Calcium orthophosphates: crystallization and dissolution

Facile synthesis of in situ bismuth-doped calcium phosphate nanocomposite integrated injectable biopolymer hydrogel slurry for bone regeneration

The bionics of natural bone structures plays an essential role in the selection of materials for bone tissue engineering. Although the content of trace metallic elements in bone is low, they have significant effects on the process of bone growth and metabolism. Up to now, the applications of "green" heavy metals in bone regeneration are limited. Herein, in this study, we present a straightforward one-pot strategy for the synthesis of in situ bismuth-doped amorphous calcium phosphate nanocomposites (RBCP), effectively integrating the beneficial properties of each component. The characterization of these products can be readily optimized by adjusting reaction parameters. Our in vitro studies show that under coordination of each component, the RBCP biomaterial demonstrates distinguished biocompatibility and significantly accelerates vascular pattern formation within just 4 h by stimulating the expression of angiogenesis-related genes in human umbilical vein endothelial cells (HUVECs). In vivo experiments indicate that the incorporation of bismuth effectively enhances bone regeneration and osseointegration in a rat femur defect model. In conclusion, the as-prepared RBCP biomaterials hold promising prospects for treating segmental bone defects, owing to the facile, cost-effective, and eco-friendly preparation process, along with their remarkable capabilities.

Hybrid Hydroxyapatite-Metal Complex Materials Derived from Amino Acids and Nucleobases

Calcium phosphates (CaPs) and their substituted derivatives encompass a large number of compounds with a vast presence in nature that have aroused a great interest for decades. In particular, hydroxyapatite (HAp, Ca10(OH)2(PO4)6) is the most abundant CaP mineral and is significant in the biological world, at least in part due to being a major compound in bones and teeth. HAp exhibits excellent properties, such as safety, stability, hardness, biocompatibility, and osteoconductivity, among others. Even some of its drawbacks, such as its fragility, can be redirected thanks to another essential feature: its great versatility. This is based on the compound's tendency to undergo substitutions of its constituent ions and to incorporate or anchor new molecules on its surface and pores. Thus, its affinity for biomolecules makes it an optimal compound for multiple applications, mainly, but not only, in biological and biomedical fields. The present review provides a chemical and structural context to explain the affinity of HAp for biomolecules such as proteins and nucleic acids to generate hybrid materials. A size-dependent criterium of increasing complexity is applied, ranging from amino acids/nucleobases to the corresponding macromolecules. The incorporation of metal ions or metal complexes into these functionalized compounds is also discussed.

Phosphorus recovery via struvite crystallization in batch and fluidized-bed reactors: Roles of microplastics and dissolved organic matter

Struvite crystallization, a promising technology for nutrient recovery from wastewater, is facing considerable challenges due to the presence of emerging contaminants such as microplastics (MPs) ubiquitously found in wastewater. Here, we investigate the roles of MPs and humic acid (HA) in struvite crystallization in batch and fluidized-bed reactors (FBRs) using synthetic and real wastewater with a Mg:N:P molar ratio of 1:3:(1-1.3) at an initial pH of 11. Batch reactor (BR) experiment results show that MPs expedited the nucleation and growth rates of struvite (e.g., the rate of crystal growth in the presence of 30 mg L-1 of polyethylene terephthalate (PET) was 1.43 times higher than that in the blank system), while HA hindered the formation of struvite. X-ray diffraction and the Rietveld refinement analysis revealed that the presence of MPs and HA can result in significant changes in phase compositions of the reclaimed precipitates, with over 80 % purity of struvite found in the precipitates from suspensions in the presence of 30 mg L-1 of MPs. Further characterizations demonstrated that MPs act as seeds of struvite nucleation, spurring the formation of well-defined struvite, while HA favors the formation of newberyite rather than struvite in both reactors. These findings highlight the need for a more comprehensive understanding of the interactions between emerging contaminants and struvite crystallization processes to optimize nutrient recovery strategies for mitigating their adverse impact on the quality and yield of struvite-based fertilizers. ENVIRONMENTAL IMPLICATION: The presence of microplastics in wastewater poses a significant challenge to struvite crystallization for nutrient recovery, as it accelerates nucleation and growth rates of struvite crystals. This can lead to changes in the phase compositions of the reclaimed precipitates, with implications for the quality and yield of struvite-based fertilizers. Additionally, the presence of humic acid hinders the formation of struvite, favoring the formation of other minerals like newberyite. Understanding the interactions between emerging contaminants and struvite crystallization processes is crucial for optimizing nutrient recovery strategies and mitigating the environmental impact of these contaminants on water quality and struvite-based fertilizers.

Application of a calcium and phosphorus biomineralization strategy in tooth repair: a systematic review

Biomineralization is a natural process in which organisms regulate the growth of inorganic minerals to form biominerals with unique layered structures, such as bones and teeth, primarily composed of calcium and phosphorus. Tooth decay significantly impacts our daily lives, and the key to tooth regeneration lies in restoring teeth through biomimetic approaches, utilizing mineralization strategies or materials that mimic natural processes. This review delves into the types, properties, and transformations of calcium and phosphorus minerals, followed by an exploration of the mechanisms behind physiological and pathological mineralization in living organisms. It summarizes the mechanisms and commonalities of biomineralization and discusses the advancements in dental biomineralization research, guided by insights into calcium and phosphorus mineral biomineralization. This review concludes by addressing the current challenges and future directions in the field of dental biomimetic mineralization.

Polyphosphate Nanoparticles: Balancing Energy Requirements in Tissue Regeneration Processes

Nanoparticles of a particular, evolutionarily old inorganic polymer found across the biological kingdoms have attracted increasing interest in recent years not only because of their crucial role in metabolism but also their potential medical applicability: it is inorganic polyphosphate (polyP). This ubiquitous linear polymer is composed of 10-1000 phosphate residues linked by high-energy anhydride bonds. PolyP causes induction of gene activity, provides phosphate for bone mineralization, and serves as an energy supplier through enzymatic cleavage of its acid anhydride bonds and subsequent ATP formation. The biomedical breakthrough of polyP came with the development of a successful fabrication process, in depot form, as Ca- or Mg-polyP nanoparticles, or as the directly effective polymer, as soluble Na-polyP, for regenerative repair and healing processes, especially in tissue areas with insufficient blood supply. Physiologically, the platelets are the main vehicles for polyP nanoparticles in the circulating blood. To be biomedically active, these particles undergo coacervation. This review provides an overview of the properties of polyP and polyP nanoparticles for applications in the regeneration and repair of bone, cartilage, and skin. In addition to studies on animal models, the first successful proof-of-concept studies on humans for the healing of chronic wounds are outlined.

Advancing dentin remineralization: Exploring amorphous calcium phosphate and its stabilizers in biomimetic approaches

OBJECTIVE

This review elucidates the mechanisms underpinning intrafibrillar mineralization, examines various amorphous calcium phosphate (ACP) stabilizers employed in dentin's intrafibrillar mineralization, and addresses the challenges encountered in clinical applications of ACP-based bioactive materials.

METHODS

The literature search for this review was conducted using three electronic databases: PubMed, Web of Science, and Google Scholar, with specific keywords. Articles were selected based on inclusion and exclusion criteria, allowing for a detailed examination and summary of current research on dentin remineralization facilitated by ACP under the influence of various types of stabilizers.

RESULTS

This review underscores the latest advancements in the role of ACP in promoting dentin remineralization, particularly intrafibrillar mineralization, under the regulation of various stabilizers. These stabilizers predominantly comprise non-collagenous proteins, their analogs, and polymers. Despite the diversity of stabilizers, the mechanisms they employ to enhance intrafibrillar remineralization are found to be interrelated, indicating multiple driving forces behind this process. However, challenges remain in effectively designing clinically viable products using stabilized ACP and maximizing intrafibrillar mineralization with limited materials in practical applications.

SIGNIFICANCE

The role of ACP in remineralization has gained significant attention in dental research, with substantial progress made in the study of dentin biomimetic mineralization. Given ACP's instability without additives, the presence of ACP stabilizers is crucial for achieving in vitro intrafibrillar mineralization. However, there is a lack of comprehensive and exhaustive reviews on ACP bioactive materials under the regulation of stabilizers. A detailed summary of these stabilizers is also instrumental in better understanding the complex process of intrafibrillar mineralization. Compared to traditional remineralization methods, bioactive materials capable of regulating ACP stability and controlling release demonstrate immense potential in enhancing clinical treatment standards.

