Luminescence Enhanced Eu(3+)/Gd(3+) Co-Doped Hydroxyapatite Nanocrystals as Imaging Agents In Vitro and In Vivo

Investigation to Understand the Role of Phase Variation in Red Emitting Eu3+-Doped Calcium Magnesium Silicate Phosphor for In Vitro Bioimaging

Eu3+-doped silicate phosphors are gaining significant attention for bioimaging and scaffold development due to their narrow red emission, high color purity, quantum yield (QY), and large Stokes shift. These phosphors offer several advantages over conventional imaging techniques, such as good selectivity and sensitivity, simpler operation, reduced data acquisition time, cost-effectiveness, and nondestructive imaging. The luminescence properties of these phosphors can be enhanced by modifying synthesis methods, annealing conditions, and hosts and introducing multiple dopants. This study explores a novel approach for improving luminescence by modifying the crystal structures of Eu3+ doped calcium magnesium silicate (CMS:Eu3+) phosphors for in vitro bioimaging and potential scaffold development. The synthesized diopside (CaMgSi2O6:xEu3+; x = 10, 15, and 20 mol %), merwinite (Ca3MgSi2O8:15 mol % Eu3+), and akermanite (Ca2MgSi2O7:15 mol % Eu3+) phases of CMS:Eu3+ exhibit distinct coordination environments for Eu3+, leading to unique excitation wavelength tunability from ultraviolet (UV) to the visible region, high emission intensity, decay time, QY > 40%, and color purity >83%. A comparative analysis of their structural and photoluminescence properties reveals the impact of phase modifications on luminescence for in vitro bioimaging by optimizing the dopant concentration. The results indicate that CaMgSi2O6: 15 mol % Eu3+ is the most efficient phosphor for in vitro bioimaging, with the highest relative emission intensity in the red region, decay time ∼2 ms, QY ∼ 77%, and color purity ∼86%. The unique morphology of Ca3MgSi2O8:15 mol %Eu3+ and Ca2MgSi2O7:15 mol % Eu3+ also supports cell adhesion, suggesting their potential in scaffold development. In brief, the study highlights the potential of CMS:Eu3+ phosphors for in vitro bioimaging and scaffold development by modifying phases and dopant concentrations.

Advancements in nanohydroxyapatite: synthesis, biomedical applications and composite developments

Nanohydroxyapatite (nHA) is distinguished by its exceptional biocompatibility, bioactivity and biodegradability, qualities attributed to its similarity to the mineral component of human bone. This review discusses the synthesis techniques of nHA, highlighting how these methods shape its physicochemical attributes and, in turn, its utility in biomedical applications. The versatility of nHA is further enhanced by doping with biologically significant ions like magnesium or zinc, which can improve its bioactivity and confer therapeutic properties. Notably, nHA-based composites, incorporating metal, polymeric and bioceramic scaffolds, exhibit enhanced osteoconductivity and osteoinductivity. In orthopedic field, nHA and its composites serve effectively as bone graft substitutes, showing exceptional osteointegration and vascularization capabilities. In dentistry, these materials contribute to enamel remineralization, mitigate tooth sensitivity and are employed in surface modification of dental implants. For cancer therapy, nHA composites offer a promising strategy to inhibit tumor growth while sparing healthy tissues. Furthermore, nHA-based composites are emerging as sophisticated platforms with high surface ratio for the delivery of drugs and bioactive substances, gradually releasing therapeutic agents for progressive treatment benefits. Overall, this review delineates the synthesis, modifications and applications of nHA in various biomedical fields, shed light on the future advancements in biomaterials research.

High Quantum Yields and Biomedical Fluorescent Imaging Applications of Photosensitized Trivalent Lanthanide Ion-Based Nanoparticles

In recent years, significant advances in enhancing the quantum yield (QY) of trivalent lanthanide (Ln3+) ion-based nanoparticles have been achieved through photosensitization, using host matrices or capping organic ligands as photosensitizers to absorb incoming photons and transfer energy to the Ln3+ ions. The Ln3+ ion-based nanoparticles possess several excellent fluorescent properties, such as nearly constant transition energies, atomic-like sharp transitions, long emission lifetimes, large Stokes shifts, high photostability, and resistance to photobleaching; these properties make them more promising candidates as next-generation fluorescence probes in the visible region, compared with other traditional materials such as organic dyes and quantum dots. However, their QYs are generally low and thus need to be improved to facilitate and extend their applications. Considerable efforts have been made to improve the QYs of Ln3+ ion-based nanoparticles through photosensitization. These efforts include the doping of Ln3+ ions into host matrices or capping the nanoparticles with organic ligands. Among the Ln3+ ion-based nanoparticles investigated in previous studies, this review focuses on those containing Eu3+, Tb3+, and Dy3+ ions with red, green, and yellow emission colors, respectively. The emission intensities of Eu3+ and Tb3+ ions are stronger than those of other Ln3+ ions; therefore, the majority of the reported studies focused on Eu3+ and Tb3+ ion-based nanoparticles. This review discusses the principles of photosensitization, several examples of photosensitized Ln3+ ion-based nanoparticles, and in vitro and in vivo biomedical fluorescent imaging (FI) applications. This information provides valuable insight into the development of Ln3+ ion-based nanoparticles with high QYs through photosensitization, with future potential applications in biomedical FI.

Porous hydrogel microspheres with excellent temperature-sensitive, magnetic and fluorescent properties for drug delivery

Porous hydrogel microspheres with temperature-sensitive, magnetic and fluorescent properties have great potential for drug delivery. In this study, porous hydrogel microspheres with excellent temperature-sensitive, magnetic and fluorescent properties were prepared through droplet microfluidics and photoinitiated radical polymerization, which were characterized via scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), fluorescence spectroscopy, ultraviolet spectrophotometry, and other techniques. The volumetric phase-transition temperature of porous hydrogel microspheres was in the range of 40-45 °C, and the volume swelling ratio reached 5.26 as the temperature decreased from 55 °C to 25 °C. Meanwhile, the saturation magnetization and optimal fluorescence emission wavelength of porous hydrogel microspheres were 1.79 emu g-1 and 616 nm, respectively, which can be an effective strategy to visually monitor and control the speed of drug release during magnetic heat therapy. Finally, bovine serum albumin (BSA) was employed as a model drug to investigate the drug loading and release of porous hydrogel microspheres. The maximal drug loading amount was 238 mg g-1, and the drug release speed and amount can be correspondingly promoted by altering the temperature.

