Mechanism Of Apatite Formation Research Articles

Pulp stones and its relation with co-morbid diseases

Pulp stones are nodular, calcified masses that can develop in the pulp of healthy, damaged or even developing teeth. In addition to a number of other factors and idiopathic factors, a number of theories have been put forward about the etiological factors behind the occurrence of pulp stones. These include age, genetic susceptibility, pulp degeneration, pulp circulatory disturbances, inductive interactions between pulp tissue and epithelium, and orthodontic tooth movements. Recently, pulp stones development has been linked to a number of systemic disorders, including diabetes, renal diseases, autoimmune diseases, and coronary artery disease. Osteopontin appears to contribute to plaque calcification and is a component of atheromatous plaques. Calcifications have also been noted in renal and carotid arteries with osteopontin, and numerous studies have shown a relationship between atheromatous plaques in arteries and the development of pulp stones. The development of pulp stones, kidney stones, joint calcification, and atheromatous plaques in arteries are thought to share the same mechanism of apatite formation. It has been hypothesized that the biological apatite that nanobacteria produce on their cell walls, which is comparable to kidney stones and calcified tissue, may be a common cause of both pulp stones and atheromatous plaques seen in coronary artery disease. As per the findings of several studies, pulp stones are more severe in coronary artery disease patients. The purpose of this research is to review the available information about pulp stones and its relation with co-morbid diseases.

Application of femtosecond laser microfabrication in the preparation of advanced bioactive titanium surfaces.

The surface activation of titanium plays a key role in the biological properties of titanium implants as bone repair materials. Improving the ability to induce apatite precipitation on the surface was a well-accepted titanium bioactivation route. In this study, advanced femtosecond laser microfabrication was applied to modify titanium surfaces, and the effect of femtosecond laser etching on apatite precipitation was investigated and compared with popular titanium modification methods. Meanwhile, the mechanism of apatite formation after femtosecond laser modification was interpreted from the point of materials science. The surface physical-chemical characterization results showed that femtosecond laser etching can improve the surface hydrophilicity and increase the surface energy. Compared with traditional abrasive paper and acid-alkali treatment, this method increased the contents of active sites including titanium oxide and titanium-hydroxyl on titanium surfaces. TiO2 on the surface was transformed to TiO after femtosecond laser treatment. The samples etched with 0.3 W and 0.5 W femtosecond lasers had a better ability to induce apatite deposition than those treated with traditional mechanical treatment and popular acid-alkali modification, which would lead to better bioactivity and osteointegration. Considering the technical advantages of femtosecond lasers in microfabrication, it provides a more efficient and controllable scheme for the bioactivation of titanium. This research would improve the application potential of femtosecond laser treatment, such as micropattern preparation and surface activation, in the field of biomaterials.

Effect of surface chemical modifications on the bioactivity of carbon fibers reinforced epoxy composites

Carbon fibers reinforced epoxy (CF/epoxy) composites have been used in orthopedic and dental implants. However, the inert surface of CF/epoxy composites cannot show ability of forming direct bone bonding with autologous bone during implantation. In order to improve the bioactivity of CF/epoxy composites, the different chemical modifications (concentrated sulfuric acid (97 wt%), CaCl2 solution, concentrated sulfuric acid (97 wt%) + CaCl2 solution) were used to modify its original surface. The bioactivity of modified CF/epoxy composites was evaluated by in vitro apatite formation ability in simulated body fluids (SBF). The result showed that -SO3H and Ca2+ were introduced on the of sample surface after chemical modification. Samples modified with concentrated sulfuric acid (97 wt%) and CaCl2 solution showed the best bioactivity. In addition, a uniform and dense apatite coating was formed on the surface of functionalized CF/epoxy composites after soaking in SBF and the presence of -SO3H would significantly improve the bond between the coating and the substrate. The transformation process of apatite morphology during its formation and the mechanism of apatite formation on the functionalized CF/epoxy composites were also analyzed systematically.

