Hydroxyapatite Volume Fraction Research Articles

Simulation of tensile strength for polymer hydroxyapatite nanocomposites by interphase and nanofiller dimensions

AbstractSeveral models have been used in literature studies to describe the mechanical behavior of hydroxyapatite (HA) polymer nanocomposites. However, previous models have often overlooked the size of HA and the properties of the interphase. In this study, we further develop an equation originally proposed by Kolarik. This advanced equation predicts the tensile strength of polymer/HA nanocomposites by considering the interphase parameter (A), rod‐like HA size, HA concentration, and interphase properties, including depth and strength. We validate our method using experimental data from various examples and through parametric inspections. Both the strength and the depth of the interphase directly affect the ‘A’ value and, consequently, the strength of the nanocomposites. For instance, an HA radius (R) of 6 nm yields the highest ‘A’ value of 4.97, enhancing the nanocomposite strength by up to 250%. In contrast, ‘R’ value of 20 nm fails to reinforce the samples effectively. Additionally, the thickness of the interphase (t) and the concentration of HA directly handle the nanocomposite strength. The strength of the samples significantly improves by 137% and 160% with an interphase thickness of 50 nm and an HA volume fraction of 0.2, respectively. Generally, the length of HA and interphase characteristics (thickness and strength) directly control the strength of samples, but the HA radius has an inverse relationship with nanocomposite strength.Highlights Kolarik equation is developed to predict the tensile strength of polymer HA nanocomposites. Interphase parameter, HA size, HA concentration and interphase properties are considered. HA radius of 6 nm produces the maximum enhancement of nanocomposite strength by 250%. Interphase properties and concentration of HA directly control the nanocomposite strength. All parameters reasonably influence the strength of samples confirming the developed model.

Synthesis and Characterization of a Titanium-Based Functionally Graded Material-Structured Biocomposite using Powder Metallurgy.

This investigation aims at synthesizing and characterizing a biocomposite of hydroxyapatite (HA) and titanium (Ti) as a functionally graded material (FGM) via an economical powder metallurgy route. Ti particles were produced through drilling and chipping, followed by compaction and sintering. Ti foams, so obtained, were then infused with varying volume fractions of HA. The pure Ti foam control sample and the FGM composite samples were then subjected to various characterizations to validate their biocompatibility, structural strength, and integrity. The interface development between the load-bearing Ti implant and living tissue was resolved through an FGM structure, where the base of the implant consisted of load-bearing Ti and the outer periphery changed to HA gradually. HA/Ti specimens of different volume fractions were tested for density measurements, microstructure, hardness, and bioactivity. The bioactive behavior was investigated using the potentiodynamic polarization technique to measure the corrosion rate of the pure Ti foam (0/100 HA/Ti) and the FGM composite (10/90 HA/Ti) samples in a simulated body fluid (SBF). The results showed that the hardness of FGM composites, despite being less than that of 0/100 HA/Ti, was still within safe limits. The corrosion rate, however, was found to be decreased by a significant value of almost 40% for the 10/90 HA/Ti FGM composite sample compared to the pure Ti foam control sample. It was concluded that the optimum composition 10/90 HA/Ti sample offers improved corrosion resistance while maintaining a sufficient allowable hardness level.

Effect of hydroxyapatite:zirconia volume fraction ratio on mechanical and corrosive properties of Ti-matrix composite scaffolds

