Hydroxyapatite Suspension Research Articles

Calcium phosphate granules for use as a 5-Fluorouracil delivery system

The possibility of tailoring apatite granules as a controlled release system for the drug model 5-Fluorouracil (5FU) has been examined. Apatite granules (SDG) were obtained by spray drying suspensions of hydroxyapatite (HAP) nanoparticles previously precipitated from citrate solutions [M.A. Martins, C. Santos, M.E.V. Costa, M.M. Almeida, Preparation of porous hydroxyapatite particles to be used as drug delivery systems, Advanced Materials Forum II (455) (2004) 353–357]. SDG had donut shape and very high specific surface area (150 m 2/g) indicative of high porosity. SDG were poorly crystalline HAP but turned into biphasic granules (HSDG) with crystalline tricalcium phosphate and HAP after annealing at 800 °C, while reducing their surface area down to ∼6 m 2/g. SDG and HSDG were soaked in a 5FU solution at pH 5.2 and room temperature during several days and then transferred to a phosphate buffered solution (PBS) at pH 7.4 and 37 °C, for releasing 5FU. The comparison between the 5FU adsorbing and releasing behaviours exhibited by SDG and HSDG shows that engineering the granules characteristics, i.e. specific surface area, surface chemical composition, porosity and crystal phase composition allows the 5FU release profile to be controlled.

Manufacture of hydroxyapatite beads for medical applications

Dense, microporous and macroporous hydroxyapatite spherical granules for medical applications were prepared by a new manufacturing procedure. This process is related to a lost wax method and yields beads with a fully controlled porosity, in terms of shape and pore size. A CaCO 3 scaffold exhibiting controlled size spherical cavities is impregnated with an aqueous hydroxyapatite suspension. After drying in a plaster mould, a thermal treatment destroys the carbonate scaffold and makes it possible to release the HA beads. By this process, HA beads with diameters in the range of 300 μm to 3 mm are obtained. A post-thermal treatment of the beads allows the ceramic to be densified at various densification levels. Porous ceramics make it possible to functionalise the hydroxyapatite granules by loading the structure with biologically active substances. Drug releasing kinetics in continuous distilled water flow were analysed as a function of time and ceramic porosity. Spheres continue to release the biological molecules for more than 5 days.

Spray-dried hydroxyapatite-5-Fluorouracil granules as a chemotherapeutic delivery system

This study describes the preparation and characterization of hydroxyapatite-5-Fluorouracil (5FU) granules, which are intended to be used as chemotherapeutic delivery matrices and bone regeneration templates. Suspensions of hydroxyapatite (Hap) nanoparticles in 5FU solution are spray dried as micro sized granules having donut type shape. Several spray drying temperatures are studied 80 °C being the optimized condition for obtaining granules composed by Hap and 5FU without secondary phases. The produced granules at 80 °C reveal a fast releasing rate of 5FU when soaked in buffer phosphate solution maintained at physiological temperature (37 °C), thereby indicating the potential application of the produced Hap matrices for drug delivery systems (DDSs).

Tierexperimentelle Untersuchung des Knochenersatzstoffs Ostim™ im knöchernen Lager des Göttinger Miniaturschweins

The aim of this study was to examine Ostim, a nanocrystalline hydroxyapatite suspension, with regard to its bio- and osteocompatibility, rate of resorption and remodeling dynamics within osseous defects. Ostim was implanted in a randomised fashion into the proximal metaphysis of either the right or the left tibia of 18 Göttinger minipigs. Based on microradiographs and histological examinations Ostim showed biocompatibility, bioactivity and osteoconductivity. This substitute material exhibited osseous integration. The degradation process stopped after six weeks. With regard to osseous regeneration within the defects, there were no significant differences between the time intervals of follow-up. Ostim could still be detected in significant amounts after one year with no complete resorption. A restitutio ad integrum could not be observed in spite of the histological evidence of the above-described reactions within the implantation site. A thorough osseous incorporation seemed to impede the degradation of the bone substitute material. The paramount goal is to improve the biological behaviour in favour of a higher rate of degradation.

