Apatite Formation Induced by Chitosan/Gelatin Hydrogel Coating Anchored on Poly(aryl ether nitrile ketone) Substrates to Promote Osteoblastic Differentiation.

Bone-like apatite is a promising coating of poly(ether ether ketone) (PEEK) for bone implantation. Poly(aryl ether nitrile ketone) containing phthalazinone moiety (PPENK) is a novel alternative for its easy synthesis. Here, chitosan/gelatin hybrid hydrogel coating is applied to induce the formation of apatite on the surface of PPENK substrate through biomineralization to improve its biocompatibility and osteogenic property. PPENK possessing allyl groups (PPENK-d) are synthesized and spin-coated on PPENK substrate to impart reactive groups. The hydrogel coating is prepared by the ultraviolet crosslinking of gelatin methacrylate (GelMA) and chitosan methacrylate (CSMA) on PPENK substrate. PPENK-d, GelMA, and CSMA are characterized by 1 H-NMR to confirm the designed structures. The presence of chitosan increases the chelation of calcium ions and thus induces the nucleation of apatite. The microstructural and compositional results reveal that the chitosan-containing hydrogel coating induced apatite coating yields a higher apatite quantity compared to the gelatin hydrogel coating. The apatite coatings on PPENK substrate promote the cytocompatibility and osteogenesis of MC3T3-E1 preosteoblasts in vitro.

Beyond dissolution: Xerostomia rinses affect composition and structure of biomimetic dental mineral in vitro.

Xerostomia, known as dry mouth, is caused by decreased salivary flow. Treatment with lubricating oral rinses provides temporary relief of dry mouth discomfort; however, it remains unclear how their composition affects mineralized dental tissues. Therefore, the objective of this study was to analyze the effects of common components in xerostomia oral rinses on biomimetic apatite with varying carbonate contents. Carbonated apatite was synthesized and exposed to one of the following solutions for 72 hours at varying pHs: water-based, phosphorus-containing (PBS), mucin-like containing (MLC), or fluoride-containing (FC) solutions. Post-exposure results indicated that apatite mass decreased irrespective of pH and solution composition, while solution buffering was pH dependent. Raman and X-ray diffraction analysis showed that the addition of phosphorus, mucin-like molecules, and fluoride in solution decreases mineral carbonate levels and changed the lattice spacing and crystallinity of bioapatite, indicative of dissolution/recrystallization processes. The mineral recrystallized into a less-carbonated apatite in the PBS and MLC solutions, and into fluorapatite in FC. Tap water did not affect the apatite lattice structure suggesting formation of a labile carbonate surface layer on apatite. These results reveal that solution composition can have varied and complex effects on dental mineral beyond dissolution, which can have long term consequences on mineral solubility and mechanics. Therefore, clinicians should consider these factors when advising treatments for xerostomia patients.

Effect of ethanol/TEOS ratios and amount of ammonia on the properties of copper-doped calcium silicate nanoceramics.

Calcium magnesium silicate glasses could be suggested for the synthesis of scaffolds for hard tissue regeneration, as they present a high residual glassy phase, high hardness values and hydroxyapatite-forming ability. The use of trace elements in the human body, such as Cu, could improve the biological performance of such glasses, as Cu is known to play a significant role in angiogenesis. Nano-bioceramics are preferable compared to their micro-scale counterparts, because of their increased surface area, which improves both mechanical properties and apatite-forming ability due to the increased nucleation sites provided, their high diffusion rates, reduced sintering time or temperature, and high mechanical properties. The aim of the present work was the evaluation of the effect of different ratios of Ethanol/TEOS and total amount of the inserted ammonia to the particle size, morphology and bioactive, hemolytic and antibacterial behavior of nanoparticles in the quaternary system SiO2-CaO-MgO-CuO. Different ratios of Ethanol/TEOS and ammonia amount affected the size and morphology of bioactive nanopowders. The optimum materials were synthesized with the highest ethanol/TEOS ratio and ammonia amount as verified by the enhanced apatite-forming ability and antibacterial and non-hemolytic properties.

