Introduction Of Hydroxyapatite Research Articles

Study on ex-situ catalytic pyrolysis of poplar to produce aromatics over a dual-catalyst system of hydroxyapatite and HZSM-5

The ex-situ catalytic pyrolysis of poplar in a dual-catalyst system of hydroxyapatite (HAP) and HZSM-5 was performed using a bench-scale device to enhance the aromatics production. Results indicated that the introduction of HAP could effectively achieve the deoxygenation of macromolecular oxygenates, which were then converted into hydrocarbon precursors. The combination of HAP and HZSM-5 exceedingly promoted the production of aromatics especially monocyclic aromatics (MAHs) than single HZSM-5. The effects of operating conditions on aromatics yield and distribution were investigated. Under the catalyst layout of mode B, with the optimum conditions reaching the catalytic temperature of 500 °C, HAP to HZSM-5 ratio of 2:4, and catalyst to biomass ratio of 1:1, the maximum aromatics yield of 9.10 wt% was achieved, accompanied by the monocyclic aromatics/polycyclic aromatics ratio enhanced to 2.33. At this point, the synergistic effect for MAHs and total aromatics reached 170.09% and 214.14%, respectively. Compared to the conventional metal oxides, the HAP/HZSM-5 dual-catalyst system exhibited superior performance in aromatics production. Besides, the anti-coking capability of HZSM-5 in the dual-catalyst system was also better than that of pure HZSM-5. This research provided a new perspective for the efficient utilization of biomass energy.

Modification of the surface of titanium alloys by the synthesis of coatings by the PEO method in alkaline electrolytes saturated with diatomite

One of the most promising directions of modern materials science is the search for methods of improving the biocompatibility properties of metals used in implantology, which will allow to reduce the percentage of rejection of implants by the living organism. Therefore, it is promising to use processing methods to change the state of the surface of metals due to surface modification, which includes the method of plasma electrolytic oxidation. The main goal of this work was to develop a technological process for obtaining coatings with higher biocompatibility compared to the base metal due to the introduction of natural components into the coating. The presence of elements in biocoatings and their quantity was determined using a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS), which allowed for targeted analysis of the surface of the samples. The elemental composition of coatings synthesised on the basis of titanium alloy in alkaline electrolytes based on KOH, liquid glass of calcium hydroxide, sodium polyphosphate and sodium pyrophosphate with the addition of hydroxyapatite and diatomite was researched in the work. A direct relationship between the composition of the electrolyte and the Ca/P ratio was established. It has been proven that biocoatings synthesised in alkaline solutions by the PEO method satisfy the conditions of biocompatibility. It has been established that in an environment containing alkalis and phosphates, coatings are synthesised for which Ca/P = 1.21. The introduction of hydroxyapatite into the electrolyte leads to an increase in the Ca/P ratio to a value of 1.28, and an increase in the concentration of the electrolyte and the addition of diatomite increases this ratio to a value of 1.57. The obtained results establish the possibility of a wide range of regulation of the Ca/P ratio in the biocoating

Synthesis of a novel TiO2/HA/RGO composite material with photocatalytic activity for dye degradation

Titanium dioxide (TiO2) is widely used as photocatalysts in the field of organic wastewater treatment in recent years.In this study, TiO2 is combined with hydroxyapatite (HA) and reduced graphene oxide (RGO) to prepare a novel ternary composite material. And methylene blue(MB) was used as the target pollutant to evaluate the photocatalytic activity of TiO2/HA/RGO. The results show that the introduction of HA and RGO can effectively enhance the catalytic performance of TiO2. Under 120min of simulated sunlight, the composite showed excellent dye removal effect, the removal rate of MB can reach 99.8%, and its degradation rate is 2 times that of TiO2/HA and 7 times that of TiO2. The improvement of the photocatalytic activity of the ternary composite is mainly due to the synergistic effect between TiO2, HA and RGO. This work provides a new idea for the synthesis of practical photocatalysts.

