Hydroxyapatite micro- and nanoparticles: nucleation and growth mechanisms in the presence of citrate species

Soil properties and nutrient uptake of maize (Zea mays) as influenced by mixed manure and blended inorganic fertilizer in Haramaya district, eastern Ethiopia

The deteriorating state of soil fertility and low agricultural productivity in Ethiopia can be traced to the lack of equivalent consideration given to the soil's biological, chemical, and physical properties. A pot experiment was conducted to investigate the effect of mixed manure and blended nitrogen, phosphorus, sulfur and boron (NPSB) fertilizer on phosphorus adsorption, and other properties of Vertisols, nutrient uptake, and growth performance of maize. The study findings indicate that the combined application of mixed manure and blended NPSB significantly reduced soil pH from 7.87 to 7.68, phosphorus adsorption efficiency from 93 to 88.5 %, and Freundlich adsorption capacity from 194 to 100.75 mg kg-1 , intensity from 1.96 to 1.27 compared to control. However, combined application of these two treatments significantly increased the organic carbon from 0.81 to 1.64 %, total nitrogen from 0.04 to 0.13 %, and available phosphorus from 6.96 to 73.82 g kg-1. The study further revealed that mixed manure and blended NPSB resulted in significantly (p ≤ 0.05) higher contents of nitrogen and phosphorus in the maize leaves as well as their uptake compared to their sole application and control. The highest values of these parameters were observed in plots treated with a combined application of 15 t ha-1 mixed manure with each rate of 100 and 150 kg ha-1 blended NPSB. Additionally, the maize plant height (p ≤ 0.05) and above-ground biomass (p ≤ 0.01) also exhibited significant increase. Compared to the control and full dose of NPSB, all the treatments that received a combined application of 15 t ha-1 mixed manure with blended NPSB ranging from 50 to 150 kg ha-1 resulted in significantly higher above-ground biomass of maize. The results suggest that the combined use of mixed manure and blended NPSB could be a practical and effective approach to improve soil properties and maize above-ground biomass yield.

Tailoring the structure and self-activated photoluminescence of carbonated amorphous calcium phosphate nanoparticles for bioimaging applications

Self-activated luminescent calcium phosphate (CaP) nanoparticles, including hydroxyapatite (HA) and amorphous calcium phosphate (ACP), are promising for bioimaging and theragnostic applications in nanomedicine, eliminating the need for activator ions or fluorophores. In this study, we developed luminescent and stable citrate-functionalized carbonated ACP nanoparticles for bioimaging purposes. Our findings revealed that both the CO32- content and the posterior heating step at 400 °C significantly influenced the composition and the structural ordering of the chemically precipitated ACP nanoparticles, impacting the intensity, broadness, and position of the defect-related photoluminescence (PL) emission band. The heat-treated samples also exhibited excitation-dependent PL under excitation wavelengths typically used in bioimaging (λexc = 405, 488, 561, and 640 nm). Citrate functionalization improved the PL intensity of the nanoparticles by inhibiting non-radiative deactivation mechanisms in solution. Additionally, it resulted in an increased colloidal stability and reduced aggregation, high stability of the metastable amorphous phase and the PL emission for at least 96 h in water and supplemented culture medium. MTT assay of HepaRG cells, incubated for 24 and 48 h with the nanoparticles in concentrations ranging from 10 to 320 μg mL-1, evidenced their high biocompatibility. Internalization studies using the nanoparticles self-activated luminescence showed that cellular uptake of the nanoparticles is both time (4-24 h) and concentration (160-320 μg mL-1) dependent. Experiments using confocal laser scanning microscopy allowed the successful imaging of the nanoparticles inside cells via their intrinsic PL after 4 h of incubation. Our results highlight the potential use of citrate-functionalized carbonated ACP nanoparticles for use in internalization assays and bioimaging procedures.

Effects of Adding Chitosan on Drug Entrapment Efficiency and Release Duration for Paclitaxel-Loaded Hydroxyapatite-Gelatin Composite Microspheres

Hydroxyapatite-gelatin microspheres with cone-like pores were synthesized via the wet-chemical method using ammonium dihydrogen phosphate ((NH4)H2PO4) and calcium nitrate (Ca(NO3)2·4H2O) as a source of calcium and phosphate ions with the addition of gelatin, which proved to be more osteoconductive than commercial products, such as fibrin glue and Osteoset® Bone Graft Substitute. Following the method of the previous study for loading paclitaxel (PTX), a drug entrapment efficiency of around 58% was achieved, which is much lower than that of the doxorubicin (DOX)-loaded one. Since PTX is hydrophobic while DOX is hydrophilic, the order of chitosan processing and addition of the solvent were tuned in this study, finally leading to an increase in drug entrapment efficiency of 94%. Additionally, the release duration of PTX exceeded six months. The MTT assay indicated that the effect of drug release on the suppression of cancer cells reached more than 40% after one week, thereby showcasing PTX's capacity to carry out its medicinal functions without being affected by the loading procedures.

Effects of ATP on the Physicochemical Properties and Cytocompatibility of Calcium Sulfate/Calcium Citrate Composite Cement

Adenosine triphosphate (ATP), acting as a source of energy, has effects on cellular activities, such as adhesion, proliferation, and differentiation. In this study, ATP-loaded calcium sulfate hemihydrate/calcium citrate tetrahydrate cement (ATP/CSH/CCT) was successfully prepared for the first time. The effect of different contents of ATP on the structure and physicochemical properties of ATP/CSH/CCT was also studied in detail. The results indicated that incorporating ATP into the cement did not significantly alter their structures. However, the addition ratio of ATP directly impacted the mechanical properties and in vitro degradation properties of the composite bone cement. The compressive strength of ATP/CSH/CCT gradually decreased with an increasing ATP content. The degradation rate of ATP/CSH/CCT did not significantly change at low concentrations of ATP, but it increased with a higher ATP content. The composite cement induced the deposition of a Ca-P layer in a phosphate buffer solution (PBS, pH = 7.4). Additionally, the release of ATP from the composite cement was controlled. The ATP was controlled releasing at the 0.5% and 1% ATP in cement by the diffusion of ATP and the degradation of the cement, whereas it was controlled by the diffusion process merely at the 0.1% ATP in cement. Furthermore, ATP/CSH/CCT demonstrated good cytoactivity with the addition of ATP and is expected to be used for the repair and regeneration of bone tissue.

