Hydroxyapatite Nuclei Research Articles

Synthesis and Properties of CaMgSi2O6 - SrO Bioceramics for Enhanced Hydroxyapatite Formation and Cell Viability in Bone Regeneration

This study aims to synthesize and evaluate the properties of diopside (CaMgSi2O6) and strontium modified diopside (CaMgSi2O6-SrO) bioceramics for potential bone regeneration applications. The substitution of strontium for calcium leads to the formation of solid solutions: Sr-CaMgSi2O6, Ca-SrMgSi2O6, and a single phase of SrMgSi2O6, along with secondary phases of Ca-Sr2MgSi2O7 and Sr2MgSi2O7. This study is the first to examine the physical and biological properties of SrMgSi2O6 and its solid solutions. Microstructural analysis reveals that the pure diopside exhibits uniformly packed fine particles, while the SrO substitution results in lattice distortion and structural damage, thus weakening the mechanical properties and biodegradation resistance. The in vitro hydroxyapatite (HAp) formation ability of CaMgSi2O6-SrO bioceramics is comprehensively investigated, revealing that the re-adsorption of Mg2+/Sr2+ is a crucial factor. Pure diopside and Sr0.25 demonstrate effective HAp formation after immersion in simulated body fluid (SBF), with Sr0.25 showing finer particles and more uniform distribution due to appropriate Sr2+ re-adsorption. In contrast, SrO-rich samples show reduced HAp formation due to excessive re-adsorption of Mg2+ and Sr2+ ions, hindering HAp nuclei development. The cell viability test reveals that SrO substitution enhances cell viability due to increased surface area and the release of beneficial ions. Overall, Sr0.25 demonstrates excellent potential for bone regeneration applications by promoting HAp uniformity.

Comparative study of hydroxyapatite synthesized using Schiff base and wet chemical precipitation methods

Hydroxyapatite (HAp) exists as an inorganic and crystalline composition present in bones and dental enamel, and hence can be utilized as a direct element or as part of the composition of biomaterials and implants for dental and orthopaedic applications. Listed below are a few synthesis techniques for HAp that are listed in the literature: solid-state and mechano-chemical methods (dry methods), wet chemical precipitation and sol-gel methods (wet methods), and combustion and pyrolysis methods (high-temperature processes). Nevertheless, there are new and more productive techniques that result in HAp with a regulated morphology, such as the Schiff base method, which, on reaction with calcium and phosphate precursors, forms chelating complexes to produce HAp nuclei. This research paper presents the comparison in characteristics between HAp synthesized using Schiff base (HAp-SB), wet chemical precipitation (HAp-WC) methods, and commercial HAp (HAp-CM) in their powdered and pelleted form. The average size of HAp-WC particles in the spherical form was found to be 603 nm ± 176, HAp-SB were found to have rod-like morphology, which is very similar to human bone-like HAp, with an average length and width of 1522 nm ± 759 and 400 nm ± 112, respectively, and HAp-CM were found to have spherical morphology with dimensions of 52 nm ± 25. Biological studies show that cell viability of HAp-SB pellet (202.01% ± 8.16) seemed to have higher cell proliferation properties than HAp-WC pellet (145.7% ± 5.11) and HAp-CM pellet (71.53% ± 3.61) due to its higher aspect ratio, and hence higher surface area for the cells to adhere. In a detailed study, it is observed that both techniques had their advantages, and there were no significant disadvantages observed.

Effect of SrO and ZnO on Densification and in Vitro Behaviors of P<sub>2</sub>O<sub>5</sub>-CaO-Na<sub>2</sub>O-SiO<sub>2</sub>-TiO<sub>2</sub> Bioactive Glass-Ceramics

Phosphate based-glass ceramics in the system of P2O5-CaO-Na2O-SiO2-TiO2 were obtained by the sintering method. For evaluating the effect of strontium and zinc, different amounts of these elements were doped in the parent glass instead of calcium oxide. Sintering behavior of the glasses was evaluated through the measurement of bulk density, liquid absorption, and open porosity percentages. Based on the results, 600 °C was determined as the optimum sintering temperature. Based on the X-Ray diffractometry, calcium pyrophosphate was precipitated during the sintering process as the main crystallized phase. It is worth noting that changing the parent glass composition led to its phase transformation. Variation in the pH and ion concentration in the simulated body fluid as well as weight loss percentages of the samples were considered to evaluate the dissolution behavior of the samples. The in vitro tests showed that increasing the amount of strontium and zinc intensified the dissolution rate. According to scanning electron micrographs, hydroxyapatite nuclei precipitated on the surfaces of the samples after three days of simulated body fluid (SBF) soaking; but, they were dissolved in the solution after 28 days due to the dissolution of the substrate. Some residues of the grown apatite-like layer were observed on the surface of the composition when 25 and 2.5 molar percent of calcium were substituted for strontium and zinc, respectively.

