Multi-substituted hydroxyapatites (ms-HAPs) are currently gaining more consideration owing to their multifunctional properties and biomimetic structure, owning thus an enhanced biological potential in orthopaedic and dental applications. In this study, nano-hydroxyapatite (HAP) substituted with multiple cations (Sr 2+ , Mg 2+ and Zn 2+ ) for Ca 2+ and anion ( Si O 4 4 − ) for P O 4 3 − and OH − , specifically HAPc-5%Sr and HAPc-10%Sr (where HAPc is HAP-1.5%Mg–0.2%Zn–0.2%Si), both lyophilized non-calcined and lyophilized calcined, were evaluated for their in vitro ions release. These nanomaterials were characterized by scanning electron microscopy, field emission-scanning electron microscopy and energy-dispersive X-ray, as well as by atomic force microscope images and by surface specific areas and porosity. Further, the release of cations and of phosphate anions were assessed from nano-HAP and ms-HAPs, both in water and in simulated body fluid, in static and simulated dynamic conditions, using inductively coupled plasma optical emission spectrometry. The release profiles were analysed and the influence of experimental conditions was determined for each of the six nanomaterials and for various periods of time. The pH of the samples soaked in the immersion liquids was also measured. The ion release mechanism was theoretically investigated using the Korsmeyer–Peppas model. The results indicated a mechanism principally based on diffusion and dissolution, with possible contribution of ion exchange. The surface of ms-HAP nanoparticles is more susceptible to dissolution into immersion liquids owing to the lattice strain provoked by simultaneous multi-substitution in HAP structure. According to the findings, it is rational to suggest that both materials HAPc-5%Sr and HAPc-10%Sr are bioactive and can be potential candidates in bone tissue regeneration.

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Pure nano-crystalline hydroxyapatite (Hap) and Hap doped with magnesium, zinc and silicon, namely Hap-0.25wt%Mg: Hap01, Hap-0.25wt%Mg-0.47wt%Si: Hap02, Hap-1.50wt%Mg-0.47wt%Si: Hap03, Hap-0.67wt%Mg-0.2wt%Zn-0.13wt%Si: Hap04, were synthesized using aqueous precipitation method. The pure and doped Hap were calcined individually at 400, 650 and 850 �C for 2h, and investigated by Brunauer-Emmett-Teller (BET) specific surface area and porosity measurements, as well as by X-ray powder diffraction (XRD). The morphology and particle size of nano-crystalline powders were investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermal stability of the obtained nanoceramics from 30�C to 1000�C and the effect of calcination temperatures (400, 650 and 850 �C) on their composition and structure were also determined by using TG, DTG, TGA and DTA techniques coupled with SEM-EDX. Results analysis shows a high thermal stability (up to 1000 �C) of these nanomaterials, including the triple-substituted Hap with Mg, Zn and Si (Hap04). Simultaneous incorporation of Mg, Zn and Si into Hap lattice represents a novelty and promotes a new generation of synthetic porous nanoceramics with unique Hap structure, and high thermal stability. Due to their chemical composition and structure rather similar to those characteristic for the inorganic component of bone, these nanoceramics can have multiple applications in biomedicine, as bone substitutes, for metal coatings and in drug delivery systems.

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ABSTRACT. In order to obtain a low crystalline nanohydrxyapatite (HAP), suitable for biomedical application, a new synthesis procedure was developed, based on the aqueous precipitation method, at room temperature, without any additives. Accordingly, lyophilized HAP powders, both calcined and non calcined, were prepared, and characterized by XRD, TEM and AFM imaging, FTIR spectroscopy, zeta potential and BET measurements. The results confirmed HAP as the only phase present. The high porosity of this nanomaterial is attained. The nanoparticle size and shape as well as the crystallinity degree of the obtained HAP samples were also determined.

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There is a continuous need for discovering new nanomaterials with antibacterial activity against various pathogens, like Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). This study was performed to assess the antimicrobial activity of two novel nanostructured forsterites, both in the absence and the presence of silver nanoparticles (AgNPs). The two nano forsterites (FS) were prepared by advanced sol-gel (FSsg) and precipitation (FSpp) methods. Preparation of colloidal AgNPs systems was realized by using the precursor, AgNO3, and the trisodium citrate and tanic acid assuring the formation and stabilization of AgNPs. The characterization of nano forsterite powders was carried out using complementary physical methods: XRD, SEM, and AFM. The AgNPs were characterized by UV-Vis spectra, STEM and AFM imaging. The antimicrobial activity was studied by the agar well diffusion method both in the FS native state, as FSsg and FSpp, and in their mixture with silver nanoparticles (AgNPs). The inhibitory effect of synthesized forsterites, FSsg and FSpp, particularly variants with AgNPs was found only on the S. aureus strain, the zones of inhibition being between 8 and 10 mm, and more intensely expressed in the FSpp-AgNPs dispersions. These findings open new orthopedic applications of these systems, particularly for antimicrobial coated metallic implants.