Calcium Phosphate Phases Research Articles

Transformation kinetics of potassium and magnesium modified high-performance brushite cement to carbonated apatite in blood-mimicked condition

As a starting cement material, brushite is beneficial due to its short setting time and fast resorbability, and is metastable, allowing in vivo and in vitro transformation into a more stable calcium phosphate (CaP) phase. The challenges for a successful application of brushite include tissue inflammation from its acidic nature, and poor mechanical strength from weakly compacted crystals. Thus, in this study, it is aimed to avoid these drawbacks through a chemical modification of brushite cement. To circumvent tissue inflammation, brushite was modified with 5% of K+ or Mg2+ to induce the transformation into a more stable phase like hydroxyapatite (HAp). Surface transformation in a Tas-stimulated body fluid (Tas-SBF) solution occurred faster for K+-modified cements (1 week, to HAp and β-TCP) than for unmodified brushite (2 weeks, to HAp), and Mg2+-modified brushite (2 weeks, to HAp and β-TCP). Bulk transformation depended on the penetration of the Tas-SBF solution. Thus, Mg2+-substituted cement exhibited the most apatitic structure (26 wt%) due to the highest porosity. To improve the mechanical properties of brushite, setting retardants (acid pyrophosphate, citric acid) and an excess amount of β-TCP as a filler material were included in the cement’s composition. Diametral tensile strength (DTS) was the highest for unsubstituted cements (4.96 ± 1.04 MPa), slightly lower for K+-enriched cement (4.01 ± 0.71 MPa), and lowest for Mg2+-doped cements (1.34 ± 0.23 MPa). This study shows that it is possible to induce the transformation of brushite cement into a more biocompatible bone-like cement and simultaneously achieve enhanced mechanical properties through compositional modification of the cement.

Consolidating efficacy of diammonium hydrogen phosphate on artificially aged and naturally weathered coarse-grained marble

• Naturally weathered marble in granular disintegration has increased porosity. • Artificially aged marble in granular disintegration was obtained by heating. • DAP can successfully consolidate weathered coarse-grained marble. • DAP efficacy is comparable on artificially aged and naturally weathered marble. • DAP improves the condition of marble from Roman Villa of Pisões. The effects induced by diammonium hydrogen phosphate (DAP) on coarse marble varieties susceptible to granular disintegration as consolidation material is still poorly addressed. The work aims at investigating the behavior and efficacy of diammonium hydrogen phosphate(DAP)-based consolidant prepared in laboratory onto weathered coarse-grained marbles and, in the process, to unveil if the treatment investigated is a possible option to consolidate Trigaches marble elements from Roman Villa of Pisões. Sound, artificially and naturally weathered coarse marble samples were used for the purpose. The condition of naturally weathered marble slabs was assessed to reproduce artificially aged samples and used for testing the efficacy of DAP consolidant. Naturally weathered slab fragments showed a uniform damage in depth, an increased porosity and water absorption, and very similar conditions were successfully achieved in laboratory by heating sound marbles up to 300 °C for 1 h. DAP consolidant has low viscosity and can easily penetrate within the porous structure of coarse marble in granular disintegration. It promotes the formation of new calcium phosphate phases with binding capabilities that partially restore cohesion in-depth. Alteration of the color was negligible which is also a positive characteristic. Pilot tests in naturally weathered marbles revealed some interference of superficial bioorganisms residues in the absorption of DAP, however this was able to treat the entire thickness of the slab fragments, improving its cohesion state to an acceptable or good condition. Good correlations between the results of artificial aged samples with those of naturally weathered marble were achieved and the DAP-based treatment revealed to be an effective option to consolidate Trigaches marble elements from Roman Villa of Pisões.