Refining nanoprobes for monitoring of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a gastrointestinal immune disease that requires clear diagnosis, timely treatment, and lifelong monitoring. The diagnosis and monitoring methods of IBD mainly include endoscopy, imaging examination, and laboratory examination, which are constantly developed to achieve early definite diagnosis and accurate monitoring. In recent years, with the development of nanotechnology, the diagnosis and monitoring methods of IBD have been remarkably enriched. Nanomaterials, characterized by their minuscule dimensions that can be tailored, along with their distinctive optical, magnetic, and biodistribution properties, have emerged as valuable contrast agents for imaging and targeted agents for endoscopy. Through both active and passive targeting mechanisms, nanoparticles accumulate at the site of inflammation, thereby enhancing IBD detection. This review comprehensively outlines the existing IBD detection techniques, expounds upon the utilization of nanoparticles in IBD detection and diagnosis, and offers insights into the future potential of in vitro diagnostics. STATEMENT OF SIGNIFICANCE: Due to their small size and unique physical and chemical properties, nanomaterials are widely used in the biological and medical fields. In the area of oncology and inflammatory disease, an increasing number of nanomaterials are being developed for diagnostics and drug delivery. Here, we focus on inflammatory bowel disease, an autoimmune inflammatory disease that requires early diagnosis and lifelong monitoring. Nanomaterials can be used as contrast agents to visualize areas of inflammation by actively or passively targeting them through the intestinal mucosal epithelium where gaps exist due to inflammation stimulation. In this article, we summarize the utilization of nanoparticles in inflammatory bowel disease detection and diagnosis, and offers insights into the future potential of in vitro diagnostics.

Investigations on anticancer activity of Eu3+ doped hydroxyapatite nanocomposites against MCF7 and 4T1 breast cancer cell lines: A structural and luminescence Perspective

Breast cancer remains a significant global health concern, necessitating the development of novel therapeutic approaches. In this study, we investigate the role of Eu3+ doped hydroxyapatite nanocomposites (Han: Eu3+) in the treatment of MCF7 and 4T1 breast cancer cell lines. Furthermore, we explored the structural and luminescent properties of these nanocomposites. Han: Eu3+ were synthesized using a modified co-precipitation method, and their morphology and crystal structure were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) in which the average crystalline size of Han: Eu3+ was found to be 25 nm, rendering them suitable for cellular uptake and targeted therapy. To gain insights into the luminescent properties of Han: Eu3+, their excitation and emission spectra were recorded using photoluminescence spectrometer. The characteristic red emission of Eu3+ ions was observed upon excitation, validating the successful doping of Eu3+ into the Han lattice, which was confirmed by the CIE chromaticity coordinate study. These luminescent properties of Han: Eu3+ hold promise for potential applications in bioimaging. To evaluate the efficacy of Han: Eu3+ in breast cancer treatment, MCF7 and 4T1 cell lines were exposed to varying concentrations of the nanocomposites. Cell viability assays revealed a concentration-dependent reduction in cell viability, indicating the potential anticancer activity of Han: Eu3+. The findings of this study contribute to the expanding field of nanomedicine, bringing targeted breast cancer treatments and us closer to more effective.

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.

pH-Sensitive Hybrid System Based on Eu3+/Gd3+ Co-Doped Hydroxyapatite and Mesoporous Silica Designed for Theranostic Applications

Nanomaterials such as pH-responsive polymers are promising for targeted drug delivery systems, due to the difference in pH between tumor and healthy regions. However, there is a significant concern about the application of these materials in this field due to their low mechanical resistance, which can be attenuated by combining these polymers with mechanically resistant inorganic materials such as mesoporous silica nanoparticles (MSN) and hydroxyapatite (HA). Mesoporous silica has interesting properties such as high surface area and hydroxyapatite has been widely studied to aid in bone regeneration, providing special properties adding multifunctionality to the system. Furthermore, fields of medicine involving luminescent elements such as rare earth elements are an interesting option in cancer treatment. The present work aims to obtain a pH-sensitive hybrid system based on silica and hydroxyapatite with photoluminescent and magnetic properties. The nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption methods, CHN elemental analysis, Zeta Potential, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), vibrational sample magnetometry (VSM), and photoluminescence analysis. Incorporation and release studies of the antitumor drug doxorubicin were performed to evaluate the potential use of these systems in targeted drug delivery. The results showed the luminescent and magnetic properties of the materials and showed suitable characteristics for application in the release of pH-sensitive drugs.

Upconversion Nanoplatform Enables Multimodal Imaging and Combinatorial Immunotherapy for Synergistic Tumor Treatment and Monitoring

Designing a novel nanoplatform that integrates multimodal imaging and synergistic therapy for precision tumor nanomedicines is challenging. Herein, we prepared rare-earth ion-doped upconversion hydroxyapatite (FYH) nanoparticles as nanocarriers coated and loaded respectively with polydopamine (PDA) and doxorubicin (DOX), i.e., FYH-PDA-DOX, for tumor theranostics. The developed FYH-PDA-DOX complexes exhibited desirable photothermal conversion, pH/near-infrared-irradiation-responsive DOX release, and multimodal upconversion luminescence/computed tomography/magnetic resonance imaging performance and helped monitor the metabolic distribution process of the complexes and provided feedback to the therapeutic effect. Upon 808 nm laser irradiation, the fast release of DOX facilitated the photothermal-chemotherapy effect, immunogenic cell death, and antitumor immune response. On combining with the anti-programmed cell death 1 ligand 1 antibody, an enhanced tri-mode photothermal-chemo-immunotherapy synergistic treatment against tumors can be realized. Thus, this treatment elicited potent antitumor immunity, producing appreciable T-cell cytotoxicity against tumors, amplifying tumor suppression, and extending the survival of mice. Therefore, the FYH-PDA-DOX complexes are promising as a smart nanoplatform for imaging-guided synergistic cancer treatment.

