Apatite-Forming Ability of Pectin Gels in Simulated Body Environment

Ca-containing anodic alumina (CAA) has been successfully prepared by anodizing Al film in an alkali solution at a constant voltage and subsequently electro-depositing calcium salts on and into porous anodic alumina. This paper studied the induction ability of Ca-containing anodic alumina (CAA) for calcium phosphates salts by immersing CAA in a simulated body fluid (SBF). The morphologies and compositions of the inductive coating are studied in depth using SEM and XRD. The results show that the porous Ca-containing anodic alumina (CAA) exhibits good induction ability of calcium phosphates in SBF. The Ca/P atomic ratio of the inductive coating on CAA after 7 days immersion in SBF is of 1.68 and the inductive coating on CAA is apatite. Consequently apatite /Al2O3 (anodic) composite has been obtained after apatite inductively formed on Ca-containing anodic alumina. Tafel polarization test indicates that apatite /Al2O3 composite has good anti-corrosion ability in simulated body environment. Therefore, Ca-containing anodic alumina films are promising substrates for fabricating functional coatings and its inductively formed apatite/Al2O3 composite is a promising material for hard tissue repair applications.

The essential prerequisite for an artificial material to show bone-bonding ability, i.e., bioactivity, is the formation of a bone-like apatite layer on its surface in a body environment. This can be reproduced in a simulated body fluid (SBF) with inorganic ion concentrations nearly equal to those of human blood plasma. It is known that some surface functional groups are effective for inducing heterogeneous apatite nucleation in SBF. Niobium is used clinically as a component in titanium alloys to improve their workability. In the present study, in order to investigate whether or not Nb-OH groups are effective for apatite nucleation, sol-gel-derived niobium oxide gels subjected to various heat treatments, and niobium metals subjected to various NaOH treatments were examined for their apatite-forming ability in SBF. The sol-gel-derived niobium oxide gels, both as-prepared, and heat-treated at 600°C, assumed an amorphous structure, and those heat-treated at 800 and 1000°C assumed orthorhombic and monoclinic structure, respectively. Apatite formation was observed on the niobium oxide gels both as-prepared, and heat-treated at temperatures below 800°C in SBF within one week, but not on the gel heat-treated at 1000°C. Niobium metals treated with the NaOH solutions did not form apatite on their surfaces, even after soaking in SBF for two weeks. It was confirmed that niobium metal formed a sodium niobate on its surface after the NaOH treatment, and that the sodium niobate formed a niobium oxide hydrogel by exchange of a Na+ ion with the H3O+ ion in SBF. Niobium oxide gels prepared by the sol-gel method have the ability to form an apatite layer on their surfaces in a body environment, when the gel has an amorphous phase structure, or an orthorhombic phase with abundant Nb-OH groups. Apatite deposition is not induced by Nb-OH groups formed on niobium metal after NaOH treatment and subsequent soaking in SBF. A niobium-based bioactive material can be developed through the design of a surface structure that effectively induces apatite nucleation.

Phosphate groups on materials surfaces are known to contribute to apatite formation upon exposure of the materials in simulated body fluid and improved affinity of the materials for osteoblast-like cells. Typically, polymers containing phosphate groups are organic matrices consisting of apatite-polymer composites prepared by biomimetic process using simulated body fluid. Ca(2+) incorporation into the polymer accelerates apatite formation in simulated body fluid owing because of increase in the supersaturation degree, with respect to apatite in simulated body fluid, owing to Ca(2+) release from the polymer. However, the effects of phosphate content on the Ca(2+) release and apatite-forming abilities of copolymers in simulated body fluid are rather elusive. In this study, a phosphate-containing copolymer prepared from vinylphosphonic acid, 2-hydroxyethyl methacrylate, and triethylene glycol dimethacrylate was examined. The release of Ca(2+) in Tris-NaCl buffer and simulated body fluid increased as the additive amount of vinylphosphonic acid increased. However, apatite formation was suppressed as the phosphate groups content increased despite the enhanced release of Ca(2+) from the polymer. This phenomenon was reflected by changes in the surface zeta potential. Thus, it was concluded that the apatite-forming ability of vinylphosphonic acid-2-hydroxyethyl methacrylate-triethylene glycol dimethacrylate copolymer treated with CaCl2 solution was governed by surface state rather than Ca(2+) release in simulated body fluid.

