Water resistance of bone-cements reinforced with bioceramics

The water absorption behavior of bone-cements of PMMA reinforced with 1.5 wt.%, 2.5 wt.%, and 3.5 wt.% silane-treated powders of hydroxyapatite (synthetic, or derived from bovine bones, or teeth enamel), β-tricalcium phosphate (TCP), bioactive glass (45S5), and zirconia, was investigated. The experimental results showed that addition of calcium phosphate in the polymeric matrix favors water absorption except in the case of enamel hydroxyapatite. Water uptake is also suppressed when 45S5-bioglass or zirconia is added. The solubility is not affected by addition of hydroxyapatite or 45S5-bioglass but it increases when β-TCP or zirconia is added. A superior behavior of bone-cements reinforced with bioglass-45S5 and enamel hydroxyapatite can be suggested.     

Ripening of calcium carbonate powders in low surface tension liquids

We have studied the ripening of calcium carbonate powders in a mother liquor for up to 18 days in relation to the content of different liquids having lower surface tension in comparison with water: dimethyl ketone, ethanol, and ethanolamine. As a result of ripening, we obtained nanopowders among which the largest specific surface area, up to 85 m²/g, was offered by the powders prepared from solutions containing ethanolamine. Their small particle size is due to the formation of an amorphous phase, about 69 wt %, and nanocrystalline vaterite with the smallest crystallite size, about 19 nm. The decrease in particle size and the associated increase in S are contributed by the low surface tension of ethanolamine: in combination with its high viscosity, this leads to the formation of powders consisting of unstable, loose aggregates.     

Hydroxyapatite-calcium carbonate ceramic composite materials

Hydroxyapatite/calcium carbonate (CC) composite powders containing up to 50 wt % CO₃²⁻, have been prepared via precipitation from aqueous solutions. According to chemical analysis data, the CO₃²⁻ content of the powders coincides with the intended one over the entire composition range studied. With increasing CO₃²⁻ content, the specific surface area of the powders decreases because of the formation and growth of large needlelike CC crystals up to 1.5 μm in size. The addition of low-melting-point alkali carbonates to the starting powder mixture reduces the sintering temperature of the powders to below 720°C, thereby preventing the thermal decomposition of CC. The highest bending strength, up to 76 MPa, is offered by the materials with the lowest CC content, about 20 wt %, and an average crystal size of 100 nm. The solubility of the composites gradually increases with CC content. In vitro experiments with a human fibroblast model (MTT test) demonstrate that the composites have zero cytotoxicity.     

Synthesis of hollow structural hydroxyapatite with different morphologies using calcium carbonate as hard template

Hydroxyapatite (HAp) with hollow structure was successfully synthesized by hydrothermal process of as-prepared calcium carbonate used as a hard template and calcium sources in a diammonium phosphate solution. Calcium carbonate was fabricated by precipitation, which possessed different morphologies such as balls, rods and blocks through regulating the amount of citric acid. The synthesized powders were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrograph (FT-IR), field-emission scanning electron microscope (FESEM) and high-resolution transmission electron microscopy (HRTEM) and nitrogen adsorption–desorption. Results indicated that different morphologies calcium carbonate could convert to hollow structural HAp with the higher BET surface area and the mesopores. Hydrothermal temperature and hydrothermal time play a slight role on transition percentage. As hydrothermal temperature and hydrothermal time increased, the conversion rate of calcium carbonate to hydroxyapatite increased. The possible formation mechanism of hydroxyapatite was preliminarily investigated. The resultants of HAp are interesting materials for drug delivery and sustained-release.     

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.     

