Functional calcium phosphate composites in nanomedicine

Dexamethasone-Loaded Lipid Calcium Phosphate Nanoparticles Treat Experimental Colitis by Regulating Macrophage Polarization in Inflammatory Sites

Background

The M1/M2 polarization of intestinal macrophages exerts an essential function in the pathogenesis of ulcerative colitis (UC), which can be adjusted to alleviate the UC symptoms.

Purpose

A kind of pH-sensitive lipid calcium phosphate core-shell nanoparticles (NPs), co-loading with dexamethasone (Dex) and its water-soluble salts, dexamethasone sodium phosphate (Dsp), was constructed to comprehensively regulate macrophages in different states towards the M2 phenotype to promote anti-inflammatory effects.

Methods

Dex and Dsp were loaded in the outer lipid shell and inner lipid calcium phosphate (Cap) core of the LdCaPd NPs, respectively. Then, the morphology of NPs and methods for determining drug concentration were investigated, followed by in vitro protein adsorption, stability, and release tests. Cell experiments evaluated the cytotoxicity, cellular uptake, and macrophage polarization induction ability of NPs. The in vivo distribution and anti-inflammatory effect of NPs were evaluated through a 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced BALB/c mice ulcerative colitis model.

Results

The LdCaPd NPs showed a particle size of about 200 nm and achieved considerable loading amounts of Dex and Dsp. The in vitro and in vivo studies revealed that in the acidic UC microenvironment, the cationic lipid shell of LdCaPd underwent protonated dissociation to release Dex first for creating a microenvironment conducive to M2 polarization. Then, the exposed CaP core was further engulfed by M1 macrophages to release Dsp to restrict the pro-inflammatory cytokines production by inhibiting the activation and function of the nuclear factor kappa-B (NF-κB) through activating the GC receptor and the NF kappa B inhibitor α (I-κBα), respectively, ultimately reversing the M1 polarization to promote the anti-inflammatory therapy.

Conclusion

The LdCaPd NPs accomplished the sequential release of Dex and Dsp to the UC site and the inflammatory M1 macrophages at this site, promoting the regulation of macrophage polarization to accelerate the remission of UC symptoms.

The Preparation and Effects of Organic-Inorganic Antioxidative Biomaterials for Bone Repair

Reactive oxygen species (ROS) has great influence in many physiological or pathological processes in organisms. In the site of bone defects, the overproduced ROS significantly affects the dynamic balance process of bone regeneration. Many antioxidative organic and inorganic antioxidants showed good osteogenic ability, which has been widely used for bone repair. It is of great significance to summarize the antioxidative bone repair materials (ABRMs) to provide guidance for the future design and preparation of osteogenic materials with antioxidative function. Here, this review introduced the major research direction of ABRM at present in nanoscale, 2-dimensional coating, and 3-dimensional scaffolds. Moreover, the referring main active substances and antioxidative properties were classified, and the positive roles of antioxidative materials for bone repair have also been clearly summarized in signaling pathways, antioxidant enzymes, cellular responses and animal levels.

Polyvinylpyrrolidone-Alginate-Carbonate Hydroxyapatite Porous Composites for Dental Applications

An alternative approach for the currently used replacement therapy in dentistry is to apply materials that restore tooth tissue. Among them, composites, based on biopolymers with calcium phosphates, and cells can be applied. In the present work, a composite based on polyvinylpyrrolidone (PVP) and alginate (Alg) with carbonate hydroxyapatite (CHA) was prepared and characterized. The composite was investigated by X-ray diffraction, infrared spectroscopy, electron paramagnetic resonance (EPR) and scanning electron microscopy methods, and the microstructure, porosity, and swelling properties of the material were described. In vitro studies included the MTT test using mouse fibroblasts, and adhesion and survivability tests with human dental pulp stem cells (DPSC). The mineral component of the composite corresponded to CHA with an admixture of amorphous calcium phosphate. The presence of a bond between the polymer matrix and CHA particles was shown by EPR. The structure of the material was represented by micro- (30-190 μm) and nano-pores (average 8.71 ± 4.15 nm). The swelling measurements attested that CHA addition increased the polymer matrix hydrophilicity by 200%. In vitro studies demonstrated the biocompatibility of PVP-Alg-CHA (95 ± 5% cell viability), and DPSC located inside the pores. It was concluded that the PVP-Alg-CHA porous composite is promising for dentistry applications.

Connecting Calcium-Based Nanomaterials and Cancer: From Diagnosis to Therapy

As the indispensable second cellular messenger, calcium signaling is involved in the regulation of almost all physiological processes by activating specific target proteins. The importance of calcium ions (Ca²⁺) makes its "Janus nature" strictly regulated by its concentration. Abnormal regulation of calcium signals may cause some diseases; however, artificial regulation of calcium homeostasis in local lesions may also play a therapeutic role. "Calcium overload," for example, is characterized by excessive enrichment of intracellular Ca²⁺, which irreversibly switches calcium signaling from "positive regulation" to "reverse destruction," leading to cell death. However, this undesirable death could be defined as "calcicoptosis" to offer a novel approach for cancer treatment. Indeed, Ca²⁺ is involved in various cancer diagnostic and therapeutic events, including calcium overload-induced calcium homeostasis disorder, calcium channels dysregulation, mitochondrial dysfunction, calcium-associated immunoregulation, cell/vascular/tumor calcification, and calcification-mediated CT imaging. In parallel, the development of multifunctional calcium-based nanomaterials (e.g., calcium phosphate, calcium carbonate, calcium peroxide, and hydroxyapatite) is becoming abundantly available. This review will highlight the latest insights of the calcium-based nanomaterials, explain their application, and provide novel perspective. Identifying and characterizing new patterns of calcium-dependent signaling and exploiting the disease element linkage offer additional translational opportunities for cancer theranostics.