Drug Molecular Immobilization and Photofunctionalization of Calcium Phosphates for Exploring Theranostic Functions

Theranostics (bifunction of therapeutics and diagnostics) has attracted increasing attention due to its efficiency that can reduce the physical and financial burden on patients. One of the promising materials for theranostics is calcium phosphate (CP) and it is biocompatible and can be functionalized not only with drug molecules but also with rare earth ions to show photoluminescence that is necessary for the diagnostic purpose. Such the CP-based hybrids are formed in vivo by interacting between functional groups of organic molecules and inorganic ions. It is of great importance to elucidate the interaction of CP with the photofunctional species and the drug molecules to clarify the relationship between the existing state and function. Well-designed photofunctional CPs will contribute to biomedical fields as highly-functional ormultifunctional theranostic materials at the nanoscales. In this review, we describe the hybridization between CPs and heterogeneous species, mainly focusing on europium(III) ion and methylene blue molecule as the representative photofunctional species for theranostics applications.

Hydrothermal Synthesis and In Vivo Fluorescent Bioimaging Application of Eu3+/Gd3+ Co-Doped Fluoroapatite Nanocrystals

In this study, Eu3+/Gd3+ co-doped fluoroapatitååe (Eu/Gd:FAP) nanocrystals were synthesized by the hydrothermal method as a fluorescent bioimaging agent. The phase composition, morphology, fluorescence, and biosafety of the resulting samples were characterized. Moreover, the in vivo fluorescent bioimaging application of Eu/Gd:FAP nanocrystals was evaluated in mice with subcutaneously transplanted tumors. The results showed that the Eu/Gd:FAP nanocrystals were short rod-like particles with a size of 59.27 ± 13.34 nm × 18.69 ± 3.32 nm. With an increasing F substitution content, the Eu/Gd:FAP nanocrystals displayed a decreased size and enhanced fluorescence emission. Eu/Gd:FAP nanocrystals did not show hemolysis and cytotoxicity, indicating good biocompatibility. In vivo fluorescent bioimaging study demonstrated that Eu/Gd:FAP nanocrystals could be used as a bioimaging agent and displayed stable fluorescence emitting in tumors, indicating an accumulation in tumor tissue due to the passive targeting ability. In addition, any adverse effects of Eu/Gd:FAP nanocrystals on major organs were not observed. This study shows that biocompatible rare earth co-doped FAP nanocrystals have the potential to be used as a bioimaging agent in vivo.

Hydroxyapatite Nanoparticles for Improved Cancer Theranostics

Beyond their well-known applications in bone tissue engineering, hydroxyapatite nanoparticles (HAp NPs) have also been showing great promise for improved cancer therapy. The chemical structure of HAp NPs offers excellent possibilities for loading and delivering a broad range of anticancer drugs in a sustained, prolonged, and targeted manner and thus eliciting lower complications than conventional chemotherapeutic strategies. The incorporation of specific therapeutic elements into the basic composition of HAp NPs is another approach, alone or synergistically with drug release, to provide advanced anticancer effects such as the capability to inhibit the growth and metastasis of cancer cells through activating specific cell signaling pathways. HAp NPs can be easily converted to smart anticancer agents by applying different surface modification treatments to facilitate the targeting and killing of cancer cells without significant adverse effects on normal healthy cells. The applications in cancer diagnosis for magnetic and nuclear in vivo imaging are also promising as the detection of solid tumor cells is now achievable by utilizing superparamagnetic HAp NPs. The ongoing research emphasizes the use of HAp NPs in fabricating three-dimensional scaffolds for the treatment of cancerous tissues or organs, promoting the regeneration of healthy tissue after cancer detection and removal. This review provides a summary of HAp NP applications in cancer theranostics, highlighting the current limitations and the challenges ahead for this field to open new avenues for research.

Progress on carbon dots and hydroxyapatite based biocompatible luminescent nanomaterials for cancer theranostics

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Biocompatible carbon dots (CDs) and nanohydroxyapatite (nHA) have attracted much attention for the development of optical imaging probes.

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This review discusses the development of CD and nHA based nanomaterials as multifunctional agents for cancer theranostics.

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The effect of synthesis strategies and doping on photoluminescent properties along with tuning of emission in biological window has been briefly reviewed.

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The cancer targeting strategies, biocompatibility and biodistribution of CDs and nHA based luminescent probes is discussed.

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A summary of current challenges and future perspectives is provided.

Despite the significant advancement in cancer diagnosis and therapy, a huge burden remains. Consequently, much research has been diverted on the development of multifunctional nanomaterials for improvement in conventional diagnosis and therapy. Luminescent nanomaterials offer a versatile platform for the development of such materials as their intrinsic photoluminescence (PL) property offers convergence of diagnosis as well as therapy at the same time. However, the clinical translation of nanomaterials faces various challenges, including biocompatibility and cost-effective scale up production. Thus, luminescent materials with facile synthesis approach along with intrinsic biocompatibility and anticancerous activity hold significant importance. As a result, carbon dots (CDs) and nanohydroxyapatite (nHA) have attracted much attention for the development of optical imaging probes. CDs are the newest members of the carbonaceous nanomaterials family that possess intrinsic luminescent and therapeutic properties, making them a promising candidate for cancer theranostic. Additionally, nHA is an excellent bioactive material due to its compositional similarity to the human bone matrix. The nHA crystal can efficiently host rare-earth elements to attain luminescent property, which can further be implemented for cancer theranostic applications. Herein, the development of CDs and nHA based nanomaterials as multifunctional agents for cancer has been briefly discussed. The emphasis has been given to different synthesis strategies leading to different morphologies and tunable PL spectra, followed by their diverse applications as biocompatible theranostic agents. Finally, the review has been summarized with the current challenges and future perspectives.

