Nanostructured Hydroxyapatite Research Articles

Agro-Industrial Waste as a Source of Raw Material: Eggshell and Ash of Useful for the Synthesis of Hydroxyapatite

Agave salmiana ash and poultry eggshell powder as CaO sources were used for obtaining nanostructured hydroxyapatite (HAP). The synthesis was carried out by the Green Chemistry Hydrothermal Biosynthesis at 180°C with a pH of 5, by reacting CaO from Agave Salmiana ash and Eggshell powder, with dibasic calcium phosphate (CaHPO4•2H2O) in an aqueous solution, with Aloe barbadensis extract. The product was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The size and shape of the hydroxyapatite particles changed dramatically in the presence of Aloe barbadensis. Large crystals of Hydroxyapatite were observed when Eggshell powder and Agave salmiana ash were used as raw materials in the presence of the Aloe barbadensis surfactant. Crystals with shapes of ribbons and plates from 1 micrometers to 8 micrometers were observed when using the eggshell powder in the presence of Aloe barbadensis and, in the case of Agave salmiana ash in the presence of Aloe barbadensis, crystals with shapes of quadrangular prisms and hexagonal (polyhedra) with sizes from 2 micrometers to 20 micrometers were observed. Hydroxyapatite was therefore successfully biosynthesized by a green and sustainable method that reduces the environmental impact.

The impact of Cu(II) ions doping in nanostructured hydroxyapatite powder: A finite element modelling study for physico-mechanical and biological property evaluation

The synthesis ofdoped nanostructured materialswith multifunctional properties and improved biocompatibility have immense potential for biomedical applications.In this present study, a facile wet chemical precipitation method was employed to synthesize hydroxyapatite (HAp) and different concentrations copper doped HAp, and Cux-HAp (x = 1, 2, and 4 mol%) nano materials. Sophisticated analytical and spectroscopic techniques were employed to confirm its physico-chemical properties, and morphological features. The synthesized HAp, Cux-HAp were further studied as a drug nanocarrier using doxorubicin hydrochloride (DOX) as a model drug, which results a maximum drug release of ∼34.3% (at pH 4.5) for 1 mol% of Cu-HAp. The nanostructured materials were further used to fabricate scaffolds by employing gel-castingmethod.The finite element modeling theoretical approach was adopted, to correlate the force distribution over the developed scaffold during mechanical characterization. The in vitro study confirmed the nontoxic behavior of the HAp and Cux-HAp scaffolds using MG-63 cell line. The developed scaffold effectively facilitates and simulates the new cell attachment, growth, and proliferation on its surface with adequate (∼7.87 MPa) compressive strengthproperties. The enhanced biocompatibility with improved mechanical stability of Cux-HAp nanomaterials could address some of the critical challenges in biomedical applications.

Radiation stability of nanostructured hydroxyapatite Ca10(PO4)6(OH)2 under ion irradiations

Radiation stability of nanostructured hydroxyapatite with different interfacial structure is studied. Hydroxyapatite nanoparticle (HAp-np) is fabricated by calcination in muffle furnace and densified nanocrystalline hydroxyapatite (HAp-nc) is synthesized by spark plasma sintering . X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations show the hexagonal structure for both HAp-np and HAp-nc. Irradiation responses of HAp-np and HAp-nc are studied via in situ TEM techniques. The samples are irradiated with 1 MeV Kr 2+ ions over the temperature range of 150 K to 523 K. In situ TEM observations reveal a higher critical amorphization dose of HAp-nc (0.075 dpa) compared to 0.05 dpa of HAp-np at room temperature, indicating enhanced amorphization resistance. The radiation tolerance shows a great dependence on temperature, and a higher critical dose can be observed at elevated temperatures. A lower critical amorphization temperature ( T c ) of HAp-nc (∼437 K) than HAp-np (∼545 K) indicates better radiation tolerance since the lower T c shows better defect annealing ability. This better radiation tolerance of HAp-nc is attributed to the higher sink strength and lower interface energy carried by densified grain boundaries as free-standing open surfaces of HAp-np can carry more isolated dangling bonds that results in a higher interface energy. This excess interface energy can lower the energy difference between crystalline phase and amorphous state, leading to HAp-np to be less radiation resistant. Radiation-induced amorphization is attributed to the accumulation of oxygen vacancies and the glass-like structure rearranged by displaced oxygen and phosphorus atoms.

