Hydroxyapatite Nano- and Microcrystals with Multiform Morphologies: Controllable Synthesis and Luminescence Properties

Hydroxyapatite (Ca-5(PO4)(3)OH) nano- and microcrystals with multiform morphologies (separated nanowires, nanorods, microspheres, microflowers, and microsheets) have been successfully synthesized by a facile hydrothermal process. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) spectra, kinetic decay, and electron paramagnetic resonance (EPR) were used to characterize the samples. The experimental results indicate that the obtained Ca-5(PO4)(3)OH samples show an intense and bright blue emission under long-wavelength UV light excitation. This blue emission might result from the CO2 center dot- radical impurities in the crystal lattice.

Synthesis and characterization of Eu-doped hydroxyapatite through a microwave assisted microemulsion process

Europium doped hydroxyapatite (Eu:HAp) nanosized particles with multiform morphologies have been successfully prepared via a simple microemulsion-mediated process assisted with microwave heating. The physicochemical properties of the samples were well 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), photoluminescence (PL) spectra, and the kinetic decays, respectively. The results reveal that the obtained Eu:HAp particles are well assigned to the hexagonal lattice structure of the hydroxyapatite phase. Additionally, it is found that samples exhibit uniform morphologies which can be controlled by altering the pH values. Furthermore, the samples show the characteristic D-5(0)-F-7(1-4) emission lines of Eu3+ excited by UV radiation.

In vivo mineralization and osteogenesis of nanocomposite scaffold of poly (lactide-co-glycolide) and hydroxyapatite surface-grafted with poly(L-lactide)

Nanocomposite of hydroxyapatite (HAP) surface-grafted with poly(L-lactide) (PLLA) (g-HAP) shows a wide application for bone fixation materials due to its improved interface compatibility, mechanical property and biocompatibility in our previous study. In this paper, a 3-D porous scaffold of g-HAP/poly (lactide-co-glycolide) (PLGA) was fabricated using the solvent casting/particulate leaching method to investigate its applications in bone replacement and tissue engineering. The composite of un-grafted HAP/PLGA and neat PLGA were used as controls. Their in vivo mineralization and osteogenesis were investigated by intramuscular implantation and replacement for repairing radius defects of rabbits. After surface modification, more uniform distribution of g-HAP particles but a lower calcium exposure on the surface of g-HAP/PLGA was observed. Intramuscular implantation study showed that the scaffold of g-HAP/PLGA was more stable than that of PLGA, and exhibited similar mineralization and biodegradability to HAP/PLGA at the 12-20 weeks post-surgery.

Preparation and Bioactivity of the Composite of PLGA and Hydroxyapatite Nanocrystals Surface-grafted with L-lactic Acid Oligomer

The hydroxyapatite (HA) nanocrystals of 100-200 nm in length and 20-30 nm in width were hydrothermally synthesized by the reaction of phosphoric acid and calcium hydroxide. Lactic acid oligomer surface grafted HA(op-HA) nanoparticles were obtained by oligomeric lactic acid with a certain molecular weight grafting onto the HA surface to form a Ca carboxylate bond in the absence of any catalyst. The op-HA was further blended with poly(lactide-co-glycolide) (PLGA) to prepare the nanocomposite of op-HA/PLGA. FTIR, TGA, ESEM and EDX were used to analyze grafting reaction, the graft ratio of op-HA, surface topography and calcium deposition of the composites, respectively. The rabbit osteoblasts were seeded and cultured on the surface of composites in vitro. The cell morphology, adhesion, proliferation and gene expression were evaluated with FITC staining, NIH image J software and the analysis of real-time PCR, respectively. The results show that the graft ratio of op-HA is 8.3% (mass fraction). The op-HA/PLGA nanocomposite possessed more suitable surface properties, including roughness and plenty of calcium and phosphor. It exhibited better cell adhesion, spreading and proliferation of rabbit osteoblasts, compared to pure PLGA.

