Ultrafast synthesis and characterization of carbonated hydroxyapatite nanopowders via sonochemistry-assisted microwave process

The Synergistic Effect of High Intensity Focused Ultrasound on In-vitro Remineralization of Tooth Enamel by Calcium Phosphate Ion Clusters

Background

Remineralization of dental enamel is an important intervention strategy for the treatment of demineralized lesions. Existing approaches have limitations such as failure to adequately reproduce both the ideal structural and mechanical properties of the native tooth. The ability of ultrasound to control and accelerate the crystallization processes has been widely reported. Therefore, a new approach was explored for in-vitro enamel remineralization involving the synergistic effect of high-intensity focused ultrasound (HIFU) coupled with calcium phosphate ion clusters (CPICs).

Methods

The demineralized enamel was treated with CPICs, with or without subsequent HIFU exposure for different periods (2.5, 5, and 10 min). The specimens were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy. The surface hardness and crystallographic properties of the treated specimens were evaluated using Vickers microhardness testing and X-ray diffraction (XRD), respectively.

Results

SEM revealed distinct, organized, and well-defined prismatic structures, showing clear evidence of remineralization in the combined CPIC/HIFU treatment groups. AFM further revealed a decrease in the surface roughness values with increasing HIFU exposure time up to 5 min, reflecting the obliteration of interprismatic spaces created during demineralization. The characteristic Raman band at 960 cm-1 associated with the inorganic phase of enamel dominated well in the HIFU-treated specimens. Importantly, microhardness testing further demonstrated that new mineral growth also recovered the mechanical properties of the enamel in the HIFU-exposed groups. Critical to our aspirations for developing this into a clinical process, these results were achieved in only 5 min.

Conclusion

HIFU exposure can synergise and significantly accelerate in-vitro enamel remineralization process via calcium phosphate ion clusters. Therefore, this synergistic approach has the potential for use in future clinical interventions.

Synthesis of nano-hydroxyapatite using emulsion, pyrolysis, combustion, and sonochemical methods and biogenic sources: a review

Hydroxyapatite (HAp) is comparable to materials in bone because its chemical components are similar to those contained in animal bone, and thus, its bioactive and biocompatible properties are similar. There are applications for HAp and relevant calcium phosphate in the medical and industrial sectors, and due to the rising demand for HAp nanoparticles, considerable work has been performed to develop a variety of synthetic pathways that incorporate scientifically and practically novel aspects. Numerous studies have been conducted to examine how changes in reaction parameters will successfully influence crucial HAp features. HAp can also be synthesized from biogenic sources such as HAp-rich fish scales or animal bones as an alternative to chemical precursors. Various preparation techniques produce crystals with varying sizes, but it has been found that nano-sized HAp exhibits a greater number of bioactive properties as compared to micron-sized HAp. Rather than considering conventional methods, this review focuses on alternative approaches such as emulsion, pyrolysis, combustion, and sonochemical methods along with waste bio-sources (biogenic sources) to obtain HAp. We summarize the currently accessible information pertaining to each synthesis process, while also focusing on their benefits and drawbacks.

Rapid Flow Synthesis of a Biomimetic Carbonate Apatite as an Effective Drug Carrier

A facile synthesis of apatite nanocrystals analogous to bioapatites with increased biocompatibility and biodegradability can remedy the shortcomings of the widely applied synthetic hydroxyapatite (HAp) for bone defect treatment. Here, we propose an expeditious synthesis method to develop a biomimetic B-type carbonate apatite (CAp) with a simple capillary microfluidic device at room temperature. The process not only eliminates fluctuations with the addition of carbonate but also produces safe CAp drug carriers through simultaneous alendronate incorporation to the CAp structure. CAp displayed superior mineralization on osteoblast-like MG-63 cells when compared with HAp and HAp drug carriers that were produced using identical methods. Furthermore, alendronate-incorporated CAp drug carriers potentially displayed higher cancer cell suppression when applied to breast cancer cells attached to the bone tissue model, which signifies enhanced cancer metastasis to bone suppression due to the likelihood of increased alendronate release of CAp owing to its faster dissolution. Overall, our results may provide promising opportunities for enhanced clinical CAp application for bone defect treatment, particularly for bone loss and cancer to bone metastasis.