Thermal decomposition of synthesised carbonate hydroxyapatite

Heat treatments are used when sintering hydroxyapatite to make porous blocks and granules and during plasma spraying of coatings. Calcium : phosphorus ratio is known to affect the thermal decomposition behavior of hydroxyapatite. Hydroxyapatite with carbonate ions substituted for phosphate ions is more similar in composition to bone mineral. While it has been shown that carbonate apatite may be sintered, relatively little is known about its high temperature stability. Various atmospheres have been used in investigations into the thermal stability of hydroxyapatites and carbonate hydroxyapatites, including nitrogen, wet carbon dioxide air, water vapor and wet oxygen, but few of these studies were directly comparable. Previous work has shown that loss of carbonate from CHA at high temperature is time dependent, which suggests that rapid high temperature treatment may prevent carbonate loss during processing. This study investigated the effect of dry carbon dioxide, carbon dioxide containing 3% water, nitrogen and nitrogen containing 3% water on the phase composition of hydroxyapatite containing between 1.0 and 11.5 wt % carbonate rapidly heated to temperatures of between 700 and 1400 °C. Carbonate ion substitution was observed to decrease the temperature at which crystallisation occurred to a minimum of 700 °C for 11.8 wt % carbonate apatite heated in wet atmospheres. Atmosphere was found to appreciably affect the crystallization temperature and phase transformations of carbonate apatite containing 7.8 wt % carbonate. In wet and dry carbon dioxide atmospheres, crystallisation began in this material at 1100 and 900 °C, TCP was formed at 1500 and 1300 °C respectively. The high temperature decomposition of carbonate hydroxyapatite would appear to depend on the composition of the apatite and the atmosphere in which it is heated.     

不同品种重质碳酸钙粉在外墙涂料中的应用

为考察不同矿种相同细度和相同矿种不同细度的重质碳酸钙粉体在涂料中的应用差异,设计3种外墙涂料基础配方,研究以不同重质碳酸钙粉为主要体质颜料的外墙涂料的白度、黏度、遮盖性、韧性、耐擦洗性。结果表明:在一定实验条件下,以高白度重质碳酸钙粉为体质颜料的涂料其白度越高,白度提高2%～11%;不同品种重质碳酸钙粉为体质颜料的涂料的韧性相差不大;以品质好、细度小的重质碳酸钙粉为体质颜料的涂料其耐洗刷性好;以粗细搭配配制成的重质碳酸钙粉为体质颜料的涂料,除涂料白度变化较小外,其黏度值降低,耐洗刷性、遮盖性分别为以单一重质碳酸钙粉为体质颜料的涂料的11.01%～27.50%,遮盖性能提高1.6%～19.0%,耐洗刷性提高0.5～3倍。     

Fabrication of mesoporous carbonated hydroxyapatite/carbon nanotube composite coatings by microwave irradiation method

Carbonated hydroxyapatite/carbon nanotube composite coatings (MHCs) with mesoporous structures were fabricated by electrophoretic deposition of nacre powders and carbon nanotubes on Ti6Al4V substrates followed by treatment with a phosphate buffer solution (PBS) by microwave irradiation method. The carbon nanotubes are dispersed uniformly on the whole MHCs. The conversion mechanism of the crack-free nacre/carbonate nanotube composite coatings (NCCs) to MHCs is a dissolution-precipitation reaction. After soaking in PBS, calcium ions are released from the nacre powders and react with phosphate ions to form carbonated hydroxyapatite nanoparticles. These nanoparticles aggregate to form mesopores with the pore sizes of ~ 3.9 nm among them. Simulated body fluid (SBF) immersion tests reveal that MHCs have a good in vitro bioactivity.     

Doped nanocrystalline calcium carbonate phosphates

The formation of nanocrystalline calcium carbonate phosphates doped with Fe²⁺, Mg², Zn²⁺, K⁺, Si⁴⁺, and Mn²⁺ has been studied by X-ray diffraction, IR spectroscopy, differential thermal analysis, and energy dispersive X-ray fluorescence analysis. The results indicate that the synthesis involves the formation of hydroxy carbonate complexes from the three calcium carbonate polymorphs (calcite, vaterite, and aragonite) in a solution of ammonium chloride and ammonium carbonate, followed by reaction with orthophosphoric acid. This ensures the preparation of a bioactive material based on chlorophosphates, octacalcium hydrogen phosphate, and calcium chloride hydroxide phosphates containing cation vacancies. Particle-size analysis data show that the materials contain nanoparticles down to 10 nm in size. Heat treatment of the doped calcium carbonate phosphates produces calcium hydroxyapatite containing cation vacancies, which can be used as a bioactive ceramic.     