Electrospun poly(L-lactide)-grafted hydroxyapatite/poly(L-lactide) nanocomposite fibers

Composite fibers composed of poly(L-lactide)-grafted hydroxyapatite (PLA-g-HAP) nanoparticles and polylactide (PLA) matrix were prepared by electro-spinning. Environmental scanning electron microscope (ESEM) and transmission electron microscopy (TEM) were employed to investigate the morphology of the composite fibers and the distribution of PLA-g-HAP nanoparticles in the fibers, respectively. At a low content (similar to 4 wt%) of PLA-g-HAP, the nanoparticles dispersed uniformly in the fibers and the composite fibrous mats exhibited higher strength properties, compared with the pristine PLA fiber mats and the simple hydroxyapatite/PLA blend fiber mats. But when the content of PLA-g-HAP further increased, the nanoparticles began to aggregate, which resulted in the deterioration of the mechanical properties of the composite fiber mats. The degradation behaviors of the composite fiber mats were closely related to the content of PLA-g-HAP. At a low PLA-g-HAP content, degradation may be delayed due to the reduction of autocatalytic degradation of PLA. When PLA-g-HAP content was high, degradation rate increased because of the enhanced wettability of the composite fibers and the escape of the nanoparticles from fiber surfaces during incubation.

Preparation of nano-hydroxyapatite/poly(L-lactide) biocomposite microspheres

Nano-hydroxyapatite (HA)/poly(L-lactide) (PLLA) composite microspheres with relatively uniform size distribution were prepared by a solid-in-oil-in-water (s/o/w) emusion solvent evaporation method. The encapsulation of the HA nanopaticles in microshperes was significantly improved by grafting PLLA on the surface of the HA nanoparticles (p-HA) during emulsion process. This procedure gave a possibility to obtain p-HA/PLLA composite microspheres with uniform morphology and the encapsulated p-HA nanoparticle loading reached up to 40 wt% (33 wt% of pure HA) in the p-HA/PLLA composite microspheres. The microstructure of composite microspheres from core-shell to single phase changed with the variation of p-HA to PLLA ratios. p-HA/PLLA composite microspheres with the diameter range of 2-3 mu m were obtained. The entrapment efficiency of p-HA in microspheres could high up to 90 wt% and that of HA was only 13 wt%. Surface and bulk characterizations of the composite microspheres were performed by measurements such as wide angle X-ray diffraction (WAXD), thermal gravimetric analysis (TGA), environmental scanning electron microscope (ESEM) and transmission electron microscopy (TEM).

Composites of poly(lactide-co-glycolide) and the surface modified carbonated hydroxyapatite nanoparticles

To improve the mechanical properties of the composites of poly(lactide-co-glycolide) (PLGA, LA/GA = 80/20) and the carbonate hydroxyapatite (CHAP) particles, the rice-form or claviform CHAP particles with 30-40 nm in diameter and 100-200 nm in length were prepared by precipitation method. The uncalcined CHAP particles have a coarse surface with a lot of global protuberances, which could be in favor of the interaction of the matrix polymer to the CHAP particles. The nanocomposites of PLGA and surface grafted CHAP particles (g-CHAP) were prepared by solution mixing method. The structure and properties of the composites were subsequently investigated by the emission scanning electron microscopy, the tensile strength testing, and the cell culture. When the contents of g-CHAP were in the range of 2-15 wt %, the PLGA/g-CHAP nanocomposites exhibited an improved elongation at break and tensile strength. At the 2 wt % content of g-CHAP, the fracture strain was increased to 20%) from 4-5% for neat PLGA samples. Especially at g-CHAP content of 15 wt %, the tensile strength of PLGA/g-CHAP composite was about 20% higher than that of neat PLGA materials. The tensile moduli of composites were increased with the increasing of filler contents, so that the g-CHAP particles had both reinforcing and toughening effects on the PLGA composites. The results of biocompatibility test showed that the higher g-CHAP contents in PLGA composite facilitated the adhesion and proliferation properties of osteoblasts on the PLGA/g-CHAP composite film.

Grafting polymerization of L-lactide on the surface of hydroxyapatite nano-crystals

A novel method of grafting ring-opening polymerization of L-lactide (LLA) onto the surface of hydroxyapatite nano-particles (n-HAP) was developed. PLLA was directly connected onto the HAP surface through a chemical linkage. The PLLA-g-HAP particles could be stably dispersed in organic solvent such as chloroform for several weeks. The n-HAP particles still retained the original dimension and shape after the grafting of PLLA. Compared with the P-31 MAS-NMR spectrum of pure HAP powders, there appeared a downfield displacement of 1.2 ppm in the spectrum of PLLA-g-HAP. Fourier transformation infrared (FT-IR) spectra further confirmed the existence of PLLA on the surface of PLLA-g-HAP. The amount of grafted polymer determined by thermal gravimetric analysis (TGA) was about 6% in weight. The tensile strength and elongation at break of the PLLA/PLLA-g-HAP composite containing 8 wt% of PLLA-g-HAP were 55 MPa and about 10-13%, respectively, while those of the PLLA/n-HAP composites were 40 MPa and 3-5%, respectively.

