ABSTRACT This review examines apatite formation on hydroxyapatite (HAp) based biomaterials in simulated body fluid (SBF), considering the combined effects of surface structure, synthesis conditions, chemical composition, and exposure time. It first explains apatite nucleation on charged HAp surfaces through ion exchange, amorphous calcium phosphate formation, and subsequent conversion into bone‐like nanocrystalline apatite. The second part examines how crystallinity, morphology, surface area, and hierarchical pore structure influence apatite formation on HAp‐based materials. Low crystallinity, nanoscale dimensions, and high porosity generally promote early nucleation, whereas highly crystalline HAp may support slower but more controlled growth of a stable apatite layer. The review compares hydrothermal, sol‐gel, wet precipitation, and biomimetic synthesis routes, together with processing variables such as pH and temperature, that govern phase purity, defect density, and morphology. It also evaluates stoichiometric, calcium‐deficient, and ion‐substituted HAp containing Sr, Mg, Mn, Zn, Ti, and graphene‐based phases, emphasizing their effects on dissolution, reactivity, and bioactivity. A time‐resolved overview of apatite development from 0 to 28 days is presented, covering induction, rapid growth, maturation, crystallinity, carbonate incorporation, and Ca/P evolution. Finally, limitations in current SBF protocols are highlighted, and standardized, data‐driven approaches are recommended for improved clinical relevance and mechanistic interpretation.

Enhancing the mechanical and biological performance of hydroxyapatite (HAP) has long been a research focus. In this study, alumina (Al₂O₃) was incorporated into HAP at 5–50 wt

Green synthesized ZnO nanoparticles derived from Azadirachta indica were incorporated into hydroxyapatite (ZnO-HAp) to enhance its mechanical strength and biocompatibility. Structural changes were studied using FESEM, EDX, and FTIR, while mechanical properties were assessed via the Vickers hardness tester. The ZnO-HAp nanocomposite exhibited a remarkable fivefold increase in hardness due to the reduction in grain size. Corrosion resistance also increased three times after doping with respect to the pure HAp. ZnO-HAp composite shows lower absorbance at 540 nm than pure HAp with time, suggesting quicker clot formation and therefore greater thrombogenicity. A significant improvement in antioxidant and antibacterial activities is also observed. A mechanistic model is proposed to explain the antimicrobial behavior against both Gram-negative and Gram-positive bacteria. The ZnO-HAp nanocomposite showed superior free radical scavenging activity compared to pure HAp. Cytotoxicity and cell viability studies using the L929 cell line confirmed its potential for supporting cell growth. The enhanced mechanical, corrosion-resistant, and biological properties are attributed to structural changes induced by the incorporation of ZnO nanoparticles.

Hydroxyapatite (HAp) is a widely used bioceramic for bone repair due to its excellent biocompatibility and bioactivity. In this work, the in vitro apatite-forming ability of pure HAp and 5 wt% Al2O3-doped HAp was investigated after immersion in phosphate buffered saline (PBS) for different durations. The evolution of elemental composition, surface morphology, crystallinity, wettability, and antibacterial behavior was studied using EDS, FESEM, AFM, XRD, and optical contact angle measurements. Both samples exhibited time-dependent apatite reprecipitation; however, the Al2O3-doped HAp showed faster peak sharpening, reduced FWHM, and larger crystallite growth, indicating accelerated nucleation and enhanced crystallinity. Quantitative XRD analysis revealed a reduction in FWHM of the (211) reflection from 0.2188 to 0.0818 for the doped sample over 28 days, corresponding to crystallite growth up to 105.55 nm. AFM analysis showed an increase in average surface roughness from 52.50 nm (pure HAp) to 62.31 nm for the doped sample, while water contact angle decreased from 21.23 degrees to 11.58 degrees, indicating enhanced hydrophilicity and higher surface energy (77.84 mN/m). EDS results confirmed progressive Ca/P enrichment during immersion, and no secondary alumina-related phases were detected in XRD patterns, confirming phase stability and homogeneous dispersion. In addition, a significantly enhanced antibacterial response was observed for the doped HAp due to surface-mediated effects. The absence of secondary phases confirmed good phase stability. The novelty of this study lies in correlating time-dependent apatite reprecipitation kinetics with surface energy, nanoscale roughness, and antimicrobial response in a low (5 wt%) alumina-doped HAp system under PBS conditions.Overall, 5 wt%Al2O3 doping effectively improves the bioactivity, wettability, and antimicrobial performance of HAp, highlighting its potential for advanced orthopedic and dental implant applications.