Injectable Self-Setting Ternary Calcium-Based Bone Cement Promotes Bone Repair

Bone defects, especially large ones, are clinically difficult to treat. The development of new bone repair materials exhibits broad application prospects in the clinical treatment of trauma. Bioceramics are considered to be one of the most promising biomaterials owing to their good biocompatibility and bone conductivity. In this study, a self-curing bone repair material having a controlled degradation rate was prepared by mixing calcium citrate, calcium hydrogen phosphate, and semi-hydrated calcium sulfate in varying proportions, and its properties were comprehensively evaluated. In vitro cell experiments and RNA sequencing showed that the composite cement activated PI3K/Akt and MAPK/Erk signaling pathways to promote osteogenesis by promoting the proliferation and osteoblastic differentiation of mesenchymal stem cells. In a rat model with femoral condyle defects, the composite bone cement showed excellent bone repair effect and promoted bone regeneration. The injectable properties of the composite cement further improved its practical applicability, and it can be applied in bone repair, especially in the repair of irregular bone defects, to achieve superior healing.

Efficient capture of recombinant SARS-CoV-2 receptor-binding domain (RBD) with citrate-coated magnetic iron oxide nanoparticles

Several vaccines against COVID-19 use a recombinant SARS-CoV-2 receptor-binding domain (RBD) as antigen, making the purification of this protein a key step in their production. In this work, citrate-coated magnetic iron oxide nanoparticles were evaluated as nano adsorbents in the first step (capture) of the purification of recombinant RBD. The nanoparticles were isolated through coprecipitation and subsequently coated with sodium citrate. The citrate-coated nanoparticles exhibited a diameter of 10 ± 2 nm, a hydrodynamic diameter of 160 ± 3 nm, and contained 1.9 wt% of citrate. The presence of citrate on the nanoparticles' surface was confirmed through FT-IR spectra and thermogravimetric analysis. The crystallite size (10.1 nm) and the lattice parameter (8.3646 Å) were determined by X-ray diffraction. In parallel, RBD-containing supernatant extracted from cell culture was exchanged through ultrafiltration and diafiltration into the adsorption buffer. The magnetic capture was then optimized using different concentrations of nanoparticles in the purified supernatant, and we found 40 mg mL^-1 to be optimal. The ideal amount of nanoparticles was assessed by varying the RBD concentration in the supernatant (between 0.113 mg mL^-1 and 0.98 mg mL^-1), which resulted in good capture yields (between 83 ± 5% and 94 ± 4%). The improvement of RBD purity after desorption was demonstrated by SDS-PAGE and RP-HPLC. Furthermore, the magnetic capture was scaled up 100 times, and the desorption was subjected to chromatographic purifications. The obtained products recognized anti-RBD antibodies and bound the ACE2 receptor, proving their functionality after the developed procedure.

Biomineralization of bone tissue: calcium phosphate-based inorganics in collagen fibrillar organic matrices

BACKGROUND

Bone regeneration research is currently ongoing in the scientific community. Materials approved for clinical use, and applied to patients, have been developed and produced. However, rather than directly affecting bone regeneration, these materials support bone induction, which regenerates bone. Therefore, the research community is still researching bone tissue regeneration. In the papers published so far, it is hard to find an improvement in the theory of bone regeneration. This review discusses the relationship between the existing theories on hard tissue growth and regeneration and the biomaterials developed so far for this purpose and future research directions.

MAINBODY

Highly complex nucleation and crystallization in hard tissue involves the coordinated action of ions and/or molecules that can produce different organic and inorganic composite biomaterials. In addition, the healing of bone defects is also affected by the dynamic conditions of ions and nutrients in the bone regeneration process. Inorganics in the human body, especially calcium- and/or phosphorus-based materials, play an important role in hard tissues. Inorganic crystal growth is important for treating or remodeling the bone matrix. Biomaterials used in bone tissue regeneration require expertise in various fields of the scientific community. Chemical knowledge is indispensable for interpreting the relationship between biological factors and their formation. In addition, sources of energy for the nucleation and crystallization processes of such chemical bonds and minerals that make up the bone tissue must be considered. However, the exact mechanism for this process has not yet been elucidated. Therefore, a convergence of broader scientific fields such as chemistry, materials, and biology is urgently needed to induce a distinct bone tissue regeneration mechanism.

CONCLUSION

This review provides an overview of calcium- and/or phosphorus-based inorganic properties and processes combined with organics that can be regarded as matrices of these minerals, namely collagen molecules and collagen fibrils. Furthermore, we discuss how this strategy can be applied to future bone tissue regenerative medicine in combination with other academic perspectives.

Chemical Bonding of Biomolecules to the Surface of Nano-Hydroxyapatite to Enhance Its Bioactivity

Hydroxyapatite (HA) is a significant constituent of bones or teeth and is widely used as an artificial bone graft. It is often used to replace the lost bones or in reconstructing alveolar bones before dental implantation. HA with biological functions finds its importance in orthopedic surgery and dentistry to increase the local concentration of calcium ions, which activate the growth and differentiation of mesenchymal stem cells (MSC). To make relevant use of HA in bone transplantation, the surfaces of orthopedic and dental implants are frequently coated with nanosized hydroxyapatite (nHA), but its low dispersibility and tendency to form aggregates, the purpose of the surface modification of bone implants is defeated. To overcome these drawbacks and to improve the histocompatibility of bone implants or to use nHA in therapeutic applications of implants in the treatment of bone diseases, various studies suggested the attachment of biomolecules (growth factors) or drugs through chemical bonding at the surface of nHA. The growth factors or drugs bonded physically at the surface of nHA are mostly unstable and burst released immediately. Therefore, reported studies suggested that the surface of nHA needs to be modified through the chemical bonding of biologically active molecules at the surface of bone implants such as proteins, peptides, or naturally occurring polysaccharides to prevent the aggregation of nHA and to get homogenous dispersion of nHA in solution. The role of irradiation in producing bioactive and antibacterial nHA through morphological variations in surfaces of nHA is also summarized by considering internal structures and the formation of reactive oxygen species on irradiation. This mini-review aims to highlight the importance of small molecules such as proteins, peptides, drugs, and photocatalysts in surface property modification of nHA to achieve stable, bioactive, and antibacterial nHA to act as artificial bone implants (scaffolds) in combination with biodegradable polymers.