Poly(methacrylic acid)/gelatin interpenetrating network hydrogels reinforced by nano-structured hydroxyapatite particles—improved drug delivery systems

Novel poly(methacrylic acid)/gelatin (PMAG) interpenetrating networks reinforced by different amounts of nanostructured particles of hydroxyapatite (HA) (HA/polymer weight ratios from 0% to 40%) were synthesized. The introduction of HA significantly enhanced mechanical properties, but slightly reduced swelling ability, pH sensibility and porosity. The increase of HA/polymer ratio to 40% increased the compressive strength from 29.83 (pure PMAG hydrogel) to 68.16 kPa. Drug release behavior investigated in simulated physiological conditions, using ciprofloxacin (hydrophilic) and oxaprozin (hydrophobic), demonstrated different drug release kinetics. In vitro antimicrobial testing demonstrated bactericidal and fungicidal activity of the drug-loaded hydrogels against E. coli, S. aureus and C. albicans.

Highly efficient separation of uranium from wastewater by in situ synthesized hydroxyapatite modified coal fly ash composite aerogel

In this work, hydroxyapatite (HAP) was in situ synthesized on coal fly ash (CFA) to prepare hydroxyapatite modified coal fly ash composite aerogel (HCFAA). The maximum removal efficiency and capability of uranium(VI) on HCFAA were 97.6 % and 205.7 mg g−1, respectively, which was much higher than those of CFA (83.6 % and 59.1 mg g−1) (pH = 3.0, m/V = 1.0 g/L and T = 298 K). The desorption efficiency of uranium(VI) by HCFAA was even more than 80 % after five cycles, demonstrating that the introduction of HAP had improved uranium(VI) removal performances. Pseudo-second-order and Langmuir models were fitted better with the experimental data, indicating the uranium(VI) removal process was a homogeneous monolayer chemisorption. Meanwhile, the uranium(VI) removal efficiency for HCFAA in actual wastewater was higher to 80.6 % and uranium(VI) could even be completely separated from actual wastewater by HCFAA during dynamic adsorption (m = 50 mg, V = 400 mL, C0 = 10 mg/L), further illustrating that the introduction of HAP was an available method to modify CFA. Characterizations results demonstrated that uranium(VI) was successfully immobilized on HCFAA through ion exchange, dissolution-precipitation and surface complexation. In conclusion, HCFAA was a prospective adsorbent for uranium(VI) separation in practical application.

Development of pH-sensitive biomaterial-based nanocomposite for highly controlled drug release

Combining non-toxic biomaterials to obtain high effective hybrids is a promising approach in medicine and drug delivery. This study aims to combine the biomaterial with different swelling behavior to attain high controlled release. Hydroxyapatite (HA) nanoparticles do not possess swelling properties and are stable in different pH solutions. HA was used to prevent the unwanted sudden release in acidic media by modifying the swelling properties of chitosan-based hydrogels (CTS). CTS being soluble in acidic pHs causes drug release as it dissolves, resulting in burst release behavior. The experiments confirmed that the introduction of HA remarkably reduced the swelling ratio, which independent of the pH led to a decrease in the release amount (approximately 38–73%) and prevented the burst release. The metronidazole-loaded CTS/MMt/HA1 with low content HA showed a high sustained pH-responsive release. However, the metronidazole-loaded CTS/MMt/HA2 with high content of HA didn't show sustained release. Indeed, the release rate was sustained by modifying the HA content. The kinetic investigations indicated the release mechanisms were changed from dissolution in CTS/MMt to diffusion in CTS/MMt/HA by introducing HA, which is compatible with the swelling ratio reduction. As well as CTS/MMt, HA grafted samples showed high encapsulation efficiency (>96%) and pH-sensitive properties. The biocompatibility of Metronidazole-loaded nanocomposites was confirmed by the cytotoxicity tests on the human nasopharyngeal carcinoma L929 cells.