Toward understanding the cellular control of vertebrate mineralization: The potential role of mitochondria

This review examines the possible role of mitochondria in maintaining calcium and phosphate ion homeostasis and participating in the mineralization of bone, cartilage and other vertebrate hard tissues. The paper builds on the known structural features of mitochondria and the documented observations in these tissues that the organelles contain calcium phosphate granules. Such deposits in mitochondria putatively form to buffer excessively high cytosolic calcium ion concentrations and prevent metabolic deficits and even cell death. While mitochondria protect cytosolic enzyme systems through this buffering capacity, the accumulation of calcium ions by mitochondria promotes the activity of enzymes of the tricarboxylic acid (TCA/Krebs) cycle, increases oxidative phosphorylation and ATP synthesis, and leads to changes in intramitochondrial pH. These pH alterations influence ion solubility and possibly the transitions and composition in the mineral phase structure of the granules. Based on these considerations, mitochondria are proposed to support the mineralization process by providing a mobile store of calcium and phosphate ions, in smaller cluster or larger granule form, while maintaining critical cellular activities. The rise in the mitochondrial calcium level also increases the generation of citrate and other TCA cycle intermediates that contribute to cell function and the development of extracellular mineral. This paper suggests that another key role of the mitochondrion, along with the effects just noted, is to supply phosphate ions, derived from the breakdown of ATP, to endolysosomes and autophagic vesicles originating in the endoplasmic reticulum and Golgi and at the plasma membrane. These many separate but interdependent mitochondrial functions emphasize the critical importance of this organelle in the cellular control of vertebrate mineralization.

Dynamic Nuclear Polarization Enhanced Multiple-Quantum Spin Counting of Molecular Assemblies in Vitrified Solutions

Crystallization pathways are essential to various industrial, geological, and biological processes. In nonclassical nucleation theory, prenucleation clusters (PNCs) form, aggregate, and crystallize to produce higher order assemblies. Microscopy and X-ray techniques have limited utility for PNC analysis due to the small size (0.5-3 nm) and time stability constraints. We present a new approach for analyzing PNC formation based on 31P nuclear magnetic resonance (NMR) spin counting of vitrified molecular assemblies. The use of glassing agents ensures that vitrification generates amorphous aqueous samples and offers conditions for performing dynamic nuclear polarization (DNP)-amplified NMR spectroscopy. We demonstrate that molecular adenosine triphosphate along with crystalline, amorphous, and clustered calcium phosphate materials formed via a nonclassical growth pathway can be differentiated from one another by the number of dipolar coupled 31P spins. We also present an innovative approach for examining spin counting data, demonstrating that a knowledge-based fitting of integer multiples of cosine wave functions, instead of the traditional Fourier transform, provides a more physically meaningful retrieval of the existing frequencies. This is the first report of multiquantum spin counting of assemblies formed in solution as captured under vitrified DNP conditions, which can be useful for future analysis of PNCs and other aqueous molecular clusters.

Phosphorylation of collagen fibrils enhances intrafibrillar mineralization and dentin remineralization

The hierarchical assembly of nanoapatite within a type I collagen matrix was achieved through biomimetic mineralization in vitro, cooperatively regulated by non-collagenous proteins and small biomolecules. Here, we demonstrated that IP6 could significantly promote intrafibrillar mineralization in two- and three-dimensional collagen models through binding to collagen fibrils via hydrogen bonds (the interaction energy ∼10.21 kJ mol-1), as confirmed by the FTIR spectra and isothermal experimental results. In addition, we find that IP6 associated with dental collagen fibrils can also enhance the remineralization of calcium-depleted dentin and restore its mechanical properties similar to the natural dentin within 4 days. The promoting effect is mainly due to the chemical modification of IP6, which alters the interfacial physicochemical properties of collagen fibrils, strengthening the interaction of calcium phosphate minerals and mineral ions with collagen fibrils. This strategy of interfacial regulation to accelerate the mineralization of collagen fibrils is essential for dental repair and the development of a clinical product for the remineralization of hard tissue.

Guidelines derived from biomineralized tissues for design and construction of high-performance biomimetic materials: from weak to strong

Living organisms in nature have undergone continuous evolution over billions of years, resulting in the formation of high-performance fracture-resistant biomineralized tissues such as bones and teeth to fulfill mechanical and biological functions, despite the fact that most inorganic biominerals that constitute biomineralized tissues are weak and brittle. During the long-period evolution process, nature has evolved a number of highly effective and smart strategies to design chemical compositions and structures of biomineralized tissues to enable superior properties and to adapt to surrounding environments. Most biomineralized tissues have hierarchically ordered structures consisting of very small building blocks on the nanometer scale (nanoparticles, nanofibers or nanoflakes) to reduce the inherent weaknesses and brittleness of corresponding inorganic biominerals, to prevent crack initiation and propagation, and to allow high defect tolerance. The bioinspired principles derived from biomineralized tissues are indispensable for designing and constructing high-performance biomimetic materials. In recent years, a large number of high-performance biomimetic materials have been prepared based on these bioinspired principles with a large volume of literature covering this topic. Therefore, a timely and comprehensive review on this hot topic is highly important and contributes to the future development of this rapidly evolving research field. This review article aims to be comprehensive, authoritative, and critical with wide general interest to the science community, summarizing recent advances in revealing the formation processes, composition, and structures of biomineralized tissues, providing in-depth insights into guidelines derived from biomineralized tissues for the design and construction of high-performance biomimetic materials, and discussing recent progress, current research trends, key problems, future main research directions and challenges, and future perspectives in this exciting and rapidly evolving research field.

Hydrogen Sulfide Delivery to Enhance Bone Tissue Engineering Cell Survival

Though crucial for natural bone healing, local calcium ion (Ca2+) and phosphate ion (Pi) concentrations can exceed the cytotoxic limit leading to mitochondrial overload, oxidative stress, and cell death. For bone tissue engineering applications, H2S can be employed as a cytoprotective molecule to enhance mesenchymal stem cell (MSC) tolerance to cytotoxic Ca2+/Pi concentrations. Varied concentrations of sodium hydrogen sulfide (NaSH), a fast-releasing H2S donor, were applied to assess the influence of H2S on MSC proliferation. The results suggested a toxicity limit of 4 mM for NaSH and that 1 mM of NaSH could improve cell proliferation and differentiation in the presence of cytotoxic levels of Ca2+ (32 mM) and/or Pi (16 mM). To controllably deliver H2S over time, a novel donor molecule (thioglutamic acid-GluSH) was synthesized and evaluated for its H2S release profile. Excitingly, GluSH successfully maintained cytoprotective level of H2S over 7 days. Furthermore, MSCs exposed to cytotoxic Ca2+/Pi concentrations in the presence of GluSH were able to thrive and differentiate into osteoblasts. These findings suggest that the incorporation of a sustained H2S donor such as GluSH into CaP-based bone graft substitutes can facilitate considerable cytoprotection, making it an attractive option for complex bone regenerative engineering applications.

Memfractance of Proteinoids

Proteinoids, or thermal proteins, are amino acid polymers formed at high temperatures by nonbiological processes. The objective of this study is to examine the memfractance characteristics of proteinoids within a supersaturated hydroxyapatite solution. The ionic solution utilized for the current-voltage (I-V) measurements possessed an ionic strength of 0.15 mol/L, a temperature of 37 °C, and a pH value of 7.4. The I-V curves exhibited distinct spikes, which are hypothesized to arise from the capacitive charging and discharging of the proteinoid-hydroxyapatite media. The experimental results demonstrated a positive correlation between the concentration of proteinoids and the observed number of spikes in the I-V curves. This observation provides evidence in favor of the hypothesis that the spikes originate from the proteinoids' capacitive characteristics. The memfractance behavior exemplifies the capacity of proteinoids to retain electrical charge within the hydrated hydroxyapatite media. Additional investigation is required in order to comprehensively identify the memcapacitive phenomena and delve into their implications for models of protocellular membranes. In a nutshell, this study provides empirical support for the existence of capacitive membrane-memfractance mechanisms in ensembles of proteinoids.

Engineering Precise Interconnected Porosity in β-Tricalcium Phosphate (β-TCP) Matrices by Means of Top-Down Digital Light Processing

This study evaluated the biocompatibility and accuracy of 3D-printed β-tricalcium phosphate (β-TCP) pure ceramic scaffolds. A specific shaping process associating a digital light processing (DLP) 3D printer and a heat treatment was developed to produce pure β-TCP scaffolds leaving no polymer binder residue. The β-TCP was characterised using X-ray diffraction, infrared spectroscopy and the detection of pollutants. The open porosity of produced matrices and their resorption were studied by hydrostatic weighing and calcium release measures. The biocompatibility of the printed matrices was evaluated by mean of osteoblast cultures. Finally, macroporous cubic matrices were produced. They were scanned using a micro-Computed Tomography scanner (micro-CT scan) and compared to their numeric models. The results demonstrated that DLP 3D printing with heat treatment produces pure β-TCP matrices with enhanced biocompatibility. They also demonstrated the printing accuracy of our technique, associating top-down DLP with the sintering of green parts. Thus, this production process is promising and will enable us to explore complex phosphocalcic matrices with a special focus on the development of a functional vascular network.

