Synthesis methods for nanosized hydroxyapatite with diverse structures

Synthesis and characterization of different nano-hydroxyapatites and their impact on dental enamel following topical application for dental bleaching

OBJECTIVE

This study aims to synthesize, characterize, and assess the penetration of hydrogen peroxide (HP), color change (CC), and surface morphology changes after the application of two distinct nano-hydroxyapatite (nano-HAp).

METHODS

Two nano-HAp were previously synthesized by co-precipitation: one with rod-shaped particles (RS) and the other with spherical-shaped particles (SS). The surface charge of the nano-HAp particles was determined at varying pH levels and characterized by X-ray diffraction patterns and Fourier transform infrared spectroscopy. The morphology of the samples was assessed using scanning electron microscopy (SEM). The nano-HAp particles were applied before the dental bleaching procedure. Forty teeth were divided into four groups (n = 10) according to the bleaching treatment: no treatment, bleaching with 35 % HP only, RS application and bleaching with 35 % HP, and SS application and bleaching with 35 % HP. HP concentration (µg mL-1) was measured using UV-Vis, while CC was evaluated with a digital spectrophotometer (ΔEab, ΔE00 and WID). Additionally, four teeth from each group were selected for SEM analysis. Statistical analysis encompassed one-way ANOVA, Tukey's, and Dunnet's tests.

RESULTS

RS and SS were successfully synthesized by coprecipitation, primarily differing in pH during synthesis. Both variations of nano-HAp morphology significantly reduced HP diffusion into the pulp chamber (p < 0.001). Regarding enamel morphology, groups analyzed post dental bleaching exhibited greater HAp deposition on the enamel surface. Notably, this deposition did not impede CC.

SIGNIFICANCE

The utilization of different nano-HAp morphologies prior to dental bleaching appears to be a promising strategy for mitigating adverse effects associated with dental bleaching procedures.

Innovative reuse of mineral waste for treatment of a contaminated soil by fluorine: synthesis of hydroxyapatite (HAP) and chemical performance assessments

This research aimed to introduce a novel method for the valorization of mineral waste, focusing on the development of hydroxyapatite (HAP) as an effective and economical adsorbent for immobilizing fluoride ions (F-) in soil. Hydroxyapatites were produced through the reaction between potassium dihydrogen phosphate (KH2PO4) and calcium-abundant limestone soil (CLS). X-ray diffraction analyses revealed that the primary phases in HAPCLS were brushite (CaHPO5·2H2O) and hydroxyapatite (Ca10(PO4)6(OH)2). The FTIR spectra exhibited characteristics akin to natural HAP, including the presence of orthophosphate groups (PO43-), hydroxyl groups (OH-), and both A/B types of carbonates in the apatite structure. The morphology of the synthesized HAP, as observed through SEM-EDS, was consistent with that of phosphocalcic hydroxyapatite crystals. The EDS results indicated a Ca/P atomic ratio of 1.7 for HAPCLS, aligning closely with the typical hydroxyapatite stoichiometry (Ca/P = 1.67). The application of HAP to reduce fluoride (F-) levels in soil proved to be successful; introducing 1% of various HAP formulations reduced the fluoride concentration from 51.4 mg/kg in untreated soil to levels below the IWSI limit (10 mg/kg), achieving a reduction to 8.1 mg/kg for HAPCLS. The sequential extraction of fluoride demonstrated that after soil treatment, fluoride was predominantly removed from the residual fraction (Fraction 4) and was effectively sequestered by the hydroxyapatites (Ca10(PO4)6(OH)2) through anionic exchange with hydroxide ions (OH-), resulting in the formation of stable and insoluble fluorapatite (Ca10(PO4)6F2).

Fishwaste Derived Hydroxyapatite Nanostructure Combined with Black Rice Wine for Potential Antioxidant and Antimicrobial Response

Hospital-acquired infection remains a serious threat globally, due to development of resistance to conventional antibiotics, which necessitates the urge for alternative therapy. Green nanotechnology has emerged as a holistic approach to address antibiotic resistance by combining environmental sustainability with improved therapeutic outcome. Nanostructure hydroxyapatite (HAP) has received significant attention in therapeutic and regenerative purposes due to its porous scaffold structure and biocompatible nature. In the present study, hydroxyapatite (HAP) nanoparticle was fabricated from the fish scale waste of red snapper fish. Black rice wine (BRW) was extracted from black rice commonly termed as Karupu kavuni/forbidden rice known for its nutritious effects. The present study focused on encapsulation of BRW within HAP nanoparticles (HAP@BRW) and evaluated its potential against nosocomial infections. Spectral and microscopic characterization of HAP@BRW revealed uniform encapsulation of BRW in HAP nanoparticles, aggregated irregular-shaped morphology of size 117.6 nm. Maximum release of BRW (72%) within 24 h indicates HAP as suitable drug delivery system suitable for biomedical applications. Antimicrobial studies revealed that HAP@BRW exhibited potent bactericidal effect against MRSA, MSSA, and Pseudomonas aeruginosa. Furthermore, HAP@BRW significantly inhibited the biofilm forming ability of MSSA and P. aeruginosa. Rich antioxidant property of HAP@BRW might be due to the presence of rich source of total polyphenolic, flavonoid, and anthocyanin content in BRW. In vitro and in vivo toxicity studies revealed biocompatible nature of HAP@BRW. Antibiofilm, antimicrobial, antioxidant, and biocompatible nature of HAP@BRW makes it a promising candidate for coating medical implants to avoid implant-associated infections and nosocomial infections.

Surface functionalization of hydroxyapatite nanoparticles for biomedical applications

This review completely covers the various aspects of hydroxyapatite (HAp) nanoparticles and their role in different biological situations, and provides the surface and interface contents on (i) hydroxyapatite nanoparticles and their hybridization with organic molecules, (ii) surface designing of hydroxyapatite nanoparticles to provide their biocompatibility and photofunction, and (iii) coating technology of hydroxyapatite nanoparticles. In particular, we summarized how the HAp nanoparticles interact with the different ions and molecules and highlighted the potential for hybridization between HAp nanoparticles and organic molecules, which is driven by the interactions of the HAp nanoparticle surface ions with several functional groups of biological molecules. In addition, we highlighted the studies focusing on the interfacial interactions between the HAp nanoparticles and proteins for exploring the enhanced biocompatibility. Such studies focus on how these interactions affect the hydration layers and protein adsorption. However, the hydration layer state involves diverse molecular interactions that can alter the shape of the adsorbed proteins, thereby affecting cell adhesion and spreading on the surfaces. We also summarized the relationship between the surface properties of the HAp nanoparticles and the hydration layer. Furthermore, we spotlighted the cytocompatible photoluminescent probes that can be developed by designing HAp/organic nanohybrid structures. We then emphasized the importance of photofunctionalization in theranostics, which involves the integration of diagnostics and therapy based on the surface design of the HAp nanoparticles. Furthermore, the coating techniques using HAp nanoparticles and HAp nanoparticle/polymer composites were outlined for fusing base biomaterials with biological tissues. The advantages of HAp/biocompatible polymer composite coatings include the ability to effectively cover porous or irregularly shaped surfaces while controlling the thickness of the coating layer, and the addition of HAp nanoparticles to the polymer matrix improves the mechanical properties, increases the roughness, and forms the morphologies that mimic bone nanostructures. Therefore, the fundamental design of hydroxyapatite nanoparticles and their surfaces was suggested from various aspects for biomedical applications.

Polysaccharide Hydroxyapatite (Nano)composites and Their Biomedical Applications: An Overview of Recent Years

Hydroxyapatite can combine with polysaccharide originating biomaterials with special applications in the biomedical field. In this review, the synthesis of (nano)composites is discussed, focusing on natural polysaccharides such as alginate, chitosan, and pectin. In this way, advances in recent years in the development of preparing materials are revised and discussed. Therefore, an overview of the recent synthesis and applications of polyssacharides@hydroxyapatites is presented. Several studies based on chitosan@hydroxyapatite combined with other inorganic matrices are highlighted, while pectin@hydroxyapatite is present in a smaller number of reports. Biomedical applications as drug carriers, adsorbents, and bone implants are discussed, combining their dependence with the nature of interactions on the molecular scale and the type of polysaccharides used, which is a relevant aspect to be explored.