Efficient removal of uranium by hydroxyapatite modified kaolin aerogel

Hydroxyapatite@kaolin aerogel (HKLA) was first prepared via a combination of coprecipitation and freeze-drying-calcination method to capture uranium from water. Characterization results demonstrated that the introduction of hydroxyapatite (HAP) could improve the adsorbent stability, change the surface morphology and bring abundant groups, which were in favor of the uranium removal. In comparison with kaolin (KL), the removal rate (93.4%), removal capacity (401.6 mg g−1) (t = 24 h, pH = 5.0, T = 298 K and m/V = 1.0 g L−1) and removal equilibrium time of uranium on HKLA all showed a great improvement. Pseudo-second-order and Langmuir model were more suitable to describe the uranium removal behavior on HKLA, illustrating that the uranium ions were immobilized on HKLA via chemical adsorption. Meanwhile, high temperature was conducive to the uranium removal on HKLA, indicating that the removal process was a spontaneous endothermic reaction. Furthermore, HKLA showed excellent anti-ion interference ability, recyclability, cyclic stability and dynamic adsorption performances. On the basis of the analysis of SEM, BET, XRD, FTIR and XPS, uranium was loaded on HKLA through complex reaction, chemical adsorption, electrostatic adsorption and ion exchange. Therefore, HKLA was a promising candidate for the removal of uranium from wastewater.

MEANS AND METHODS OF STIMULATION OF SALIVATION (LITERATURE REVIEW)

Currently, a large number of tools and methods are proposed to reduce dryness in the mouth and restore the deficiency of biologically active substances entering the mouth with saliva. Stimulation of salivation can be carried out by both local and systemic means.
 The aim of our study was to analyze pharmacological and systemic stimulators of salivation.
 Results and discussion
 Only three drugs were subjected to a detailed study - bromhexidine, anethole trithione and pilocarpine hydrochloride.
 Currently, the development of long-acting (prolonged) drugs is underway, which is a promising solution for long-term treatment of patients with dry mouth.
 Local stimulation of salivation is based on irritation of the nerve endings of the oral cavity, which transmit a signal to the salivary glands. Various methods are offered, it is chewing of gums, menthol-containing substances, inert means like paraffin. Chewing gum, mint or citric acid tablets (lollipops) and rinses are recommended in everyday life. Frequent use of these tools is not always effective due to various negative factors. The most important of them is short-term effect, but not the possibility of frequent use. In some patients, drugs such as citric acid can irritate the mucous membranes, especially if its content is increased due to dry mouth. Frequent use of these tools can cause demineralization of teeth.
 Many authors recommend so-called "saliva substitutes" or "saliva compensators". Various options of replacement therapy in the form of gels, rinses, sprays, toothpastes, etc. are offered.
 To prevent caries during hyposalivation, the authors propose a composition of artificial saliva with a high content of fluoride ions, with the introduction of hydroxyapatite from animal bones.
 Researchers offer various methods of stimulation the functional activity of the salivary glands, but the main factor in choosing the appropriate treatment is a favorable assessment of the degree of violation of the patient's salivary glands and the mechanism of violation.
 Conclusion. Owing to the review of the literature, we can conclude that the timely diagnosis and treatment of xerostomia is an urgent problem of modern dentistry. Patients need xerostomia correction, because the deficiency of oral fluid significantly affects the condition of teeth, mucous membranes of the mouth and periodontal tissues and the quality of life in general.
 Due to the fact that the treatment of xerostomia in some cases is ineffective and impossible, such patients need symptomatic therapy to alleviate the manifestations and consequences of xerostomia. The dental market offers a large number of tools for symptomatic correction of xerostomia. Many literature sources contain conflicting data on their effectiveness.
 Therefore, we consider it appropriate to study the comparative evaluation of tools that facilitate the manifestations of xerostomia, as well as to assess the effectiveness of correction of xerostomia depending on the causes of its development.