A Short Review on <i>In Vitro</i> Bioactivity Behavior of Magnesium Composites

Research and development on the biomaterials are increasing due to the demand for materials that can bond to the living bones and by any chance can avoid second surgery procedure. Good bonding between bones and biomaterials or artificial implant can avoid loosening that due to the friction and wear. Currently, magnesium alloys are being actively researched because of their ability to serve as structural support in short term and can be absorbed in the body after healing process is completed. The addition of bioactive components such as hydroxyapatite and bioglass into magnesium is made to improve the bioactivity behavior of magnesium alloys. This paper summarizes the past and current studies of magnesium alloys in regards of in vitro bioactivity behavior, biomineralization and apatite formation mechanism.

Are lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) ferroelectrics bioactive?

The use of functional materials, such as ferroelectrics, as platforms for tissue growth in situ or ex situ, is new and holds great promise. But the usage of materials in any bioapplication requires information on biocompatibility and desirably on bioactive behavior when bone tissue engineering is envisaged. Both requirements are currently unknown for many ferroelectrics. Herein the bioactivity of LiNbO3 and LiTaO3 is reported. The formation of apatite-like structures on the surface of LiNbO3 and LiTaO3 powders after immersion in simulated body fluid (SBF) for different soaking periods indicates their bioactive potential. The mechanism of apatite formation is suggested. In addition, the significant release of lithium ions from the ferroelectric powders in the very first minutes of soaking in SBF is examined and ways to overcome this likely hurdle addressed.

Response of Functionality Graded Hydroxyapatite/F-75 in Saline Solution 0.9% NaCl

Functionally graded hydroxyapatite (HAP) /F-75 was fabricated using powder metallurgy technique. Samples fabricated were tested inside 0.9% NaCl to check their bioactivity reaction. After immersed, samples were analyzed using Fourier Transform Infrared (FTIR) and mass change. Result showed that mass gain decreased as the percentage of HAP in the intermediate layer increased. Mass gain obtained after immersion test because of the passive layer formation on the F-75 surface. Dissolution of HAP was occurred as the FTIR analysis detected the existence of phosphate, and hydroxide ions bands inside the solution. The dissolution process is the part of the mechanism of apatite formation. The apatite layer formation is important to encourage the formation of new bone.

Effect of HCl concentrations on apatite-forming ability of NaOH–HCl- and heat-treated titanium metal

Titanium (Ti) metal was treated with water or HCl solutions after 5 M NaOH solution treatment and then subjected to heat treatment at 600 degrees C. The apatite-forming abilities of the treated Ti metals were examined in simulated body fluid. The apatite-forming ability of the Ti metal subjected to NaOH, water and heat treatment was lower than that of just NaOH and heat treatments. Ti metals subjected to NaOH, HCl and heat treatment showed apatite-forming abilities, which increased with increasing HCl concentrations up to the same level as that of NaOH- and heat-treated Ti metal. The former did not show a decrease in its apatite-forming ability, even in a humid environment for a long period, whereas the latter decreased its ability. The increase in the apatite-forming ability with increasing HCl concentrations suggests a different mechanism of apatite formation from that previously proposed.

Mechanism of apatite formation on silicon suboxide film prepared by pulsed metal vacuum arc deposition

Pulsed metal vacuum arc deposition technology was employed to fabricate SiO x ( x ≤ 2) film at the oxygen partial pressure at 0.6 × 10 −2 Pa. Surface characteristics of the as-deposited SiO x film were studied by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results show that the film is substoichiometric and abundant oxygen vacancies exist in the film. The as-deposited film was immersed in simulated body fluid (SBF) for evaluation of in vitro bioactivity. After incubation in SBF, ball-like apatite particles were found on the film surfaces by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The mechanism of apatite deposition on the SiO x film was explained in terms of the silanol functional groups formed on the surface of the film after immersion in SBF. There are abundant active oxygen vacancies in the SiO x film that were attacked by the water molecules in the solution and then formed silanol groups in the film. The silanol groups adsorbed calcium and phosphate ions from the solution to the hydrated surface to form critical apatite cluster. Once the apatite nuclei are formed, they spontaneously grow by consuming calcium and phosphate ions in the surrounding fluid.