Silver ions possess inherent antioxidant properties, whereas hydroxyapatite (HAP) is a structural support within the body. The research methodology involves synthesizing HAP and 3% silver-doped hydroxyapatite (Ag-HAP) via the sol-gel method, followed by comprehensive characterization using X-ray diffraction, Fourier transform infrared, Raman spectroscopy, and field emission scanning electron microscopy, antioxidant, thrombogenicity, and cell viability. The investigation reveals that Ag-HAP exhibits superior antioxidant properties and thrombogenicity compared to other metals doped so far. Remarkably, Ag-HAP demonstrates moderate clotting behavior compared to HAP. Additionally, the (3-(4, 5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide) MTT assay evaluates cellular viability, shedding light on the biocompatibility of the materials. The study uncovers the potential of silver doping to enhance the antioxidant capabilities of HAP significantly, offering promising prospects for orthopaedic implants. The antioxidant activity of the materials is evaluated through a 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay, whereas the thrombogenicity is assessed using a whole blood clotting method. The improvement indicates that incorporating silver ions influences HAP crystalline structure and increased grain size, contributing to enhanced antioxidant efficacy and favorable cellular responses, thus underlining the potential of Ag-HAP for advanced implant materials in orthopaedic surgery. The results also discuss that how Ag-HAP is better than Co-HAP.

Hydroxyapatite (HAp) is a renowned bioceramic, having high biocompatibility, osteoconductivity, and osteogenesis properties. However, its mechanical properties are suboptimal. By introducing a hydrophilic polymer to HAp, a biomaterial with enhanced characteristics is formed. Furthermore, doping HAp with Mg2+, Ag+, and Zn2+ ions significantly boosts its biocompatibility, positioning it as a promising biomaterial. This study focuses on incorporating a low-weight percentage of polyvinyl alcohol (PVA) and the mentioned metal ions into HAp. Analysis via X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), and Raman spectroscopy reveals the successful integration of dopants into the HAp matrix. Composite samples exhibit a more compact morphology with reduced pore count and the crystallite size and cell volume decrease with tri dopants and PVA. The hardness of the composite sample increases and corrosion resistance improves. Dielectric studies confirm the conductive nature of the samples due to PVA. The composite sample's reduced pore size suggests enhanced hardness. Both samples show moderate thrombogenicity. Antimicrobial efficacy against E. coli and S. aureus is notably higher in the composite sample, showcasing its potential as an advanced biomaterial. A mechanism for antimicrobial efficacy

This study investigates the impact of sintering conditions at temperatures of 500, 700, 900, and 1200 °C on the microstructure, phase composition, microhardness, and corrosion resistance of hydroxyapatite (HAp) pellets synthesized using a sol-gel method. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the presence of functional groups characteristic of HAp, while x-ray Diffraction (XRD) revealed the development of crystalline HAp phases with increasing sintering temperature. Crystallite size first decreases from 49.26 nm at 500 °C to 47.64 nm at 700 °C and then increases significantly to 51.72 nm at 900 °C and 110.55 nm at 1200 °C respectively, as measured from the Williamson-Hall equation. Field Emission Scanning Electron Microscopy (FESEM) showed morphological evolution with higher sintering temperatures, including increased grain size and densification. The hardness of the samples, as determined by Vickers microhardness testing, increased from 36.15 HV at 500 °C to a maximum of 41.69 HV at 1200 °C, indicating enhanced mechanical properties at higher sintering temperatures. Corrosion resistance, evaluated through electrochemical analysis in Ringer’s solution, showed superior performance at lower sintering temperatures, with the 500 °C sample exhibiting the lowest corrosion current density of 20.70 µA/cm2. This study highlights the relationship between sintering temperature, microstructural evolution, and hardness and corrosion resistance of HAp, offering insights into optimizing these materials for biomedical applications.