Inorganic Nanoparticles in Bone Healing Applications

Modern biomedicine aims to develop integrated solutions that use medical, biotechnological, materials science, and engineering concepts to create functional alternatives for the specific, selective, and accurate management of medical conditions. In the particular case of tissue engineering, designing a model that simulates all tissue qualities and fulfills all tissue requirements is a continuous challenge in the field of bone regeneration. The therapeutic protocols used for bone healing applications are limited by the hierarchical nature and extensive vascularization of osseous tissue, especially in large bone lesions. In this regard, nanotechnology paves the way for a new era in bone treatment, repair and regeneration, by enabling the fabrication of complex nanostructures that are similar to those found in the natural bone and which exhibit multifunctional bioactivity. This review aims to lay out the tremendous outcomes of using inorganic nanoparticles in bone healing applications, including bone repair and regeneration, and modern therapeutic strategies for bone-related pathologies.

Probing the Structure, Cytocompatibility, and Antimicrobial Efficacy of Silver-, Strontium-, and Zinc-Doped Monetite

Calcium phosphate phases are among the most widely accepted compounds for biomaterial applications, of which the resorbable phases have gained particular attention in recent years. Brushite and its anhydrous form monetite are among the most interesting resorbable calcium phosphate phases that can be applied as cements and for in situ fabrication of three-dimensional (3D) implants. Of these two dicalcium phosphate compounds, monetite is more stable and undergoes slower degradation than brushite. The purpose of the current study is to synthesize and dope monetite with the antimicrobial elements silver and zinc and the osteoinductive element strontium and investigate the possible structural variations as well as their biocompatibility and antimicrobial effectiveness. For this, powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and cryo-transmission electron microscopy (cryo-TEM) were used to thoroughly study the synthesized structures. Moreover, the ASTM E-2149-01 protocol and a cell proliferation assay were used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) and the cytocompatibility of the different phases with the Soas-2 cell line, respectively. The results confirm the successful synthesis and doping procedures, such that zinc was the most incorporated element into the monetite phase and strontium was the least incorporated element. The microbiological studies revealed that silver is a very effective antimicrobial agent at low concentrations but unsuitable at high concentrations because its cytotoxicity would prevail. On the other hand, doping the compounds with zinc led to a reasonable antimicrobial activity without compromising the biocompatibility to obviously high concentrations. The study also highlights that strontium, widely known for its osteoinductivity, bears an antimicrobial effect at high concentrations. The generated doped compounds could be beneficial for prospective studies as bone cements or for scaffold biomaterial applications.

Anhydrous calcium phosphate crystals stabilize DNA for dry storage

The resilience of ancient DNA (aDNA) in bone gives rise to the preservation of synthetic DNA with bioinorganic materials such as calcium phosphate (CaP). Accelerated aging experiments at elevated temperature and humidity displayed a positive effect of co-precipitated, crystalline dicalcium phosphate on the stability of synthetic DNA in contrast to amorphous CaP. Quantitative PXRD in combination with SEM and EDX measurements revealed distinct CaP phase transformations of calcium phosphate dihydrate (brushite) to anhydrous dicalcium phosphate (monetite) influencing DNA stability.

pH-programmed responsive nanoplatform for synergistic cancer therapy based on single atom catalysts

The development of stimuli-responsive nanoplatform provides powerful tool for simultaneously enhancing the efficiency and accuracy of cancer therapies. Herein, we develop a pH-programmed responsive and synergistically theranostic nanoplatform based on CaCO₃ mineralized single atom iron nanoparticles (SAF NPs). Basically, the highly active site on SAF NPs nanoagent can trigger in-situ produce toxic •OH in tumor microenvironment (TME) that kill cancer cells for Fenton-reaction-based chemodynamic therapy (CDT). The porous structure of SAF NPs can serve as delivery platforms to package and programmed release chemotherapeutic drug doxorubicin (DOX) to enhance chemotherapy (CT) efficiency. The nanoplatform was simultaneously in-situ mineralized with CaCO₃ and A549 cell membrane (CM) which could avoid DOX leakage during transport in bloodstream and target homologous cancer cells. In addition, overload Ca²⁺ decomposed from CaCO₃ triggers mitochondrial dysfunction, induces cytoskeleton collapse and oxidative stress to formulate calcium ions interference therapy (CIT). With the combination of CDT, CT and CIT, the designed multi-synergetic nanoplatform exhibits excellent biocompatibility, specificity and tunable drug release behavior, which has a broad application prospect in tumor therapy.

