HAP Composites Research Articles

Biomimetic growth of hydroxyapatite on phosphorylated electrospun cellulose nanofibers

In biomimicking the formation of collagen fiber/hydroxyapatite (HAp) in natural bone, electrospun cellulose nanofiber (CelluNF)/HAp composites were synthesized in simulated body fluid (SBF). Their morphology and structure were characterized by SEM, TEM, XRD and XPS. CelluNFs showed low bioactivity in inducing the growth of HAp. In order to improve this ability, CelluNFs were slightly phosphorylated with a degree of substitution of phosphate group of 0.28. The modified CelluNFs were highly effective in guiding the HAp growth along the fibers. The HAp crystal size in the composites was ca. 24nm, and the lattice spacing of (211) plane was 2.83Å. It was found that the HAps in the composites were calcium deficient. The CelluNF/HAp composites are highly porous materials with micro-, meso-, and macro-pores. A mechanism for the HAp growth on CelluNFs was presented. Such CelluNF/HAp composites can be potentially useful in the field of bone tissue engineering.

Friction, wear, and tensile properties of vacuum hot pressing crosslinked UHMWPE/nano‐HAP composites

Ultra high molecular weight polyethylene (UHMWPE) is a thermoplastic engineering plastic with excellent mechanical properties. In this study, nonirradiated and irradiated UHMWPE/nano-hydroxyapatite (nano-HAP) composites were prepared by vacuum hot-pressing method, and then friction, wear, and tensile properties were investigated. To explore mechanisms of these properties, differential scanning calorimetry, infrared spectrum, and scanning electron microscopy with energy dispersive spectrometry analysis were carried out on the samples. The results in this study indicated that reduced friction coefficients and wear rate could be obtained when nonirradiated and irradiated UHMWPE were filled with 7% nano-HAP. The irradiated UHMWPE/7% nano-HAP also had a synergistic function of wear reduction as compared with irradiated UHMWPE and nonirradiated UHMWPE/7% nano-HAP. Samples filled with 7% nano-HAP showed a brittle fracture behavior, and a linear relationship between modulus and crystallinity for a nonirradiated and irradiated sample was found in this study.

Comparative property study on extruded Mg–HAP and ZM61–HAP composites

Present investigation explored the development of Mg–HAP (magnesium-hydroxyapatite) and ZM61–HAP composites by melting and extrusion route. The ZM61 matrix consisted of 93 wt% Mg, 6 wt% Zn and 1 wt% Mn. The different amounts of chemically synthesized HAP powder (0, 5, 10, and 15 wt%) were added to Mg melts and mechanical stir was used for the dispersion of HAP particles in the matrix. The as-cast billets were subjected to homogenization at 450 °C and finally extruded at 320 °C. The presence of HAP particles during extrusion resulted in decrease of grain size of the composites. The ZM61–HAP composites showed finer grain and higher hardness than Mg–HAP composites. The tensile and compressive properties of ZM61–HAP were found to be higher than Mg–HAP composites.

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.

Preparation and applications of a variety of fluoroalkyl end-capped oligomer/hydroxyapatite composites

A variety of fluoroalkyl end-capped oligomers were applied to the preparation of fluorinated oligomer/hydroxyapatite (HAp) composites (particle size: 38–356 nm), which exhibit a good dispersibility in water and traditional organic solvents. These fluoroalkyl end-capped oligomer/HAp composites were easily prepared by the reactions of disodium hydrogen phosphate and calcium chloride in the presence of self-assembled molecular aggregates formed by fluoroalkyl end-capped oligomers in aqueous solutions. In these fluorinated HAp composites thus obtained, fluoroalkyl end-capped acrylic acid oligomers and 2-methacryloyloxyethanesulfonic acid oligomer/HAp nanocomposites afforded transparent colorless solutions toward water; however, fluoroalkyl end-capped N , N -dimethylacrylamide oligomer and acryloylmorpholine oligomer were found to afford transparent colorless solutions with trace amounts of white-colored HAp precipitants under similar conditions. HAp could be encapsulated more effectively into fluorinated 2-methacryloyloxyethanesulfonic acid oligomeric aggregate cores to afford colloidal stable fluorinated oligomer/HAp composites, compared to that of fluorinated acrylic acid oligomers. These fluorinated oligomer/HAp composites were applied to the surface modification of glass and PVA to exhibit a good oleophobicity imparted by fluorine. HAp formation was newly observed on the modified polyethylene terephthalate film surface treated with fluorinated 2-methacryloyloxyethanesulfonic acid oligomers and acrylic acid oligomer/HAp composites by soaking these films into the simulated body fluid.