Lanthanum-silicate-substituted apatite synthesized by fast mechanochemical method: Characterization of powders and biocoatings produced by micro-arc oxidation.

Lanthanum-silicate substituted apatite with equal concentrations of the substituents in the range of 0.2-6.0 mol were produced by a fast method - mechanochemical synthesis. This method makes it possible to synthesize a nanosized single-phase product by activating reaction mixtures containing CaHPO4, CaO, La(OH)3 and SiO2·H2O for 25-30 min in AGO-2 and AGO-3 planetary mills. The structure of the apatites was investigated by the FTIR and XRD methods. It was found that the synthesized samples with substituent concentrations up to 2 mol are substituted oxy-hydroxyapatites, at higher concentrations, they are substituted oxyapatites. The mechanochemically synthesized apatite with a substituent concentration of 0.5 mol was used for depositing biocoatings on titanium substrates by the micro-arc oxidation method. The structure of the coatings is mainly amorphous. In vitro biological tests demonstrated high biocompatibility of the coatings and the absence of cytotoxic action on mesenchymal stem cells.

Fluoride containing bioactive glass composite for orthodontic adhesives - Apatite formation properties.

OBJECTIVES: Dental materials that can form apatite offer the potential to not only prevent demineralisation but enhance remineralisation of the enamel. The objective of this study was to investigate the ability of a novel BAG-resin adhesive to form apatite in 3 immersion media. METHODS: A novel fluoride containing BAG-resin adhesive described previously, with 80% by weight filler load, was used to fabricate 90 disks. Each disk was immersed in 10ml of either tris buffer (TB), or artificial saliva at pH=7 (AS7) or pH=4 (AS4). At ten time points (from 6h to 6 months), three disks were taken from each of the solutions and investigated by ATR-FTIR, XRD and SEM. RESULTS: The BAG-resin formed apatite on the disk surface, which increased with time, especially in AS4 and AS7. The apatite crystals formed in AS7 were highly oreintated and the oreintation increased with time. SIGNIFICANCE: This novel BAG-resin adhesive differs from the currently used adhesives by promting apatite formation, particularly under acidic conditions. Thus, applied in the clinical situation to bond orthodontic brackets, it may discourage the frequent occurrence of white spot lesion formation around the brackets.

In-vitro apatite formation capacity of a bioactive glass - containing toothpaste.

OBJECTIVES: The in-vitro dissolution of bioactive glass-based toothpastes and their capacity to form apatite-like phases in buffer solutions have been investigated. MATERIALS AND METHODS: The commercial toothpaste samples were tested on immersion in artificial saliva, Earle's salt solution and Tris buffer for duration from 10min to four days. The powder samples collected at the end of the immersion were studied using solid-state 31P and 19F nuclear magnetic resonance spectroscopy (NMR), X-ray powder diffraction and Fourier transform infrared (FTIR) spectroscopy. The fluoride concentration in the solution remained after the immersion was measured. RESULTS: In artificial saliva and in presence of sodium monofluorophosphate (MFP), the bioactive glass and bioactive glass-based toothpastes formed fluoridated apatite-like phases in under 10min. A small amount of apatite-like phase was detected by 31P NMR in the toothpaste with MFP but no bioactive glass. The toothpaste with bioactive glass but no fluoride formed an apatite-like phase as rapidly as the paste containing bioactive glass and fluoride. By contrast, apatite-like phase formation was much slower in Earle's salt solution than artificial saliva and slower than Tris buffer. CONCLUSIONS: The results of this lab-based study showed that the toothpaste with MFP and bioactive glass formed a fluoridated apatite in artificial saliva and in Tris buffer, as did the mixture of bioactive glass and MFP. CLINICAL SIGNIFICANCE: The presence of fluoride in bioactive glass-containing toothpastes can potentially lead to the formation of a fluoridated apatite, which may result in improved clinical effectiveness and durability. However, this should be further tested intra-orally.