Hybrid coating of hydroxyapatite and collagen within poly(D,L‐lactic‐co‐glycolic acid) scaffold

To improve the cell-affinity of biodegradable polymer scaffold, coating hydroxyapatite (HA) or collagen on the surface of polymer materials seemed to be a strategy to combine both advantages of them. The objective of this study was to develop a novel method to introduce HA and collagen inside polymer scaffold uniformly. HA and collagen suspension was mixed with paraffin microspheres, and molded to form a composite sample. After the sample was dried, HA/collagen composite was left among and on the surface of paraffin microspheres. Poly(D,L-lactic-co-glycolic acid) (PLGA) (50/50) solution was cast into the inter-space of the paraffin microspheres and dried. Afterwards, the paraffin was dissolved and removed, HA/collagen was transferred to the surface and even inside of the pore wall of PLGA scaffolds. Collagen fibers and HA particles which were inlaid inside the PLGA pore wall could help to enhance the coating strength between HA/Col coating and the pore wall surface of the PLGA scaffold. The scaffolds with HA/Col coating were expected to exhibit desirable properties in bone tissue engineering.

The Effects of HAp and BCP Nano Powders Synthesized by Microwave-Assisted Synthesis on the Activation ofOsteoblast and Osteoclast

Hydroxyapatite (HAp) and biphasic calcium phosphate (BCP) nano powders were synthesized using the microwave-assisted synthesis process dependent on pH and microwave irradiation time. The average size of a powder was less than 100 nm in diameter. Through in-vitro cytotoxicity tests by an extract dilution method, the HAp and BCP nano powders have shown to be cytocompatible for L-929 fibroblast cells, osteoblastlike MG-63 cells and osteoclast-like Raw 264.7 cells. The activation of osteoblast was estimated by alkaline phosphatase (ALP) activity. When the HAp and BCP were treated to MG-63 cells, alkaline phosphatase activities increased on day 3, compared with those of the untreated cells. Also, the collagen fibers increased when the HAp and BCP powders suspension were treated to MG-63 cells, compared to those of the untreated cells. Quantitative alizarin red S mineralization assays showed a trend toward increasing mineralization in osteoblast cultured with powder suspension. In conclusion, hydroxyapatite and biphasic calcium phosphate appeared to be a bone graft substitute material with optimal biocompatibility and could be further applied to clinical use as an artificial bone graft substitute.

Development of nano-hydroxyapatite coating by electrohydrodynamic atomization spraying

Electrohydrodynamic atomisation (EHDA) spraying of a hydroxyapatite (HA) suspension consisting of nano-particles (nHA) has been used to produce a HA coating comprising of nanostructured surface topography. In EHDA the suspension is jetted from a needle under an electric field. Obtaining the stable cone-jet mode of EHDA is critical to improve the quality and optimise the morphology of HA coatings, therefore a systematic investigation of the effects of several key processing parameters, such as suspension flow rate, applied voltage and distance between the needle and substrate, and needle size was carried out in this work. The HA coatings processed under different spraying parameters were compared and then scored according to uniformity and microstructural integrity. It was found that all of these parameters had a very significant influence on the morphology of nHA coating prepared. Under an optimised processing condition, where a needle orifice diameter of 300 microm, kept at a distance of 20 mm from the substrate, a flow rate of 20 microL/min, and the applied voltage kept within 4.3 kV and 5.2 kV, a uniform nHA coating was obtained. This is a crucial step forward in obtaining advanced nano-hydroxyapatite coatings of high quality for biomedical applications by using EHDA spraying.