The research investigates the integration of 3% silver-doped hydroxyapatite (Ag-HAP) onto a hexagonal alumina substrate with a matching structure to reduce interface strain utilizing radio frequency magnetron sputtering (RFMS). This method aims to improve film adhesion while enhancing the bioactivity, antimicrobial properties, and wear resistance of biomedical implants. Hydroxyapatite (HAP) has excellent biocompatibility and is widely used in bone implants due to its similarity to bone minerals, but it suffers from brittleness and limited mechanical strength. By doping Ag with HAP, mechanical and antimicrobial properties are enhanced, addressing infection and material longevity challenges. Alumina (Al2O3) is known for its mechanical strength and wear resistance, making it a suitable substrate for implants; however, its lack of bioactivity requires modification. The RFMS technique ensures a uniform and well-adhered nanocoating of Ag-HAP on alumina, creating a composite material that balances alumina's durability with silver-doped HAP bioactivity and antimicrobial benefits. The study reveals improved mechanical properties, such as increased hardness and wear resistance, along with enhanced antibacterial efficacy, making the composite material promising for orthopedic applications. The characterization of coatings using various analytical techniques such as EDS, FESEM, FTIR, and XRD confirms the formation and stability of Ag-HAP, while electrical properties are described by dielectric measurements. The changes in the lattice parameters, grain size, and pore size led to changes in hardness, coefficient of friction, and ultimately, the material's biocompatibility. Improvement in corrosion resistance after coating can be due to intermetallic compound formation at the interface. Biocompatibility was studied through assays that show favorable results, supporting the potential of Ag-HAP/Al2O3 in implantology. The mechanism of improvement in the antibacterial mechanism against E. coli and S. aureus is proposed. This research proposes a novel solution to implant-related challenges by combining silver-doped hydroxyapatite mechanical and biological advantages with alumina, thereby optimizing both biocompatibility and structural integrity for long-term use in biomedical implants.

This research investigates the enhancement of mechanical, physicochemical, and biocompatible properties of cobalt-doped hydroxyapatite (Co-HAP) nanocoatings on alumina (Al2O3) substrates using RF magnetron sputtering. Pure HAP and Co-HAP powders were synthesized via the sol-gel method and pressed into 3-inch pellet targets. Thin films of 100 nm of HAP and Co-HAP were deposited on alumina to evaluate improvements over pure HAP pellets, pure alumina pellets, and undoped HAP coatings on alumina (HAP/Al2O3). Characterization was performed using FESEM, EDS, GIXRD, and BET analyses. Tafel plots in Ringer's solution assessed corrosion resistance, while FESEM after immersion in simulated body fluid revealed apatite formation. Co-HAP/Al2O3 exhibited superior hardness (1189 HV compared to 39.49 HV for HAP), reduced corrosion rate (0.50 vs. 60.94 mmpy), enhanced adhesion, and improved antimicrobial activity against E. coli and S. aureus. BET results confirmed increased surface area and pore volume, promoting better implant integration. Additionally, the dielectric constant of Co-HAP/Al2O3 was comparable to natural bone. Although the coatings exhibited hydrophobic behavior, the overall findings establish Co-HAP/Al2O3 as a promising candidate for orthopedic implant applications, owing to its enhanced mechanical strength, biocompatibility, corrosion resistance, and antimicrobial efficacy.

