Phosphate Phases Research Articles

Phosphate (Bio)mineralization Remediation of 90Sr-Contaminated Groundwaters.

Historical operations at nuclear mega-facilities such as Hanford, USA, and Sellafield, UK have led to a legacy of radioactivity-contaminated land. Calcium phosphate phases (e.g., hydroxyapatite) can adsorb and/or incorporate radionuclides, including 90Sr. Past work has shown that aqueous injection of Ca-phosphate-generating solutions into the contaminated ground on both laboratory and field scales can reduce the amount of aqueous 90Sr in the systems. Here, two microbially mediated phosphate amendment techniques which precipitated Ca-phosphate, (i) Ca-citrate/Na-phosphate and (ii) glycerol phosphate, were tested in batch experiments alongside an abiotic treatment ((iii) polyphosphate), using stable Sr and site relevant groundwaters and sediments. All three amendments led to enhanced Sr removal from the solution compared to the sediment-only control. The Ca-citrate/Na-phosphate treatment removed 97%, glycerol phosphate 60%, and polyphosphate 55% of the initial Sr. At experimental end points, scanning electron microscopy showed that Sr-containing, Ca-phosphate phases were deposited on sediment grains, and XAS analyses of the sediments amended with Ca-citrate/Na-phosphate and glycerol phosphate confirmed Sr incorporation into Ca-phosphates occurred. Overall, Ca-phosphate-generating treatments have the potential to be applied in a range of nuclear sites and are a key option within the toolkit for 90Sr groundwater remediation.

Early age properties and water resistance of calcium hydroxide modified volcanic ash‐based phosphate geopolymer binders

AbstractThis work aims to improve the early age characteristics and water resistance of volcanic ash‐based phosphate geopolymer materials by modifying the chemistry of the binder with calcium hydroxide (CH). Phosphate geopolymer binders with Ca/P molar ratios ranging from 0.49 to 0.80 were prepared. Then the early and late age physical properties were then determined. The hardened binder was characterized by various analytical techniques involving XRD, TGA‐DSC, and SEM‐EDS. The results showed that the use of CH decreases the initial setting time from several hours to less than 5 min. At the same time, the 1 d compressive strength was increased from 0 to 15 MPa with the increase in the Ca/P molar ratio. Moreover, the slow dissolution rate of volcanic ash was responsible for the low strength at an early age but beneficial to improving the geopolymerisation with time. This favored the high strength of the control phosphate geopolymer, which reached 52.5 MPa at 56d and was higher than those with CH (28.5–45.2 MPa). However, the control phosphate geopolymer had poor water resistance, with strength retention ranging from 21%–57% compared to 76%–90% for phosphate geopolymer with CH. This is because of the leaching of the reactive phase underwater that inhibits further reaction progress. In addition, the modification of the binder chemistry with CH leads to the formation of new calcium phosphate phases that also contribute to enhancing water resistance.

A comparative study of the biofunctionality and intercalation capacity of two metal phosphate phases intercalated with antimicrobials

A comparative study of the biofunctionality and intercalation capacity of two metal phosphate phases intercalated with antimicrobials

Application of deep eutectic solvents (DESs) as a green lixiviant for extraction of rare earth elements from caustic-treated monazite concentrate

Rare earth elements (REEs) with unique metallurgical properties are listed as some of the most strategically important elements in today’s world. Monazite is one of the main natural minerals for REEs which is being processed using inefficient conventional hydrometallurgical approaches with extreme environmental footprints. In this paper, an attempt was made to apply deep eutectic solvents (DESs) as a green replacement for conventional solvents such as sulfuric acid and hydrochloric acid in the process of monazite leaching. After the characterization of the monazite concentrate, eleven different DESs were synthesized and employed for the leaching experiments. Results showed that each of the synthesized DES was unable to extract REEs from the phosphate phase. By sodium hydroxide roasting at 500 °C for 2 h followed by water leaching, rare earth hydroxides were formed from the monazite concentrate, and the new phase was characterized. Each of the eleven synthesized DES was tested on the roasted sample and it was revealed that 2ChCl:1PTSA, 2ChCl:1PTSA:1EG, and 1PEG-400:1PTSA have respectively the highest extraction efficiency. The DES comprised of 2ChCl:1PTSA exhibited significant capability for extraction of REEs from the roasted sample with more than 90 % recovery. Further experiments were carried out on the leaching process with 2ChCl:1PTSA for studying the effect of temperature, solid percentage, and time on the final recovery. At the optimum condition, the recoveries of the main REEs including Ce, La, and Nd reached 99.8 %, 99.9 %, and 94 %, respectively. These findings have implications for the development of more efficient and eco-friendly methods for REE recovery from monazite.