Ti-based scaffolds reinforced with zirconia and hydroxyapatite were produced successfully by a hybrid method with an eco-friendliness and low cost to obtain low elastic modulus (E) with sufficient physical, electrochemical and biological properties. The effect of simultaneous modification of the volume fraction of hydroxyapatite (HA) and zirconia (ZrO2) on scaffolds was investigated in terms of mechanical, corrosive, and antibacterial properties. Scanning electron microscopy with attached electron dispersive spectroscopy and X-ray diffraction were used for the characterization of scaffolds. Compression and electrochemical tests were performed to determine mechanical properties with detailed fracture mechanism and in-vitro corrosion susceptibility to simulated body fluid at 37 °C, respectively. Antibacterial tests were carried out by comparing the inhibition areas of E.coli and S.aureus bacteria. It was observed that the mechanical strength of the scaffolds decreased with increasing HA:ZrO2 volume fraction ratio. The lowest E was achieved (6.61 GPa) in 6:4 HA:ZrO2 composite scaffolds. Corrosion current density (Jcorr) values were calculated to be 21, 337, and 504 µA/cm2 for unreinforced Ti, 3:2 and 6:4 HA:ZrO2 reinforced scaffolds, respectively. The inhibition capacity of the 6:4 reinforced composite scaffold was found to be more effective against S.aureus bacteria than other scaffolds.

Effect of pH condition during sol-gel synthesis on the volume fraction of hydroxyapatite from sea coral

A research Hydroxyapatite synthesis has been carried out using the sol-gel method with variations in acidity (pH). Hydroxyapatite sources are obtained from marine corals from Banyuwangi. Hydroxyapatite synthesis is carried out by reacting calcium hydroxide Ca(OH)2 obtained from the powder coral with phosphoric acid (H3PO4) using the sol-gel method. synthesis is carried out with a pH variation from values 5 to 13 at intervals of 2 and is characterized using XRD (X-Ray Diffractometer). The XRD results show that for hydroxyapatite synthesis using the sol gel method the most optimal pH value is 11 with a volume fraction of 92.7% and the impurities are Lime CaO and Portlandite Ca(OH)2.

"Variances" and "in-variances" in hierarchical porosity and composition, across femoral tissues from cow, horse, ostrich, emu, pig, rabbit, and frog.

It is very well known that bone is a hierarchically organized material produced by bone cells residing in the fluid environments filling (larger) vascular pores and (smaller) lacunar pores. The extracellular space consists of hydroxyapatite crystals, collagen type I molecules, and water with non-collageneous organics. It is less known to which extent the associated quantities (mineral, organic, and water concentrations; vascular, lacunar, and extracellular porosities) vary across species, organs, and ages. We here investigate the aforementioned quantities across femoral shaft tissues from cow, horse, emu, frog, ostrich, pig, and rabbit; by means of light microscopy and dehydration-demineralization tests; thereby revealing interesting invariances: The extracellular volume fractions of organic matter turn out to be similar across all tested non-amphibian tissues; as do the extracellular volume fractions of hydroxyapatite across all tested mammals. Hence, the chemical composition of the femoral extracellular bone matrix is remarkably "invariant" across differently aged mammals; while the water content shows significant variations, as does the partitions of water between the different pore spaces. The latter exhibit strikingly varying morphologies as well. This finding adds to the ample "universal patterns" in the sense of evolutionary developmental biology; and it provides interesting design requirements for the development of novel biomimetic tissue engineering solutions.

Quantification of the trabecular bone volume fraction for bone marrow dosimetry in molecular radiotherapy by using a dual-energy (SPECT/)CT