Synthesis and application of nanometer hydroxyapatite in biomedicine

Nano-hydroxyapatite (nano-HA) has been widely studied as a promising biomaterial because of its potential mechanical and biological properties. In this article, different synthesis methods for nano-HA were summarized. Key factors for the synthesis of nano-HA, including reactant concentration, effects of temperature, PH, additives, aging time, and sintering, were separately investigated. The biological performances of the nano-HA depend strongly on its structures, morphology, and crystallite sizes. Nano-HA with different morphologies may cause different biological effects, such as protein adsorption, cell viability and proliferation, angiogenesis, and vascularization. Recent research progress with respect to the biological functions of the nano-HA in some specific biological applications are summarized and the future development of nano-sized hydroxyapatite is prospected.

On the Comprehensive Precipitation of Hydroxyapatites Unraveled by a Combined Kinetic-Thermodynamic Approach

The present study combines experimental and theoretical approaches to investigate the competitive precipitation of calcium phosphates (CaPs) in aqueous solution in order to understand and control both the structural and textural properties of the synthesized hydroxyapatites (HAps). Some of the precipitation reactions were followed by in situ Raman spectroscopy or achieved under kinetically controlled conditions. The CaP precursors of HAps were identified as a function of the precipitation pH of the medium and the order of introduction of the precursor ions in the synthesis reactor. Their formation was rationalized by calculations based on a homogeneous nucleation model. Depending on the synthesis conditions, precipitation reaction pathways of HAps are proposed by bringing together the kinetic model developed in the present study and our previous thermodynamic model. HAps are complex materials due to the ease with which large amounts of crystallographic defects, such as carbonates and hydrogen phosphates, can be incorporated in their structure. As these defects play a key role in material sciences (bone substitute, heterogeneous acid-base catalysis, etc.), the present work also includes the analysis of the formation of these crystallographic defects in the apatitic framework, allowing a better control of their incorporation through careful selection of operating parameters.

Nanostructural control of transparent hydroxyapatite nanoparticle films using a citric acid coordination technique

Hydroxyapatite (HA), as the main mineral component in hard tissues, has good biocompatibility. In particular, HA films are widely used as bioactive coatings for artificial bones and dental implants in biomedical fields. However, it is currently difficult to prepare a nanostructure-controlled HA film by a wet process for further applications. Herein, we report the synthesis of HA nanoparticles coordinated by citric acid (Cit/HA) based on the interactions between carboxylate and calcium ions to control the sizes and shapes of the hybrid nanoparticles, to improve their dispersibility in water and to eventually form uniform transparent films with nanospaces, and investigated the film formation mechanism. As compared with the well-known rod-like HA nanoparticles (size: 48 × 15 nm²), we successfully synthesized spherical and negatively charged Cit/HA nanoparticles (size: 25 × 23 nm²) to achieve highly transparent Cit/HA films using the spin-coating technique. The Cit/HA films had uniform and crack-free appearance. About the nanostructures, we found that the Cit/HA film surfaces had meso-scaled nanospaces with a diameter of 4.2 nm based on the regular arrangement of spherical nanoparticles, instead of the HA film with a nanospace diameter of 24.5 nm formed by non-uniform accumulation. Therefore, we successfully achieved the control of the nanospace sizes of the films with the nanoparticle arrangement and realized transparent nanoparticle film formation in a very simple way, which will provide more convenient bioceramic films for biomedical applications.

The effect of chemical structure of carboxylate molecules on hydroxyapatite nanoparticles. A structural and morphological study

Being the most abundant non-macromolecular organic component of bone, the role of citrate (Cit) in hydroxyapatite (HA) crystallization is of high relevance. In this work we have investigated the influence of hydroxycitrate (CitOH) and glutarate (Glr) on HA crystallization in terms of particle growth, composition, and morphology in comparison to Cit. CitOH and Glr have been selected for this work because they share the same backbone structure of Cit but bear different functional groups in the central region. Our data has revealed that CitOH strongly inhibits HA crystallization more efficiently than Cit. CitOH-HA nanoparticles are composed of platy, elongated particles similar to those of Cit-HA but they are ca. twice smaller and have a lower crystal order. On the other hand, Glr does not inhibit HA crystallization as Cit, but leads to the formation of OCP platelets that convert with maturation time to HA nanorods with larger aspect ratio than Cit-HA. In comparison to Cit-HA samples, Glr-HA nanoparticles have bigger dimensions, and higher structural order. Overall, our data reveal that the central carboxyl group of Cit is involved in the selective binding with HA crystal surface and in regulating HA crystal growth. The results of this work highlight new possibilities to control the formation of HA for designing advanced bioactive materials and give new insights on the role of the structure of Cit in regulating the HA morphology.

Molecular Dynamics Exploration of the Growth Mechanism of Hydroxyapatite Nanoparticles Regulated by Glutamic Acid

Morphological control can enhance the performance of materials like hydroxyapatite (HAP), a well-known bioceramic with various morphologies, including spheres, rods, whiskers, needles, and plates. To obtain certain HAP morphologies, the crystal growth mechanisms at different planes should be investigated. Here, molecular dynamics was employed to understand the mechanism of HAP nanoparticle growth regulated by glutamic acid (Glu). Long-time dynamics simulations and free energy calculations were performed to explore the effect of Glu on calcium and phosphate ion precipitation on the HAP (100) and (001) faces. Without Glu, PO₄^3- prefers binding to the HAP (100) surface, whereas with Glu, the (001) surface is preferred. This could partially explain why HAP changes from needle-like to plate-like with Glu addition in experiments. Our theoretical results indicate that Glu inhibits calcium and phosphate ion deposition on the crystal surfaces by occupying the calcium sites on the outermost layers. In addition, Glu has a strong concentration gradient effect on HAP deposition. At Glu concentrations of >80 mM, ion deposition was inhibited more on the (100) than on the (001) surface. Our results agree with experimental observations and afford insights into complicated HAP crystal growth mechanisms with foreign additives, which will aid in HAP synthesis with morphological control.

Simulation Insight into the Synergic Role of Citrate and Polyaspartic Peptide in Biomineralization

Hydroxyapatite (HAP) is one of the most important inorganic components in biological minerals such as bones and teeth. More than 90% of the total citrate is accumulated in human bones and other biomineralized tissues. In addition, mineralizing proteins are enriched in glutamate and aspartate residues, which are important for their mineral-regulating properties. However, how citrate ions (CITs) and/or acidic amino acids regulate the formation of HAP is still unclear. In this work, molecular dynamics simulations were performed to study how CIT regulates the adsorption behavior of polyaspartic acid (PASP) on the HAP surface in the calcium phosphate solution. The simulation results indicate that PASP can be used as an ion chelator to complex Ca²⁺ and can serve as templates for HAP mineralization by templating the distribution of Ca²⁺ on its surface, which are attributed to the -COO^- and α-helix structure. Most importantly, the orientation distributions of PASP in all systems are narrower with the help of CIT, thereby PASP can be adsorbed on the HAP surface stably with a "lying-down" orientation. This indicates that CIT can be used as a bridging agent to bond the acidic peptide to the HAP surface in biomineralization. Thus, the synergic role of CIT and the acidic peptide on the HAP surface were revealed in this work, which can provide new insights into the interfacial phenomena during the biomineralization.