Construction of physical-crosslink chitosan/PVA double-network hydrogel with surface mineralization for bone repair

Weak mechanical properties, lack biocompatibility and relatively bioinert are formidable obstruct in application of bone repair materials. Multifunctional composite materials have been considered as a viable solution to this problem. Here, a new double network (DN) hydrogel was constructed by physical cross-linking of medical grade poly (vinyl alcohol) (PVA) and chitosan in KOH/urea dissolution system. The obtained hydrogel demonstrated excellent tensile strength (0.24 MPa), elongation at break (286%), and high compressive strength (0.11 MPa on the strain of 60%). Our studies showed that the prepared hydrogel had excellent biocompatibility in vitro and the introduction of hydroxyapatite (HAp) by surface mineralization imparted hydrogel the ability to induce rat bone marrow stem cells (rBMSCs) differentiation. The in vivo experiments revealed that the surface mineralized double network hydrogel significantly accelerated simultaneous regeneration of bone defects in a rabbit bone defect model. All the results indicated that this hydrogel has the potential as a bone repair material.

THEORETICAL STUDY OF MODIFIED ELASTIC AND HIGH-ELASTIC PARAMETERS OF HIGH DENSITY POLYETHYLENE BASED ON EXPERIMENTAL RELAXATION CURVES

The article provides an alternative method of determining the physical and mechanical parameters of the polymer by the preselected law of stress-strain connection. The non-linear generalized Maxwell-Gurevich equation is chosen as the specified law. It contains one elastic parameter - the modulus of elasticity, and three highly elastic: the modulus of elasticity, the modulus of velocity and the coefficient of initial relaxation viscosity. Existing techniques determine the specified parameters of the polymer as a function of one variable, usually temperature. In the article, using the example of relaxation curves of high-density polyethylene (HDPE), an algorithm is given for determining the characteristics of a material with the subsequent construction of the law of their change as a function of two variables: the level of ionizing radiation and the proportion of hydroxyapatite additive. Analysis of the results showed that the irradiation of the sample and the introduction of the additive have a different effect on the elastic and highly elastic parameters of the polymer. With simultaneous irradiation of the material and the introduction of additives, the polymer velocity modulus increases much more than the effects of each factor separately. In turn, the combined effect of radiation and additives leads to a certain decrease in the value of the coefficient of initial relaxation viscosity in comparison with the level achieved in the presence of either ionizing radiation or the introduction of hydroxyapatite. At the end, a model experiment is presented for constructing polymer relaxation curves using the physic and mechanical parameters obtained. The good agreement between the theoretical and experimental curves allows to speak about the reliability of the method used.

Electrospinning of hydroxyapatite–chitosan nanofibers for tissue engineering applications

ABSTRACTAn organic/inorganic composite scaffold was synthesized by the introduction of hydroxyapatite (HA) nanopowder within electrospun chitosan fibers. The effects of HA dispersion on the cross‐linking process have been investigated. The obtained chitosan–HA electrospun samples were characterized in terms of morphology, chemical structure, mechanical properties, and bioactivity. Positive results were obtained in terms of homogeneous nanofibrous sample morphology, preservation of HA structure in the electrospun membranes, and improvement of sample bioactivity. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.

Effects of Hydroxyapatite-Containing Composite Nanofibers on Osteogenesis of Mesenchymal Stem Cells In vitro and Bone Regeneration In vivo

Among a variety of polymers, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a microbial polyester, with biodegradable, nonantigenic, and biocompatible properties, is attracting more and more attention in tissue engineering. Hydroxyapatite (HA), similar to the mineral component of natural bone, is known to be osteoconductive, nontoxic, and noninflammatory. In this study, aligned and random-oriented PHBV nanofibrous scaffolds loaded with HA nanoparticles were fabricated through electrospinning technique. Mesenchymal stem cells (MSCs) derived from rat bone marrow were used to investigate the effects of HA and orientation of fibers on cell proliferation and differentiation in vitro. Cell proliferation tested with CCK-8 assay indicated that the MSCs attached and proliferated more favorably on random-oriented PHBV nanofibrous meshes without HA. After one, two and four weeks of cell seeding, osteogenic markers including alkaline phosphate (ALP), osteocalcin (OCN), and mineralized matrix deposits were detected, respectively. The results indicated that the introduction of HA could induce MSCs to differentiate into osteoblasts. Moreover, 3D PHBV/HA scaffolds made from aligned and random-oriented nanofibers were implanted into critical-sized rabbit radius defects and exhibited significant effects on the repair of critical bone defects, implying their promising applications in bone tissue engineering.