Radiation-Induced Stable Radicals in Calcium Phosphates: Results of Multifrequency EPR, EDNMR, ESEEM, and ENDOR Studies

This article presents the results of a study of radiation-induced defects in various synthetic calcium phosphate (CP) powder materials (hydroxyapatite—HA and octacalcium phosphate—OCP) by electron paramagnetic resonance (EPR) spectroscopy at the X, Q, and W-bands (9, 34, 95 GHz for the microwave frequencies, respectively). Currently, CP materials are widely used in orthopedics and dentistry owing to their high biocompatibility and physico-chemical similarity with human hard tissue. It is shown that in addition to the classical EPR techniques, other experimental approaches such as ELDOR-detected NMR (EDNMR), electron spin echo envelope modulation (ESEEM), and electron-nuclear double resonance (ENDOR) can be used to analyze the electron–nuclear interactions of CP powders. We demonstrated that the value and angular dependence of the quadrupole interaction for 14N nuclei of a nitrate radical can be determined by the EDNMR method at room temperature. The ESEEM technique has allowed for a rapid analysis of the nuclear environment and estimation of the structural positions of radiation-induced centers in various crystal matrices. ENDOR spectra can provide information about the distribution of the nitrate radicals in the OCP structure.

Chitosan and Curcumin Nanoformulations against Potential Cardiac Risks Associated with Hydroxyapatite Nanoparticles in Wistar Male Rats

Nanoparticle-induced cardiovascular diseases have attracted much attention. Upon entering the blood circulation system, these particles have the potency to induce cardiomyocytes, leading to cardiac failure or myocardial ischemia, and the molecular mechanism remains to be completely clarified. In this study, the cardiac toxicity of rats orally exposed to hydroxyapatite nanoparticles (HAPNPs) has been observed through an increase in myocardial infarction serum markers including CK-MB and alterations in routine blood factors, expression of apoptosis-related protein P53, and increased levels of serum inflammatory markers represented by the tumor necrosis factor alpha and Interleukin-6, as well as a decline in heart antioxidant enzymes and reduced glutathione level, while an induction in lipid peroxidation and nitric oxide has been observed, as well as notable histological and histochemical alterations in the heart of these animals. mRNA and protein expressions of vascular endothelial growth factor (VEGF-A), cyclooxygenase-2 (COX-2), and atrial natriuretic factor (ANF) were elevated in the myocardium. However, the coadministration of chitosan nanoparticles (CsNPs) and/or curcumin nanoparticles (CurNPs) successfully modulated these alterations and induced activation in antioxidant parameters. The present data suggest that HAPNPs-induced apoptosis via the mitochondrial pathway may play a crucial role in cardiac tissue damage and the early treatment with CsNPs and CurNPs may protect the heart from infarction induced by HAPNPs toxic effect.

Biological and Medical Applications of Calcium Phosphate Nanoparticles

Calcium phosphate nanoparticles have a high biocompatibility and biodegradability due to their chemical similarity to human hard tissue, for example, bone and teeth. They can be used as efficient carriers for different kinds of biomolecules such as nucleic acids, proteins, peptides, antibodies, or drugs, which alone are not able to enter cells where their biological effect is required. They can be loaded with cargo molecules by incorporating them, unlike solid nanoparticles, and also by surface functionalization. This offers protection, for example, against nucleases, and the possibility for cell targeting. If such nanoparticles are functionalized with fluorescing dyes, they can be applied for imaging in vitro and in vivo. Synthesis, functionalization and cell uptake mechanisms of calcium phosphate nanoparticles are discussed together with applications in transfection, gene silencing, imaging, immunization, and bone substitution. Biodistribution data of calcium phosphate nanoparticles in vivo are reviewed.

X-Ray Diffraction and Multifrequency EPR Study of Radiation-Induced Room Temperature Stable Radicals in Octacalcium Phosphate

Octacalcium phosphate (OCP) {Ca8H2(PO4)6×5H2O] has attracted increasing attention over the last decade as a transient intermediate to the biogenic apatite for bone engineering and in studies involving the processes of pathological calcification. In this work, OCP powders obtained by hydrolysis of dicalcium phosphate dehydrate were subjected to X- and γ-ray irradiation and studied by means of stationary and pulsed electron paramagnetic resonance at 9, 36 and 94 GHz microwave frequencies. Several types of paramagnetic centers were observed in the investigated samples. Their spectroscopic parameters (components of the g and hyperfine tensors) were determined. Based on the extracted parameters, the induced centers were ascribed to H0, CO33-, CO2- and nitrogen-centered (presumably NO32-) radicals. The spectroscopic parameters of the nitrogen-centered stable radical in OCP powders were found to be markedly different from those in hydroxyapatite. According to X-ray diffraction data, γ-ray irradiation allowed the phase composition of calcium phosphates to change; all minor phases with the exception of OCP and hydroxyapatite disappeared, while the OCP crystal lattice parameters changed after irradiation. The obtained results could be used for the tracing of mineralization processes from their initiation to completion of the final product, identification of the OCP phase, and to follow the influence of radiation processes on phase composition of calcium phosphates.

Exploring the interplay of mucin with biologically-relevant amorphous magnesium-calcium phosphate nanoparticles

HYPOTHESIS

It has been recently shown that, in our organism, the secretions of Ca²⁺, Mg²⁺ and phosphate ions lead to the precipitation of amorphous magnesium-calcium phosphate nanoparticles (AMCPs) in the small intestine, where the glycoprotein mucin is one of the most abundant proteins, being the main component of the mucus hydrogel layer covering gut epithelium. Since AMCPs precipitate in vivo in a mucin-rich environment, we aim at studying the effect of this glycoprotein on the formation and features of endogenous-like AMCPs.

