Synthesis and characterization of hydroxyapatite, fluoride-substituted hydroxyapatite and fluorapatite

Comparative study of pulpal response following direct pulp capping using synthesized fluorapatite and hydroxyapatite nanoparticles

OBJECTIVE

This study aimed to investigate and compare the histological response of rabbit dental pulp after direct pulp capping with 3 different materials: mineral trioxide aggregate (MTA), nanoparticles of fluorapatite (Nano-FA), and nanoparticles of hydroxyapatite (Nano-HA) after 4 and 6-week time intervals.

MATERIAL AND METHODS

A total of 72 upper and lower incisor teeth from 18 rabbits were randomly categorized into 3 groups)24 incisors from six rabbits each. MTA Group: teeth were capped with MTA. Nano-FA Group: teeth were capped with fluorapatite nanoparticles. Nano-HA Group: teeth were capped with hydroxyapatite nanoparticles. Blood samples were collected to examine some antioxidant enzymes nitric oxide (NO), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione (GSH), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α). After that, three rabbits from each group were euthanized after 4 and 6 weeks, respectively. Pulp tissues of all teeth in all groups were histologically observed.

RESULTS

The obtained results showed that both Nano-HA induced the formation of thick dentin bridges with irregular dentin patterns at 6 weeks, while MTA and Nano-FA induced no dentin bridge with no tubular dentin pattern. Blood examination at the two intervals revealed no significant increase or decrease in the values of NO, SOD, CAT, GPx, GSH, and TNF-α. However, there was a significant increase in p-values of IL-6 in the Nano-FA treated group compared to both MTA and Nano-HA treated groups at the two intervals. Regarding the inflammatory reaction of the dental pulp, the MTA and Nano-HA groups displayed moderate inflammation, followed by Nano-FA, which showed the highest prevalence of nonpathological inflammation. Histological results were consistent with the blood examination. After 4 weeks, the Nano-FA and Nano-HA groups showed pulp fibrosis at the operating site, but the MTA showed only granulation tissues. Plus, dilated blood vessels appeared in the Nano-FA group. After 6 weeks, MTA and Nano-FA groups showed pulp fibrosis at the operating site with the persistence of dilated blood vessels with Nano-FA. The nano-HA group showed dentin bridge formation at the operating site.

CONCLUSION

MTA and Nano-HA could be considered favorable materials for direct pulp capping, while Nano-FA produces nonpathological inflammatory cell reactions. Moreover, the Nano-HA was the best in dentin bridge formation. Although nano-FA increased the operating site closure, it was noticed that it significantly increased IL-6 compared to MTA at the two intervals and significantly increased IL-6 compared to Nano-HA at 6 weeks, which may be manifested as some nonpathological inflammations in the Nano-FA group compared to the other groups, but it was deemed acceptable to direct pulp capping procedures.

Effects of Copper Doping on Fluorohydroxyapatite Coating: Analysis of Microstructure, Biocompatibility, Corrosion Resistance, and Cell Adhesion Characteristics

In this research, Cu-doped fluorohydroxyapatite (Cu-FHAp) coatings containing varying levels of Cu in electrolyte as a dopant were synthesized by the ultrasonic-assisted pulse-reverse electrodeposition method on AZ31 alloy to improve the biocompatibility and corrosion resistance of the alloy for biomedical applications. Microstructural analysis revealed that the inclusion of the Cu dopant results in the formation of a more uniform coating. Energy dispersive spectroscopy analysis highlights a notable incorporation of copper within the fluorohydroxyapatite structure. The increase in Cu content significantly affected surface roughness and elevated hydrophobicity, leading to a contact angle of up to 136°. Electrochemical impedance spectroscopy analysis revealed that all samples containing copper exhibited favorable corrosion resistance, with the sample prepared using the electrolyte containing 0.036 g/L Cu(NO3)2 demonstrating the highest corrosion resistance. Cell adhesion evaluation yielded a satisfactory cell adhesion to the coated samples, indicating that the presence of the optimum value of Cu does not induce considerable cytotoxic effects.

A Porous Fluoride-Substituted Bovine-Derived Hydroxyapatite Scaffold Constructed for Applications in Bone Tissue Regeneration

Hydroxyapatite is widely used in bone implantation because of its similar mineral composition to natural bone, allowing it to serve as a biocompatible osteoconductive support. A bovine-derived hydroxyapatite (BHA) scaffold was developed through an array of defatting and deproteinization procedures. The BHA scaffold was substituted with fluoride ions using a modified sol-gel method to produce a bovine-derived fluorapatite (BFA) scaffold. Fourier-transform infrared spectroscopy and X-ray diffraction analysis showed that fluoride ions were successfully substituted into the BHA lattice. According to energy dispersive X-ray analysis, the main inorganic phases contained calcium and phosphorus with a fluoride ratio of ~1-2 wt%. Scanning electron microscopy presented a natural microporous architecture for the BFA scaffold with pore sizes ranging from ~200-600 μm. The BHA scaffold was chemically stable and showed sustained degradation in simulated-body fluid. Young's modulus and yield strength were superior in the BFA scaffold to BHA. In vitro cell culture studies showed that the BFA was biocompatible, supporting the proliferative growth of Saos-2 osteoblast cells and exhibiting osteoinductive features. This unique technique of producing hydroxyapatite from bovine bone with the intent of producing high performance biomedically targeted materials could be used to improve bone repair.

Effects of a Two-Step Silver Diamine Fluoride Varnish on Shear Bond Strength of Restorations, Dentin and Enamel Hardness, and Biofilm Formation

INTRODUCTION

Dental caries are a limiting factor in maintaining dental and medical readiness in the military. Untreated dental caries can lead to dire health consequences. Consistent and comprehensive access to dental care is often limited due to the intensive operational demands on our nation's warfighters. The standard of care for dental caries is a surgical model where diseased tooth tissue is surgically removed and restored with appropriate restorative materials. While effective, it is not practical in the military operational environment, especially under time constraints. Dental restoratives offer military personnel a simple and preventive treatment of dental caries and are suitable as self-applied first aids. The purpose of this study was to measure the shear bond strengths of two dental restorative materials to human teeth paired with two different fluoride treatments and the hardness and biofilm formation on teeth after applying the fluoride varnishes.