Reduced Graphene Oxide Supported Cobalt-Calcium Phosphate Composite for Electrochemical Water Oxidation

We report the oxygen evolution reaction (OER) catalyst composed of cobalt–calcium phosphate on reduced graphene oxide (CoCaP/rGO). Our catalyst is prepared by the anodic electrolysis of calcium phosphate/rGO mixture loaded on indium-tin-oxide (ITO) in Co2+ aqueous solution. TEM, XPS and XRD experiments confirm that the crystal phase of calcium phosphate (CaP) is transferred into an amorphous phase of calcium oxide with phosphate (5.06 at%) after anodic electrolysis. Additionally, the main cation component of calcium is replaced by cobalt ion. The current–voltage characteristics of CoCaP/rGO showed a shoulder peak at 1.10 V vs. NHE, which originated from Co2+ to higher oxidation states (Co3+ or Co4+) and a strong wave from water oxidation higher +1.16 V vs. NHE at neutral condition (pH 7). CoCaP and CoCaP/rGO showed 4.8 and 10 mA/cm2 at 0.47 V of overpotential, respectively. The enhanced OER catalytic activity of CoCaP/rGO arises from the synergetic interaction between the amorphous phase of CoCaP and electric conducting graphene sheets.

Synthesis and characterization of hydroxyapatite bioceramics from shells of serai snail and mangrove crab in Tanjung Jabung beach: effect of milling process

Hydroxyapatite (HA) is a calcium phosphate compound that is used as a substitute for damaged body tissues, such as bone and dental implants. HA has been synthesized from the serai snail shells and the mangrove crab of west Tanjung Jabung, Jambi province using the dry method. Calcination of the shell at 1000 °C for 12 hours produces CaO, then contact of CaO with air produces Ca(OH)2 which is used as a source of calcium in HA synthesis. Milling time variations for 0 hours, 3 hours, and 6 hours. Sintering at 600 °C for 2 hours produces HA as characterized by using X-Ray Diffraction (XRD), Fourier Transform Infrared (FTIR), and particle size analysis using Particle Size Analyzer (PSA). HA which has the highest accuracy of lattice parameters is that which is milling for 3 hours. The diffraction pattern shows the formation of the HA phase accompanied by several other calcium phosphate phases at an angle of 2θ. The FTIR spectrum shows the presence of PO4 3- and OH−groups from HA. PSA analysis shows the longer the milling makes the smaller particle size.

Suspension of Amorphous Calcium Phosphate Nanoparticles Impact Commitment of Human Adipose-Derived Stem Cells In Vitro.

Simple SummaryCalcium phosphate is an important component in natural bone. Bone defects caused by trauma or resection of tumors demand bone substitutes to close the defect. One viable option is to use a scaffold material seeded with stem cells. Stem cells can differentiate towards bone cells (osteoblasts), among other cell types. To trigger stem cells towards the osteoblast type of cell, particular supplementation of the culture medium is needed. This study tests whether calcium phosphate nanoparticles can induce a commitment towards the osteoblast type of cell. In addition, we test for other commitments, such as endothelial cell, chondrocyte, or adipocyte commitment. After 1 or 2 weeks, with either 5 or 50 µg/mL nanoparticles in the culture medium, gene expression is analyzed. We find a significant increase of two specific bone marker genes after two weeks in 50 µg/mL nanoparticles compared to 5 µg/mL for two out of three tested human donors of adipose-derived stem cells. Moreover, endothelial cell commitment is also induced. Hence, such nanoparticles have the potential to trigger osteogenic and endothelial cell commitment.Amorphous calcium phosphate (aCaP) nanoparticles may trigger the osteogenic commitment of adipose-derived stem cells (ASCs) in vitro. The ASCs of three human donors are investigated using basal culture medium DMEM to either 5 or 50 µg/mL aCaP nanoparticles suspension (control: no nanoparticles). After 7 or 14 days, stem cell marker genes, as well as endothelial, osteogenic, chondrogenic, and adipogenic genes, are analyzed by qPCR. Free calcium and phosphate ion concentrations are assessed in the cell culture supernatant. After one week and 5 µg/mL aCaP, downregulation of osteogenic markers ALP and Runx2 is found, and averaged across the three donors. Our results show that after two weeks, ALP is further downregulated, but Runx2 is upregulated. Endothelial cell marker genes, such as CD31 and CD34, are upregulated with 50 µg/mL aCaP and a 2-week exposure. Inter-donor variability is high: Two out of three donors show a significant upregulation of ALP and Runx2 at day 14 with 50 µg/mL aCaP compared to 5 µg/mL aCaP. Notably, all changes in stem cell commitment are obtained in the absence of an osteogenic medium. While the chemical composition of the culture medium and the saturation status towards calcium phosphate phases remain approximately the same for all conditions, gene expression of ASCs changes considerably. Hence, aCaP nanoparticles show the potential to trigger osteogenic and endothelial commitment in ASCs.