EXPERIMENTS

AMCPs were synthesized from aqueous solution in the presence of different concentrations of mucin, and the obtained particles were characterised in terms of crystallinity, composition and morphology. Solid State NMR investigation was also performed in order to assess the interplay between mucin and AMCPs at a sub-nanometric level.

FINDING

Results show that AMCPs form in the presence of mucin and the glycoprotein is efficiently incorporated in the amorphous particles. NMR indicates the existence of interactions between AMCPs and mucin, revealing how AMCPs in mucin-hybrid nanoparticles affect the features of both proteic and oligosaccharidic portions of the glycoprotein. Considering that the primary function of mucin is the protection of the intestine from pathogens, we speculate that the nature of the interaction between AMCPs and mucin described in the present work might be relevant to the immune system, suggesting a novel type of scenario which could be investigated by combining physico-chemical and biomedical approaches.

Supramolecular self-assembly of a hybrid 'hyalurosome' for targeted photothermal therapy in non-small cell lung cancer

Despite the excellent efficacy and low toxicity of photoresponse therapy, which has attracted considerable attention for use in non-small cell lung cancer (NSCLC) therapy, unsatisfactory cellular permeability, and instability, both in vitro and in vivo have limited further clinical applications of indole cyanine photosensitizers. Here, we explore the supramolecular self-assembly of a ‘hyalurosome’ that is mediated by calcium phosphate nanonuclei. Through hyaluronate-mediated CD44 targeting, the constructed hyalurosome specifically delivers ICG into NSCLC cells and then induces severe hyperthermia accompanied by the generation of singlet oxygen upon photoirradiation. In contrast to the action of the native form, indocyanine green encapsulated in a hyalurosome showed significantly increased cellular endocytosis and inhibited cell proliferation both in vitro and in vivo. Our study indicated that this hyalurosome is a promising candidate for the targeted delivery of photosensitizers, which may be useful in NSCLC therapy.

Nanostructured Biomaterials for Bone Regeneration

This review article addresses the various aspects of nano-biomaterials used in or being pursued for the purpose of promoting bone regeneration. In the last decade, significant growth in the fields of polymer sciences, nanotechnology, and biotechnology has resulted in the development of new nano-biomaterials. These are extensively explored as drug delivery carriers and as implantable devices. At the interface of nanomaterials and biological systems, the organic and synthetic worlds have merged over the past two decades, forming a new scientific field incorporating nano-material design for biological applications. For this field to evolve, there is a need to understand the dynamic forces and molecular components that shape these interactions and influence function, while also considering safety. While there is still much to learn about the bio-physicochemical interactions at the interface, we are at a point where pockets of accumulated knowledge can provide a conceptual framework to guide further exploration and inform future product development. This review is intended as a resource for academics, scientists, and physicians working in the field of orthopedics and bone repair.

Electrospun Fibre Webs Templated Synthesis of Mineral Scaffolds Based on Calcium Phosphates and Barium Titanate

The current work focuses on the development of mineral scaffolds with complex composition and controlled morphology by using a polymeric template in the form of nonwoven fibre webs fabricated through electrospinning. By a cross-linking process, gelatine fibres stable in aqueous solutions were achieved, these being further subjected to a loading step with two types of mineral phases: calcium phosphates deposited by chemical reaction and barium titanate nanoparticles as decoration on the previously achieved structures. Thus, hybrid materials were obtained and subsequently processed in terms of freeze-drying and heat treating with the purpose of burning the template and consolidating the mineral part as potential bone implants with improved biological response by external stimulation. The results confirmed the tunable morphology, as well as the considerable applicability of both as-prepared and final samples for the development of medical devices, which encourages the continuation of research in the direction of assessing the synergistic contribution of barium titanate domains polarisation/magnetisation by external applied fields.

Composite scaffolds based on calcium phosphates and barium titanate obtained through bacterial cellulose templated synthesis

Taking into account the potential of barium titanate to deliver electrical stimulation to the physiological microenvironment and offer beneficial conditions for the cellular metabolism, this mineral phase was selected for the development of new composites. In this context, calcium phosphates and barium titanate were deposited on bacterial cellulose membranes under ultrasonic irradiation, the resulting system being subjected to a thermal treatment in optimized conditions in order to remove the polymeric template and achieve 3D porous architectures. The complex characterization performed on the intermediate and final samples demonstrated the suitability of such materials for hard tissue engineering applications.

Calcium Phosphate Nanoparticles-Based Systems for RNAi Delivery: Applications in Bone Tissue Regeneration

Bone-related injury and disease constitute a significant global burden both socially and economically. Current treatments have many limitations and thus the development of new approaches for bone-related conditions is imperative. Gene therapy is an emerging approach for effective bone repair and regeneration, with notable interest in the use of RNA interference (RNAi) systems to regulate gene expression in the bone microenvironment. Calcium phosphate nanoparticles represent promising materials for use as non-viral vectors for gene therapy in bone tissue engineering applications due to their many favorable properties, including biocompatibility, osteoinductivity, osteoconductivity, and strong affinity for binding to nucleic acids. However, low transfection rates present a significant barrier to their clinical use. This article reviews the benefits of calcium phosphate nanoparticles for RNAi delivery and highlights the role of surface functionalization in increasing calcium phosphate nanoparticles stability, improving cellular uptake and increasing transfection efficiency. Currently, the underlying mechanistic principles relating to these systems and their interplay during in vivo bone formation is not wholly understood. Furthermore, the optimal microRNA targets for particular bone tissue regeneration applications are still unclear. Therefore, further research is required in order to achieve the optimal calcium phosphate nanoparticles-based systems for RNAi delivery for bone tissue regeneration.