Nano-Hydroxyapatite vs. Xenografts: Synthesis, Characterization, and In Vitro Behavior

This research focused on the synthesis of apatite, starting from a natural biogenic calcium source (egg-shells) and its chemical and morpho-structural characterization in comparison with two commercial xenografts used as a bone substitute in dentistry. The synthesis route for the hydroxyapatite powder was the microwave-assisted hydrothermal technique, starting from annealed egg-shells as the precursor for lime and di-base ammonium phosphate as the phosphate precursor. The powders were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM), X-ray fluorescence spectroscopy (XRF), and cytotoxicity assay in contact with amniotic fluid stem cell (AFSC) cultures. Compositional and structural similarities or differences between the powder synthesized from egg-shells (HA1) and the two commercial xenograft powders-Bio-Oss®, totally deproteinized cortical bovine bone, and Gen-Os®, partially deproteinized porcine bone-were revealed. The HA1 specimen presented a single mineral phase as polycrystalline apatite with a high crystallinity (Xc 0.92), a crystallite size of 43.73 nm, preferential growth under the c axes (002) direction, where it mineralizes in bone, a nano-rod particle morphology, and average lengths up to 77.29 nm and diameters up to 21.74 nm. The surface of the HA1 nanoparticles and internal mesopores (mean size of 3.3 ± 1.6 nm), acquired from high-pressure hydrothermal maturation, along with the precursor's nature, could be responsible for the improved biocompatibility, biomolecule adhesion, and osteoconductive abilities in bone substitute applications. The cytotoxicity assay showed a better AFSC cell viability for HA1 powder than the commercial xenografts did, similar oxidative stress to the control sample, and improved results compared with Gen-Os. The presented preliminary biocompatibility results are promising for bone tissue regeneration applications of HA1, and the study will continue with further tests on osteoblast differentiation and mineralization.

S. N. SN, Sagadevan S, Hoque ME, Kulandaivelu R. Advanced lithium substituted hydroxyapatite nanoparticles for antimicrobial and hemolytic studies

In this study, pure hydroxyapatite (HAP) and lithium substituted hydroxyapatite (Li-HAP) nanoparticles were synthesized by a sonochemical synthesis process and investigated for their antimicrobial and hemolytic activities.

In Vitro Osteogenesis Stimulation via Nano-Hydroxyapatite/Carbon Nanotube Thin Films on Biomedical Stainless Steel

We evaluated the electrophoretic deposition of nanohydroxyapatite/superhydrop hilic multiwalled carbon nanotube composites (nHAp/MWCNT) onto stainless steel biomedical alloys for applications in bone tissue engineering. First, nHAp/MWCNT composites were dispersed into 0.042 mol·L⁻¹ of Ca(NO₃)₂·4H₂O + 0.025 mol·L⁻¹ NH₄H₂PO₄ electrolytes (pH = 4.8) at two different concentrations. Next, a voltage of −2 V was applied using 316L stainless steel as a working electrode (0.27 cm²), a high-purity platinum coil wire was used as the auxiliary electrode, and an Ag/AgCl (3 M) electrode was used as the reference electrode. The nHAp/MWCNT composites were characterized by transmission electron microscopy. The deposited nHAp and nHAp/MWCNT films were characterized by profilometry, scanning electron microscopy, X-ray diffractometry and Raman spectroscopy. Human osteoblast cells were cultivated with the different materials and in vitro cytotoxicity was evaluated using lactate dehydrogenase (LDH) assay. The osteogenesis process was evaluated by mRNA levels of the three genes that are directly related to bone repair: Alkaline Phosphatase, Osteopontin and Osteocalcin. We showed that rough, crystalline apatite thin films containing phases of nHAp were successfully deposited onto 316L stainless steel alloys. Also, we noticed that nHAp/MWCNT thin films deposited onto 316L stainless steel alloys upregulated the expression of important genes related to bone mineralization and maturation. Our results strongly support the possibility of this new alternative to modify the surface of metallic biomedical alloys to promote bone tissue regeneration.

Structural features of hydroxyapatite and carbonated apatite formed under the influence of ultrasound and microwave radiation and their effect on the bioactivity of the nanomaterials

The samples of hydroxyapatite and carbonate substituted hydroxyapatite (CHA) were obtained under the influence of physical factors, namely ultrasound (US) and microwave (MW) radiations. The results of Fourier transform infrared spectroscopy and X-ray diffraction analysis have proved the formation of the calcium deficient hydroxyapatite and B-type CHA with the Ca/P ratio in the ranges 1.62-1.87. In vitro studies have showed the increased bioactivity of the samples, synthesized under the influence of physical factors as compared to the standard ones. The samples of both groups, synthesized under the influence of 600 W MW, have shown the greatest stability in biological environment. In vivo tests confirm that obtained under US and MW radiations hydroxyapatite-based biomaterials are biocompatible, non-toxic and exhibit osteoconductive properties. The usage of US and MW radiations can significantly shorten the time (up to 5-20 min) of obtaining of calcium deficient hydroxyapatite and B-type CHA in nanopowder form, close in structure and composition to the biological hydroxyapatite.