3D-Bioprinted Gelatin Methacryloyl-Strontium-Doped Hydroxyapatite Composite Hydrogels Scaffolds for Bone Tissue Regeneration

New gelatin methacryloyl (GelMA)-strontium-doped nanosize hydroxyapatite (SrHA) composite hydrogel scaffolds were developed using UV photo-crosslinking and 3D printing for bone tissue regeneration, with the controlled delivery capacity of strontium (Sr). While Sr is an effective anti-osteoporotic agent with both anti-resorptive and anabolic properties, it has several important side effects when systemic administration is applied. Multi-layer composite scaffolds for bone tissue regeneration were developed based on the digital light processing (DLP) 3D printing technique through the photopolymerization of GelMA. The chemical, morphological, and biocompatibility properties of these scaffolds were investigated. The composite gels were shown to be suitable for 3D printing. In vitro cell culture showed that osteoblasts can adhere and proliferate on the surface of the hydrogel, indicating that the GelMA-SrHA hydrogel has good cell viability and biocompatibility. The GelMA-SrHA composites are promising 3D-printed scaffolds for bone repair.

Synthesis of hydroxyapatite from eggshells via wet chemical precipitation: a review

In conjunction with the global trend towards sustainable industry, this review provides a summary of the research endeavors and efforts made in the field of exploiting eggshells in the production of hydroxyapatite (HA). HA is one of the most used biomaterials and has attracted considerable attention over the years towards biomedical applications. As the traditional production of HA from calcium and phosphorus chemical precursors synthetically has bottlenecks of being expensive, complex, time consuming, and results in a low biocompatible product, natural resources have become an attractive alternative option to synthesize HA, with trace elements providing a higher performance. Eggshell, with a growing production annually, is potentially a promising natural resource for HA production. Many studies have used different wet chemical precipitation routes to produce HA with properties comparable to synthetic HA. Thus, this review provides an overview of the various routes that can be used to synthesize HA from eggshells. In this review, the synthesis of HA from eggshells via wet chemical precipitation methods is specifically discussed in term of synthesis parameters and properties of the synthesized HA. This review should aid in choosing the most suitable route for HA production with the optimum parameters for obtaining the desired properties to meet the requirements of biomedical applications such as tissue engineering.

Synthesis of HAp by Means of Sonoprecipitation Method

Biomaterials, like hydroxyapatite (HAp), are the subject of many scientific investigations. Their specific application, however, is determined by the form and some characteristic features of the resulting material. Synthesis methods and optimization procedures leading to a product of predetermined characteristics are therefore of great interest. To broaden the existing knowledge, sonoprecipitation was investigated as a potential method for the production of nanosized HAp particles. The research was carried out in a static mixer (STM) immersed in the ultrasonic bath. The influence of operating conditions, e.g., ultrasonic power PUS (εUS), ultrasonic frequency (fUS), and unit mixing power (εmix), was investigated in terms of nucleation intensity, product quality, and characteristics (particle size distribution (PSD), mean size, shape, etc.). As a result, the optimal conditions for the HAp nanoparticles synthesis (mean size: d~150 nm; length: L1~250 nm; width: L2~80 nm) in the form of needles/whiskers/rods-similar to the shape of the HAp present in natural human bones, free from agglomerates, with negligible signs of particle destruction-were determined. The formation of HAp of smaller sizes (d ≤ 100 nm) and more compact shapes (L1~155 nm, L2~90 nm), useful in bone regeneration processes, was also discussed.

Hydroxyapatite synthesis and characterization from waste animal bones and natural sources for biomedical applications

Hydroxyapatites (HAps) synthesized from waste animal bones have recently gained attention due to their outstanding properties. This is because there is a need to fabricate scaffolds with desirable mechanical strength, ability to withstand high temperatures, and insoluble in solvents such as water, acetone, ethanol, and isopropyl alcohol. This study is an extensive summary of many articles on the routes of synthesis/preparation of HAp, and the optimum processing parameter, and the biomedical application areas, such as: drug administration, dental implants, bone tissue engineering, orthopedic implant coatings, and tissue regeneration/wound healing. A broad catalog of the synthesis methods (and combination methods), temperature/time, shape/size, and the calcium-to-phosphorous (Ca/P) value of diverse waste animal bone sources were reported. The alkaline hydrolysis method is proposed to be suitable for synthesizing HAp from natural sources due to the technique's ability to produce intrinsic HAp. The method is also preferred to the calcination method owing to the phase transformation that takes place at high temperatures during calcinations. However, calcinations aid in removing impurities and germs during heating at high temperatures. When compared to calcination technique, alkaline hydrolysis method results in crystalline HAp; the higher degree of crystallinity is disadvantageous to HAp bioactivity. In addition, the standardization and removal of impurities and contaminants, thorough biocompatibility to ensure clinical safety of the HAp to the human body, and improvement of the mechanical strength and toughness to match specific requirements for the various biomedical applications are the important areas for future studies.

Nickel-ion substituted hydroxyapatite matrices for metal-affinity chromatographic purification of recombinant proteins

Hydroxyapatite (HAp) is a calcium phosphate ceramic, widely used as a matrix for protein chromatography. The crystal structure of HAp is amenable to a wide range of substitutions, thus allowing for the alteration of its properties. In this study, nickel-ion substituted HAp (NiSHAp) was synthesized using a wet-precipitation method, followed by spray drying. This resulted in the structural incorporation of nickel ions within well-defined microspheres, which were suitable for chromatographic applications. The chromatographic experiments were conducted with NiSHAp and compared with spray-dried hydroxyapatite (SHAp) matrices. Protein purification experiments were conducted using refolded recombinant L-asparaginase (L-Asp), which was produced as inclusion bodies in Escherichia coli. The results showed that NiSHAp effectively adsorbed L-Asp, which was selectively eluted using a phosphate buffer, surpassing the efficiency of imidazole-based elution. In contrast, SHAp showed weaker binding and lower selectivity. The significance of this study lies in developing a scalable NiSHAp matrix for protein purification, especially for large-scale applications. The NiSHAp matrix offers a cost-effective alternative to commercial immobilized metal affinity chromatography (IMAC) adsorbents, especially for purifying His-tagged proteins. This innovative approach exhibits the advantages of mixed-mode chromatography by combining the properties of hydroxyapatite and IMAC in a single matrix, with the potential of improved industrial-scale protein purification.

Cell viability assessment and ion release profiles of GICs modified with TiO2- and Mg-doped hydroxyapatite nanoparticles

OBJECTIVES

To assess and compare the cell viability and ion release profiles of two conventional glass ionomer cements (GICs), Fuji IX and Ketac Molar EasyMix, modified with TiO2 and Mg-doped-HAp nanoparticles (NPs).

METHODS

TiO2 NPs, synthesized via a sol-gel method, and Mg-doped hydroxyapatite, synthesized via a hydrothermal process, were incorporated into GICs at a concentration of 5 wt.%. The biocompatibility of prepared materials was assessed by evaluating their effects on the viability of dental pulp stem cells (DPSCs), together with monitoring ion release profiles. Statistical analysis was performed using One-way analysis of variance, with significance level p < 0.05.

RESULTS

The addition of NPs did not significantly affect the biocompatibility of GICs, as evidenced by comparable decreased levels in cell viability to their original formulations. Distinct variations in cell viability were observed among Fuji IX and Ketac Molar, including their respective modifications. FUJI IX and its modification with TiO2 exhibited moderate decrease in cell viability, while other groups exhibited severe negative effects. While slight differences in ion release profiles were observed among the groups, significant variations compared to original cements were not achieved. Fluoride release exhibited an initial "burst release" within the initial 24 h in all samples, stabilizing over subsequent days.

CONCLUSIONS

The addition of NPs did not compromise biocompatibility, nor anticariogenic potential of tested GICs. However, observed differences among FUJI IX and Ketac Molar, including their respective modifications, as well as induced low viability of DPSC by all tested groups, suggest the need for careful consideration of cement composition in their biological assessments.

CLINICAL SIGNIFICANCE

The findings contribute to understanding the complex interaction between NPs and GIC matrices. However, the results should be interpreted recognizing the inherent limitations associated with in vitro studies. Further research avenues could explore long-term effects, in vivo performance, and potential clinical applications.