Effect of sintering parameters on the density and microstructure of carbonate hydroxyapatite

This work documents an investigation into the effect of water on the density and microstructure of carbonate hydroxyapatite in carbon dioxide sintering atmospheres. Carbonate apatites with carbonate contents of between 3.2 and 7.8 wt % were precipitated and the precipitates were formed into dry gels. Isothermal and isochronal sintering experiments were performed under dry carbon dioxide and wet carbon dioxide (containing 3 wt % water) atmospheres. The effect of carbonate content was studied by using two gels both with a green density of 37% and with carbonate contents of 5.8 and 7.8 wt %. Both isothermal and isochronal experiments demonstrated that bloating of the apatite occurred and this behavior was associated with the loss of carbonate from the apatite. It was found that only in wet carbon dioxide atmospheres fully dense translucent carbonate apatite could be formed. 93% dense carbonate apatite was formed after 4 h sintering at temperatures as low as 700 °C. © 2000 Kluwer Academic Publishers     

Development of graded hydroxyapatite/CaCO<Subscript>3</Subscript> composite structures for bone ingrowth

Ceramic composites composed of constituents with different bone cell reactions present an interesting consideration for a new bone replacement material. The first component of the composite used in this study, hydroxyapatite, is known to be replaced by natural tissue significantly slower than the second, calcium carbonate, which has limited structural stability. A graded hydroxyapatite/calcium carbonate composite with bimodal component distribution was developed using a combined slip infiltration and dip-coating technique from a porous polyurethane sponge replica. A graded hydroxyapatite scaffold with porosities from 5 to 90% was produced and then infiltrated with a calcium carbonate slip and sintered. The resultant composite had improved mechanical properties compared with the monolith as measured by crushing and moduli tests.     

Effect of ammonium carbonate on formation of calcium-deficient hydroxyapatite through double-step hydrothermal processing

Double-step hydrothermal processing is a process where powder compacts of calcium phosphates are exposed to vapor of solvent solution, followed by being immersed in the solution. In the present study, we investigated the effects of ammonium carbonate on formation of calcium-deficient hydroxyapatite (CDHA) through double-step hydrothermal processing. The synthesized CDHA has high crystallinity when the solution has relatively low concentration of the ammonium carbonate ranging from 0.01 to 0.25 mol dm⁻³. Carbonate content in the prepared samples were distinctly increased with increasing the concentration of ammonium carbonate to indicate formation of carbonate-containing calcium-deficient hydroxyapatite (CHAp) with low crystallinity. Morphology of the CHAp formed on the compacts varied progressively from rods and rosette-like shape to irregular shape with increase in the initial concentration of the ammonium carbonate in the solution. Application of ammonium carbonate in the double-step hydrothermal processing allows fabrication of irregular-shaped CDHA containing carbonate ions in both phosphate and hydroxide site, with low crystallinity, when the initial concentration of ammonium carbonate was 0.5 mol dm⁻³ and more.     

Fabrication of mesoporous carbonated hydroxyapatite microspheres by hydrothermal method

Mesoporous carbonated hydroxyapatite microspheres (MCHMs) have been converted from calcium carbonate microspheres (CCMs) by hydrothermal method. After soaking the CCMs in disodium hydrogen phosphate solutions, carbonated hydroxyapatite nanoparticles are formed via a dissolution-precipitation reaction. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) reveal that the as-obtained samples are calcium deficient hydroxyapatite with B-type CO₃²⁻ substitution. The transmission electron microscopy (TEM) indicates that the MCHMs are composed of many nanoparticles within the whole microspheres. These nanoparticles aggregate to form mesopores with a pore size of 4.5-14.0 nm among them. The formation mechanism of MHAMs has been discussed.     