Injectable hydroxyapatite cement patch as an on-lay graft for the sellar reconstructions following endoscopic endonasal approach

Skull base reconstruction after endoscopic endonasal resection of a variety of skull base lesions remains challenging because of some lethal complications such as cerebrospinal fluid (CSF) leaks. We investigated the outcomes of hydroxyapatite (HA) cement patch as on-lay graft for skull base defects following endoscopic endonasal approach (EEA). We analyzed 53 consecutive patients who underwent sellar reconstruction using HA cement following EEA at our institution between July 2009 and March 2011. Patients were composed of 23 men and 30 women with a mean age of 47 years, ranging from 10 to 72 years. Among these patients, 29 patients (54.7%) experienced intraoperative CSF leaks with high-output, 10 patients (18.9%) underwent CSF leaks with low output, and 14 patients (26.4%) experienced no intraoperative CSF leak. Mean follow-up period for clinical outcomes was 8.6 months (range, 3-22 months). We performed injectable HA patch as on-lay graft over fascia lata for the skull base defects. Routine lumbar CSF drainage was not performed postoperatively in any patients since the introduction of HA. During the follow-up period, three of 53 patients (5.6%) demonstrated meningitis associated with postoperative CSF leaks and underwent re-do reconstruction surgery. There was no allergic symptoms associated with HA cement. At an outpatient clinic, the defects were found to be covered with surrounding nasal mucosa at an average of 14 weeks (range, 3-28 weeks). The use of HA cement as an on-lay patch for the reconstruction of sellar defect demonstrated a low incidence of CSF leaks with minimal complications. HA cement may be an alternative option for repair of CSF leaks following EEA.

Fabrication of Porous Scaffolds with a Controllable Microstructure and Mechanical Properties by Porogen Fusion Technique

Macroporous scaffolds with controllable pore structure and mechanical properties were fabricated by a porogen fusion technique. Biodegradable material poly (d, l-lactide) (PDLLA) was used as the scaffold matrix. The effects of porogen size, PDLLA concentration and hydroxyapatite (HA) content on the scaffold morphology, porosity and mechanical properties were investigated. High porosity (90% and above) and highly interconnected structures were easily obtained and the pore size could be adjusted by varying the porogen size. With the increasing porogen size and PDLLA concentration, the porosity of scaffolds decreases, while its mechanical properties increase. The introduction of HA greatly increases the impact on pore structure, mechanical properties and water absorption ability of scaffolds, while it has comparatively little influence on its porosity under low HA contents. These results show that by adjusting processing parameters, scaffolds could afford a controllable pore size, exhibit suitable pore structure and high porosity, as well as good mechanical properties, and may serve as an excellent substrate for bone tissue engineering.

Synthesis and Swelling Behaviors of Poly (sodium acrylate)/Hydroxyapatite Superabsorbent Nanocomposites

Superabsorbent nanocomposites based on partially neutralized acrylic acid (AA) and hydroxyapatite (HP) were prepared by free radical solution polymerization using N, N′-methylenebisacrylamide (MBA) as the crosslinker and ammonium persulfate (APS) as the initiator. The developed nanocomposites were characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of HP content on water absorbency of the nanocomposites were investigated, and the swelling behaviors of the nanocomposites in various pH solutions and their reswelling capability in distilled water were also systematically evaluated. FTIR spectra revealed that the P–OH groups of HP participated in graft polymerization reaction with AA. TEM analysis showed the needle-like crystals of HP present in the PAA/HP nanocomposite with a diameter of about 40 nm and a length of about 270 nm. The swelling rate and reswelling capability of the superabsorbents were improved due to the introduction of HP into PAA polymeric network, and this result implied that the nanocomposites acted as a recyclable water-saving material.

