Precipitation Of Hydroxyapatite Research Articles

Processing and cytocompatibility of Cu-doped and undoped fluoride-containing bioactive glasses

Sintered or additive-manufactured bioactive glass (BG) scaffolds are highly interesting for bone replacement applications. However, crystallization often limits the high-temperature processability of bioactive glasses (BGs). Thus, the BG composition must combine high bioactivity and processability. In this study, three BGs with nominal molar (%) compositions 54.6SiO2-1.7P2O3-22.1CaO-6.0Na2O-7.9K2O-7.7MgO (13–93), 44.8SiO2-2.5P2O3-36.5CaO-6.6Na2O-6.6K2O-3.0CaF2 (F3) and 44.8SiO2-2.5P2O3-35.5CaO-6.6Na2O-6.6K2O-3.0CaF2-1.0CuO (F3–Cu) were investigated. The dissolution and ion release kinetics were investigated on milled glass powder and crystallized particles (500–600 μm). All glasses showed the precipitation of hydroxyapatite (HAp) crystals after 7 days of immersion in simulated body fluid. No significant differences in ion release from glass and crystalline samples were detected. The influence of surface roughness on cytocompatibility and growth of pre-osteoblast cells (MC3T3-E1) was investigated on sintered and polished BG pellets. Results showed that sintered BG pellets were cytocompatible, and cells were seen to be well attached and spread on the surface after 5 days of incubation. The results showed an inverse relation of cell viability with the surface roughness of pellets, and cells were seen to attach and spread along the direction of scratches.

Pore graded borosilicate bioactive glass scaffolds: in vitro dissolution and cytocompatibility

3D borosilicate bioactive glass (1393B20 and B12.5MgSr) scaffolds were prepared by robocasting, with and without a dense layer at the top. Pore graded scaffolds are promising as they allow for membrane deposition and could limit the risk of soft tissue infiltration. In vitro dissolution was studied in tris(hydroxymethyl)aminomethane (TRIS) and Simulated Body Fluid (SBF). 1393B20 scaffolds dissolved faster than B12.5MgSr in TRIS whereas they dissolved slower in SBF. The difference in dissolution profiles, as a function of the medium used, is assigned to the different rates of precipitation of hydroxyapatite (HA). While the precipitation of calcium phosphate (CaP) in the form of HA, first sign of bioactivity, was confirmed by ICP, FTIR-ATR and SEM-EDX analysis for both compositions, 1393B20 was found to precipitate HA at a faster rate. The presence of a dense top layer did not significantly impact the dissolution rate and CaP precipitation. In vitro cell culture was performed using human adipose-derived stem cells (hADSCs). Prior to cell plating, a preincubation of 3 days was found optimum to prevent burst ion release. In direct contact, cells proliferate and spread on the scaffolds while maintaining characteristic spindle morphology. Cell plated on 1393B20 scaffolds showed increased viability when compared to cell plated on B12.5MgSr. The lower cell viability, when testing B12.5MgSr, was assigned to the depletion of Ca2+ ions from culture medium and higher pH. Static cell culture leads to believe that the scaffold produced from the 1393B20 glass composition are promising in bone regeneration applications.Graphical

Boosting the Biodegradation and Bioactivity of PBS‐DLS Copolymers via Incorporation of PEG

AbstractBiodegradable polymers play a crucial role in the development of materials for biomedical applications. This study investigates the enzymatic biodegradation, bioactivity, and cytotoxicity of poly(butylene succinate‐dilinoleic succinate) (PBS‐DLS) copolymers modified with poly(ethylene glycol) (PEG). Two copolymer variations with different segmental compositions (70 wt.% and 60 wt.% of hard segments) are synthesized. After modifying the copolymers with PEG, the presence of a lipase catalyst accelerated degradation after 20 days, evidenced by reduced residual content. Gel permeation chromatography analysis showed up to 40% decrease in molecular weight, while gravimetric analysis indicated a mass loss of up to 10%. Morphological examination revealed that the enzymatic breakdown, facilitated by hydrolase activity (boosted by the presence of PEG), resulted in surface erosion, holes, and changes in spherulitic morphology. Bioactivity studies demonstrated the formation of biomimetic calcium/phosphate (Ca/P) crystals. Copolymers with higher crystallinity (70 wt.% hard segments) favored tricalcium phosphate‐like crystal formation, while those with lower crystallinity (60 wt.% hard segments) are more susceptible to hydroxyapatite precipitation. In vitro cytotoxicity tests exhibited excellent cell viability and attachment for all copolymers. The ability to control degradation through PEG modification, along with their bioactivity and cell compatibility, positions them as promising candidates for diverse biomedical applications.