"Fabrication of arbitrarily shaped carbonate apatite foam based on the interlocking process of dicalcium hydrogen phosphate dihydrate".

Carbonate apatite (CO3Ap) foam with an interconnected porous structure is highly attractive as a scaffold for bone replacement. In this study, arbitrarily shaped CO3Ap foam was formed from α-tricalcium phosphate (α-TCP) foam granules via a two-step process involving treatment with acidic calcium phosphate solution followed by hydrothermal treatment with NaHCO3. The treatment with acidic calcium phosphate solution, which is key to fabricating arbitrarily shaped CO3Ap foam, enables dicalcium hydrogen phosphate dihydrate (DCPD) crystals to form on the α-TCP foam granules. The generated DCPD crystals cause the α-TCP granules to interlock with each other, inducing an α-TCP/DCPD foam. The interlocking structure containing DCPD crystals can survive hydrothermal treatment with NaHCO3. The arbitrarily shaped CO3Ap foam was fabricated from the α-TCP/DCPD foam via hydrothermal treatment at 200 °C for 24 h in the presence of a large amount of NaHCO3.

A soft environmental control effect of apatite doped with mineral traces in the fowl droppings.

Fowl-dropping apatite (Ca10-z[PO4]6-z[OH]2-z) synthesized from carbonized, incinerated fowl droppings contains PO4 and OH groups that are partially substituted by CO32- ions. It shows stronger ion conductivity than commercially available hydroxyapatite in a wide range of temperatures from 23°C to 800°C. Fowl-dropping apatite readily adsorbs NO2 and SO2 gases and, without re-releasing these gases, slowly decomposes them at room temperature under sunlight via ultraviolet-visible (UV-Vis) irradiation. A limited amount of minerals and organics contained in fowl droppings causes light-induced activities in fowl-dropping apatite with a crystal structure that has a developed c face; this initiates excitation-induced atomic transfer on the solid surface derived from PO4 exposed on the c face, which then advances the decomposition reaction.

Mechanochemical synthesis of zinc-apatitic calcium phosphate and the controlled zinc release for bone tissue engineering.

In this study, in order to control zinc (Zn)-release from calcium phosphate (CaP), the crystalline forms of CaP-containing Zn were modified by wet ball milling and/or heat treatment. The CaP (CaO:CaHPO4:ZnO = 7:20:3, molar ratio) was ground in a ball mill with the addition of purified water, and the ground products were heated to 400 °C and 800 °C. The physicochemical properties of these ground products were measured by powder X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy and energy-dispersive X-ray spectroscopy. Zn release characteristics from the samples were evaluated using a dissolution tester. The results of XRD and IR suggested that the structures of the starting materials were destroyed after 2.5 h of grinding, and new apatite-like amorphous solid containing Zn was generated. The Zn-release from the ground products was markedly suppressed after 2.5 h of grinding.

Biomimetic apatite-based composite materials obtained by spark plasma sintering (SPS): physicochemical and mechanical characterizations.

Nanocrystalline calcium phosphate apatites are biomimetic compounds analogous to bone mineral and are at the origin of the bioactivity of most biomaterials used as bone substitutes. Their unique surface reactivity originates from the presence of a hydrated layer containing labile ions (mostly divalent ones). So the setup of 3D biocompatible apatite-based bioceramics exhibiting a high reactivity requests the development of «low¼ temperature consolidation processes such as spark plasma sintering (SPS), in order to preserve the characteristics of the hydrated nanocrystals. However, mechanical performances may still need to be improved for such nanocrystalline apatite bioceramics, especially in view of load-bearing applications. The reinforcement by association with biopolymers represents an appealing approach, while preserving the advantageous biological properties of biomimetic apatites. Herein, we report the preparation of composites based on biomimetic apatite associated with various quantities of microcrystalline cellulose (MCC, 1-20 wt%), a natural fibrous polymer. The SPS-consolidated composites were analyzed from both physicochemical (X-ray diffraction, Fourier transform infrared, solid state NMR) and mechanical (Brazilian test) viewpoints. The preservation of the physicochemical characteristics of apatite and cellulose in the final material was observed. Mechanical properties of the composite materials were found to be directly related to the polymer/apatite ratios and a maximum crushing strength was reached for 10 wt% of MCC.