4-META/MMA-TBB resin containing nano hydroxyapatite induces the healing of periodontal tissue repair in perforations at the pulp chamber floor

We aimed to evaluate the materials based on 4-methacryloxyethyl trimellitate anhydride/methyl methacrylate tri-n-butylborane (Super-bond [SB]) and nano hydroxyapatite (naHAp) for the repair of perforation at pulp chamber floor (PPF) in vitro and in vivo models. SB and naHAp were mixed in the mass ratio of 10% or 30% to produce naHAp/SB. Human periodontal ligament stem cells (HPDLSCs) were cultured on resin discs of SB or naHAp/SB to analyze the effects of naHAp/SB on cell adhesion, proliferation, and cementoblastic differentiation. A rat PPF model was treated with SB or naHAp/SB to examine the effects of naHAp/SB on the healing of defected cementum and periodontal ligament (PDL) at the site of PPF. HPDLSCs were spindle-shaped and adhered to all resin discs. Changing the resin from SB to naHAp/SB did not significantly alter cell proliferation. Both 10% and 30% naHAp/SB were more effective than SB in promoting cementoblastic differentiation of HPDLSCs. In the rat PPF model, 30% naHAp/SB was more effective than SB in promoting the formation Sharpey's fiber-like structures with expression of the PDL-related marker and cementum-like structures with expression of cementum-related markers. In conclusion, 30% naHAp/SB can be the new restorative material for PPF because it exhibited the abilities of adhering to dentin and healing of defected periodontal tissue.

Probing the influence of strontium doping and annealing temperature on the structure and biocompatibility of hydroxyapatite nanorods

Among numerous biologically important metal cations, strontium (Sr2+) has received much attention in bone tissue regeneration because of its osteoinductive properties combined with its ability to inhibit osteoclast activity. In this study, strontium-doped hydroxyapatite (Sr-HAp) nanorods with varying molar ratios of Ca : Sr (10 : 0, 9 : 1, 5 : 5, 3 : 7 and 0 : 10) were synthesized using the chemical precipitation technique. The synthesized Sr-HAp nanostructures were characterized using powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy, energy dispersive X-ray spectroscopy, and Raman and Fourier transform infrared (FTIR) spectroscopies to understand their structural and morphological features, and composition. XRD results revealed the formation of HAp nanostructures, whose unit cell volume increased as a function of the dopant level. The reaction process investigation showed the formation of hydroxyapatite (HAp), strontium apatite (SAp) and various Sr-HAp phases. FESEM micrographs displayed the morphological transformation of Sr-HAp from nanorods to nanosheets upon increasing the dopant level. In the FTIR spectra, the bands of the PO43- group shifted towards a lower wavenumber upon increasing the dopant concentration in Sr-HAp that signifies the structural distortion due to the presence of a large amount of strontium ions. The peaks of PO43- and OH- vibrations in the Raman spectra were further analysed to corroborate the structural distortion of Sr-HAp. Selected area electron diffraction patterns obtained using TEM reveal the reduced crystallinity of Sr-HAp due to Sr-doping, which is in line with the XRD results. Finally, the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay showed that the synthesized Sr-HAp has no toxic effect on the survival and growth of mesenchymal stem cells. In summary, the synthesized novel Sr-HAp nanorods exhibit great promise for bone tissue engineering applications.

Surface Modification of Nano-Hydroxyapatite/Polymer Composite for Bone Tissue Repair Applications: A Review

Nano-hydroxyapatite (n-HA) is the main inorganic component of natural bone, which has been widely used as a reinforcing filler for polymers in bone materials, and it can promote cell adhesion, proliferation, and differentiation. It can also produce interactions between cells and material surfaces through selective protein adsorption and has therefore always been a research hotspot in orthopedic materials. However, n-HA nano-particles are inherently easy to agglomerate and difficult to disperse evenly in the polymer. In addition, there are differences in trace elements between n-HA nano-particles and biological apatite, so the biological activity needs to be improved, and the slow degradation in vivo, which has seriously hindered the application of n-HA in bone fields, is unacceptable. Therefore, the modification of n-HA has been extensively reported in the literature. This article reviewed the physical modification and various chemical modification methods of n-HA in recent years, as well as their modification effects. In particular, various chemical modification methods and their modification effects were reviewed in detail. Finally, a summary and suggestions for the modification of n-HA were proposed, which would provide significant reference for achieving high-performance n-HA in biomedical applications.

In-depth knowledge of the low-temperature hydrothermal synthesis of nanocrystalline hydroxyapatite from waste green mussel shell (Perna Viridis)

ABSTRACTThis study presents the use of a low-temperature hydrothermal method for extracting calcium sources from green mussel shell (P. Viridis) wastes and converting them into synthetic nanosized hydroxyapatite (HA). In this study, raw mussel shells were washed, pulverised, and sieved to start producing a fine calcium carbonate-rich powder. XRD quantitative analysis confirmed that the powder contains 97.6 wt. % aragonite. This powder was then calcined for 5 h at 900 °C to remove water, salt, and mud, yielding a calcium-rich feedstock with major minerals of calcite (68.7 wt.%), portlandite (24.7 wt.%), and minor aragonite (6.5 wt.%). The calcined powders were dissolved in aqueous stock solutions of HNO3 and NH4OH before hydrothermally reacting with phosphoric acid [(NH4)2HPO4], yielding pure, nanoscale (16-18 nm) carbonated HA crystals, according to XRD, FT-IR, and SEM analyses. The use of a low-temperature hydrothermal method for a feedstock powder produced by the calcination of low-cost mussel shell wastes would be a valuable processing approach for the industry's development of large-scale hydroxyapatite nanoparticle production.

Fmoc-FF hydrogels and nanogels for improved and selective delivery of dexamethasone in leukemic cells and diagnostic applications

Dexamethasone (DEX) is a synthetic analogue of cortisol commonly used for the treatment of different pathological conditions, comprising cancer, ocular disorders, and COVID-19 infection. Its clinical use is hampered by the low solubility and severe side effects due to its systemic administration. The capability of peptide-based nanosystems, like hydrogels (HGs) and nanogels (NGs), to serve as vehicles for the passive targeting of active pharmaceutical ingredients and the selective internalization into leukemic cells has here been demonstrated. Peptide based HGs loaded with DEX were formulated via the "solvent-switch" method, using Fmoc-FF homopeptide as building block. Due to the tight interaction of the drug with the peptidic matrix, a significant stiffening of the gel (G' = 67.9 kPa) was observed. The corresponding injectable NGs, obtained from the sub-micronization of the HG, in the presence of two stabilizing agents (SPAN®60 and TWEEN®60, 48/52 w/w), were found to be stable up to 90 days, with a mean diameter of 105 nm. NGs do not exhibit hemolytic effects on human serum, moreover they are selectively internalized by RS4;11 leukemic cells over healthy PBMCs, paving the way for the generation of new diagnostic strategies targeting onco-hematological diseases.

Synthesis of pure and doped nano-calcium phosphates using different conventional methods for biomedical applications: a review

The applications of calcium phosphates (hydroxyapatite, tetracalcium phosphate, tricalcium phosphate (alpha and beta), fluorapatite, di-calcium phosphate anhydrous, and amorphous calcium-phosphate) are increasing day by day. Calcium hydroxyapatite, commonly known as hydroxyapatite (HAp), represents a mineral form of calcium apatite. Owing to its close molecular resemblance to the mineral constituents of bones, teeth, and hard tissues, HAp is often employed in the biomedical domain. In addition, it is extensively employed in various sectors such as the remediation of water, air, and soil pollution. The key advantage of HAp lies in its potential to accommodate a wide variety of anionic and cationic substitutions. Nevertheless, HAp and tricalcium phosphate (TCP) syntheses typically involve the use of chemical precursors containing calcium and phosphorus sources and employ diverse techniques, such as solid-state, wet, and thermal methods or a combination of these processes. Researchers are increasingly favoring natural sources such as bio-waste (eggshells, oyster shells, animal bones, fish scales, etc.) as viable options for synthesizing HAp. Interestingly, the synthesis route significantly influences the morphology, size, and crystalline phase of calcium phosphates. In this review paper, we highlight both dry and wet methods, which include six commonly used synthesis methods (i.e. solid-state, mechano-chemical, wet-chemical precipitation, hydrolysis, sol-gel, and hydrothermal methods) coupled with the variation in source materials and their influence in modifying the structural morphology from a bulky state to nanoscale to explore the applications of multifunctional calcium phosphates in different formats.