A plant-mediated synthesis of nanostructured hydroxyapatite for biomedical applications: a review

The engineering of calcium-based phosphate materials at the nanoscale gains several unique properties compared to the bulky state. The effort to scale down, e.g., from bulky state to nanoscale in order to control the morphology and improve structural properties requires the use of varying reagents that can be detrimental to the environment. A typical example of these materials is hydroxyapatite (HAp), one of the well-known calcium phosphate materials, which has a close resemblance to human bone tissue. HAp has valuable applications in catalysis, drug delivery, bone and dental implant formation, and adsorption. Hydroxyapatite-based nanomaterials synthesized through conventional routes make use of reagents that are not environmental friendly and are very costly. Since the current research trends are geared towards producing/synthesizing nanomaterials through an eco-friendly approach, there is the need to consider the techniques and reagents involved in the synthesis of HAp. This review touches on the possible replacement of such synthetic chemical reagents, synthesis routes, and toxic capping agents with plant extracts for synthesizing HAp-based nanomaterials for multi-functional applications. The influence of biomolecules from plants on synthesized HAps and the attainable mechanism during these green approaches are discussed. Viable future modifications of the methods used to obtain extracts from plants are also studied.

Lanthanides-Substituted Hydroxyapatite/Aloe vera Composite Coated Titanium Plate for Bone Tissue Regeneration

PURPOSE

To develop the surface-treated metal implant with highly encouraged positive properties, including high anti-corrosiveness, bio-activeness and bio-compatibleness for orthopedic applications.

METHODS

In this work, the surface of commercially pure titanium (Ti) metal was treated with bio-compatible polydopamine (PD) by merely immersing the Ti plate in PD solution. The composite of trivalent lanthanide minerals (La3+, Ce3+ and Gd3+)-substituted hydroxyapatite (MHAP) with Aloe vera (AV) gel was prepared and coated on the PD-Ti plate by electrophoretic deposition (EPD) method. The choice of trivalent lanthanide ions is based on their bio-compatible nature and bone-seeking properties. The formation of the PD layer, composites, and composite coatings on Ti plate and PD-Ti surface was confirmed by FT-IR, XRD, SEM and HR-TEM observations. In-vitro assessments such as osteoblasts like MG-63 cell viability, alkaline phosphatase activity and mineralization ability of the MHAP/AV composite were tested, and the composite-coated plate was implanted into a rat bone defect model for in-vivo bone regeneration studies.

RESULTS

The coating ability of the MHAP/AV composite was highly preferred to PD-treated Ti plate than an untreated Ti plate due to the metal absorption ability of PD. This was confirmed by SEM analysis. The in-vitro and in-vivo studies show the better osteogenic ability of MHAP/AV composite at 14th day and 4th week of an experimental period, respectively.

CONCLUSION

The osteoblast ability of the fabricated device without producing any adverse effect in the rat model recommends that the fabricated device would serve as a better platform on the hard tissue regeneration for load-bearing applications of orthopedics.

Citrate zinc hydroxyapatite nanorods with enhanced cytocompatibility and osteogenesis for bone regeneration

The development of biomaterials that mimicking the hydroxyapatite nanoparticles existent in the immature bone tissue is crucial, especially to accelerate the bone remodeling and regeneration. In this work, it was developed for the first time, hydroxyapatite nanoparticles (NPs) incorporating citrate and zinc (cit-Zn-Hap) in their composition towards a one-step hydrothermal procedure. For comparison purposes, hydroxyapatite NPs incorporating only zinc (Zn-Hap) or citrate (cit-Hap), as well as hydroxyapatite without any of these elements (Hap) were synthesised. The physicochemical characterization was carried out reveling that, the presence of zinc on hydroxyapatite (cit-Zn-Hap), reduced the size of nanoparticles, changed the phosphate environment and decreased the surface charge when compared with cit-Hap nanoparticles. The osteogenic potential of cit-Zn-Hap NPs was analysed in human bone marrow-derived stromal cells (BMSCs), in the absence of osteoinductive factors. NPs were internalized by endocytosis appearing trapped in endosomes and lysosomes scattered through the cytoplasm. Exposure to these NPs resulted in a significant induction of ALP activity, extracellular matrix mineralization, and gene expression of early and later osteogenic transcription factors, as well as of osteoblastic markers. The osteoinductive effect might be regulated, at least in part, by the increased signalling through the canonical WNT pathway. Evaluation of the cell behaviour following exposure to Zn-Hap and cit-Hap strongly suggested a synergistic effect of citrate and Zn in cit-Zn-Hap NPs towards the induction of the osteogenic commitment and functionality of BMSCs. These findings will allow the design of new biomimetic hydroxyapatite nanoparticles with great potential for bone regeneration.

Citrate therapy for calcium phosphate stones

PURPOSE OF REVIEW

Calcium phosphate (CaP) stones represent an increasingly encountered form of recurrent nephrolithiasis, but current prophylactic medical regimens are suboptimal. Although hypocitraturia is a well-described risk factor for CaP stones, strategies that enhance citrate excretion have not consistently been effective at reducing CaP saturation and stone recurrence. This review summarizes the role of citrate therapy in CaP nephrolithiasis.

RECENT FINDINGS

Citrate in urine inhibits CaP stone formation through multiple mechanisms, including the formation of soluble citrate-calcium complexes, and inhibition of CaP nucleation, crystal growth and crystal aggregation. Recent in-vitro studies demonstrate that citrate delays CaP crystal growth through distinct inhibitory mechanisms that depend on supersaturation and citrate concentration. The impact of pharmacological provision of citrate on CaP saturation depends on the accompanying cation: Potassium citrate imparts a significant alkali load that enhances citraturia and reduces calciuria, but could worsen urine pH elevation. Conversely, citric acid administration results in minimal citraturia and alteration in CaP saturation.

SUMMARY

Citrate, starting at very low urinary concentrations, can significantly retard CaP crystal growth in vitro through diverse mechanisms. Clinically, the net impact on CaP stone formation of providing an alkali load during pharmacological delivery of citrate into the urinary environment remains to be determined.