The fabrication and characterization of biodegradable HA/PHBV nanoparticle–polymer composite scaffolds

This study reports the fabrication and characterization of nano-sized hydroxyapatite (HA)/poly(hydroxyabutyrate-co-hydroxyvalerate) (PHBV) polymer composite scaffolds with high porosity and controlled pore architectures. These scaffolds were prepared using a modified thermally induced phase-separation technique. This investigation focuses on the effect of fabrication conditions on the overall pore architecture of the scaffolds and the dispersion of HA nanocrystals within the composite scaffolds. The morphologies, mechanical properties and in vitro bioactivity of the composite scaffolds were investigated. It was noted that the pore architectures could be manipulated by varying phase-separation parameters. The HA particles were dispersed in the pore walls of the scaffolds and were well bonded to the polymer. The introduction of HA greatly increased the stiffness and strength, and improved the in vitro bioactivity of the scaffolds. The results suggest these newly developed nano-HA/PHBV composite scaffolds may serve as an effective three-dimensional substrate in bone tissue engineering.

Investigation of a Collagen-Chitosan-Hydroxyapatite System for Novel Bone Substitutes

Collagen (Col) and chitosan (Chi) are both natural polymers and have received extensive investigation in recent years in the field of tissue engineering, but there are few reports on the introduction of hydroxyapatite (HA) into the Col-Ch system. In this study, based on the miscibility of these two polymers under proper condition, hydroxyapatite (HA) was synthesis in the Col-Chi system by in-situ co-precipitate method to give rise to a novel nanocomposite. The structural characterization of such Col-Ch-HA nano-materials was carried out by using FT-IR, XRD, SEM and TGA analyses with main components and Col-Chi samples used for comparison. It was found that there exist interactions between Col and Chi molecules. The nucleation and growth of inorganic phase occurs in the Col-Chi system and final products are uniform dispersion of nano-sized HA in the Col-Chi network without obvious phase separation. This novel nanocomposite would be a promising material for bone tissue engineering.

The influence of hydroxyapatite modification on the cross-linking of polydimethylsiloxane/HAp composites

Hydroxyapatite (HAp) was modified by the action of various hydrophobic agents based on silicon-containing compounds. The influence of the type of applied agent on the thermodynamic and kinetic parameters of the cross-linking of poly(dimethyl siloxane)/HAp composites was investigated. All the modified HAp particles became hydrophobic and these samples were used to synthesize the polysiloxane/hydroxyapatite composites (PDMS/HAp). The possible modes of interaction between the hydroxyapatite and hydrophobing agents were discussed. The most probable interaction between hydroxyapatite and the applied hydrophobing agents is hydrogen bonding. PDMS/HAp composites were formed directly in the cell of the DSC and cross-linking was investigated in situ. It was determined that the introduction of hydroxyapatite into polysiloxane matrices changed the enthalpy of cross-linking, as well as the activation energy of cross-linking and reaction order, while the introduction of modified HAp led to thermodynamic and kinetic parameters more similar to those of the cross-linking of unfilled elastomer.

The exothermal behavior in the hydration process of calcium phosphate cement

The exothermal behavior in the hydration process of calcium phosphate cement (CPC) and their effect factors were investigated systematically. One CPC formulation is composed of tetracalcium phosphate (TECP) and dicalcium phosphate anhydrous (DCPA), and its hydration reaction is an exothermic reaction. Hydration includes five processes, namely, the start, induction, acceleration, deceleration and the terminating process. The introduction of hydroxyapatite (HAP) as crystal seed shortens induction and advances on the reaction peak position, which resulted from the introduction of crystal seed that reduced the activation energy of heterogeneous nucleation. The increase in temperature not only makes the reaction advance but also enlarges it. The activation energy of the hydration reaction is 176 kJ/mol by calculation. The particle size of the raw material and the ratio of calcium to phosphate in the specimen have large effects on the hydration process. Decrease in particle size of TECP and in the ratio of calcium to phosphate resulted in marked acceleration of reaction and made the reaction peak advance evidently, but the effect of particle size of DCPA is not so remarkable. Based on the heat liberation in the hydration of CPC specimens taking Ca/P as 1.5 and 1.67, the standard mole enthalpies of formation of TECP and calcium-deficient hydroxyapatite are −5908 and −11119 kJ mol −1, respectively.