Structural and biological evaluation of novel vanadium/Yttrium co-doped hydroxyapatite for bone tissue engineering applications

Hydroxyapatite (HA) is widely used in various medical fields due to its exceptional bioactivity, bio-affinity, and biocompatibility. However, the potential of biomaterials co-doped with metal ions for specific biomedical applications remains underexplored. In this study, we modified the HA structure by introducing vanadium (V) and yttrium (Y) to enhance its physicochemical and biological properties. V-Y co-doped HA (V-Y:HA) samples were prepared by the wet precipitation method using a reflux condensation setup with three different concentrations (0.005 M, 0.01 M, and 0.02 M) of V and Y. The addition of V and Y significantly influenced the biochemical properties and crystal structure of HA. X-ray diffraction (XRD) analysis revealed a modified crystal structure and the presence of the β-tricalcium phosphate (β -TCP) phase in the sample with a higher V concentration. V and Y incorporation resulted in smaller crystallite sizes and noticeable changes in lattice parameters. Scanning electron microscopy (SEM) images displayed sphere-like morphology with extensive aggregation. Fourier-transform infrared spectroscopy (FT-IR) and Raman analysis confirmed the presence of functional groups and phosphate vibrational modes in V-Y:HA samples. X-ray photoelectron spectroscopy (XPS) revealed the ionic and oxide forms of vanadium and the electronic states of yttrium. The as-prepared samples exhibited excellent mechanical strength, reduced porosity, and improved hemocompatibility compared to pure HA. The V-Y:HA sample with a higher V concentration demonstrated enhanced antibacterial activity against P. aeruginosa and S. aureus. In-vitro bioactivity assessment after 21 days revealed enhanced apatite formation on the surface of HA and V-Y:HA materials. These findings suggest that the novel V-Y:HA nanomaterials have great potential as biomaterials for bone tissue engineering and related applications.

Nucleation & growth of α-Ti(HPO4)2·H2O single-crystal and its structure determination from X-ray single–crystal data

α-titanium phosphate phase [α-Ti(HPO4)2·H2O; abbreviated as α-TiP] is a nanolayered metal phosphate with several industrial and recent biotechnological applications related to their nanolayered morphology and ion exchange capabilities. Structural wise, α-TiP is a tetravalent metal phosphate that tends to crystallize into microcrystalline powder. Here we report that the crystallization of single α-TiP crystals with suitable dimensions (>50 μm) for single-crystal X-ray diffraction could be effectuated using a prolonged hydrothermal treatment of a metallic titanium alloy (Ti–6Al–4V) in a highly concentrated phosphoric acid aqueous solution. Accordingly, the single-crystal X-ray diffraction analysis revealed the crystalline structure in a monoclinic space group, P21/c, with a = 8.6288(5) Å, b = 5.00546(17) Å, c = 19.1468(11) Å, and β = 127.555(9)°. Although the space group is the same crystallographic space group that was previously reported from the microcrystalline powder relying on powder X-ray diffraction (PXRD) and neutron powder diffraction, the obtained unit cell volume is slightly larger. Bulk of the obtained crystals were also subjected to detailed analyses using polarization optical microscopy (POM), scanning electron microscopy combined with energy dispersive X-ray microanalysis (SEM-EDX), Fourier transform Infrared Spectroscopy (FTIR) and thermal analysis (TG/SDTA). The single crystals are hexagonally shaped and exhibit the exact titanium to phosphorus ratio expected for α-TiP. The bulk sample PXRD pattern resembles perfectly that reported for the α-TiP polycrystalline powder with clearly sharper peaks. TGA-SDTA analysis revealed the expected thermal behaviour for α-TiP phase and demonstrated their higher thermal stability when compared to the polycrystalline powder.