Organically modified silicates containing calcium ion have a potential to bond to bone via an apatite layer deposited on their surfaces in the body environment. In this study, we examined the relationship between apatite deposition and the microstructure of the organically modified silicates synthesized from tetraethoxysilane (TEOS) and poly (dimethylsiloxane) (PDMS) with a different amount of calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) and hydrochloric acid (HCl). Apatite deposition was evaluated in vitro using a simulated body fluid (Kokubo solution). Copolymerization was confirmed between TEOS and PDMS even if PDMS free from —SiOH termination are used as one of the starting materials. The porosity and Ca content incorporated in the structure depended on the amount of HCl, whereas analysis of 29Si MAS NMR spectra indicates that it caused few effects on the local structure around Si atoms. Apatite-forming ability is enhanced by optimal amounts of HCl and Ca (NO3)2·4H2O. The difference in apatite-forming ability among the hybrid gels was attributed to both Ca(II) contents in the structure and aggregation states of the Si—OH groups. Better bioactivity of the hybrid gels is achieved by the release of Ca(II) ions trapped in structure at gelation and the formation of hydrated silica rich in Si—OH.

A simulated body fluid (SBF) with ion concentrations similar to body fluid, proposed by Kokubo et al., is widely used to evaluate bone-bonding potential through the formation of an apatite layer. To be confident of the evaluation of the potential for the apatite formation in SBF, standard substrates are required. Although Na(2)O-CaO-SiO(2) glasses have been focused upon as candidate standard substrates, it has not been clarified whether the preparation conditions of the glasses affect their apatite formation potential in SBF. In this study, Na(2)O-CaO-SiO(2) glasses were prepared by a conventional melting-quenching method with different melting periods and annealing processes to examine their properties, including apatite formation in SBF. The Na(2)O-CaO-SiO(2) glasses show reproducible apatite-forming ability when prepared using moderate melting and annealing processes, and can be useful substrates to test the reproducibility of SBF.

So-called bioactive ceramics can directly bond to living bone through the apatite layer formed on their surfaces in the body. However, hard and brittle character of ceramics limits their clinical applications to low loaded portions. The apatite deposition on the bioactive ceramics is known to be triggered by a catalytic effect of silanol (Si-OH) groups formed on their surfaces and by release of calcium ions (Ca2+) that increases degree of supersaturation of the surrounding fluid with respect to the apatite. It is expected that organic modification of these components would produce bioactive materials with mechanical properties analogous to natural bone. We previously reported that bioactive organic-inorganic hybrids can be prepared from starch by modification with glycidoxypropyltrimethoxysilane (GPS) that provides with Si-OH groups and calcium chloride that releases calcium ions. In this study, we examined effect of synthetic conditions of the hybrids on their bioactivity and mechanical properties. We prepared several hybrids with different content of divinylsulfone as a cross-linking agent. Their bioactivity was examined in simulated body fluid (SBF, Kokubo solution) with inorganic ion concentrations nearly equal to those of human extracellular fluid. Materials that form the apatite on their surfaces in SBF are known to have a potential to show the bone-bonding. It was found that the added cross-linking agent did not decrease apatite-forming ability of the hybrids in SBF. Mechanical properties of the hybrids were further evaluated by a tensile test. Tensile strength and Young’s modulus increased with increasing content of divinylsulfone.

Apatite formation from simulated body fluid on various phases of TiO 2 thin films prepared by filtered cathodic vacuum arc deposition

Failure behavior of plasma-sprayed HAp coating on commercially pure titanium substrate in simulated body fluid (SBF) under bending load

Bioactive glasses and glass-ceramics exhibit osteoconductivity, which is the ability to form a direct bond with living bone tissue. This property is typically assessed by observing the formation of a hydroxyapatite layer in vitro using simulated body fluid (SBF), a solution designed to mimic the inorganic constituents of human blood plasma. SBF was developed by Kokubo et al. (T. Kokubo, H. Kushitani, S. Sakka, T. Kitsugi and T. Yamamuro, J. Biomed. Mater. Res., 1990, 24, 721-734), and its preparation and storage procedures are precisely regulated according to ISO 23317. However, despite following the regulations, SBF may precipitate during storage owing to local ion concentration fluctuations during preparation because it is a supersaturated solution of hydroxyapatite. The present study is focused on designing a preparation process that enhances the stability of SBF-type biomimetic solutions. Solutions with a nominal composition that is the same as that of SBF were prepared by mixing stock solutions containing calcium or phosphate ions separately. Depending on the preparation procedure, two types of solutions-modified biomimetic solution (mBS) and evolved biomimetic solution (eBS)-were proposed. To evaluate the stability of these solutions, variants with 1.5 times the concentration of the original solutions were prepared, and the prepared solutions were denoted as xSBF, xmBS, and xeBS (where x = 1.0 or 1.5). It was found that the formation of calcium phosphate precipitates in 1.5mBS and 1.5eBS was slower than that in 1.5SBF. Additionally, the precipitate in 1.5eBS exhibited a different morphology from hydroxyapatite precipitate, which may be due to a higher hydrogencarbonate concentration than that in 1.5SBF. eBS demonstrated increased stability and a higher concentration of carbonic acid species (carbonate ions) than SBF, while mBS showed increased stability with a lower carbonate concentration than SBF. The newly proposed routes allow the production of an aqueous solution supersaturated with hydroxyapatite as a conventional SBF that has the potential to evaluate apatite formation via in vitro examination under high initial stability.

