Mechanical, pH and Thermal Stability of Mesoporous Hydroxyapatite

5-Fluorouracil adsorption on graphene oxide-amine modified graphene oxide/hydroxyapatite composite for drug delivery applications: Optimization and release kinetics studies

The present study focused on investigation of graphene oxide/hydroxyapatite (GO/HAp) and amine modified graphene oxide/hydroxyapatite (GO-NH2/HAp) composites as potential drug carrier agents for 5-Fluorouracil (5-FU). Incorporation of 5-Fluorouracil drug was performed via adsorption through π-π interactions and electrostatic attractions. Modification of graphene oxide was performed for the production of amine modified graphene oxide/hydroxyapatite composite with the intention of enhancing adsorption performance. The X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and zeta potential/particle size analysis were performed for particle characterization while Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis were used to analyze detailed morphological properties. Experimental design studies were followed out in order to determine the effect of adsorption parameters including graphene oxide amount, pH and initial drug concentration on 5-Fluorouracil adsorption behavior. Adsorption isotherms of both composites with unmodified and modified GO were best fitted to Freundlich model with R2 values of 0.9616 and 0.9682 respectively. The maximum adsorption capacities (qm) were calculated as 47.3 mg/g and 18.4 for graphene oxide/hydroxyapatite and amine modified graphene oxide/hydroxyapatite composites respectively at pH 2.0. The highest adsorption percentage was obtained for amine modified graphene oxide/hydroxyapatite composite as 40.87 % at pH 2.0 condition. In vitro release kinetic studies revealed that compliance with Higuchi and Korsmeyer-Peppas kinetic models were observed for graphene oxide/hydroxyapatite, whereas zero order and Korsmeyer-Peppas kinetic models pointed out as the well-fitted model for amine modified graphene oxide/hydroxyapatite composite. The release period of 5-FU drug from all composites were continued up to 8-10 h in physiological conditions (pH 7.4, 37 °C) indicating an achieved controlled release. Based on the overall findings, graphene oxide/hydroxyapatite and amine modified graphene oxide/hydroxyapatite composites could be suggested as a potential drug delivery agent for 5-FU in clinical applications.

Correlation between positron annihilation lifetime and photoluminescence measurements for calcined Hydroxyapatite

Hydroxyapatite (HAp) Ca10(PO4)6(OH)2 is a compound that has stable chemical properties, composition, and an affinity for human bone. As a result, it can be used in odontology, cancer treatment, and orthopedic grafts to repair damaged bone. To produce calcined HAp at 600 °C with different pH values, a wet chemical precipitation method was employed. All synthesized HAp samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), photoluminescence (PL), Zeta potential, and positron annihilation lifetime spectroscopy (PALS). The XRD results revealed that all calcined HAp samples were formed in a hexagonal structure with a preferred (002) orientation at different pH values. The crystal size of the samples was determined using the Scherrer equation, which ranged from 16 to 25 nm. The SEM and TEM results showed that the morphology of the samples varied from nanorods to nanospheres and rice-like structures depending on the pH value of the sample. The PL measurements indicated that the blue and green emission peaks of HAp were due to defects (bulk, surface, and interface) in the samples, which created additional energy levels within the band gap. According to Zeta potential measurements, the charge carrier changed from a positive to negative value, ranging from 3.94 mV to - 2.95 mV. PALS was used to understand the relationship between the defects and the photoluminescence (PL) properties of HAp. Our results suggest that HAp nanoparticles have excellent potential for developing non-toxic biomedical and optical devices for phototherapy.

Enhanced Release of Calcium Ions from Hydroxyapatite Nanoparticles with an Increase in Their Specific Surface Area

Synthetic calcium phosphates, e.g., hydroxyapatite (HAP) and tricalcium phosphate (TCP), are the most commonly used bone-graft materials due to their high chemical similarity to the natural hydroxyapatite-the inorganic component of bones. Calcium in the form of a free ion or bound complexes plays a key role in many biological functions, including bone regeneration. This paper explores the possibility of increasing the Ca2+-ion release from HAP nanoparticles (NPs) by reducing their size. Hydroxyapatite nanoparticles were obtained through microwave hydrothermal synthesis. Particles with a specific surface area ranging from 51 m2/g to 240 m2/g and with sizes of 39, 29, 19, 11, 10, and 9 nm were used in the experiment. The structure of the nanomaterial was also studied by means of helium pycnometry, X-ray diffraction (XRD), and transmission-electron microscopy (TEM). The calcium-ion release into phosphate-buffered saline (PBS) was studied. The highest release of Ca2+ ions, i.e., 18 mg/L, was observed in HAP with a specific surface area 240 m2/g and an average nanoparticle size of 9 nm. A significant increase in Ca2+-ion release was also observed with specific surface areas of 183 m2/g and above, and with nanoparticle sizes of 11 nm and below. No substantial size dependence was observed for the larger particle sizes.

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

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

Biocompatibility performance evaluation of high flux hydrophilic CO3Ap/HAP/PSF composite membranes for hemodialysis application

Carbonate apatite/hydroxyapatite (CO3Ap/HAP) additive was obtained by calcination of wasted chicken bones at 900°C. Intermolecular attraction exists between CO3Ap/HAP additive and blended polysulfone (PSF) polymer. Electron dispersive X-ray (EDX) and FTIR analysis were carried out to check the elemental composition and bonding chemistry of prepared additive. The instantaneous demixing process generated consistent finger-like networks in CO3Ap/HAP/PSF-based composite membranes while sponge-like structure was shown by PSF as revealed by SEM images. The increase in weight % of additive loading is also confirmed by EDX analysis. Furthermore, the interaction mechanism of CO3Ap/HAP additive with polysulfone medium was analyzed by FTIR exploration. The water absorption experiment defined a 93% expansion in hydrophilic performance. Change in porosity occurs with additive loading and pure water permeation flux improved up to 11 times. Approximately, antifouling results revealed that 87% of water flux was recovered after treating with a protein solution, whereas a 30% improvement in antifouling capability in case of bovine serum albumin solution occurred. In vitro cytotoxicity, and clotting times study was carried out to evaluate virulent behavior and anticoagulation activity of formulated membranes.