Long acting tariquidar loaded stearic acid-modified hydroxyapatite enhances brain penetration and antitumor effect of temozolomide

Temozolomide (TMZ) is the first line chemotherapy for glioblastoma (GBM) treatment, but the P-glycoprotein (P-gp) expressed in blood-brain barrier (BBB) will pump out TMZ from the brain leading to decreased TMZ concentration. Tariquidar (TQD), a selective and potent P-gp inhibitor, may be suitable for combination therapy to increase concentration of TMZ in brain. Hydroxyapatite (HAP) is a biodegradable material with sustained release characteristics, and stearic acid surface-modified HAP (SA-HAP) can increase hydrophobicity to facilitate TQD loading. TQD-loaded stearic acid surface-modified HAP (SA-HAP-TQD) was prepared with optimal size and high TQD loading efficiency, and in vitro release and cellular uptake of SA-HAP-TQD showed that SA-HAP-TQD were taken up into lysosome and continuously released TQD from macrophages. In vivo studies have found that over 70 % of SA-HAP was degraded and 80 % of TQD was released from SA-HAP-TQD 28 days after administration. SA-HAP-TQD could increase brain penetration of TMZ, but it would not enhance adverse effects of TMZ in healthy mice. SA-HAP-TQD and TMZ combination had longer median survival than TMZ single therapy in GL261 orthotopic model. These results suggest that SA-HAP-TQD has sustained release characteristics and are potential for improving antitumor effect with TMZ treatment.

Double-layered microneedle patch loaded with bioinspired nano-vaccine for melanoma treatment and wound healing

Malignant melanoma is a challenging problem worldwide, because the remaining tumor cells and extensive skin defects following surgical resection are difficult to treat. Biomaterial-mediated immunotherapy has emerged as a superior strategy for anti-tumor applications in recent years. Herein, a unique double-layer MNP was developed to address the problem of malignant melanoma. Hydroxyapatite (HAP) and short-chain peptides from tumor cells were self-assembled to prepare the bioinspired nano-vaccine, and then they were loaded onto the microneedle tips of methacrylated gelatin (GelMA)-based MNP. The products (dubbed HVMN) demonstrated relatively good biocompatibility and immune activity, inhibiting the proliferation and inducing apoptosis of malignant melanoma in a B16 cell-bearing model of C57BL/6 mice, and promoting skin tissue regeneration in a full thickness skin defect model of SD rats in 15 days. The putative molecular pathways were examined preliminarily. In conclusion, this research will develop a competitive microneedle patch with dual anti-tumor and pro-regenerative properties for the postoperative treatment of malignant melanoma.

Improved CaP Nanoparticles for Nucleic Acid and Protein Delivery to Neural Primary Cultures and Stem Cells

Efficiently delivering exogenous materials into primary neurons and neural stem cells (NSCs) has long been a challenge in neurobiology. Existing methods have struggled with complex protocols, unreliable reproducibility, high immunogenicity, and cytotoxicity, causing a huge conundrum and hindering in-depth analyses. Here, we establish a cutting-edge method for transfecting primary neurons and NSCs, named teleofection, by a two-step process to enhance the formation of biocompatible calcium phosphate (CaP) nanoparticles. Teleofection enables both nucleic acid and protein transfection into primary neurons and NSCs, eliminating the need for specialized skills and equipment. It can easily fine-tune transfection efficiency by adjusting the incubation time and nanoparticle quantity, catering to various experimental requirements. Teleofection's versatility allows for the delivery of different cargos into the same cell culture, whether simultaneously or sequentially. This flexibility proves invaluable for long-term studies, enabling the monitoring of neural development and synapse plasticity. Moreover, teleofection ensures the consistent and robust expression of delivered genes, facilitating molecular and biochemical investigations. Teleofection represents a significant advancement in neurobiology, which has promise to transcend the limitations of current gene delivery methods. It offers a user-friendly, cost-effective, and reproducible approach for researchers, potentially revolutionizing our understanding of brain function and development.

Microfabrication of Gelatin Methacrylate/Hydroxyapatite Composites by Utilizing Alternate Soaking Process

To construct a complex three-dimensional (3D) structure mimicking bone microstructure, hydrogel models of polymerized gelatin methacrylate (pGelMA) were fabricated by using stereolithography and modified with hydroxyapatite (HAp) via an alternate soaking process (ASP) using a solution of calcium and phosphate ions. Fabricated pGelMA line models whose widths were designed as 100, 300, and 600 μm were modified with HAp by ASP by changing the immersion time and number of cycles. After ASP, all of the line models with widths of 100, 300, and 600 μm were successfully modified with HAp, and large amounts of HAp were covered with the fabricated models by increasing both the immersion time and the number of cycles in ASP. HAp was observed near the surface of the line model with a width of 600 μm after ASP at an immersion time of 10 s, while the entire model was modified with HAp using ASPs for longer immersion times. The adhesion and spread of mesenchymal stem cells (MSCs) on the pGelMA-HAp discs depended on the ASP conditions. Moreover, the HAp modification of 3D pyramid models without alteration of the microstructure was also conducted. This two-step fabrication method of first fabricating frameworks of hydrogel models by stereolithography and subsequently modifying the fabricated models with HAp will lead to the development of 3D cell culture systems to support bone grafts or to create biological niches, such as artificial bone marrow.

Nano-hydroxyapatite structures for bone regenerative medicine: Cell-material interaction

Bone tissue engineering holds great promise for the regeneration of damaged or severe bone defects. However, several challenges hinder its translation into clinical practice. To address these challenges, interdisciplinary efforts and advances in biomaterials, cell biology, and bioengineering are required. In recent years, nano-hydroxyapatite (nHA)-based scaffolds have emerged as a promising approach for the development of bone regenerative agents. The unique similarity of nHA with minerals found in natural bones promotes remineralization and stimulates bone growth, which are crucial factors for efficient bone regeneration. Moreover, nHA exhibits desirable properties, such as strong chemical interactions with bone and facilitation of tissue growth, without inducing inflammation or toxicity. It also promotes osteoblast survival, adhesion, and proliferation, as well as increasing alkaline phosphatase activity, osteogenic differentiation, and bone-specific gene expression. However, it is important to note that the effect of nHA on osteoblast behavior is dose-dependent, with cytotoxic effects observed at higher doses. Additionally, the particle size of nHA plays a crucial role, with smaller particles having a more significant impact. Therefore, in this review, we highlighted the potential of nHA for improving bone regeneration processes and summarized the available data on bone cell response to nHA-based scaffolds. In addition, an attempt is made to portray the current status of bone tissue engineering using nHA/polymer hybrids and some recent scientific research in the field.

Hydroxyapatite/Polyurethane Scaffolds for Bone Tissue Engineering

Polyurethane (PU) and PU ceramic scaffolds are the principal materials investigated for developing synthetic bone materials due to their excellent biocompatibility and biodegradability. PU has been combined with calcium phosphate (such as hydroxyapatite [HA] and tricalcium phosphate) to prepare scaffolds with enhanced mechanical properties and biocompatibility. This article reviews the latest progress in the design, synthesis, modification, and biological attributes of HA/PU scaffolds for bone tissue engineering. Diverse HA/PU scaffolds have been proposed and discussed in terms of their osteogenic, antimicrobial, biocompatibility, and bioactivities. The application progress of HA/PU scaffolds in bone tissue engineering is predominantly introduced, including bone repair, bone defect filling, drug delivery, and long-term implants.

p75NTR antibody-conjugated microspheres: an approach to guided tissue regeneration by selective recruitment of endogenous periodontal ligament cells

Repairing defects in alveolar bone is essential for regenerating periodontal tissue, but it is a formidable challenge. One promising therapeutic approach involves using a strategy that specifically recruits periodontal ligament cells (PDLCs) with high regenerative potential to achieve in situ regeneration of alveolar bone. In this study, we have created a new type of microsphere conjugated with an antibody to target p75 neurotrophin receptor (p75NTR), which is made of nano-hydroxyapatite (nHA) and chitosan (CS). The goal of this design is to attract p75NTR+hPDLCs selectively and promote osteogenesis. In vitro experiments demonstrated that the antibody-conjugated microspheres attracted significantly more PDLCs compared to non-conjugated microspheres. Incorporating nHA not only enhances cell adhesion and proliferation on the surface of the microsphere but also augments its osteoinductive properties. Microspheres effectively recruited p75NTR+ cells at bone defect sites in SD rats, as observed through immunofluorescent staining of p75NTR antibodies. This p75NTR antibody-conjugated nHA/CS microsphere presents a promising approach for selectively recruiting cells and repairing bone defects.