MATERIALS AND METHODS

Specimens were made of human molar teeth treated with each of the following four materials: glass ionomer cement GC Fuji II LC Capsules, Filtek Z250, Riva Star steps 1 and 2, or Mark3 NaF varnish. Step 1 of Riva Star consists of silver diamine fluoride and step 2 contains potassium iodide. On human molar slabs, 10 circular specimens of 5 cm in diameter were prepared with restoratives according to manufacturer procedures. Etch-Rite and a proprietary aluminum chloride-based cavity conditioner were used as etchants on tooth surfaces for the Filtek Z250 and glass ionomer cement, respectively. After at least 24 hours underwater, each assembly was removed, and the shear bond strength of the adhesive was measured according to International Organization for Standardization (ISO) 29022.The hardness was measured according to ISO 14233. Hardness measurements were performed before varnish application, then after storage in an incubator at 37 °C for 4 hours in a demineralization solution (pH = 4.5), and after 1 day in a mineralization solution (pH = 7). A crystal violet staining assay was used to measure biofilm formation of Streptococcus mutans bacteria on human molar teeth after the application of fluoride varnish.

RESULTS

We report a 16% increase in shear bond strength of the Filtek Z250/Riva Star coupled treatment compared to the Filtek Z250/Mark3 NaF coupled treatment. We also demonstrate a significant 84% decrease in bond strength with a GC Fuji II LC/Mark3 NaF treatment compared to control (P = .0002), while Riva Star remains statistically unchanged. Enamel and dentinal hardness are significantly improved when Riva Star is applied compared to NaF varnish. A 25%-35% (P < .0001) decrease in oral biofilm formation was observed on samples where a Riva Star or NaF varnish was applied.

CONCLUSIONS

Mechanical and antimicrobial testing indicated Riva Star, compared favorably with and in some cases, performed better in the laboratory than a Mark3 NaF varnish. Hardness measurements indicated Riva Star is more effective in dentin tubule occlusion compared to NaF varnish. Our findings help provide practical suggestions to dental treatment, particularly to the unique dental environments seen in the military. Riva Star may be used as an adjunctive treatment prior to placing a final restoration. This study supports the use of Riva Star in conjunction with GC Fuji II LC or Filtek Z250 restorative materials, making it a promising treatment in military dental applications.

Fluoride-Incorporated Apatite Coating on Collagen Sponge as a Carrier for Basic Fibroblast Growth Factor

Coating layers consisting of a crystalline apatite matrix with immobilized basic fibroblast growth factor (bFGF) can release bFGF, thereby enhancing bone regeneration depending on their bFGF content. We hypothesized that the incorporation of fluoride ions into apatite crystals would enable the tailored release of bFGF from the coating layer depending on the layer's fluoride content. In the present study, coating layers consisting of fluoride-incorporated apatite (FAp) crystals with immobilized bFGF were coated on a porous collagen sponge by a precursor-assisted biomimetic process using supersaturated calcium phosphate solutions with various fluoride concentrations. The fluoride content in the coating layer increased with the increasing fluoride concentration of the supersaturated solution. The increased fluoride content in the coating layer reduced its solubility and suppressed the burst release of bFGF from the coated sponge into a physiological salt solution. The bFGF release was caused by the partial dissolution of the coating layer and, thus, accompanied by the fluoride release. The concentrations of released bFGF and fluoride were controlled within the estimated effective ranges in enhancing bone regeneration. These findings provide useful design guidelines for the construction of a mineralized, bFGF-releasing collagen scaffold that would be beneficial for bone tissue engineering, although further in vitro and in vivo studies are warranted.

Highly cyto- and immune compatible new synthetic fluorapatite nanomaterials co-doped with rubidium(I) and europium(III) ions

In the present study, biocompatible luminescent of nanosized fluorapatite doped with rubidium(I) (Rb+ ion) and europium(III) (Eu3+ ion) ions were synthesized via hydrothermal method. It was investigated the influence of co-doped Rb+ and Eu3+ ions on the structural, and morphological characteristics of the obtained fluorapatite materials. The characterization techniques utilized included: X-ray powder diffraction (XRPD), infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). Moreover, to establish the influence of the co-doped Rb+ and Eu3+ ions on the luminescence properties of the lanthanide ion, emission excitation, emission spectrum and luminescence decays were measured. This confirmed a distinct red emission originating from Eu3+ ions and an increased emission lifetime. To determine the biocompatibility of the obtained fluorapatite compounds, in vitro studies using normal dermal human fibroblasts were performed. The results of these studies clearly demonstrate the remarkable biocompatibility of our compounds. This discovery opens exciting prospects for the use of synthetic fluorapatites doped with Eu3+ and Rb+ ions in various biomedical contexts. In particular, these materials hold great promise for potential applications in regenerative engineering, but also serve as innovative and practical solutions as bone scaffolds and dental implants containing nano-fluorapatite. Further discussion of these properties can be found in this article, along with a discussion of their importance and potential in the field of biomedical applications. However, according to our pervious study and based on our current investigations but also based on available scientific records, it was proposed potential molecular mechanism of Rb+ ions in the process of osteoclastogenesis.

Physicochemical understanding of biomineralization by molecular vibrational spectroscopy: From mechanism to nature

The process and mechanism of biomineralization and relevant physicochemical properties of mineral crystals are remarkably sophisticated multidisciplinary fields that include biology, chemistry, physics, and materials science. The components of the organic matter, structural construction of minerals, and related mechanical interaction, etc., could help to reveal the unique nature of the special mineralization process. Herein, the paper provides an overview of the biomineralization process from the perspective of molecular vibrational spectroscopy, including the physicochemical properties of biomineralized tissues, from physiological to applied mineralization. These physicochemical characteristics closely to the hierarchical mineralization process include biological crystal defects, chemical bonding, atomic doping, structural changes, and content changes in organic matter, along with the interface between biocrystals and organic matter as well as the specific mechanical effects for hardness and toughness. Based on those observations, the special physiological properties of mineralization for enamel and bone, as well as the possible mechanism of pathological mineralization and calcification such as atherosclerosis, tumor micro mineralization, and urolithiasis are also reviewed and discussed. Indeed, the clearly defined physicochemical properties of mineral crystals could pave the way for studies on the mechanisms and applications.

Hydrothermal Synthesis of Fluorapatite Coatings over Titanium Implants for Enhanced Osseointegration-An In Vivo Study in the Rabbit

This work aims at the development and characterization of fluorapatite coatings, innovatively prepared by the hydrothermal method, aiming for enhanced osseointegration of titanium implants. Fluoride-containing coatings were prepared and characterized by scanning and transmission electron microscopy, Fourier-transform infrared spectroscopy-attenuated total reflectance, and X-ray photoelectron spectroscopy. The biological response was characterized by microtomographic evaluation and histomorphometric analysis upon orthotopic implantation in a translational rabbit experimental model. Physic-chemical analysis revealed the inclusion of fluoride in the apatite lattice with fluorapatite formation, associated with the presence of citrate species. The in vivo biological assessment of coated implants revealed an enhanced bone formation process-with increased bone-to-implant contact and bone volume. The attained enhancement of the osteogenic process may be attributable to the conjoined modulatory activity of selected fluoride and citrate levels within the produced coatings. In this regard, the production of fluorapatite coatings with citrate, through the hydrothermal method, entails a promising approach for enhanced osseointegration in implant dentistry and orthopedic applications.