Fe3O4/hydroxyapatite/graphene quantum dots as a novel nano-sorbent for preconcentration of copper residue in Thai food ingredients: Optimization of ultrasound-assisted magnetic solid phase extraction

Fe₃O₄/hydroxyapatite/graphene quantum dots (Fe₃O₄/HAP/GQDs) nanocomposite was synthesized and used as a novel magnetic adsorbent. This nanocomposite was characterized using scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and magnetization property. The Fe₃O₄/HAP/GQDs was applied to pre-concentrate copper residues in Thai food ingredients (so-called "Tom Yum Kung") prior to determination by inductively coupled plasma-atomic emission spectrometry. Based on ultrasound-assisted extraction optimization, various parameters affecting the magnetic solid-phase extraction, such as solution pH, amount of magnetic nanoparticles, adsorption and desorption time, and type of elution solvent and its concentration were evaluated. Under optimal conditions, the linear range was 0.05-1500ngmL^-1 (R²>0.999), limit of detection was 0.58ngmL^-1, and limit of quantification was 1.94ngmL^-1. The precision, expressed as the relative standard deviation of the calibration curve slope (n=5), for intra-day and inter-day analyses was 0.87% and 4.47%, respectively. The recovery study of Cu for real samples was ranged between 83.5% and 104.8%. This approach gave the enrichment factor of 39.2, which guarantees trace analysis of Cu residues. Therefore, Fe₃O₄/HAP/GQDs can be a potential and suitable candidate for the pre-concentration and separation of Cu from food samples. It can easily be reused after treatment with deionized water.

Physico-mechanical and morphological features of zirconia substituted hydroxyapatite nano crystals

Zirconia doped Hydroxyapatite (HAP) nanocrystals [Ca₁₀(PO₄)_6−x(ZrO₂)_x(OH)₂]; (0 ≤ x ≤ 1 step 0.2) were synthesized using simple low cost facile method. The crystalline phases were examined by X-ray diffraction (XRD). The crystallinity percentage decreased with increasing zirconia content for the as-synthesized samples. The existence of zirconia as secondary phase on the grain boundaries; as observed from scanning electron micrographs (FESEM); resulted in negative values of microstrain. The crystallite size was computed and the results showed that it increased with increasing annealing temperature. Thermo-gravimetric analysis (TGA) assured the thermal stability of the nano crystals over the temperature from room up to 1200 °C depending on the zirconia content. The corrosion rate was found to decrease around 25 times with increasing zirconia content from x = 0.0 to 1.0. Microhardness displayed both compositional and temperature dependence. For the sample (x = 0.6), annealed at 1200 °C, the former increased up to 1.2 times its original value (x = 0.0).

Super-Paramagnetic Nanoparticles with Spinel Structure: A Review of Synthesis and Biomedical Applications

The study of ceramic materials has attracted the attention of many researchers due to the possibility of their use in nanotechnology. The spinel ferrites form a large group of materials with a broad range of applications. Some examples include electronic devices such as high-frequency transformer cores, antenna rods, induction-tuners, among many others. However, when the ferritic materials display superparamagnetic behavior, their potential for biological applications like drug delivery, hyperthermia, resonance magnetic imaging and magnetic separation, become amazingly high. Therefore, the superparamagnetism is a characteristic strongly desired for spinel ferrites. Since this phenomenon is size-dependent, the methodologies to synthesize these materials has emerged as a crucial step in order to obtain the desired properties. In this regarding, several synthetic processes have been developed. For example, co-precipitation is a fast and cheap method to synthesize superparamagnetic spinel ferrites. However, methodologies involving microwave, ultrasound or polymers frequently result in these kind of materials. Therefore, this review brings a brief historic introduction about spinel ferrites as well as essential concepts to understand their structure and magnetic properties. In addition to this, recent advances in synthesis and applications of the superparamagnetic spinel ferrites are mentioned. Contents of Paper

Structural and microstructural interpretations of Zn-doped biocompatible bone-like carbonated hydroxyapatite synthesized by mechanical alloying