Bioglass Ti coatings: Influence of thermal annealing on the evolution of calcium phosphate formation, phase and morphology

Bioglass films were prepared on Ti disks used for dental implants using very simple sol-gel synthesis and dip-coating process. The influence of annealing temperatures, 37 °C and 600 °C, on the surface morphology and chemical composition was investigated using SEM, AFM, DRIFT and XPS techniques. Biocompatible calcium phosphate phases were successfully formed when the disks were kept in contact with simulated biological fluid at three different immersion times: 7, 24 and 160 h. For the films annealed at 37 °C calcium phosphate was formed which was confirmed through the analysis of the intensity ratios of P-O, Ti-O-Ti and Si-O absorption bands in the DRIFT spectra. Ca/P and O/Ca surface atomic ratios obtained by XPS data indicated the formation of dibasic calcium phosphate dehydrate and dibasic calcium phosphate, revealing a coated material at low temperatures, 37 °C, promising for medical applications.

Moxifloxacin-loaded in situ synthesized Bioceramic/Poly(L-lactide-co-ε-caprolactone) composite scaffolds for treatment of osteomyelitis and orthopedic regeneration

High local intraosseous levels of antimicrobial agents are required for adequate long-term treatment of chronic osteomyelitis (OM). In this study, biodegradable composite scaffolds of poly-lactide-co-ε-caprolactone/calcium phosphate (CaP) were in-situ synthesized using two different polymer grades and synthesis pathways and compared to composites prepared by pre-formed (commercially available) CaP for delivery of the antibiotic moxifloxacin hydrochloride (MOX). Phase identification and characterization by Fourier transform infra-red (FTIR) spectroscopy, X-ray powder diffraction (XRPD) and scanning electron microscope (SEM) confirmed the successful formation of different CaP phases within the biodegradable polymer matrix. The selected in-situ formed CaP scaffold showed a sustained release for MOX for six weeks and adequate porosity. Cell viability study on MG-63 osteoblast-like cells revealed that the selected composite scaffold maintained the cellular proliferation and differentiation. Moreover, it was able to diminish the bacterial load, inflammation and sequestrum formation in the bones of OM-induced animals. The results of the present work deduce that the selected in-situ formed CaP composite scaffold is a propitious candidate for OM treatment, and further clinical experiments are recommended.

Monetite-based composite cranial implants demonstrate long-term clinical volumetric balance by concomitant bone formation and degradation

The use of calcium phosphates (CaPs) as synthetic bone substitutes should ideally result in a volumetric balance with concomitant bone formation and degradation. Clinical data on such properties is nevertheless lacking, especially for monetite-based CaPs. However, a monetite-based composite implant has recently shown promising cranial reconstructions, with both CaP degradation and bone formation. In this study, the volumetric change at the implant site was quantified longitudinally by clinical computed tomography (CT).The retrospective CT datasets had been acquired postoperatively (n = 10), in 1-year (n = 9) and 3-year (n = 5) follow-ups. In the 1-year follow-up, the total volumetric change at the implant site was -8 ± 8%. A volumetric increase (bone formation) was found in the implant–bone interface, and a volumetric decrease was observed in the central region (CaP degradation). In the subjects with 2- or 3-year follow-ups, the rate of volumetric decrease slowed down or plateaued. The reported degradation rate is lower than previous clinical studies on monetite, likely due to the presence of pyrophosphate in the monetite-based CaP-formulation. A 31-months retrieval specimen analysis demonstrated that parts of the CaP had been remodeled into bone. The CaP phase composition remained stable, with 6% transformation into hydroxyapatite. In conclusion, this study demonstrates successful bone-bonding between the CaP-material and the recipient bone, as well as a long-term volumetric balance in cranial defects repaired with the monetite-based composite implant, which motivates further clinical use. The developed methods could be used in future studies for correlating spatiotemporal information regarding bone regeneration and CaP degradation to e.g. patient demographics. Statement of significanceIn bone defect reconstructions, the use of calcium phosphate (CaP) bioceramics ideally results in a volumetric balance between bone formation and CaP degradation. Clinical data on the volumetric balance is nevertheless lacking, especially for monetite-based CaPs. Here, this concept is investigated for a composite cranial implant. The implant volumes were quantified from clinical CT-data: postoperatively, one year and three years postoperatively.In total, -8 ± 8% (n = 9) volumetric change was observed after one year. But the change plateaued, with only 2% additional decrease at the 3-year follow-up (n = 5), indicating a lower CaP degradation rate. Osseointegration was seen at the bone–implant interface, with a 9 ± 7% volumetric change after one year. This study presented the first quantitative spatiotemporal CT analysis of monetite-based CaPs.