Lithium ion doped carbonated hydroxyapatite compositions: Synthesis, physicochemical characterisation and effect on osteogenic response in vitro

Hydroxyapatite is a commonly researched biomaterial for bone regeneration applications. To augment performance, hydroxyapatite can be substituted with functional ions to promote repair. Here, co-substituted lithium ion (Li⁺) and carbonate ion hydroxyapatite compositions were synthesised by an aqueous precipitation method. The co-substitution of Li⁺ and CO₃^2- is a novel approach that accounts for charge balance, which has been ignored in the synthesis of Li doped calcium phosphates to date. Three compositions were synthesised: Li⁺-free (Li 0), low Li⁺ (Li 0.25), and high Li⁺ (Li 1). Synthesised samples were sintered as microporous discs (70-75 % theoretical sintered density) prior to being ground and fractionated to produce granules and powders, which were then characterised and evaluated in vitro. Physical and chemical characterisation demonstrated that lithium incorporation in Li 0.25 and Li 1 samples approached design levels (0.25 and 1 mol%), containing 0.253 and 0.881 mol% Li⁺ ions, respectively. The maximum CO₃^2- ion content was observed in the Li 1 sample, with ~8 wt% CO₃, with the carbonate ions located on both phosphate and hydroxyl sites in the crystal structure. Measurement of dissolution products following incubation experiments indicated a Li⁺ burst release profile in DMEM, with incubation of 30 mg/ml sample resulting in a Li⁺ ion concentration of approximately 140 mM after 24 h. For all compositions evaluated, sintered discs allowed for favourable attachment and proliferation of C2C12 cells, human osteoblast (hOB) cells, and human mesenchymal stem cells (hMSCs). An increase in alkaline phosphatase (ALP) activity with Li⁺ doping was demonstrated in C2C12 cells and hMSCs seeded onto sintered discs, whilst the inverse was observed in hOB cells. Furthermore, an increase in ALP activity was observed in C2C12 cells and hMSCs in response to dissolution products from Li 1 samples which related to Li⁺ release. Complementary experiments to further investigate the findings from hOB cells confirmed an osteogenic role of the surface topography of the discs. This research has shown successful synthesis of Li⁺ doped carbonated hydroxyapatite which demonstrated cytocompatibility and enhanced osteogenesis in vitro, compared to Li⁺-free controls.

Combination of Two Synchrotron Radiation-Based Techniques and Chemometrics to Study an Enhanced Natural Remineralization of Enamel

The limitations to assess dental enamel remineralization have been overcome by a methodology resulting from the appropriate combination of synchrotron radiation-based techniques on both, infrared microspectroscopy and micro X-ray diffraction, with the help of specific data mining. Since amelogenin plays a key role in modulating the mineralization of tooth enamel, we propose a controlled ion release for fluorapatite structural ions (Ca²⁺, PO₄^3–, and F^–, also including Zn²⁺) by using weak acid and weak base ion-exchange resins in the presence of amelogenin to remineralize the surface of etched teeth. This combination provides the necessary ions for enamel remineralization and a guide for crystal growth due to the protein. Remineralized tooth samples were analyzed by applying the indicated methodology. The synchrotron data were treated using principal component analysis and multivariate curve resolution to analyze the mineral layer formed in the presence and absence of amelogenin. The remineralizing treatment created a fluorapatite layer free of carbonate impurities and with a similar orientation to that of the natural enamel thanks to amelogenin contribution.

The power of weak ion-exchange resins assisted by amelogenin for natural remineralization of dental enamel: an in vitro study

This study aims to develop an innovative dental product to remineralize dental enamel by a proper combination of ion-exchange resins as controlled release of mineral ions that form dental enamel, in the presence of amelogenin to guide the appropriate crystal growth. The novel product proposed consists of a combination of ion-exchange resins (weak acid and weak base) individually loaded with the remineralizing ions: Ca²⁺, PO₄^3- and F^-, also including Zn²⁺ in a minor amount as antibacterial, together with the protein amelogenin. Such cocktail provides onsite controlled release of the ions necessary for enamel remineralization due to the weak character of the resins and at the same time, a guiding tool for related crystal growth by the indicated protein. Amelogenin protein is involved in the structural development of natural enamel and takes a key role in controlling the crystal growth morphology and alignment at the enamel surface. Bovine teeth were treated by applying the resins and protein together with artificial saliva. Treated teeth were evaluated with nanoindentation, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The innovative material induces the dental remineralization creating a fluorapatite layer with a hardness equivalent to sound enamel, with the appropriate alignment of corresponding nanocrystals, being the fluorapatite more acid resistant than the original mineral. Our results suggest that the new product shows potential for promoting long-term remineralization leading to the inhibition of caries and protection of dental structures.

Evaluation and comparison of synthesised hydroxyapatite in bone regeneration: As an in vivo study

Objectives

Many patients suffer from non-repaired bone defects and subsequent aesthetic and psychological problems following bone fractures from accidents. The main goal of the study was to compare and evaluate synthetic hydroxyapatite with xenograft and commercial hydroxyapatite for bone repair and reconstruction.

Methods

In this study, synthetic hydroxyapatite was fabricated and verified. Cytotoxicity tests (i.e., induction coupled plasma [ICP], density and porosity analysis, scanning electron microscope [SEM] analysis, and thiazolyl blue tetrazolium blue [MTT] assay) were performed. Synthetic, xenograft, and commercial hydroxyapatite were tested in the animal study. Finally, bone regeneration was assessed using haematoxylin and eosin (H&E) staining.

Results

The Ca/P ratio was measured for xenograft and commercial samples, and values were lower than those for the synthesised hydroxyapatite. The amount of surface porosity in the synthesised sample was greater than in the commercial and xenograft samples. Additionally, the density of the synthesised hydroxyapatite was lower than that of the xenograft and commercial samples. A small amount of ossification from natural bone margins was observed at 4 weeks in the xenograft and commercial hydroxyapatite group. In the synthetic group, immature bone formation was observed at 4 weeks. The rate of ossification and cell infiltration in the xenograft and commercial hydroxyapatite samples was higher at 8 weeks than at 4 weeks, and this rate was lower than in the synthesised hydroxyapatite group. The synthesised hydroxyapatite group exhibited greater ossification than the xenograft and commercial hydroxyapatite, and control groups at 12 weeks.

Conclusion

This study showed that synthesised hydroxyapatite had better effects on bone regeneration and could be used in bone tissue engineering.