Effects of cooling conditions and chitosan coating on the properties of porous calcium phosphate granules produced from hard clam shells

The main inorganic components of clam shells are calcium carbonate and trace elements of magnesium, strontium, and zinc. Clam shells can be used as a calcium source to synthesize calcium phosphates, and these trace elements promote the growth of bone tissue and improve the performance of bioceramics. In this study, hydroxyapatite (HA) powders were synthesized from clam shells, and porous calcium phosphate granules were prepared through the gas foaming technique. In addition, the effects of a chitosan coating and cooling conditions on the strength of the porous granules were investigated. The results indicated that the samples produced under the furnace cooling condition were biphasic hydroxyapatite/β-tricalcium phosphate granules (HA/β-TCP), whereas the samples produced under the air-cooling condition were triphasic hydroxyapatite/β-tricalcium phosphate/α-tricalcium phosphate granules (HA/β-TCP/α-TCP). The compressive strength of the porous granules prepared through air cooling was 79% higher than that of the granules produced through furnace cooling. The compressive strength of the air-cooled sample after the subsequent application of the chitosan coating further increased by 21%. A degradability test revealed that the weight loss rate of the air-cooled samples was greater than that of the furnace-cooled samples, which was due to the presence of high-solubility α-TCP in the air-cooled samples.     

The biomimetic deposition of carbonate apatite induced by titanium base calcium enriched silica films

Abstract

In order to obtain a fast biomimetic coating on titanium substrates, calcium enriched silica films were prepared on pure titanium substrates by sol–gel method under the following conditions: pH?=?3 and the molar ratio of tetraethyl orthosilicate (TEOS)/H₂O/EtOH/Ca²⁺?=?1∶4∶11∶0·08. The titanium base calcium enriched silica film is soaked in a slightly supersaturated Ca/P solution, with the concentration of calcium ion and phosphate group being 1·5 times of that of simulated body fluid, for seven days, a uniform apatite layer is precipitated onto the surfaces of calcium enriched silica films, which is quite rapidly. The investigation adopted SEM, EDX, Fourier transform infrared spectroscope and XRD to indicate that the coating was carbonate hydroxyapatite. The results show that it is a feasible way to obtain carbonate hydroxyapatite through functionalising the pure titanium substrates by preparing calcium enriched silica films on it from a sol–gel method.     

Morphological control of precipitated calcium carbonates and phosphates by colloidal additives

The precipitation of calcium carbonate and calcium phosphates from solutions with and without additives such as hydroxyethyl cellulose, colloidal silica and potato starch, has been studied by X-ray diffraction and scanning electron microscopy. A constant rate of 10^–6 mol s^–1 of reactant was added into the mixed solutions with and without additives. Nucleation frequency and morphology were dramatically altered by the addition of colloidal potato starch. It was found to be effective for non-specific nucleation of calcite and hydroxyapatite and specific nucleation of monetite. The nucleation frequency of calcite is increased by adding starch by about a factor of 10⁴. Starch also alters the shape of hydroxyapatite to fibre-like.     

Calcium silicate ceramic scaffolds toughened with hydroxyapatite whiskers for bone tissue engineering

Calcium silicate possessed excellent biocompatibility, bioactivity and degradability, while the high brittleness limited its application in load-bearing sites. Hydroxyapatite whiskers ranging from 0 to 30 wt.% were incorporated into the calcium silicate matrix to improve the strength and fracture resistance. Porous scaffolds were fabricated by selective laser sintering. The effects of hydroxyapatite whiskers on the mechanical properties and toughening mechanisms were investigated. The results showed that the scaffolds had a uniform and continuous inner network with the pore size ranging between 0.5 mm and 0.8 mm. The mechanical properties were enhanced with increasing hydroxyapatite whiskers, reached a maximum at 20 wt.% (compressive strength: 27.28 MPa, compressive Young's modulus: 156.2 MPa, flexural strength: 15.64 MPa and fracture toughness: 1.43 MPa·m^1/2) and then decreased by addition of more hydroxyapatite whiskers. The improvement of mechanical properties was due to whisker pull-out, crack deflection and crack bridging. Moreover, the degradation rate decreased with the increase of hydroxyapatite whisker content. A layer of bone-like apatite was formed on the scaffold surfaces after being soaked in simulated body fluid. Human osteoblast-like MG-63 cells spread well on the scaffolds and proliferated with increasing culture time. These findings suggested that the calcium silicate scaffolds reinforced with hydroxyapatite whiskers showed great potential for bone regeneration and tissue engineering applications.     