Incorporation of Chloramphenicol Loaded Hydroxyapatite Nanoparticles into Polylactide.

Chloramphenicol (CAM) has been encapsulated into hydroxyapatite nanoparticles displaying different morphologies and crystallinities. The process was based on typical precipitation of solutions containing phosphate and calcium ions and the addition of CAM once the hydroxyapatite nuclei were formed. This procedure favored a disposition of the drug into the bulk parts of the nanoparticles and led to a fast release in aqueous media. Clear antibacterial activity was derived, being slightly higher for the amorphous samples due to their higher encapsulation efficiency. Polylactide (PLA) microfibers incorporating CAM encapsulated in hydroxyapatite nanoparticles were prepared by the electrospinning technique and under optimized conditions. Drug release experiments demonstrated that only a small percentage of the loaded CAM could be delivered to an aqueous PBS medium. This amount was enough to render an immediate bacteriostatic effect without causing a cytotoxic effect on osteoblast-like, fibroblasts, and epithelial cells. Therefore, the prepared scaffolds were able to retain CAM-loaded nanoparticles, being a reservoir that should allow a prolonged release depending on the polymer degradation rate. The studied system may have promising applications for the treatment of cancer since CAM has been proposed as a new antitumor drug.

Effect of inorganic and organic bioactive signals decoration on the biological performance of chitosan scaffolds for bone tissue engineering.

The present work is focused on the design of a bioactive chitosan-based scaffold functionalized with organic and inorganic signals to provide the biochemical cues for promoting stem cell osteogenic commitment. The first approach is based on the use of a sequence of 20 amino acids corresponding to a 68-87 sequence in knuckle epitope of BMP-2 that was coupled covalently to the carboxyl group of chitosan scaffold. Meanwhile, the second approach is based on the biomimetic treatment, which allows the formation of hydroxyapatite nuclei on the scaffold surface. Both scaffolds bioactivated with organic and inorganic signals induce higher expression of an early marker of osteogenic differentiation (ALP) than the neat scaffolds after 3 days of cell culture. However, scaffolds decorated with BMP-mimicking peptide show higher values of ALP than the biomineralized one. Nevertheless, the biomineralized scaffolds showed better cellular behaviour than neat scaffolds, demonstrating the good effect of hydroxyapatite deposits on hMSC osteogenic differentiation. At long incubation time no significant difference among the biomineralized and BMP-activated scaffolds was observed. Furthermore, the highest level of Osteocalcin expression (OCN) was observed for scaffold with BMP2 mimic-peptide at day 21. The overall results showed that the presence of bioactive signals on the scaffold surface allows an osteoinductive effect on hMSC in a basal medium, making the modified chitosan scaffolds a promising candidate for bone tissue regeneration.

L-arginine directed and ultrasonically aided growth of nanocrystalline hydroxyapatite particles with tunable morphology

Hydroxyapatite, Ca10(PO4)6(OH)2, a main inorganic component of bone material is widely used in various biomedical applications due to its excellent bioactivity and biocompatibility. Synthesizing hydroxyapatite of desired morphology by a prior and conscious manipulation of interfacial electrostatic interaction has been a challenge to be addressed in the arena of biomaterials research. In the present study, l-arginine as an amino acid has been chosen as a growth modifier of hydroxyapatite particles, as its isoelectric point (10.75) is comparable to the conducive alkaline pH for the synthesis of hydroxyapatite and consequently owing to its strong interaction of guanidino group below the isoelectric point with phosphate group of hydroxyapatite than its counterparts. Further, efforts have been made to investigate the nature of interaction of l-arginine with hydroxyapatite nanopartilces at pH above and below the isoelectric point of l-arginine by chemical precipitation and ultrasonically assisted chemical precipitation technique as synthetic protocols. This study reveals that synthesizing hydroxyapatite below the isoelectric point leads to the formation of plate like morphology and that above the isoelectric point to rod like morphology. Ultrasonication promotes the effective interaction of l-arginine with the growing hydroxyapatite nuclei thereby enhancing the growth in a given direction. A tentative mechanism has been proposed for the directional role of l-arginine by selective blocking of crystallographic planes in the growth of hydroxyapatite nuclei and is further supported by Density Functional Theory calculations.