Hydroxyapatite nanomaterials with tailored length regulated by different fatty acids

The morphology and structures of hydroxyapatite (HA) nanomaterials greatly influence their physicochemical properties and bio-applications. In this study, HA nanostructures with tailored length regulated by different fatty acids were prepared via a solvothermal route. By using ricinoleic acid, linoleic acid and oleic acid as the template, the growth of HA crystals was regulated and the morphology of HA nanomaterials was transformed from long nanowires to short nanowires and then nanorods. The underlying mechanism for the formation of HA nanomaterials synthesized by different kinds of fatty acids under solvothermal condition was proposed. This study provides a simple and environmentally friendly way to obtain HA nanomaterials with tailored length for biomedical applications.

Synthesis and Characterization of Yttrium-Doped Hydroxyapatite Nanoparticles and Their Potential Antimicrobial Activity

This study reports a detailed analysis of the yttrium doping effects into hydroxyapatite (HAp) nano-structures at different amounts (e.g., 0, 1, 2.5, 5, 7.5, 10, and 15%) on the structural, spectroscopic, dielectric, and antimicrobial properties. For this purpose, seven HAp samples having the Y-contents mentioned above were prepared using the microwave-assisted sol-gel precipitation technique. The structure of synthesized samples was fully described via X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transforms infrared (FTIR). Raman spectroscopy and dielectric measurements were used to characterize the spectroscopic properties. Furthermore, the samples’ antimicrobial features have been assisted through the agar disk diffusion technique. This study showed that the crystallinity decreased with the adding of Y-ions inside the HAp matrix. The Y-contents have influenced the crystallite size, lattice parameters, dislocation density, lattice strain, and unit cell volume. The surface morphology is composed of the agglomerated smaller particles. Remarkable changes in the dielectric properties were observed with the adding of Y-ions. The alternating current conductivity obeys the Jonscher’s relation. Y-doped hydroxyapatite nanoparticles have a considerable inhibitory effect against bacteria and fungi(Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli,andCandida albicans).The Y-doped hydroxyapatite nanoparticles are a promising material for bone cement engineering with a potential bio-activity

PL, TL and Persistent Luminescence Characterization of Undoped and Eu Doped Nanostructured Hydroxyapatite

Hydroxyapatite (HAp, Ca10(PO4)6(OH)2) possesses the closest mineralized structure to natural bone tissue and has been widely using in as bone substitutes and for various biomedical applications. Undoped and doped with rare earth elements HAps are the basis of promising biomedical imaging, bone tissue engineering, gene and drug delivery applications. In the present work, we present the results of investigation of the photoluminescence (PL), thermoluminescence (TL) and persistent luminescence (PersL) of synthetic nanostructured HAp (n-HAp). Undoped and Eudoped (0.0, 0.1, 0.5, 1.0, 2.0 mol %) n-HAp powders were synthesized by solution-precipitation method and characterized by SEM-EDS, FTIR and Raman techniques. The 3D excitation-emission spectrum of undoped n-HAp exhibits a broad band with excitation/emission maximum at 376/454 nm, respectively. The maximum position slightly shifts to shorter excitation and emission wavelengths with increases of the Eu concentration that could be due to a possible overlapping between the Eu emission band and intrinsic emission of undoped n-HAp. It was found that (similarly to behavior of PL in Si nanocrystals, Xin et al., RSC Adv., 2019, 9, 8310) the emission peak is red-shifted as the excitation wavelength red-shifts. The typical Eu3+ emission bands were observed for high Eu doping concentrations. TL glow curves of n-HAp samples exposed to beta radiation from Sr-Y source display a broad TL peak with maxima in-between 145 and 165 oC depending on the Eu concentration. The highest TL intensity is observed for undoped n-HAp, showing quenching effect of Eu on TL emission. This TL quenching effect contrasted with the PersL decay emission measured immediately after irradiation exposure, which was highest for 0.1 mol % Eu. The intrinsic defects in n-HAp host is related to the PL, TL and PersL emissions; however, the nature of the radiative and non-radiative recombination mechanisms requires further investigation. The PL, TL and PersL of undoped HAp may have prospective application in the fields of radiation detection, ionizing radiation dosimetry and biomedical imaging. Keywords: Hydroxylapatite, thermoluminescence, persistent luminescence.