The structure and properties of the carbon non-wovens modified with bioactive nanoceramics for medical applications.

The paper presents the results of the manufacture of carbon fibers (CF) from polyacrylonitrile fiber precursor containing bioactive ceramic nanoparticles. In order to modify the precursor fibers two types of bio-glasses and wollastonite in the form of nanoparticles were used. The processing variables of the thermal conversion of polyacrylonitrile (PAN) precursor fibers into carbon fibers were determined using the FTIR method. The carbonization process of oxidized PAN fibers was carried out up to 1000°C. The carbon fibers were characterized by a low ordered crystalline structure. The bioactivity tests of carbon fibers modified with a ceramic nanocomponent carried out in the artificial serum (SBF) revealed the apatite precipitation on the fibers' surfaces.

In vitro apatite formation and drug loading/release of porous TiO2 microspheres prepared by sol-gel processing with different SiO2 nanoparticle contents.

Bioactive titania (TiO2) microparticles can be used as drug-releasing cement fillers for the chemotherapeutic treatment of metastatic bone tumors. Porous anatase-type TiO2 microspheres around 15 µm in diameter were obtained through a sol-gel process involving a water-in-oil emulsion with 30:70 SiO2/H2O weight ratio and subsequent NaOH solution treatment. The water phase consisted of methanol, titanium tetraisopropoxide, diethanolamine, SiO2 nanoparticles, and H2O, while the oil phase consisted of kerosene, Span 80, and Span 60. The resulting microspheres had a high specific surface area of 111.7 m(2)·g(-1). Apatite with a network-like surface structure formed on the surface of the microspheres within 8 days in simulated body fluid. The good apatite-forming ability of the microspheres is attributed to their porous structure and the negative zeta potential of TiO2. The release of rhodamine B, a model for a hydrophilic drug, was rapid for the first 6 h of soaking, but diffusion-controlled thereafter. The burst release in the first 6h is problematic for clinical applications; nonetheless, the present results highlight the potential of porous TiO2 microspheres as drug-releasing cement fillers able to form apatite.

Isolation and preparation of nanoscale bioapatites from natural sources: a review.

This review summarizes recent work on isolating and preparing bioapatites from various natural sources. First, the physicochemical properties of bioapatites are described and discussed. Then, a general summary of natural (animals and vegetals) sources for bioapatite production from various environments (terrestrial and water) is made. Special attention is paid to describing individual methods for acquiring bioapatite from biogenic sources, e.g., direct isolation of bioapatite, or indirect biomimetic synthesis, with the aid of naturally derived biomolecules or biomembranes. The results of a comprehensive physicochemical characterization and a biological evaluation (in vitro and in vivo) for bioapatites and their applications in clinical practice are presented. Finally, future perspectives are summarized and discussed.

In vitro apatite formation on porous anodic alumina induced by a phosphorylation treatment.

In this study, a phosphorylation treatment of porous anodic alumina (PAA) was performed by wet impregnation in phosphoric acid and a subsequent heat treatment. The PAA and phosphorylated PAA specimens were analyzed using a field emission scanning electron microscope, an energy-dispersive X-ray spectrometer, and Fourier transform infrared spectroscopy. The apatite-forming ability of the phosphorylated PAA was evaluated by soaking the specimens in simulated body fluid for 1, 3, and 7 days. The surface microstructures and chemical property changes after soaking in simulated body fluid were again characterized by field emission scanning electron microscope, energy-dispersive X-ray spectrometer, and Fourier transform infrared spectroscopy. Results of this study demonstrated that the functional -PO4 groups introduced onto the PAA surface dramatically promoted the deposition of bone-like apatite on PAA. The results from this study indicated that the phosphorylation treatment of anodic alumina is an effective method for inducing bone-like apatite formation, and this phosphorylated PAA can be a promising candidate to be used as bioactive surface coatings on implant metals and alloys for orthopedic and dental applications.