Gallic acid–coated nanolayer on mineral trioxide aggregate for regulating the inflammatory and differentiation cellular response profile of human dental pulp stem cells

Mineral trioxide aggregate (MTA) is a biomaterial used in endodontics due to its high bioactivity, antibacterial behaviors, and good biocompatibility. However, it has several disadvantages related to certain physical properties, including a long setting time and poor mechanical properties. Therefore, we hypothesized that coating MTA with gallic acid (GA) would regulate physical properties and lead to enhanced adhesion, proliferation, and secretion of angiogenic- and odontogenic-related proteins. This study examined whether MTA can be modified with GA to form GAMTA cement and evaluated its physicochemical and biological behaviors and immune suppression, angiogenesis, and odontogenesis capabilities. We soaked MTA in Tris buffer containing different concentrations of GA to coat the MTA powders. X-ray diffraction (XRD) and diametral tensile strength analyses were conducted to assess the physical characteristics of GAMTA. Then, we immersed GAMTA cement in simulated body fluid to evaluate its hydroxyapatite precipitation capabilities and silicon ion release profile. We used human dental pulp stem cells to assess the cell responses and the immunosuppressive, angiogenic, and odontogenic capabilities of GAMTA. The XRD results showed that GA was successfully coated onto MTA without the disruption or loss of MTA’s advantageous original structural properties. GAMTA demonstrated excellent physicochemical and biological properties, improving hydroxyapatite formation and angiogenic, odontogenic, and anti-inflammatory properties compared with MTA alone. Our results indicate that the GAMTA cement is a useful dental material for future tissue engineering and clinical applications.

Applying the Alkali-Activation Method to Encapsulate Silicon Nitride Particles in a Bioactive Matrix for Augmented Strength and Bioactivity.

The development of bioactive ceramics still poses challenges in finding a good compromise between bioactivity and mechanical robustness. Moreover, a facile, low-cost and energy-saving synthesis technique is still needed. This study concerns the synthesis of a bioactive material by growing a bioactive Na-Ca-Mg-Si-based ceramic matrix produced using the alkali-activation method on silicon nitride (Si3N4) particles. This technique simultaneously forms the matrix precursor and functionalizes the Si3N4 particles' surface. The optimal strength-bioactivity compromise was found for the composition containing 60 wt.% Si3N4 and 40 wt.% of the matrix exhibiting good compressive strength of up to 110 MPa and extensive precipitation of hydroxyapatite on the sample surface after 7 days of soaking in simulated body fluid. This innovative approach merging strong non-oxide binary ceramics with the versatile and low-cost alkali-activation method holds great expectations for the future in biomaterials.

Evaluation of Solubility, and Volumetric and Morphological Alterations of Bioceramic Filling Material for Primary Teeth: A New Methodological Approach.

To evaluate the solubility and the volumetric and morphological alterations of bioceramic filling material (Bio-CP) for primary teeth. Bio-CP, Calen thickened with zinc oxide (Calen-ZO), and with zinc oxide eugenol (ZOE) were placed in 1- or 2-mm-diameter polyethylene tubes and immersed in water or phosphate-buffered saline (PBS) for 30 days. The solubility (mass loss) was assessed using methodology modified from ISO 6876. Filling capacity, volumetric changes, and presence of voids were assessed by microcomputed tomography (micro-CT). The surface distribution of the chemical elements and the crystalline phases was evaluated by energy scattering X-ray scanning electron microscopy (SEM-EDX) and X-ray diffraction (XRD) to detect hydroxyapatite precipitate and components. The Shapiro-Wilk, Kruskal-Wallis, and Dunn's or two-way ANOVA and Tukey post hoc test were used (α = 0.05). The solubility was ZOE > Calen-ZO = Bio-CP. Calen-ZO and Bio-CP were more soluble in water than in PBS. All the materials showed greater solubility in 2-mm tube diameter in both PBS and distilled water, except for Bio-CP in distilled water, which showed no difference between both tube diameters (1 and 2 mm). Only Calen-ZO and ZOE were analyzed by micro-CT, because Bio-CP separated into two phases during scanning. Calen-ZO had greater volumetric loss and presence of voids than ZOE in water, but there was no difference in PBS. The hydroxyapatite precipitate on the surface of Bio-CP and Calen-ZO was detected after immersion in PBS. Although Bio-CP had acceptable solubility and filling capacity, its composition did not allow a proper volumetric and void assessment. From a clinical perspective, Bio-CP has the potential to become a suitable material for root canal filling in primary teeth. Nonetheless, its composition must first be revised to achieve better chemical stability prior to its recommendation.