Effect of anions on the structural, morphological and dielectric properties of hydrothermally synthesized hydroxyapatite nanoparticles

Abstract

Synthetic nano hydroxyapatites (HA) have been considered as potential biomaterials for bone tissue engineering applications because of its excellent biological properties. The present work deals with the synthesis of HA nanoparticles from different anion source materials via autoclave assisted hydrothermal method. All the prepared HA nanoparticles were characterized by X-ray diffraction (XRD), Fourier transformation infrared spectra, field emission scanning electron microscopy, energy dispersive spectra and high resolution transmission electron microscopy. The XRD patterns reveal the pure and hexagonal phase structure with smaller crystallite size for HA obtained from various calcium salt precursors. HA particles prepared from nitrate precursors show spherical morphology with 32 nm grain size whereas those derived from the acetate, chloride and egg shell precursors respectively show needle-like, irregular and oval morphology. The effect of different anions on the dielectric properties and alternating conductivity of HA is investigated, as a polarized surface can trigger biological reactions. For the particles obtained from nitrate, acetate, chloride and egg shell precursors respectively give dielectric constant (εʹ) values of 9.96, 13.22, 9.92 and 10.86 at 5 MHz. The εʹ and dielectric loss (εʹʹ) values for the HA nanoparticles decrease with increase in the applied frequency as well. The alternating current conductivity values confirm that the as-synthesized HA samples exhibit insulating behavior. In short this article provides the various applicability of HA particles in optoelectronics and drug delivery.

Graphic abstract

Preparation of Small-Particle and High-Density Cobalt Carbonate Using a Continuous Carbonate Precipitation Method and Evaluation of Its Growth Mechanism

Spherical CoCO₃ powder with a small particle size and high density was successfully prepared using a continuous carbonate liquid precipitation method with a raw material of cobalt chloride solution, a precipitant of NH₄HCO₃, and without a template. The effects of the concentration of ammonium carbonate, process pH, and feeding rate on the tap density and apparent density of cobalt carbonate were investigated. It was found that the apparent and tap density values of 4.4 µm of cobalt carbonate were 1.27 g/cm³ and 1.86 g/cm³, respectively, when the initial concentration of NH₄HCO₃ solution was 60 g/L, the pH was 7.15–7.20, and the feeding rate of cobalt chloride was 2 L/h. The anisotropic growth process of the crystal lattice plane of CoCO₃ under the aforementioned optimal conditions were studied. The results demonstrated that the crystal grew fastest along the (110) facet orientation, which was the dominant growth surface, determining the final morphology of the primary particles. The scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) results demonstrated that the primary particle morphology of the cobalt carbonate was a nanosheet. The unit cell of cobalt carbonate, of a hexagonal structure in the horizontal direction, grew horizontally along the (110) facet orientation, while 20–35 unit cells of the carbon carbonate were stacked along the c-axis in the thickness direction. Finally, the sheet-shaped particles were agglomerated into dense spherical secondary particles, as presented through the crystal re-crystallization model.

Management Strategies to Optimize Soil Phosphorus Utilization and Alleviate Environmental Risk in China

In the last decade, crop production in China has dramatically improved due to greater phosphorus (P) input. As P fertilizer application rates increased from 88 to 123 kg PO ha yr during 2004 to 2014, total P use efficiency (total P output in crops as a percentage of total P input) dropped from 68 to 20%, leading to an accumulation of >90 kg PO ha in the soil each year. Phosphorus lost from agriculture is the second greatest contributor to waterbody eutrophication in China, accounting for 25% of total P losses in 2010; the main contributor is livestock husbandry. Given these problems, as well as the finite nature of P reserves, three strategies are proposed here to reduce P fertilizer application rates, improve P use efficiency, and minimize the environmental risk caused by P loss in China: (i) improving soil legacy P utilization by modifying cropping systems, rhizosphere management, or microbial engineering, (ii) increasing P use efficiency by reducing P fertilizer applications and minimizing P fertilizer fixation, and (iii) promoting the extension of soil P management strategies. For these management strategies to succeed in China, close cooperation should be established among farmers, scientists, and governments in the future.

Metal and polymer-mediated synthesis of porous crystalline hydroxyapatite nanocomposites for environmental remediation

This study was focused on the preparation of metal and polymer-mediated porous crystalline hydroxyapatite (HAp) nanocomposites for environmental applications. Four different nano HAp systems were synthesized, namely, microwave irradiated HAp (M1), Zn doped HAp (M2), Mg-doped HAp (M3) and sodium alginate incorporated HAp (M4), and characterized using X-ray diffraction (XRD), Fourier transform infra-red spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, nuclear magnetic resonance (NMR), X-ray fluorescence, thermogravimetric analysis and Brunauer-Emmett-Teller (BET) analyses. Systems M1-M4 showed morphologies similar to coral shapes, polymer-like interconnected structures, sponges and feathery mycelium assemblies. Using XRD, selected area electron diffraction patterns and 1H and 31P CP/MAS solid-state NMR studies, crystallinity variation was observed from highest to lowest in the order of M4 > M1 > M3 > M2. Surface area estimates using BET isotherm reflected the highest surface area for M3, and M1 > M2 > M4. Four systems of M1-M4 were used as potential adsorbent materials for the removal of metal containing azo dye from aqueous system. Adsorption data were correlated to Freundlich and Langmuir isotherm models. According to the results, the highest capacity of 212.8 mg g-1 was exhibited by M4 having mycelium like morphology with alginate groups. This study highlights the possibility of developing HAp nanocomposites for the effective removal of dye contaminants in the environment.

EDTA and NTA Effectively Tune the Mineralization of Calcium Phosphate from Bulk Aqueous Solution

This study describes the effects of nitrilotriacetic acid (NTA) and ethylenediaminotetraacetic acid (EDTA) on the mineralization of calcium phosphate from bulk aqueous solution. Mineralization was performed between pH 6 and 9 and with NTA or EDTA concentrations of 0, 5, 10, and 15 mM. X-ray diffraction and infrared spectroscopy show that at low pH, mainly brushite precipitates and at higher pH, mostly hydroxyapatite forms. Both additives alter the morphology of the precipitates. Without additive, brushite precipitates as large plates. With NTA, the morphology changes to an unusual rod-like shape. With EDTA, the edges of the particles are rounded and disk-like particles form. Conductivity and pH measurements suggest that the final products form through several intermediate steps.

