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 effect of surface-modified nano-hydroxyapatite on biocompatibility of poly(ε-caprolactone)/hydroxyapatite nanocomposites

We describe the effect of surface-modified hydroxyapatite (HAp) nano-crystals on biocompatibility of a new-type nanocomposite consisting of poly(ε-caprolactone) (PCL) and HAp. Surface-modified hydroxyapatite (HAp) nano-crystals were prepared by chemically grafting PCL on HAp surfaces. Time-dependent phase monitoring indicated that PCL surface-grafting contributed to the enhanced dispersion of HAp at nano-level in the PCL solution. The protein adhesion and cell experiments showed that the presence of PCL-grafted HAp nano-crystals in nanocomposites contributed to the enhanced biocompatibility. PCL-grafted HAp in nanocomposites provided more favorable environments for protein adsorption, compared with unmodified HAp. Nanocomposites containing PCL-grafted nanophase HAp showed positive effects on adhesion and proliferation of NIH3T3 fibroblasts.     

Biocomposites of nanohydroxyapatite with collagen and poly(vinyl alcohol)

Biocomposites of hydroxyapatite, HAp, in conjunction with various binders including poly(vinyl alcohol), PVA, and collagen have the potential of serving in various tissue engineering applications, such as in bone repair and reconstruction tasks, especially if the nanoparticles of hydroxyapatite are used. Here, hydroxyapatite nanoparticles (n-HAp) were synthesized at the ultimate size range of 10-50 nm and then incorporated into PVA or in situ synthesized in collagen/PVA. The biocomposites of HAp with PVA exhibited relatively high elasticity (as revealed by the linear viscoelastic material functions, characterized upon small-amplitude oscillatory shear) especially upon cryogenic treatment. The incorporation of the collagen into the PVA/HAp biocomposite provided internal porosity to the biocomposite with the pores in the 50-100 nm range for collagen/HAp and 50-500 nm for the collagen/HAp/PVA.     

Aqueous microgels for the growth of hydroxyapatite nanocrystals

In present article, we demonstrate that aqueous microgels can be used as containers for the in-situ synthesis of hydroxyapatite. The hydroxyapatite nanocrystals (HAp NCs) become integrated into microgels forming hybrid colloids. The HAp NCs loaded in the microgel can be varied over a broad range. The HAp NCs are localized within the microgel corona. The deposition of the inorganic nanocrystals decreases the colloidal stability of the microgels and leads to particle aggregation at high HAp NCs loading. Because of the strong interactions between HAp NCs and polymer chains, the swelling degree of microgels decreases, and temperature-sensitive properties disappear at high loading of the inorganic component. We demonstrate that hybrid colloids can be used as building blocks for the preparation of nanostructured films on solid substrates.     

Hydroxyapatite For Poly(α-Hydroxy Esters) Biocomposites Applications

This article focuses on providing a systematic review on various fundamental properties of composite based on poly(α-hydroxy esters) and hydroxyapatite (HAp) for application in bone tissue engineering. Poly(α-hydroxy esters), a well-known synthetic biopolymer has attracted considerable interest to be employed for synthesis of bone graft substitute material with HAp mainly due to its bioresorbability, variable biodegradation rate and melt-processibility. Such features are simultaneously attractive for both biomedical application and industrial-scale productions. Besides the main function of hydroxyapatite as bioactive ceramic filler in composite to induce new bone formation upon polymer bioresorption, HAp can also serve as reinforcement for matrix polymer by providing sufficient mechanical support for cell attachment. Moreover, HAp plays a significant role in determining other composite properties, such as resistance to ingress of body fluid, body temperature ageing, relaxation movement of polymer segment, and in vivo biodegradation. These properties constitute as the fundamental requirements in field of bone tissue regeneration which is desirable to be achieved by unique composite system based on poly(α-hydroxyesters) and HAp particles.     