Synchrotron radiation X-ray diffraction computed tomography (XRDCT): a new tool in cultural heritage and stone conservation for 3D non-destructive probing and phase analysis of inorganic re-treatments

The issue of preserving carbonatic stones of cultural heritage (CH) restored in the past that have undergone new decay phenomena is strongly emerging and conservation science has not yet found a reliable solution. In this paper, we propose the application of synchrotron radiation X-ray diffraction computed tomography (XRDCT) to explore the effects of using inorganic-mineral products (ammonium oxalate; ammonium phosphate) in sequence as a novel, compatible and effective re-treatment approach to consolidate decayed carbonatic stones already treated with inorganic-mineral treatments. High-quality XRDCT datasets were used to qualitatively/quantitatively investigate and 3D localize the complex mixture of crystalline phases formed after the conservation re-treatments within a porous carbonatic stone substrate. The XRDCT reconstruction images and the structural refinements of XRD patterns with the Rietveld methods showed that the phase composition of reaction products, their volume distribution, and weight fraction vary as a function of the treatment sequence and penetration depth. The high potential of XRDCT allows (i) assessment of peculiar trends of each treatment/treatment sequence; (ii) exploration of the reaction steps of the sequential treatments and (iii) demonstration of the consolidating effect of inorganic re-treatments, non-destructively and at the micron scale. Above all, our study (i) provides new analytical tools to support the conservation choices, (ii) showcases new analytical possibilities for XRDCT in conservation science, including in investigations of CH materials and decay processes, and (iii) opens up new perspectives in analytical chemistry and material characterisation for the non-destructive and non-invasive analysis of reactions within heterogeneous polycrystalline systems.

Amorphous 1-D nanowires of calcium phosphate/pyrophosphate: A demonstration of oriented self-growth of amorphous minerals

Amorphous inorganic solids are traditionally isotropic, thus, it is believed that they only grow in a non-preferential way without the assistance of regulators, leading to the morphologies of nanospheres or irregular aggregates of nanoparticles. However, in the presence of (ortho)phosphate (Pi) and pyrophosphate ions (PPi) which have synergistic roles in biomineralization, the highly elongated amorphous nanowires (denoted ACPPNs) form in a regulator-free aqueous solution (without templates, additives, organics, etc). Based on thorough characterization and tracking of the formation process (e.g., Cryo-TEM, spherical aberration correction high resolution TEM, solid state NMR, high energy resolution monochromated STEM-EELS), the microstructure and its preferential growth behavior are elucidated. In ACPPNs, amorphous calcium orthophosphate and amorphous calcium pyrophosphate are distributed at separated but close sites. The ACPPNs grow via either the preferential attachment of ∼2 nm nanoclusters in a 1-dimension way, or the transformation of bigger nanoparticles, indicating an inherent driving force-governed process. We propose that the anisotropy of ACPPNs microstructure, which is corroborated experimentally, causes their oriented growth. This study proves that, unlike the conventional view, amorphous minerals can form via oriented growth without external regulation, demonstrating a novel insight into the structures and growth behaviors of amorphous minerals.

Development of nanobiosilicate, tricalcium phosphate and chlorhexidine materials for biomineralization with crystallographic similarity to hydroxyapatite and biomodified collagen

OBJECTIVES

The aim of this work is to test experimental cements, doped with a silicate based bioactive nanoparticle (NanoBiosilicate). Methods, we synthesized a glass nanoparticle by Sol-Gel Stöber method, used to be incorporated in a dental material for endodontic uses.

MATERIALS AND METHODS

We assess the mineralizing properties and biocompatibility. Besides the crystallography characterization of the resultant new crystals. Results, After analysis, and comparison with commercial materials, the material tested was similar in mechanical properties required by ISO, The ion release was effective after 2 hr. of setting and the novel material was cell compatible accepted by ISO.

RESULTS

We found new formed Calcium Phosphate peaks in the spectroscopic analysis (FTIR), remarkably the crystals formed were comparable to hydroxyapatite when analyzed with a Selected Area Electron Diffractometer, with rings of 2.84 Å for 002, and the 2.77 Å is also visible for 210. The 6.83 Å and 6.88 Å, for respective 222 and 004. The incorporation of Chlorhexidine was not detrimental for this property, Significance, the features mentioned represented a progress in biomineralization field that was associated to an improved mineral structure formation with increased crystallographic similarity to natural hydroxyapatite. When chlorhexidine was added a favorable biomodification of the remaining collagen in dentinal walls and antimicrobial activity potential were also observed.

Autoimmune inflammatory myopathy biomarkers

The autoimmune inflammatory myopathy disease spectrum, commonly known as myositis, is a group of systemic diseases that mainly affect the muscles, skin and lungs. Biomarker assessment helps in understanding disease mechanisms, allowing for the implementation of precise strategies in the classification, diagnosis, and management of these diseases. This review examines the pathogenic mechanisms and highlights current data on blood and tissue biomarkers of autoimmune inflammatory myopathies.

Direct observations of nanoscale brushite dissolution by the concentration-dependent adsorption of phosphate or phytate

With the development of agricultural intensification, phosphorus (P) accumulation in croplands and sediments has resulted in the increasingly widespread interaction between inorganic and organic P species, which has been, previously, underestimated or even ignored. We quantified the nanoscale dissolution kinetics of sparingly soluble brushite (CaHPO4·2H2O, DCPD) over a broad range of phosphate and/or phytate concentrations by using in situ atomic force microscopy (AFM). Compared to water, we found that low concentrations of phosphate (1-1000 µM) or phytate (1-100 µM) inhibited brushite dissolution by slowing single step retraction. However, with increasing phosphate or phytate concentrations to 10 mM, there was a reverse effect of dissolution promotion at brushite-water interfaces. In situ observations of the coupled dissolution-reprecipitation showed that phosphate precipitated more readily than phytate on brushite surfaces, with the formation of amorphous calcium phosphate (ACP). For a fundamental understanding, zeta potential and in situ Raman spectroscopy (RS) revealed that the concentration-dependent dissolution is attributed to the reverse of outer-sphere to inner-sphere adsorption with increasing phosphate or phytate concentrations. In addition, the mineralization of phytate with outer-sphere adsorption by phytase was higher than that with inner-spere adsorption, and the presence of phytate delayed ACP phase transformation to hydroxylapatite (HAP). These in situ observations and analyses may fill the knowledge gaps of interaction between inorganic and organic P species in P-rich terrestrial and aquatic environments, thereby implicating their biogeochemical cycling and the associated availability.

Octacalcium phosphate, a promising bone substitute material: a narrative review

Biomaterials have been used to supplement and restore function and structure by replacing or restoring parts of damaged tissues and organs. In ancient times, the medical use of biomaterials was limited owing to infection during surgery and poor surgical techniques. However, in modern times, the medical applications of biomaterials are diversifying owing to great developments in material science and medical technology. In this paper, we introduce biomaterials, focusing on calcium phosphate ceramics, including octacalcium phosphate, which has recently attracted attention as a bone graft material.

ACP-Mediated Phase Transformation for Collagen Mineralization: A New Understanding of the Mechanism

Despite significant efforts utilizing advanced technologies, the contentious debate surrounding the intricate mechanism underlying collagen fibril mineralization, particularly with regard to amorphous precursor infiltration and phase transformation, persists. This work proposes an amorphous calcium phosphate (ACP)-mediated pathway for collagen fibril mineralization and utilizing stochastic optical reconstruction microscopy technology, and has experimentally confirmed for the first time that the ACP nanoparticles can infiltrate inside collagen fibrils. Subsequently, the ACP-mediated phase transformation occurs within collagen fibrils to form HAP crystallites, and significantly enhances the mechanical properties of the mineralized collagen fibrils compared to those achieved by the calcium phosphate ion (CPI)-mediated mineralization and resembles the natural counterpart. Furthermore, demineralized dentin can be effectively remineralized through ACP-mediated mineralization, leading to complete restoration of its mechanical properties. This work provides a new paradigm of collagen mineralization via particle-mediated phase transformation, deepens the understanding of the mechanism behind the mineralization of collagen fibrils, and offers a new strategy for hard tissue repair.