A complete characterization of spongiosa (bone marrow plus trabecular bone) is required to calculate the absorbed dose to active bone marrow. Due to the complex microanatomy, it is necessary to apply non-conventional imaging methods in nuclear medicine. The aim of this study is validating a phantomless quantification method using dual-energy quantitative computed tomography (DEQCT) for the quantification of trabecular bone volume fraction for bone marrow dosimetry in molecular radiotherapy.First, a phantomless quantification method (mass fraction method) based on x-ray beam and detector sensitivity was validated in an integrated dual energy SPECT/CT and in a dual source computed tomography (DSCT) system for comparison. The validation was performed in a phantom consisting of different water, fat and hydroxyapatite compositions. Moreover, the European spine phantom (ESP) was used to simulate the spine geometry. Bone mineral content (BMC) of the whole vertebra and bone mineral density (BMD) in the spongiosa region of each phantom vertebra were measured using DEQCT and dual energy x-ray absorptiometry (DEXA). Lastly, BMC was measured in a patient using DEQCT and DEXA.Measured values of hydroxyapatite fraction and nominal values in the homemade phantom showed a good correlation. The relative error remained below 14.2%. Quantification of BMC (in whole vertebra) and BMD (in spongiosa) in the ESP showed a good agreement between measured values and nominal values. The relative error remained between 0.7% and 7.5% for BMCSPECT/CT, 1.1% and 7.7% for BMCDSCT, 5.4% and 32.0 for BMDSPECT/CT, and 59.4% and 10.0% for BMDDSCT. Quantification of BMC in lumbar vertebrae 1 and 2 of a patient showed relative errors of 7.6% and −8.4% between DEXA and DSCT.Our study shows that DEQCT using a mass fraction method (phantomless) enables quantification of hydroxyapatite in a clinical nuclear medicine setting. An overestimation of the hydroxyapatite volume fraction was observed in all quantified regions, in particular in the spongiosa region of ESP. This result might be related to insufficient information about the x-ray spectra and the detector sensitivity function.

Physical and Mechanical Properties Estimation of Ti/HAP Functionally Graded Material Using Artificial Neural Network

This study presents the effort in applying neural network-based system identification techniques by using Back- propagation algorithm to predict somephysical mechanical properties of functionally graded and compositesamples from Ti/HAP, these samples were fabricated by powder metallurgy method at various volume fraction of hydroxyapatite and at n equal (0.8, 1, and 1.2). Because of important of advanced materials such as FGMs as alternative industrial material, it is necessary to measure the physical properties of these materials such as porosity, density, hardness, compression …etc. Therefore the ANN will be used to estimate these properties and give a good performance to the network.

Acellular hydroxyapatite-collagen scaffolds support angiogenesis and osteogenic gene expression in an ectopic murine model: Effects of hydroxyapatite volume fraction.

Acellular hydroxyapatite (HA) reinforced collagen scaffolds were previously reported to induce angiogenesis and osteogenesis after ectopic implantation but the effect of the HA volume fraction was not investigated. Therefore, the objective of this study was to investigate the effect of HA volume fraction on in vivo angiogenesis and osteogenesis in acellular collagen scaffolds containing 0, 20, and 40 vol % HA after subcutaneous ectopic implantation for up to 12 weeks in mice. Endogenous cell populations were able to completely and uniformly infiltrate the entire scaffold within 6 weeks independent of the HA content, but the cell density was increased in scaffolds containing HA versus collagen alone. Angiogenesis, remodeling of the original scaffold matrix, mineralization, and osteogenic gene expression were evident in scaffolds containing HA, but were not observed in collagen scaffolds. Moreover, HA promoted a dose-dependent increase in measured vascular density, cell density, matrix deposition, and mineralization. Therefore, the results of this study suggest that HA promoted the recruitment and differentiation of endogenous cell populations to support angiogenic and osteogenic activity in collagen scaffolds after subcutaneous ectopic implantation. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2178-2188, 2016.

A multiscale analytical approach for bone remodeling simulations: Linking scales from collagen to trabeculae

