Hardness Of Hydroxyapatite Research Articles

The Effect of Limestone Particle Size on Hardness of Polylactic Acid/Hydroxyapatite Composite

Limestone is a mineral that mainly contained calcium oxide. Limestone has been used in manufacture industries for decades. Many researchers utilized limestone as a material for hydroxyapatite. Hydroxyapatite is a biocompatible material for human body and it is a potential material to restore the damaging bone. However, the hardness of hydroxyapatite is low. In this research, hydroxyapatite made from limestone and disodium hydrogen phosphate dihydrate were mixed with polylactic acid. The limestone was added as a source of calcium and increased the hardness of the composite. Polylactic acid was added to increase the compatibility between the components. The limestone particles sizes effect was studied using limestone powder size of 56 μm, 100 μm, and 150 μm. The composite was prepared by weighting, pre-heating, mixing, heating and pressing of the ingredients. The mechanical characterization was carried out through Micro Vickers Hardness Test. The composition of the composite was analyzed using X-ray Fluorescence. The surface morphology, interface adhesion, and element distribution were observed using scanning electron microscope and energy dispersive spectroscopy. The calcium-phosphor ratio of the composite similar with the one in the human bone. The composite that contained the finer size of limestone powder has the highest hardness. The ratio of the calcium to phosphor is 1.63.

Hydroxyapatite-carboxymethyl cellulose-graphene composite coating development on AZ31 magnesium alloy: Corrosion behavior and mechanical properties

In this study, hydroxyapatite (HA) coatings containing carboxymethyl cellulose (CMC) and graphene (Gr) were developed on AZ31 magnesium alloy through two-step electrophoretic deposition method. The morphology and chemical bonding of coatings were characterized and also the phase identification was done using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction, respectively. Moreover, the corrosion behavior of the applied coatings was compared with the bare AZ31 Mg alloy substrate in the simulated body fluid by the means of potentiodynamic polarization test and electrochemical impedance spectroscopy. Obtained results revealed that the novel HA-CMC-Gr coating possesses the highest corrosion resistance compared to the HA, HA-CMC, and HA-Gr coatings due to its uniform and compact structure. To investigate the mechanical properties and to elucidate the effect of CMC on the adhesion of coating-alloy interface, pull-off test was employed, where results demonstrated that the addition of CMC increases the adhesion force from 1.06 MPa to 1.62 MPa. Besides, the modulus of elasticity and the hardness of HA and HA-Gr composite coatings were compared by applying nanoindentation test. Interestingly, it is detected that the presence of Gr has considerably increased the elastic modulus of the coating by approximately 30% in comparison to the pure HA coating.

Hard Tissue-Forming Ability and Ultra-Micro Structure of Newly Developed Sponges as Scaffolds Made with Sodium Alginate Gel and Chondroitin Sulfate

To regenerate teeth and bones, a scaffold is essential. Hydroxyapatite has been used in many studies, but scaffolds made of hydrogel or sponge are also effective. The hardness of hydroxyapatite is a disadvantageous property for shaping. A sponge is suitable as a scaffold because the shape of the scaffold can be matched to the defect. Sodium alginate (AL) has excellent biocompatibility and a sponge can be made from this gel by lyophilization. The purpose of this study was to promote hard tissue formation with a sponge made of AL gel or AL gel and chondroitin sulfate (Chs). Sponges were made from AL gel, which were then used as a scaffold to investigate their effectiveness for the formation of hard tissue or bone. Hard tissue formation in the pores of these AL sponges was estimated in vitro and in vivo. In the sponge made from AL gel, the concentration of AL and the addition of Chs affected bone formation. Concentration of AL would affect the shape and size of the pores. ALP activity in the sponges was also enhanced by Chs. The amount of osteocalcin (OC) produced in the sponge by rat bone marrow cells increased depending on the AL and Chs concentrations in the gel. The level of OC amount in the sponges made from AL gel containing Chs was notable in vivo. Bone formation in the sponge in vivo was affected by the addition of Chs in AL gel. The quantity of OC and the bone formation in AL sponges in subcutaneous tissue in vivo suggested that AL sponges can be useful as a scaffold.

The Effects of Sintering Temperature on Densification and Mechanical Properties of Hydroxyapatite/Sodium Alginate Biocomposites

Hydroxyapatite (HA) has been studied for their excellent performances which are suitable for use in bone defects or regeneration of bone. Hydroxyapatite (HA) has poor mechanical properties which make it limited used in a load bearing area. In this case, sodium alginate (SA) was used to be mixed with hydroxyapatite (HA) by using precipitation method to increase the mechanical and physical properties. The mixing of hydroxyapatite/sodium alginate effectively increases the densification and hardness of hydroxyapatite. It could contribute to the development of the artificial implants of hydroxyapatite (HA) for bone implants applications in load bearing area. The behaviors during densification were studied together with the mechanical properties of samples. The influence of mixed powder and the sintering temperature on densification, microstructure and mechanical properties of hydroxyapatite (HA)/sodium alginate (SA) composite were studied. The maximum density were attained by 99.5/0.5% (HA/SA) at 1.47g/cm3 and 1.82g/cm3 for both temperature 1000°C and 1100°C respectively while, the maximum values of hardness were also attained by 99.5/0.5% for temperature 1000°C and 1100°C at 0.053GPa and 0.266GPa respectively.