Pulsed laser deposition of nanostructured bioactive glass and hydroxyapatite coatings: Microstructural and electrochemical characterization

Bioactive coatings on metallic implants promote osseointegration between bone and implant interfaces. A suitable coating enhances the life span of the implant and reduces the requirement of revision surgery. The coating process needs to be optimized such that it does not alter the bioactivity of the material. To understand this, the biocompatibility of nanostructured bioactive glass and hydroxyapatite-coated Titanium substrate by pulsed laser deposition method is evaluated. Raman and IR spectroscopic techniques based on silica and phosphate functional groups mapping have confirmed homogeneity in coatings by pulse laser deposition method. Comparative studies on nanostructured bioactive glass and hydroxyapatite on titanium surface elaborated the significance of bioactivity, hemocompatibility, and cytocompatibility of the coated surface. Notably, both hydroxyapatite and bioactive glass show good hemocompatibility in powder form. Hemocompatibility and cytocompatibility results validate the enhanced sustenance for hydroxyapatite coating. These results signify the importance of the choice of coating methodology of bioceramics towards implant applications.

A new thermoshock-based method for rapid preparation of ultra-pure hydroxyapatite nanodebris from bovine bone

Hydroxyapatite can be obtained in its ultra-pure form and ultra-small size under appropriate thermal treatments. To prepare hydroxyapatite nanostructures, commercial bovine bone was heated to 900 °C before the red-hot specimens were rapidly quenched by a water bath at 4 °C. TEM images reveal a debris-like morphology at nanoscale with average size observed under 10 nm. XRD patterns prove neither phase change nor crystalline impurity occurring given the correspondence of all registered peaks with ICDD-PDF No. 00.024.0033. Scherrer’s equation estimates the mean size of granular grains at ca. 5 nm, confirming a quasi-monocrystalline structure going by the consistency with TEM result. EDX data provides demonstration for a high degree of purity, borne out by exclusive five elements Ca, P, Mg, Na, and O trace-detected. The average Ca/P ratio of 1.87 is consistent with the acceptable range for biological hydroxyapatite. Thermal shock behaviour of brittle ceramic hydroxyapatite at nanoscale speculates a top-down approach for the mechanism. Chitosan- and glucosamine-based functionalisation proves potentiality in biological application of the prepared hydroxyapatite nanomaterials. The results introduce a contamination-free and time-effective procedure to prepare biocompatible hydroxyapatite nanostructures from biological sources.

Bioactivity and Antibacterial Behaviors of Nanostructured Lithium-Doped Hydroxyapatite for Bone Scaffold Application.