Controlled release of strontium ions from a bioactive Ti metal with a Ca-enriched surface layer.

A nanostructured sodium hydrogen titanate layer ∼1µm in thickness was initially produced on the surface of titanium metal (Ti) by soaking in NaOH solution. When the metal was subsequently soaked in a mixed solution of CaCl2 and SrCl2, its Na ions were replaced with Ca and Sr ions in an Sr/Ca ratio in the range 0.18-1.62. The metal was then heat-treated at 600°C to form strontium-containing calcium titanate (SrCT) and rutile on its surface. The treated metal did not form apatite in a simulated body fluid (SBF) even after 7days. When the metal formed with SrCT was subsequently soaked in water at 80°C, the treated metal formed bone-like apatite on its surface within 1day in SBF since the Ca ions were partially replaced with H3O(+) ions. However, it released only 0.06ppm of Sr ions even after 7days in phosphate-buffered saline. When the metal was soaked after the heat treatment in 1M SrCl2 solution instead of water, the treated metal released 0.92ppm of Sr ions within 7days while maintaining its apatite-forming ability. The Ti formed with this kind of bioactive SrCT layer on its surface is expected to be highly useful for orthopedic and dental implants, since it should be able to promote bone growth by releasing Sr ions and tightly bond to the bone through the apatite formed on its surface.

Three-dimensional printing of strontium-containing mesoporous bioactive glass scaffolds for bone regeneration.

In this study, we fabricated strontium-containing mesoporous bioactive glass (Sr-MBG) scaffolds with controlled architecture and enhanced mechanical strength using a three-dimensional (3-D) printing technique. The study showed that Sr-MBG scaffolds had uniform interconnected macropores and high porosity, and their compressive strength was ∼170 times that of polyurethane foam templated MBG scaffolds. The physicochemical and biological properties of Sr-MBG scaffolds were evaluated by ion dissolution, apatite-forming ability and proliferation, alkaline phosphatase activity, osteogenic expression and extracelluar matrix mineralization of osteoblast-like cells MC3T3-E1. The results showed that Sr-MBG scaffolds exhibited a slower ion dissolution rate and more significant potential to stabilize the pH environment with increasing Sr substitution. Importantly, Sr-MBG scaffolds possessed good apatite-forming ability, and stimulated osteoblast cells' proliferation and differentiation. Using dexamethasone as a model drug, Sr-MBG scaffolds also showed a sustained drug delivery property for use in local drug delivery therapy, due to their mesoporous structure. Therefore, the 3-D printed Sr-MBG scaffolds combined the advantages of Sr-MBG such as good bone-forming bioactivity, controlled ion release and drug delivery and enhanced mechanical strength, and had potential application in bone regeneration.

Relationship between in vitro apatite-forming ability measured using simulated body fluid and in vivo bioactivity of biomaterials.

In a large number of studies, it has been assumed that the in vitro apatite-forming ability measured by simulated body fluid (SBF) test is a predictor of in vivo bioactivity. Several researchers have argued in favor and against this assumption; but the actual experimental evidence is not yet fully examined. The purpose of this study is to review the currently available evidence that supports or rejects the above-mentioned assumption. Ultimately, it is important that SBF tests could simulate the actual physiological conditions experienced by biomaterials within the human body. Given that in vivo animal experiments provide the best pre-clinical test conditions, all studies in which both in vitro apatite forming ability and in vivo performance of two or more biomaterials are compared were found by searching the literature. From all studies that satisfied the inclusion criteria (33), in 25 studies in vitro apatite-forming ability could predict the relative performance of the tested biomaterials in vivo. In 8 studies, in vitro performance did not correctly predict the relative in vivo performance. In majority of failure cases (i.e. 5/8), none of the compared biomaterials formed apatite, while all compared biomaterials showed bioactive behavior in vivo. It is therefore concluded that, in majority of cases, the SBF immersion test has been successful in predicting the relative performance of biomaterials in vivo. However, the details of the test protocols and the (expected) mechanisms of bioactivity of tested biomaterials should be carefully considered in the design of SBF immersion tests and in interpretation of their results. Certain guidelines are devised based on the results of this review for the design of SBF immersion test protocols and interpretation of the test results. These guidelines could help in designing better SBF test protocols that have better chances of predicting the bioactivity of biomaterials for potential application in clinical orthopedics.

