Hydroxyapatite Whiskers Research Articles

Effects of the reinforcement morphology on the fatigue properties of hydroxyapatite reinforced polymers

The objective of this study was to examine the effects of the hydroxyapatite (HA) reinforcement morphology and content on the fatigue behavior of HA reinforced high density polyethylene (HDPE). To this end, HDPE was reinforced with 20 and 40 vol% of either HA whiskers or an equiaxed HA powder, and tested in four-point bending fatigue under simulated physiological conditions. The fatigue life, mechanical property degradation and failure surfaces were compared between experimental groups. HDPE reinforced with HA whiskers exhibited a four- to five-fold increase ( p < 0.001 , T-test) in fatigue life compared to an equiaxed powder for either the 20 and 40 vol% reinforcement level. Composites containing 40 vol% HA exhibited decreased fatigue life compared to those with 20 vol% HA for either reinforcement morphology ( p < 0.0001 , ANOVA). HA whisker reinforced HDPE exhibited less stiffness loss, permanent deformation (creep) and energy dissipation at a given number of cycles compared to HA powder. Thus, HA whisker reinforced HDPE was more tolerant of fatigue damage due to either microcracking or polymer plasticity. Scanning electron microscopy of failure surfaces and surface microcracks showed evidence of toughening by uncracked ligaments, crack tip plasticity, polymer fibril bridging and HA whisker pullout. The results of this study suggest that the use of HA whiskers, in place of HA powder, is a straightforward means to improve the fatigue life and damage tolerance of HA reinforced polymers for synthetic bone substitutes.

Conduction properties of non-stoichiometric hydroxyapatite whiskers for biomedical use

Hydroxyapatite (HA) whiskers were synthesized by a hydrothermal method and ion conductive property was investigated in order to develop HA whisker electrets for biomedical utilization. Based on infrared (IR) spectroscopy and inductively coupled plasma optical emission spectrometry (ICP-OES), the obtained whiskers were assumed to be Ca deficient HA with a composition of Ca9.18[HPO4]0.82[PO4]5.18[OH]1.18·n H2O. The results of complex impedance measurements proved that the conduction properties of whiskers and powders showed almost the same temperature dependence as those of sintered HA above 600°C. The mechanism is understood by the migration of protons originating in OH- ions. In the temperature range below 600°C, however, the non-linear Arrhenius relationship of conductivity (σ vs. 1/T) was only observed in the whiskers and powders. In particular, a drastic change in conductivity with temperature appeared in the whiskers within 250-600°C; the conductivity increased to 5.0 × 10-9 S/cm at 500°C, then decreased to 1.7 × 10-9 S/cm with the temperature elevated to 600°C. Since HPO42- ions are reportedly supposed to convert into P2O74- in almost the same temperature range where the drastic change in conductivity appeared, the increase in whisker conductivity up to 500°C is presumably the result of an increase in the number of mobile protons generated from HPO42-. The subsequent decrease in conductivity seemed to be caused by a decrease in the number of protons achieved by water elimination, causing the conversion of HPO42- to P2O74-.

Hydrothermal synthesis of hydroxyapatite whiskers with sharp faceted hexagonal morphology

We report an effective method for the synthesis of hydroxyapatite whiskers with sharp faceted hexagonal shape employing a low temperature (90 °C) hydrothermal route with calcium nitrate tetrahydrate, diammonium phosphate and urea as starting materials. The key parameters of the synthesis process i.e. duration, temperature cycle of the treatment and starting pH value are carefully varied and the end products are investigated using powder X-ray diffraction (XRD), Raman-scattering, infrared spectroscopy (IR), elemental analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), electron diffraction (ED), and high-resolution TEM (HRTEM) in order to find the optimal reaction conditions that lead to the desired hexagonal morphology of HA whiskers. The results demonstrate that gradual and greater increase in solution pH during the hydrothermal process favors large quantity of the single-crystalline hydroxyapatite whiskers with well defined hexagonal morphology.

Synthesis of hydroxyapatite whiskers through dissolution–reprecipitation process using EDTA

Abstract Hydroxyapatite (HA) has been of interest in many industrial applications, such as ion exchange, catalysis and biomaterials. Chelating agents have often been used to prepare inorganic powders in the form of sphere, rod, whisker and fiber. In this study, HA whiskers were synthesized directly from typically shaped HA powders by refluxing at 80 and 100 °C for 24 h using ethylenediamine tetraacetic acid (EDTA). 3% or 6% of hydrogen peroxide (H 2 O 2 ) was used to promote precipitation of HA crystals. The pH of the solution was adjusted at 7 or 9 by adding ammonia solution. The higher the H 2 O 2 concentration, pH value and refluxing temperature, the longer and thinner whiskers were formed. The whiskers produced at 100 °C with 6% of H 2 O 2 and pH 9 had the highest aspect ratio of about 50–60 (a length of 3 μm and a width of 0.05 μm).