Recent Progress of Rare Earth Doped Hydroxyapatite Nanoparticles: Luminescence Properties, Synthesis and Biomedical Applications

Hydroxyapatite nanoparticles (HAP NPs) are host materials and can be modified with various substrates and dopants. Among them, rare earth (RE) ions doped HAP NPs have gathered attention due to their unique physicochemical and imaging properties. Compared to other fluorescence probes, RE-doped HAP NPs display advantages in high brightness, high contrast, photostability, nonblinking, and narrow emission bands. Meanwhile, their intrinsic features (composition, morphology, size, crystallinity, and luminescence intensity) can be adjusted by changing the dopant ratio, synthesizing temperature, reaction time, and techniques. And they have been used in various biomedical applications, including imaging probe, drug delivery, bone tissue engineering, and antibacterial studies. This review surveys the luminescent properties, fluorescence enhancement, synthetic methods, and biocompatibility of various RE-doped HAP NPs consolidated from different research works, for their employments in biomedical applications. For this literature review, an electronic search was conducted in the Pubmed, Web of Science, Google Scholar, Scopus and SciFinder databases, using the keywords: hydroxyapatite, rare earth, lanthanide, fluorescence, and imaging. Literature searches of English-language publications from 1979 with updates through April, 2022, and a total of 472 potential papers were identified. In addition, a few references were located by noting their citation in other studies reviewed. STATEMENT OF SIGNIFICANCE: Hydroxyapatite nanoparticles (HAP NPs) have a broad range of promising biological applications. Although prospective biomedical applications are not limited to rare earth-doped hydroxyapatite nanoparticles (RE-doped HAP NPs), some cases do make use of the distinctive features of RE-elements to achieve the expected functions for HAP families. This review surveys the luminescent properties, synthetic methods, and biocompatibility of various RE-doped HAP NPs consolidated from different research works, for their employments in biomedical applications, including imaging probe, drug delivery, bone tissue repair and tracking, and anti-bacteria. Overall, we expect to shed some light on broadening the research and application of RE-doped HAP NPs in biomedical field.

A Study of Vanadate Group Substitution into Nanosized Hydroxyapatite Doped with Eu3+ Ions as a Potential Tissue Replacement Material

In this study, nanosized vanadate-substituted hydroxyapatites doped with 1 mol% and 2 mol% Eu3+ ions were obtained via the precipitation method. To evaluate the structure and morphology of the obtained compounds, the XRPD (X-ray powder diffraction) technique, Rietveld refinement, SEM-EDS (scanning electron microscopy-energy-dispersive spectrometry) and TEM (transmission electron microscopy) techniques as well as FTIR (Fourier transform infrared) spectroscopy were performed. Moreover, the chemical formula was confirmed using the ICP-OES (Inductively coupled plasma optical emission spectroscopy spectroscopy). The calculated average grain size for powders was in the range of 25 to 90 nm. The luminescence properties of vanadium-substituted hydroxyapatite were evaluated by recording emission spectra and excitation spectra as well as luminescence kinetics. The crucial step of this research was the evaluation of the biocompatibility of the synthesized nanomaterials. Therefore, the obtained compounds were tested toward sheep red blood cells and normal human dermal fibroblast to confirm the nontoxicity and biocompatibility of new nanosized Eu3+ ion-doped vanadate-hydroxyapatite. Moreover, the final step of the research allowed us to determine the time dependent ion release to the simulated body fluid environment. The study confirmed cytocompatibility of vanadium hydroxyapatite doped with Eu3+ ions.

Eggshell Derived Europium Doped Hydroxyapatite Nanoparticles for Cell Imaging Application

Hen's eggshell, a biological waste product, was turned into a cell imaging probe: europium doped hydroxyapatite (HAp: Eu) nanoparticle using hydrothermal method. Luminescence of the synthesized nanoparticle was studied for various doping concentrations of the lanthanide ion europium (Eu³⁺). Eu doped HAp showed a hexagonal crystal structure and rod-shaped morphology. Well-defined emission peaks of europium, corresponding to the substitution of Eu³⁺ at the Ca²⁺(I) site of HAp, were confirmed from the samples' photoluminescence (PL) spectra. Good biocompatibility up to 500 μg/mL of the samples indicates their potential applications in bioimaging. Synthesized nanoparticles were internalized and used for in vitro imaging of the PC12 cells without any surface modification. The materials' use as a potential in vivo imaging agent is proposed from the haemolysis study.

Ba/Mg co-doped hydroxyapatite/PLGA composites enhance X-ray imaging and bone defect regeneration

Hydroxyapatite (HA) is the most commonly used orthopedic implant material. In recent years, the emergence of cationic doped hydroxyapatite has revealed more possibilities for the biological application of HA. Conventional HA does not promote new bone formation because of its poor osteoinductive activity, and has a similar density to that of bone, leading to difficulty in distinguishing both via imaging. Magnesium ions are useful for regulating the cellular behavior and promoting bone regeneration. Ba ion related compounds, such as BaSO4, have a strong X-ray shielding effect. In this study, Ba/Mg@HA was synthesized to prepare Ba/Mg@HA/PLGA composites, and we aimed to investigate if Ba/Mg@HA/PLGA composites enhanced bone repair on osteoblasts and tibial defects, as well as the X-ray and CT imaging ability of bone implants in rats. The in vitro experimental results showed that the Ba/Mg@HA/PLGA composites significantly improved the attachment and osteogenic differentiation of MC3T3-E1 cells. These include the promotion of mineral deposition, enhancement of alkaline phosphatase activity, upregulation of OCN and COL-1 gene expression, and increase in COL-1 and OCN protein expression in a time- and concentration-dependent manner. The in vivo experimental results showed that the Ba/Mg@HA/PLGA composites significantly increased the rate of bone defect healing and the expression of BMP-2 and COL-1 in the bones of rats. X-ray and CT imaging results showed that the Ba/Mg@HA/PLGA composites enhanced the X-ray imaging ability. These findings indicate that the Ba/Mg@HA/PLGA composites can effectively promote bone formation and improve the X-ray and CT imaging abilities to a certain extent.

Fabrication of Nd3+ and Yb3+ doped NIR emitting nano fluorescent probe: A candidate for bioimaging applications

The intentional design of rare earth doped luminescent architecture exhibits unique optical properties and it can be considered as a promising and potential probe for optical imaging applications. Calcium fluoride (CaF₂) nanoparticles doped with optimum concentration of Nd³⁺ and Yb³⁺ as sensitizer and activator, respectively, were synthesized by wet precipitation method and characterized by x-ray diffraction (XRD) and photoluminescence. In spite of the fact that the energy transfer takes place from Nd³⁺ to Yb³⁺, the luminescence intensity was found to be weak due to the lattice defects generated from the doping of trivalent cations (Nd³⁺ and Yb³⁺) for divalent host cations (Ca²⁺). These defect centres were tailored via charge compensation approach by co-doping Na⁺ ion and by optimizing its concentration and heat treatment duration. CaF₂ doped with 5 mol% Nd³⁺, 3 mol% Yb³⁺ and 4 mol% Na⁺ after heat treatment for 2 h exhibited significantly enhanced emission intensity and life time. The ex vivo fluorescence imaging experiment was done at various thickness of chicken breast tissue. The maximum theoretical depth penetration of the NIR light was calculated and the value is 14 mm. The fabricated phosphor can serve as contrast agent for deep tissue near infrared (NIR) light imaging.