Grain‐Size Dependence of the Hardness of Submicrometer and Nanometer Hydroxyapatite

Dense hydroxyapatite (HA) bodies (at 99% of the theoretical density or higher) with grain sizes ranging from 67 to 732 nm have been obtained via a process of morphology‐enhanced low‐temperature sintering at temperatures as low as 850°C. The Knoop indentation study reveals that the hardness of HA exhibits a linear dependence on the inverse square root of the grain diameter, consistent with the Hall–Petch relationship. This is the first report of the grain‐size dependence of the HA hardness in the nanometer range, and the phenomena observed suggest that the deformation of HA under indentation is dislocation mediated.

Nanocrystalline hydroxyapatite with simultaneous enhancements in hardness and toughness

Using a series of dense hydroxyapatite (HA) bodies with well controlled grain sizes ranging from sub-micrometers to nanometers, we show that simultaneous improvements in hardness and toughness can be attained for nanocrystalline (nc) HA. It is demonstrated that the hardness of HA follows the Hall–Petch relationship as the grain size decreases from sub-micrometers to nanometers. In the same grain size range, the toughness of HA increases by as much as 74% because of the enhanced crack deflection associated with a transition from transgranular to intergranular cracking, promoted by the reduced grain size in the nanoscale. The mechanisms for simultaneous enhancements in the hardness and toughness of nc HA are discussed. It is anticipated that the principle of simultaneous improvements in hardness and toughness discovered in this study is also applicable to other nc ceramics, particularly non-cubic ceramics, with anisotropic elastic and thermal expansion properties.

Mechanochemical–hydrothermal preparation of nano-crystallite hydroxyapatite using statistical design

Hydroxyapatite (HA) is extensively used in medicine as an ideal substitute for bone. Mean particle size, particle size distribution critically influence the hardness of HA and its mechanical properties. Statistical design was used to determine the optimum conditions of HA preparation by mechanochemical–hydrothermal procedure in MICROS mill for varying times, speed of milling as well as the quantity of surfactant. The produced powder was subjected to X-ray diffraction to analyse its crystallinity, phases, and crystal size calculations using Scherrer's equation. Reaction and milling time seems to be the most significant factor in determining particle size, the longer the reaction and milling time the smaller the crystal size with crystallite sizes ranged from 5.55 to 23.9 nm.

ハイドロキシアパタイトの多孔質化の試み

Calcium phosphate is a main inorganic constituent of bone, which can be interpreted as a composite material of calcium phosphate and collagen. This calcium phosphate shows a similar chemical composition with hydroxyapatite (HAP). Many devices with HAP have been developed for medical use because of its excellent biocompatibility. The hardness of HAP is adequate to supportive and protective functions in the skeleton and it also plays an important roll as homeostatic regulator of Ca and PO4 in the blood and other body fluids. The regulation process is closely connected to the remodeling of bone. Bone is renewed and reconstructed throughout the lifetime of the individual and therefore, HAP as biomaterial should be compatible to this dynamic remodeling process. We developed a new technology to control the pore size in HAP. The size of pore was controlled by applying HAP powder of nm-size and nylon- and acryl-monofilaments. The HAP processed with nylon-monofilament (f=80μm) showed the similar micro-pores to those of the Haversian canal in the natural bone. This porous HAP can be applied to a biofilter and a drug-delivery system.

Sintering behaviour and mechanical properties of hydroxyapatite and dicalcium phosphate

The sintering behaviour of powders of two calcium phosphates, namely hydroxyapatite (HA) and dicalcium phosphate (DCP), were studied at various temperatures and in various environments. The density, flexural strength and Knoop hardness of HA sintered in air for 4 h initially increased with the sintering temperature, reaching maxima at around 1150°C, and then decreased due to decomposition of HA into tri- (TCP) and tetracalcium phosphates. Sintering in vacuum caused decomposition of HA at lower temperatures, and consequently the mechanical properties were poorer than those of HA sintered in air. The densification and mechanical properties of DCP sintered in air and vacuum showed similar behaviour to those of HA. In air DCP underwent phase transformation from γ- to β- and to α-phases. In vacuum DCP started to decompose into tricalcium phosphate at 1000°C. To reduce dehydroxylation, HA powder was sintered in moisture at various temperatures up to 1350°C and X-ray diffraction study did not indicate any decomposition at the highest sintering temperature. The density, flexural strength and hardness of HA sintered in moisture increased with the sintering temperature and eventually reached plateaux at about 1300°C, but below 1200°C they were lower than those of HA sintered in air at corresponding temperatures. Thus, it is seen that dehydroxylation did not hinder sintering of HA. On the other hand, decomposition obstructed sintering of both HA and DCP.