Droplet microfluidics as a tool for production of bioactive calcium phosphate microparticles with controllable physicochemical properties

Affordable and therapeutically effective biomaterials are required for successful treatment of orthopaedic critical-size bone defects. Calcium phosphate (CaP) ceramics are widely used for bone repair and regeneration, however, further optimization of their properties and biological performance is still required. To improve the existing CaP bone graft substitutes, novel synthesis and production approaches are needed that provide a fine control over the chemical and physical properties and versatility in the delivery format. In this study, a microfluidic strategy for production of CaP microparticles with different sizes derived from highly monodisperse droplets is proposed for the controlled synthesis of bioactive CaP ceramics. Microfluidic droplets, that served as microreactors for CaP precipitation, allowed the production of different CaP phases, as well as strontium-substituted CaP. By varying the concentration of the precursor solution, microparticles with different porosity were obtained. The droplet microfluidic system allowed direct visualization and quantification of the reaction kinetics. Upon production and purification of the microparticles, the biocompatibility and bioactivity were tested in vitro using human mesenchymal stromal cells (hMSCs). Cell attachment was analysed by imaging of the cytoskeleton and focal adhesions Moreover, cell proliferation, metabolic activity, alkaline phosphatase activity and mRNA expression of a set of osteogenic markers were quantified. We demonstrated that droplet microfluidics is a functional technique for the synthesis of a range of bioactive CaP-based ceramics with controlled properties. Statement of significanceCalcium phosphate (CaP) ceramics are widely applied synthetic biomaterials for repair and regeneration of damaged bone; yet, CaP bone graft substitutes require further improvement to fully replace natural bone grafts in challenging clinical situations. To this end, novel synthesis and production approaches are needed that provide a fine control over the chemical and physical properties. Here, we developed a microfluidic platform for production of CaP microparticles with different size, composition and porosity, derived from monodisperse droplets. We demonstrated that CaP microparticles produced using this platform supported growth and differentiation of human mesenchymal stromal cells. This platform is a useful tool for developing a variety of CaPs in a controlled manner to study their physicochemical properties in relation to their bioactivity.

Structural Role and Spatial Distribution of Carbonate Ions in Amorphous Calcium Phosphate

The local structures of a series of amorphous calcium phosphate (ACP) phases with increasing carbonate contents (2–14 wt %) were studied by multinuclear 1H, 13C, 23Na, and 31P magic-angle spinning ...