Artificial Bioaugmentation of Biomacromolecules and Living Organisms for Biomedical Applications

The synergistic union of nanomaterials with biomaterials has revolutionized synthetic chemistry, enabling the creation of nanomaterial-based biohybrids with distinct properties for biomedical applications. This class of materials has drawn significant scientific interest from the perspective of functional extension via controllable coupling of synthetic and biomaterial components, resulting in enhancement of the chemical, physical, and biological properties of the obtained biohybrids. In this review, we highlight the forefront materials for the combination with biomacromolecules and living organisms and their advantageous properties as well as recent advances in the rational design and synthesis of artificial biohybrids. We further illustrate the incredible diversity of biomedical applications stemming from artificially bioaugmented characteristics of the nanomaterial-based biohybrids. Eventually, we aim to inspire scientists with the application horizons of the exciting field of synthetic augmented biohybrids.

Luminescent net-like inorganic scaffolds with europium-doped hydroxyapatite for enhanced bone reconstruction

Bone reconstruction is an urgent problem during clinical treatment. In the past few decades, the construction of composite scaffolds has been a hot spot in the research field of bone tissue engineering (BTE). However, the disadvantages of composite materials raise our awareness to explore the potential application of hydroxyapatite (HAp) in bone substitutes due to the closest properties of HAp to natural bone tissue. In our study, we synthesized Eu³⁺-doped HAp (HAp:Eu³⁺) ultralong nanowires, which can be transformed to hydrophilic net-like scaffolds via a thiol-ene click reaction. The property of luminescence of HAp from Eu³⁺ is beneficial for identifying the relative position of materials and bone marrow mesenchymal stem cells (BMSCs). HAp:Eu³⁺ scaffolds with excellent cell biocompatibility could promote the expression of early bone formation markers (ALP and ARS) and enhance the expression of genes and proteins associated with osteogenesis (Runx 2, OCN, and OPN). In the end, the results of the in vivo osteogenesis experiment showed that pure HAp scaffolds presented different effects of bone tissue reconstruction compared with the composite scaffolds with HAp nanorods and polymer materials. The superior osteogenic effect could be observed in net-like pure HAp scaffold groups. Furthermore, the absorption of HAp:Eu³⁺ scaffolds could be monitored due to the luminescence property of Eu³⁺. This strategy based on ultralong HAp nanowires proved to be a new method for the construction of simple reticular scaffolds for potential osteogenic applications.

On enhancement and control of green emission of rare earth co-doped hydroxyapatite nanoparticles: synthesis and upconversion luminescence properties

In this work, low-temperature hydrothermal synthesis of a series of xMo–1%Er–10%Yb (x:mol%) doped hydroxyapatite (HA) phosphors was studied.

Characterization and Luminescence of Eu3+- and Gd3+-Doped Hydroxyapatite Ca10(PO4)6(OH)2

Luminescence properties of europium-doped Ca10-xEux(PO4)6(OH)2 (xEu = 0, 0.01, 0.02, 0.10 and 0.20) and gadolinium-doped hydroxyapatite Ca9.80Gd0.20(PO4)6(OH)2 (HA), synthesized via solid-state reaction at T = 1300 °C, were investigated using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR), and luminescence spectroscopy. Crystal structure characterization (from unit cell parameters determination to refined atomic positions) was achieved in the P63/m space group. FTIR analyses show only slight band shifts of (PO4) modes as a function of the rare earth concentration. Structural refinement, achieved via the Rietveld method, and luminescence spectroscopy highlighted the presence of dopant at the Ca2 site. Strong luminescence was observed for all Eu- and Gd-doped samples. Our multi-methodological study confirms that rare-earth (RE)-doped synthetic hydroxyapatites are promising materials for bio-imaging applications.

Update on the development of molecular imaging and nanomedicine in China: Optical imaging

Molecular imaging has received increased attention worldwide, including in China, because it offers noninvasive characterization of widely diverse clinically significant pathologies. To achieve these goals, nanomedicine has evolved into a broad interdisciplinary field with flexible designs to accommodate and concentrate imaging and therapeutic payloads into pathological cells through selective binding to disease specific cell membrane biomarkers. This concept of personalized medicine reflects the vision of "magic bullets" proposed by German biochemist Paul Ehrlich over 100 years ago. As happening worldwide, Chinese scientists are contributing to this tsunami of science and technologies through impactful national programs and international research collaborations. This review provides a comprehensive update of Chinese innovations to address intractable unmet medical need in China and worldwide in the optical sciences. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging.

Emission-tunable probes using terbium(III)-doped self-activated luminescent hydroxyapatite for in vitro bioimaging

Lanthanide ion (Ln³⁺)-doped nanoscale hydroxyapatites (nHAp) with tunable luminescence have attracted increasing attention due to their potential applications as useful biomedical tools (e.g., imaging and clinical therapy). In this study, we reported that doping Terbium (III) ions (Tb³⁺) in self-activated luminescent nHAp via a facile hydrothermal reaction, using trisodium citrate (Cit^3-), generates unique emission-tunable probes known as Cit/Tb-nHAp. The morphology, crystal phase, and luminescence properties of these Cit/Tb-nHAp probes are studied in detail. Moreover, the results demonstrate that the luminescence of self-activated nHAp originates from the carbon dots trapped within the nHAp crystals, in which partial energy transfer occurs from carbon dots (CDs) to Tb³⁺. The color tunability is successfully achieved by regulating the addition of Cit^3-. Biocompatibility study indicates that when co-cultured with C6 glioma cells in vitro for 3 days, ≤800 ppm Cit/Tb-nHAp is not cytotoxic for C6 glioma cells. We also present in vitro data showing efficient cytoplasmic localization of transferrin conjugated Cit/Tb-nHAp into C6 glioma cells by fluorescence cell imaging. We have successfully engineered Cit/Tb-nHAp, a promising biocompatible agent for future in vitro and in vivo fluorescence bioimaging.