Mesoporous Iron(III)-Doped Hydroxyapatite Nanopowders Obtained via Iron Oxalate

Mesoporous hydroxyapatite (HA) and iron(III)-doped HA (Fe-HA) are attractive materials for biomedical, catalytic, and environmental applications. In the present study, the nanopowders of HA and Fe-HA with a specific surface area up to 194.5 m²/g were synthesized by a simple precipitation route using iron oxalate as a source of Fe³⁺ cations. The influence of Fe³⁺ amount on the phase composition, powders morphology, Brunauer–Emmett–Teller (BET) specific surface area (S), and pore size distribution were investigated, as well as electron paramagnetic resonance and Mössbauer spectroscopy analysis were performed. According to obtained data, the Fe³⁺ ions were incorporated in the HA lattice, and also amorphous Fe oxides were formed contributed to the gradual increase in the S and pore volume of the powders. The Density Functional Theory calculations supported these findings and revealed Fe³⁺ inclusion in the crystalline region with the hybridization among Fe-3d and O-2p orbitals and a partly covalent bond formation, whilst the inclusion of Fe oxides assumed crystallinity damage and rather occurred in amorphous regions of HA nanomaterial. In vitro tests based on the MG-63 cell line demonstrated that the introduction of Fe³⁺ does not cause cytotoxicity and led to the enhanced cytocompatibility of HA.

Novel Hydroxyapatite Beads for the Adsorption of Radionuclides from Decommissioned Nuclear Power Plant Sites

Although a powdered form of hydroxyapatite (p-HdA) has been studied for the adsorption of heavy metals that contaminate the restoration sites of decommissioned nuclear power plants, most of the studies are limited in the laboratory due to the head loss and post-separation in practical applications. Herein, we fabricated a porous bead form of HdA (b-HdA) as a novel adsorbent for removing radionuclides from aqueous environments via a facile synthesis by mixing the p-HdA precursor and polyvinyl butyral (PVB) as a binder and added a sintering process for the final production of a porous structure. The spherical b-HdA with an approximate diameter of 2.0 mm was successfully fabricated. The effectiveness of the b-HdA at removing Co(II) was investigated via the adsorption equilibrium at various experimental temperatures. The b-HdA exhibited the adsorption capacity for Co(II) ions with a maximum of 7.73 and 11.35 mg/g at 293 K and 313 K, respectively. The experimental kinetic data were well described using a pseudo-second-order kinetic model, and the adsorption mechanisms of Co(II) onto the b-HdA were revealed to be a chemisorption process with intraparticle diffusion being the rate-limiting step. In addition, the competitive adsorption onto the b-HdA with the order of U(VI) > Co(II) > Ni(II) > Sr(II) > Cs(I) was also observed in the multi-radionuclides system. Considering the advantages of the size, applicability to the continuous-flow column, and the easy separation from treated water, the b-HdA can be an excellent absorbent with high potential for practical applications for removing radionuclides.

An ecofriendly nanocomposite of bacterial cellulose and hydroxyapatite efficiently removes lead from water

An environmentally friendly nanocomposite adsorbent composed of two renewable biomaterials, bacterial cellulose (BC) nanofibrils and hydroxyapatite (HA) nanocrystals, was synthetized by an in situ wet chemical precipitation technique, using clam shell biowaste as feedstock. HA nanocrystals embedded in an ultrafine BC network were confirmed and characterized trough different instrumental techniques (SEM, FTIR, XRD, EDS, surface charge and BET analysis), describing its nanostructure, chemical composition and thermal stability. The adsorptive removal of lead ions by the nanocomposite was investigated through batch experiments conducted under different pH, contact times and Pb(II) initial concentrations, proving that the process was highly favorable according to the Langmuir isotherm model (monolayer adsorption) with chemisorption as the main mechanism and kinetic data obeying a nonlinear pseudo-second order kinetic model. The developed nanocomposite showed a strong removal capacity of Pb(II) both in batch experiments (192 mg/g) and packed-bed column systems (188 mg/g), placing this new nanocomposite among top-performing BC-based biomaterials for lead removal.

Comparison between three in vitro methods to measure magnesium degradation and their suitability for predicting in vivo degradation

A lot of research has been done in the field of magnesium-based implant material. This study is focused on finding an explanation for the large disparity in results from similar experiments in literature. The hypothesis is that many different measurement protocols are used to quantify magnesium degradation and this leads to inconsistent results. Cylindrical, pure magnesium samples were used for this study. The degradation took place in revised simulated body fluid at 37°C. Hydrogen evolution was measured to quantify the degradation. Two commonly used experimental protocols were examined: static conditions and a fluid changing method. For static testing, the samples stayed in fluid. For the fluid changing method, the fluid was changed after 2 and 5 days of immersion. In addition, a new method with continuous fluid flow was established. After an initial phase, the results confirm that for all three methods, the degradation behavior differs strongly. The static condition results in a very slow degradation rate. The fluid change method leads to a similar behavior like the static condition except that the degradation was speeded up after the fluid changes. The continuous degradation is linear for a long period after the initial phase. In comparison with in vivo degradation behavior, the degradation process in continuous flow shows the best fitting. The accumulation of degradation products, especially the increasing pH value, has a strong inhibiting effect. This cannot be observed in vivo so that a constant experimental environment realizable by continuous flow is more suitable for magnesium-based implant material testing.