An in vitro evaluation of PCL–TCP composites as delivery systems for platelet-rich plasma

The surfaces of ethylene-vinyl alcohol copolymer (EVOH) substrates were modified with silanol (Si-OH) groups, and their apatite forming ability was examined in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma or in a solution with ion concentrations 1.5 times those of SBF (1.5SBF). The surface modification of EVOH was carried out by reacting 3-isocyanatopropyltriethoxysilane, followed by hydrolysis of the ethoxysilyl groups into Si-OH groups. However, no apatite formation was observed on the EVOH substrate thus modified, even after 3 weeks in SBF and 1.5SBF. The Si-OH modified EVOH substrate was further modified by hydrolysis and polycondensation of tetraethyoxysilane (TEOS). It was found that the apatite forms on the TEOS-modified substrate within 3 weeks in 1.5SBF. These results suggest that the presence of a large amount of Si-OH groups (i.e., a cluster of Si-OH groups) on the substrate is prerequisite to apatite formation in the body environment. Apatite-EVOH composites prepared by this process might be useful as hard tissues substitutes.

3D printing of polylactic acid/boron nitride bone scaffolds: Mechanical properties, biomineralization ability and cell responses

Growth of Hydroxyapatite on Silk Fibers Using Simulated Body Fluid

The ingress of water and Kokubo simulated body fluid (SBF) into poly(2-hydroxyethyl methacrylate) (PHEMA), and its co-polymers with tetrahydrofurduryl methacrylate (THFMA), loaded with either one of two model drugs, vitamin B12 or aspirin, was studied by mass uptake over the temperature range 298–318 K. The polymers were studied as cylinders and were loaded with either 5 wt% or 10 wt% of the drugs. From DSC studies it was observed that vitamin B12 behaved as a physical cross-linker restricting chain segmental mobility, and so had a small anti-plasticisation effect on PHEMA and the co-polymers rich in HEMA, but almost no effect on the T g of co-polymers rich in THFMA. On the other hand, aspirin exhibited a plasticising effect on PHEMA and the co-polymers. All of the polymers were found to absorb water and SBF according to a Fickian diffusion mechanism. The polymers were all found to swell to a greater extent in SBF than in water, which was attributed to the presence of Tris buffer in the SBF. The sorptions of the two penetrants were found to follow Fickian kinetics in all cases and the diffusion coefficients at 310 K for SBF were found to be smaller than those for water, except for the polymers containing aspirin where the diffusion coefficients were higher than for the other systems. For example, for sorption into PHEMA the diffusion coefficient for water was 1.41 × 10−11 m2/s and for SBF was 0.79 × 10−11 m2/s, but in the presence of 5 wt% aspirin the corresponding values were 1.27 × 10−11 m2/s and 1.25 × 10−11 m2/s, respectively. The corresponding values for PHEMA loaded with 5 wt% B12 were 1.25 × 10−11 m2/s and 0.74 × 10−11 m2/s, respectively.

The present work deals with a comparative study of ceramic/ceramic composites for the development of scaffolds for biomedical applications. Wollastonite and forsterite were synthesized by a sol–gel combustion method. The influence of constituents and composition on apatite deposition was studied by fabricating wollastonite/forsterite composites. The X-ray diffraction pattern explains the bone like-apatite deposition within early stages of immersion. The atomic force microscopy micrographs revealed that with an increase in wollastonite content in the composites the roughness was enhanced. Dissolution studies further confirmed the rapid consumption of Ca and P ions from the simulated body fluid. Hence, apatite formation was observed to be more on the surface of a composite containing a higher amount of wollastonite. The results suggest that composites have more influence on the biomineralization activity when compared with pure bioceramics.