Self-healing of surface cracks in mortars with expansive additive and crystalline additive

This research studies the self-healing potential of cement-based materials incorporating calcium sulfoaluminate based expansive additive (CSA) and crystalline additive (CA). Mortar specimens were used throughout the study. At the age of 28 days, specimens were pre-cracked to introduce a surface crack width of between 100 and 400 μm. Thereafter, the specimens were submerged in water to create a self-healing process. The experimental results indicated that the mixtures with CSA and CA showed favorable surface crack closing ability. The optimal mix design was found to be a ternary blend of Portland cement, 10 wt.% CSA and 1.5 wt.% CA, by which a surface crack width up to about 400 μm was completely closed, and the rate of water passing was dropped to zero within 28 days. It was hypothesized that the amount of leached Ca²⁺ from the matrix plays an important role on the precipitation of calcium carbonate which is the major healing product. The analyses showed that those specimens with CSA/CA additions released more Ca²⁺ than that control specimen. Moreover, those specimens with additives had higher pH value which would favor calcium carbonate precipitation.     

Preparation and characterization of selenite substituted hydroxyapatite

Selenite-substituted hydroxyapatite (Se-HA) with different Se/P ratios was synthesized by a co-precipitation method, using sodium selenite (Na₂SeO₃) as a Se source. Selenium has been incorporated into the hydroxyapatite lattice by partially replacing phosphate (PO₄^3 ?) groups with selenite (SeO₃^2 ?) groups. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) techniques reveal that substitutions of phosphate groups by selenite groups cause lower carbonate groups occupying at phosphate sites and change the lattice parameters of hydroxyapatite. The powders obtained are nano-crystalline hydroxyapatite when the Se/P ratios are not more than 0.1. The particle shape of Se-HA has not been altered compared with selenite-free hydroxyapatite but Se-incorporation reduces the crystallite size. The crystallinity was reduced as the Se/P ratios increased until amorphous phase (Se/P = 0.3) appeared in the Se-HA powder obtained, and then another crystal phase presented as calcium selenite hydrate (Se/P = 10). In addition, the sintering tests show that the Se-HA powders with the Se/P ratio of 0.1 have thermal stability at 900 °C for 2 h; hence they have great potential in the fabrication of bone repair scaffolds.     

Carbonated hydroxyapatite nanopowders for preparation of bioresorbable materials

Incorporation of carbonate ions to the crystal structure of carbonated hydroxyapatite (CHAp) leads to the formation of point defects (vacancies) in Ca‐ and OH‐sublattices as well as to microstrains revealed in CHAp nanocrystals. Various techniques, such as XRD, FTIR, TEM, FESEM/EDX, TG/DTA, AES (ICP), wet chemical analysis, Ca‐ionometry, microvolumetric analysis of evolved CO₂, BET adsorption, were applied to determine an efficiency of carbonate substitution, and to quantify the elemental composition, as well as to characterize the structure of the carbonated hydroxyapatite and the site(s) of carbonate substitution. It was shown that there is insignificant incorporation of Na into the crystal structure of HAp. Over the range of 0–4 % wt. (x<0.25), the substitution of OH‐ by CO₃^2‐ takes place leading to A‐Type of CHAp, further increase of CO₃^2‐‐content enhances PO₄^3‐‐substitution giving AB‐type of CHAp. According to in vitro test, the bioactivity of the samples is increasing with the growth of carbonate content due to accumulation of the defects in CHAp nanocrystals.