Calcium phosphate nanoparticles improve growth parameters and mitigate stress associated with climatic variability in avocado fruit

The avocado cv. Hass is one of the most dynamic fruits in the world and is of particular significance in tropical areas, where climate variability phenomena have a high impact on productivity and sustainability. Nanotechnology-based tools could be an alternative to mitigate and/or adapt plants to these phenomena. Our approach was based on identifying changes in temperature and precipitation associated with climate variability in avocado areas in Colombia and proposing mitigation strategies based on the use of nanotechnology. This study had two objectives: (i) to identify variations in temperature and precipitation in avocado-producing areas in Colombia and (ii) to evaluate the effect of calcium phosphate nanoparticles (nano CP) as an alternative to reduce stress in avocados under simulate climatic variability condition. Climatic clusters were determined based on the spatial K-means method and with the climatic temporal series data (1981–2020), a time series analysis we carried out. Later changes in each cluster were simulated in growth chambers, evaluating physiological and developmental responses in avocado seedlings subjected to nanoCaP after adjusting the application form and dose. XRD diffraction shows that the calcium phosphate phases obtained by solution combustion correspond to a mixture of hydroxyapatite and witocklite nanoparticles with irregular morphologies and particle sizes of 100 nm. Three clusters explained ∼90% of the climate variation, with increases and decreases in temperature and precipitation in the range of 1-1.4 °C and 4.1–7.3% respectively. The best-fitted time series models were of stationary autoregressive integrated moving averages (SARIMA). The avocado seedlings had differential responses (P<0.05) depending on the clusters, with a decrease in physiological behavior and development between 10 and 35%. Additionally, the nanoCaP reduced the climatic stress (P< 0.05) in a range between 10 and 22.5%. This study identified the negative effect of climate variability on avocado seedlings and how nanoCaP can mitigate these phenomena.

Effect of copper phosphate on the sintering and ablation resistance of novel ZrSiO4 based composites

ZrSiO4 based composites (ZSCC) were synthesized using copper phosphate as a sintering aid, via sintering at 1000 °C without pressure. The research aimed to investigate the microstructure, mechanical properties, thermophysical properties, and ablation resistance of ZSCC. This was done to enhance the understanding of the ceramic transformation mechanism and ablation mechanism of ZSCC at high temperatures. Results showed that the ZSCC obtained at low-temperature curing had oxide and phosphate phases at room temperature. As the temperature increased, the density of the sample improved, its porosity reduced, and its mechanical properties became more robust. Furthermore, a zirconium silicate ceramic phase was formed. The ZSCC showed remarkable ablation resistance due to the formation of dense oxide layers of ZrSiO4 and ZrO2. After oxyacetylene flame ablation lasting 60 s at 2000 °C, the mass and linear ablation rate of ZSCC were 5.38 mg/s and 8.38 μm/s, respectively.

Trivalent actinides and lanthanides incorporation and partitioning in UMo glass-ceramics

This article focuses on the Am incorporation and location in the UMo-glass ceramic designed to manage fission product solutions enriched in 241Am generated by the reprocessing of UMo spent fuel. This type of glass ceramic contains crystalline phases, which are phosphates, molybdates and zircons, embedded in a durable borosilicate glass matrix.Two types of UMo-glass ceramics were considered in this study. One type of samples was doped with different amounts of Am and/or Nd to assess the comparative role of Nd versus Am in terms of incorporation, location and microstructure. A second type of sample was doped with 244Cm, in order to specify the behavior of 244Cm compared with that of Nd and Am, with a view to using this short-lived isotope for aging experiments.These matrices were characterized by gamma spectrometry and isothermal calorimetry to check the overall homogeneity of Am and Cm, then by Raman spectroscopy, SEM, EPMA and XRD to determine the microstructure and the actinide/Nd distribution in the different phases. The microstructure of the samples was heterogeneous as expected, with the presence of phosphate, molybdate and zircon crystalline phases. A great enrichment of Am, Cm and Nd was observed in the phosphate and molybdate phases compared to the embedding glassy matrix and the zircon crystals. A partition coefficient of around x 6 – 7 for Am and Nd was calculated in these two crystalline phases compared to the mean target doping value. Finally, Nd behaved like trivalent actinides in the UMo matrix and could therefore be considered as a relevant surrogate.