Biomineral Nano-Theranostic agent for Magnetic Resonance Image Guided, Augmented Radiofrequency Ablation of Liver Tumor

Theranostic nanoparticles based on biocompatible mineral compositions can significantly improve the translational potential of image guided cancer nano-therapy. Here, we report development of a single-phase calcium phosphate biomineral nanoparticle (nCP) with dual-mode magnetic resonance contrast (T1-T2) together with radiofrequency (RF) mediated thermal response suitable for image-guided RF ablation of cancer. The nanoparticles (NP) are engineered to provide dual MR contrast by an optimized doping concentration (4.1 at%) of paramagnetic ion, Fe³⁺, which also renders lossy dielectric character for nCP leading to thermal response under RF exposure. In vivo compatibility and dual-mode MR contrast are demonstrated in healthy rat models. MRI and T2 mapping suggest hepatobiliary clearance by ~96 hours. MRI guided intratumoral injection in subcutaneous rat glioma and orthotopic liver tumor models provide clear visualization of NP in MRI which also helps in quantifying NP distribution within tumor. Furthermore, by utilising RF mediated thermal response, NP treated tumor could be ablated using clinically approved RF ablation system (10 W,13.3 GHz). Real-time in vivo thermal imaging exhibits 119 ± 10% increase in temperature change (ΔT) for NP treated orthotopic liver tumor (ΔT = 51.5 ± 2 °C), compared to untreated healthy liver control (ΔT = 21.5 ± 2 °C). In effect, we demonstrate a promising nano-biomineral theranostic agent for dual-mode MRI combined with radiofrequency ablation of solid tumors.

Separation and preconcentration of riboflavin from human plasma using polythionine coated magnetite/hydroxyapatite nanocomposite prior to analysis by surfactant-enhanced fluorimetry

The exploration of novel adsorption properties of conductive polymers based on hybridization with biocompatible nanomaterials receives an increasing interest. In this regard, hydroxyapatite (HA) bioceramic is of critical importance mainly owing to its facile synthesis, high surface area, economic and low toxicity in biological environments. In this work, we first prepared and characterized a magnetite/hydroxyapatite (Fe₃O₄/HA) nanocomposite using the bio-waste chicken eggshell via an attractive green way that involved low cost and irrespective of toxicity. Then, polythionine as a novel class of conductive polymers was in situ coated on the synthesized magnetic bioceramic for the separation and preconcentration of riboflavin (vitamin B₂) in human plasma before its fluorimetric determination. Considering the putative role of riboflavin in protecting against cancer and cardiovascular diseases, it is essential to evaluate this vitamin in biological fluids. The described method possesses a linear range of 0.75-262.5μgL^-1 (R²=0.9985) and a detection limit of 0.20μgL^-1 (signal-to-noise ratio of 3). The relative standard deviations (RSDs) for single-sorbent repeatability and sorbent-to-sorbent reproducibility were less than 4.0% and 7.6% (n=5), respectively. The respective enrichment factor and extraction recovery of the method found to be 35.7 and 98.4%. The analytical performance of method for riboflavin was characterized by good consistency of the results with those obtained by the enzyme-linked immunosorbent assay (ELISA) conventional method (p-value of <0.05). The optimized protocol intended for control determinations of riboflavin in human subjects and is addressed to clinical laboratories.

On the surface effects of citrates on nano-apatites: evidence of a decreased hydrophilicity

The surface structure and hydrophilicity of synthetic nanocrystalline apatite with strongly bound citrates on their surface are here investigated at the molecular level, by combining advanced IR spectroscopy, microgravimetry and adsorption microcalorimetry. Citrate are found to form unidentate-like and ionic-like complexes with surface Ca²⁺ ions, with a surface coverage closely resembling that present in bone apatite platelets (i.e., 1 molecule/(n nm)², with n ranging between 1.4 and 1.6). These surface complexes are part of a hydrated non-apatitic surface layer with a sub-nanometre thickness. Noticeably, it is found that the hydrophilicity of the nanoparticles, measured in terms of adsorption of water molecules in the form of multilayers, decreases in a significant extent in relation to the presence of citrates, most likely because of the exposure toward the exterior of –CH₂ groups. Our findings provide new insights on the surface properties of bio-inspired nano-apatites, which can be of great relevance for better understanding the role of citrate in determining important interfacial properties, such as hydrophobicity, of bone apatite platelets. The evaluation and comprehension of surface composition and structure is also of paramount interest to strictly control the functions of synthetic biomaterials, since their surface chemistry strongly affects the hosting tissue response.

Isoexergonic Conformations of Surface-Bound Citrate Regulated Bioinspired Apatite Nanocrystal Growth

The superior biomechanical properties of bone and dentin are dictated, in part, by the unique plate-like morphology of hydroxyapatite (HAP) nanocrysals within a hierarchically assembled collagen matrix. Understanding the mechanism of crystal growth and thus morphology is important to the rational design of bioinspired apatite nanocrystals for orthopedic and dental applications. Citrate has long been proposed to modulate apatite crystal growth, but major questions exist regarding the HAP-bound citrate conformations and the identities of the interacting functional groups and HAP surface sites. Here, we conducted a comprehensive investigation of the mechanism from the angstrom to submicrometer scale by detailed correlation of the results of high-level metadynamics simulations, employing force-fields benchmarked to experiment and density functional theory calculations with the results of high resolution transmission electron microscopy, nuclear magnetic resonance spectroscopy, solution analysis, and thermogravimetric analysis. Crystal morphology changed from needle- to plate-like with increasing citrate concentration. Citrate adsorbed more strongly on the HAP (100) face than on the (001) face, thus resulting in preferential growth in the [001] direction and the plate-like morphology. Two very different bound conformations were obtained, involving interactions of either one or both terminal carboxyl groups with three or five surface calcium ions, respectively, and a hydrogen bond between the citrate hydroxyl and the HAP surface. Remarkably, despite fewer interaction sites in the single bound carboxyl conformation, the structures were isoexergonic, so both exist at equilibrium. Identification of the former conformation is significant because it allows a greater adsorption density than is traditionally assumed and can help explain concentration-dependence of citrate in modulating crystal morphology. These unique results were enabled first by the application of advanced metadynamics, a technique necessary for the accurate simulation of ionic materials but which is rarely employed in the biomaterials and biomineralization fields and second by the detailed correlation of computational, spectroscopic, and analytical results.