The development of green technology is generating interest of researchers towards utilization of environmental-friendly, cost-effective, economical in nature and biocompatible reducing agents for the synthesis of nanoparticles. The main objective of this study was the synthesis of Ag2O NPs from the roots of the Kniphofia foliosa and evaluates the antioxidant activity. The chemical constituents of the root extract of K. foliosa were analyzed using standard phytochemical screening methods. Green synthesis of Ag2O NPs was done, and the material was characterized by using were characterized using UV–Vis, FTIR, XRD and SEM. Both the extract and synthesized NPs were evaluated as antioxidant property for medical application. The crystalline size of the formed nanoparticle was obtained to be 30.84 nm from the XRD data by using Scherrer formula. The morphological makeup of the nanoparticles was determined using SEM examination showed small sized spherical nanoparticles. The phytochemicals in root extract indicated the presence of alkaloids, flavonoids, phenols, anthraquinone and tannins. The synthesis of Ag₂O nanoparticles (NPs) from Kniphofia foliosa roots demonstrated a significant antioxidant activity of 97.29 % in the DPPH assay, surpassing the 69.21 % activity of the methanol extract. This correlation suggests that the green synthesis method not only produces effective NPs but also enhances their potential for medical applications.

Materials possessing low density and high specific strength are essential for enhancing the performance and fuel efficiency of gas turbine engines in aerospace applications. IMI 834 is specifically engineered for hightemperature environments up to 873 K. However, its application in components such as jet engine compressor is constrained by surface oxidation occurring near 500 degrees C, which leads to the formation of a brittle oxygenenriched surface layer and consequent degradation in mechanical performance. To mitigate this limitation, plasma nitriding was employed at 500 degrees C for 8 h to enhance its oxidation resistance. Comprehensive structural and surface characterization was conducted FTIR, FESEM, XRD, XPS, and SXAS, with elemental composition assessed using EDS, RBS. EDS and SXAS analysis confirmed nitrogen incorporation responsible for the formation of TiN as revealed by XRD, affirming the uniform and continuous TiN layer as observed using FESEM. Vickers hardness measurements demonstrated two-fold increase in surface hardness at 1kgf, attributed to the presence of the hard TiN phase. Furthermore, high-temperature oxidation tests conducted at 1000 degrees C for 48 h exhibited substantially reduced mass gain in the plasma nitrided sample, indicating improved oxidation resistance. These findings establish a clear correlation between the formation of the TiN surface layer responsible for the enhancement in mechanical hardness and oxidation resistance. The study validates plasma nitriding as an effective surface modification strategy for extending the high-temperature applicability of IMI 834 alloy in demanding aerospace environments.

The antioxidant activity of 3 wt% copper-doped hydroxyapatite (Cu-HAP) was evaluated using the DPPH radical-scavenging assay. Cu-HAP was synthesised by the sol-gel technique, and its structural properties were characterised using energy-dispersive X-ray spectroscopy (EDX), field-emission scanning electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The XRD analysis reveals that the Ca atom is substituted by the Cu atom in pure HAP, decreasing the crystallite size. FESEM analysis confirms grain size reduction from 134.99 to 72.69 nm. Better apatite formation in SBF solution is observed in Cu-HAP in comparison to pure HAP using FESEM. The DPPH test showed that samples displayed significant DPPH radical scavenging capability in a dose-dependent fashion. A plausible mechanism of the antioxidation activity of Cu-HAP with standard DPPH is discussed. It is observed that Cu-doped HAP samples showed better antioxidant activity than pure HAP, excelling in scavenging ability at specific concentrations. Improved IC50 value of 25.03 for Cu-HAP sample is measured in comparison to 35 for pure HAP. In vitro cytotoxicity assay with L929 cell lines shows better cell viability at lower concentrations for the Cu-HAP in comparison to pure HAP.

Hydroxyapatite (HAP), a cornerstone of bone and teeth, has ignited interest due to its potential bioactivity and therapeutic implications. This study comprehensively assesses the multifaceted nature of HAP, delving into its antioxidant, thrombogenic, and cytocompatibility properties. HAP was synthesized via the sol-gel method, achieving a Ca/P ratio 1.66, confirmed by energy-dispersive X-ray spectroscopy (EDS). X-ray diffraction (XRD) verified compound formation, while Fourier transform infrared spectroscopy (FTIR) identified functional groups. Field emission electron microscopy revealed the surface morphology of HAP. Its structural characterization delves into HAP’s functional potential. Utilizing the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, pure HAP’s ability to neutralize free radicals, a symbol of antioxidant activity, was evaluated. Additionally, thrombogenic studies using the whole blood clotting assay explored HAP’s influence on blood clotting, a crucial factor for biocompatibility. The MTT (3-(4, 5-dimethythiazol-2-yl)-2, 5-diphenyl tetrazolium bromide) assay was employed in the L929 cell line to assess its interaction with living cells further, shedding light on HAP’s cytotoxicity or potential cell viability enhancement.