Preparation of waterborne polyurethane nanocomposites: Polymerization from functionalized hydroxyapatite

We report the preparation and characterization of waterborne polyurethane (WBPU)/hydroxyapatite (HAp) nanocomposites through in situ polymerization from functionalized HAp. The HAp nanoparticles (HAp NPs) were urethanated with 3-isocyanatemethyl-3,5,5-trimethyl-cyclohexylisocyanate (isophorone diisocyanate) to obtain grafted HAp NPs containing isocyanate groups (HAp-g-NCO) as crosslinkers and then the HAp-g-NCO is further polymerized with WBPU monomers to form the WBPU/HAp nanocomposites. The HAp NPs were homogeneously dispersed in the polyurethane matrix at low loading levels (?2.0 wt%), thus the mechanical strength and the elongation at break of the WBPU/HAp nanocomposites were significantly improved. Thermal stability and water resistance of the WBPU/HAp nanocomposites are also enhanced. These results suggest that the WBPU/HAp nanocomposites prepared by in situ polymerization hold the potential as new materials with improved mechanical properties, thermal stability and water resistance.     

Fabrication of platy apatite nanocrystals loaded with TiO2 nanoparticles by two-step emulsion method and their photocatalytic activity

Nanometer-sized TiO(2) island structure on the platy hydroxyapatite nanocrystals (HAp) has been accomplished by two-step emulsion process. At the first step, platy HAp nanocrystals, of which size was in the range of 70-200 nm after heat-treatment at 1078 K for 1 h, were prepared using the W/O emulsion system. Before the second step, HAp nanocrystals were immersed in NaH(2)PO(4) solution for the formation of hydroxyl group on their surface. In the following, titanium tetraisopropoxide reacted with the hydroxyl group of HAp surface to form TiO(2) nanoparticles on the surface of HAp nanocrystals, which were dispersed in the micrometer-sized methanol droplets of polyethylene cetylether-cyclohexane mixture (methanol/oil emulsion). The resulting hydroxyapatite nanocrystals loaded with TiO(2) nanoparticles showed the high photocatalytic activity comparing to the commercial TiO(2) catalyst.     

羟基磷灰石负载放射性18F作为分子影像纳米探针在生物医学中的应用

采用简便有效的方法,制备了生物兼容性强、放射性标记羟基磷灰石(HAp)纳米粒子的正电子发射计算机断层显像(PET)纳米探针。在合成HAp纳米粒子的过程中,放射性的~(18)F作为掺杂剂,占据HAp晶格中羟基位置,在短时间内牢固地标记到HAp上。~(18)F不仅标记在纳米粒子的表面,而且还通过强的化学键标记在纳米颗粒的内部。以达到提高标记量并防止辐射泄漏的目的。设计的高标记量的放射性纳米探针应用于动物实验并靶向到达脏器器官。     

In situ mineralization of hydroxyapatite on poly(vinyl alcohol) monolithic scaffolds for tissue engineering

A poly(vinyl alcohol) (PVA)/hydroxyapatite (HAp) composite monolithic scaffold is prepared via thermally impacted non-solvent induced phase separation method, successively followed by an alternate soaking process. The morphology of the resulting composite monolith is observed by scanning electron microscopy (SEM). The formation of hydroxyapatite is confirmed by X-ray diffraction, SEM in combination with energy dispersive X-ray analysis, and Fourier transform infrared spectroscopy. The effects of soaking cycle and soaking time upon the formation of hydroxyapatite on the monolith surface are systematically investigated. With the increase of soaking cycle and soaking time, the amount of the formed hydroxyapatite increases. As the soaking cycle increases, the water uptake of the composite monolith decreases. The PVA/HAp composite monolith greatly has a promising application as scaffold of bone tissue engineering.     

羟基磷灰石/胶原矿化机理的研究进展

仿生合成的羟基磷灰石(HAp)/胶原复合材料的结构和成分与天然骨相似,具有很好的生物相容性、生物活性和生物可降解性,有望成为新一代的骨替代材料。羟基磷灰石/胶原矿化过程其实质是晶体在自组装的胶原纤维上形成的过程,但这一过程在体内是如何进行的至今仍然不清楚。对胶原矿化机理的研究能为制备具有更优越结构和功能的新型骨替代材料提供理论参考。本文概述了羟基磷灰石/胶原矿化机理的研究进展。     