Single-phase nanocrystalline biocompatible Zn-dopedA-type carbonated hydroxyapatite (A-cHAp) powder has been synthesizedviamechanical alloying of a stoichiometric mixture of CaCO3, CaHPO4·2H2O and ZnO powders in open air at room temperature by 10 h of milling. TheA-type carbonation in HAp (A-cHAp) is confirmed by Fourier transform IR analysis. The structural and microstructural parameters of the as-milled powders are revealed by Rietveld powder structure refinement analysis and transmission electron microscopy. Zn substitution along with mechanical alloying causes partial amorphization of crystallineA-cHAp, analogous to native bone mineral. Zn2+cations substitute into the ninefold-coordinated Ca2+sites in theA-cHAp unit cell. An assay test using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] reveals a high percentage of cell viability and hence confirms the biocompatibility of the sample. The overall results indicate that the processedA-cHAp has a chemical composition very close to that of natural biological apatite.

Microwave irradiation of nanohydroxyapatite from chicken eggshells and duck eggshells

Due to similarity in composition to the mineral component of bones and human hard tissues, hydroxyapatite with chemical formula Ca₁₀(PO₄)₆(OH)₂ has been widely used in medical field. Both chicken and duck eggshells are mainly composed of calcium carbonate. An attempt has been made to fabricate nanohydroxyapatite (nHA) by chicken (CES) and duck eggshells (DES) as calcium carbonate source (CaCO₃). CES and DES were reacted with diammonium hydrogen [(NH₄)₂HPO₄] solution and subjected to microwave heating at 15 mins. Under the effect of microwave irradiation, nHA was produced directly in the solution and involved in crystallographic transformation. Sample characterization was done using by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).

Advances in synthesis of calcium phosphate crystals with controlled size and shape

Calcium phosphate (CaP) materials have a wide range of applications, including biomaterials, adsorbents, chemical engineering materials, catalysts and catalyst supports and mechanical reinforcements. The size and shape of CaP crystals and aggregates play critical roles in their applications. The main inorganic building blocks of human bones and teeth are nanocrystalline CaPs; recently, much progress has been made in the application of CaP nanocrystals and their composites for clinical repair of damaged bone and tooth. For example, CaPs with special micro- and nanostructures can better imitate the biomimetic features of human bone and tooth, and this offers significantly enhanced biological performances. Therefore, the design of CaP nano-/microcrystals, and the shape and hierarchical structures of CaPs, have great potential to revolutionize the field of hard tissue engineering, starting from bone/tooth repair and augmentation to controlled drug delivery devices. Previously, a number of reviews have reported the synthesis and properties of CaP materials, especially for hydroxyapatite (HAp). However, most of them mainly focused on the characterizations and physicochemical and biological properties of HAp particles. There are few reviews about the control of particle size and size distribution of CaPs, and in particular the control of nano-/microstructures on bulk CaP ceramic surfaces, which is a big challenge technically and may have great potential in tissue engineering applications. This review summarizes the current state of the art for the synthesis of CaP crystals with controlled sizes from the nano- to the macroscale, and the diverse shapes including the zero-dimensional shapes of particles and spheres, the one-dimensional shapes of rods, fibers, wires and whiskers, the two-dimensional shapes of sheets, disks, plates, belts, ribbons and flakes and the three-dimensional (3-D) shapes of porous, hollow, and biomimetic structures similar to biological bone and tooth. In addition, this review will also summarize studies on the controlled formation of nano-/microstructures on the surface of bulk ceramics, and the preparation of macroscopical bone grafts with 3-D architecture nano-/microstructured surfaces. Moreover, the possible directions of future research and development in this field, such as the detailed mechanisms behind the size and shape control in various strategies, the importance of theoretical simulation, self-assembly, biomineralization and sacrificial precursor strategies in the fabrication of biomimetic bone-like and enamel-like CaP materials are proposed.

Synthesis and spectral characterization of silver/magnesium co-substituted hydroxyapatite for biomedical applications

The present work is aimed at the synthesis of antibacterial and bioactive silver/magnesium co-substituted hydroxyapatite (Ag/Mg-HAP) powders. For this purpose, firstly, different concentrations (0.5, 1.5, 2.5wt.%) of silver substituted HAP (Ag-HAP) powders were prepared by ultrasonic irradiation technique and were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). Secondly, magnesium (Mg) is co-substituted as secondary material into Ag-HAP to offset the potential cytotoxicity of Ag, as higher concentration of Ag is toxic. The antibacterial activity of as-synthesized powders was evaluated by Escherichia coli (E. coli) and was found to be effectively high against bacterial colonization. Also, the in vitro cell-material interaction is evaluated with human osteosarcoma MG63 (HOS MG63) cells for cell proliferation. The results showed the evidence of cytotoxic effects of the higher concentration of Ag-HAP characterized by poor cellular viability whereas, Ag/Mg-HAP showed better cell viability indicating that co-substitution of Mg in Ag-HAP effectively offset the negative effects of Ag and improve performance compared with pure HAP. Thus, the as synthesized Ag/Mg-HAP will serve as a better candidate for biomedical applications with good antibacterial property and bone bonding ability.