A modified TEGDMA-based resin infiltrant using polyurethane acrylate oligomer and remineralising nano-fillers with improved physical properties and remineralisation potential

OBJECTIVES

This study aimed to modify an experimental triethylene glycol dimethacrylate (TEGDMA) based resin infiltrant using PUA oligomer and two remineralising fillers, including fluorohydroxyapatite (FHA) and fluoride-doped bioactive glass (FD-BG), to improve the mechanical and physical properties and induce remineralising potential.

MATERIALS AND METHODS

The polyurethane acrylate oligomer (PUA) was synthesised and characterised. Experimental resin infiltrant was prepared by mixing 10% of synthesised PUA with 88% TEGDMA. Water contact angle, penetration coefficient, and penetration depth were then measured. The FHA and FD-BG fillers were synthesised and characterised. To prepare nano-filled resin infiltrant, 5% of each powder was mixed with the prepared resin infiltrant. The prepared resin infiltrants were characterised to evaluate their degree of conversion, mechanical properties, water sorption, and solubility. The ion release of filled resin was also assessed. The non-infiltrated and infiltrated enamel specimens underwent fourteen days of pH-cycling, and a surface microhardness was done to assess the resistance to demineralisation.

RESULTS

The results showed that the addition of PUA to TEGDMA increased the mechanical properties and decreased water sorption and solubility. The addition of synthesised FD-BG fillers to resin infiltrant significantly improved the resistance to demineralisation of enamel samples compared with other groups (p ≤ 0.001). The FHA fillers also improved the resistance to demineralisation; however, the produced changes were not statistically meaningful (p > 0.05).

CONCLUSIONS

Based on the results, the PUA+TEGDMA+ FD-BG/FHA composite can be used as an alternative material for pure TEGDMA in enamel infiltration approaches owing to its better mechanical properties, lower water sorption and solubility, and also remineralisation potential.

CLINICAL SIGNIFICANCE

A resin infiltrant with remineralisation potential, lower water sorption and solubility and higher mechanical properties may enhance the management of early caries lesions.

Incorporation of Hydroxyapatite into Glass Ionomer Cement (GIC) Formulated Based on Alumino-Silicate-Fluoride Glass Ceramics from Waste Materials

Glass ionomer cement (GIC) is a well-known restorative material applied in dentistry. The present work aims to study the effect of hydroxyapatite (HA) addition into GIC based on physical, mechanical and structural properties. The utilization of waste materials namely clam shell (CS) and soda lime silica (SLS) glass as replacements for the respective CaO and SiO₂ sources in the fabrication of alumino-silicate-fluoride (ASF) glass ceramics powder. GIC was formulated based on ASF glass ceramics, polyacrylic acid (PAA) and deionized water, while 1 wt.% of HA powder was added to enhance the properties of the cement samples. The cement samples were subjected to four different ageing times before being analyzed. In this study, the addition of HA caused an increment in density and compressive strength results along with ageing time. Besides, X-ray Diffraction (XRD) revealed the formation of fluorohydroxyapatite (FHA) phase in HA-added GIC samples and it was confirmed by Fourier Transform Infrared (FTIR) analysis which detected OH‒F vibration mode. In addition, needle-like and agglomeration of spherical shapes owned by apatite crystals were observed from Field Emission Scanning Electron Microscopy (FESEM). Based on Energy Dispersive X-ray (EDX) analysis, the detection of chemical elements in the cement samples were originated from chemical compounds used in the preparation of glass ceramics powder and also the polyacid utilized in initiating the reaction of GIC.

Evolution of Corrosion Products Formed during the Corrosion of MgZr Alloy in Poral Solutions Extracted from Na-Geopolymers Used as Conditioning Matrix for Nuclear Waste

Geopolymer, a nanoporous aluminosilicate filled with water and ions, has been selected as a potential matrix to encapsulate MgZr alloy fuel cladding. In this study, we investigate the evolution of the corrosion products formed during the corrosion of MgZr in poral solutions extracted from geopolymers with and without NaF as corrosion inhibitor. Using various characterization techniques such as Scanning Electron and Scanning Transmission Electron Microscopies coupled to Energy Dispersive X-ray spectroscopy and Grazing Incidence X-ray Diffraction, we show that the amounts of dissolved silica and fluoride species in solution are the key parameters driving the nature of corrosion products and probably their passivating properties regarding MgZr corrosion.

Preparation of a New Biocomposite Designed for Cartilage Grafting with Antibiofilm Activity

New polymer–inorganic composites with antibiofilm features based on the granulated poly(tetrafluoroethylene) (PTFE) and apatite materials were obtained using a standard hydraulic press. The study was performed in hydroxy- and fluorapatites doped with different amounts of silver ions and followed by heat treatment at 600 °C. The structural, morphological, and physicochemical properties were determined by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy-energy-dispersive spectrometry (SEM-EDS), and transition electron microscopy (TEM). The antibacterial properties of the obtained materials were evaluated against Gram-negative pathogens such as Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli as well as against Gram-positive bacteria Staphylococcus epidermidis. The cytotoxicity assessment was carried out on the red blood cells (RBC) as a cell model for in vitro study. Moreover, the biofilm formation on the biocomposite surface was studied using confocal laser scanning microscopy (CLSM).

Characterization and Evaluation of Bone-Derived Nanoparticles as a Novel pH-Responsive Carrier for Delivery of Doxorubicin into Breast Cancer Cells

Background: The limitations of conventional treatment modalities in cancer, especially in breast cancer, facilitated the necessity for developing a safer drug delivery system (DDS). Inorganic nano-carriers based on calcium phosphates such as hydroxyapatite (HA) and carbonate apatite (CA) have gained attention due to their biocompatibility, reduced toxicity, and improved therapeutic efficacy. Methods: In this study, the potential of goose bone ash (GBA), a natural derivative of HA or CA, was exploited as a pH-responsive carrier to successfully deliver doxorubicin (DOX), an anthracycline drug into breast cancer cells (e.g., MCF-7 and MDA-MB-231 cells). GBA in either pristine form or in suspension was characterized in terms of size, morphology, functional groups, cellular internalization, cytotoxicity, pH-responsive drug (DOX) release, and protein corona analysis. Results: The pH-responsive drug release study demonstrated the prompt release of DOX from GBA through its disintegration in acidic pH (5.5–6.5), which mimics the pH of the endosomal and lysosomal compartments as well as the stability of GBA in physiological pH (pH 7.5). The result of DOX binding with GBA indicated an increment in binding affinity with increasing concentrations of DOX. Cell viability and cytotoxicity analysis showed no innate toxicity of GBA particles. Both qualitative and quantitative cellular uptake analysis in both cell lines displayed an enhanced cellular internalization of DOX-loaded GBA compared to free DOX molecules. The protein corona spontaneously formed on the surface of GBA particles exhibited its affinity toward transport proteins, structural proteins, and a few other selective proteins. The adsorption of transport proteins could extend the circulation half-life in biological environment and increase the accumulation of the drug-loaded NPs through the enhanced permeability and retention (EPR) effect at the tumor site. Conclusion: These findings highlight the potential of GBA as a DDS to successfully deliver therapeutics into breast cancer cells.