Bone is a dynamic and hierarchical porous material whose spatial and temporal mechanical properties can vary considerably due to differences in its microstructure and due to remodeling. Hence, a multiscale analytical approach, which combines bone structural information at multiple scales to the remodeling cellular activities, could form an efficient, accurate and beneficial framework for the prognosis of changes in bone properties due to, e.g., bone diseases. In this study, an analytical formulation of bone remodeling integrated with multiscale micromechanical models is proposed to investigate the effects of structural changes at the nanometer level (collagen scale) on those at higher levels (tissue scale). Specific goals of this study are to derive a mechanical stimulus sensed by the osteocytes using a multiscale framework, to test the accuracy of the multiscale model for the prediction of bone density, and to demonstrate its multiscale capabilities by predicting changes in bone density due to changes occurring at the molecular level.At each different level, the bone composition was modeled as a two-phase material which made it possible to: 1) find a closed-form solution for the energy-based mechanical stimulus sensed by the osteocytes and 2) describe the anisotropic elastic properties at higher levels as a function of the stiffness of the elementary components (collagen, hydroxyapatite and water) at lower levels. The accuracy of the proposed multiscale model of bone remodeling was tested first by comparing the analytical bone volume fraction predictions to those obtained from the corresponding μFE-based computational model. Differences between analytical and numerical predictions were less than 1% while the computational time was drastically reduced, namely by a factor of 1million. In a further analysis, the effects of changes in collagen and hydroxyapatite volume fractions on the bone remodeling process were simulated, and it was found that such changes considerably affect the bone density at the millimeter scale. In fact, smaller tissue density induces remodeling activities leading to finally higher overall bone density. The multiscale analytical model proposed in this study potentially provides an accurate and efficient tool for simulating patient-specific bone remodeling, which might be of importance in particular for the hip and spine, where an accurate assessment of bone micro-architecture is not possible.

Adsorption of Fluoride from Water Using Sintered Clay-Hydroxyapatite Composites

AbstractThis paper proposes a new method of removing fluoride from drinking water. It presents the results of an experimental study on the effects of the temperature and mixture ratio on the adsorption characteristics of fluoride on clay-hydroxyapatite (C-HA) composites. The writers fabricated the C-HA materials from composites of hydroxyapatite (HA), redart clay, and fine wood chips (sawdust) in well-controlled proportions. Five different ratios of clay to HA at five different temperatures (500, 600, 700, 800, and 900°C) were sintered. The results of the adsorption tests demonstrated that the defluoridation capacity of the adsorbent that contains only HA decreases with increasing sintering temperature. The adsorption capacities of the C-HA adsorbents also increase with increasing HA volume fraction. The adsorption capacity of the porous C-HA mixtures and HA are well modeled by the Freundlich equation. The changes in the free energy reveal the spontaneous nature of the adsorption process. A particle and i...

Sol-Gel Derived Titania/Hydroxyapatite Layer on Titanium Substrate

In this study, calcium nitrate(Ca(NO3)2•4H2O) and phosphorus pentoxide(P2O5) were used as precursor to prepare hydroxyapatite(HA) layer by sol-gel method, followed by a dipping-coating method to coat HA layer onto Ti. Phase formation and microstructure were investigated by XRD and SEM to study the influence of atmosphere on the property of HA layer. The results revealed that there exists no large cracks in the layer which was heated in the nitrogen, leading to a good surface quality compared with the layer which was heated in the air. And there is no obvious difference in crystallinity and volume fraction of HA in the layer when adopting heat treatment in different atmospheres.

Variability in the elastic properties of bovine dentin at multiple length scales

Various methods are used to investigate the variability in elastic properties across a population of deciduous bovine incisor root dentin samples spanning different animals, incisor types, and locations within teeth. First, measurements of elastic strains by high-energy synchrotron X-ray scattering during compressive loading of dentin specimens provided the effective modulus–the ratio of applied stress to elastic phase strain–for the two main phases of dentin (hydroxyapatite crystals and mineralized collagen fibrils), shedding light on load transfer operating at the nanoscale between collagen and mineral phases. Second, Young’s moduli were measured at the macroscale by ultrasonic time-of-flight measurements. Third, thermogravimetry quantified the volume fractions of hydroxyapatite, protein and water at the macroscale. Finally, micro-Computed Tomography determined spatial variations of the mineral at the sub-millimeter scale. Statistical comparison of the above properties reveals: (i) no significant differences for dentin samples taken from different animals or different incisor types but (ii) significant differences for samples taken from the cervical or apical root sections as well as from different locations between buccal and lingual edges.