Preparation and performance analysis of Ti-25Nb-3Zr-2Sn-3Mo microarc oxidized macro-micro-nano tertiary structure film layers

After undergoing microarc oxidation, titanium alloys exhibit significantly enhanced biocompatibility, making them a subject of extensive research in the field of biomedical applications. In this study, a two-step microarc oxidation method was used to prepare a film layer with both macro-micro-nano tertiary structures on β-type titanium alloy Ti-3Zr-2Sn-3Mo-25Nb (TLM), using a phosphate-nitrate mixed electrolyte for the first step of microarc oxidation and a borate body electrolyte for the second step of microarc oxidation. The effects of NaOH concentration, microarc oxidation voltage, and time on the size and distribution of macropores prepared by microarc oxidation in the first step were investigated by SEM, energy dispersive spectroscopy, XRD, and metallurgical microscopy. The wettability of the prepared three-level structured film and its ability to induce hydroxyapatite deposition were evaluated through contact angle testing and simulated body fluid immersion experiments. The overall research findings indicate that the two-step microarc oxidation process yielded macropores with diameters ranging from 200 to 400 μm, along with micro-nanostructures measuring 2–15 μm and 10–100 nm. The increase in the NaOH concentration in the electrolyte decreased the size of the macropores. The increase in the microarc oxidation time increased the size of macropores; the voltage affected the distribution and number of macropores. The prepared macro-micro-nano tertiary structured membrane layers have excellent wettability and the ability to induce hydroxyapatite precipitation, indicating that they possess good biocompatibility. This study provides a reference for the medical development of alloys.

Mathematical model of physicochemical regulation of precipitation of bone hydroxyapatite

IntroductionFormation of hydroxyapatite in bone, dentin, and enamel occurs at restricted molecular sites of specific extracellular matrix proteins and is controlled by multiple mineralization inhibitors. However, the role of physicochemical factors, such as the availability of required ions and the saturation status of the aqueous environment in biological mineralization, is not fully understood. The goal of this study was to use mathematical modeling to describe the complex physicochemical environment permissive to the precipitation of biological hydroxyapatite.MethodsWe simulated the processes occurring in the bone interstitial fluid (ISF) defined as an aqueous environment containing seven chemical components (calcium, phosphate, carbonate, sodium, potassium, magnesium, and chloride) that form 30 chemical species. We simulated reversible equilibrium reactions among these chemical species, and calculated supersaturation for hydroxyapatite and its precipitation rate using kinetic theory.Results and DiscussionThe simulated ISF was of correct ionic strength and predicted the equilibrium component concentrations that were consistent with the experimental findings. Supersaturation of physiological ISF was ~15, which is consistent with prior findings that mineralization inhibitors are required to prevent spontaneous mineral precipitation. Only total calcium, total phosphate and to a lesser degree total carbonate affected ion availability, solution supersaturation and hydroxyapatite precipitation rate. Both calcium and phosphate levels directly affected hydroxyapatite precipitation, and phosphate was affected by pH, which additionally influenced hydroxyapatite precipitation. Integrating mathematical models capturing the physiochemical and biological factors regulating bone mineralization will allow in silico studies of complex clinical scenarios associated with alterations in ISF ion composition, such as rickets, hypophosphatemia, and chronic kidney disease.

Calcium silicate biocomposites: effects of selenium oxide on the physico-mechanical features and their in-vitro biological assessments