Functionally Gradient and Micro‐Channeled Al2O3–(t‐ZrO2)/HAp Composites

Functionally gradient and micro‐channeled Al2O3–(t‐ZrO2)/HAp composites were fabricated using the multi‐pass extrusion process depending on the sintering temperature. The continuous pores were homogeneously formed in the second‐passed samples and their size was about 180 μm in diameter. The functionally gradient Al2O3–(t‐ZrO2)/HAp composites consisted of three layers, i.e., HAp/HAp–Al2O3–ZrO2/Al2O3–ZrO2. The relative density and bending strength increased as the sintering temperature increased and in the sample sintered at 1400°C, their maximum values were about 62.2% and 107.8 MPa, respectively.

Physical properties and in vitro bioactivity of hierarchical porous silica–HAP composites

In two recent papers (J. Andersson, S. Areva, B. Spliethoff and M. Lindén, Biomaterials, 2005, 26, 6827–6835 and J. Andersson, E. Johannessen, S. Areva, M. Järn and M. Lindén, J. Nanosci. Nanotechnol., 2006, 6, 2438–2444) we have presented new means of synthesizing silica–calcium phosphate (hydroxyapatite or tricalcium phosphate) composite materials, where the calcium phosphate is covered by a mesoporous layer of silica. These materials are bifunctional biomaterials, as they can be used both as drug carrier matrices and osteoconductive materials. Some of these materials, especially if synthesized according to a one-pot method, exhibit a very high in vitro bioactivity, and nucleate and grow calcium phosphate on their surfaces in less than 24 h if exposed to a simulated body fluid. In the present study, we have carried out a thorough characterization of the one-pot sol–gel derived composite materials by the means of solid state 29Si magic angle spinning (MAS) NMR, 31P MAS NMR, 23Na MAS NMR, and transfer of population in double resonance (TRAPDOR) NMR spectroscopy, scanning electron microscopy, and transmission electron microscopy. The aim of the study is to relate the material properties to the in vitro bioactivity. The reason for high bioactivity of the composites cannot be ascribed to the silica content, but primarily to the presence of a highly soluble second calcium phosphate phase, NaCaPO4, co-existing with the hydroxyapatite in the hybrid material. Furthermore, the hydroxyapatite becomes increasingly calcium deficient with increasing silica content, which adds to increase the bioactivity. Also the overall crystallinity of the apatitic calcium phosphate phase could contribute to the bioactivity of the composites in vitro.

조성 경사구조를 갖는 다공질 Al2O3-(t-ZrO2)/HAp 복합체의 제조 및 In-Vitro 실험

Functionally gradient porous Al₂O₃-(t-ZrO₂)/HAp composites consist of 3 layers were fabricated using the multi-pass extrusion process at the various temperatures. The continuous pores were homogeneously formed in the 2 nd passed samples and their size was about 180 ㎛ in diameter. In the porous composites sintered at 1200-1400℃, the relative density and bending strength increased with the sintering temperature. The maximum values of relative density and bending strength in the 2 nd passed Al₂O₃-(t-ZrO₂)/HAp composites were 6₂.₂% and 107.8MPa, respectively. In order to investigate the growth behavior of osteogenic cells on the functionally gradient porous Al₂O₃-(t-ZrO₂)/HAp composites, an in vitro test was performed, using human osteoblast-like MG-63 cells. The cells were well attached and grown on the rough surface of the inside of the functionally gradient porous body.

수산화아파타이트/알루미나 복합체의 기계적 특성에 미치는 불화물 첨가제의 영향

Hydroxyapatite (HAp, Ca₁?(PO₄)?(OH)₂)/alumina composites were fabricated with the addition of fluorides, such as MgF₂ and CaF₂. In this study, the effect of fluorides on the inhibition of phase decomposition and the mechanical properties of HAp was investigated. Due to the higher solubility of F ion in HAp structure, MgF₂ additive was more effective compared to CaF₂ additive in the lowering decomposition temperature of HAp. Therefore, the dissociation tendency of HAp was fully inhibited below 1400℃. The mechanical properties of HAp composites with MgF₂ additive showed higher value (flexural strength: ~170 ㎫, Vickers hardness: ~7 ㎬, fracture toughness: ~1.5 MPam 1/2 ) compared to MgF₂-free composites. The linear thermal expansion coefficient of HAp composites with MgF₂ showed the value of l6.4×l0??/℃ at 20~400℃.