Synthesis of Hydroxyapatite Nanorods under Mild Conditions and Their Drug Release Properties

AbstractHydroxyapatite (HAp) nanorods possess vast potential applications in various fields, and here HAp nanorods with high aspect ratio were synthesized via a convenient two‐stage precipitation‐hydrolysis process at 60°C under atmospheric pressure. The precursor of CaHPO4 at precipitation stage is well crystallized as nubby morphology with CTAB as surfactant, while CaHPO4 was dissolved and CTA+ stabilized the HAp nuclei during the hydrolysis stage. OH− ions were absorbed onto the active crystal surface, where Ca2+ and PO43+ reacted with OH− to make the nuclei grow into larger crystals, and highly crystalline HAp nanorods were obtained by Ostwald ripening. The loaded drug of IBU on the HAp crystals can be 100% released in 24 h. PVP modified HAp nanorods can increase the drug‐loading capacity and release drug faster than pure HAp nanorods. The results indicate that HAp nanorods modified with suitable surfactants are of great use in drug delivery system.

Microwave assisted deposition of hydroxyapatite coating on a magnesium alloy with enhanced corrosion resistance

In this work, a thick, dense and uniform microstructural hydroxyapatite coating was deposited on a magnesium alloy in an aqueous solution under microwave irradiation at 100°C in a short time of 10min. The results showed that the high driving force of interfacial growth under microwave irradiation greatly promoted the growth of hydroxyapatite nuclei into rod-like crystals, and the thickness of obtained hydroxyapatite coating was ∼9.9μm, larger than that of ∼6.3μm derived by water-bath heating. The coating derived by microwave heating offered preferable corrosion resistance for the magnesium alloy compared with the coating derived by water-bath heating. The corrosion current density of the coated magnesium alloy was reduced by 100-fold as compared to the naked magnesium alloy.

Electrochemical and In Vitro Behavior of Nanostructure Sol-Gel Coated 316L Stainless Steel Incorporated with Rosemary Extract

The corrosion resistance of AISI 316L stainless steel for biomedical applications, was significantly enhanced by means of hybrid organic-inorganic sol-gel thin films deposited by spin-coating. Thin films of less than 100 nm with different hybrid characters were obtained by incorporating rosemary extract as green corrosion inhibitor. The morphology, composition, and adhesion of hybrid sol-gel coatings have been examined by SEM, EDX, and pull-off test, respectively. Addition of high additive concentrations (0.1%) did not disorganize the sol-gel network. Direct pull-off test recorded a mean coating-substrate bonding strength larger than 21.2 MPa for the hybrid sol-gel coating. The effect of rosemary extract, with various added concentrations from 0.012 to 0.1%, on the anticorrosion properties of sol-gel films have been characterized by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in simulated body fluid (SBF) solution and has been compared to the bare metal. Rosemary extract additions (0.05%) have significantly increased the corrosion protection of the sol-gel thin film to higher than 90%. The in vitro bioactivity of prepared films indicates that hydroxyapatite nuclei can form and grow on the surface of the doped sol-gel thin films. The present study shows that due to their excellent anticorrosion properties, bioactivity and bonding strength to substrate, doped sol-gel thin films are practical hybrid films in biomedical applications.

Observation of Transformation Behavior of Octacalcium Phosphate to Hydroxyapatite

Octacalcium phosphate (OCP) is regarded as a precursor of hydroxyapatite (HA) which is a main inorganic comstituent of human bones and teeth. OCP is becoming regarded as an important biomaterial. Recently, implanted OCP was found to be converted to apatitic phase in the body and support bone regeneration. Therefore, it is important to reveal the transformation mechanism of OCP to HA for revealing the mechanism of bone formation and for the development of biomedical materials for bone. In this study, we focused on the dissolution of OCP and precipitation of HA. OCP particles were immersed in distilled water at 60 °C. The temporal change of the immersed powders and immersing solution were examined, and the transformation mechanism of OCP to HA was discussed. As there was an unreactive period in the first stage of the transformation, HA crystals seemed to grow easily once HA nuclei were formed. It is speculated that HA nuclei formed on OCP crystals by heterogeneous nucleation, and then HA crystals grow using calcium and phosphoric ions supplied from dissolved OCP.