The Effect of Reaction Conditions on Hydroxyapatite Particle Morphology and Applications to the Reticulated Foam Method of Scaffold Production

The production of nano-scale hydroxyapatite (HA) suspensions to be used for the reticulated foam method of scaffold production was investigated at temperatures of between 10 and 60OC. An increase in reaction temperature was associated with an increase in the particle size and some decrease in the aspect ratio of the particles. Pre-treatment of the polyurethane foam template using PPDS (potassium peroxodisulfate) solution resulted in a significantly improved coating of HA when compared to the untreated samples or those treated with ethanol. Initial trials coating the polyurethane with HA produced at the different reaction temperatures showed a superior coating with the suspension produced at 10OC compared to that at 60OC. A scaffold was produced using the HA suspension produced at room temperature, but further understanding of the suspension properties and the optimum conditions for coating of the PU foam are required for improved mechanical performance.

Electrosprayed Nanoapatite: A New Generation of Bioactive Material

Fine nanoapatite relics were deposited on glass substrates by electrohydrodynamic atomisation, using nanohydroxyapatite (nHA), nano-carbonated hydroxyapatite (nCHA) and nanosilicon- substituted hydroxyapatite (nSiHA) suspensions. These electrosprayed nanoapatites were evaluated in-vitro using simulated body fluid (SBF) and human osteoblast (HOB) cells. The SBF study revealed that newly-formed apatite layers were observed on the surface of the relics. Furthermore, enhanced HOB cell growth was observed on each of the nanoapatites at all time points. Hence, this work demonstrated that electrosprayed nanoapatites offer considerable potential as biomaterials.

Nanosized bioceramic particles could function as efficient gene delivery vehicles with target specificity for the spleen

We have compared the ability of several nanosized bioceramic particles including negatively charged silica (SiO(2)), neutrally charged hydroxyapatite (HA) and positively charged zirconia (ZrO(2)) nanoparticles as non-viral vectors for efficient in vivo gene delivery. A mixture of highly monodispersed aqueous suspension of HA or SiO(2) nanoparticles, coated with protamine sulfate (PS), complexed efficiently with plasmid DNA and significantly enhanced transgene expression in vitro. In comparison, ZrO(2) nanoparticles gave poor transfection efficiency under similar conditions tested. It was also determined that, under the same conditions, PS-SiO(2)-DNA, but not PS-HA-DNA-nanoplexes, were able to mediate efficient transgene expression in vitro in the presence of 50% serum. Intraperitoneal injections of PS-SiO(2)-luciferase DNA nanoplexes targeted the highest level of transgene expression in the spleen of recipient mice that lasted for more than 48 h. Injection of PS-SiO(2)-pNGVL-hFLex-MUC-1 nanoplexes was able to mediate the production of Flt-3L in the sera of recipient mice. Simultaneously, the production of Flt-3L was accompanied by the stimulation of IL-2 and interferon-gamma (IFN-gamma). Most importantly, the injection of PS-SiO(2)-pNGVL-hFLex-MUC-1 nanoplexes could mount potent anti-tumour specific immune responses that led to the subsequent regression of parental tumor cells containing the muc-1 determinant.

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.

Nanomechanical analysis of bone tissue engineering scaffolds

Copolymers of (2-hydroxyethyl methacrylate) (HEMA) and methacrylamide monomers conjugated with amino acids were synthesized and crosslinked with ethylene glycol dimethacrylate. The resulting library of copolymers was mineralized in vitro using two distinct methods. In the first mineralization method, the copolymers were polymerized in the presence of a sub-micron hydroxyapatite (HA) suspension. In the second method, copolymers were mineralized with HA using a urea-mediated process. The mechanical properties of all of the copolymers, both mineralized and not, were determined using nanoindentation under both load and displacement control. A power law fit to the initial unloading curve was used to determine a reduced elastic modulus for each material. Between 30 and 300 indentations were performed on each material, and ANOVA analysis was run to determine the statistical significance of differences in modulus between samples. Using nanoindentation, the 22 different samples had reduced modulus values ranging from 840 MPa to 4.14 GPa. Aspartic acid-methacrylate (Asp-MA) copolymers were not distinguishable from the pHEMA control material. Polymerization in the presence of HA created a more uniform material than the urea method of mineralization. Several challenges and solutions encountered in the nanomechanical testing of soft, heterogeneous materials are discussed. These results demonstrate that with proper experimental design, the mechanical properties of tissue engineering scaffold materials based on polymer-ceramic composite materials can be determined using small samples and nanoindentation techniques.