Dentine surface modification and remineralization induced by bioactive toothpastes.

In this study, dentine surface was analysed through Environmental-scanning-electron-microscopy (ESEM) with energy-dispersive-X-ray-spectrometry (EDX) and Fourier-transform-infrared-spectroscopy (FTIR) with attenuated total-reflectance (ATR) to assess the morpho-chemical changes and variations in mineralization degree after demineralizing treatment, after five toothpastes application (HA & Citrate toothpaste, Zinc-HA toothpaste, Calcium Sodium Phosphosilicate toothpaste, Arginine & Calcium carbonate toothpaste, Colgate-Triple-Action, and Control toothpaste), after soaking in artificial saliva and after citric acid attack. Ca/P, Ca/N and P/N ratios were calculated from EDX atomic data to evaluate the mineralization degree of dentine surface. The IR calcium phosphate (CaP)/collagen and carbonate/collagen ratios has been evaluated to assess the remineralization changes in dentine; the carbonate/collagen IR ratio was calculated to identify the nucleation of B-type-carbonated apatite and calcium carbonate. ESEM-EDX and ATR-FTIR showed residuals of toothpastes after the treatments in all cases, with a general increase in the mineralization degree after soaking in artificial saliva and a decrease after acid attack. Treatment with Arginine & Calcium carbonate toothpaste showed the highest Ca/P value after treatment (Ca/P 1.62) and acid attack (Ca/P 1.5) in confirmation, IR showed the highest amount of carbonate after treatment and soaking in artificial saliva. Arginine and calcium carbonate toothpaste and HA and citrate toothpaste remained to a higher extent on the dentine surface and revealed a higher remineralization activity. These formulations showed higher resistance to demineralization attack, as demonstrated by a higher ICaP/IAmide II intensity ratio than those obtained after EDTA treatment. Toothpastes that remained to a higher extent on dentine surface (arginine and calcium carbonate toothpaste in particular) were more able to promote remineralization. The formed calcium phosphate (CaPs) phase was intimately bound to dentine rather than a simple deposit.

Hierarchically porous bioceramics based on geopolymer-hydroxyapatite composite as a novel biomaterial: Structure, mechanical properties and biocompatibility evaluation

In this study, open-cell porous bioceramics based on geopolymers were synthesized by the replica technique. The composition consisted of a mixture of metakaolin (MK) and hydroxyapatite (HA) that combined are suitable for application in bone tissue engineering. Metakaolin is a cheap natural aluminosilicate known for its mechanical properties, while hydroxyapatite stands out for its biocompatibility due to the chemical structure similar to the bone matrix. After undergoing heat treatment (HT), the geopolymer-hydroxyapatite (GMK-HA) synthesized materials, referred to as GMK-HA-HT, presented pores in the range from 1 to 5 mm. In the compressive strength tests, they exhibited values between 1.18 and 2.9 MPa. These ranges of values signify a proper balance between mechanical strength and porosity. X-ray diffraction analysis showed phosphate and/or calcium crystalline phases in all heat-treated samples, indicating HA's successful incorporation in the geopolymer structure. In vitro tests using human adipose-derived mesenchymal stem cells (ADSCs) were conducted to evaluate the biocompatibility of the synthesized materials. The extracts obtained from the GMK-HA-HT were found to be non-cytotoxic. ADSCs in contact with extracts have no morphological changes and when cultured on the GMK-HA-HT surface, the cells interacted with the scaffold and formed a monolayer. Here, for the first time, we provide insights into this new class of materials as a promising biomaterial candidate which could be associated with ADSCs to promote bone healing.