Effect of the Fluorine Substitution for –OH Group on the Luminescence Property of Eu3+ Doped Hydroxyapatite

In this study, different fluoridated hydroxyapatite doped with Eu3+ ion nanoparticles were prepared by the hydrothermal method. The relationship between luminescence enhancement of Eu3+ ions and a fluorine substitution ratio for hydroxyl group in hydroxyapatite was discussed. Moreover, the effect of fluorine substitution for a hydroxyl group on phase composition, crystallinity, and crystal size was studied. Phase composition and chemical structures were identified by X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) Spectroscopy analyses. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) patterns were performed to analyze the morphology and particle size. X-ray Photoelectron Spectroscopy (XPS) patterns were observed to analyze fluorine substitution for the hydroxyl group and chemical state of Eu3+ ions in fluoridated hydroxyapatite. The results of these experiments indicated that the samples with a different fluorine substitution ratio were prepared successfully by maintaining the apatite structure. With an increasing fluorine substitution ratio, the morphology maintained a rod-like structure but the aspect ratio tended to decrease. XPS patterns displayed that the fluorine replaced the hydroxyl group and brought environmental variation. The fluorine ions could affect the crystal field environment and promote luminescence conversion. There was a linear relationship between the fluorine substitution ratio and luminescence enhancement.

A method to visually observe the degradation-diffusion-reconstruction behavior of hydroxyapatite in the bone repair process

Nanostructured hydroxyapatite (HAp) has been applied widely as a scaffold material for bone tissue engineering for its good osteoinduction and biodegradability. However, the degradation process and the distribution of degraded HAp within the bone-defect cavity is still not clear. To visually study the behavior of HAp in bone repair process, a membrane of HAp/terbium (Tb)-HAp nanowires (NWs) was prepared with a concentric circle structure (CCS), of which the inner circle and the outer ring were constructed with Tb-HAp and HAp NWs, respectively. HAp/Tb-HAp CCS membrane possessed good osteogenic capacity and efficient fluorescence in the center for visualization. The in vitro experimental results proved that the Tb-HAp and HAp NWs membranes both presented high cytocompatibility and adequate efficiency to induce osteogenic differentiation of bone marrow stem cells (BMSCs). HAp/Tb-HAp CCS membranes were then implanted into a rat calvarial bone-defect model to study the behavior of HAp in bone repair process in vivo by tracking the fluorescence distribution. The results showed that the fluorescence of Tb-HAp diffused gradually from the inner circle to the outer ring, which suggested that the HAp was first degraded, and then the degraded product was diffused and finally reconstructed. Further, the histological results proved that the doping of Tb did not impair the promotive effect of HAp on bone repair process. Therefore, this study provided a visual method to observe the degradation-diffusion-reconstruction behavior of HAp nanomaterials in bone repair process. STATEMENT OF SIGNIFICANCE: The study of dynamic degradation process of implanted hydroxyapatite (HAp) materials in bone-defect cavity is of great significance to bone tissue engineering applications. Here, we designed a HAp/Tb-HAp nanowires (NWs) membrane with concentric circle structure (CCS) to visibly observe the behavior of HAp during bone repair process. HAp/Tb-HAp CCS membrane possessed both osteoinduction ability and fluorescence property. Calvarial bone-defect repair experiments in vivo showed that the fluorescence of Tb-HAp diffused gradually from inner circle to outer ring, which suggested that HAp was first degraded, then diffused and finally reconstructed. Therefore, this invention provides not only a visible method to observe the degradation-diffusion-reconstruction behavior of HAp-based biomaterials, but also a basic understanding of the dynamic change of HAp-based biomaterials.

BMP-2-Loaded HAp:Ln3+ (Ln = Yb, Er, Gd) Nanorods with Dual-Mode Imaging for Efficient MC3t3-E1 Cell Differentiation Regulation

Effective bone tissue reconstitution improves the treatment success rate of dental implantation and preserves natural teeth during periodontal tissue repair. Hydroxyapatite (HAp) has received much attention in bone remodeling field because its mineralized structure is similar to that of the natural bone tissue. For this reason, it has been used as a carrier for growth factors. Although HAp possesses outstanding biomedical properties, its capacity of loading and releasing bone growth factors and promoting osteogenesis is not well understood. In this study, Ln³⁺ (Ln = Yb³⁺, Er³⁺, Gd³⁺)-doped HAp (HAp:Ln³⁺) nanorods were synthesized by one-step hydrothermal method. To improve its biocompatibility and surface properties, bone morphogenetic protein-2 (BMP-2) was loaded onto the surface of HAp:Ln³⁺ nanorods. The results showed that BMP-2 incorporation promoted bone formation and enhanced the expression of early bone-related gene and protein (RunX2, SP7, OPN). In addition, Yb³⁺- and Er³⁺-doped HAp nanorods were examined by upconversion luminescence with 980 nm near-infrared laser irradiation to monitor the delivery position of BMP-2 protein. Furthermore, due to the positive magnetism correlated with the concentration of Gd³⁺, HAp:Ln³⁺ with enhanced contrast brightening can be deemed as T₁ MIR contrast agents. These findings indicate that HAp doped with rare-earth ions and loaded with BMP-2 has the potential to promote bone tissue repair and execute dual-mode imaging.

Rare-earth (Gd3+,Yb3+/Tm3+, Eu3+) co-doped hydroxyapatite as magnetic, up-conversion and down-conversion materials for multimodal imaging

Taking advantage of the flexibility of the apatite structure, nano- and micro-particles of hydroxyapatite (HAp) were doped with different combinations of rare earth ions (RE³⁺ = Gd, Eu, Yb, Tm) to achieve a synergy among their magnetic and optical properties and to enable their application in preventive medicine, particularly diagnostics based on multimodal imaging. All powders were synthesized through hydrothermal processing at T ≤ 200 °C. An X-ray powder diffraction analysis showed that all powders crystallized in P6₃/m space group of the hexagonal crystal structure. The refined unit-cell parameters reflected a decrease in the unit cell volume as a result of the partial substitution of Ca²⁺ with smaller RE³⁺ ions at both cation positions. The FTIR analysis additionally suggested that a synergy may exist solely in the triply doped system, where the lattice symmetry and vibration modes become more coherent than in the singly or doubly doped systems. HAp:RE³⁺ optical characterization revealed a change in the energy band gap and the appearance of a weak blue luminescence (λ_ex = 370 nm) due to an increased concentration of defects. The "up"- and the "down"-conversion spectra of HAp:Gd/Yb/Tm and HAp:Gd/Eu powders showed characteristic transitions of Tm³⁺ and Eu³⁺, respectively. Furthermore, in contrast to diamagnetic HAp, all HAp:RE³⁺ powders exhibited paramagnetic behavior. Cell viability tests of HAp:Gd/Yb/Tm and HAp:Gd/Eu powders in human dental pulp stem cell cultures indicated their good biocompatibility.