Mechanism of Apatite Formation on Sol-Gel Derived PDMS-Modified SiO<sub>2</sub>-CaO-P<sub>2</sub>O<sub>5</sub> Hybrids with Various P<sub>2</sub>O<sub>5</sub> Content

The mechanism of apatite formation on the surface of novel PDMS modified SiO2-CaO- P2O5 hybrids is presented. The bioactive hybrids with different P2O5 content were synthesized by sol-gel method and soaked in the simulated body fluid (SBF) for different periods. The surface and the cross-section of the specimens were examined by use of Fourier transform infrared reflection spectroscopy, thin-film X-ray diffraction technique and scanning electron microscopy. The PDMS-SiO2-CaO-P2O5 hybrid containing 0.03 mole ratio of TEP(triethyl phosphate) / TEOS (tetraethoxysilane) exhibited faster apatite formation compared to P2O5-free hybrids. This composition resulted in the thickest apatite layer (~6µm) and this might be attributed to faster formation of the silica hydrogel on the surface of the P2O5-containing hybrids than on the surface of the P2O5-free hybrids. Resultingly, the apatite nucleation on the surface of the P2O5-containing hybrids is effectively induced by the hydrated silica at a lower degree of supersaturation. Changes in concentrations of the calcium, silicon and phosphorus in the SBF and the SEM-EDS line analysis depicting the variation of Si, Ca and P elements for the bulk, the interface and the apatite are reported. These were found to be quite correlative with each other. The rate of the concentration changes for the P2O5-containing hybrids is higher than that of the P2O5-free hybrids. The increases in the calcium and silicon concentrations are attributed to dissolution of the calcium and silicate ions from the hybrids, and the decrease in the phosphorus concentration is ascribed to formation of the amorphous calcium phosphate and crystalline apatite on the surface of hybrids by consuming the phosphate ion from the fluid.

Bonelike apatite formation on carbon microspheres

Carbon microspheres with a diameter of 2 μm were prepared by hydrothermal process. The apatite-formation ability of the carbon microspheres was evaluated by soaking them in a simulated body fluid (SBF) for 5 and 10 d and apatite-formation mechanism was also analyzed. The result showed that bonelike apatite was formed on the surface of carbon microspheres. Our study indicates that the carbon microspheres synthesized by this method possess apatite-formation ability and may be used as a bioactive injectable filler for bone tissue regeneration.

Mechanism of apatite formation on hydrogen plasma-implanted single-crystal silicon

Hydrogen is implanted into single-crystal silicon wafers using plasma ion immersion implantation to improve the surface bioactivity and the mechanism of apatite formation is investigated. Our micro-Raman and transmission electron microscopy results reveal the presence of a disordered silicon surface containing Si–H bonds after hydrogen implantation. When the sample is immersed in a simulated body fluid, the Si–H bonds on the silicon wafer initially react with water to produce a negatively charged surface containing the functional group (Si–O−) that subsequently induces the formation of apatite. A good understanding of the formation mechanism of apatite on hydrogen implanted silicon is not only important from the viewpoint of biophysics but also vital to the actual use of silicon-based microchips and MEMS inside a human body.

Bone-like apatite layer formation on hydroxyapatite prepared by spark plasma sintering (SPS)

Hydroxyapatite (HA) compacts with high density and superior mechanical properties were fabricated by spark plasma sintering (SPS) using spray-dried HA powders as feedstock. The formation of bone-like apatite layer on SPS consolidated HA compacts were investigated by soaking the HA compacts in simulated body fluid (SBF) for various periods (maximum of 28 days). The structural changes in HA post-SBF were analyzed with scanning electron microscopy, grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy. It was found that a layer consisting microcrystalline carbonate-containing hydroxyapatite was formed on the surface of HA compacts after soaking for 24 h. The formation mechanism of apatite on the surface of HA compacts after soaking in SBF was attributed to the ion exchange between HA compacts and the SBF solution. The increase in ionic concentration of calcium and phosphorus as well as the increase in pH after SBF immersion resulted in an increase in ionic activity product of apatite in the solution, and provided a specific surface with a low interface energy that is conducive to the nucleation of apatite on the surface of HA compacts.