The material for bone scaffold replacement should be biocompatible and antibacterial to prevent scaffold-associated infection. We biofunctionalized the hydroxyapatite (HA) properties by doping it with lithium (Li). The HA and 4 Li-doped HA (0.5, 1.0, 2.0, 4.0 wt.%) samples were investigated to find the most suitable Li content for both aspects. The synthesized nanoparticles, by the mechanical alloying method, were cold-pressed uniaxially and then sintered for 2 h at 1250 °C. Characterization using field-emission scanning electron microscopy (FE-SEM) revealed particle sizes in the range of 60 to 120 nm. The XRD analysis proved the formation of HA and Li-doped HA nanoparticles with crystal sizes ranging from 59 to 89 nm. The bioactivity of samples was investigated in simulated body fluid (SBF), and the growth of apatite formed on surfaces was evaluated using SEM and EDS. Cellular behavior was estimated by MG63 osteoblast-like cells. The results of apatite growth and cell analysis showed that 1.0 wt.% Li doping was optimal to maximize the bioactivity of HA. Antibacterial characteristics against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were performed by colony-forming unit (CFU) tests. The results showed that Li in the structure of HA increases its antibacterial properties. HA biofunctionalized by Li doping can be considered a suitable option for the fabrication of bone scaffolds due to its antibacterial and unique bioactivity properties.

Hydroxyapatite-Coated Titanium by Micro-Arc Oxidation and Steam-Hydrothermal Treatment Promotes Osseointegration.

Titanium (Ti)-based alloys are widely used in tissue regeneration with advantages of improved biocompatibility, high mechanical strength, corrosion resistance, and cell attachment. To obtain bioactive bone–implant interfaces with enhanced osteogenic capacity, various methods have been developed to modify the surface physicochemical properties of bio-inert Ti and Ti alloys. Nano-structured hydroxyapatite (HA) formed by micro-arc oxidation (MAO) is a synthetic material, which could facilitate osteoconductivity, osteoinductivity, and angiogenesis on the Ti surface. In this paper, we applied MAO and steam–hydrothermal treatment (SHT) to produce HA-coated Ti, hereafter called Ti–M–H. The surface morphology of Ti–M–H1 was observed by scanning electron microscopy (SEM), and the element composition and the roughness of Ti–M–H1 were analyzed by energy-dispersive X-ray analysis, an X-ray diffractometer (XRD), and Bruker stylus profiler, demonstrating the deposition of nano-HA particles on Ti surfaces that were composed of Ca, P, Ti, and O. Then, the role of Ti–M–H in osteogenesis and angiogenesis in vitro was evaluated. The data illustrated that Ti–M–H1 showed a good compatibility with osteoblasts (OBs), which promoted adhesion, spreading, and proliferation. Additionally, the secretion of ALP, Col-1, and extracellular matrix mineralization was increased by OBs treated with Ti–M–H1. Ti–M–H1 could stimulate endothelial cells to secrete vascular endothelial growth factor and promote the formation of capillary-like networks. Next, it was revealed that Ti–M–H1 also suppressed inflammation by activating macrophages, while releasing multiple active factors to mediate osteogenesis and angiogenesis. Finally, in vivo results uncovered that Ti–M–H1 facilitated a higher bone-to-implant interface and was more attractive for the dendrites, which promoted osseointegration. In summary, MAO and SHT-treated Ti–M–H1 not only promotes in vitro osteogenesis and angiogenesis but also induces M2 macrophages to regulate the immune environment, which enhances the crosstalk between osteogenesis and angiogenesis and ultimately accelerates the process of osseointegration in vivo.

3D printing of hierarchical porous biomimetic hydroxyapatite scaffolds: Adding concavities to the convex filaments