Impacts of pre-treatment methods on the morphology, crystal structure, and defects formation of hydroxyapatite extracted from Nile tilapia scales

The comprehensive control of hydroxyapatite (HAp), involving morphological and structural variations, particle sizes, and defect formations, has garnered considerable attention for its versatile functionalities, rendering it applicable in diverse contexts. This work examined the shape, structure and optical characteristics, and defect formation in hydroxyapatite (HAp) extracted from Nile tilapia (Oreochromis niloticus) scales with various pre-treatments through experiments and density functional theory (DFT) calculations. Utilizing scanning electron microscopy, our findings revealed that dried fish scales (FS-D) exhibited a layered pattern of collagen fibers, while boiled fish scales (FS-B) had smoother surfaces and significantly reduced collagen content. After calcination, the FS-D sample produced nanorods with an average length of 150 ± 44 nm, whereas the FS-B samples yielded agglomerated spherical particles whose size increased with the rising calcining temperature. In-depth analysis through X-ray diffraction and Fourier-transform infrared spectroscopy confirmed the presence of biphasic calcium phosphates in the FS-B samples, while the FS-D sample presented a pure HAp phase. The boiled fish scale calcined at 800 °C (FS-B800) exhibited an optical band gap (Eg) of 5.50 eV, whereas the dried fish scale calcined at 800 °C (FS-D800) showed two Eg values of 2.87 and 3.97 eV, as determined by UV-visible spectroscopy. DFT calculations revealed that the band gap of 3.97 eV correlated with OH- vacancies, while that of 2.87 eV indicated Mn-substituted HAp, explaining the blue powder. The Eg value for the white powder resembled pure HAp, S- and Cl- substituted OH- vacancies, and various cations substituting Ca sites of HAp. Different pre-treatment procedures influence the characteristics of HAp, offering opportunities for applications in bone replacement and scaffolds for bone tissue engineering.

Synthesis of nano-hydroxyapatite using emulsion, pyrolysis, combustion, and sonochemical methods and biogenic sources: a review

Hydroxyapatite (HAp) is comparable to materials in bone because its chemical components are similar to those contained in animal bone, and thus, its bioactive and biocompatible properties are similar. There are applications for HAp and relevant calcium phosphate in the medical and industrial sectors, and due to the rising demand for HAp nanoparticles, considerable work has been performed to develop a variety of synthetic pathways that incorporate scientifically and practically novel aspects. Numerous studies have been conducted to examine how changes in reaction parameters will successfully influence crucial HAp features. HAp can also be synthesized from biogenic sources such as HAp-rich fish scales or animal bones as an alternative to chemical precursors. Various preparation techniques produce crystals with varying sizes, but it has been found that nano-sized HAp exhibits a greater number of bioactive properties as compared to micron-sized HAp. Rather than considering conventional methods, this review focuses on alternative approaches such as emulsion, pyrolysis, combustion, and sonochemical methods along with waste bio-sources (biogenic sources) to obtain HAp. We summarize the currently accessible information pertaining to each synthesis process, while also focusing on their benefits and drawbacks.

New Three-Dimensional Bioactive Reinforcing Filler for Improving the Properties of Biomedical Polymers: Synthesis and Application

In general, the efficiency of reinforcement for filler-based composites is greatly influenced by the filler properties. While much research has been conducted on filler percentage and filler-matrix bonding quality, there is not much research directed to the effect of filler geometry. Therefore, the aim of this article is to examine how a three-dimensional (3D) bioactive filler influences the strength enhancement of biomedical polymers. This was accomplished by first synthesizing highly regular dandelion-like hydroxyapatite (DHA) as a 3D bioactive filler using an optimized hydrothermal method, followed by surface modification with silane molecules. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was then used as a biomedical polymer model to fabricate solution-casted composites by using the as-synthesized DHA particles. The results showed that the composites loaded with the surface-modified DHA particles had significantly higher tensile strength and elastic modulus compared to the neat PHBV and composites having irregular particles. In addition to the mechanical properties, our research found that the 3D DHA filler had a significant impact on the biological characteristics of the PHBV, such as water wettability, biodegradability, bioactivity, and in vitro cell response. These findings suggested that particle geometry can play a more significant role in affecting the biological and mechanical performance of biomedical polymers than previously thought.

Preparation and Properties of GO/ZnO/nHAp Composite Microsphere Bone Regeneration Material

The purpose of this study is to explore the possibility of using graphene-zinc oxide-hydroxyapatite (GO/ZnO/nHAp) composite microspheres as bone regeneration materials by making use of the complementary advantages of nanocomposites, so as to provide reference for the clinical application of preventing and solving bacterial infection after implantation of synthetic materials. Firstly, GO/ZnO composites and hydroxyapatite nanoparticles were synthesized using the hydrothermal method, and then GO/ZnO/nHAp composite microspheres were prepared via high-temperature sintering. The graphene-zinc oxide-calcium phosphate composite microspheres were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), energy dispersion spectroscopy (EDS), water contact angle measurement, degradation and pH determination, and differential thermal analysis (DiamondTG/DTA). The biocompatibility, osteogenic activity, and antibacterial activity of GO/ZnO/nHAp composite microspheres were further studied. The results of the cell experiment and antibacterial experiment showed that 0.5% and 1% GO-ZnO-nHAp composite microspheres not only had good biocompatibility and osteogenic ability but also inhibited Escherichia coli and Staphylococcus aureus by more than 45% and 70%. Therefore, GO/ZnO/nHAp composite microspheres have good physical and chemical properties and show good osteogenic induction and antibacterial activity, and this material has the possibility of being used as a bone regeneration material.

Synthesis, characterization, mechanical and magnetic characteristics of Gd3+ /PO4 3 - substituted zircon for application in hard tissue replacements

The study reports on the use of sol-gel technique to yield zircon type [Zr(1-0.1-x) GdxTi0.1 ] [(SiO4 )1-x (PO4 )x ] solid solution. Titanium has been used as a mineralizer to trigger zircon formation while equimolar concentrations of Gd3+ and PO4 3- were added to determine their accommodation limits in the zircon structure. The crystallization of t-ZrO2 as a dominant phase alongside the crystallization of m-ZrO2 and zircon were detected at 1200°C while their further annealing revealed the formation of zircon as a major phase at 1300°C. Heat treatment at 1400°C revealed the formation of zircon-type solid solution [Zr(1-0.1-x) Gdx Ti0.1 ][(SiO4 )1-x (PO4 )x ] comprising the accommodation of 10 mol.% of Gd3+ /PO4 3- at the zircon lattice. Beyond 10 mol.% of Gd3+ /PO4 3- , the crystallization of GdPO4 as a secondary phase is noticed. Structural analysis revealed the expansion of zircon lattice due to the simultaneous occupancy of Gd3+ /PO4 3- for the corresponding Zr4+ /SiO4 4- sites. The mechanical strength of single-phase zircon solid solution was higher in comparison to that of multiphase materials, namely in the presence of GdPO4 formed as a secondary phase in samples with added equimolar Gd3+ /PO4 3- contents beyond 10 mol.%. Nevertheless, the paramagnetic behavior of the samples demonstrated a steady surge as a function of enhanced Gd3+ content.

Synthesis and in vitro characteristics of biogenic-derived hydroxyapatite for bone remodeling applications

The inorganic component of bone matrix, hydroxyapatite (HAp) (with formula Ca10(PO4)6(OH)2), can be obtained from inexpensive waste resources that serve as excellent calcium precursors. In the present study, HAp nano-powder was synthesized from eggshells (ES) and crab shells (CS) by wet chemical precipitation method. Also, a hybrid sample was considered which is a mixture of HAp nano-powder synthesized from eggshells (25%) and crab shells (75%) (EC). The presence of phosphate, carbonate, and hydroxyl groups in the synthesized powder was confirmed through FTIR analysis. The phase composition was determined using XRD, and elemental analysis revealed a Ca/P ratio ranging from 1.5 to 1.8, confirming the HAp nature of the nano-powder, which ranged in size from 73 to 375 nm. Importantly, preliminary in vitro tests were conducted using mouse preosteoblast cell line MC3T3-E1 to evaluate the cytotoxic effects of the synthesized HAp. The results indicated excellent biocompatibility. Moreover, sample EC exhibited a significantly higher proliferation on days 3, 6, 9, and 12. EC demonstrated promising antimicrobial properties by exhibiting a significantly higher inhibitory effect against the bacteria Streptococcus mutans and Escherichia coli, and the fungi Candida albicans and Aspergillus niger. Additionally, EC displayed notable antioxidant activity, with IC50 values of 271.543 µg/ml and 407.764 µg/ml in DPPH and H2O2 assays, respectively. Furthermore, it showed strong anti-inflammatory properties, with a dose-dependent inhibition against protein denaturation. Given these findings, the synthesized HAp holds promise as a potential bone filler and could be beneficial for bone remodeling applications.