A multiscale modeling approach to scaffold design and property prediction

The optimum scaffold architecture for bone tissue regeneration is a porous structure with a narrow range of pore sizes, pore density, and a high degree of interconnectivity among pores. To achieve such a design, the microstructure of the scaffold material must be optimized in order to satisfy both biological and mechanical function requirements. In this paper, we present a multiscale modeling approach for designing a scaffold with an optimized porosity and mechanical properties made from a two-phase composite of spherical hydroxyapatite (HAp) particles embedded in a collagen matrix. In particular, first-principles computation is used to calculate the elastic properties and theoretical strengths of nanoscaled HAp particles. The constitutive properties of the HAp/collagen composites are subsequently computed as a function of HAp content via FEM-based micromechanical modeling. The constitutive relations of the composite are then utilized to optimize the mechanical properties of a three-dimensional scaffold for either cortical or cancellous bone by varying the pore size, pore density and volume fractions of HAp in the composite. For the pore size, pore density, volume fractions of HAp considered, the scaffold can be designed to match the mechanical properties of cancellous bone, but not those of cortical bone. The optimized scaffold is one with a pore diameter of 1000 μm, a channel diameter of 100 μm, 27% pore density and at least 20% HAp by volume.

Formulation of the Wear Behaviour of Nickel-Free Stainless-Steel/Hydroxyapatite Bio-Composites by Response Surface Methodology

This article deals with the formulation of wear behaviours of nickel-free stainless steel/hydroxyapatite bio-composites that were tested in air and Ringer's physiological solution. The model is based on experimental data related to wear tests of the composites with various hydroxyapatite contents under various wear loads and distances. The wear load, hydroxyapatite volume fraction, and wear distance were considered as the independent variables (input para-meters) and the wear volume loss as the target value (output parameter) to develop a database. A non-linear regression procedure based on simulated surface methodology was employed to develop an approximate formula for predicting the wear volume loss. The results obtained by formulation were compared with the results achieved from experiments for investigating their accuracy and agreement. Then, the formula was used for determining the wear volume loss sensitivity of the composites related to each effective parameter (wear load, hydroxyapatite content, and wear distance) on the wear behaviour of the composites. The results were presented by plots and graphs herein. Generally, this formula describes the wear behaviour of nickel-free stainless steel-hydroxyapatite bio-composites with good precision.

Mechanical Properties of ZrO<sub>2</sub> (Y<sub>2</sub>O<sub>3</sub>)-Al<sub>2</sub>O<sub>3</sub> Nanocomposites with Addition of Hydroxyapatite Prepared by Spark Plasma Sintering

TZP-3Y20A/HA composites with addition of different volume fraction of hydroxyapatite (HA) were fabricated successfully using spark plasma sintering (SPS). The densification behavior and mechanical properties of composites are investigated as a function of sintering temperature and HA content respectively. The density of TZP-3Y20A composite increases steadily with temperature and a maximum value of 97.8% is obtained after sintering at 1400°C. Sintering the TZP-3Y20A/HA composites at 1400°C led to the decomposition of HA in the samples. Flexural strength, fracture toughness and Vickers hardness values increase with increasing sintering temperature, show decrease trend with increasing of HA content at the same temperature. They compared well with densities obtained at different sintering temperature. The maximum flexural strength, fracture toughness and Vickers hardness of 967.1 MPa, 5.27 MPam1/2 and 13.26 GPa were achieved for TZP-3Y20A composite respectively. Flexural strength, fracture toughness and Vickers hardness values of TZP-3Y20A/HA composite fell within the value range of dense HA and of TZP-3Y20A composite.

J0401-2-6 放電プラズマ焼結法によるHA/β-TCP/TiH_2系傾斜機能材料の機械的特性の評価(生体材料およびその表面改質材(2))

Functionally gradient material (FGM) with four concentric layers was fabricated by spark plasma sintering (SPS). SPS can consolidate compacts at lower sintering temperature and in shorter sintering duration compared with conventional sinterings, such as hot-pressing or HIP. The FGMs were composed of hydroxyapatite (HA), β-tricalcium phosphate (β-TCP), and titanium hydride (TiH_2). The effect of sintering voltage, volume fraction of HA and β-TCP on the bending strength of FGMs will be discussed.