Carboxymethyl Hyaluronan-Stabilized Nanoparticles for Anticancer Drug Delivery

Carboxymethyl hyaluronic acid (CMHA) is a semisynthetic derivative of HA that is recognized by HA binding proteins but contains an additional carboxylic acid on some of the 6-hydroxyl groups of the N-acetyl glucosamine sugar units. These studies tested the ability of CMHA to stabilize the formation of calcium phosphate nanoparticles and evaluated their potential to target therapy resistant, CD44⁺/CD24^−/low human breast cancer cells (BT-474_EMT). CMHA stabilized particles (nCaP^CMHA) were loaded with the chemotherapy drug cis-diamminedichloroplatinum(II) (CDDP) to form nCaP^CMHACDDP. nCaP^CMHACDDP was determined to be poorly crystalline hydroxyapatite, 200 nm in diameter with a −43 mV zeta potential. nCaP^CMHACDDP exhibited a two-day burst release of CDDP that tapered resulting in 86% release by 7 days. Surface plasmon resonance showed that nCaP^CMHACDDP binds to CD44, but less effectively than CMHA or hyaluronan. nCaP^CMHA-AF488 was taken up by CD44⁺/CD24⁻ BT-474_EMT breast cancer cells within 18 hours. nCaP^CMHACDDP was as cytotoxic as free CDDP against the BT-474_EMT cells. Subcutaneous BT-474_EMT tumors were more reproducibly inhibited by a near tumor dose of 2.8 mg/kg CDDP than a 7 mg/kg dose nCaP^CMHACDDP. This was likely due to a lack of distribution of nCaP^CMHACDDP throughout the dense tumor tissue that limited drug diffusion.

In vitro enamel remineralization by low-fluoride toothpaste with calcium citrate and sodium trimetaphosphate

The objective of this study was to evaluate in vitro the effect of a low fluoride toothpaste (450 µgF/g, NaF) combined with calcium citrate (Cacit) and sodium trimetaphosphate (TMP) on enamel remineralization. Bovine enamel blocks had the enamel surface polished sequentially to determine the surface hardness. After production of artificial carious lesions, the blocks selected by their surface hardness were submitted to remineralization pH cycling and daily treatment with dentifrice suspensions (diluted in deionized water or artificial saliva): placebo, 275, 450, 550 and 1,100 µgF/g and commercial dentifrice (positive control, 1,100 µgF/g). Finally, the surface and cross-section hardness was determined for calculating the change of surface hardness (%SH) and mineral content (%∆Z). Fluoride in enamel was also determined. The data from %SH, %∆Z and fluoride were subjected to two-way analysis of variance followed by Student-Newman-Keuls's test (p<0.05). The mineral gain (%SH and %∆Z) was higher for toothpastes diluted in saliva (p<0.05), except for the 450 µgF/g dentifrice with Cacit/TMP (p>0.05). The 450 Cacit/TMP toothpaste and the positive control showed similar results (p>0.05) when diluted in water. A dose-response was observed between fluoride concentration in toothpastes and fluoride present in enamel, regardless of dilution. It was concluded that it is possible to enhance the remineralization capacity of low F concentration toothpaste by of organic (Cacit) and inorganic (TMP) compounds with affinity to hydroxyapatite.

Effect of organic acids on calcium phosphate nucleation and osteogenic differentiation of human mesenchymal stem cells on peptide functionalized nanofibers

Carboxylate-rich organic acids play an important role in controlling the growth of apatite crystals and the extent of mineralization in the natural bone. The objective of this work was to investigate the effect of organic acids on calcium phosphate (CaP) nucleation on nanofiber microsheets functionalized with a glutamic acid peptide and osteogenic differentiation of human mesenchymal stem cells (hMSCs) seeded on the CaP-nucleated microsheets. High molecular weight poly(dl-lactide) (DL-PLA) was mixed with low molecular weight L-PLA conjugated with Glu-Glu-Gly-Gly-Cys peptide, and the mixture was electrospun to generate aligned nanofiber microsheets. The nanofiber microsheets were incubated in a modified simulated body fluid (mSBF) supplemented with different organic acids for nucleation and growth of CaP crystals on the nanofibers. Organic acids included citric acid (CA), hydroxycitric acid (HCA), tartaric acid (TART), malic acid (MA), ascorbic acid (AsA), and salicylic acid (SalA). HCA microsheets had the highest CaP content at 240 ± 10% followed by TART and CA with 225 ± 8% and 225 ± 10%, respectively. The Ca/P ratio and percent crystallinity of the nucleated CaP in TART microsheets was closest to that of stoichiometric hydroxyapatite. The extent of CaP nucleation and growth on the nanofiber microsheets depended on the acidic strength and number of hydrogen-bonding hydroxyl groups of the organic acids. Compressive modulus and degradation of the CaP nucleated microsheets were related to percent crystallinity and CaP content. Osteogenic differentiation of hMSCs seeded on the microsheets and cultured in osteogenic medium increased only for those microsheets nucleated with CaP by incubation in CA or AsA-supplemented mSBF. Further, only CA microsheets stimulated bone nodule formation by the seeded hMSCs.

Gold-dotted hydroxyapatite nanoparticles as multifunctional platforms for medical applications

Hydroxyapatite nanoparticles decorated with gold dots, synthesized by a citrate mediated chemical method, enhance the osteogenic differentiation of HMSC.

A novel controlled-release system for antibacterial enzyme lysostaphin delivery using hydroxyapatite/chitosan composite bone cement

In this work, a lysostaphin-loaded, control-released, self-setting and injectable porous bone cement with efficient protein delivery was prepared by a novel setting method using hydroxyapatite/chitosan (HA/CS) composite scaffold. The cement samples were made through cementitious reactions by mixing solid powder, a mixture of HA/CS composite particles, lysostaphin, Ca(OH)2, CaCO3 and NaHCO3, with setting liquid containing citric acid, acetic acid, NaH2PO4, CaCl2 and poloxamer. The setting parameters of the cement samples were determined. The results showed that the final setting time was 96.6±5.2 min and the pH value increased from approximately 6.2 to nearly 10 during the setting process and the porosity was 34% at the end. And the microstructure and composition were detected by scanning electron microscopy (SEM), x-ray diffraction and Fourier transform-infrared spectroscopy. For the release behavior of lysostaphin loaded in the cement sample, the in vitro cement extract experiment indicated that about 94.2±10.9% of the loaded protein was released before day 8 and the in vivo Qdot 625 fluorescence tracking experiment showed that the loaded protein released slower than the free one. Then the biocompatibility of the cement samples was evaluated using the methylthiazol tetrazolium assay, SEM and hematoxylin-eosin staining, which suggested good biocompatibility of cement samples with MC 3T3-E1 cells and subcutaneous tissues of mice. Finally the antibacterial activity assay indicated that the loaded lysostaphin had good release ability and strong antibacterial enzymatic activity against methicillin-resistant Staphylococcus aureus. Collectively, all the results suggested that the lysostaphin-loaded self-setting injectable porous bone cement released the protein in a controlled and effective way and the protein activity was well retained during the setting and releasing process. Thus this bone cement can be potentially applied as a combination of artificial bone substitute and controlled-release system for delivery of lysostaphin to treat bone defects and infections.