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

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

Application of apatite particles for remediation of contaminated soil and groundwater: A review and perspectives

With rapid industrial development and population growth, the pollution of soil and groundwater has become a critical concern all over the world. Yet, remediation of contaminated soil and water remains a major challenge. In recent years, apatite has gained a surging interest in environmental remediation because of its high treatment efficiency, low cost, and environmental benignity. This review summarizes recent advances in: (1) natural apatite of phosphate ores and biological source; (2) synthesis of engineered apatite particles (including stabilized or surface-modified apatite nanoparticles); (3) treatment effectiveness of apatite towards various environmental pollutants in soil and groundwater, including heavy metals (e.g., Pb, Zn, Cu, Cd, and Ni), inorganic anions (e.g., As oxyanions and F-), radionuclides (e.g., thorium (Th), strontium (Sr), and uranium (U)), and organic pollutants (e.g., antibiotics, dyes, and pesticides); and (4) the removal and/or interaction mechanisms of apatite towards the different contaminants. Lastly, the knowledge or technology gaps are identified and future research needs are proposed.

Removal of Aqueous Uranyl and Arsenate Mixtures after Reaction with Limestone, PO43-, and Ca2

The co-occurrence of uranyl and arsenate in contaminated water caused by natural processes and mining is a concern for impacted communities, including in Native American lands in the U.S. Southwest. We investigated the simultaneous removal of aqueous uranyl and arsenate after the reaction with limestone and precipitated hydroxyapatite (HAp, Ca10(PO4)6(OH)2). In benchtop experiments with an initial pH of 3.0 and initial concentrations of 1 mM U and As, uranyl and arsenate coprecipitated in the presence of 1 g L-1 limestone. However, related experiments initiated under circumneutral pH conditions showed that uranyl and arsenate remained soluble. Upon addition of 1 mM PO43- and 3 mM Ca2+ in solution (initial concentration of 0.05 mM U and As) resulted in the rapid removal of over 97% of U via Ca-U-P precipitation. In experiments with 2 mM PO43- and 10 mM Ca2+ at pH rising from 7.0 to 11.0, aqueous concentrations of As decreased (between 30 and 98%) circa pH 9. HAp precipitation in solids was confirmed by powder X-ray diffraction and scanning electron microscopy/energy dispersive X-ray. Electron microprobe analysis indicated U was coprecipitated with Ca and P, while As was mainly immobilized through HAp adsorption. The results indicate that natural materials, such as HAp and limestone, can effectively remove uranyl and arsenate mixtures.

Tumor-targeting hydroxyapatite nanoparticles for remodeling tumor immune microenvironment (TIME) by activating mitoDNA-pyroptosis pathway in cancer

In recent years, immunotherapy has emerged as a promising strategy for treating solid tumors, although its efficacy remains limited to a subset of patients. Transforming non-responsive "cold" tumor types into immuno-responsive "hot" ones is critical to enhance the efficacy of immune-based cancer treatments. Pyroptosis, a programmed cell death mechanism, not only effectively eliminates tumor cells but also triggers a potent inflammatory response to initiate anti-tumor immune activities. This sheds light on the potential of pyroptosis to sensitize tumors to immune therapy. Hence, it is urgent to explore and develop novel treatments (e.g., nanomedicines) which are capable of inducing pyroptosis. In this study, we constructed tumor-targeting nanoparticles (CS-HAP@ATO NPs) by loading atorvastatin (ATO) onto chondroitin sulfate (CS) modified hydroxyapatite (HAP) nanoparticles (CS-HAP). CS was strategically employed to target tumor cells, while HAP exhibited the capacity to release calcium ions (Ca2+) in response to the tumor microenvironment. Moreover, ATO disrupted the mitochondrial function, leading to intracellular energy depletion and consequential changes in mitochondrial membrane permeability, followed by the influx of Ca2+ into the cytoplasm and mitochondria. CS and HAP synergetically augmented mitochondrial calcium overload, inciting the production of substantial amount of reactive oxygen species (ROS) and the subsequent liberation of oxidized mitochondrial DNA (OX-mitoDNA). This intricate activation process promoted the assembly of inflammasomes, most notably the NLRP3 inflammasome, followed by triggering caspase-1 activation. The activated caspase-1 was able to induce gasderminD (GSDMD) protein cleavage and present the GSDM-N domain, which interacted with phospholipids in the cell membrane. Then, the cell membrane permeability was raised, cellular swelling was observed, and abundant cell contents and inflammatory mediators were released. Ultimately, this orchestrated sequence of events served to enhance the anti-tumor immunoresponse within the organism.

Glucose oxidase-instructed biomineralization of calcium-based biomaterials for biomedical applications

In recent years, glucose oxidase (GOx) has aroused great research interest in the treatment of diseases related to abnormal glucose metabolisms like cancer and diabetes. However, as a kind of endogenous oxido-reductase, GOx suffers from poor stability and system toxicity in vivo. In order to overcome this bottleneck, GOx is encapsulated in calcium-based biomaterials (CaXs) such as calcium phosphate (CaP) and calcium carbonate (CaCO3) by using it as a biotemplate to simulate the natural biomineralization process. The biomineralized GOx holds improved stability and reduced side effects, due to the excellent bioactivity, biocompatibitliy, and biodegradability of CaXs. In this review, the state-of-the-art studies on GOx-mineralized CaXs are introduced with an emphasis on their application in various biomedical fields including disease diagnosis, cancer treatment, and diabetes management. The current challenges and future perspectives of GOx-mineralized CaXs are discussed, which is expected to promote further studies on these smart GOx-mineralized CaXs biomaterials for practical applications.

Alumina-Hydroxyapatite Millimetric Spheres for Cadmium(II) Removal in Aqueous Medium

Heavy metals can act as selective agents in the development and proliferation of antibiotic-resistant bacteria through a process called coselection. In the year 2050, an estimated 10 million deaths will be caused by antibiotic-resistant bacteria; therefore, the presence of heavy metals in bodies of water represents an environmental and sanitary threat that requires efficient treatment processes and/or materials for their removal. In the present study, the effect of the hydroxyapatite coating on the adsorbent capacity of cadmium in alumina spheres was evaluated. The hydroxyapatite coating on the alumina sphere increased the surface area from 0.66 to 0.96 m2/g and the number of acid sites from 0.064 to 0.306 meq/g and displaced the IEP of hydroxyapatite from 5.37 to 4.2, increasing the Cd2+ adsorbing capacity from 59.87 mg/g to 89.37 mg/g and promoting adsorption by surface complexation. Alumina-hydroxyapatite spheres stand out for their improved adsorbent properties and easy handling, which positioned this material as a potential alternative in adsorption processes.

Synthesis Technology of Magnesium-Doped Nanometer Hydroxyapatite: A Review

Ion substitution techniques for nanoparticles have become an important neighborhood of biomedical engineering and have led to the development of innovative bioactive materials for health systems. Magnesium-doped nanohydroxyapatite (Mg-nHA) has good bone conductivity, biological activity, flexural strength, and fracture toughness due to particle doping technology, making it an ideal candidate material for biomedical applications. In this Review, we have systematically presented the synthesis methods of Mg-nHA and their application in the field of biomedical science and highlighted the pros and cons of each method. Finally, some future prospects for this important neighborhood are proposed. The purpose of this Review is to provide readers with an understanding of this new field of research on bioactive materials with innovative functions and systematically introduce the latest technologies for obtaining uniform, continuous, and morphologically diverse Mg-nHA.