HDPE‐Al2O3‐HAp composites for biomedical applications: Processing and characterizations

The objective of this work is to demonstrate how the stiffness, hardness, as well as the biocompatibility property, of bioinert high-density polyethylene (HDPE) can be significantly improved by the combined addition of both bioinert and bioactive ceramic fillers. For this purpose, different volume fractions of hydroxyapatite and alumina, limited to a total of 40 vol %, have been incorporated in HDPE matrix. All the hybrid composites and monolithic HDPE were developed under optimized hot pressing condition (130 degrees C, 0.5 h, 92 MPa pressure). The results of the mechanical property characterization reveal that higher elastic modulus (6.2 GPa) and improved hardness (226.5 MPa) could be obtained in the developed HDPE-20 vol %-HAp-20 vol % Al(2)O(3) composite. Under the selected fretting conditions against various counterbody materials (steel, Al(2)O(3), and ZrO(2)), an extremely low COF of (0.07-0.11) and higher wear resistance (order of 10(-6) mm(3)/Nm) are obtained with the HDPE/20 vol % HAp/20 vol % Al(2)O(3) composite in both air and simulated body fluid environment. Importantly, in-vitro cell culture study using L929 fibroblast cells confirms favorable cell adhesion properties in the developed hybrid composite.

Mechanical characterization of ultra-high molecular weight polyethylene–hydroxyapatite nanocomposites

An experimental study of Ultra-High Molecular Weight Polyethylene (UHMWPE) and hydroxyapatite (HAP) nanocomposites for the purpose of joint prosthesis is investigated under quasi-static and dynamic loading conditions. By employing compression mold process, five different volume fractions of hydroxyapatite nanoparticle reinforced nanocomposites are made. Quasi-static tension and compression tests are performed using ASTM test methods. Dynamic compression characterization is performed using split Hopkinson pressure bar technique. The nanocomposite performance as a function of volume fraction under a typical loading rate is investigated. The results of the fabricated nanocomposites are compared with currently employed UHMWPE in the joint implants. For comparison purposes, separate sets of tests are performed on currently employed UHMWPE. This comparison provides a valid measure to identify the optimum volume fraction of hydroxyapatite that can be used without compromising the integrity of the UHMPWPE in joint prosthesis.

Morphology and quantitative characteristics of ceramic phase in Ti-HA composites with ⩽ 20vol% HA

This paper studied Ti-HA composites with low volume fractions of hydroxyapatite (HA), which are usually used as internal layers of functionally graded materials to withstand heavy load. Optical microscopy (OM), X-ray diffractometry (XRD), and scanning electron microscopy (SEM) were used to analyze the microstructure of cold-pressed composites after sintering at 1,100°C. Quantitative analysis of volume fractions and mean particle volumes of the ceramic phase was adopted to further discuss the reaction between Ti and HA. CaO and TixPy were produced in the Ti-HA reaction. With the increase of HA volume fraction, the Ti-HA reaction could be divided into three stages including stable initiation, stimulating term and re-stabilization according to the quantitative characteristics of the ceramic phase.

High strength and bioactive hydroxyapatite nano-particles reinforced ultrahigh molecular weight polyethylene

Nano-sized hydroxyapatite (HA) particles reinforced UHMWPE composite was developed for biomedical applications. The biocomposite with HA volume fraction of 0.5 was successfully processed by combined swelling/twin-screw extrusion, compression molding, and then hot drawing. SEM and EDAX characterization revealed that HA nano-particles were homogeneously dispersed in UHMWPE. WAXD showed that hot drawing effectively oriented the UHMWPE chains along the drawing direction. The composite exhibited tensile strength of 100 ± 22 MPa after hot drawing, which was comparable to that of cortical bone. The composite also exhibited great ability of inducing calcium phosphate precipitates on its surface in simulated body fluid, which was widely accepted as an indication of bioactivity.