduction. In CoHAp there is significant crystal elongation in [001], and the average size decreases with increasing cobalt content. The crystallite morphology transforms from rod-like for the pure HAp to lamellae at the highest degree of Co substitution. The results of Rietveld refinement (symmetry, size and morphology of the crystallites) were confirmed by TEM and HRTEM analysis.

Development and characterization of titanium-containing hydroxyapatite for medical applications

Hydroxyapatite containing levels of titanium (TiHA) of up to 1.6 wt.% has been produced via a chemical co-precipitation route. The distribution of Ti was seen by transmission electron microscopy/energy-dispersive X-ray analysis to be uniform throughout as-prepared nanosized TiHA particles (20 nm x 100 nm). The incorporation of Ti into the HA structure was found to influence the ceramic microstructure on sintering and the grain size was found to decrease from 0.89 microm with HA to 0.63 microm with 0.8 wt.% TiHA (0.8 TiHA) and 0.45 microm with 1.6 wt.% TiHA (1.6 TiHA). Rietveld refinement analysis showed that there was a proportional increase in both the a and c axis with incorporation of Ti into the HA lattice structure, leading to an increase in the cell volume with the addition of Ti. Fourier transform-Raman analysis showed a slight increase in the ratio of O-H/P-O peaks on TiHA, in comparison with HA. A bone-like apatite layer was formed on the surface of TiHA after immersion in simulated body fluid for 3 days, which demonstrated the high in vitro bioactivity of TiHA. In vitro culture with primary human osteoblast (HOB) cells revealed that TiHA was able to support the growth and proliferation of HOB cells in vitro, with a significantly higher cell activity being observed on 0.8 TiHA after 7 days of culture in comparison with that on HA. Well-organized actin cytoskeletal protein was developed after 1 day of culture, and an increase in cell filopodia (attachment) was observed on TiHA sample surfaces. The results indicate that TiHA has great potential for biomedical applications.