Bone tissue regenerative material serves as a prospective recovery candidate with self-adaptable biological properties of bio-activation, degradability, compatibility, and antimicrobial efficacy instead of metallic implants. Such materials are highly expensive due to chemical reagents and complex synthesis procedures, making them unaffordable for patients with financial constraints. This research produced an efficient bone tissue regenerative material using inexpensive naturally occurring source materials, including silica sand and limestone. The extracted SiO2 and CaO particles (75:25 wt%) were subjected to hydrothermal synthesis (water treatment instead of chemical solvents) to produce the CaSiO3 biomaterial (code: S). Selenium oxide was doped with calcium silicate at 3, 5, and 10 wt.% to enhance its properties, yielding biocomposite materials (i.e. S3, S5, and S10). The physico-mechanical properties of these materials were investigated with x-ray diffraction, Fourier transform infrared, FESEM-EDS, and micro-universal testing machine. The results revealed that the synthesized biocomposites have a crystalline wollastonite phase with a porously fused rough surface. From structural parametric calculations, we found that the biocomposites have reduced particle size and enhanced surface area due to the influence of selenium oxide. The biocomposite S10, having high SeO2 content, attained the maximum compressive strength of 75.2 MPa. In-vitro studies of bioactivity, biodegradability, biocompatibility, and antibacterial activity were performed. At 7 and 14 d of bioactivity, the synthesized biocomposites are capable of dissolving their ions into simulated body fluid (SBF) solution to precipitate hydroxyapatite and a required Ca/P ratio of 1.69 was achieved by S3. A comparative analysis has been performed on the degradation activity in Tris-HCl and the consequent pH changes during SBF treatment. The bio-analysis revealed that the biocomposite S3 shows enhanced bioactivity through a controlled degradation rate and secured cell viability of 88% at a concentration of 100 μg ml−1. It also offers significant bacterial inhibition potency against E.coli and S.aureus bacteria.

Screening of fluoride-free PEO coatings on cast Mg3Zn0.4Ca alloy for orthopaedic implants

In order to improve the corrosion behaviour of Mg3Zn0.4Ca alloy, fluorine-free PEO coatings, developed at different treatment times using a novel transparent electrolyte and a conventional suspension electrolyte, were compared. The surface morphology and chemical composition of the PEO coatings were evaluated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The corrosion behaviour of the PEO coatings was carried out by potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution test in modified α-MEM solution. The coatings formed in both electrolytes showed very similar morphologies and compositions that were independent of the nature of the electrolyte. At short immersion times, all PEO coatings showed an improvement in corrosion resistance by PDP measurements, while by EIS measurements only the coatings at short treatment times showed a significant improvement. After >24 h of immersion, the PEO coating formed in transparent electrolyte suffered a drastic acceleration of the degradation rate that exceeded that of the uncoated substrate. The acceleration was attributed to the presence of a crack at the PEO/substrate interface, and the formation of ZnO from the oxidation of Zn-rich secondary phases of the Mg3Zn0.4Ca alloy. The PEO coating formed in the suspended electrolyte on the Mg3Zn0.4Ca alloy showed great corrosion protection, which was attributed to the precipitation of hydroxyapatite that remains trapped in the pores and cracks of the PEO coatings by the hydrolysed silica, impeding the progress of corrosive species.

Sustainable removal of nutrients (n and p) in a wastewater treatment plant, with eggshell (biocalcium)

Biological treatments have become insufficient to treat municipal wastewater with greater toxicity and excess nitrogen and phosphate species, thus affecting the organisms that consume the water. In this work, a process was implemented for the removal of nutrients through three stages: stage A, complete aeration (24 h, 43 months); stage B, decreased aeration (12 h, 17 months); and stage C, decreased aeration with biocalcium (12 h, 19 months). The addition of biocalcium from eggshell promoted the formation of flocks, which resulted in the removal of nitrites (61 %), nitrates (84 %), total nitrogen (57 %), total phosphorus (8.3 %), sedimentable solids (50 %), total suspended solids (69 %), BOD5 (76 %), helminth eggs (50 %) and fecal coliforms (54 %). The statistical analyses in the three stages indicated that there is a strong correlation between the concentration of fats and oils and the removal of sedimentable solids and total suspended solids, since these parameters were correlated by 97 and 89 %, respectively. Sedimentable solids were correlated with total suspended solids by 94 %, while nitrates and total nitrogen were correlated 92 %, which favors the removal of nutrients in wastewater. The increase in the concentration of nitrogen in the sludge in stage C generated a C:N ratio of 7.98. This ratio shows that the sludge is feasible for use as a mediator of soils and a biofertilizer because of the high contents of calcium, phosphorus and nitrogen. In addition, biocalcium promoted the precipitation of hydroxyapatite, struvite, calcite and quartz. In general, the three stages of the treatment contributed to the stabilization of the wastewater treatment plant (WWTP) in an efficient, economical, and safe way.