Performance and mechanism of phosphorus removal by slag ceramsite filler

Ceramsite made from BOF (basic oxygen furnace) slag was used in column test to deal with aquatic phosphate. The objective of this study was to identify the phosphorus (P) removal mechanisms of slag ceramsite and to evaluate its potential use in efficient phosphorus adsorption filter. The relationships of Ca2+, pH and phosphorus removal, as well as filler regeneration were investigated. Chemical extraction, SEM-EDX, XRD, FTIR, XPS were employed to determine the mechanisms of phosphorus removal. The slag-ceramsite column showed good adaptability for low strength phosphate. Results demonstrated that suitable HRT facilitated the efficient phosphorus removal for stable and long-term operating. As HRT was 2.8 h and influent PO4-P was 10 mg/L, the P-uptake capacity of ceramsite filler was 10.5 mg/g in 158 days. The P-uptake mechanisms of slag-ceramsite filler including surface adsorption, Ca2+/OH− release, and chemical precipitation. Weakly adsorptive phosphorus and precipitated calcium phosphate were dominant in the sequestered phosphorus. Amorphous Ca-deficient hydroxyapatite (CDHA) and carbonated hydroxyapatite (CO3-HA) were the dominant calcium phosphate phases. The exhausted ceramsite filler could be regenerated by NaHCO3 elution and calcination process.

Multilayer Mg-pyrophosphate glass ceramic with discontinuous bioactivity. Physicochemical characterization

Novel pyrophosphate glass ceramic scaffolds (3D-Ca-P2) were fabricated and coated with several layers of CaO-P2O5-SiO2-MgO [3D-[Ca/P/Si]-XMg (X = 1,3 and 10 mol%)] as potential bioactive scaffolds for bone regeneration. The core scaffolds present a homogeneous distribution of polygonal grains consisting of 97% Ca2P2O7 with CaO-P2O5 glass as the matrix phase. Incorporating MgO into coatings led to extremely porous layers, assembled by nanosized equiaxed particles, which favoured the formation of different phases of tricalcium phosphate instead of pyrophosphate. Possible applications were determined based on Standard ISO/FDIS 23317:2014 for ceramics and powder samples. The 3D-Ca-P2 scaffolds’ non-bioactivity was modulated by coatings of different bioactivity behaviours depending on MgO contents. 3D-[Ca/P/Si]-10Mg was the best scaffold as precipitated hydroxyapatite (HA), was more amorphous than in the other scaffolds because Mg was incorporated into the HA network, which could favour subsequent cell adhesion. The multilayer scaffold provides advantages over others developed until now because in a unique structure all the characteristics required for an implant are combined. On a physical level, mechanical resistance, and porosity, and on a chemical level, a combination of calcium phosphate phases, similar to the mineral phase of bone, doped with Mg ions, which are capable of being transformed into HA in different periods of time.

Concentrating rare earth elements to phosphate in molten coal ash by a temperature gradient approach

Synthetic coal ash bearing 560 ppm europium oxide, blended with aluminum phosphate, was heat treated above its melting temperature and crystal evolutions with respect to europium concentration under controlled cooling were studied. The sample in a boat crucible was subjected to a temperature gradient of 100 °C across it to cause zone refining effects on crystallization behaviors in the melt (slag). Post analysis found six mineral phases formed from the melt while europium was only present in calcium phosphate, implying the majority of europium was segregated to the calcium phosphate. Europium concentrations in the calcium phosphate phase tended to be higher at zones with higher temperatures: as high as 7200 ppm, a 13-fold increase from the initial concentration.

Phosphorus retention by granulated apatite: assessing maximum retention capacity, kinetics and retention processes

Natural apatites have previously shown a great capacity for phosphate retention from wastewater. However, its fine particle size distribution may lead to a premature clogging of the filter. Accordingly, a granulated apatite product was developed and manufactured in order to control the particle size distribution of the media. Experiments were conducted on laboratory columns to assess their phosphorus retention capacity, to identify the processes involved in phosphorus retention and to evaluate their kinetic rates. The results showed phosphorus retention capacities of 10.5 and 12.4 g PO4-P·kg-1 and kinetic rate coefficients in the range of 0.63 and 0.23 h-1 involving lower values than those found for natural apatites in previous studies. Scanning Electron Microscopy images showed that apatite particles in the granules were embedded in the binder and were not readily accessible to act as seeds for calcium phosphate precipitation. The retention processes differ depending on the supersaturation of the solution with respect to calcium phosphate phases: at low calcium concentrations (69.8 ± 3.9 mg·L-1), hydroxyapatite precipitates fill up the porosity of the binder up to a depth of 100-300 μm from the granule surface; at higher calcium concentrations (112.7 ± 7.4 mg·L-1) precipitation occurs at the granule surface, forming successive layers of hydroxyapatite and carbonated calcium phosphates.