Effects of Temperature and Concentration on the Nano-Sized Hydroxyapatite Whisker Prepared by Chemical Precipitation Method

Chemical precipitation is a popular method for the preparation of hydroxyapatite(Ca10 (PO4)6 (OH)2, HA) because of its simple operation. In this work, nano-sized HA whiskers were synthesized at various synthetic temperatures and concentration by chemical precipitation with Ca (NO3) 2·4H2O and (NH4) 2HPO4 as raw materials. Heat treatment was carried out after they were synthesized. The HA powders were analyzed by using X-ray diffraction (XRD), transmission electron microscope (TEM) and strength test in order to find the favorable growing condition for HA whiskers. The results show that the HA prepared at different synthetic temperatures show no impurity diffraction peak, indicating that they have a high purity. Prior to heat treatment, the crystallinity and length/diameter ratio of the HA whiskers become larger with the increasing of synthetic temperature. So a higher synthetic temperature can promote the growth of the HA whiskers. There is no obvious difference in crystallinity after the heat treatment. Besides, a lower reaction concentration can also promote the growth of HA whiskers. The strength test results show that the compressive strength of the HA prepared gets a maximum value at 50°C.

Whisker‐Reinforced Calcium Phosphate Cements

Self‐setting calcium phosphate cements (CPC) consisting of hydroxyapatite (HA) and tetracalcium phosphate were reinforced with various amounts of hydrothermally synthesized HA whiskers with an aspect ratio of 10. Flexural strength (σb) and work of fracture (γwof) were calculated by four‐point bending tests, and fracture surfaces were analyzed by scanning electron microscopy (SEM). σb and γwof of the CPCs that were reinforced with 30 vol% HA whiskers increased by 60% to 7.4 MPa and by 122% to 102 J/m2, respectively. SEM analyses reveal that this increase could be correlated to energy‐dissipating processes (e.g., whisker pull‐out) at the crack tip.

RETRACTED: A novel technique to synthesize hydroxyapatite whiskers

HA whiskers with high crystalline, uniform morphology and high aspect ratio have been successfully synthesized by the reflux-hydrothermal combined method with the aid of urea, citric acid and Na 2 EDTA additives. The effects of additives on the whiskers have been investigated in detail. The shape and composition of obtained products were characterized by XRD, FTIR, SEM, TEM and ICP-AES. It is revealed that larger aspect ratios, more uniform morphology, more pure phase composition (Ca/P), shorter reaction time and more mild reaction conditions were reached in contrast to sole reflux or hydrothermal treatment. Urea has the most remarkable effect on the aspect ratio and phase purity of HA whiskers.

Hydrolysis of α-TCP and Development of Hydroxyapatite Whiskers

Calcium deficient (Ca/P = 1.53-1.61, molar ratio) whisker shaped hydroxyapatite (HAp) with a high aspect ratio ~26 (diameter: 0.2-0.3 µm) has been prepared by the hydrolysis of a-Ca3(PO4)2 (a-TCP) in an aqueous solvent system under controlled conditions. The influence of processing variables on the conversion of a-TCP to HAp, and the microstructure and composition of the HAp was characterized by means of XRD, SEM, TEM and ICP instruments.

Processing and tensile properties of hydroxyapatite-whisker-reinforced polyetheretherketone

Polyetheretherketone (PEEK) was reinforced with 0–50 vol% hydroxyapatite (HA) whiskers using a novel powder processing and compression molding technique which enabled uniform mixing at high whisker content. Texture analysis showed that viscous flow during compression molding produced a preferred orientation of whiskers along the specimen tensile axis. Consequently, the elastic modulus or ultimate tensile strength of HA-whisker-reinforced PEEK was able to be tailored to mimic human cortical bone. PEEK reinforced with 40 and 50 vol% HA whiskers exhibited elastic moduli of 17 and 23 GPa, respectively. Elastic constants were measured using ultrasonic wave propagation and revealed an orthotropic anisotropy also similar to that measured in human cortical bone. PEEK reinforced with 10 and 20 vol% HA whiskers exhibited an ultimate tensile strength of 90 and 75 MPa, respectively. Tensile specimen fracture surfaces showed evidence of brittle failure in both reinforced and un-reinforced PEEK. Whisker pullout was observed with PEEK adhered to HA whiskers, suggesting a relatively strong interface between the PEEK matrix and HA whisker reinforcements.