The effect of supplementing the calcium phosphate cement containing poloxamer 407 on cellular activities.

Calcium phosphate cement (CPC) is generally used for bone repair and augmentation. Poloxamers are tri-block copolymers that are used as surfactants but have applications in drug and antibiotic delivery. However, their biological effects on bone regeneration systems remain unelucidated. Here, we aimed to understand how supplementing the prototype CPC with poloxamer would impact cellular activity and its function as a bone-grafting material. A novel CPC, modified beta-tricalcium phosphate (mβ-TCP) powder, was developed through a planetary ball-milling process using a beta-tricalcium phosphate (β-TCP). The mβ-TCP dissolves rapidly and accelerates hydroxyapatite precipitation; successfully shortening the cement setting time and enhancing the strength. Furthermore, the addition of poloxamer 407 to mβ-TCP could reduce the risk of leakage from bone defects and improve fracture toughness while maintaining mechanical properties. In this study, the poloxamer addition effects (0.05 and 0.1 g/mL) on the cellular activities of MC3T3-E1 cells cultured in vitro were investigated. The cell viability of mβ-TCP containing poloxamer 407 was similar to that of mβ-TCP. All specimens showed effective cell attachment and healthy polygonal extension of the cytoplasm firmly attached to hydroxyapatite (HA) crystals. Therefore, even with the addition of poloxamer to mβ-TCP, it does not have a negative effect to osteoblast growth. These data demonstrated that the addition of poloxamer 407 to mβ-TCP might be considered a potential therapeutic application for the repair and regeneration of bone defects.

Sol-gel synthesis of spherical monodispersed bioactive glass nanoparticles co-doped with boron and copper

In this work, an optimized sol-gel process for the synthesis of spherical and monodispersed bioactive glass nanoparticles doped with boron and copper was developed, by investigating different synthesis parameters. The obtained glasses were characterized in terms of morphology, composition, dispersibility, structure and in vitro reactivity. The performed characterizations demonstrated that shape, dimension and dispersion can be tailored by acting on the timing of the addition of the catalyst and on the synthesis process, in particular the centrifugation step. The optimized glass particles showed a spherical shape, good ions incorporation and good dispersion. In vitro bioactivity test demonstrated that the boron and copper addition did not interfere with the glass ability to induce the precipitation of hydroxyapatite. The shape, dispersion, bioactive behavior and content of boron and copper of these novel bioactive glass particles make them very promising for both hard and soft tissue engineering applications.

Hydroxyapatite (HAP) formation in acetate-driven partial denitrification process: Enhancing sludge granulation and phosphorus removal

Partial denitrification/anammox (PD/A) processes have emerged as a promising technology for efficient nitrogen removal from wastewater. However, these processes fail to remove phosphorus (P), a key pollutant that contributes to water eutrophication. To address this issue, the potential of inducing hydroxyapatite (HAP) precipitation in PD processes to achieve simultaneous P removal was investigated for the first time. Specifically, three SBRs (R1-R3) for PD were operated with adding varying concentrations of external Ca (30, 60, and 120 mg/L, respectively). Results demonstrated significant P reduction in all three SBRs, particularly in R3 with high Ca, which achieved an 80 % removal efficiency. Notably, sludge granulation was observed during operation, with the granule size in R3 with high Ca reaching 906.1 μm during the stable period, exceeding those in R2 (788.7 μm) and R1 (707.1 μm). This led to good settle ability of the PD sludge, as demonstrated by the lowest SVI5 (20 mL/g MLSS). Moreover, the decrease in the MLVSS/MLSS ratio suggested that the inorganic content accumulated, as observed by confocal laser scanning microscopy in the interior of the granules. Elemental composition analysis suggested that PD granules contained high P and Ca, while the X-ray diffraction (XRD) results confirmed the formation of HAP. Overall, this study demonstrated that PD-HAP coupled granular sludge process has potential as a robust and efficient method for nitrite production, as well as effective P removal and recovery, thereby advancing the application of anammox processes in wastewater treatment.