Nanocore-Shell Bone Filler Contained Mesoporous Silica Modified with Hydroxyapatite Precursors; Wrapped in a Natural Metal-Phenolic Network

Various therapeutic strategies have been developed to address bone diseases caused by aging society and skeletal defects caused by trauma or accidental events. One such approach is using bone fillers, such as hydroxyapatite (HA) and bioactive glasses. Although they have provided effective osteogenesis, infection and inflammation due to the surgical procedure and uncontrolled ion release can hinder the efficiency of bone regeneration. In response to these challenges, immobilizing a neutral metal-phenolic network on the surface of osteoconductive nanoparticles would be the master key to achieving a gradual, controlled release during the mineralization period and reducing infection and inflammation through biological pathways. In this regard, a mesoporous silica nanocomposite modified by an HA precursor was synthesized to enhance bone regeneration. In addition, to improve the therapeutic effects, its surface was wrapped with a magnesium-phenolic network made from pomegranate extract, which can simultaneously produce anti-inflammatory and antibacterial effects. The obtained core-shell nanocomposite was characterized by its physicochemical properties, biocompatibility, and bioactivity. The in vitro studies revealed that the synthesized nanocomposite exhibits higher osteogenic activity than the control groups, as confirmed by alizarin red staining. Moreover, the nanocomposite maintained low toxicity as measured by the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay and increased antibacterial activity against Staphylococcus aureus and Escherichia coli compared with the control groups. Therefore, this research presents a promising strategy for bone regeneration, combining the advantages of mesoporous silica nanocomposite modified by an HA precursor with the beneficial effects of a magnesium-phenolic network.

Towards Polycaprolactone-Based Scaffolds for Alveolar Bone Tissue Engineering: A Biomimetic Approach in a 3D Printing Technique

The alveolar bone is a unique type of bone, and the goal of bone tissue engineering (BTE) is to develop methods to facilitate its regeneration. Currently, an emerging trend involves the fabrication of polycaprolactone (PCL)-based scaffolds using a three-dimensional (3D) printing technique to enhance an osteoconductive architecture. These scaffolds are further modified with hydroxyapatite (HA), type I collagen (CGI), or chitosan (CS) to impart high osteoinductive potential. In conjunction with cell therapy, these scaffolds may serve as an appealing alternative to bone autografts. This review discusses research gaps in the designing of 3D-printed PCL-based scaffolds from a biomimetic perspective. The article begins with a systematic analysis of biological mineralisation (biomineralisation) and ossification to optimise the scaffold's structural, mechanical, degradation, and surface properties. This scaffold-designing strategy lays the groundwork for developing a research pathway that spans fundamental principles such as molecular dynamics (MD) simulations and fabrication techniques. Ultimately, this paves the way for systematic in vitro and in vivo studies, leading to potential clinical applications.

Hydroxyapatite: A journey from biomaterials to advanced functional materials

Hydroxyapatite (HAp), a well-known biomaterial, has witnessed a remarkable evolution over the years, transforming from a simple biocompatible substance to an advanced functional material with a wide range of applications. This abstract provides an overview of the significant advancements in the field of HAp and its journey towards becoming a multifunctional material. Initially recognized for its exceptional biocompatibility and bioactivity, HAp gained prominence in the field of bone tissue engineering and dental applications. Its ability to integrate with surrounding tissues, promote cellular adhesion, and facilitate osseointegration made it an ideal candidate for various biomedical implants and coatings. As the understanding of HAp grew, researchers explored its potential beyond traditional biomaterial applications. With advances in material synthesis and engineering, HAp began to exhibit unique properties that extended its utility to other disciplines. Researchers successfully tailored the composition, morphology, and surface characteristics of HAp, leading to enhanced mechanical strength, controlled drug release capabilities, and improved biodegradability. These modifications enabled the utilization of HAp in drug delivery systems, biosensors, tissue engineering scaffolds, and regenerative medicine applications. Moreover, the exceptional biomineralization properties of HAp allowed for the incorporation of functional ions and molecules during synthesis, leading to the development of bioactive coatings and composites with specific therapeutic functionalities. These functionalized HAp materials have demonstrated promising results in antimicrobial coatings, controlled release systems for growth factors and therapeutic agents, and even as catalysts in chemical reactions. In recent years, HAp nanoparticles and nanostructured materials have emerged as a focal point of research due to their unique physicochemical properties and potential for targeted drug delivery, imaging, and theranostic applications. The ability to manipulate the size, shape, and surface chemistry of HAp at the nanoscale has paved the way for innovative approaches in personalized medicine and regenerative therapies. This abstract highlights the exceptional evolution of HAp, from a traditional biomaterial to an advanced functional material. The exploration of novel synthesis methods, surface modifications, and nanoengineering techniques has expanded the horizon of HAp applications, enabling its integration into diverse fields ranging from biomedicine to catalysis. Additionally, this manuscript discusses the emerging prospects of HAp-based materials in photocatalysis, sensing, and energy storage, showcasing its potential as an advanced functional material beyond the realm of biomedical applications. As research in this field progresses, the future holds tremendous potential for HAp-based materials to revolutionize medical treatments and contribute to the advancement of science and technology.

Synthesis and characterization of hydroxyapatite nanoparticles and their effects on remineralization of demineralized enamel in the presence of Er,Cr: YSGG laser irradiation

BACKGROUND

This study aims to synthesize and characterize hydroxyapatite nanoparticles (nano-HA) and evaluate their effects on the remineralization of demineralized enamel in the presence to Er,CR: YSGG laser irradiation.

MATERIALS AND METHODS

Enamel specimens from 44 human molars were divided into four groups: control, demineralized enamel, demineralized enamel treated with nano-HA, and demineralized enamel treated with nano-HA followed by Er,Cr:YSGG laser irradiation (0.5, 20 Hz, 60 µs, 20 s). Vickers microhardness test was used to evaluate the enamel surface hardness. The morphology and chemistry of enamel surfaces were assessed using scanning electron microscopy (SEM) and Raman spectroscopy, respectively.

RESULT

The result of this study showed that the application of Er,CR: YSGG laser irradiation to demineralized enamel treated with nano-HA had the highest impact on its microhardness.

CONCLUSION

ER,CR: YSGG laser irradiation promotes enamel remineralization after treatment with nano HA.

Design and fabrication of biomimicking radially graded scaffolds via digital light processing 3D printing for bone regeneration

Scaffolds are an essential component in bone tissue engineering (BTE). However, most of the current BTE scaffolds are homogeneous structures and do not resemble the graded architectures of native bone. In the current study, four types of biomimicking scaffold designs based on gyroid (G) and primitive (P) units with radially graded pore sizes were devised, and scaffolds of these designs with two porosity groups (65 vol% and 75 vol%) were fabricated via digital light processing (DLP) 3D printing using biphasic calcium phosphate (BCP). Scaffolds of the gyroid-gyroid (G-G) design displayed better dimensional accuracy, compressive property, and cell proliferation rate than gyroid-primitive (G-P), primitive-gyroid (P-G), and primitive-primitive (P-P) scaffolds. Subsequently, graded G-G scaffolds with different porosities were fabricated and the relationship between compressive strength and porosity was determined. Furthermore, the sintered BCP bioceramics fabricated via current manufacturing process exhibited excellent biocompatibility and bioactivity, indicating their high potential for BTE.

Biocompatible, Europium-Doped Fluorapatite Nanoparticles as a Wide-Range pH Sensor

The development of a simple, biocompatible, pH sensor with a wide range of detection, using a single fluorescent probe is highly important in the medical field for the early detection of diseases related to the pH change of tissues and body fluids. For this purpose, europium-doped fluorapatite (FAP: Eu) nanoparticles were synthesized using the coprecipitation method. Doping with the rare earth element europium (Eu) makes the non-luminescent phosphate mineral fluorapatite, luminescent. The luminous response of the sample upon dissolution in hydrochloric acid (HCl), in highly acidic to weakly basic media, makes it a potential pH sensor. A linear variation was observed with an increase in pH, in both the total intensity of emission and the R-value or the asymmetry ratio. The ratiometric pH sensing enabled by the variation in R-value makes the sensor independent of external factors. The structural, optical, and photoluminescent (PL) lifetime analysis suggests a particle size-dependent pH sensing mechanism with the changes in the coordinated water molecules around the Eu3+ ion in the nanoparticle. Given its exceptional biocompatibility and pH-dependent fluorescence intensity for a wide range of pH from 0.83 to 8.97, the probe can be used as a potential candidate for pH sensing of biological fluid.