Porosity plays a key role on the osteogenic performance of bone scaffolds. Direct Ink Writing (DIW) allows the design of customized synthetic bone grafts with patient-specific architecture and controlled macroporosity. Being an extrusion-based technique, the scaffolds obtained are formed by arrays of cylindrical filaments, and therefore have convex surfaces. This may represent a serious limitation, as the role of surface curvature and more specifically the stimulating role of concave surfaces in osteoinduction and bone growth has been recently highlighted. Hence the need to design strategies that allow the introduction of concave pores in DIW scaffolds. In the current study, we propose to add gelatin microspheres as a sacrificial material in a self-setting calcium phosphate ink. Neither the phase transformation responsible for the hardening of the scaffold nor the formation of characteristic network of needle-like hydroxyapatite crystals was affected by the addition of gelatin microspheres. The partial dissolution of the gelatin resulted in the creation of spherical pores throughout the filaments and exposed on the surface, increasing filament porosity from 0.2 % to 67.9 %. Moreover, the presence of retained gelatin proved to have a significant effect on the mechanical properties, reducing the strength but simultaneously giving the scaffolds an elastic behavior, despite the high content of ceramic as a continuous phase. Notwithstanding the inherent difficulty of in vitro cultures with this highly reactive material an enhancement of MG-63 cell proliferation, as well as better spreading of hMSCs was recorded on the developed scaffolds. Statement of significanceRecent studies have stressed the role that concave surfaces play in tissue regeneration and, more specifically, in osteoinduction and osteogenesis. Direct ink writing enables the production of patient-specific bone grafts with controlled architecture. However, besides many advantages, it has the serious limitation that the surfaces obtained are convex. In this article, for the first time we develop a strategy to introduce concave pores in the printed filaments of biomimetic hydroxyapatite by incorporation and partial dissolution of gelatin microspheres. The retention of part of the gelatin results in a more elastic behavior compared to the brittleness of hydroxyapatite scaffolds, while the needle-shaped nanostructure of biomimetic hydroxyapatite is maintained and gelatin-coated concave pores on the surface of the filaments enhance cell spreading.

A green and economical approach to derive nanostructured hydroxyapatite from Garra mullya fish scale waste for biocompatible energy storage applications

In this work, we spotlight an economical, green fabrication of bio-supercapacitor material using nanostructured hydroxyapatite (FNHAp). FNHAp employed is derived from the abundant fish scale waste acquired from Garra mullya fish via a facile alkaline heat treatment technique. The structural geometry, functional groups, morphological views and compositional analysis has been done by powder X-ray diffractometer (PXRD), Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), and Energy-dispersive X-ray spectroscopy (EDX). All the results authenticate the successful synthesis of FNHAp. The capacitive performance has been studied by the electrochemical techniques such as cyclic voltammetry (CV), Electrochemical impedance spectroscopy (EIS), and Galvanostatic charge–discharge method (GCD). The mechanical cyclic stability over 1000 cycles at a current density of 1 mA/g with good coulombic efficiency of 84%. The developed biocompatible material displays great potential to offer a green alternative to conventional supercapacitors.

Nanostructured biological hydroxyapatite from Tilapia bone: A pathway to control crystallite size and crystallinity

Hydroxyapatite is the main mineral component of the bone and the main responsible for their hardness and mechanical strength. It shows enormous scientific and technological value as it presents a potential for application in medical purposes and pharmaceutical, chemical, and environmental remedy industries. Many authors have demonstrated the possibility of hydroxyapatite synthesis from different sources and synthesis methodologies. However, studies which lead to an effectively controlled crystallite size and crystallinity are still scarce. Our study aims to evaluate the effects of heat treatment temperature and high energy milling time on obtaining nanometric hydroxyapatite from a natural source. The characterization has been performed by employing thermal, chemical, structural, morphological, and surface area analysis. It has been possible to verify only hydroxyapatite formation. In the milled samples, it's been possible to verify a reduction in the crystallite size and crystallinity. The surface area increased from 0.07 to 41.37 m2/g, but excessive milling times caused agglomeration and reduced the surface area. The results showed that it is possible to synthetize nanostructured hydroxyapatite (9,8–95 nm) with crystallinity ranging from 3 to 99% from Tilapia bones. ANOVA has validated the results. The produced materials present an excellent potential for application in the biomedical or adsorption substances area.