Improvement of corrosion performance of 316L stainless steel via PVTMS/henna thin film

Metallic materials are the most used materials as orthopedic or dental implants due to their excellent mechanical properties. However they are not able to create a natural bonding with the mineralized bone and occasionally suffer localized corrosion. This work describes the electrochemical behavior of a hybrid sol–gel thin film with the addition of green inhibitor. These films enhance the ability of the implant to make a union with the existing bone and improve its resistance to aggressive environment. An ethanol solution of the polymerized vinyltrimethoxysilane (PVTMS) was mixed with an aqueous solution of henna extract (Lawsonia inermis) and refluxed to give homogeneous sols. Nanostructure hybrid PVTMS/henna thin films were deposited on the stainless steel 316L by spin-coating. The morphology, composition and adhesion of hybrid sol–gel coatings have been examined by SEM, EDX and pull-off test, respectively. Addition of high additive concentrations (0.1%) did not disorganize the sol–gel network. Direct pull-off test recorded a mean coating-substrate bonding strength larger than 20.6MPa for the hybrid sol–gel coating. The effect of henna extract, with various added concentrations from 0.012% to 0.1%, on the anticorrosion properties of sol–gel films have been characterized by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in simulated body fluid (SBF) solution and has been compared to the bare metal. Henna extract additions (0.05%) have significantly increased the corrosion protection of the sol–gel thin film to higher than 90%. The in vitro bioactivity of prepared films indicates that hydroxyapatite nuclei can form and grow on the surface of the doped sol–gel thin films. The present study shows that due to their excellent anticorrosion properties, bioactivity and bonding strength to substrate, doped sol–gel thin films are practical hybrid films in biomedical applications.

Evolution of the magnesium incorporated amorphous calcium phosphate to nano-crystallized hydroxyapatite in alkaline solution

A homogeneous amorphous calcium phosphate (ACP) coating containing magnesium was achieved on titanium substrates by electrochemical deposition (ECD). Its amorphous structure is confirmed by transmission electron microscope (TEM) together with grazing reflection absorption infrared spectroscopy (IR) spectrometer. In the images of high-resolution transmission electron microscope (HRTEM), the ACP spheres are assembled by nano-particles with the diameter of 5–10 nm. In the alkaline environment, nucleation of hydroxyapatite (HAP) occurs on the surfaces of ACP spheres. By consuming the Ca and PO 4 ions inside the ACP spheres, the HAP nuclei grow outward. Confirmed by TEM, the ACP spheres converse to hollow HAP spheres composed of HAP nano-needles. The coating is finally constructed by the HAP nano-needles, which are themselves aggregated by numerous nano-particles.

Bonding Strength, Hardness and Bioactivity of Nano Bioglass-Titania Nano Composite Coating Deposited on NiTi Nails

In the present investigation a titania network encapsulating nano bioactive glass 58s (NBG) particulate phase is proposed as a bioceramic composite coating. The grain size of NBG particles was uniform and its nano scale (50 – 60 nm) confirmed with transmission electron microscopy (TEM). XRD pattern of NBG particles, calcinated at 600°C in air confirmed that the calcinated glass generally existed in amorphous state. Thermogravimetry (TG) curves for the bulk of NBG – Titania gel indicated that the organic and inorganic precursors have been decomposed completely before 600° C. Nickel-titanium alloy (Nitinol® ) Nails was dip-coated with NBG – Titania composite via the sol-gel route. The morphology, structure and component of the composites films were evaluated using environmental scanning electron microscope (SEM) and field emission scanning electron microscope (FESEM). Also, FTIR confirmed the presence of Si-OSi bands on the calcinated NBG-Titania films. The hardness of the prepared films was investigated using micro hardness test method. The results verified that the presence of NBG particles in titania matrix enhanced gradually the mechanical data of the prepared films (450 VHN). Direct pull-off test recorded a mean coating-substrate bonding strength larger than 16 MPa. The in vitro bioactivity of prepared films indicates that hydroxyapatite nuclei can form and grow on the surface of NBG-Titania films coated on Nitinol alloy. The present study shows that due to their excellent bioactivity, hardness and bonding strength to substrate, NBG-Titania coatings are practical biocomposite films in biomedical applications.

Calcium orthophosphates: crystallization and dissolution.

Calcium orthophosphates: crystallization and dissolution.

Hydroxyapatite micro- and nanoparticles: Nucleation and growth mechanisms in the presence of citrate species

Hydroxyapatite (HAP) particles with different morphologies were precipitated from homogeneous calcium/citrate/phosphate solutions at physiological temperature. Small variations of the starting solution pH in the range 7.4 < pH < 8.5 made it possible to switch the precipitated particle morphology from a micrometric bundlelike to a nanometric needlelike shape. The role of the existing citrate species as calcium chelates is here discussed within the framework of particle nucleation and growth mechanisms. While temperature-dependent calcium citrate complex (Cacit) stability is here suggested to control the free calcium availability and thereby the nucleation rate, the adsorbed citrate species are proposed to control the nanoparticle stability. Moreover, an attempt to detail the role of citrate species in the ordered aggregation of HAP nuclei leading to the observed peanut and bundlelike microparticles morphology is also presented.