High-aspect-ratio nanostructured hydroxyapatite: towards new functionalities for a classical material

Hydroxyapatite-based materials have been widely used in countless applications, such as bone regeneration, catalysis, air and water purification or protein separation. Recently, much interest has been given to controlling the aspect ratio of hydroxyapatite crystals from bulk samples. The ability to exert control over the aspect ratio may revolutionize the applications of these materials towards new functional materials. Controlling the shape, size and orientation of HA crystals allows obtaining high aspect ratio structures, improving several key properties of HA materials such as molecule adsorption, ion exchange, catalytic reactions, and even overcoming the well-known brittleness of ceramic materials. Regulating the morphogenesis of HA crystals to form elongated oriented fibres has led to flexible inorganic synthetic sponges, aerogels, membranes, papers, among others, with applications in sustainability, energy and catalysis, and especially in the biomedical field.

Eco-friendly soil stabilization method using fish bone as cement material

The method of soil improvement by calcium phosphate precipitation is a novel, environmentally friendly, and non-toxic technique. Such technology provides advantages over ureolytic induced calcite precipitation (UICP), the most popular and widely used method in the field of geotechnical engineering. In this paper, an investigation of the consolidation of fine and coarse sand samples by enzyme induced calcium phosphate precipitation (EICPP) was carried out. Tuna bones were used as an alternative source of calcium and phosphorus ions, as one of the most popular fish species in Japan and the main source of food industry waste. Unconfined compressive strength (UCS) of the samples after 21 days of daily injection of the solution showed an increase in strength up to 6,05 MPa in fine and up to 4,3 MPa in coarse sand samples. X-ray powder diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (SEM-EDS) analysis were performed to investigate the nature and type of deposition. Analyses confirmed that deposition is composed of brushite with needle-like crystals in the case of Toyoura sand and flower-like crystals in the case of Mikawa sand. SEM-EDS showed a presence of both, calcium, and phosphorus in the precipitate, indicating the presence of calcium phosphate compounds (CPCs). This study reveals that tuna bones are a rich source of calcium and phosphorus for EICPP, which results in a strengthening of silicate soil up to 3.4-6.05 MPa and is able to reduce ammonia emissions by 85.7 % - 97.5 % compared to UICP.

Hyaluronic acid-mediated collagen intrafibrillar mineralization and enhancement of dentin remineralization

Non-collagenous proteins (NCPs) in the extracellular matrix (ECM) of bone and dentin are known to play a critical regulatory role in the induction of collagen fibril mineralization and are embedded in hyaluronic acid (HA), which acts as a water-retaining glycosaminoglycan and provides necessary biochemical and biomechanical cues. Our previous study demonstrated that HA could regulate the mineralization degree and mechanical properties of collagen fibrils, yet its kinetics dynamic mechanism on mineralization is under debate. Here, we further investigated the role of HA on collagen fibril mineralization and the possible mechanism. The HA modification can significantly promote intrafibrillar collagen mineralization by reducing the electronegativity of the collagen surface to enhance calcium ions (Ca2+) binding capacity to create a local higher supersaturation. In addition, the HA also provides additional nucleation sites and shortens the induction time of amorphous calcium phosphate (ACP)-mediated hydroxyapatite (HAP) crystallization, which benefits mineralization. The acceleration effect of HA on intrafibrillar collagen mineralization is also confirmed in collagen hydrogel and in vitro dentin remineralization. These findings offer a physicochemical view of the regulation effect of carbohydrate polymers in the body on biomineralization, the fine prospect for an ideal biomaterial to repair collagen-mineralized tissues.

Development of a Novel Peptide with Antimicrobial and Mineralising Properties for Caries Management

The purpose of the study is to develop a novel peptide for caries management. Gallic-Acid-Polyphemusin-I (GAPI) was synthesised by grafting Polyphemusin I (PI) and gallic acid (GA). Biocompatibility was evaluated using a Cell Counting Kit-8 Assay. Antimicrobial properties were assessed using minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC). The bacterial and fungal morphology after GAPI treatment was investigated using transmission electron microscopy (TEM). The architecture of a consortium biofilm consisting of Streptococcus mutans, Lacticaseibacillus casei and Candida albicans was evaluated using scanning electron microscopy (SEM) and confocal laser scanning microscopy. The growth kinetics of the biofilm was examined using a propidium monoazide-quantitative polymerase chain reaction. The surface and calcium-to-phosphorus molar ratio of GAPI-treated enamel after pH cycling were examined with SEM and energy-dispersive X-ray spectroscopy. Enamel crystal characteristics were analysed using X-ray diffraction. Lesion depths representing the enamel's mineral loss were assessed using micro-computed tomography. The MIC of GAPI against S. mutans, L. casei and C. albicans were 40 μM, 40 μM and 20 μM, respectively. GAPI destroyed the biofilm's three-dimensional structure and inhibited the growth of the biofilm. SEM showed that enamel treated with GAPI had a relatively smooth surface compared to that treated with water. The calcium-to-phosphorus molar ratio of enamel treated with GAPI was higher than that of the control. The lesion depths and mineral loss of the GAPI-treated enamel were less than the control. The crystallinity of the GAPI-treated enamel was higher than the control. This study developed a biocompatible, mineralising and antimicrobial peptide GAPI, which may have potential as an anti-caries agent.

Interlayer expansion of octacalcium phosphate via forced oxidation of the intercalated molecules within its interlayers

Octacalcium phosphate (OCP), a precursor to apatite, has a layered structure that allows various molecules to be intercalated within its interlayers. Previous research on the phase conversion process of OCP to apatite indicated that the layered structures typically collapse due to the shrinking of the OCP layers. In contrast, this study presents a novel phenomenon involving OCP layer expansion during phase conversion. This expansion is based on a forced oxidation process of the intercalated molecules within the hydrous layers of OCP. By introducing NaClO to an OCP interlayer containing dithiodiglycolic acid (DSG), the OCP layers are expanded. This process involves DSG decomposition through its reaction with NaClO. Specifically, the process occurs when a DSG-substituted OCP (containing disulfide bonds (-S-S-)) is immersed in a NaClO solution. This is the first study to report the expansion phenomenon during the phase conversion process from OCP to apatite, providing a new perspective to the conventional understanding that these layers only shrink.

Design Strategies for Hydroxyapatite-Based Materials to Enhance Their Catalytic Performance and Applicability

Hydroxyapatite (HAP) is a green catalyst that has a wide range of applications in catalysis due to its high flexibility and multifunctionality. These properties allow HAP to accommodate a large number of catalyst modifications that can selectively improve the catalytic performance in target reactions. To date, many studies have been conducted to elucidate the effect of HAP modification on the catalytic activities for various reactions. However, systematic design strategies for HAP catalysts are not established yet due to an incomplete understanding of underlying structure-activity relationships. In this review, tuning methods of HAP for improving the catalytic performance are discussed: 1) ionic composition change, 2) morphology control, 3) incorporation of other metal species, and 4) catalytic support engineering. Detailed mechanisms and effects of structural modulations on the catalytic performances for attaining the design insights of HAP catalysts are investigated. In addition, computational studies to understand catalytic reactions on HAP materials are also introduced. Finally, important areas for future research are highlighted.

Enhanced Release of Calcium Ions from Hydroxyapatite Nanoparticles with an Increase in Their Specific Surface Area

Synthetic calcium phosphates, e.g., hydroxyapatite (HAP) and tricalcium phosphate (TCP), are the most commonly used bone-graft materials due to their high chemical similarity to the natural hydroxyapatite-the inorganic component of bones. Calcium in the form of a free ion or bound complexes plays a key role in many biological functions, including bone regeneration. This paper explores the possibility of increasing the Ca2+-ion release from HAP nanoparticles (NPs) by reducing their size. Hydroxyapatite nanoparticles were obtained through microwave hydrothermal synthesis. Particles with a specific surface area ranging from 51 m2/g to 240 m2/g and with sizes of 39, 29, 19, 11, 10, and 9 nm were used in the experiment. The structure of the nanomaterial was also studied by means of helium pycnometry, X-ray diffraction (XRD), and transmission-electron microscopy (TEM). The calcium-ion release into phosphate-buffered saline (PBS) was studied. The highest release of Ca2+ ions, i.e., 18 mg/L, was observed in HAP with a specific surface area 240 m2/g and an average nanoparticle size of 9 nm. A significant increase in Ca2+-ion release was also observed with specific surface areas of 183 m2/g and above, and with nanoparticle sizes of 11 nm and below. No substantial size dependence was observed for the larger particle sizes.