Preparation and preliminary evaluation of bio-nanocomposites based on hydroxyapatites with antibacterial properties against anaerobic bacteria

Hexagonal nanocrystalline powders of the non-doped Ca₁₀(PO₄)₆(OH)₂ as well as activated with Ag⁺ and Eu³⁺ ions were synthesized by using different wet chemistry methods. Moreover, the obtained hydroxyapatite was loaded with Ag⁰, as well as nitroimidazole antimicrobials: metronidazole and tinidazole. The structural properties of the products were analyzed by X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) electron microscopy as well as infrared (IR) and Raman spectroscopy. The photoluminescence properties of the Eu³⁺ and Ag⁺ co-doped Ca₁₀(PO₄)₆(OH)₂ were characterized via the PL emission, excitation spectra and the luminescence decay curve. The antimicrobial activity of the obtained materials against Prevotella bivia and Parabacteroides distasonis was studied. The cytotoxicity assessment was carried out on the human osteosarcoma cell line (U2OS) as well as human red blood cells (RBC). The choice of the in vitro model was based on the fact that U2OS is a cancer cell line derived from bone tissue which is rich in apatites that play a pivotal role in the extracellular matrix formation. RBCs are the most abundant blood cells and they are used as a cell model in the study of biocompatibility of new prepared biocompounds with potential medical applications. The obtained multifunctional materials do not exhibit the haemolytic activity, therefore, they could be used as a promising antimicrobial agent and for anaerobic bacteria.

Osteogenic and antibacterial dual functions of a novel levofloxacin loaded mesoporous silica microspheres/nano-hydroxyapatite/polyurethane composite scaffold

Lev/MSNs/n-HA/PU has been proved to be a novel scaffold material to treat bone defect caused by chronic osteomyelitis. We have previously identified that this material can effectively treat chronic osteomyelitis caused by Staphylococcus aureusin vivo. However, the potential mechanisms of antibacterial and osteogenic induction properties remain unclear. Thus, for osteogenesis property, immunohistochemistry, PCR, and Western blot were performed to detect the expression of osteogenic markers. Furthermore, flow cytometry and TUNEL were applied to analyze MC3T3-E1 proliferation and apoptosis. For antibacterial property, the material was co-cultivated with bacteria, bacterial colony forming units was counted and the release time of the effective levofloxacin was assayed by agar disc-diffusion test. Moreover, scanning electron microscope was applied to observe adhesion of bacteria. In terms of osteogenic induction, we found BMSCs adherently grew more prominently on Lev/MSNs/n-HA/PU. Lev/MSNs/n-HA/PU also enhanced the expression of osteogenic markers including OCN and COL1α1, as well as effectively promoted the transition from G1 phase to G2 phase. Furthermore, Lev/MSNs/n-HA/PU could reduce apoptosis of MC3T3-E1. Besides, both Lev/MSNs/n-HA/PU and n-HA/PU materials could inhibit bacterial colonies, while Lev/MSNs/n-HA/PU possessed a stronger antibacterial activities, and lower bacterial adhesion than n-HA/PU. These results illustrated that Lev/MSNs/n-HA/PU composite scaffold possess favorable compatibility in vitro, which induce osteogenic differentiation of MSCs, promote proliferation and differentiation of MC3T3-E1, and inhibit apoptosis. Moreover, clear in vitro antibacterial effect of Lev/MSNs/n-HA/PU was also observed. In summary, this study replenishes the potential of Lev/MSNs/n-HA/PU composite scaffold possess dual functions of anti-infection and enhanced osteogenesis for future clinical application.

The importance of being amorphous: calcium and magnesium phosphates in the human body

This article focuses on the relevance of amorphous calcium (and magnesium) phosphates in living organisms. Although crystalline calcium phosphate (CaP)-based materials are known to constitute the major inorganic constituents of human hard tissues, amorphous CaP-based structures, often in combination with magnesium, are frequently employed by Nature to build up components of our body and guarantee their proper functioning. After a brief description of amorphous calcium phosphate (ACP) formation mechanism and structure, this paper is focused on the stabilization strategies that can be used to enhance the lifetime of the poorly stable amorphous phase. The various locations of our body in which ACP (pure or in combination with Mg²⁺) can be found (i.e. bone, enamel, small intestine, calciprotein particles and casein micelles) are highlighted, showing how the amorphous nature of ACP is often of paramount importance for the achievement of a specific physiological function. The last section is devoted to ACP-based biomaterials, focusing on how these materials differ from their crystalline counterparts in terms of biological response.