Mechanism of Apatite Formation on Anodically Oxidized Titanium Metal in Simulated Body Fluid

Mechanism of Apatite Formation on Anodically Oxidized Titanium Metal in Simulated Body Fluid

Mechanism of apatite formation on wollastonite coatings in simulated body fluids

The formation mechanism of apatite on the surface of wollastonite coating was examined. Plasma-sprayed wollastonite coatings were soaked in a lactic acid solution (pH=2.4) to result in the dissolution of calcium from the coating to form silanol (Si–OH) on the surface. Some calcium-drained samples were soaked in a trimethanol aminomethane solution (pH=10) for 24 h to create a negatively charged surface with the functional group (Si–O −). These samples before and after treatment in a trimethanol aminomethane solution were immersed in simulated body fluids (SBF) to investigate the precipitation of apatite on the coating surface. The results indicate that the increase of calcium in the SBF solution is not the critical factor affecting the precipitation of apatite on the surface of the wollastonite coating and the apatite can only form on a negatively charged surface with the functional group (Si–O −). The mechanism of apatite formation on the wollastonite coating is proposed. After the wollastonite coatings are immersed into the SBF, calcium ions initially exchange with H + leading to the formation of silanol (Si–OH) on the surface of the layer and increase in the pH value at the coating–SBF interface. Consequently, a negatively charged surface with the functional group (Si–O −) forms on the surface. Due to the negatively charged surface, Ca 2+ ions in the SBF solution are attracted to the interface between the coating and solution, thereby increasing the ionic activity of the apatite at the interface to the extent that apatite precipitates on the coating surface.

Mechanism of Apatite Formation on Bioactive Tantalum Metal in Simulated Body Fluid

Mechanism of Apatite Formation on Bioactive Tantalum Metal in Simulated Body Fluid

Mechanism of Apatite Formation on Single Crystal Silicon in an Aqueous Solution at Room Temperature.

Single crystal silicon was soaked in a solution with ion concentrations 1.5 times those of human blood plasma (1.5 SBF) and a bone-like apatite layer formed on it. From analyzing the surface structural change of single crystal silicon and the composition change of solution during soaking, the mechanism of apatite formation was interpreted as follows. The single crystal silicon reacts with 1.5 SBF to form a silica gel layer on its surface. The gel layer induces apatite nucleation on its surface and the apatite nuclei grow by consuming calcium and phosphate ions from 1.5 SBF. By continuously supplying the ions, a dense and uniform layer of apatite with desired thickness can be formed. This method is promising for developing advanced functional medical devices such as biosensors.

Reactivity of plasma-sprayed wollastonite coating in simulated body fluid.

We incubated wollastonite coatings prepared with plasma spraying in simulated body fluids for different periods to investigate the reactivity. The surface structures of wollastonite coatings immersed in simulated body fluids were analyzed with scanning electron microscopy, Auger electron spectroscopy, and transmission electron microscopy. The results showed a carbonate-containing hydroxyapatite layer formed on the surface of a plasma-sprayed wollastonite coating soaked in simulated body fluids, and a silica-rich layer appeared on the surface of the coating before the formation of the carbonate-containing hydroxyapatite layer. The formation mechanism of apatite on the coating surface could be explained in terms of the ionic exchange between H(+) within simulated body fluids and Ca(2+) in the coating, which resulted in an increase in the ionic activity product of the apatite in simulated body fluids and provided a specific surface with a lower interface energy to the formation of apatite nuclei.

TEM-EDX study of mechanism of bonelike apatite formation on bioactive titanium metal in simulated body fluid.

Bioactive titanium metal, which forms a bonelike apatite layer on its surface in the body and bonds to the bone through the apatite layer, can be prepared by NaOH and heat treatments to form an amorphous sodium titanate layer on the metal. In the present study, the mechanism of apatite formation on the bioactive titanium metal has been investigated in vitro. The metal surface was examined using transmission electron microscopy and energy dispersive X-ray spectrometry as a function of the soaking time in a simulated body fluid (SBF) and complemented with atomic emission spectroscopy analysis of the fluid. It was found that, immediately after immersion in the SBF, the metal exchanged Na(+) ions from the surface sodium titanate with H(3)O(+) ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after they were formed, incorporated the calcium ions in the fluid to form an amorphous calcium titanate. After a long soaking time, the amorphous calcium titanate incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate with a low Ca/P atomic ratio of 1.40. The amorphous calcium phosphate thereafter converted into bonelike crystalline apatite with a Ca/P ratio of 1.65, which is equal to the value of bone mineral. The initial formation of the amorphous calcium titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania, which are dissociated from the Ti-OH groups, with the positively charged calcium ions in the fluid. The amorphous calcium titanate is speculated to gain a positive charge and to interact with the negatively charged phosphate ions in the fluid to form the amorphous calcium phosphate, which eventually stabilizes into bonelike crystalline apatite.