New bone substitute based on nanodispersed calcium ceramics

The article is devoted to developing a synthetic material for bone tissue restoration. The synthesis of bioactive nanostructured ceramic materials was optimized by selecting temperature regimes, parameters of precursors, etc. A new nanostructured bioactive inorganic material - a complex of nanostructured bioactive ceramics with the most effective osteotropic properties was created. It contains calcium phosphate phases, bioactive glasses, and sitalls, including those doped with bioactive elements that give the material unique biological properties, particularly - the prevention and suppression of concomitant diseases. The new material was obtained using gallium and germanium doping of calcium nanodisperse ceramics. The material has been tested experimentally on animals

Properties of hydroxyapatite from tilapia (Oreochromis niloticus) bones: An approach towards its potential use as a dye adsorbent

The properties of hydroxyapatite (HAp) obtained from tilapia (Oreochromis niloticus) bones and its potential use as a dye adsorbent using methyl orange (MO) as a model dye were evaluated. HAp was produced by the calcination of dried tilapia bones at 900 °C for 4 h. Then, HAp was characterized using thermogravimetric (TGA) and differential thermogravimetric (dTG) analyses, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), x-ray diffraction (XRD), among others. The HAp obtained was used for MO dye adsorption in a batch process. The yield of HAp was 51.6%. FTIR showed characteristic bands of functional groups of HAp [OH- and (PO4)3-]. FESEM images showed HAp with different morphologies and a porous surface. The EDS analysis indicated the presence of calcium and phosphorus with an atomic ratio of Ca/P of 1.60, TEM images revealed the formation of agglomerates and an average particle size of 655.1 nm. HAp and β-tricalcium phosphate (β-TCP) phases were identified through XRD. The HAp point of zero charge (pHpzc) was 9.7 indicating a possible adsorption of anionic dyes at pH&lt; pHpzc and cationic dyes at pH&gt; pHpzc. The HAp was able to successfully adsorb 82.6% of MO dye from aqueous solution. These findings demonstrated that the HAp obtained from tilapia (O. niloticus) bones possesses suitable properties to be used as a potential material to remove dyes.

Assessment of glycosaminoglycan content in bone using Raman spectroscopy.

Glycosaminoglycans (GAGs) are responsible for preserving bone tissue toughness as well as regulating collagen formation and mineralization in the extracellular matrix. However, current methods for characterization of GAGs in bone are destructive, thus unable to capture in situ changes or differences in GAGs between experimental groups. As an alternative, Raman spectroscopy is a non-destructive method and can detect concurrent changes in GAGs and other bone constituents. In this study, we hypothesized that the two most prominent Raman peaks of sulfated GAGs (at ~1066cm-1 and at ~1378cm-1) could be used to detect differences in GAGs content of bone. To test this hypothesis, three experimental models were utilized: an in vitro model (enzymatic removal of GAGs from human cadaver bone), an ex vivo mouse model (biglycan KO vs. WT), and an ex vivo aging model (comparing cadaveric bone samples from young and old donors). All Raman measurements were compared to Alcian blue measurements to confirm the validity of Raman spectroscopy in detecting GAGs changes in bone. Irrespective of different models, it was found that the ~1378cm-1 peak in Raman spectra of bone was uniquely sensitive to changes of GAGs content in bone when normalized with respect to the phosphate phase (~960cm-1); i.e., 1378cm-1/960cm-1 (peak intensity ratio) or 1370-1385cm-1/930-980cm-1 (integrated peak area ratio). In contrast, the 1070cm-1 peak, which includes another major peak of GAGs (1066cm-1), seemed to be compromised to detect changes of GAGs in bone due to concurrent changes of carbonate (CO3) in the similar peak range. This study validates the ability of Raman spectroscopy to detect in situ treatment-, genotype-, and age-related changes in GAG levels of bone matrix.