Facile synthesis of calcium silicate hydrate using sodium dodecyl sulfate as a surfactant assisted by ultrasonic irradiation

Calcium silicate hydrate (CSH) consisting of nanosheets has been successfully synthesized assisted by a tip ultrasonic irradiation (UI) method using calcium nitrate (Ca(NO3)·4H2O), sodium silicate (Na2SiO3·9H2O) and sodium dodecyl sulfate (SDS) in water. Systematic studies found that reaction time of ultrasonic irradiation and concentrations of surfactant (SDS) in the system were important factors to control the crystallite size and morphologies. The products were characterized by X-ray power diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectrometry (FTIR). The size-strain plot (SSP) method was used to study the individual contributions of crystallite sizes and lattice strain on the peak broadening of the CSH. These characterization techniques revealed the successful formation of a crystalline phase with an average crystallite size of about 13 nm and nanosheet morphology at a reaction time of 10 min UI with 0.2 g SDS in solvent which were found to be optimum time and concentrations of SDS for the synthesis of CSH powders.

Effect of ultrasound irradiation on the production of nHAp/MWCNT nanocomposites

Large amounts of nanohydroxyapatite (nHAp)-multiwall carbon nanotube (MWCNT) nanocomposites are produced by two different aqueous precipitation methods. The ultrasonic irradiation (UI) and slow-drip addition under continuous magnetic stirring (DMS) methods were used to investigate the precipitation of nHAp acicular crystals. Calcium-nitrate, diammonium hydrogen phosphate, and ammonium hydroxide were used as precursor reagents. Superhydrophilic MWCNT were also employed. XPS analysis evidences that the functionalized MWCNTs are composed of 18 to 20 at.% of oxygen and that this property influences the nHAp formation. The high surface area of the MWCNT decreases the mean free path of ions, favoring the nHAp formation assisted by UI. The crystallinity was evaluated using the Scherrer equation. Semi-qualitative energy dispersive spectroscopy (EDS) analysis showed that the main components of HAp powders were calcium and phosphorus in the ratio Ca/P around of 1.67. Bioactivity properties of the nHAp/MWCNT-UI nanocomposites could be evaluated after 14 days soaking in simulated body fluid medium. Scanning electron microscopy, EDS, Fourier transform infrared attenuated total reflection spectroscopy, and X-ray diffraction techniques proved that the apatites formed on the surface and to points that the nHAp/MWCNT-UI have potential biological applications.

Obtaining Ca(H2PO4)(2)·H2O, monocalcium phosphate monohydrate, via monetite from brushite by using sonication

Brushite was synthesized by precipitation of calcium chloride (CaCl(2)) and sodium phosphate monobasic (Na(2)HPO(4)) dried in vacuum and monetite was obtained from this brushite by sonication with a frequency of 90kHz at 500W for 90min. Monetite itself was also transformed in Ca(H(2)PO(4))(2)·H(2)O, monocalcium phosphate monohydrate (MCPM), by sonication with a frequency of 90kHz at 500W for 60min followed by lyophilization. The MCPM was sonicated and lyophilized by three times more until reach over 240min, but any other phase transformation was observed. All these phase transformations were analyzed by X-ray diffraction (XRD) and infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated a grain size of about 200nm in all the samples. The morphology observed was a corn-flake-like grain for brushite, a pseudo-needle-like grains for monetite, and lamellar-like grains for MCPM.

The effect of ultrasonic irradiation on the crystallinity of nano-hydroxyapatite produced via the wet chemical method

Nanohydroxyapatite (nHAp) powders were produced via aqueous precipitation by adopting four different experimental conditions, assisted or non-assisted by ultrasound irradiation (UI). The nHAp powders were characterized by X-ray diffraction, energy-dispersive X-ray fluorescence, Raman and attenuated total reflection Fourier transform infrared spectroscopies, which showed typical surface chemical compositions of nHAp. Analysis found strong connections between UI and the crystallization process, crystal growth properties, as well as correlations between calcination and substitution reactions.