Micro-PIXE analysis of bioconductive hydroxyapatite coatings on titanium alloy

Bioconductive materials and in particular implants using Ti alloy (Ti6–Al4–V) coated with hydroxyapatite (HAp) have proved to be a suitable surgical procedure. However, experience has shown that these implants not always have the required reliability to guarantee their expected life-span of approximate 15 years. In this research, experimental Ti alloy-implants coated with HAp and incubated in a simulated body fluid (r-SBF) under controlled physiological conditions were studied by nuclear microprobe (NMP). Selected HAp coatings, were analysed by micro-PIXE using protons of 1.5 MeV at the iThemba LABS NMP facility. Major elements (Ti, Al, V, Ca and P) as well as trace elements (Si, K, Fe, Zn and Sr) were determined. The effect of longer incubation time was of particular interest. Results confirmed that secondary Ca-deficient defect hydroxyapatite precipitated from the simulated body solution onto the HAp coating surface after prolonged incubation. This newly formed layer is thought to be of vital importance for bonding of implants with living bone tissue.     

Anti-Microbial Hydroxyapatite Particles Synthesized by a Sol–Gel Route

Sol–gel route was applied to synthesize anti-microbial hydroxyapatite (HAp) powders by the addition of silver 200–20000 ppm or zinc salts. The bacteria strain, Streptococcus mutans (S. mutans, ATCC 25175) was used in the anti-bacterial tests. HAp phase was reproducibly obtained by the preparation conditions: Ca(NO₃)₂-4H₂O and trietheyl phosphate as sources of calcium and phosphorus sources, respectively, and ethanol as the solvent, aging for 16 h at 80°C, gelation and drying at 80°C for 24 h, then calcining at above 350°C. TGA was used to analyze thermal properties of the as-prepared gel. XRD and FTIR were used to identify the crystalline phase and chemical structure. CaO appeared as an impurity after calcining above 650°C. In the solid-state anti-microbial tests on the brain heart infusion (BHI) agar plates, there formed a microbial inhibition zone surrounding the Ag/Zn added (greater than 2000 ppm) samples. In the liquid-state anti-microbial tests, S. mutans cells readily precipitated with pure HAp powders but not with Ag/Zn added (greater than 2000 ppm) HAp powders. The concentration of silver or zinc ions releasing from the Ag/Zn added HAp powders into the supernatant of the BHI broth was under detection limit of ICP-AES analyses. However, the growth of S. mutans reached same magnitude (6 × 10⁸ CFU/mL) whether pure HAp, 2000 ppm-Ag or 2000 ppm-Zn were added. Therefore, Ag/Zn added HAp powders developed in this research present microbial inhibition properties and are of potential as a solid-state anti-microbial agent.     

Synthesis of porous hollow silica nanostructures using hydroxyapatite nanoparticle templates

Porous hollow spherical and rod-like silica nanoparticles were obtained via a surfactant templating method adopting hydroxyapatite (HAp) nanoparticles as an etchable core material.     

Solvothermal synthesis and characterization of Ln (Eu3+, Tb3+) doped hydroxyapatite

Luminescent Ln (Eu3+, Tb3+) doped hydroxyapatite (Eu:HAp, Tb:HAp) phosphors were successfully fabricated via the cetyltrimethylammonium bromide (CTAB)/n-octane/n-butanol/water microemulsion-mediated solvothermal process. The structure, morphology, and optical properties were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), and photoluminescence (PL) spectra as well as the kinetic decays, respectively. The XRD results reveal that the obtained Eu:HAp and Tb:HAp show the characteristic peaks of hydroxyapatite in a hexagonal lattice structure. It is observed that the as-prepared luminescent samples exhibit rod-like morphology with well dispersed and non-aggregated size distribution. Upon excitation by UV radiation, the phosphors demonstrate the characteristic 5D 0-7F 1-4 emission lines of Eu3+ and the characteristic 5D4-7F 3-6 emission lines of Tb3+. Moreover, the photoluminescence intensities (PL) of Eu3+ and Tb3+ can be tuned by altering the solvothermal temperature and the doping concentration of Eu3+ and Tb3+.     

Surface modification of hydroxyapatite nanocrystals by grafting polymers containing phosphonic acid groups

A novel approach for the surface modification of hydroxyapatite (HAp) nanocrystals is described by grafting polymerization of vinyl phosphonic acid (VPA) using a redox initiating system in an aqueous media. Fourier transform infrared (FT-IR) and XRD analyses confirmed the modification reaction on HAp surfaces. Inductively coupled plasma mass spectroscopy (ICP MS) showed that the Ca/P molar ratio decreased from 1.67 to 1.36 with increasing the feed VPA amount. Zeta potentials of unmodified HAp and modified HAp in phosphate-buffered saline (PBS) solutions (pH 7.4, ionic strength = 10 mM) were negative and decreased with increasing the amount of grafted PVPA. Transmission electron microscopy (TEM) measurements and time-dependent phase monitoring indicated that the colloidal stability of modified HAp over unmodified HAp in water dramatically increased and tended to exist as single nanocrystals without aggregation.     