Synthetic Calcium-Phosphate Materials for Bone Grafting

Synthetic bone grafting materials play a significant role in various medical applications involving bone regeneration and repair. Their ability to mimic the properties of natural bone and promote the healing process has contributed to their growing relevance. While calcium-phosphates and their composites with various polymers and biopolymers are widely used in clinical and experimental research, the diverse range of available polymer-based materials poses challenges in selecting the most suitable grafts for successful bone repair. This review aims to address the fundamental issues of bone biology and regeneration while providing a clear perspective on the principles guiding the development of synthetic materials. In this study, we delve into the basic principles underlying the creation of synthetic bone composites and explore the mechanisms of formation for biologically important complexes and structures associated with the various constituent parts of these materials. Additionally, we offer comprehensive information on the application of biologically active substances to enhance the properties and bioactivity of synthetic bone grafting materials. By presenting these insights, our review enables a deeper understanding of the regeneration processes facilitated by the application of synthetic bone composites.

Spectroscopic characterization of calcium phosphate precipitated under human eye conditions: An in vitro study

Calcification is a well-known process of calcium phosphate mineralization observed in intraocular lenses. Despite the many works conducted in this field, there is no strict explanation of the mechanisms of this process. In order to better understand the phenomenon, i.e., the mechanisms and structural conditions that promote calcification, any research observations should be conducted under conditions that best reflect those of the human eye. Taking into account the specific anatomy and physicochemical conditions of the human eye, the problem under discussion becomes difficult to solve in vitro. In the present study, calcium phosphates formed under conditions similar to those in the human eye were characterized using SEM/EDS and infrared spectroscopy. Conducted study showed the formation of white spherical precipitates, which are unstable when extracted from solution. Such precipitates were characteristic of solutions containing 1.5-3.0 mM² of solutes. Elemental analysis showed a Ca/P ratio of 1.64-1.65, which is similar to the ratio for hydroxyapatite (1.67). Chemical structure analysis revealed the presence of broad bending and stretching bands at 475-830 cm^-1 and 880-1250 cm^-1, respectively, which are characteristic of PO₄^3- groups in apatite calcium phosphates. In further analysis involving numerical fitting the bands corresponding to apatitic PO₄^3- and indicating the presence of calcium phosphates hydration were found. The results allow the selection of immersion media for further studies involving the incubation of hydrogel intraocular lenses.

Fabrication and characterization of ceramic-polymer composite 3D scaffolds and demonstration of osteoinductive propensity with gingival mesenchymal stem cells

The fabrication of biomaterial 3D scaffolds for bone tissue engineering applications involves the usage of metals, polymers, and ceramics as the base constituents. Notwithstanding, the composite materials facilitating enhanced osteogenic differentiation/regeneration are endorsed as the ideally suited bone grafts for addressing critical-sized bone defects. Here, we report the successful fabrication of 3D composite scaffolds mimicking the ECM of bone tissue by using ∼30 wt% of collagen type I (Col-I) and ∼70 wt% of different crystalline phases of calcium phosphate (CP) nanomaterials [hydroxyapatite (HAp), beta-tricalcium phosphate (βTCP), biphasic hydroxyapatite (βTCP-HAp or BCP)], where pH served as the sole variable for obtaining these CP phases. The different Ca/P ratio and CP nanomaterials orientation in these CP/Col-I composite scaffolds not only altered the microstructure, surface area, porosity with randomly oriented interconnected pores (80-450 μm) and mechanical strength similar to trabecular bone but also consecutively influenced the bioactivity, biocompatibility, and osteogenic differentiation potential of gingival-derived mesenchymal stem cells (gMSCs). In fact, BCP/Col-I, as determined from micro-CT analysis, achieved the highest surface area (∼42.6 m2 g-1) and porosity (∼85%), demonstrated improved bioactivity and biocompatibility and promoted maximum osteogenic differentiation of gMSCs among the three. Interestingly, the released Ca2+ ions, as low as 3 mM, from these scaffolds could also facilitate the osteogenic differentiation of gMSCs without even subjecting them to osteoinduction, thereby attesting these CP/Col-I 3D scaffolds as ideally suited bone graft materials.

Understanding the Nanoscale Affinity between Dissolved Organic Matter and Noncrystalline Mineral with the Implication for Water Treatment

In recent decades, the concentration of dissolved organic matter (DOM) in aquatic ecosystems has gradually increased, leading to water pollution problems. Understanding the interfacial chemical processes of DOM on natural minerals is important to the exploration of high-efficiency absorbents. However, studying DOM chemical processes and adsorption mechanisms are still challenging due to the complex DOM structure and environmental system. Hence, we characterized the microstructure changes after the formation of amorphous calcium phosphate (ACP) at the interface of montmorillonite (Mt) minerals in a simulated environment system. Combined with atomic force microscopy and density functional theory (DFT) simulation, the mechanism of interfacial interaction between Mt-ACP and DOM was characterized at the molecular level. Moreover, we further evaluated the adsorption behavior of Mt-ACP as a potential adsorbent for organic matter. The comprehensive investigation of humic acid adsorption, intermolecular force, and DFT simulation is conducive to our understanding of the interfacial interaction mechanism between organic matter and noncrystalline minerals in aquatic environments and provides new perspectives on the application of clay-based mineral materials in pollutant removal under exposure from DOM.

Amorphous Calcium Phosphate and Amorphous Calcium Phosphate Carboxylate: Synthesis and Characterization

Amorphous calcium phosphate (ACP) is the first solid phase precipitated from a supersaturated calcium phosphate solution. Naturally, ACP is formed during the initial stages of biomineralization and stabilized by an organic compound. Carboxylic groups containing organic compounds are known to regulate the nucleation and crystallization of hydroxyapatite. Therefore, from a biomimetic point of view, the synthesis of carboxylate ions containing ACP (ACPC) is valuable. Usually, ACP is synthesized with fewer steps than ACPC. The precipitation reaction of ACP is rapid and influenced by pH, temperature, precursor concentration, stirring conditions, and reaction time. Due to phosphates triprotic nature, controlling pH in a multistep approach becomes tedious. Here, we developed a new ACP and ACPC synthesis approach and thoroughly characterized the obtained materials. Results from vibration spectroscopy, nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), true density, specific surface area, and ion release studies have shown a difference in the physiochemical properties of the ACP and ACPC. Additionally, the effect of a carboxylic ion type on the physiochemical properties of ACPC was characterized. All of the ACPs and ACPCs were synthesized in sterile conditions, and in vitro analysis was performed using MC-3T3E1 cells, revealing the cytocompatibility of the synthesized ACPs and ACPCs, of which the ACPC synthesized with citrate showed the highest cell viability.

There Are over 60 Ways to Produce Biocompatible Calcium Orthophosphate (CaPO4) Deposits on Various Substrates

A The present overview describes various production techniques for biocompatible calcium orthophosphate (abbreviated as CaPO4) deposits (coatings, films and layers) on the surfaces of various types of substrates to impart the biocompatible properties for artificial bone grafts. Since, after being implanted, the grafts always interact with the surrounding biological tissues at the interfaces, their surface properties are considered critical to clinical success. Due to the limited number of materials that can be tolerated in vivo, a new specialty of surface engineering has been developed to desirably modify any unacceptable material surface characteristics while maintaining the useful bulk performance. In 1975, the development of this approach led to the emergence of a special class of artificial bone grafts, in which various mechanically stable (and thus suitable for load-bearing applications) implantable biomaterials and artificial devices were coated with CaPO4. Since then, more than 7500 papers have been published on this subject and more than 500 new publications are added annually. In this review, a comprehensive analysis of the available literature has been performed with the main goal of finding as many deposition techniques as possible and more than 60 methods (double that if all known modifications are counted) for producing CaPO4 deposits on various substrates have been systematically described. Thus, besides the introduction, general knowledge and terminology, this review consists of two unequal parts. The first (bigger) part is a comprehensive summary of the known CaPO4 deposition techniques both currently used and discontinued/underdeveloped ones with brief descriptions of their major physical and chemical principles coupled with the key process parameters (when possible) to inform readers of their existence and remind them of the unused ones. The second (smaller) part includes fleeting essays on the most important properties and current biomedical applications of the CaPO4 deposits with an indication of possible future developments.