Anisotropic nanomaterials for shape-dependent physicochemical and biomedical applications

This review contributes towards a systematic understanding of the mechanism of shape-dependent effects on nanoparticles (NPs) for elaborating and predicting their properties and applications based on the past two decades of research. Recently, the significance of shape-dependent physical chemistry and biomedicine has drawn ever increasing attention. While there has been a great deal of effort to utilize NPs with different morphologies in these fields, so far research studies are largely localized in particular materials, synthetic methods, or biomedical applications, and have ignored the interactional and interdependent relationships of these areas. This review is a comprehensive description of the NP shapes from theory, synthesis, property to application. We figure out the roles that shape plays in the properties of different kinds of nanomaterials together with physicochemical and biomedical applications. Through systematic elaboration of these shape-dependent impacts, better utilization of nanomaterials with diverse morphologies would be realized and definite strategies would be expected for breakthroughs in these fields. In addition, we have proposed some critical challenges and open problems that need to be addressed in nanotechnology.

Synergistic Effects of Novel Superparamagnetic/Upconversion HA Material and Ti/Magnet Implant on Biological Performance and Long-Term In Vivo Tracking

To solve the clinical challenges presented by the long-term tracking of implanted hydroxyapatite (HA) bone repair material and to investigate the synergistic effects of superparamagnetic HA and a static magnetic field (SMF) on the promotion of osteogenesis, herein a new type of superparamagnetic/upconversion-generating HA material (HYH-Fe) is developed via a two-step doping method, as well as a specially-designed titanium implant with a built-in magnet to provide a local static magnetic field in vivo. The results show that the prepared HYH-Fe material maintains the crystal structure of HA and exhibits good cytocompatibility. The combined use of the superparamagnetic HYH-Fe material and SMF can effectively and synergistically promote osteogenesis/osteointegration surrounding the Ti implants. In addition, the HYH-Fe material exhibits distinct advantages in terms of both long-term fluorescence tracking and microcomputed tomography (micro-CT) tracking. The new material and tracking strategy in this study provide scientific feasibility and will have important clinical value for long-term tracking and evaluation of implanted materials and the bone repair effect.

Red- and green-emitting nano-clay materials doped with Eu3+ and/or Tb3

Trivalent europium (Eu³⁺ ) and terbium (Tb³⁺ ) ions are important activator centers used in different host lattices to produce red and green emitting materials. The current work shows the design of new clay minerals to act as host lattices for rare earth (RE) ions. Based on the hectorite structure, nano-chlorohectorites and nano-fluorohectorites were developed by replacing the OH^- present in the hectorite structure with Cl^- or F^- , thus avoiding the luminescence quenching expected due to the OH^- groups. The produced matrices were characterized through X-ray powder diffraction (XPD), transmission electron microscopy (TEM), FT-IR, ²⁹ Si MAS (magic angle spinning) NMR, nitrogen sorption, thermogravimetry-differential scanning calorimetry (TGA-DSC) and luminescence measurements, indicating all good features expected from a host lattice for RE ions. The nano-clay materials were successfully doped with Eu³⁺ and/or Tb³⁺ to yield materials preserving the hectorite crystal structure and showing the related luminescence emissions. Thus, the present work shows that efficient RE³⁺ luminescence can be obtained from clays without the use of organic 'antenna' molecules.

Nano-hydroxyapatite polymeric hydrogels for dye removal

Herein, two kinds of nano-hydroxyapatite were synthesized from Clam and Magellan shell by wet chemical precipitation method. Mainly, carboxymethyl cellulose/acrylamide/nano-hydroxyapatite composite hydrogels were developed via a free-radical polymerization process and investigated as a sorbent for Acid Blue 113 (AB) from aqueous AB solution. The swelled and kinetic behaviours of hydrogels were investigated using a gravimetric method. The swelling properties of the CMC-AM-hydrogels were influenced by the calcium electrolytes (Ca²⁺) content in nano-hydroxyapatites. The diffusion coefficient value increased with the increase of nano-hydroxyapatite content in the CMC-AM/nHA-CS (0.22353–0.27681 cm² s⁻¹) and CMC-AM/nHA-MS (0.22377–0.29737 cm² s⁻¹) hydrogels. The mechanism of water diffusion was found to be anomalous transport. The CMC-AM/nHA-MS hydrogels showed high AB absorption efficiency and adsorption capacities. These results explained that the nano-hydroxyapatites of Magellan shells based hydrogels are attractive nanocomposite hydrogels for the adsorption of dye in the water purification applications.

Schematic diagram of nHA and nHA based hydrogels development via wet chemical and free-radical polymerization process and absorbent process of nHA hydrogel.

Calcium-based biomaterials for diagnosis, treatment, and theranostics

Calcium-based (CaXs) biomaterials including calcium phosphates, calcium carbonates, calcium silicate and calcium fluoride have been widely utilized in the biomedical field owing to their excellent biocompatibility and biodegradability. In recent years, CaXs biomaterials have been strategically integrated with imaging contrast agents and therapeutic agents for various molecular imaging modalities including fluorescence imaging, magnetic resonance imaging, ultrasound imaging or multimodal imaging, as well as for various therapeutic approaches including chemotherapy, gene therapy, hyperthermia therapy, photodynamic therapy, radiation therapy, or combination therapy, even imaging-guided therapy. Compared with other inorganic biomaterials such as silica-, carbon-, and gold-based biomaterials, CaXs biomaterials can dissolve into nontoxic ions and participate in the normal metabolism of organisms. Thus, they offer safer clinical solutions for disease theranostics. This review focuses on the state-of-the-art progress in CaXs biomaterials, which covers from their categories, characteristics and preparation methods to their bioapplications including diagnosis, treatment, and theranostics. Moreover, the current trends and key problems as well as the future prospects and challenges of CaXs biomaterials are also discussed at the end.