Biomimetic Hydroxyapatite Crystals Growth on Phosphorylated Chitosan Films by In Vitro Mineralization Used as Dental Substitute Materials.

Chitosan (CS) films exhibit great potential as a substrate for the in vitro mineralization process. In this study, to mimic the formation of nanohydroxyapatite (HAP) as natural tissue, CS films coated with a porous calcium phosphate were investigated using scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), Fourier transforms infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). Calcium phosphate coating deposited on phosphorylated derivatives of CS was obtained by a process based on phosphorylation, Ca(OH)2 treatment and artificial saliva solution (ASS) immersion. The phosphorylated CS films (PCS) were obtained by partial hydrolysis of the PO4 functionalities. It was demonstrated that this precursor phase could induce the growth and the nucleation of the porous calcium phosphate coating when immersed in ASS. Moreover, oriented crystals and qualitative control of calcium phosphate phases on CS matrices are obtained in a biomimetic mode. Furthermore, in vitro antimicrobial activity of PCS was evaluated against three species of oral bacteria and fungi. It revealed an increase in antimicrobial activity with minimum inhibition concentration (MIC) values of 0.10% (Candida albicans), 0.05% (Staphylococcus aureus) and 0.025% (Escherichia coli) which proves their possible use as dental substitute materials.

Growth of hydroxyapatite plate-like nanoparticles by additive free precipitation for the deposition of aligned coatings

In recent years, nanoparticles' morphology has been tailored to tune nanoparticle specific properties for several applications. In particular, plate-like particles have been synthesized to create an analog of nacre microstructure exhibiting outstanding mechanical performance attributed to nacre's micro and nano hierarchy. However, the synthesis of equiaxed hydroxyapatite (HA) plates for constructing an oriented architecture has remained as an astounding challenge. In this study, we designed an additive-free chemical precipitation route in which the pH was increased stepwise to maintain the particles' equiaxed 2d shape. Our results showed that the produced particles exhibited HA's crystal structure and highly sustained the equiaxed/rectangular plate morphology of the octacalcium phosphate (OCP) phase, formed as an interphase during the precipitation. The reaction time, reactant concentration, and heat treatment were found essential in controlling the particles' morphology, size, and crystal symmetry. The crystal features of the particles were dissected via high-resolution scanning and transmission electron microscopes (HRSEM and HRTEM) and X-ray diffraction (XRD) analysis. Moreover, the Williamson-Hall plot and Rietveld Size-strain algorithm were implemented to calculate the crystallite size and strain of the particles. HRSEM and HRTEM micrographs showed that ultrathin (10–20 nm) 2d HA particles with mean lengths of 140–150 nm grew through the c-axis. In the last stage, we attempted to use the particles to deposit oriented coatings by electrophoretic deposition (EPD).

Enhancement of surface properties of cementitious materials by phosphate treatments

This study aims at investigating the ability of aqueous phosphate solutions to improve the surface properties of cement pastes via the formation of low-solubility calcium phosphate (CaP) phases. Diammonium hydrogen phosphate (DAP), dipotassium hydrogen phosphate (DPP) and disodium hydrogen phosphate (DSP) were investigated based on thermodynamic modeling and experiments. For DPP, the influence of concentration and cement age was evaluated. A 1 M DPP + 1 mM CaCl2 solution applied to cement hydrated for 7 days was most promising. The CaP coating formed after 24 h of exposure resulted in significant improvements in the cement pastes' resistance to abrasion, surface indentation and staining. Preliminary durability tests by immersion in water were successfully carried out to ascertain that no efflorescence due to soluble salts appeared and that mechanical improvement was retained. Compared to DAP, DPP has the advantage of not releasing NH3 into the atmosphere, thus preventing unpleasant odor and improving the treatment's environmental sustainability.