Dual delivery of nucleic acids and PEGylated-bisphosphonates via calcium phosphate nanoparticles

Despite many years of research and a few success stories with gene therapeutics, efficient and safe DNA delivery remains a major bottleneck for the clinical translation of gene-based therapies. Gene transfection with calcium phosphate (CaP) nanoparticles brings the advantages of low toxicity, high DNA entrapment efficiency and good endosomal escape properties. The macroscale aggregation of CaP nanoparticles can be easily prevented through surface coating with bisphosphonate conjugates. Bisphosphonates, such as alendronate, recently showed promising anticancer effects. However, their poor cellular permeability and preferential bone accumulation hamper their full application in chemotherapy. Here, we investigated the dual delivery of plasmid DNA and alendronate using CaP nanoparticles, with the goal to facilitate cellular internalization of both compounds and potentially achieve a combined pharmacological effect on the same or different cell lines. A pH-sensitive poly(ethylene glycol)-alendronate conjugate was synthetized and used to formulate stable plasmid DNA-loaded CaP nanoparticles. These particles displayed good transfection efficiency in cancer cells and a strong cytotoxic effect on macrophages. The in vivo transfection efficiency, however, remained low, calling for an improvement of the system, possibly with respect to the extent of particle uptake and their physical stability.

Ammonium-Induced Synthesis of Highly Fluorescent Hydroxyapatite Nanoparticles with Excellent Aqueous Colloidal Stability for Secure Information Storage

In this paper, uniform hydroxyapatite (HA) nanoparticles, with excellent aqueous colloidal stability and high fluorescence, have been successfully synthesized via a citrate-assisted hydrothermal method. The effect of the molar ratio of ammonium phosphate in phosphate (RAMP) and hydrothermal time on the resultant products was characterized in terms of crystalline structure, morphology, colloidal stability, and fluorescence behavior. When the RAMP is 50% and the hydrothermal time is 4 h, the product consists of a pure hexagonal HA phase and a uniform rod-like morphology, with 120- to 150-nm length and approximately 20-nm diameter. The corresponding dispersion is colloidally stable, and transparent for at least one week, and has an intense bright blue emission (centered at 440 nm, 11.6-ns lifetime, and 73.80% quantum efficiency) when excited by 340-nm UV light. Although prolonging the hydrothermal time and increasing the RAMP had no appreciable effect on the aqueous colloidal stability of HA nanoparticles, the fluorescence intensity was enhanced. The cause of HA fluorescence are more biased towards carbon dots (which are mainly polymer clusters and/or molecular fluorophores constituents) trapped in the hydroxyapatite crystal structure. Owing to these properties, a highly fluorescent HA colloidal dispersion could find applications in secure information storage.

Apatite enrichment by rare earth elements: A review of the effects of surface properties

Apatite subspecies depend on their halogen and hydroxyl content; chlorapatite, hydroxylapatite and fluorapatite, with additional substitution of other elements within the lattice such as rare earth elements (REE), sodium, strontium and manganese also possible. Rare earth elements are vital to green and emerging technologies, with demand set to outstrip supply. Apatite provides a possible future source of REE. Processing rare earth deposits is often complex, with surface behaviour having a significant effect on the optimization of a process flow sheet. The effect of enrichment of natural apatite and the doping of synthetic apatite on surface behaviour can be determined by measuring the zeta potential and the isoelectric point of the mineral. In this paper, we review zeta potential studies of natural and synthetic apatite to determine the effect of elemental enrichment on surface behaviour. Fifty three studies of natural apatite and forty four studies of synthetic apatite were reviewed. The isoelectric point of apatite varied from pH 1 to pH 8.7, with studies of apatite specified to be >90% pure reducing the variation to pH 3 to pH 6.5. Of the four studies of rare earth enriched apatite found, three had IEP values between pH 3 and pH 4. A study of synthetic apatite showing enrichment of between 1 and 10% by the REE europium does not affect surface behaviour. However, no studies were found that investigated the effect of common REE processing reagents on REE enriched apatite zeta potentials. Therefore, in addition to comparing previous studies we also therefore present new zeta potential measurements of apatite from a REE enriched deposit under water and common flotation collector conditions. The IEP value of this apatite under water conditions was at pH 3.6, shifting to <3.5 under both hydroxamic acid and betacol conditions. When compared to previous studies, the behaviour of REE enriched apatite under collector conditions is similar to non-REE apatite. This result could be important for future processing of apatite enriched with REE, and therefore global apatite and rare earth supply.

A Systematic Study of the Effect of pH on the Initialization of Ca-deficient Hydroxyapatite to β-TCP Nanoparticles

The formation of β-tricalcium phosphate (β-TCP) nanoparticles via a wet precipitation technique was studied in a systematical way, taking reaction pH and sintering temperature parameters into account. A full transformation of Ca-deficient hydroxyapatite (CDHA) to β-TCP at 750 °C in under 3 hours from Ca++ and PO₄3- precursor solutions prepared under a pH of 5.5 was observed. For pH values higher than 6.5, CDHA can only partially transform into β-TCP and only at temperatures higher than 750 °C confirmed using X-Ray diffraction and Raman spectroscopy. The morphologies of the particles were also examined by Transmission electron microscopy. The lower temperatures and the shorter sintering time allow for a fine needle-like morphology, but with a high crystallinity, likely eliminating the possibility of excessive grain growth that is otherwise expected to occur under high-temperature treatment with long process times. We show that sintering of nanostructured, high crystallinity β-TCP at relatively low temperatures is possible via adjustment of the precursor solution parameters. Such an outcome is important for the use of β-TCP with a fine morphology imitating that of the skeletal tissues, enhancing the osteointegration of a base, load-bearing alloy to the host tissue. MTT analysis was used to test the effect of the obtained β-TCP particles on the viability of MG-63 human osteoblast-like cells.