Micro-Nano Surface Characterization and Bioactivity of a Calcium Phosphate-Incorporated Titanium Implant Surface.

The surface topography of dental implants and micro-nano surface characterization have gained particular interest for the improvement of the osseointegration phases. The aim of this study was to evaluate the surface micro-nanomorphology and bioactivity (apatite forming ability) of Ossean® surface, a resorbable blast medium (RBM) blasted surface further processed through the incorporation of a low amount of calcium phosphate. The implants were analyzed using environmental scanning electronic microscopy (ESEM), connected to Energy dispersive X-ray spectroscopy (EDX), field emission gun SEM-EDX (SEM-FEG) micro-Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) before and after immersion in weekly refreshed Hank’s balanced salt solution (HBSS) for 28 days. The analysis of the samples before immersion showed a moderately rough surface, with micropits and microgrooves distributed on all of the surface; EDX microanalysis revealed the constitutional elements of the implant surface, namely titanium (Ti), aluminum (Al) and vanadium (V). Limited traces of calcium (Ca) and phosphorous (P) were detected, attributable to the incorporated calcium phosphate. No traces of calcium phosphate phases were detected by micro-Raman spectroscopy. ESEM analysis of the implant aged in HBSS for 28 days revealed a significantly different surface, compared to the implant before immersion. At original magnifications <2000×, a homogeneous mineral layer was present on all the surface, covering all the pits and microgrooves. At original magnifications ≥10,000×, the mineral layer revealed the presence of small microspherulites. The structure of these spherulites (approx. 2 µm diameter) was observed in nanoimmersion mode revealing a regular shape with a hairy-like contour. Micro-Raman analysis showed the presence of B-type carbonated apatite on the implant surface, which was further confirmed by XPS analysis. This implant showed a micro-nano-textured surface supporting the formation of a biocompatible apatite when immersed in HBSS. These properties may likely favor bone anchorage and healing by stimulation of mineralizing cells.

Fate of hydroxyapatite nanoparticles during dynamic in vitro gastrointestinal digestion: the impact of milk as a matrix.

This study investigated the behavior of nano-sized particles of hydroxyapatite (nHA) during dynamic in vitro gastrointestinal digestion, alone or dispersed within skim milk. The dissolution and the structural changes of nHA were investigated by analyzing the dissolution of calcium and using transmission electron microscopy and X-ray diffraction. The dissolution of nHA during gastric digestion involved a rapid early stage and a much slower later stage. It was incomplete by the end of gastric digestion, both with and without milk. However, there was no sign of nHA recrystallization in the intestinal phase. X-ray diffraction analysis of digesta showed the breakdown of the crystalline structure of nHA and the formation of potentially new calcium phosphate phases during digestion. Skim milk formed a structural clot and significantly retarded the dissolution of nHA during gastric digestion. Possible mechanisms leading to the incomplete dissolution of nHA and the matrix effect of milk are discussed.

Bioglass-fibre reinforced hydroxyapatite composites synthesized using spark plasma sintering for bone tissue engineering

Hydroxyapatite (HA) exhibits several desirable characteristics, but it still lacks osteoinduction, which is a necessary requirement for a bone scaffold. HA-based composites with different amounts of Bioglass? (BG) were prepared using spark plasma sintering (SPS). Careful selection of the SPS parameters avoided undesirable reactions between the calcium phosphate (CaP) and bioglass (BG present in the form of powder and fibres), as confirmed through X-ray diffraction analysis. Scanning electron microscopy images of the composite scaffolds revealed a fibre like appearance of the glassy region. The in vitro bioactivity and biodegradation analyses were performed by immersing the composites in simulated body fluid (SBF) and tris(hydroxymethyl)aminomethane (Tris), respectively. The ability to obtain only the CaP phase and glassy phase with desirable bioactive and biodegradation behaviour, indicated that these SPS scaffolds can be employed as bone scaffolds for clinical trials, after further in vivo analyses.