Nanofertilizers: Types, Delivery and Advantages in Agricultural Sustainability

In an alarming tale of agricultural excess, the relentless overuse of chemical fertilizers in modern farming methods have wreaked havoc on the once-fertile soil, mercilessly depleting its vital nutrients while inflicting irreparable harm on the delicate balance of the surrounding ecosystem. The excessive use of such fertilizers leaves residue on agricultural products, pollutes the environment, upsets agrarian ecosystems, and lowers soil quality. Furthermore, a significant proportion of the nutrient content, including nitrogen, phosphorus, and potassium, is lost from the soil (50–70%) before being utilized. Nanofertilizers, on the other hand, use nanoparticles to control the release of nutrients, making them more efficient and cost-effective than traditional fertilizers. Nanofertilizers comprise one or more plant nutrients within nanoparticles where at least 50% of the particles are smaller than 100 nanometers. Carbon nanotubes, graphene, and quantum dots are some examples of the types of nanomaterials used in the production of nanofertilizers. Nanofertilizers are a new generation of fertilizers that utilize advanced nanotechnology to provide an efficient and sustainable method of fertilizing crops. They are designed to deliver plant nutrients in a controlled manner, ensuring that the nutrients are gradually released over an extended period, thus providing a steady supply of essential elements to the plants. The controlled-release system is more efficient than traditional fertilizers, as it reduces the need for frequent application and the amount of fertilizer. These nanomaterials have a high surface area-to-volume ratio, making them ideal for holding and releasing nutrients. Naturally occurring nanoparticles are found in various sources, including volcanic ash, ocean, and biological matter such as viruses and dust. However, regarding large-scale production, relying solely on naturally occurring nanoparticles may not be sufficient or practical. In agriculture, nanotechnology has been primarily used to increase crop production while minimizing losses and activating plant defense mechanisms against pests, insects, and other environmental challenges. Furthermore, nanofertilizers can reduce runoff and nutrient leaching into the environment, improving environmental sustainability. They can also improve fertilizer use efficiency, leading to higher crop yields and reducing the overall cost of fertilizer application. Nanofertilizers are especially beneficial in areas where traditional fertilizers are inefficient or ineffective. Nanofertilizers can provide a more efficient and cost-effective way to fertilize crops while reducing the environmental impact of fertilizer application. They are the product of promising new technology that can help to meet the increasing demand for food and improve agricultural sustainability. Currently, nanofertilizers face limitations, including higher costs of production and potential environmental and safety concerns due to the use of nanomaterials, while further research is needed to fully understand their long-term effects on soil health, crop growth, and the environment.

Microcalcification crystallography as a potential marker of DCIS recurrence

Ductal carcinoma in-situ (DCIS) accounts for 20-25% of all new breast cancer diagnoses. DCIS has an uncertain risk of progression to invasive breast cancer and a lack of predictive biomarkers may result in relatively high levels (~ 75%) of overtreatment. To identify unique prognostic biomarkers of invasive progression, crystallographic and chemical features of DCIS microcalcifications have been explored. Samples from patients with at least 5-years of follow up and no known recurrence (174 calcifications in 67 patients) or ipsilateral invasive breast cancer recurrence (179 microcalcifications in 57 patients) were studied. Significant differences were noted between the two groups including whitlockite relative mass, hydroxyapatite and whitlockite crystal maturity and, elementally, sodium to calcium ion ratio. A preliminary predictive model for DCIS to invasive cancer progression was developed from these parameters with an AUC of 0.797. These results provide insights into the differing DCIS tissue microenvironments, and how these impact microcalcification formation.

Surface Oxygen Vacancies of Rutile Nanorods Accelerate Biomineralization

Titanium dioxide (TiO₂) materials have been widely used in biomedical applications of bone tissue engineering. However, the mechanism underlying the induced biomineralization onto the TiO₂ surface still remains elusive. In this study, we demonstrated that the surface oxygen vacancy defects of rutile nanorods could be gradually eliminated by the regularly used annealing treatment, which restrained the heterogeneous nucleation of hydroxyapatite (HA) onto rutile nanorods in simulated body fluids (SBFs). Moreover, we also observed that the surface oxygen vacancies upregulated the mineralization of human mesenchymal stromal cells (hMSCs) on rutile TiO₂ nanorod substrates. This work therefore emphasized the importance of subtle changes of surface oxygen vacancy defective features of oxidic biomaterials during the regularly used annealing treatment on their bioactive performances and provided new insights into the fundamental understanding of interactions of materials with the biological environment.

Competitive adsorption of heavy metals between Ca-P and Mg-P products from wastewater during struvite crystallization

Wastewater usually contains high concentration of calcium (Ca), posing a competitive reaction with magnesium (Mg) on phosphorus (P) recovery during the struvite crystallization. The differences in the adsorption of heavy metals by Ca-P and Mg-P (struvite) generated are still unclear. Herein, we analyzed the residues of four kinds of common heavy metals (Cu, Zn, Cd, Pb) in Ca-P and Mg-P (struvite) under varying conditions (solution pH, N/P ratio, Mg/Ca ratio) in the swine wastewater and explored their possible competitive adsorption mechanisms. The experiments using synthetic wastewater and real wastewater have similar experimental patterns. However, under the same conditions, the metal (Pb) content of struvite recovered from the synthetic wastewater (16.58 mg/g) was higher than that of the real wastewater (11.02 mg/g), as predicted by the Box-Behnken Design of Response Surface Methodology (BBD-RSM). The results demonstrated that Cu was the least abundant in the precipitates compared to Zn, Cd, and Pb of almost all experimental groups with an N/P ratio greater than or equal to 10. The fact might be mainly attributed to the its stronger binding capacity of Cu ion with NH₃ and other ligands. Compared with struvite, the Ca-P product had a higher adsorption capacity for heavy metals and a lower P recovery rate. In addition, the higher solution pH and N/P ratio were favorable to obtain qualified struvite with lower heavy metal content. It can be applied to reduce the incorporation of heavy metals by modulating pH and N/P ratio through RSM, which is suitable for different Mg/Ca ratios. It is anticipated that the results obtained would offer support for the safe utility of struvite from wastewater containing Ca and heavy metals.

Towards advanced simultaneous nitrogen removal and phosphorus recovery from digestion effluent based on anammox-hydroxyapatite (HAP) process: Focusing on a solution perspective

In this paper, the state-of-the-art information on the anammox-HAP process is summarized. The mechanism of this process is systematically expounded, the enhancement of anammox retention by HAP precipitation and the upgrade of phosphorus recovery by anammox process are clarified. However, this process still faces several challenges, especially how to deal with the ∼ 11% nitrogen residues and to purify the recovered HAP. For the first time, an anaerobic fermentation (AF) combined with partial denitrification (PD) and anammox-HAP (AF-PD-Anammox-HAP) process is proposed to overcome the challenges. By AF of the organic impurities of the anammox-HAP granular sludge, organic acid is produced to be used as carbon source for PD to remove the nitrogen residues. Simultaneously, pH of the solution drops, which promotes the dissolution of some inorganic purities such as CaCO₃. In this way, not only the inorganic impurities are removed, but the inorganic carbon is supplied for anammox bacteria.

Surface Multifunctionalization of Inert Ceramic Implants by Calcium Phosphate Biomimetic Coating Doped with Nanoparticles Encapsulating Antibiotics

Aseptic loosening and periprosthetic infections are complications that can occur at the interface between inert ceramic implants and natural body tissues. Therefore, the need for novel materials with antibacterial properties to prevent implant-related infection is evident. This study proposes multifunctionalizing the inert ceramic implant surface by biomimetic calcium phosphate (CaP) coating decorated with antibiotic-loaded nanoparticles for bioactivity enhancement and antibacterial effect. This study aimed to coat zirconium dioxide (ZrO₂) substrates with a bioactive CaP-layer containing drug-loaded degradable polymer nanoparticles (NPs). The NPs were loaded with two antibiotics, gentamicin or bacitracin. The immobilization of NPs happened by two deposition methods: coprecipitation and drop-casting. X-ray diffraction (XRD), scanning electron microscopy (SEM), and cross-section analyses were used to characterize the coatings. MG-63 osteoblast-like cells and human mesenchymal stem cells (hMSC) were chosen for in vitro tests. Antibacterial activity was assessed with S. aureus and E. coli. The coprecipitation method allowed for a favorable homogeneous distribution of the NPs within the CaP coating. The CaP coating was constituted of hydroxyapatite and octacalcium phosphate; its thickness was 3.8 ± 1 μm with cavities of around 1 μm suitable for hosting NPs with a size of 200 nm. Antibiotics were released from the coatings in a controlled manner for 1 month. The cell culture study has confirmed the excellent behavior of the coprecipitated coating, showing cytocompatibility and a homogeneous distribution of the cells on the coated surfaces. The increase in alkaline phosphatase activity showed osteogenic differentiation. The materials were found to inhibit the growth of bacteria. Newly developed coatings with antibacterial and bioactive properties are promising candidates to prevent peri-implant infectious bone diseases.