Effects of carbonate species and chloride ions on calcium phosphate nucleation of biological apatite

Apatite is the principal inorganic component of biological hard tissues such as bone and teeth, and thus is essential to the existence of vertebrate life. Because carbonate species and chloride ions are ubiquitous in the fluids of vertebrate life forms, and these species are known to compete with phosphate species, it is critical to understand the influence of these anions on the nucleation of biological apatite. In this study, the important roles of carbonate and chloride ions in mediating inorganic calcium phosphate (CaP) phase nucleation are revealed both theoretically and experimentally. Theoretical investigations suggest that the Ca-O coordination number is an important descriptor for the nucleation of CaP and the interface interaction of the CaP-additive. Positive surface charges on the outermost Ca2+ ions of CaP clusters could attract carbonate species and Cl− ions, promoting the formation of CaP phase. In the presence of carbonate species and Cl− ions, the crystallization of hydroxyapatite (HA) from its precursor brushite (DCPD) has been observed in our experimental studies. The Cl− ion-doped B-type HA is proposed to be the most likely biological apatite based on equilibrium oxygen isotope fractionation and vibrational spectroscopic analysis. The insight gained here may help rationalize the control of biomineralization, and will guide the synthesis of anion-doped biological functional apatite materials.

Biomineralization in Three-Dimensional Scaffolds Based on Bacterial Nanocellulose for Bone Tissue Engineering: Feature Characterization and Stem Cell Differentiation.

Bacterial nanocellulose (BNC) has a negative surface charge in physiological environments, which allows the adsorption of calcium ions to initiate the nucleation of different calcium phosphate phases. The aim of this study was to investigate different methods of mineralization in three-dimensional microporous bacterial nanocellulose with the intention of mimicking the composition, structure, and biomechanical properties of natural bone. To generate the 3D microporous biomaterial, porogen particles were incorporated during BNC fermentation with the Komagataeibacter medellinensis strain. Calcium phosphates (CPs) were deposited onto the BNC scaffolds in five immersion cycles, alternating between calcium and phosphate salts in their insoluble forms. Scanning electron microscopy (SEM) showed that the scaffolds had different pore sizes (between 70 and 350 µm), and their porous interconnectivity was affected by the biomineralization method and time. The crystals on the BNC surface were shown to be rod-shaped, with a calcium phosphate ratio similar to that of immature bone, increasing from 1.13 to 1.6 with increasing cycle numbers. These crystals also increased in size with an increasing number of cycles, going from 25.12 to 35.9 nm. The main mineral phase observed with X-ray diffraction was octacalcium dihydrogen hexakis phosphate (V) pentahydrate (OCP). In vitro studies showed good cellular adhesion and high cell viability (up to 95%) with all the scaffolds. The osteogenic differentiation of human bone marrow mesenchymal stem cells on the scaffolds was evaluated using bone expression markers, including alkaline phosphatase, osteocalcin, and osteopontin. In conclusion, it is possible to prepare 3D BNC scaffolds with controlled microporosity that allow osteoblast adhesion, proliferation, and differentiation.

Anionic Polysaccharide Cryogels: Interaction and In Vitro Behavior of Alginate-Gum Arabic Composites.

In the present study, polysaccharide-based cryogels demonstrate their potential to mimic a synthetic extracellular matrix. Alginate-based cryogel composites with different gum arabic ratios were synthesized by an external ionic cross-linking protocol, and the interaction between the anionic polysaccharides was investigated. The structural features provided by FT-IR, Raman, and MAS NMR spectra analysis indicated that a chelation mechanism is the main process linking the two biopolymers. In addition, SEM investigations revealed a porous, interconnected, and well-defined structure suitable as a scaffold in tissue engineering. The in vitro tests confirmed the bioactive character of the cryogels through the development of the apatite layer on the surface of the samples after immersion in simulated body fluid, identifying the formation of a stable phase of calcium phosphate and a small amount of calcium oxalate. Cytotoxicity tests performed on fibroblast cells demonstrated the non-toxic effect of alginate-gum arabic cryogel composites. In addition, an increase in flexibility was noted for samples with a high gum arabic content, which determines an appropriate environment to promote tissue regeneration. The newly obtained biomaterials that exhibit all these properties can be successfully involved in the regeneration of soft tissues, wound management, or controlled drug release systems.