Fluorapatite ceramics for bone tissue regeneration: Synthesis, characterization and assessment of biomedical potential

Calcium phosphates, due to their similarity to the inorganic fraction of mineralized tissues, are of great importance in treatment of bone defects. In order to improve the biological activity of hydroxyapatite (HAP), its fluoride-substituted modification (FAP) was synthesized using the sol-gel method and calcined at three different temperatures in the range of 800-1200 °C. Physicochemical and biological properties were evaluated to indicate which material would support bone regeneration the best. X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS), and Fourier transform infrared spectroscopy (FTIR) revealed that fluoride ions were incorporated into the apatite lattice structure. In studies it was found that fluorapatite sintered at the highest temperature had the lowest porosity, no internal pores and the highest density. In vitro ion reactivity assessments showed that during the 28-day immersion of the samples in the simulated body fluid, the uptake of calcium and phosphorus ions was inversely correlated to the calcination temperature. All tested materials were non-toxic since the cytotoxicity MTT assay demonstrated that the viability of preosteoblast cells incubated with sample extracts was high. Fluorapatite sintered at 800 °C was determined to be of optimal porosity and fluoride release capacity and then used in cell proliferation studies. The results showed that it significantly shortened the doubling time and thus enhanced the proliferation of osteogenic cells, as compared to the fluoride solutions and control group. Therefore, this material is proposed for the use in orthopedic applications and bone tissue engineering.

In vitro biomineralization on poly(vinyl alcohol)/biphasic calcium phosphate hydrogels

Biomineralized tissue is considered the final product of successful cell culture in bone tissue engineering. Dulbecco’s modified Eagle’s medium (DMEM) with fetal bovine serum (FBS) not only is used as a common culture medium but also provides a natural biomineralization environment, due to having similar ionic concentrations as blood plasma. Here, poly(vinyl alcohol) hydrogel with incorporated biphasic calcium phosphate nanoparticles was immersed in a DMEM–FBS cell culture medium, and then biomineralization occurred on the nanocomposite surface, which was characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. Such formed bone-like apatite on the surface facilitated the proliferation of osteoblasts, identified by Cell Counting Kit-8 analysis and fluorescent microscopy. This study verified the spontaneous biomineralization on the surface of a calcium phosphate-based nanocomposite by using a simple DMEM–FBS immersion strategy, which was promising for biomodification of bone substitutes.

Fe/Mg-Modified Carbonate Apatite with Uniform Particle Size and Unique Transport Protein-Related Protein Corona Efficiently Delivers Doxorubicin into Breast Cancer Cells

Breast cancer is the abnormal, uncontrollable proliferation of cells in the breast. Conventional treatment modalities like chemotherapy induce deteriorating side effects on healthy cells. Non-viral inorganic nanoparticles (NPs) confer exclusive characteristics, such as, stability, controllable shape and size, facile surface modification, and unique magnetic and optical properties which make them attractive drug carriers. Among them, carbonate apatite (CA) particles are pH-responsive in nature, enabling rapid intracellular drug release, but are typically heterogeneous with the tendency to self-aggregate. Here, we modified the nano-carrier by partially substituting Ca²⁺ with Mg²⁺ and Fe³⁺ into a basic lattice structure of CA, forming Fe/Mg-carbonate apatite (Fe/Mg-CA) NPs with the ability to mitigate self-aggregation, form unique protein corona in the presence of serum and efficiently deliver doxorubicin (DOX), an anti-cancer drug into breast cancer cells. Two formulations of Fe/Mg-CA NPs were generated by adding different concentrations of Fe³⁺ and Mg²⁺ along with a fixed amount of Ca²⁺ in bicarbonate buffered DMEM (Dulbecco's Modified Eagle's Medium), followed by 30 min incubation at 37 °C. Particles were characterized by turbidity analysis, z-average diameter and zeta potential measurement, optical microscopy, field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray (EDX), flame atomic absorption spectroscopy (FAAS), pH dissolution, drug binding, cellular uptake, thiazolyl blue tetrazolium bromide (MTT) assay, stability analysis, and protein corona study by LCMS (Liquid chromatography-mass spectrometry). Both formulations of Fe/Mg-CA displayed mostly uniform nano-sized particles with less tendency to aggregate. The EDX and FAAS elemental analysis confirmed the weight (%) of Ca, Fe and Mg, along with their Ca/P ratio in the particles. A constant drug binding efficiency was noticed with 5 μM to 10 μM of initial DOX concentration. A pH dissolution study of Fe/Mg-CA NPs revealed the quick release of DOX in acidic pH. Enhancement of cytotoxicity for the chemotherapy drug was greater for Fe/Mg-CA NPs as compared to CA NPs, which could be explained by an increase in cellular internalization as a result of the small z-average diameter of the former. The protein corona study by LCMS demonstrated that Fe/Mg-CA NPs exhibited the highest affinity towards transport proteins without binding with opsonins. Biodistribution study was performed to study the effect of DOX-loaded Fe/Mg-CA NPs on the tissue distribution of DOX in Balb/c 4T1 tumor-bearing mice. Both formulations of Fe/Mg-CA NPs have significantly increased the accumulation of DOX in tumors. Interestingly, high Fe/Mg-CA NPs exhibited less off-target distribution compared to low Fe/Mg-CA NPs. Furthermore, the blood plasma analysis revealed prolonged blood circulation half-life of DOX-loaded low and high Fe/Mg-CA NPs compared to free DOX solution. Modifying CA NPs with Fe³⁺ and Mg²⁺, thereby, led to the generation of nano-sized particles with less tendency to aggregate, enhancing the drug binding efficiency, cellular uptake, and cytotoxicity without hampering drug release in acidic pH, while improving the circulation half-life and tumor accumulation of DOX. Therefore, Fe/Mg-CA which predominantly forms a transport protein-related protein corona could be a proficient carrier for therapeutic delivery in breast cancer.