Biomimetic Apatite Deposition on Calcium Silicate Gel Glasses

In order to understand the Biomimetic apatite formation mechanism on gel glasses, a glass (in mol-%) SiO2 80%—CaO 20% (80S20C) was prepared by the sol-gel method and its behaviour in a simulated body fluid (SBF) was studied. To study the role of phosphorous in the in vitro apatite formation, a gel glass (in mol-%) SiO2 80%—CaO 17%—P2O5 3% (80S17C3P) was prepared comparing its behaviour in SBF with that of 80S20C. In both studies, a protocol without renovation of SBF (static) was used. To mimic the conditions in the living organisms, an in vitro protocol with continuous renovation of solution (dynamic) was proposed. To check the feasibility of dynamic protocol, 80S20C and 80S17C3P were studied in dynamic and results compared with obtained in static. Static studies of 80S20C allowed us to verify that phosphorus is not essential for bioactivity because the apatite-like layer was formed from the phosphorous in SBF. However, a 3 mol-% of P2O5 in 80S17C3P gel glass favoured apatite crystallization. In dynamic, complete assays were performed with ionic concentrations and pH in solution almost equal to human plasma. After 7 days in dynamic, apatite crystals and crystalline aggregates were larger than in static. Besides, compositional variations were observed in the newly formed layer as a function of the protocol. In static, the layer formed in both glasses contained calcium and phosphorous, (Ca/P molar ratio = 1.6) and silicon. In dynamic, the layer did not contain silicon and the Ca/P molar ratio was 1.2. Differences in composition and pH of assay solution, 8 in static and 7.3 in dynamic could explain these variations. In static, an apatite close to stoichiometric could be formed. In dynamic, a mixture of calcium deficient apatite and other calcium phosphates could constitute the layer.

Apatite Formation in the CaO–PbO–P2O5–H2O System at 23°± 1°C

Lead is a toxic heavy metal that is commonly used to manufacture products such as storage batteries and electroceramics. In an effort to minimize the health risks to humans, the low‐cost stabilization of lead via its incorporation into the apatite crystal structure has been explored. Therefore, apatite formation in the quaternary system CaO–PbO–P2O5–H2O at room temperature (23°± 1°C) and atmospheric pressure from PbO, CaHPO4, Ca4(PO4)2O, and H3PO4 was studied. Apatites were prepared via precipitation from aqueous‐based mixtures with a constant (Ca + Pb):P molar ratio of 1.67. Aqueous mixtures that contained up to 1 mol of PbO (massicot) per mole of apatite (Ca10−xPbx(PO4)6(OH)2) resulted in the precipitation of weakly crystalline Ca10(PO4)6(OH)2 as the predominant phase. Highly crystalline Pb10(PO4)6(OH)2 was formed from mixtures that contained 8–9 mol of PbO per mole of apatite. Intermediate proportions of lead oxide, which entailed 4.5–7 mol of PbO per mole of apatite, produced a stable quaternary apatite phase of moderate crystallinity, with an approximate composition of Ca5Pb5(PO4)6(OH)2. The lattice parameters of this quaternary apatite were calculated using a least‐squares refinement program and other existing X‐ray diffraction software. Experimental observation, along with computer modeling of the solution chemistry, enabled the mechanism of apatite formation to be established. Dissolution of lead oxide and calcium‐bearing minerals, such as monetite (CaHPO4), with the aid of H3PO4, resulted in the precipitation of lead‐rich apatites. This phenomenon was followed by their slow conversion to the stable quaternary apatite (Ca5Pb5(PO4)6(OH)2).