Electrophoretic deposition and characterization of nano-sized hydroxyapatite particles

Hydroxyapatite Ca10(PO4)6(OH)2 (HAP), a major inorganic component of bone, has been used extensively for biomedical implant applications and bone regeneration due to its bioactive, biodegradable and osteoconductive properties [1–3]. However, the pure HAP is very brittle and its poor mechanical properties have limited its clinical applications. For this reason, a great deal of research concentrates on the development of HAP coatings and/or composites. Deposition of HAP coatings onto the surface of metal implants is a relatively recent development in clinical orthopaedics and has been achieved by a number of methods, such as plasma spraying [4, 5], dip coating [6], sputter coating [7], biomimetic coating [8], and electrophoretic deposition [9,10]. Plasma spraying [4] is the most developed process and thermally sprayed implants have been used in clinical practice for some years by now. However, plasma spraying, for extreme high temperatures of the plasma flame acting on HAP, results in the formation of resoluble molten phases. Unfortunately, they degrade in a short time after implantation, decreasing the adhesion of the HAP layer to the surrounding bone, as well as to the metal substrate. Furthermore, thermal spraying is a costly procedure and line-of-sight process, so it is not ideal for coating implants of complex shape or morphology. Electrophoretic deposition (EPD) uses an applied electric field to deposit charged particles from suspension in a liquid onto a substrate, which acts as an electrode. The rate of deposition can be easily controlled by varying the applied current density or voltage and the composition of the deposited layer is determined by the composition of the particles in suspension. EPD is a low-cost, simple, non-line-of-sight and flexible ceramic coating process, and it can be used to deposit coatings on substrates of complex shape or surface morphology. Previous research demonstrates that EPD is an attractive method for formation of biomedical implants and a number of advantages and important possibilities of this method have been suggested [10]. Just like many other ceramic coating techniques, EPDcoated implants need a subsequent densification stage. The main problem associated with this process is the difficulty in sintering of the coatings. High sintering temperature is required for densification of the green coatings [11]. Lower sintering temperature can lead

Effects of coatings on the mechanical properties of carbon fiber reinforced HAP composites

The HAP/carbon-fiber composite for bone re-construction was prepared and its mechanism of interfacial interaction between HAP and carbon fibers was investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected-area diffraction (SAD) in this paper. Results show that composite reinforced by carbon fibers with a layer of β-TCP coatings exhibits significantly better biomechanical properties, comparing these composites with non-coated fibers. It can be explained that the existence of β-TCP coatings, changing the surface properties of carbon fibers into hydrophilic, greatly enhance the interfacial bonding strength by adhering to the HAP matrix directly. On the other hand, the β-TCP coatings, as a mid-layer between HAP and carbon fibers, can reduce the gradient of thermal stress on its phase boundary with HAP matrix, which can eliminate the cracking problems during cooling of sintered. Consequently causing improvement of mechanical properties of composites.

1363 樹脂導入 HAp 多孔体の破壊靱性と破壊メカニズム

1363 樹脂導入 HAp 多孔体の破壊靱性と破壊メカニズム

Mechanical properties of bioactive amorphous calcium phosphate/methacrylate composites

Objectives. The aim of this study was to determine whether amorphous calcium phosphate (ACP)-containing composites, which have the ability to release mineralizing levels of Ca and PO 4 ions, have appropriate mechanical properties for use as base and lining materials. Methods. Composites of pyrophosphate-stabilized ACP particulates (mass fraction of 40%) and photo-activated methacrylate resins (mass fraction of 60%) were tested for biaxial flexure strength (BFS), diametral tensile strength (DTS), and compressive strength (CS). Hydroxyapatite (HAP; mass fraction of 40%), and micro-sized glass (mass fraction of 50%) composites as well as a commercial visible light curable base/liner were also tested. The significance between mean values was determined by Student–Newman–Keuls multiple comparisons ( p<0.05). Results. BFS of dry and wet (24 h at 37°C in water) ACP composites (60.3 and 62.0 MPa, respectively) were significantly lower than those of the comparison materials (79.2–109.3 MPa). CS values were likewise lower (62.9 MPa dry and 67.6 MPa wet vs 80.6–196.8 MPa) except for the wet base/liner (58.5 MPa). DTS of the dry ACP composite (21.8 MPa) was comparable with that of the HAP (22.8 MPa) and glass (25.5 MPa) composites, but lower than that of the base/liner (36.2 MPa). DTS decreased significantly when the ACP composite was wet (17.8 MPa). Significance. These results suggest that the remineralizing ACP polymeric composites, although mechanically weaker in some respects than other polymeric composites, have properties suitable for use as base and lining materials.