Vibrational spectral fingerprinting for chemical recognition of biominerals

Pathologies associated with calcified tissue, such as osteoporosis, demand in vivo and/or in situ spectroscopic analysis to assess the role of chemical substitutions in the inorganic component. High energy X-ray or NMR spectroscopies are impractical or damaging in biomedical conditions. Low energy spectroscopies, such as IR and Raman techniques, are often the best alternative. In apatite biominerals, the vibrational signatures of the phosphate group are generally used as fingerprint of the materials although they provide only limited information. Here, we have used first principles calculations to unravel the complexity of the complete vibrational spectra of apatites. We determined the spectroscopic features of all the phonon modes of fluoroapatite, hydroxy-apatite, and carbonated fluoroapatite beyond the analysis of the phosphate groups, focusing on the effect of local corrections induced by the crystalline environment and the specific mineral composition. This provides a clear and unique reference to discriminate structural and chemical variations in biominerals, opening the way to a widespread application of non-invasive spectroscopies for in vivo diagnostics, and biomedical analysis.

In-vitro bioactivity evaluation and physical properties of an epoxy-based dental sealer reinforced with synthesized fluorine-substituted hydroxyapatite, hydroxyapatite and bioactive glass nanofillers

The purpose of this study was to evaluate the physical properties and bioactivity potential of epoxy-based dental sealers modified with synthesized bioactive glass (BAG), hydroxyapatite (HA) and fluorine substituted hydroxyapatite (FHA) nanoparticles.

The synthesized powders were incorporated at 10% and 20% into the epoxy-based dental sealer. The setting time, flow and solubility and microhardness of the modified and unmodified samples were examined. The bioactivity was evaluated using FESEM-EDX and elemental mapping, ATR-FTIR and XRD.

The flow value of all of the experimental groups except the FHA modified samples, was greater than 20 mm. Concerning solubility, no specimens exhibited more than 1% weight loss. The solubility value of the FHA groups was statistically significant lower than other groups (p ≤ 0.001). The mean hardness values of all of the modified samples were significantly higher than the unmodified group (p ≤ 0.001).

Regarding bioactivity, in vitro study revealed that after 3 days immersion in SBF a compact and continuous calcium phosphate layer formed on the surface of epoxy sealers containing BAG and HA nanoparticles.

Based on these results, the addition of BAG and HA nanoparticles did not adversely alter the physical properties of epoxy sealers. Additionally, they improved the in vitro bioactivity of the epoxy sealer.

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Since root canal sealers are in direct contact with the periapical tissue, ideally, they should be composed of a bioactive material.

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It is important that the added bioactive fillers don't adversely affect the physical properties of the material.

Nanocrystalline Zn2+ and SO42- binary doped fluorohydroxyapatite: A novel biomaterial with enhanced osteoconductive and osteoinconductive properties

In this study, we have successfully doped hydroxyapatite (HA) with zinc (Zn²⁺), sulphate (SO₄^2-) and fluoride (F^-) ions to develop a new composition of bioceramic, Ca_10-x Zn_x(PO₄)_6-y(SO₄)_y(OH)_2-z-yF_z(SO₄)_y, (x = 0, 0.2, 0.6, 1.0, y = 0, 0.5 and z = 0,1.0 mol), using wet precipitation method. The obtained materials were analysed using XRD, FTIR, FESEM, and XPS techniques to investigate the phase purity, particle morphology and elemental composition, respectively. A model anticancer drug (Doxorubicin, DOX) was loaded onto the surface of the Zn/SO₄-FHA materials. About 100% loading of DOX with a controlled release profile was obtained. Degradation of materials in Simulated body fluid (SBF) was greatly improved with the incorporation of Zn²⁺/SO₄^2- ions in comparison to HA/FHA, which makes it highly bioactive materials. In vitro cell viability and adhesion of Human fetal osteoblast (hFOB) cell were investigated. Cell viability has demonstrated that the hFOB cells proliferated at a high rate on Zn/SO₄-FHA materials, confirming the in vitro biocompatibility of the materials. Alkaline phosphatase (ALP) activity and intracellular calcium deposition of hFOB cells seeded on 1ZnSO₄-FHA disc surface was statistically higher than observed on pure HA and FHA discs, indicating that hFOB cells differentiated into mature osteoblasts on 1Zn/SO₄-FHA disc surfaces. Taken together, our results suggest that HA substituted by (Zn²⁺, 0.2 mol), (SO₄^2-, 0.5 mol) and (F^-, 1 mol) (1Zn/SO₄-FHA) material was a promising material for hard tissue scaffolds.

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

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

Detection and Characterization of Human Teeth Caries Using 2D Correlation Raman Spectroscopy

BACKGROUND

Carious lesions are formed by a complex process of chemical interaction between dental enamel and its environment. They can cause cavities and pain, and are expensive to fix. It is hard to characterize in vivo as a result of environment factors and remineralization by ions in the oral cavity.

OBJECTIVES

The development of a technique that gives early diagnosis which is non-invasive, is of crucial importance for publichealth. Raman spectroscopy is a technique that can fulfil these requirements. The main goal of this work was to use Raman spectroscopy to differentiate between normal and carious human teethinvivo. The samples used in this study were collected by traditional human teeth.

MATERIAL AND METHOD

An in vivo Raman spectroscopy system andspecialized fiber optic probe has been designed to obtain spectra from tissue. Theseprobes are filtered to reduce the background signal from the fiber optics and the collection fiberutilizes beam steering to optimize the collection effectiv.

RESULTS

In order to detect any demineralization and carious versus sound pit and fissure enamel, the spectral data sets are analyzed by the proposed scheme to demonstrate the utility of generalized 2D correlation spectra. Potential applications of this 2D correlation approach are then explored. The Raman spectra in the normal tissue showed thepresence of vibrational bands in 437.87 cm^-1, 581.89 cm^-1, 953.89 cm^-1 and 1054.73 cm^-1 with smaller intensity than in the carious spectra. Image construction from the peak intensity produced chemical maps of apatite concentration.

CONCLUSION

Such two-dimensional correlation spectra emphasize spectral features not readily observable in conventional one-dimensional spectra.No correlation is observed in mode-to-mode intensity fluctuations indicating that the changes inmode intensities are completely independent. Theoretical calculations provide convincing evidence that the fluctuationsare not the result of diffusion, orientation or local electromagnetic field gradients but rather are the result of subtle variations ofthe excited-state lifetime, energy and geometry of the molecule and producing a signature response for carious detection.

Mechanism of Nanostructured Fluorapatite Formation from CaO, CaF2 and P2O5 Precursors by Mechanochemical Synthesis

We determined the mechanism of mechanochemical synthesis of fluorapatite from CaO, CaF2 and P2O5 by characterisation of the intermediate compounds. We used atomic absorption spectroscopy, X-ray diffraction, field emission scanning electron microscopy, FTIR spectroscopy and transmission electron microscopy to find the transitional compounds. Investigation of the binary and ternary powder mixtures revealed the appearance of H3PO4, Ca(OH)2, Ca2P2O7 and CaCO3 as the intermediate compounds. At early stages of the milling, conversions of P2O5 to H3PO4 and CaO to Ca(OH)2 occurred in the wet atmosphere. Later, a combination of Ca(OH)2 and H3PO4 formed C a2P2O7 while the unreacted CaO was converted to CaCO3 by CO2 of the ambient atmosphere. Spherical crystalline Ca10 (PO4)6F2 particles formed after 48 hours of milling due to the reaction between Ca2P2O7, CaCO3 and CaF2.