Oriented nano-structured hydroxyapatite from the template

Natural bone is one kind of compounds consisting of hydroxyapatite (HAp) nano-rods, which are embedded in the template of collagen matrix in vivo with the same crystallographic organization. Herein HAp nano-rods precursors were synthesized via wet chemical method. Large-scale HAp nano-wires with the same crystallographic organization as the template of anodic aluminum oxide (AAO) were obtained by the electrophoretic deposition and the technology of the template. It provides a meaningful method to study and understand the information of biological molecules' mineralization process.

Low-pressure synthesis and characterisation of hydroxyapatite derived from mineralise red algae

There is a great need to design functional bioactive substitute materials capable of surviving harsh and diverse conditions within the human body. Calcium-phosphate ceramics, in particular hydroxyapatite are well established substitute materials for orthopaedic and dental applications. The aim of this study was to develop a bioceramic from alga origins suitable for bone tissue application. This was achieved by a novel synthesis technique using ambient pressure at a low temperature of 100 degrees C in a highly alkaline environment. The algae was characterised using SEM, BET, XRD and Raman Spectroscopy to determine its physiochemical properties at each stage. The results confirmed the successful conversion of mineralised red alga to hydroxyapatite, by way of this low-pressure hydrothermal process. Furthermore, the synthesised hydroxyapatite maintained the unique micro-porous structure of the original algae, which is considered beneficial in bone repair applications. (C) 2007 Elsevier B.V. All rights reserved.

Development of composite tissue scaffolds containing naturally sourced mircoporous hydroxyapatite

The aims of this work were to investigate the conversion of a marine alga into hydroxyapatite (HA), and furthermore to design a composite bone tissue engineering scaffold comprising the synthesised HA within a porous bioresorbable polymer. The marine alga Phymatolithon calcareum, which exhibits a calcium carbonate honeycomb structure, with a natural architecture of interconnecting permeable pores (microporosity 4-11 mu m), provided the initial raw material for this study. The objective was to convert the alga into hydroxyapatite while maintaining its porous morphology using a sequential pyrolysis and chemical synthesis processes. Semi-quantitative XRD analysis of the post-hydrothermal material (pyrolised at 700-750 degrees C), indicated that the calcium phosphate (CaP) ceramic most likely consisted of a calcium carbonate macroporous lattice, with hydroxyapatite crystals on the surface of the macropores. Cell visibility (cytotoxicity) investigations of osteogenic cells were conducted on the CaP ceramic (i.e., the material post-hydrothermal analysis) which was found to be non-cytotoxic and displayed good biocompatibility when seeded with MG63 cells. Furthermore, a hot press scaffold fabrication technique was developed to produce a composite scaffold of CaP (derived from the marine alga) in a polycaprolactone (PCL) matrix. A salt leaching technique was further explored to introduce macroporosity to the structure (50-200 mu m). Analysis indicated that the scaffold contained both micro/macroporosity and mechanical strength, considered necessary for bone tissue engineering applications. (C) 2008 Published by Elsevier B.V.

High-solid-content hydroxyapatite slurry for the production of bone substitute scaffolds

Key to various bone substitute scaffold production techniques is the development of free-flowing ceramic slurry with optimum theological properties. The aim is to achieve a colloidal suspension with as high a solid content as possible while maintaining a low viscosity which easily penetrates the pores of relevant sacrificial templates. The following investigation describes the optimization of a hydroxyapatite slip and demonstrates its potential application in scaffold production. Using predominantly spherical particles of hydroxyapatite of between 0.82 mu m and 16.2 mu m, coupled with a 2 wt % addition of the anionic polyelectrolyte, ammonium polyacrylate, an 80 wt % (55.9 vol %) hydroxyapatite solid loaded slip with a viscosity of approximately 126 mPa s has been developed. Its ability to infiltrate and replicate porous preforms has been shown using polyurethane foam. The enhanced particle packing achieved has allowed for the production of scaffolds with highly dense and uniform grain structures. The results represent a significant improvement in current slurry production techniques and can be utilized to develop high-density ceramic bone substitute scaffolds.