Improved osteogenic activity of NiTi orthopedic implant by HAp-Nb2O5 composite coatings: Materials and biological points of view

The surface properties of NiTi, as an interface between the synthetic implant and living tissue, play a vital role in guaranteeing implantation success, especially during the initial stage. This contribution endeavors to enhance the surface features of NiTi orthopedic implants through the application of HAp-based coatings, placing emphasis on assessing the influence of Nb₂O₅ particles concentration in the electrolyte on resultant properties of HAp-Nb₂O₅ composite electrodeposits. The coatings were electrodeposited via pulse current mode under galvanostatic current control from an electrolyte containing 0-1 g/L of Nb₂O₅ particles. Surface morphology, topography, and phase composition were evaluated using FESEM, AFM, and XRD, respectively. EDS was employed to study surface chemistry. In vitro biomineralization and osteogenic activity of the samples were studied by immersing the samples in SBF and incubating them with osteoblastic SAOS-2 cells, respectively. The added Nb₂O₅ particles, at the optimum concentration, stimulated biomineralization, suppressed the Ni ion leaching, and improved SAOS-2 cell adhesion and proliferation. NiTi implant coated by HAp-0.50 g/L Nb₂O₅ layer showed tremendous osteogenic properties. Overall, the HAp-Nb₂O₅ composite layers bring forth fascinating coating in vitro biological performance, reducing Ni leaching, and promoting osteogenic activity, which are fundamental for the successful use of NiTi in vivo.

Phase evolution and arsenic immobilization of arsenate-bearing amorphous calcium phosphate

The formation of As(V) substituted hydroxylapatite (HAP) has a vital influence on the fate of As(V) in the environment. However, despite growing evidence showing that HAP crystallizes in vivo and in vitro with amorphous calcium phosphate (ACP) as a precursor, a knowledge gap exists concerning the transformation from arsenate-bearing ACP (AsACP) to arsenate-bearing HAP (AsHAP). Here we synthesized AsACP nano-particles with varied As contents and investigated the arsenic incorporation during their phase evolution. The phase evolution results showed that the transformation process of AsACP to AsHAP could be divided into three Stages. A higher As(V) loading significantly delayed the transformation of AsACP, increased the distortion degree, and decreased the crystallinity of AsHAP. NMR result showed that the PO₄^3- tetrahedral is geometrically preserved when PO₄^3- is substituted by AsO₄^3-. From AsACP to AsHAP, the As-substitution led to the transformation inhibition and As(V) immobilization.

Regulation of Hydroxyapatite Nucleation In Vitro through Ameloblastin-Amelogenin Interactions

Amelogenin (Amel) and ameloblastin (Ambn) are two primary extracellular enamel matrix proteins that play crucial roles for proper thickness, prismatic structure, and robust mechanical properties. Previous studies have shown that Amel and Ambn bind to each other, but the effect of their coassembly on the nucleation of hydroxyapatite (HAP) is unclear. Here, we systematically investigated the coassembly of recombinant mouse Amel and Ambn in various ratios using in situ atomic force microscopy, dynamic light scattering, and transmission electron microscopy. The size of protein particles decreased as the Ambn:Amel ratio increased. To define the coassembly domain on Ambn, we used Ambn-derived peptides and Ambn variants to examine their effects on the amelogenin particle size distribution. We found that the peptide sequence encoded by exon 5 of Ambn affected Amel self-assembly but the variant lacking this sequence did not have any effect on Amel self-assembly. Furthermore, through monitoring the pH change in bulk mineralization solution, we tracked the nucleation behavior of HAP in the presence of Ambn and Amel and found that their coassemblies at different ratios showed varying abilities to stabilize amorphous calcium phosphate. These results demonstrated that Ambn and Amel coassemble with each other via a motif within the sequence encoded by exon 5 of Ambn and cooperate in regulating the nucleation of HAP crystals, enhancing our understanding of the important role of enamel matrix proteins in amelogenesis.

Role of carboxylic organic molecules in interfibrillar collagen mineralization

Bone is a composite material made up of inorganic and organic counterparts. Most of the inorganic counterpart accounts for calcium phosphate (CaP) whereas the major organic part is composed of collagen. The interfibrillar mineralization of collagen is an important step in the biomineralization of bone and tooth. Studies have shown that synthetic CaP undergoes auto-transformation to apatite nanocrystals before entering the gap zone of collagen. Also, the synthetic amorphous calcium phosphate/collagen combination alone is not capable of initiating apatite nucleation rapidly. Therefore, it was understood that there is the presence of a nucleation catalyst obstructing the auto-transformation of CaP before entering the collagen gap zone and initiating rapid nucleation after entering the collagen gap zone. Therefore, studies were focused on finding the nucleation catalyst responsible for the regulation of interfibrillar collagen mineralization. Organic macromolecules and low-molecular-weight carboxylic compounds are predominantly present in the bone and tooth. These organic compounds can interact with both apatite and collagen. Adsorption of the organic compounds on the apatite nanocrystal governs the nucleation, crystal growth, lattice orientation, particle size, and distribution. Additionally, they prevent the auto-transformation of CaP into apatite before entering the interfibrillar compartment of the collagen fibril. Therefore, many carboxylic organic compounds have been utilized in developing CaP. In this review, we have covered different carboxylate organic compounds governing collagen interfibrillar mineralization.

Selective excitation with recoupling pulse schemes uncover properties of disordered mineral phases in bone-like apatite grown with bone proteins

Bone construction has been under intensive scrutiny for many years using numerous techniques. Solid-state NMR spectroscopy helped unravel key characteristics of the mineral structure in bone owing to its capability of analyzing crystalline and disordered phases at high-resolution. This has invoked new questions regarding the roles of persistent disordered phases in structural integrity and mechanical function of mature bone as well as regarding regulation of early events in formation of apatite by bone proteins which interact intimately with the different mineral phases to exert biological control. Here, spectral editing tethered to standard NMR techniques is employed to analyze bone-like apatite minerals prepared synthetically in the presence and absence of two non-collagenous bone proteins, osteocalcin and osteonectin. A ¹H spectral editing block allows excitation of species from the crystalline and disordered phases selectively, facilitating analysis of phosphate or carbon species in each phase by magnetization transfer via cross polarization. Further characterization of phosphate proximities using SEDRA dipolar recoupling, cross-phase magnetization transfer using DARR and T₁/T₂ relaxation times demonstrate that the mineral phases formed in the presence of bone proteins are more complex than bimodal. They reveal disparities in the physical properties of the mineral layers, indicate the layers in which the proteins reside and highlight the effect that each protein imparts across the mineral layers.

Kinetic Study of Calcium Phosphate Mineralisation in Biomimetic Conditions: An Enzymatic Model Approach

Although it has been studied for decades, calcium phosphate (CaP) biomineralisation remains an unclear process involving many possible pathways depending on subtle biological parameters that are hard to mimic. In this work, we explore the catalytic activity of enzymes to direct CaP crystallisation. This idea derives from the remarkable capacity of matrix vesicles (MVs) to control CaP biomineralisation in vivo by involving a variety of proteins, including enzymes. We highlight how the enzymatic control of the release of phosphate ions allows to better steer when and how the minerals form by tuning the enzymatic activity. We also illustrate how this enzymatic control enables the deeper understanding of the role of a crystallisation inhibitor, magnesium ions. Moreover, we propose in this study the original and extensive use of both dynamic (DLS) and static (SLS) light scattering measurements to follow the mineralisation in real-time and to provide kinetic quantitative parameters to describe this phenomenon. The combination of the techniques reveals noticeable differences in terms of nucleation and growth process between the two levers used in this approach: (i) adjusting the time evolution of the supersaturation or (ii) moderating the crystallisation process. This study allowed also to pinpoint specific intermediate structures, rarely seen and difficult to isolate, that differ when magnesium ions are introduced in the mixture.

Acidity-Triggered Transformable Polypeptide Self-Assembly to Initiate Tumor-Specific Biomineralization

Biomineralization is a normal physiological process that includes nucleation, crystal growth, phase transformation, and orientation evolution. Notably, artificially induced biomineralization in the tumor tissue has emerged as an unconventional yet promising modality for malignancy therapy. However, the modest ion-chelating capabilities of carboxyl-containing biomineralization initiators lead to a deficient blockade, thus compromising antitumor efficacy. Herein, a biomineralization-inducing nanoparticle (BINP) is developed for blockade therapy of osteosarcoma. BINP is composed of dodecylamine-poly((γ-dodecyl-l-glutamate)-co-(l-histidine))-block-poly(l-glutamate-graft-alendronate) and combines a cytomembrane-insertion moiety, a tumor-microenvironment (TME)-responsive component, and an ion-chelating motif. After intravenous injection into osteosarcoma-bearing mice, BINP responds to the acidic TME to expose the dodecyl group on the surface of the expanded nanoparticles, facilitating their cytomembrane insertion. Subsequently, the protruding bisphosphonic acid group triggers continuous ion deposition to construct a mineralized barrier around the tumor, which blocks substance exchange between the tumor and surrounding normal tissues. The BINP-mediated blockade therapy displays tumor inhibition rates of 59.3% and 52.1% for subcutaneous and orthotopic osteosarcomas, respectively, compared with the Control group. In addition, the suppression of osteoclasts by the alendronate moiety alleviates bone dissolution and further inhibits pulmonary metastases. Hence, the BINP-initiated selective biomineralization provides a promising alternative for clinical osteosarcoma therapy.