Formation of Apatite Pattern by Electrophoretic Deposition of Apatite Nuclei

Resist pattern was developed on a cathode for EPD and a polytetrafluoroethylene (PTFE) film was set on the cathode. Then EPD was performed with a suspension of hydroxyapatite (HA) nuclei in ethanol. In this process, HA nuclei were deposited on a porous PTFE film so as to transcribe the resist pattern. The substrate was soaked in simulated body fluid (SBF) and HA was selectively induced on HA nuclei. As a result, HA pattern whose resolution was as high as the resist pattern was fabficated.

In situ synthesis and characterization of nano-size hydroxyapatite in poly(vinyl alcohol) matrix

Hydroxyapatite (HAp) crystals were prepared via an in situ biomimetic process in the presence of poly(vinyl alcohol) (PVA). The effect of polymer amount and its molecular weight on the physical properties of the HAp crystals were investigated. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) analysis, confirmed the formation of the crystalline HAp at room temperature. Microstructural features such as size and morphology of the resulting HAp samples were characterized using BET, scanning and transmission electron microscopy. The results indicate that the development (size and shape) of the HAp nanocrystals precipitated in an aqueous solution of PVA was influenced by the molecular weight of the polymer in such a way that smallest crystallite size was observed in the case of PVA with the highest molecular weight. It is believed that the HAp formation was initiated through the interaction of Ca 2+ ions with the negative side groups on the polymer surface. The larger number of reaction sites in the PVA polymer with higher molecular weight led to a higher number of HAp nuclei and therefore smaller crystallite size.

Crystallization of Hydroxyapatite on Oxadiazole-Based Homopolymers

Oxadiazole homopolymer was found to be a substrate favoring the deposition of hydroxyapatite (HAP) crystals from stable supersaturated solutions at pH 7.40, 37 °C, and 0.15 M NaCl. The second-order dependence of the precipitation of HAP on oxadiazole polymer on the solution supersaturation suggested a surface diffusion controlled mechanism. The surface energy of the HAP nuclei growing on oxadiazole homopolymer was calculated to be 158 mJ m-2 from the dependence of crystal growth rate on the solution supersaturation. The overgrowth of HAP on the polymer was done selectively possibly through active site formation on −N−N− groups on the macromolecules as confirmed by computational chemistry calculations at 310 K.

Highly Orientated Calcification in Newly Formed Bones on Negatively Charged Hydroxyapatite Electrets

Large negative charges induced by electrical polarization on hydroxyapatite (HA) ceramics has been demonstrated to enhance their osteoconductivities. The newly formed bones in the vicinities of the negatively charged surfaces were investigated in the views of crystallography and histology. The newly formed bone layers accompanied by mono-layered osteoblastic cells showed 4 perfect extinction positions in a 360° rotation, parallel and perpendicular to the HA surfaces by the optically polarizing images. The observation revealed that the newly formed bone layers directly bonding to the N-surface were consisted of the well-crystallized and highly orientated HA. Therefore, it was presumed that the enhanced osteobonding by negative surface charges was ascribed to the activation of myeloid cells and the intensified attraction of the HA nuclei by the electrostatic force.

Synthesis and in vitro bioactivity of dicalcium silicate powders

Abstract In the present investigation, β-dicalcium silicate (β-Ca 2 SiO 4 ) and γ-dicalcium silicate (γ-Ca 2 SiO 4 ) powders were synthesized by sol-gel process and hydrothermal synthesis, respectively. The in vitro bioactivity of both β-, and γ-Ca 2 SiO 4 was investigated by soaking the powders in simulated body fluid (SBF) for various time periods to analyze the nucleation and growth of hydroxyapatite (HAp) on the surface of the powders. After soaked in SBF for 6 h, HAp appeared on the surface of β-, and γ-Ca 2 SiO 4 particles, and uniform lathlike aggregates with typical morphology of HAp crystals formed after 5 days. The β-Ca 2 SiO 4 showed strong hydration when soaked in SBF and the hydration was favorable for formation of carbonate-containing hydroxyapatite on the surface of the materials. The γ-Ca 2 SiO 4 was not hydrated in SBF solution and showed a slower formation of carbonate-containing hydroxyapatite on the surface when compared with β-Ca 2 SiO 4 . In addition, the Si concentration in the SBF increased quickly up to 5 days and remained invariable with increased soaking time. The results obtained indicate that hydroxyapatite nuclei can form and grow on the β-, and γ-Ca 2 SiO 4 particles, and these two dicalcium silicates are potential candidates as biomaterials for hard tissue repair.