Engineering photoluminescent and magnetic lamellar hydroxyapatite by facile one-step Se/Gd dual-doping

A novel selenium (Se) and gadolinium (Gd) dual-doped lamellar hydroxyapatite has been produced by facile one-step template-assisted synthesis.

Europium Doped Calcium Deficient Hydroxyapatite as Theranostic Nanoplatforms: Effect of Structure and Aspect Ratio

We present the development of theranostic nanoplatforms (NPs) based on a europium (Eu³⁺) doped calcium deficient hydroxyapatite (CDHA) core functionalized with cyclodextrin (β-CD) and cucurbitural (CB[7]). The composition, crystalline structure, aspect ratio, surface area, morphology, and luminescence property of the NPs were investigated by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDAX), the Brunauer-Emmett-Teller (BET) method, transmission electron microscopy (TEM), and fluorescence spectroscopy. The perceivable effects of Eu³⁺ doping appear in the minor peak shift to larger angles attributed to lower crystallite size and smaller aspect ratios coupled with greater structural strain in the rod shaped theranostic NPs and a shift in their zeta potential toward less negative values. Cell parameter calculations suggest that the doping of Eu³⁺ would cause the a-axis parameter to decrease slightly as the ionic radius of Eu³⁺ is smaller than that of Ca²⁺. Moreover drug release profiles employing 5-fluorouracil (5FU) suggest that these luminescent NPs depict controlled and sustained release profiles. Further the emissive intensities of the NPs in the carrier systems increase with cumulative released amounts of 5FU, suggesting that release of the drug can be monitored by changes in luminescent intensity. In addition, native NPs manifest commendable cytocompatibility as demonstrated by MTT and live/dead protocols, whereas the 5FU loaded NPs demonstrated over 80% HeLa cell death, signifying their therapeutic potential. We envision that these NPs can serve as effective and practical multifunctional probes for theranostic applications.

Manipulating the emission intensity and lifetime of NaYF4:Yb3+,Er3+ simultaneously by embedding it into CdS photonic crystals

Photonic crystals (PCs) have long been considered effective for tuning upconversion luminescence due to their photonic band gap (PBG) and the redistribution of density of optical states (DOS). Although the emission intensity can be changed obviously by the PC effect, rarely an obvious lifetime change consistent with theory is observed due to the low refractive index of PS or SiO₂ spheres in the commonly used PCs. Herein, CdS/NaYF₄:Yb³⁺,Er³⁺ composite PCs with a high refractive index contrast are fabricated in one step with upconversion nanoparticles filled inside CdS PCs. When the upconversion emission peak lies at the edge of the PBGs of the composite PCs, a dramatic decrease in lifetime by 28% and 41% is observed for the green and red emissions, respectively. At the same time, obvious emission intensity enhancements are also observed. In contrast, PS PCs with a low refractive index contrast show a slight effect on the lifetime of upconversion luminescence with their emission peak at the edge of the PBGs. Our results agree well with theory and prove that a sufficiently large refractive index contrast is necessary for PCs to dramatically tune the luminescence lifetime and intensity simultaneously.

Monodisperse selenium-substituted hydroxyapatite: Controllable synthesis and biocompatibility

Hydroxyapatite (HA) is the major inorganic component of natural bone tissue. As an essential trace element, selenium involves in antioxidation and anticancer of human body. So far, ion-doped hydroxyapatites (HAs) are widely investigated owing to their great applications in field of biomaterial, biological labeling. In this paper, series of monodisperse HA doped with SeO₃^2- (SeHA) was successfully synthesized based on the liquid-solid-solution (LSS) strategy. The obtained samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and energy-dispersive spectrometer (EDS). The results indicated that the SeO₃^2- doping level of the Se/(P+Se) molar ratio of 0-0.4 can be requisitely controlled, and the morphology of SeHA nanoparticles varied from nanorods to nanoneedles with increasing Se/(P+Se) molar ratio. Significantly, the as-synthesized SeHA nanocrystals exhibit a low cytotoxicity for osteoblastic cells, showing exciting potentials for application in artificial scaffold materials inhibiting of tumor growth in bone.

Calcium Phosphate as a Key Material for Socially Responsible Tissue Engineering

Socially responsible technologies are designed while taking into consideration the socioeconomic, geopolitical and environmental limitations of regions in which they will be implemented. In the medical context, this involves making therapeutic platforms more accessible and affordable to patients in poor regions of the world wherein a given disease is endemic. This often necessitates going against the reigning trend of making therapeutic nanoparticles ever more structurally complex and expensive. However, studies aimed at simplifying materials and formulations while maintaining the functionality and therapeutic response of their more complex counterparts seldom provoke a significant interest in the scientific community. In this review we demonstrate that such compositional simplifications are meaningful when it comes to the design of a solution for osteomyelitis, a disease that is in its natural, non-postoperative form particularly prevalent in the underdeveloped parts of the world wherein poverty, poor sanitary conditions, and chronically compromised defense lines of the immune system are the norm. We show that calcium phosphate nanoparticles, which are inexpensive to make, could be chemically designed to possess the same functionality as a hypothetic mixture additionally composed of: (a) a bone growth factor; (b) an antibiotic for prophylactic or anti-infective purposes; (c) a bisphosphonate as an antiresorptive compound; (d) a viral vector to enable the intracellular delivery of therapeutics; (e) a luminescent dye; (f) a radiographic component; (g) an imaging contrast agent; (h) a magnetic domain; and (i) polymers as viscous components enabling the injectability of the material and acting as carriers for the sustained release of a drug. In particular, calcium phosphates could: (a) produce tunable drug release profiles; (b) take the form of viscous and injectable, self-setting pastes; (c) be naturally osteo-inductive and inhibitory for osteoclastogenesis; (d) intracellularly deliver bioactive compounds; (e) accommodate an array of functional ions; (f) be processed into macroporous constructs for tissue engineering; and (g) be naturally antimicrobial. All in all, we see in calcium phosphates the presence of a protean nature whose therapeutic potentials have been barely tapped into.

An aerosol synthesized CeO2:Eu3+/Na+ red nanophosphor with enhanced photoluminescence

In this work, CeO₂:Eu³⁺/Na⁺ nanoparticles were synthesized via a one-pot spray pyrolysis process using ethylene glycol as an organic additive. The luminescence intensity of CeO₂:Eu³⁺ was improved about 16.5 times via Na⁺ codoping.