Micromechanical model for hydroxyapatite whisker reinforced polymer biocomposites

A micromechanical model was developed to predict the elastic moduli of hydroxyapatite (HA) whisker reinforced polymer biocomposites based upon the elastic properties of each phase and the reinforcement volume fraction, morphology, and preferred orientation. The effects of the HA whisker volume fraction, morphology, and orientation distribution were investigated by comparing model predictions with experimentally measured elastic moduli for HA whisker reinforced high-density polyethylene composites. Predictions using experimental measurements of the HA whisker aspect ratio distribution and orientation distribution were also compared to common idealized assumptions. The best model predictions were obtained using the experimentally measured HA whisker aspect ratio distribution and orientation distribution.

Kinetic Effects on Hydroxyapatite Whiskers Synthesized by the Chelate Decomposition Method

Hydroxyapatite (HA) whiskers have been synthesized using a number of chemical solution methods, including the chelate decomposition method. Numerous previous studies have investigated the effects of the reagents, reagent concentrations, solution pH, and reaction temperature on HA whisker morphology and composition. However, purely kinetic effects, such as the reaction heating and stirring rates, have not been rigorously investigated and are rarely reported in the literature. Therefore, the objective of this study was to investigate kinetic effects on the morphology of HA whiskers synthesized using the chelate decomposition method. In order to study the kinetic effects on the morphology of HA whiskers, three experimental parameters were varied independently: the reaction heating rate (0.36°–3.0°C/min), stirring rate (0–250 rpm), and temperature (80°–200°C). At all heating and stirring rates, precipitated whiskers were confirmed by XRD and FT‐IR to comprise phase‐pure, calcium‐deficient HA (Ca/P=1.57–1.62). The length and aspect ratio of HA whiskers increased with decreased heating rate, decreased stirring rate, and increased reaction temperature. The mean length and aspect ratio of HA whiskers increased approximately twofold with decreased heating rate over the range studied, following a power‐law relationship. Therefore, the reaction heating rate is a key variable that can be used to tailor the morphology of HA whiskers and ought to be reported in the literature. The reaction heating rate and temperature had relatively little effect on the width of HA whiskers. However, the precipitate morphology was altered significantly from micro‐scale whiskers to nano‐scale plates with increased stirring rate. These results offered new insights and provided clarification regarding the reaction mechanism, which is discussed in detail.

Preparation of Porous Composites with a Porous Framework Using Hydroxyapatite Whiskers and Poly(L-Lactic Acid) Short Fibers

A new type of porous composite with a porous framework was prepared using a mixture of hydroxyapatite whiskers (W-HA) and poly(L-lactic acid) short fibers (F-PLLA) by a particle-leaching technique. The material, composed of a porous framework with interconnecting pore of &gt;1 µm, has large-sized pores of about 200 µm. The large-sized pores were formed by leaching sucrose granules. The porosity can be controlled in the range from 60 to 85 % by the sucrose content. The small-sized pores in the framework formed due to the poor densification of the W-HAs / F-PLLAs mixture. The pore distribution in the framework can be controlled by the compressing pressure without change in the distribution of large-sized pores.

The effects on the devitrification mechanism for a certain composition of CaO/P2O5 glasswith additives of HAp, TCP and β-CaP2O6 whisker

In previous works, the effects on the devitrification mechanism of a certain composition calcium phosphate with additives of TiO2, SiO2, Al2O3, CeO2 have been studied. It was found that some metal oxide additives played a key role as the nucleation agent in calcium phosphate glass-ceramics, and the devitrification mechanism of calcium phosphate glass system was changed drastically by addition such as metal oxide. Hydroxyapatite (HAp), tricalcium phosphate (TCP) and β-calcium phosphate (β-CaP2O6) whisker are the three most biologically compatible materials to human bone in bio-ceramics field. In this work, the effect on devitrification mechanism and the physical properties of certain composition calcium phosphate glass with three above additives were investigated, and the result shown that although no fine crystalline was induced in the certain composition of calcium phosphate glass when a large amount of additive was added, but such additives play a catalyst role by lowering the activation energies of devitrification. It would supplement the mechanical properties and the biocompatibility for the calcium phosphate glasses.

Preparation of Porous Poly(l-lactic acid) Composite Containing Hydroxyapatite Whiskers

Abstract A new type of porous biomaterial for bone repair was successfully prepared using poly(l-lactic acid) short fibers of ≈700 μm and hydroxyapatite whiskers (W-HAs) of 60 μm (in average length). When W-HAs of ≤70 wt % were introduced, the composites could have about 80% porosity including numerous, interconnecting pores of &amp;gt;10 μm in diameter. W-HAs play an important role in formation of the pores, which allow penetration of nutriments and ingrowth of bone cells.