Synthesis and Characterization of a Laminated Hydroxyapatite/Gelatin Nanocomposite Scaffold with Controlled Pore Structure for Bone Tissue Engineering

In this study, a nanostructured scaffold was designed for bone repair using hydroxyapatite (HA) and gelatin (GEL) as its main components. Nanopowders of HA were synthesized, and together with GEL, used to engineer a 3-dimensional nanocomposite combining 3 techniques of layer solvent casting, freeze-drying, and lamination. The results show that the scaffold possesses a 3-dimensional interconnected homogenous porous structure with a porosity of 82% and pore sizes ranging from 300 to 500 μm. It has also been shown that mechanical indices are in the range of spongy bones. Cultured osteoblast-like cells (SaOS-2) have shown an excellent level of cell attachment, migration, and penetration into the porosities of the nanocomposite scaffold. Here, we have shown that by a combination of widely available methods with simple experimental operations, nano-HA powders can be synthesized and used to make 3-dimensional HA/GEL nanocomposites in any desired shape, with mechanical properties comparable to spongy bone.

Magnetic properties and cytocompatibility of transition-metal-incorporated hydroxyapatite

A detailed magnetization study, along with an assessment of the cellular proliferation, has been carried out on transition-metal-doped hydroxyapatite (HA), Ca_10-xM_x(PO₄)₆(OH)₂, where M = Mn, Co, and Fe. In particular, a series of MnHA powder samples with an x value of 0.04 ≤ x ≤ 1.21, one CoHA (x = 0.48) and one FeHA sample (x = 1.06) were synthesized using a wet chemical method along with an ion-exchange procedure. Characterization by transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) indicated that the substitution of M elements does not change the morphology and crystalline structure of pure HA that showing a single phased HA nano-rod. In every case, the magnetization isotherms for 10 K ≤ T ≤ 300 K were linear through the origin characteristic of a paramagnetic response with no indication of superparamagnetic behavior, hysteresis, or magnetic ordering. The magnetic behavior for all samples could be fit to the Curie-Weiss law yielding values for the M ion magnetic moments. The Mn²⁺ magnetic moments were close to the spin-only value of S = 5/2 or 5.92 μ_B, while the Co²⁺ moment (4.41 μ_B) was larger than the spin-only value for S = 3/2, indicating an orbital contribution due to incomplete quenching. The magnetic behavior for the FeHA sample showed a possible spin-state transition. In addition, no statistically significant differences were observed when cells were treated with the same dose of HA or MnHA up to 50 μg/mL, suggesting that the substituted Mn introduces no cytotoxicity to the HA powders.

Formation of Fluorohydroxyapatite with Silver Diamine Fluoride

Silver diamine fluoride (SDF) is found to promote remineralization and harden the carious lesion. Hydroxyapatite crystallization is a crucial process in remineralization; however, the role of SDF in crystal formation is unknown. We designed an in vitro experiment with calcium phosphate with different SDF concentrations (0.38, 1.52, 2.66, 3.80 mg/mL) to investigate the effect of this additive on the nucleation and growth of apatite crystals. Two control groups were also prepared-calcium phosphate (CaCl2·2H2O + K2HPO4 in buffer solution) and SDF (Ag[NH3]2F in buffer solution). After incubation at 37 oC for 24 h, the shape and organization of the crystals were examined by bright-field transmission electron microscopy and electron diffraction. Unit cell parameters of the obtained crystals were determined with powder X-ray diffraction. The vibrational and rotational modes of phosphate groups were analyzed with Raman microscopy. The transmission electron microscopy and selected-area electron diffraction confirmed that all solids precipitated within the SDF groups were crystalline and that there was a positive correlation between the increased percentage of crystal size and the concentration of SDF. The powder X-ray diffraction patterns indicated that fluorohydroxyapatite and silver chloride were formed in all the SDF groups. Compared with calcium phosphate control, a contraction of the unit cell in the a-direction but not the c-direction in SDF groups was revealed, which suggested that small localized fluoride anions substituted the hydroxyl anions in hydroxyapatite crystals. This was further evidenced by the Raman spectra, which displayed up-field shift of the phosphate band in all the SDF groups and confirmed that the chemical environment of the phosphate functionalities indeed changed. The results suggested that SDF reacted with calcium and phosphate ions and produced fluorohydroxyapatite. This preferential precipitation of fluorohydroxyapatite with reduced solubility could be one of the main factors for arrest of caries lesions treated with SDF.

Changes in physicochemical and biological properties of porcine bone derived hydroxyapatite induced by the incorporation of fluoride

As the main inorganic component of xenogenic bone graft material, bone-derived biological apatite (BAp) has been widely used in implant dentistry, oral and maxillofacial surgery and orthopedics. However, BAp produced via calcination of animal bones still suffers from some drawbacks, such as insufficient mechanical strength and inadequate degradation rate, which impede its application. Fluoride is known to play important roles in both physiological and pathological processes of human hard tissues for its double effects on bones and teeth. In order to understand the effects of fluoride on the properties of BAp, as well as the mechanism behind them, porcine bone derived hydroxyapatite (PHAp) was prepared via thermal treatment, which was then fluoride incorporated at a series concentrations of sodium fluoride, and noted as 0.25-FPHAp, 0.50-FPHAp, and 0.75-FPHAp respectively. The physicochemical characteristics of the materials, including crystal morphology, crystallinity, functional groups, elemental composition, compressive strength, porosity and solubility, were then determined. The biological properties, such as protein adsorption and cell attachment, were also evaluated. It was found that the spheroid-like crystals of PHAp were changed into rod-like after fluoride substitution, resulting in a fluoride concentration-dependent increase in compressive strength, as well as a decreased porosity and solubility of the apatite. However, even though the addition of fluoride was demonstrated to enhance protein adsorption and cell attachment of the materials, the most favorable results were intriguingly achieved in FPHAp with the least fluoride content. Collectively, low level of fluoride incorporation is proposed promising for the modification of clinically used BAp based bone substitute materials, because of its being able to maintain a good balance between physicochemical and biological properties of the apatite.