Nanoscale confinement controls the crystallization of calcium phosphate: relevance to bone formation.

A key feature of biomineralization processes is that they take place within confined volumes, in which the local environment can have significant effects on mineral formation. Herein, we investigate the influence of confinement on the formation mechanism and structure of calcium phosphate (CaP). This is of particular relevance to the formation of dentine and bone, structures of which are based on highly mineralized collagen fibrils. CaP was precipitated within 25-300 nm diameter, cylindrical pores of track etched and anodised alumina membranes under physiological conditions, in which this system enables systematic study of the effects of the pore size in the absence of a structural match between the matrix and the growing crystals. Our results show that the main products were polycrystalline hydroxapatite (HAP) rods, together with some single crystal octacalcium phosphate (OCP) rods. Notably, we demonstrate that these were generated though an intermediate amorphous calcium phosphate (ACP) phase, and that ACP is significantly stabilised in confinement. This effect may have significance to the mineralization of bone, which can occur through a transient ACP phase. We also show that orientation of the HAP comparable, or even superior to that seen in bone can be achieved through confinement effects alone. Although this simple experimental system cannot be considered, a direct mimic of the in vivo formation of ultrathin HAP platelets within collagen fibrils, our results show that the effects of physical confinement should not be neglected when considering the mechanisms of formation of structures, such as bones and teeth.

Insight into biological apatite: physiochemical properties and preparation approaches.

Biological apatite is an inorganic calcium phosphate salt in apatite form and nano size with a biological derivation. It is also the main inorganic component of biological hard tissues such as bones and teeth of vertebrates. Consequently, biological apatite has a wide application in dentistry and orthopedics by using as dental fillers and bone substitutes for bone reconstruction and regeneration. Given this, it is of great significance to obtain a comprehensive understanding of its physiochemical and biological properties. However, upon the previous studies, inconsistent and inadequate data of such basic properties as the morphology, crystal size, chemical compositions, and solubility of biological apatite were reported. This may be ascribed to the differences in the source of raw materials that biological apatite are made from, as well as the effect of the preparation approaches. Hence, this paper is to provide some insights rather than a thorough review of the physiochemical properties as well as the advantages and drawbacks of various preparation methods of biological apatite.

The effect of crystallization of bioactive bioglass 45S5 on apatite formation and degradation.

OBJECTIVE: Amorphous bioglass 45S5 has been used for many years as bone substitute material. Bioactive glasses are also suitable as coating materials for implants in order to improve the bone ongrowth behavior. We hypothesize that both the apatite formation on the surface and the chemical stability can be improved by crystallization of the bioglass. METHODS: Synthesized amorphous bioglass 45S5 specimens as well as samples which were crystallized at 1000 °C were stored in simulated body fluid for 1, 7, and 14 days. The respective apatite formation was gravimetrically determined and characterized by SEM and XRD analysis. Moreover, the degradation behavior was studied after storage in distilled water. RESULTS: The weight of the crystallized samples decreased 6.3% less than that of the amorphous samples. Calcium silica and calcium carbonate layers were found on amorphous bioglass after 7 and 14 days. However, apatite formation was observed only on the crystallized 45S5 samples after storage. SIGNIFICANCE: We conclude that the chemical resistance can be improved and, in parallel, a pronounced apatite formation on the surface of 45S5 can be obtained by controlled crystallization of the material for the particular test setup. Therefore, crystallized bioactive glasses should be considered to be promising coating material for dental implants.