Biomimetic ion substituted and Co-substituted hydroxyapatite nanoparticle synthesis using Serratia Marcescens

Biomimicry is becoming deep-rooted as part of bioceramics owing to its numerous functional advantages. Naturally occurring hydroxyapatite (HA) apart from primary nano structures are also characterised by various ionic substitutions. The ease of accommodating such key elements into the HA lattice is known to enhance bone healing properties of bioceramics. In this work, hydroxyapatite synthesized via biomimetic approach was substituted with individual as well as multiple cations for potential applications in bone repair. Ion substitutions of Sr, Mg and Zn was carried out on HA for the first time by using Serratia grown in a defined biomineralization medium. The individual ions of varying concentration substituted in Serratia HA (SHA) (Sr SHA, Mg SHA and Zn SHA) were analysed for crystallinity, functional groups, morphology and crystal size. All three showed decreased crystallinity, phase purity, large agglomerated aggregates and needle-shaped morphologies. Fourier transform infrared spectroscopy (FTIR) spectra indicated increased carbonate content of 5.8% resembling that of natural bone. Additionally, the reduced O-H intensities clearly portrayed disruption of HA lattice and subsequent ion-substitution. The novelty of this study lies primarily in investigating the co-substitution of a combination of 1% Sr, Zn and Mg in SHA and establishing the associated change in bone parameters. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images clearly illustrated uniform nano-sized agglomerates of average dimensions of 20-50 nm length and 8-15 nm width for Sr SHA; 10-40 nm length and 8-10 nm width for both Zn SHA and Mg SHA and 40-70 nm length and 4-10 nm width in the case of 1% Sr, Zn, Mg SHA. In both individual as well as co-substitutions, significant peak shifts were not observed possibly due to the lower concentrations. However, cell volumes increased in both cases due to presence of Sr²⁺ validating its dominant integration into the SHA lattice. Rich trace ion deposition was presented by energy dispersive X-ray spectroscopy (EDS) and quantified using inductively coupled plasma optical emission spectrometer (ICP-OES). In vitro cytotoxicity studies in three cell lines viz. NIH/3T3 fibroblast cells, MG-63 osteosarcoma cells and RAW 264.7 macrophages showed more than 90% cell viability proving the biocompatible nature of 1% Sr, Zn and Mg in SHA. Microbial biomineralization by Serratia produced nanocrystals of HA that mimicked "bone-like apatite" as evidenced by pure phase, carbonated groups, reduced crystallinity, nano agglomerates, variations in cell parameters, rich ion deposition and non-toxic nature. Therefore ion-substituted and co-substituted biomineralized nano SHA appears to be a suitable candidate for applications in biomedicine addressing bone injuries and aiding regeneration as a result of its characteristics close to that of the human bone.

In vitrocellular biocompatibility andin vivodegradation behavior of calcium phosphate-coated ZK60 magnesium alloy

Calcium phosphate (Ca-P) surface coating is a simple but effective way to enhance both corrosion resistance and biocompatibility of ZK60 magnesium alloy. However, cell compatibility on different Ca-P layers coated on ZK60 alloy has seldom been investigated. In this study, the effects of type, morphology and corrosion protection of several Ca-P coatings formed at pH 6.5, 7.8 and 10.2 on cell behavior were examined by using an osteoblastic cell line MC3T3-E1. Furthermore,in vivobehavior in rabbits of the alloy coated with the optimum Ca-P layer was also studied. It was found that the surface factors governed the cell morphology and density. The coating morphology plays a dominant role in these surface factors. The sample coated at pH 7.8 showed the best cellular biocompatibility, suggesting that the hydroxyapatite (HAp) layer formed at pH 7.8 was the optimum coating. In rabbits, this optimum coating enhanced remarkably the corrosion resistance of the alloy. During implantation, the outermost crystals of the HAp coating were shortened and thinned due to the dissolution of HAp caused by the body fluid of the rabbits. It is indicated that ZK60 alloy coated at pH 7.8 can be applied as a biodegradable implant.

The many facets of micropetrosis - Magnesium whitlockite deposition in bisphosphonate-exposed human alveolar bone with osteolytic metastasis

The lacuno-canalicular space of apoptotic osteocytes eventually becomes mineralised in vivo. This condition is known as micropetrosis and is a fundamental characteristic of ageing bone. Increased prevalence of such hypermineralised osteocyte lacunae is viewed as a structural marker of impaired bone function - both mechanical and biological. Within the lacuno-canalicular space, mineralised apoptotic debris typically occurs as micrometre-sized, spherical nodules of magnesium-rich, carbonated apatite. Moreover, characteristically facetted, rhomboidal nodules of magnesium whitlockite [Mg-whitlockite; Ca₁₈Mg₂(HPO₄)₂(PO₄)₁₂] have been reported in human alveolar bone exposed to the bisphosphonate alendronate. This work provides supporting evidence for Mg-whitlockite formation in the alveolar bone of a 70-year-old male exposed to the bisphosphonate zoledronic acid to suppress osteolytic changes in skeletal metastasis. Backscattered electron scanning electron microscopy (BSE-SEM) revealed spherical and rhomboidal nodules within the lacuno-canalicular space. A variant of spherical nodules exhibited a fuzzy surface layer comprising radially extending acicular crystallites. The rhomboidal nodules ranged between ∼200 nm to ∼2.4 µm across the widest dimension (652 ± 331 nm). Micro-Raman spectroscopy and energy dispersive X-ray spectroscopy confirmed that rhomboidal nodules are compositionally distinct from spherical nodules, exhibiting higher Mg content and lower Ca/P ratio. Formation of Mg-whitlockite within osteocyte lacunae is multifactorial in nature and suggests altered bone biomineralisation. Nevertheless, the underlying mechanism(s) and sequence of events remain poorly understood and warrant further investigation. The possibility to discriminate between carbonated apatite and Mg-whitlockite nodules within osteocyte lacunae, based on particle morphology, attests to the diagnostic potential of BSE-SEM with or without additional analyses of material composition.

The material design of octacalcium phosphate bone substitute: increased dissolution and osteogenecity

Octacalcium phosphate (OCP) has been advocated as a precursor of bone apatite crystals. Recent studies have shown that synthetic OCP exhibits highly osteoconductive properties as a bone substitute material that stems from its ability to activate bone tissue-related cells, such as osteoblasts, osteocytes, and osteoclasts. Accumulated experimental evidence supports the proposition that the OCP-apatite phase conversion under physiological conditions increases the stimulatory capacity of OCP. The conversion of OCP progresses by hydrolysis toward Ca-deficient hydroxyapatite with Ca²⁺ ion incorporation and inorganic phosphate ion release with concomitant increases in the solid Ca/P molar ratio, specific surface area, and serum protein adsorption affinity. The ionic dissolution rate during the hydrolysis reaction was controlled by introducing a high-density edge dislocation within the OCP lattice by preparing it through co-precipitation with gelatin. The enhanced dissolution intensifies the material biodegradation rate and degree of osteogenecity of OCP. Controlling the biodegradation rate relative to the dissolution acceleration may be vital for controlling the osteogenecity of OCP materials. This study investigates the effects of the ionic dissolution of OCP, focusing on the structural defects in OCP, as the enhanced metastability of the OCP phase modulates biodegradability followed by new bone formation. STATEMENT OF SIGNIFICANCE: Octacalcium phosphate (OCP) is recognized as a highly osteoconductive material that is biodegradable by osteoclastic resorption, followed by new bone formation by osteoblasts. However, if the degradation rate of OCP is increased by maintaining the original osteoconductivity or acquiring a bioactivity better than its current properties, then early replacement with new bone can be expected. Although cell introduction or growth factor addition by scaffold materials is the standard method for tissue engineering, material activity can be augmented by introducing dislocations into the lattice of the OCP. This review article summarizes the effects of introducing structural defects on activating OCP, which was obtained by co-precipitation with gelatin, as a bone substitute material and the mechanism of improved bone replacement performance.