Dissolution Studies of Silicon Containing Self Setting Bone Cement

Silicon containing self setting bone cement has been prepared by adding silicon containing hydroxyapatite whisker to obtain a biomaterial having an improved resorption properties. Silicon containing calcium phosphate bone cement was composed of a-TCP: TeCP: DCPD: Si-HA whisker with a NH4H2PO4 as a setting liquid. From the XRD analysis, it was confirmed that calcium deficient hydroxyapatite phase appeared when it immersed in PBS solution. The dissolution rate of silicon containing calcium phosphate cement was measured in PBS solution and showed high dissolution rate. Based on in-vivo test, silicon containing self setting bone cement can be considered a useful material for bone bonding materials.

Tensile Properties of Hydroxyapatite Whisker Reinforced Polyetheretherketone

AbstractPolyetheretherketone (PEEK) was reinforced with 0-40 vol% hydroxyapatite (HA) whiskers using a novel powder processing and compression molding technique. A powder mixture was uniaxially pressed into a composite powder compact and compression molded into a flat composite bar using an open-channel die, such that the HA whiskers exhibited a preferred orientation along the length of the bar and tensile specimens. As expected, increased HA whisker reinforcement resulted in increased elastic modulus, but decreased ultimate tensile strength and strain- or work-to-failure. PEEK reinforced with 40 vol% HA whiskers exhibited an elastic modulus of 16-18 GPa. PEEK reinforced with 20 vol% HA whiskers had an ultimate tensile strength of 70-80 MPa. Human cortical bone exhibits an elastic modulus of 17-26 GPa and an ultimate tensile strength of 80-150 MPa in the longitudinal direction (direction of principal stress). Stiffness coefficients measured by ultrasonic wave propagation indicated a level orthotropy also similar to that of human cortical bone tissue.

Biphasic composite of Tricalcium phosphate reinforced with Hydroxyapatite Whiskers

AbstractBiphasic calcium phosphates have received considerable attention due to their optimum dissolution rate in the human body after implantation. These materials are composed of hydroxyapatite (HA) and resorbable tricalcium phosphate (TCP). In the present investigation, HA whiskers are reinforced into TCP to enhance the mechanical properties of this biphasic composite. Various amounts (30-50 wt%) HA whiskers are reinforced in TCP matrix. Microstructural characterization has been carried out using field-emission scanning electron microscope. Mechanical properties have been investigated by microindentation in a universal testing machine (UTM). As TCP is resorbable, it will dissolve in body fluid and there is a strong possibility for the faceted HA whiskers to interact with functional groups present in the body fluid surroundings.

Synthesis of hydroxyapatite whiskers by hydrolysis of α-tricalcium phosphate using microwave heating

Calcium hydroxyapatite (Ca 10(PO 4) 6(OH) 2, HAp) whiskers have been processed using microwave and conventional heating. During microwave heating, well developed whisker shaped HAp was formed by a hydrolysis reaction of α-Ca 3(PO 4) 2 (α-TCP) at 70–90 °C for 6–15 h. The hydrolysis time required for complete conversion of α-TCP to HAp was half than that required for conventional heating. The morphology of the reaction product was controlled by varying the hydrolysis temperature and time. The reaction product obtained at 70 °C for 15 h exhibited a conversion rate ∼95% to HAp, and a whisker-like morphology with an aspect ratio >10 (≤0.2 μm in diameter), a specific surface area ( S BET) of 5.34 m 2 g −1 and a Ca/P molar ratio of 1.66.

Large-sized hydroxyapatite whiskers derived from calcium tripolyphosphate gel

Hydrothermal methods using calcium phosphate gels as precursor have an advantage in high production efficiency of hydroxyapatite (HAp), but almost no large-sized HAp has been obtained so far. In the present work, large-sized HAp whiskers were prepared by a hydrothermal treatment of calcium tripolyphosphate gel controlled at pH 4–6 using various alcohols at 140 °C for 24 h. Long HAp whiskers of 30–50 μm in length were successfully prepared using 2-propanol; their sizes were several ten times larger than those prepared via conventional gel processes. The whisker length and aspect ratio were controlled by content of additive solvents with high specific dielectric constant.

Mechanical Properties of Hydroxyapatite Composites Reinforced with Hydroxyapatite Whiskers

Mechanical Properties of Hydroxyapatite Composites Reinforced with Hydroxyapatite Whiskers