Hydroxyapatite (HAp) is a well-known biomaterial due to its bioactivity, osteoconductivity and biocompatibility. The present research aims to study the effects of addition of a polymer and two different ions in the HAp matrix to make it a better participant to function as an orthopaedic implant. The polymer taken for the study is polyvinyl alcohol and ions taken was magnesium (Mg2+) and zinc (Zn2+) ions. The synthesis of Pure HAp and composite fabricated HAp was performed using ethanol-based Sol-gel method. The X-Ray diffractions studies showed that composite fabricated showed slight increase in the crystallite size than Pure HAp with a value of 39.7363 nm. Moreover, both the lattice parameters 'a' and 'c' showed an increase with values of 9.41 (& Aring;) and 6.92 (& Aring;) respectively. The corrosion rate as calculated from the Tafel plot was found to be lower for composite sample in comparison to pure HAp with a value of 3.95 mmpy. Lower pore size and lower pore volume was exhibited by the composite sample as calculated from BET studies. The composite samples exhibited good antimicrobial activity against both E. coli and S. aureus bacteria.The composite fabricated samples could be a potential participant to function as a future hard tissue implant.

This research investigates the antioxidant properties and thrombogenic evaluation of a novel biomaterial-copper and manganese doped hydroxyapatite (CuMn-HAP) in comparison to un-doped hydroxyapatite (HAP). The alloy, containing 1 wt% Cu and 2 wt% Mn, introduces advanced functionalities to enhance clinical outcomes. Essential trace elements, Cu and Mn, are strategically incorporated due to their established roles as micronutrients with antioxidant properties. The study employs microstructural investigation, phase and compound formation, changes in absorbance, clotting behaviour of the blood, and antioxidant behaviour. Comprehensive synthesis, characterization, and in vitro evaluation methods reveal the alloy 's potential to mitigate oxidative stress and reduce thrombotic risk. This exploration contributes to biomaterials science, addressing critical issues in implantable materials and promising improved outcomes for regenerative medicine and medical devices.

Paper describes the doping of hydroxyapatite (HAp) with three different metal ions Mg2+, Ag+ and Zn2+ for enhancing the biocompatibility of HAp. Samples morphology reveals an increase in grain size and the presence of rod-like structures. Tri dopants cause the crystallite size and cell volume to decrease. The sample was found to become harder. Rate of corrosion improved by 14 % as studied in the Ringer's solution. The dielectric studies confirmed that the samples were conducting in nature due to the presence of PVA in the sample. Lesser number of pores was observed for the composite sample which implied improved hardness of those samples. Clotting behaviour decreased after doping due to the increased conducting behaviour after the doping. To test the antibacterial activity, two strains of the bacteria E. coli and S. aureus were used. 10 wt% PVA-Ag/Mg/Zn-HAp demonstrated higher efficacy against both the strains of the bacteria.

Direct numerical simulation (DNS) is very accurate; however, the computational cost increases significantly with the increase in Reynolds number. On the other hand, we have the Reynolds-averaged Navier–Stokes (RANS) method for simulating turbulent flows, which needs less computational power. Turbulence models based on linear eddy viscosity models (LEVM) in the RANS method, which use a linear stress–strain rate relationship for modeling the Reynolds stress tensor, do not perform well for complex flows (Shih et al. in Comput Methods Appl Mech Eng 125:287–302, 1995). In this work, we intend to study the performance of nonlinear eddy viscosity model (NLEVM) hypothesis for turbulent forced plumes in a linearly stratified environment and modify the standard RANS model coefficients obtained from machine learning. The general eddy viscosity hypothesis supported by the closure coefficients generated from the tensor basis neural network (TBNN) is used to develop TBNN-based K-ϵ model. The aforementioned model is used to evaluate the plume’s mean velocity profile, and maximum height reached. The comparison between standard LEVM, NLEVM, and the experimental results indicates a significant improvement in the maximum height achieved, and a good improvement in the mean velocity profile.