Structure and biological compatibility of polycaprolactone/zinc-hydroxyapatite electrospun nanofibers for tissue regeneration

Although guided tissue regeneration (GTR) is a useful tool for regenerating lost tissue as bone and periodontal tissue, a biocompatible membrane capable of regenerating large defects has yet to be discovered. This study aimed to characterize the physicochemical properties and biological compatibility of polycaprolactone (PCL) membranes associated with or without nanostructured hydroxyapatite (HA) (PCL/HA) and Zn-doped HA (PCL/ZnHA), produced by electrospinning. PCL, PCL/HA, and PCL/ZnHA were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). Nanoparticles of HA or ZnHA were homogeneously distributed and dispersed inside the PCL fibers, which decreased the fiber thickness. At 1 wt% of HA or ZnHA, these nanoparticles acted as nucleating agents. Moreover, HA and ZnHA increased the onset of the degradation temperature and thermal stability of the electrospun membrane. All tested membranes showed no cytotoxicity and allowed murine pre-osteoblast adhesion and spreading; however, higher concentrations of PCL/ZnHA showed less cells and an irregular cell morphology compared to PCL and PCL/HA. This article presents a cytocompatible, electrospun, nanocomposite membrane with a novel morphology and physicochemical properties that make it eligible as a scaffold for GTR.

Effectiveness of xenogeneic and synthetic bone-block substitute materials with/without recombinant human bone morphogenetic protein-2: A preclinical study using a rabbit calvarium model.

To investigate new bone (NB) formation by using bone-block substitute materials with/without recombinant human bone morphogenetic protein-2 (rhBMP-2). Three synthetic bone-block substitute materials [biphasic calcium phosphate (BCP); nanostructured hydroxyapatite (NH); 3D-printed tricalcium phosphate/hydroxyapatite (3DP)] and one xenogeneic deproteinized bovine bone mineral (DBBM) block substitute were affixed to rabbit calvarium using osteosynthesis screws, either with rhBMP-2 (n=12) or without rhBMP-2 (n=16). At 2 or 12weeks (n=6 with rhBMP-2 and n=8 without rhBMP-2 for each week), histologic, histomorphometric and microcomputed tomography analyses were performed. The application of rhBMP-2 increased NB formation in all experimental groups at both weeks. DBBM resulted in a greater area of NB compared with synthetic blocks either with or without rhBMP-2 at 2weeks (2.8±0.9 vs. 1.4±0.5-1.9±1.4mm2 ; 1.4±1.0 vs. 0.6±0.3-0.9±0.5mm2 ) and without rhBMP-2 at 12weeks (3.0±0.8 vs. 1.7±0.7-2.6±1.5mm2 ) (p>0.05). NB formation did not differ significantly for DBBM and the three types of synthetic block with rhBMP-2 at 12weeks (4.5±2.0 vs. 3.8±0.7-5.1±1.1mm2 ; p>0.05). rhBMP-2 enhanced NB in all blocks. DBBM blocks yielded more NB than synthetic blocks without rhBMP-2. The application of rhBMP-2 appears to compensate for differences in late healing.

Effect of stacking faults on structural, morphological, and electrical properties of hydroxyapatite polycrystals

This article reports the defect mediated electrical properties of three hydrothermally grown pure hydroxyapatite (HAp) nanocrystals synthesized between 120 °C and 180 °C, at a constant pH = 10 with changing morphology from nanorods to nanoflakes at higher temperatures. The analyses of X-Ray Diffraction (XRD) patterns, Field-Emission Scanning-Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), High-Resolution Transmission Electron Microscopy (HRTEM) images, Selected-Area Electron Diffraction (SAED) pattern, and Energy-Dispersive X-ray Analysis (EDAX) spectra confirm the growth of pristine hexagonal HAp nanostructures. The presence of significant stacking fault obtained from the Rietveld refinement of XRD patterns and HRTEM analysis helps to enhance the ionic conductivity, dielectric, and electrical transport properties of the samples. The Urbach energy enhances as bandgap reduces due to trap energy states with decreasing hydrothermal temperatures. The unique crystal defect-controlled dielectric nature of HAp may find promising applications in the future electronic ceramic industry.