Advances in synthesis of calcium phosphate crystals with controlled size and shape

Calcium phosphate (CaP) materials have a wide range of applications, including biomaterials, adsorbents, chemical engineering materials, catalysts and catalyst supports and mechanical reinforcements. The size and shape of CaP crystals and aggregates play critical roles in their applications. The main inorganic building blocks of human bones and teeth are nanocrystalline CaPs; recently, much progress has been made in the application of CaP nanocrystals and their composites for clinical repair of damaged bone and tooth. For example, CaPs with special micro- and nanostructures can better imitate the biomimetic features of human bone and tooth, and this offers significantly enhanced biological performances. Therefore, the design of CaP nano-/microcrystals, and the shape and hierarchical structures of CaPs, have great potential to revolutionize the field of hard tissue engineering, starting from bone/tooth repair and augmentation to controlled drug delivery devices. Previously, a number of reviews have reported the synthesis and properties of CaP materials, especially for hydroxyapatite (HAp). However, most of them mainly focused on the characterizations and physicochemical and biological properties of HAp particles. There are few reviews about the control of particle size and size distribution of CaPs, and in particular the control of nano-/microstructures on bulk CaP ceramic surfaces, which is a big challenge technically and may have great potential in tissue engineering applications. This review summarizes the current state of the art for the synthesis of CaP crystals with controlled sizes from the nano- to the macroscale, and the diverse shapes including the zero-dimensional shapes of particles and spheres, the one-dimensional shapes of rods, fibers, wires and whiskers, the two-dimensional shapes of sheets, disks, plates, belts, ribbons and flakes and the three-dimensional (3-D) shapes of porous, hollow, and biomimetic structures similar to biological bone and tooth. In addition, this review will also summarize studies on the controlled formation of nano-/microstructures on the surface of bulk ceramics, and the preparation of macroscopical bone grafts with 3-D architecture nano-/microstructured surfaces. Moreover, the possible directions of future research and development in this field, such as the detailed mechanisms behind the size and shape control in various strategies, the importance of theoretical simulation, self-assembly, biomineralization and sacrificial precursor strategies in the fabrication of biomimetic bone-like and enamel-like CaP materials are proposed.

Photoluminescence and doping mechanism of theranostic Eu3+/Fe3+ dual-doped hydroxyapatite nanoparticles

Theranostic nanoparticles currently have been regarded as an emerging concept of 'personalized medicine' with diagnostic and therapeutic dual-functions. Eu3+ doped hydroxyapatite (HAp) has been regarded as a promising fluorescent probe for in vivo imaging applications. Additionally, substitution of Ca2+ with Fe3+ in HAp crystal may endow the capability of producing heat upon exposure to a magnetic field. Here we report a preliminary study of doping mechanism and photoluminescence of Eu3+ and Fe3+ doped HAp nanoparticles (Eu/Fe:HAp). HAp with varied concentration of Eu3+ and Fe3+ doping are presented as Eu(10 mol%):HAp, Eu(7 mol%)-Fe(3 mol%):HAp, Eu(5 mol%)-Fe(5 mol%):HAp, Eu(3 mol%)-Fe(7 mol%):HAp, and Fe(10 mol%):HAp in the study. The results showed that the HAp particles, in nano-size with rod-like morphology, were successfully doped with Eu3+ and Fe3+, and the particles can be well suspended in cell culture medium. Photoluminescence analysis revealed that particles have prominent emissions at 536 nm, 590 nm, 615 nm, 650 nm and 695 nm upon excitation at a wavelength of 397 nm. Moreover, these Eu/Fe:HAp nanoparticles belonged to B-type carbonated HAp, which has been considered an effective biodegradable and biocompatible drug/gene carrier in biological applications.

Stabilizing amorphous calcium phosphate phase by citrate adsorption

Citrate controls nucleation by association with a precursor amorphous phase, which inhibits the surface reaction for nucleation.

The facile and low temperature synthesis of nanophase hydroxyapatite crystals using wet chemistry

A simple and facile wet chemistry route was used to synthesize nanophase hydroxyapatite (HaP) crystals at low temperature. The synthesis was carried out at a pH of 11.0 and at a temperature of 37°C. The resulting samples were washed several times and subjected to further analysis. XRD studies revealed that the HaP crystals were polycrystalline in nature with a crystallite size of ~15-60 ± 5 nm. SEM-EDXA images confirmed the presence of calcium (Ca), phosphorous (P), and oxygen (O) peaks. Likewise, FTIR confirmed the presence of characteristic phosphate and hydroxyl peaks in samples. Lastly, HRTEM images clearly showed distinctive lattice fringes positioned in the 100 and 002 planes. TGA analysis shows that HaP crystals can withstand higher calcination temperatures and are thermally stable.

Interactions between inorganic and organic phases in bone tissue as a source of inspiration for design of novel nanocomposites

Mimicking the nanostructure of bone and understanding the interactions between the nanoscale inorganic and organic components of the extracellular bone matrix are crucial for the design of biomaterials with structural properties and a functionality similar to the natural bone tissue. Generally, these interactions involve anionic and/or cationic functional groups as present in the organic matrix, which exhibit a strong affinity for either calcium or phosphate ions from the mineral phase of bone. This study reviews the interactions between the mineral and organic extracellular matrix components in bone tissue as a source of inspiration for the design of novel nanocomposites. After providing a brief description of the various structural levels of bone and its main constituents, a concise overview is presented on the process of bone mineralization as well as the interactions between calcium phosphate (CaP) nanocrystals and the organic matrix of bone tissue. Bioinspired synthetic approaches for obtaining nanocomposites are subsequently addressed, with specific focus on chemical groups that have affinity for CaPs or are involved in stimulating and controlling mineral formation, that is, anionic functional groups, including carboxyl, phosphate, sulfate, hydroxyl, and catechol groups.