Preparation and properties of titania–apatite hybrid films

TiO₂–hydroxyapatite (HAp) hybrid films were prepared by laminating TiO₂ films with holes on the HAp film. We prepared transparent porous HAp film through spray pyrolysis deposition (SPD) method. The HAp possessed affinity against proteins. TiO₂ films were prepared using phase separation of alkoxide. The holes provided from this process serve as an adsorption field and photocatalytic reaction field for reactants. This work demonstrated that the TiO₂–HAp hybrid films produced by this process are candidates for photocatalytic decomposition of germs, viruses, and other biohazardous substances in the environment.     

Cell Evaluation on Alginate/Hydroxyapatite Block for Biomedical Application

Initial cell evaluation on alginate/hydroxyapatite block was investigated. Sodium alginate with 1, 3 and 5% concentration was obtained via neutral extraction of locally obtained brown seaweed, Sargassumpolycystum. Commercially available hydroxyapatite (HAp) powder was pressed uniaxially at 3 MPa to obtain the HAp block. The HAp block was then sintered at 900̊C. The sintered HAp block was then immersed in the sodium alginate solution at different concentration for 24 hours under vacuum condition. Morphological observations show that normal cell growth was observed on alginate/HAp blockafter post treatment for day 1 and 2. However, the cell starts to show some distinct morphological changes when compared to the control cells for day 5 and 7. Cell viability assay results shows that a consistent cell growth was obtained with HAp block incorporated with 3 and 5% sodium alginate. While HAp block without the incorporation of sodium alginate and HAp block incorporated with 1% sodium alginate concentration shows inconsistent cell growth. Initial cell evaluation results suggest that alginate/HAp block shows no toxicity on cell attachment and proliferation.     

Growth of highly oriented hydroxyapatite arrays tuned by quercetin

Crystal calls: the remarkable crystal modulation ability of quercetin (QUE) in highly oriented hydroxyapatite (HAp) array crystallization is reported. Organized HAp crystals were obtained by hydrothermal exchange of α-tricalcium phosphate (α-TCP) precursor in solution with a progressive increase in QUE concentration. Experimental results revealed that QUE would be a potentially effective crystal modulation assistant.     

Growth of hydroxyapatite nanocrystals on polymer particle surface

In the present paper, we describe the preparation of hybrid particles consisting of polymeric core with deposited hydroxyapatite (HAp) nanocrystals. Polystyrene submicron particles modified by β-diketone groups have been used as templates for the growth of HAp. Hybrid particles with HAp nanocrystal content between 7 and 50 wt% have been prepared. Microscopy studies indicate that hybrid particles exhibit “raspberry” morphology, and HAp nanoparticles are not homogeneously distributed on the polymer particle surface. The increase in the HAp content on the polymer particle surface reduces the colloidal stability of the hybrid particles because of the vanishing of the surface charge.     

Thermotropic Colloidal Liquid-Crystalline Hydroxyapatite Nanorod Hybrids Containing a Forklike Mesogen

We here report the development of new thermotropic colloidal liquid-crystalline (LC) organic/inorganic hybrids consisting of a hydroxyapatite (HAp)/poly(acrylic acid) (PAA) nanorod and a dendritic forklike mesogen. Complexation of the HAp/PAA nanorod covered with negatively charged PAA and a cationic forklike mesogen through electrostatic interactions and cation metathesis results in the surface modification of the HAp/PAA nanorod with the forklike mesogen. While the HAp/PAA nanorod forms a lyotropic colloidal LC phase in the aqueous dispersion, the HAp/PAA nanorod modified with the forklike mesogen exhibits thermotropic colloidal LC phases in the solvent-free states. The biomineral-based organic/inorganic colloidal liquid crystals exhibiting thermotropic LC properties have potential for the development of new stimuli-responsive sustainable materials.