Effect of Molar Ratios in the Crystallochemical Structure of Biomimetic Nanostructured Hydroxyapatite on the Characteristics of the Product

Effect of Molar Ratios in the Crystallochemical Structure of Biomimetic Nanostructured Hydroxyapatite on the Characteristics of the Product

Production and Characterization of Poly (Lactic Acid)/Nanostructured Carboapatite for 3D Printing of Bioactive Scaffolds for Bone Tissue Engineering.

Biocompatible scaffolds are porous matrices that are bone substitutes with great potential in tissue regeneration. For this, these scaffolds need to have bioactivity and biodegradability. From this perspective, 3D printing presents itself as one of the techniques with the greatest potential for scaffold manufacturing with porosity and established structure, based on 3D digital modeling. Thus, the objective of the present work was to produce 3D scaffolds from the poly (lactic acid) (PLA) and the nanostructured hydroxyapatite doped with carbonate ions (CHA). For this purpose, filaments were produced via fusion for the fused-filament 3D printing and used to produce scaffolds with 50% porosity in the cubic shape and 0/90°configuration. The dispersive energy spectroscopy and Fourier transform infrared spectroscopy (FTIR) analysis demonstrated the presence of CHA in the polymeric matrix, confirming the presence and incorporation into the composite. The thermogravimetric analysis made it possible to determine that the filler concentration incorporated in the matrix was very similar to the proposed percentage, indicating that there were no major losses in the process of obtaining the filaments. It can be assumed that the influence of CHA as a filler presents better mechanical properties up to a certain amount. The biological results point to a great potential for the application of PLA/CHA scaffolds in bone tissue engineering with effective cell adhesion, proliferation, biocompatibility, and no cytotoxicity effects.

Secular and semi-nonsecular models of cross-polarization kinetics for remote spins: an application for nano-structured calcium hydroxyapatite

The 1H → 31P cross-polarization (CP) kinetics in the nanostructured calcium hydroxyapatite (nano-CaHA) was measured under moderate (5 kHz) magic-angle spinning (MAS) rate. This material was chosen as it contains the distanced 1H–31P spin pairs and the interactions between them are characterized by a relatively low dipolar coupling (b) that could be comparable with the spin-diffusion rates (R). Therefore, the physical legitimacy to use the secular solution of the quantum Liouville–von Neumann equation is doubtful. The semi-nonsecular model of spin dynamics was applied, and the results were compared with those obtained by the secular approach. The comparable results obtained by both models show that the secular model is applicable, with certain reservation, also in the case of |b| ≈ R. The extremely high anisotropy of spin diffusion in the nano-CaHA was deduced. This can be a matter of the applied approach, as the interactions of the 31P spins with the proton bath were neglected in both models. The high anisotropy could also be caused by the physical reasons that stem from the structural and proton diffusion features of CaHA. This material belongs to low-dimensional proton conductors possessing a large motional freedom for protons along OH– chains.

Sinterability of Calcium Phosphate Through Rapid Sintering

Development of dense nanostructured hydroxyapatite (HA) with the major concern to enhance densification while limiting its grain growth has received great demand. This is due to inherent brittleness and lower mechanical strength of HA ceramic. A promising way to obtain this could be a fabrication of nanostructured HA materials through rapid sintering process. In this work, eggshell derived hydroxyapatite powder has been prepared via solid state route and its sinterability was investigated through microwave sintering (1000-1250 °C). The phase stability, microstructural evolution, relative density and hardness of the microwave sintered HA were reflected. The results indicate that the rapid sintering regime has been successfully employed with pure HA phase stability remained up to 1200°C and the relative density and hardness increase with increase in sintering temperature. On top of that, the result also showed good correlation of grain size and mechanical properties of HA and supported that microwave sintering did not promote extensive grain growth of HA.