Simultaneous removal of fluoride and phosphate from semiconductor wastewater via chemical precipitation of calcium fluoride and hydroxyapatite using byproduct of recycled aggregate

Semiconductor wastewater with high concentrations of fluoride and phosphate is an environmental issue that cannot be ignored. Moreover, the byproduct of recycled aggregates, concrete fines, cannot be reused in concrete manufacturing, which is a key issue to address for the sustainable development of the concrete industry. The objective of this study was to tackle the crucial environmental issues of these two industries by developing concrete fines as an alternative material to treat semiconductor wastewater. The chemical precipitation of calcium fluoride and hydroxyapatite in the presence of concrete fines was determined as the mechanism underpinning the removal of fluoride and phosphate in wastewater. Owing to the wide range of contaminant concentration and solution pH and the possibility of multi-stage treatment, the effects of the initial contaminant concentration (F: 100–1000 mg/L; P: 20–200 mg/L) and solution pH (pH: 2–7) on the removal reactions were determined. The highest F and P removal percentages were more than 99%, and the final F and P concentrations met the effluent standard (F: 15 mg/L, P: 1.3 mg/L). The removal reactions of F and P are generally in competition, and the removal of F has priority over the removal of P. The pseudo-second-order model can describe the kinetics of the removal reactions well. The formation of fluorapatite can reduce the F concentration below the concentration achievable by CaF2 precipitation alone. Furthermore, using the byproduct of recycled aggregates instead of conventional chemicals to treat semiconductor wastewater is promising in terms of reducing CO2 emissions, and prospective applications are discussed. This study can lead to the development of a sustainable and clean process for semiconductor wastewater treatment using byproducts from the concrete industry.

Preparation and characterization of novel poly (lactic acid)/calcium oxide nanocomposites by electrospinning as a potential bone tissue scaffold

Calcium oxide nanoparticles (n-CaO) ca. 22 nm were obtained from eggshell waste. The n-CaO was incorporated into the PLA matrix in 10 and 20 wt% of filler content by electrospinning process to get PLA/n-CaO fibers with homogenous morphology and diameter as a potential use in scaffold for bone tissue regeneration. The incorporation of n-CaO into PLA modifies the mechanical properties, having a reinforcement effect on the matrix. The Young modulus for PLA/n-CaO nanocomposites increased between 122 and 138 % concerning neat PLA fibers, showing a more rigid behavior. The PLA/n-CaO nanocomposite fibers showed in vitro bioactivity, capable of inducing the precipitation of hydroxyapatite (HA) layer in the fiber surface after seven days in SBF solution. The biocidal and biological properties of PLA/n-Cao with 20 wt% showed a 30 % reduction in bacterial viability against S. aureus and 11 % against E. coli after 6 h of bacterial exposure. Furthermore, the fibers did not show a cytotoxic effect on the bone marrow ST-2 cell line, allowing cell adhesion and proliferation in the RPMI medium. The PLA/n-CaO with 20 wt% of nanoparticles showed a higher capacity to promote osteogenic differentiation, significantly increasing the alkaline phosphatase (ALP) expression after seven days compared to PLA and cell control. The in vivo analysis corroborated the biocompatibility of the prepared scaffolds; the presence of n-CaO in PLA reduced the formation of fibrous encapsulation of the material, improving the healing process. These results validated using n-CaO to enhance the functionality of polymer matrices as a PLA, bringing bioactive, biocide, and biocompatible properties, opening a new and interesting route to develop new biomaterials as a scaffold for bone tissue engineering.

Geochemical processes of phosphorus‑iron on sediment-water interface during discharge of groundwater to freshwater lakes: Kinetic and mechanistic insights

Groundwater is widely recognized as a source of lake materials. When it discharges into lakes, phosphorus(P)‑iron(Fe) geochemical reactions occur due to environmental changes, affecting P discharge from groundwater. However, redox kinetics of Fe and associated P geochemical processes at the sediment-water interface are not fully understood. Taking Dongting Lake as an example, this study explored Fe and P geochemical processes at the sediment-water interface under groundwater discharge with high Fe and P concentrations. We incubated sediments from Dongting Lake under anoxic-oxic conditions with different initial aqueous P/Fe ratios and pH. Aqueous PO43−-P and Fe2+, and solid P and Fe phases in sediments were analyzed, and experimental data were further simulated using numerical reactive models. At the beginning of the experiment, aqueous P and Fe were adsorbed rapidly on sediments. Under anoxic conditions, the Fe reduction rate decreased with decreasing content of poorly crystalline ferric (oxyhydr)oxides, and the addition of aqueous P and Fe at neutral pH enhanced the reduction rate. The increased aqueous P was dominated by desorption caused by sediment Fe reduction and then fixed by gibbsite adsorption and hydroxyapatite precipitation. Under oxic conditions, Fe(II) oxidation under was pH- and (P:Fe)ini-independent, with a sharp rate decline. Furthermore, the final sediment Fe(II) content was higher than the initial content, indicating the formation of a low-oxidizability Fe(II) phase. The P dynamics were dominated by adsorption on the produced Fe-oxides. The numerical models also suggested that heterogeneity in natural sediments promotes hydroxyapatite formation at low pH, but restricts it at high pH. The findings reveal that although aqueous P concentration decreased during groundwater discharge to lakes, PO43−-P concentration remained much higher than that in natural lake water, increasing the risk of lake eutrophication. The paper provides references for further understanding of P loading from groundwater discharge into lakes.