Effect of phosphate additives on the microstructure, bioactivity, and degradability of microarc oxidation coatings on Mg-Zn-Ca-Mn alloy

Calcium phosphate coatings were prepared on the surface of self-designed Mg-Zn-Ca-Mn alloy using microarc oxidization technology. To characterize the microstructures, cross-section morphologies, and compositions of the coatings, the authors used scanning electron microscopy equipped with an energy-disperse spectrometer, x-ray diffraction, and Fourier transform infrared spectroscopy. Potentiodynamic polarization in the simulated body fluid (SBF) was used to evaluate the corrosion behaviors of the samples. An SBF immersion test was used to evaluate the coating bioactivity and degradability. After the immersion tests, some bonelike apatite formed on the coating surfaces indicate that bioactivity of the coatings is excellent. The coating prepared in electrolyte containing (NaPO3)6 had slower degradation rate after immersion test for 21 days.

Effects of Laser Power Level on Microstructural Properties and Phase Composition of Laser-Clad Fluorapatite/Zirconia Composite Coatings on Ti6Al4V Substrates

Hydroxyapatite (HA) is one of the most commonly used materials for the coating of bioceramic titanium (Ti) alloys. However, HA has poor mechanical properties and a low bonding strength. Accordingly, the present study replaces HA with a composite coating material consisting of fluorapatite (FA) and 20 wt % yttria (3 mol %) stabilized zirconia (ZrO₂, 3Y-TZP). The FA/ZrO₂ coatings are deposited on Ti6Al4V substrates using a Nd:YAG laser cladding system with laser powers and travel speeds of 400 W/200 mm/min, 800 W/400 mm/min, and 1200 W/600 mm/min, respectively. The experimental results show that a significant inter-diffusion of the alloying elements occurs between the coating layer (CL) and the transition layer (TL). Consequently, a strong metallurgical bond is formed between them. During the cladding process, the ZrO₂ is completely decomposed, while the FA is partially decomposed. As a result, the CLs of all the specimens consist mainly of FA, Ca₄(PO₄)₂O (TTCP), CaF₂, CaZrO₃, CaTiO₃ and monoclinic phase ZrO₂ (m-ZrO₂), together with a small amount of θ-Al₂O₃. As the laser power is increased, CaO, CaCO₃ and trace amounts of tetragonal phase ZrO₂ (t-ZrO₂) also appear. As the laser power increases from 400 to 800 W, the CL hardness also increases as a result of microstructural refinement and densification. However, at the highest laser power of 1200 W, the CL hardness reduces significantly due to the formation of large amounts of relatively soft CaO and CaCO₃ phase.

Functional hydroxyapatite bioceramics with excellent osteoconductivity and stern-interface induced antibacterial ability

Osteogenic Ag/HAp bioceramics possess significant bacteria-killing abilities under ultra-low Ag⁺concentrations and the stern-interface induced antibacterial mechanism was explicitly proposed.

A solid-state NMR study of selenium substitution into nanocrystalline hydroxyapatite

The substitution of selenium oxyanions in the hydroxyapatite structure was examined using multinuclear solid-state resonance spectroscopy (ssNMR). The study was supported by powder X-ray diffractometry (PXRD) and wavelength dispersion X-ray fluorescence (WD-XRF). Samples of pure hydroxyapatite (HA₃₀₀) and selenate (HA₃₀₀-1.2SeO₄) or selenite (HA₃₀₀-1.2SeO₃) substituted hydroxyapatites were synthesized using the standard wet method and heated at 300 °C to remove loosely bonded water. PXRD data showed that all samples are single-phase, nanocrystalline hydroxyapatite. The incorporation of selenite and selenate ions affected the lattice constants. In selenium-containing samples the concentration of Se was very similar and amounted to 9.55% and 9.64%, for HA₃₀₀-1.2SeO₄ and HA₃₀₀-1.2SeO₃, respectively. PXRD and ssNMR data showed that the selenite doping significantly decreases the crystallite size and crystallinity degree. ³¹P and ¹H NMR experiments demonstrated the developed surface hydrated layer in all samples, especially in HA₃₀₀-1.2SeO₃. ¹H NMR studies showed the dehydroxylation of HA during the selenium oxyanions substitution and the existence of hydrogen bonding in structural hydroxyl group channels. ¹H→⁷⁷Se cross polarization NMR experiments indicated that selenites and selenates are located in the crystal lattice and on the crystal surface.

Use of laser fluorescence in dental caries diagnosis: a fluorescence x biomolecular vibrational spectroscopic comparative study

The aim of this work was to verify the existence of correlation between Raman spectroscopy readings of phosphate apatite (~960 cm-1), fluoridated apatite (~575 cm-1) and organic matrix (~1450 cm-1) levels and Diagnodent® readings at different stages of dental caries in extracted human teeth. The mean peak value of fluorescence in the carious area was recorded and teeth were divided in enamel caries, dentin caries and sound dental structure. After fluorescence readings, Raman spectroscopy was carried out on the same sites. The results showed significant difference (ANOVA, p<0.05) between the fluorescence readings for enamel (16.4 ± 2.3) and dentin (57.6 ± 23.7) on carious teeth. Raman peaks of enamel and dentin revealed that ~575 and ~960 cm-1 peaks were more intense in enamel caries. There was significant negative correlation (p<0.05) between the ~575 and ~960 cm-1 peaks and dentin caries. It may be concluded that the higher the fluorescence detected by Diagnodent the lower the peaks of phosphate apatite and fluoridated apatite. As the early diagnosis of caries is directly related to the identification of changes in the inorganic tooth components, Raman spectroscopy was more sensitive to variations of these components than Diagnodent.

Preparation of laminated poly(ε-caprolactone)-gelatin-hydroxyapatite nanocomposite scaffold bioengineered via compound techniques for bone substitution

In this research, new bioactive nanocomposite scaffolds were successfully developed using poly(ε-caprolactone) (PCL), cross-linked gelatin and nanoparticles of hydroxyapatite (HAp) after testing different solvents and methods. First, HAp powder was synthesized via a chemical precipitation technique and characterized. Then, the nanocomposites were prepared through layer solvent casting combined with freeze-drying and lamination techniques. According to the results, the increasing of the PCL weight in the scaffolds led to the improvement of the mechanical properties. The amount of ultimate stress, stiffness and also elastic modulus increased from 8 MPa for 0% wt PCL to 23.5 MPa for 50% wt PCL. The biomineralization study revealed the formation of an apatite layer on the scaffolds after immersion in simulated body fluid (SBF). The Ca-P ratios were in accordance to nonstoichiometric biological apatite, which was approximately 1.67. The in vitro biocompatibility and cytocompatibility of the scaffolds were tested using mesenchymal stem cells (MSCs), and the results indicated no sign of toxicity, and cells were found to be attached to the scaffold walls. The in vivo biocompatibility and osteogenesis of these scaffolds in the animal experiments is also under investigation, and the result will be published at the end of the study.