Electrophoretic deposition of composite hydroxyapatite-chitosan coatings

Cathodic electrophoretic deposition has been utilized for the fabrication of composite hydroxyapatite-chitosan coatings on 316L stainless steel substrates. The addition of chitosan to the hydroxyapatite suspensions promoted the electrophoretic deposition of the hydroxyapatite nanoparticles and resulted in the formation of composite coatings. The obtained coatings were investigated by X-ray diffraction, thermogravimetric and differential thermal analysis, scanning and transmission electron microscopy, potentiodynamic polarization measurements, and electrochemical impedance spectroscopy. It was shown that the deposit composition can be changed by a variation of the chitosan or hydroxyapatite concentration in the solutions. Experimental conditions were developed for the fabrication of hydroxyapatite-chitosan nanocomposites containing 40.9–89.8 wt.% hydroxyapatite. The method enabled the formation of adherent and uniform coatings of thicknesses up to 60 μm. X-ray studies revealed that the preferred orientation of the hydroxyapatite nanoparticles in the chitosan matrix increases with decreasing hydroxyapatite content in the composite coatings. The obtained coatings provided the corrosion protection for the 316L stainless steel substrates.

Emulsion Technique Preparation of Nano-HA/PMMA Composites and In Vitro Evaluation

Nano-sized hydroxyapatite (HA) chloroform suspensions were firstly prepared by reactions in an emulsion system of Ca(OH)2-H3PO4-chloroform-lecithin, then, HA/PMMA composites with well dispersed HA could be obtained by adding PMMA into the suspension. The residual water in the HA suspension could lead to a porous surface which demonstrated better bioactivity in in vitro test. The residual water could cause HA particles to exist on pore walls during the composite formation, resulting in the increase of the HA amount per unit surfac

Effect of suspension stability on electrophoretic deposition of hydroxyapatite coatings

In order to prepare densely packed hydroxyapatite (HAp) coating onto titanium substrate through electrophoretic deposition (EPD), it is highly desirable to produce stable HAp suspension. In this study, nano-HAp particles prepared by hydrothermal method were employed for EPD. The stability of HAp suspensions in various primary aliphatic alcohols (C1–C4) has been studied by measurement of sedimentation tests and electricity conductivity. Furthermore, to make a stable suspension, a dispersant [triethanolamine (TEA)] was added. Maximum stability is observed for the suspension containing n-butanol as the dispersion medium and TEA as the dispersant. The HAp coating deposited in this suspension was observed to be a crack-free and densely packed coating through scanning electron microscopy examination. The shear strength and nano-indention tests have confirmed the good adhesion between the coating and the substrate.

Preparation of highly concentrated aqueous hydroxyapatite suspensions for slip casting

This paper reports the preparation of highly concentrated aqueous hydroxyapatite (HA) suspensions for slip casting of dense bone implants. The dispersing behaviour of HA powders in aqueous media was monitored by viscosity and zeta potential analyses as a function of pH of the slurry. The rheological properties of concentrated aqueous hydroxyapatite suspensions have been characterized with varying pH, NH4PAA concentration and solids loading. The intrinsic pH of the suspension was found suitable for slip casting. The optimum dispersant concentration is 0.75 wt.% for 75 wt.% solid loading. A stable suspension with 75 wt.% solid was suitable for slip casting with viscosity of 0.36 Pa s at 100 s−1. Finally, crack-free and dense microstructures have been obtained successfully with a grain size of 2–5 μm.