Biomimetic Mineralization of Hierarchical Nanofiber Shish-Kebabs in a Concentrated Apatite-Forming Solution

Recently, hierarchical polymer nanostructures called nanofiber shish-kebabs (NFSKs) have shown great potential in directing the distribution of minerals for biomineralization. In this work, we report controlled biomimetic mineralization in block copolymer-containing NFSKs. NFSKs were formed by crystallizing polycaprolactone-block-poly(acrylic acid) (PCL-b-PAA) kebabs on PCL fiber backbones. The block copolymer kebabs were periodically distributed on PCL nanofibers with a spacing of ∼100–300 nm. Free ions could infiltrate into anionic PAA nanodomains and initiate the NFSK-templated biomimetic mineralization process. A concentrated calcium phosphate solution was used in the present study, which led to significantly accelerated mineralization kinetics compared with the previously studied simulated body fluid systems. Electron microscopy, Fourier-transform infrared spectroscopy, and wide-angle X-ray diffraction were used to characterize the structure and morphology of the mineralized NFSKs. A three-stage mineralization process was identified, and carbonated nonstoichiometric hydroxyapatite was observed after stage 2 with the mineral location templated within kebabs. This accelerated mineralization process yielded a periodic mineral distribution of a biomimetic calcium phosphate phase along the fibers, and the decrease in mineral formation time allows for more efficient biomineralization study and composite formation.

Multiphase phosphate cements from steel slags

The use of industrial waste in the synthesis of phosphate ceramics opens the door to new ways of production and marketing of this kind of product, as well as contributing to the reduction of the environmental impact of industrial waste. In the present study, chemically bonded phosphate ceramics (CBPC) were synthesized from steel slags (electric arc furnace slag (EAF), basic oxygen furnace slag (BOF), and ladle furnace basic slag (LF) and aqueous solutions of H3PO4. A chemical analysis was performed of the steel slags, which were selected through standard sampling before being ground and milled to obtain the appropriate granulometry. In the evaluated slags, iron oxides and calcium oxides, present both in their free state and in compounds with other elements, were identified as the elements with the greatest presence and potential to form CBPC. Design of experiments (DOE) was applied to form multiphase cements, in order to make the variables present in the obtainment of cements workable, thereby allowing the formation reactions of cement to be better understood. The cements obtained were analyzed through XRD, SEM-EDS, FTIR, XPS, and mechanical compressive strength tests. The synthesized cement exhibited mainly vitreous structure for the iron phosphate phases (Fe(H2PO4)2) or (FeHPO4), and mainly crystalline structure for the calcium phosphate phases, present as dihydrogen phosphate of calcium hydrate (Ca(H2PO4)2·xH2O) and brushite (CaHPO4·2H2O). Compression strength between 10 and 19 MPa was recorded for the different compositions evaluated, with short setting times.

Effect of aspartic acid on the crystallization kinetics of ACP and dentin remineralization

Type I collagen and non-collagen proteins are the main organic components of dentin. This study aimed to investigate the biomimetic remineralization of demineralized dentin by aspartic acid (Asp), which is abundant in non-collagenous proteins (NCPs). Asp was added to a mineralizing solution containing polyacrylic acid (PAA) to explore the mechanism of Asp regulating the pure amorphous calcium phosphate (ACP) phase transition process. The remineralization process and superstructure of the remineralized layer of demineralized dentin were evaluated and analyzed by transmission electron microscope (TEM) and scanning electron microscope (SEM), and the biological stability of the remineralized layer was investigated by collagenase degradation experiment. It demonstrated that Asp promoted the crystallization kinetics of PAA-stabilized amorphous calcium phosphate to hydroxyapatite (HAP), and shortened the remineralization time of demineralized dentin from 7 days to 2 days. The newly formed remineralized dentin had similar morphology and biological stability to the natural dentin layer. The presence of a large number of Asp residues in NCPs promoted the phase transformation of ACP, and further revealed the mechanism of action of NCPs in dentin biomineralization. This experiment also showed that Asp promoted the biomimetic remineralization of dentin; the morphology and hierarchical structure of remineralized layer was similar to that of natural teeth, and had good biological properties.