A bio-inspired mineral precipitation method to improve the freeze-thaw resistance of cement concrete pavement

Mineral precipitation has been proven to be an effective surface treatment for reducing the porosity of Portland cement concrete (PCC), leading to significant improvement in its freeze-thaw (F-T) resistance. Inspired by human teeth, this study proposes to produce a protective surface layer for PCC through in-situ precipitating hydroxyapatite (HAP), the same mineral found in the tooth enamel, on the concrete surface to improve its freeze-thaw resistance. This protective layer was generated by simply treating the mortar surface with a diammonium hydrogen phosphate (DAP) solution. Experimental results reveal that the F-T resistance is significantly improved, with the DAP-treated specimens surviving three times as many cycles as the control group. The proposed treatment also enhances the compressive strength of the mortar specimens by 35% and reduces saturated water absorption by up to 50%. Analysis of mineralogy suggests that DAP reacts with calcium ions from hydrated cement, leading to HAP precipitation and calcium phosphate on the cement mortars' surface. Particularly, the nanoindentation results indicate that the mineral phase with a lower density tends to react more readily with DAP, leading to its conversion into minerals with significantly higher packing density. Quantitative backscattered scanning electrons (BSE) images and mercury intrusion porosimetry (MIP) analysis verify that the microstructure of the cement mortar surface was densified by the formation of HAP and calcium phosphate induced by the proposed treatment. The proposed method exhibits great potential in enhancing the longevity of PCC pavements in cold regions.

Functional evaluation of mineral trioxide aggregate cement with choline dihydrogen phosphate.

To improve the cytocompatibility of mineral trioxide aggregate (MTA) cement and its ability for reparative dentin formation, the effect of adding choline dihydrogen phosphate (CDHP), which is reported to be biocompatible, to MTA cement was investigated. The L929 cell proliferation showed that the addition of CDHP improved cell viability. The addition of CDHP shortened the setting time of MTA cement, with a significant decrease in consistency above 0.4 g/mL. Diametral tensile strength of the set cement was improved by the addition of 0.4 g/mL CDHP. Solubility was judged to be within the range of clinical application. The spontaneous precipitation of low crystalline hydroxyapatite was examined by immersing the set cement in phosphate buffer saline, and it was found that the ability of the cement with 0.4 g/mL of CDHP was significantly improved compared with that of the cement without CDHP.

Anammox-Mediated Hydroxyapatite Granules: Physicochemical Properties, 3D Hierarchy, and Biofilm Thickness.

Biomineralization inspired the development of simultaneous biological transformations and chemical precipitation for simultaneous nitrogen removal and phosphorus recovery from wastewater, which could compensate for the incapacity of phosphorus management in the new biological route of anaerobic ammonium oxidation (anammox). In this study, we strengthened anammox-mediated biomineralization by long-term feeding of concentrated N, P, and Ca substrates, and a self-assembled matrix of anammox bacteria and hydroxyapatite (HAP) was fabricated in a granular shape, defined as HAP-anammox granules. HAP was identified as the dominant mineral using elemental analysis, X-ray diffraction, and Raman spectroscopy. The intensive precipitation of HAP resulted in a higher inorganic fraction and substantially improved settleability of anammox biomass, which facilitated HAP precipitation by acting as nucleation and metabolically elevated pH. By using X-ray microcomputed tomography, we visually represented the hybrid texture of interwoven HAP pellets and biomass, the core-shell layered architecture of different-sized HAP-anammox granules, and their homogeneously regulated thickness of the outer biofilm (from 118 to 635 μm). This unique architecture endows HAP-anammox granules with outstanding settleability, active biofilm, and tightly bonded biofilm with the carrier, which may explain the excellent performance of these HAP-anammox granules under various challenging operational conditions in previous studies.