Influence of powder pre-treatments and milling on dispersion ability of aqueous hydroxyapatite-based suspensions

The rheological properties and the dispersion stability of highly concentrated aqueous hydroxyapatite (HAP) powder suspensions in the presence of an anionic polyelectrolyte dispersant have been investigated. Dispersed suspensions with high content of HAP powder (up to 75 wt.%) and low viscosity were obtained. HAP suspensions with solids loading as high as 75 wt.% could be prepared following a slow process of increasing the solids weight fraction in steps of 3 wt.%, starting from 66 wt.%. After each increment of solids, ball milling was conducted for periods of 6 h, which then increased up to 24 h with solids loading increasing. Zeta potential measurements were conducted on HAP powders evaluate the influence of calcination on surface-charge properties of the particles. It was concluded that both aqueous ball milling and calcining enhance the repulsive interaction forces between particles, like the presence of the dispersant.

A Method for Simultaneously Precipitating and Dispersing Nano-Sized Calcium Phosphate Suspensions

Stable and relatively concentrated aqueous suspensions of nano-sized stoichiometric hydroxyapatite could be prepared by a precipitation method in the presence of suitable surface active agent (SAA). The method includes the precipitation, vacuum filtration and washing of the precipitated powders, followed by re-dispersion. It could be concluded that the added amount of the SAA should be enough to cover the primary particles surface, and that washing should be better carried out using a SAA solution. The method developed enables the precipitation of the powders and the preparation of suspensions, while significantly shortening the overall time required for colloidal processing consuming.

Rheology of Hydroxyapatite Dispersions

Hydroxyapatite (HA) is an interesting ceramic material for orthopedic applications, in particular for implant operations and bone regeneration, owing to its bioactivity and biocompatibility with the surrounding tissues. Even if different shaping processes can be used in order to obtain porous ceramic bodies with optimal final properties, the sponge impregnation method with aqueous HA dispersions is particularly suitable to achieve an appropriate macroporosity to bone regeneration. As for conventional slip or tape casting, the rheological behavior of HA suspensions must be properly fitted to process conditions and controlled through a satisfactory stabilization of the disperse phase, i.e., through an appropriate dispersant dosage and an accurate homogenization of dispersed powder. In the present work, HA powders with different crystallinity degree were used to prepare aqueous dispersions with different contents of solids and dispersant (ammonium polyacrylate). The specific surface area of HA powders is very high, and then special attention must be dedicated to the dispersant selection and the dispersion process since the rheology of HA suspensions is strongly influenced by the structural conditions of the disperse phase. Even small differences in dispersant concentration can lead to dramatic changes in the rheological properties also at relatively low values of solids volume concentration. Above a critical concentration, the viscosity drop associated with the apparently plastic behavior is confined within a very narrow stress range, a neat transition is observed in the linear viscoelastic properties, and the time‐dependent effects induced by the shear history become quite important and crucial for the experimental characterization.

Fabrication of hydroxyapatite ceramics with controlled pore characteristics by slip casting

Porous hydroxyapatite (HAp) ceramics with controlled pore characteristics were fabricated using slip casting method by mixing PMMA with HAp powder. The optimum conditions of HAp slip for slip casting was achieved by employing various experimental techniques, zeta potential and sedimentation, as a function of pH of the slips in the pH range of 4-12. HAp suspensions displayed an absolute maximum in zeta potential values and a minimum in sedimentation height at pH 11.5. The optimal amount of dispersant for the HAp suspensions was found at 1.0 wt% according to the viscosity of 25 vol% HAp slurry. The rheological behaviour of HAp slurry displays a shear-thinning behavior without thixotropy, which is needed in slip casting processing. The pore characteristics of sintered porous hydroxyapatite bioceramics can be controlled by added PMMA particle size and volume. The obtained ceramics exhibit higher strength than those obtained by dry pressing.