Chitosan Oligosaccharide Lactate Coated Hydroxyapatite Nanoparticles as a Vehicle for the Delivery of Steroid Drugs and the Targeting of Breast Cancer Cells

Low targeting efficiency and fast metabolism of antineoplastic drugs are hindrances to effective chemotherapies and there is an ongoing search for better drugs, but also better carriers. Steroid derivatives, 3β-hydroxy-16-hydroxymino-androst-5-en-17-one (A) and 3β,17β-dihydroxy-16-hydroxymino-androst-5-ene (B) as cancer growth inhibitors were chemically synthesized and captured in a carrier composed of hydroxyapatite (HAp) nanoparticles coated with chitosan oligosaccharide lactate (ChOLS). The only difference between the two derivatives is that A has a carbonyl group at the C17 position of the five-membered ring and B has a hydroxyl. This small difference in the structure resulted not only in different physicochemical properties of the A- and B-loaded HAp/ChOSL, but also in different biological activities. The morphology of drug-loaded HAp/ChOSL particles was spherical, but the size depended on the drug identity: d₅₀=138 nm for A-loaded HAp/ChOSL and d₅₀=223 nm for B-loaded HAp/ChOSL. Cell-selective toxicity was tested against human breast carcinoma (MCF7 and MDA-MB-231), human lung carcinoma (A549) and human lung fibroblasts (MRC-5). The small selectivity of pure derivatives A and B toward breast cancer cells became drastically increased when they were delivered using HAp/ChOSL particles. Whereas the ratio of the cytotoxicity imposed onto breast cancer cells and the cytotoxicity imposed onto healthy MRC-5 fibroblasts ranged from 1.5 to 1.7 for pure A and from 1.5 to 2.3 for pure derivative B depending on the concentration, it increased to 5.4 for A-loaded HAp/ChOSL and 5.1 for B-loaded HAp/ChOSL. FACS analysis demonstrated poor uptake of HAp/ChOSL particles by MCF7 cells, suggesting that the drug release occurs extracellularly. The augmented activity of the drugs was most likely due to sustained release, although the favorable positive charge of the carrier, allowing it to adhere to the negatively charged plasma membrane and release the drugs steadily and directly to the hydrophobic cell membrane milieu, was delineated as a possible complementary mechanism.

Inorganic kernel - Supported asymmetric hybrid vesicles for targeting delivery of STAT3-decoy oligonucleotides to overcome anti-HER2 therapeutic resistance of BT474R

As a recombinant humanized monoclonal antibody that targets the extracellular region of HER2 tyrosine kinase receptor, trastuzumab (TRAZ) has demonstrated comparable clinical efficacy and improved survival in patients with HER2-positive breast cancer. Nevertheless, the therapeutic potential of TRAZ is often limited due to its frequent resistance to anti-HER2 therapy. Therefore, we investigate the reversal effect of STAT3-specific decoy oligonucleotides (STAT3-decoy ODNs) on TRAZ resistance, which contain the consensus sequence within the targeted gene promoter of STAT3. Considering the shortcomings of poor cellular permeability and rapid degradation in vivo limit the further clinical applications of ODNs, we report here an asymmetric hybrid lipid/polymer vesicles with calcium phosphate as the solid kernel (CaP@HA). Through hyaluronan-mediated CD44 targeting, the constructed vesicles can specifically carry STAT3-decoy ODNs into TRAZ-resistant breast cancer cells and then regulate TRAZ-induced apoptosis. In comparison with the native ones, ODNs packaged with CaP@HA showed significantly increased serum stability, cellular transfection, synergistic cytotoxicity and apoptosis in vitro. The improved TRAZ sensitization is attributed to the blockade of STAT3 signaling as well as the expression of downstream target genes associated with TRAZ resistance. With the synergistic action of STAT3-decoy ODNs loaded CaP@HA, TRAZ inhibited the growth of its resistant breast cancer xenograft dramatically and induced significant tumor cell apoptosis in vivo. These results suggested that CaP@HA mediated targeted delivery of STAT3-decoy ODNs might be a promising new strategy to overcome anti-HER2 resistance in breast cancer therapy.

Construction and evaluation of BSA-CaP nanomaterials with enhanced transgene performance via biocorona-inspired caveolae-mediated endocytosis

Non-viral nanovectors have attracted much attention owing to their ability to condense genetic materials and their ease of modification. However, their poor stability, low biocompatibility and gene degradation in endosomes or lysosomes has significantly hampered their application in vivo and in the clinic. In an attempt to overcome these difficulties a series of bovine serum albumin (BSA)-calcium phosphate (CaP) nanoparticles were constructed. The CaP condenses with DNA to form nanocomplexes coated with a biomimetic corona of BSA. Such complexes may retain the inherent endocytosis profile of BSA, with improved biocompatibility. In particular the transgene performance may be enhanced by stimulating the cellular uptake pathway via caveolae-mediated endocytosis. Two methods were employed to construct and optimize the formulation of BSA-CaP nanomaterials. The optimized BSA-CaP-50-M2 nanoparticles prepared by our second method exhibited good stability, negligible cytotoxicity and enhanced transgene performance with long-term expression for 72 h in vivo even with a single dose. Determination of the cellular uptake pathway and Western blot revealed that cellular uptake of the designed BSA-CaP-50-M2 nanoparticles was mainly via caveolae-mediated endocytosis in a non-degradative pathway in which the biomimetic uptake profile of BSA was retained.