Sol-Gel Technologies to Obtain Advanced Bioceramics for Dental Therapeutics

The aim of this work is to review the application of bioceramic materials in the context of current regenerative dentistry therapies, focusing on the latest advances in the synthesis of advanced materials using the sol-gel methodology. Chemical synthesis, processing and therapeutic possibilities are discussed in a structured way, according to the three main types of ceramic materials used in regenerative dentistry: bioactive glasses and glass ceramics, calcium phosphates and calcium silicates. The morphology and chemical composition of these bioceramics play a crucial role in their biological properties and effectiveness in dental therapeutics. The goal is to understand their chemical, surface, mechanical and biological properties better and develop strategies to control their pore structure, shape, size and compositions. Over the past decades, bioceramic materials have provided excellent results in a wide variety of clinical applications related to hard tissue repair and regeneration. Characteristics, such as their similarity to the chemical composition of the mineral phase of bones and teeth, as well as the possibilities offered by the advances in nanotechnology, are driving the development of new biomimetic materials that are required in regenerative dentistry. The sol-gel technique is a method for producing synthetic bioceramics with high purity and homogeneity at the molecular scale and to control the surfaces, interfaces and porosity at the nanometric scale. The intrinsic nanoporosity of materials produced by the sol-gel technique correlates with the high specific surface area, reactivity and bioactivity of advanced bioceramics.

Effect of foliar application of phosphorus nanoparticles on the performance and sustainable agriculture of sweet corn

Traditional phosphorus fertilizers are necessary for plant growth but about 80-90% are lost into the surrounding environment via irrigation, therefore nano-fertilizers have been developed as slow-release fertilizers to achieve sustainable agriculture. This trial investigated the impact of the foliar application of hydroxyapatite nanoparticles (HA-NPs) as a source of nano-phosphorus (P-NPs) on two cultivars of sweet corn (yellow and white) throughout two seasons. The morphology and structure of the prepared HA-NPs were characterized via transmission electron microscopy (TEM) and X-ray diffractometry (XRD). In addition, agro-morphological criteria, chemical contents (i.e., photosynthetic pigments, phenols, indoles, minerals, etc.), and genomic template stability percentage (GTS%) were evaluated in the produced sweet corn. The application of 50 mg/l HA-NPs improved the growth characteristics, yield per hectare, leaf pigments, and chemical content of yellow sweet corn, whereas the application of 100 mg/l of HA-NPs to white sweet corn enhanced the vegetative characteristics, production, photosynthetic pigments, phenols, and indoles. The difference in results may be due to the presence of a +ve unique band with SCoT-4 and SCot-2 primers at 1250 and 470 bp in yellow and white corn treated with 50 and 100 mg/l, respectively. The minimum GTS% was recorded at a concentration of 75 mg/l for both white and yellow corn. The HA-NPs can be applied as a foliar source of P-NPs to achieve agricultural sustainability.

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.

Latest Research of Doped Hydroxyapatite for Bone Tissue Engineering

Bone tissue engineering has attracted great interest in the last few years, as the frequency of tissue-damaging or degenerative diseases has increased exponentially. To obtain an ideal treatment solution, researchers have focused on the development of optimum biomaterials to be applied for the enhancement of bioactivity and the regeneration process, which are necessary to support the proper healing process of osseous tissues. In this regard, hydroxyapatite (HA) has been the most widely used material in the biomedical field due to its great biocompatibility and similarity with the native apatite from the human bone. However, HA still presents some deficiencies related to its mechanical properties, which are essential for HA to be applied in load-bearing applications. Bioactivity is another vital property of HA and is necessary to further improve regeneration and antibacterial activity. These drawbacks can be solved by doping the material with trace elements, adapting the properties of the material, and, finally, sustaining bone regeneration without the occurrence of implant failure. Considering these aspects, in this review, we have presented some general information about HA properties, synthesis methods, applications, and the necessity for the addition of doping ions into its structure. Also, we have presented their influence on the properties of HA, as well as the latest applications of doped materials in the biomedical field.

Current surface modification strategies to improve the binding efficiency of emerging biomaterial polyetheretherketone (PEEK) with bone and soft tissue: A literature review

PURPOSE

The aim of this study was to review the literature on current surface modification strategies used to improve the binding efficiency of an emerging biological material, polyetheretherketone (PEEK), with bone and soft tissues.

STUDY SELECTION

This review was based on articles retrieved from PubMed, Google Scholar, Web of Science, and ScienceDirect databases. The main keywords used during the search were "polyetheretherketone (PEEK)," "implant," "surface modification," "biomaterials," "bone," "osseointegration," and "soft tissue."

RESULTS

The suitability of PEEK surface modification strategies has been critically analyzed and summarized here. Many cell and in vivo experiments in small animals have shown that the use of advanced modification technologies with appropriate surface modification strategies can effectively improve the surface inertness of PEEK, thereby improving its binding efficiency with bone and soft tissues.

CONCLUSIONS

Surface modifications of PEEK have revealed new possibilities for implant treatment; however, most results are based on in vitro or short-term in vivo evaluations in small animals. To achieve a broad application of PEEK in the field of oral implantology, more in vivo experiments and long-term clinical evaluations are needed to investigate the effects of various surface modifications on the tissue integration ability of PEEK to develop an ideal implant material.

Fabrication and Characterisation of Calcium Sulphate Hemihydrate Enhanced with Zn- or B-Doped Hydroxyapatite Nanoparticles for Hard Tissue Restoration

A composite based on calcium sulphate hemihydrate enhanced with Zn- or B-doped hydroxyapatite nanoparticles was fabricated and evaluated for bone graft applications. The investigations of their structural and morphological properties were performed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy techniques. To study the bioactive properties of the obtained composites, soaking tests in simulated body fluid (SBF) were performed. The results showed that the addition of 2% Zn results in an increase of 2.27% in crystallinity, while the addition of boron causes an increase of 5.61% compared to the undoped HAp sample. The crystallite size was found to be 10.69 ± 1.59 nm for HAp@B, and in the case of HAp@Zn, the size reaches 16.63 ± 1.83 nm, compared to HAp, whose crystallite size value was 19.44 ± 3.13 nm. The mechanical resistance of the samples doped with zinc was the highest and decreased by about 6% after immersion in SBF. Mixing HAp nanoparticles with gypsum improved cell viability compared to HAp for all concentrations (except for 200 µg/mL). Cell density decreased with increasing nanoparticle concentration, compared to gypsum, where the cell density was not significantly affected. The degree of cellular differentiation of osteoblast-type cells was more accentuated in the case of samples treated with G+HAp@B nanoparticles compared to HAp@B. Cell viability in these samples decreased inversely proportionally to the concentration of administered nanoparticles. From the point of view of cell density, this confirmed the quantitative data.

Biocompatibility analysis and chemical characterization of Mn-doped hydroxyapatite

The present work studies the effect of Mn doping on the crystalline structure of the Hap synthesized by the hydrothermal method at 200 °C for 24 h, from Ca(OH)2 and (NH4)2HPO4, incorporating MnCl2 to 0.1, 0.5, 1.0, 1.5 and 2.0 %wt of Mn concentrations. Samples were characterized by the X-Ray Diffraction technique, which revealed the diffraction peaks that corresponded to the hexagonal and monoclinic phase of the Hap; it was observed that the average size of crystallite decreased from 23.67 to 22.69 nm as the concentration of Mn increased. TEM shows that in all samples, there are two distributions of particle sizes; one corresponds to nanorods with several tens of nanometers in length, and the other in which the diameter and length are very close. FTIR analysis revealed absorption bands corresponding to the PO4-3 and OH- groups characteristic of the Hap. It was possible to establish a substitution mechanism between the Mn and the ions of Ca+2 of the Hap. From the Alamar blue test, a cell viability of 86.88% ± 5 corresponding to the sample of Hap at 1.5 %wt Mn was obtained, considered non-cytotoxic according to ISO 10993-5. It also evaluated and demonstrated the good osteoinductive properties of the materials, which were verified by histology and immunofluorescence expression of osteogenic markers. Adhesion, viability, biocompatibility and osteoinductive properties, make these materials candidates for future applications in bone tissue engineering with likely uses in regenerative medicine.