In the present work, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay was used to examine the antioxidant activity of hydroxyapatite (HAP) and of 3 % cobalt doped HAP (Co-HAP). The DPPH assay revealed that 3 % Co-HAP had significant DPPH radical scavenging activity. Co-HAP was synthesised using the sol-gel method, and its characteristics were assessed using energy-dispersive X-ray spectroscopy (EDS), Field emission scanning electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). As the ionic radius of Co is smaller than Ca ion, XRD study reveals that crystallite size reduces from 40.82 nm to 24.91 nm after incorporation of Co into HAP implying substitution of Ca by Co ions. Compared to ascorbic acid, Co-HAP showed exceptional antioxidant potential and, at some doses, even outperformed ascorbic acid in scavenging capability. Notably, the IC50 value for pure HAP was 35, whereas it was substantially lower for Co-HAP at 20.85, indicating that it has stronger antioxidant properties. According to these results, 3 % Co-HAP has much potential for biomedical uses, especially in tissue engineering biomaterials and antioxidant-based therapeutics. Its capacity to prevent diseases brought on by oxidative stress and encourage tissue regeneration makes it a promising option for additional biomedical research.

Velocity gradient dynamics play a pivotal role in understanding various nonlinear phenomena in turbulent flows. In the evolution of velocity gradient dynamics, the pressure Hessian and the viscous Laplacian are two mathematically unclosed terms which need separate modeling. The current study models the pressure Hessian term using the tensor basis neural network (TBNN). The network is trained on direct numerical simulation (DNS) data of stationary incompressible turbulence conditioned on local flow topologies. We compare the topology-based TBNN model performance with the DNS results as well as with the unconditioned (raw) TBNN model. The model results are evaluated in terms of the strain rate and the pressure Hessian eigenvector alignments. The model captures some of the essential alignment features of the DNS results.

The objective of the study was to investigate the effects of doping hydroxyapatite (HAp) with Ag+, Mg2+, and Zn2+ ions on its microstructure, physiochemical properties, and mechanical properties for use as a hard tissue implant. The sol-gel wet chemical synthesis method was used to prepare the tri-doped HAp. The insertion of the three metal ions intensified and sharpened X-ray diffraction (XRD) peaks. The study confirmed successful substitution of the metal ions in the HAp matrix using Raman spectra. Brunauer-Emmett-Teller (BET) studies confirmed that tri-doping reduced pore size from 2.48 to 2.06 nm. Surface area decreased from 3.29 to 0.63 m2/ g. These changes led to an increase in the mechanical strength of the tri-doped samples, with a value from 40.36 to 66.01VHN at a 300 gf load. The morphology studies revealed grain agglomeration. The presence of Ag+ reduced the corrosion rate of the alloyed sample compared to pure hydroxyapatite, decreasing it from 60.94 to 35.58 mmpy. The hydroxyapatite with the alloyed ions exhibited a highly hydrophilic surface, with an optical contact angle close to 0 degrees. The clotting behavior of both pure HAp and the alloy-fabricated HAp was found to be moderate. Moreoverlower value of IC50 indicated that Ag/Mg/Zn-HAp was less cytotoxic to the L929 cell line and has greater biocompatibility. In summary, the study suggests that the tri-doping of hydroxyapatite with Ag+, Mg2+, and Zn2+ ions resulted in several beneficial changes, including improved mechanical strength, reducedcorrosion rate, enhanced wettability, and moderate thrombogenicity.These findings are promising for the potential use of tri-doped hydroxyapatite as a material for hard tissue implants.