Amiloride-enhanced gene transfection of octa-arginine functionalized calcium phosphate nanoparticles

Nanoparticles represent promising gene delivery systems in biomedicine to facilitate prolonged gene expression with low toxicity compared to viral vectors. Specifically, nanoparticles of calcium phosphate (nCaP), the main inorganic component of human bone, exhibit high biocompatibility and good biodegradability and have been reported to have high affinity for protein or DNA, having thus been used as gene transfer vectors. On the other hand, Octa-arginine (R8), which has a high permeability to cell membrane, has been reported to improve intracellular delivery systems. Here, we present an optimized method for nCaP-mediated gene delivery using an octa-arginine (R8)-functionalized nCaP vector containing a marker or functional gene construct. nCaP particle size was between 220–580 nm in diameter and all R8-functionalized nCaPs carried a positive charge. R8 concentration significantly improved nCaP transfection efficiency with high cell compatibility in human mesenchymal stem cells (hMSC) and human osteoblasts (hOB) in particular, suggesting nCaPs as a good option for non-viral vector gene delivery. Furthermore, pre-treatment with different endocytosis inhibitors identified that the endocytic pathway differed among cell lines and functionalized nanoparticles, with amiloride increasing transfection efficiency of R8-functionalized nCaPs in hMSC and hOB.

Inorganic Kernel-Reconstituted Lipoprotein Biomimetic Nanovehicles Enable Efficient Targeting "Trojan Horse" Delivery of STAT3-Decoy Oligonucleotide for Overcoming TRAIL Resistance

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can selectively induce apoptosis in a variety of tumor cells, but not most normal cells. Nevertheless, its therapeutic potential is limited due to the frequent occurrence of resistance in tumor cells, especially hepatocellular carcinoma cell lines. Therefore, we investigated the reversal effect of STAT3-decoy oligonucleotides (ODNs) on TRAIL resistance. Methods. Considering that the drawback of poor cellular permeability and rapid degradation in vivo limited ODNs' further clinical applications, we developed a biomimetic calcium phosphate-reconstituted low density lipoprotein nanovehicle (CaP@LDL) that would serve as a “Trojan horse” to carry STAT3-decoy ODNs into tumor cells and then regulate TRAIL-induced apoptosis. Results. In comparison with native ODNs, the reconstituted CaP@LDL packaged ODNs showed significantly increased serum stability, cellular transfection, in vitro synergistic cytotoxicity and apoptosis in hepatoma cells, while there was no cytotoxicity to normal cells. The improved TRAIL sensitization is attributed to blocking of STAT3 signaling and consequent expression of the downstream target antiapoptotic gene. Following systemic administration, CaP@LDL displayed LDL-mimicking pharmacokinetic behavior such as attenuated blood clearance as well as enhanced accumulation in tumor and hepatorenal sites. With the synergistic combination of decoyODN/CaP@LDL, TRAIL dramatically inhibited hepatic tumor growth in a xenograft model and induced significant tumor apoptosis in vivo. Conclusion. These results suggested that CaP@LDL-mediated STAT3-decoy ODN delivery might be a promising new strategy for reversing TRAIL resistance in hepatocellular carcinoma therapy.

Synthesis and characterization of amino acid-functionalized calcium phosphate nanoparticles for siRNA delivery

Small interfering RNAs (siRNA) are short nucleic acid fragments of about 20-27 nucleotides, which can inhibit the expression of specific genes. siRNA based RNAi technology has emerged as a promising method for the treatment of a variety of diseases. However, a major limitation in the therapeutic use of siRNA is its rapid degradation in plasma and cellular cytoplasm, resulting in short half-life. In addition, as siRNA molecules cannot penetrate into the cell efficiently, it is required to use a carrier system for its delivery. In this work, chemically and morphologically different calcium phosphate (CaP) nanoparticles, including spherical-like hydroxyapatite (HA-s), needle-like hydroxyapatite (HA-n) and calcium deficient hydroxyapatite (CDHA) nanoparticles were synthesized by the sol-gel technique and the effects of particle characteristics on the binding capacity of siRNA were investigated. In order to enhance the gene loading efficiency, the nanoparticles were functionalized with arginine and the morphological and their structural characteristics were analyzed. The addition of arginine did not significantly change the particle sizes; however, it provided a significantly increased binding of siRNA for all types of CaP nanoparticles, as revealed by spectrophotometric measurements analysis. Arginine functionalized HA-n nanoparticles showed the best binding behavior with siRNA among the other nanoparticles due to its high, positive zeta potential (+18.8mV) and high surface area of Ca⁺⁺ rich "c" plane. MTT cytotoxicity assays demonstrated that all the nanoparticles tested herein were biocompatible. Our results suggest that high siRNA entrapment in each of the three modified non-toxic CaP nanoparticles make them promising candidates as a non-viral vector for delivering therapeutic siRNA molecules to treat cancer.